Let's see how spaceships actually return - is2006. Landing vehicles

Introduction

Also, for both devices, the main target was the Moon. The USA did not spare money for the lunar race, because until 1966 the USSR had priority in all significant space achievements. The first satellite, the first lunar stations, the first man in orbit and the first man in outer space - all these achievements were Soviet. The Americans struggled to "catch up and overtake" the Soviet Union. And in the USSR, the task of a manned lunar program against the background of space victories was overshadowed by other urgent tasks, for example, it was necessary to catch up with the United States in terms of the number ballistic missiles. Manned lunar programs are a separate big conversation, but here we will talk about vehicles in an orbital configuration, such as they met in orbit on July 17, 1975. Also, since the Soyuz spacecraft has been flying for many years and has undergone many modifications, speaking of the Soyuz, we will mean versions close in time to the Soyuz-Apollo flight.

Launch vehicles

The USSR decided to use a new modification of the rocket of the R-7 family to launch a new spacecraft into near-Earth orbit. On the Voskhod launch vehicle, the third-stage engine was replaced with a more powerful one, which increased the carrying capacity from 6 to 7 tons. The ship could not have a diameter greater than 3 meters, because in the 60s, analog control systems could not stabilize the over-caliber fairings.

On the left is the scheme of the Soyuz launch vehicle, on the right is the launch of the Soyuz-19 spacecraft of the Soyuz-Apollo mission

In the United States, the Saturn-I launch vehicle, specially designed for the Apollos, was used for orbital flights. In the -I modification, it could put 18 tons into orbit, and in the -IB modification, 21 tons. The diameter of the Saturn exceeded 6 meters, so the restrictions on the size of the spacecraft were minimal.

On the left is a Saturn-IB in a section, on the right is the launch of the Apollo spacecraft of the Soyuz-Apollo mission

In size and weight, the Soyuz is lighter, thinner and smaller than the Apollo. The Soyuz weighed 6.5-6.8 tons and had a maximum diameter of 2.72 m. The Apollo had a maximum mass of 28 tons (in the lunar version, fuel tanks were not completely filled for near-Earth missions) and a maximum diameter of 3, 9 m

Appearance

"Soyuz" and "Apollo" implemented the already standard scheme dividing the ship into compartments. Both ships had an instrument-aggregate compartment (in the USA it is called a service module), a descent vehicle (command module). The Soyuz descent vehicle turned out to be very cramped, so a household compartment was added to the ship, which could also be used as an airlock for spacewalks. In the Soyuz-Apollo mission, the American ship also had a third module, a special airlock for transition between ships.

According to the Soviet tradition, the Soyuz was launched entirely under the fairing. This made it possible not to care about the aerodynamics of the ship during launch and to place fragile antennas, sensors, solar panels and other elements on the outer surface. Also, the household compartment and the descent vehicle are covered with a layer of space thermal insulation. The Apollos continued the American tradition - the launch vehicle was only partially closed, the nose was covered by a ballistic cover, made structurally together with the rescue system, and from the tail the ship was closed with an adapter-fairing.

"Soyuz-19" in flight, shooting from the board of "Apollo". Dark green coating - thermal insulation

Apollo, shot from the Soyuz. On the main engine, it seems that the paint has swelled in places

"Union" of a later modification in the context

"Apollo" in the cut

The shape of the descent vehicle and thermal protection

The Soyuz and Apollo descent vehicles are more similar to each other than they were in previous generations space ships. In the USSR, the designers abandoned the spherical descent vehicle - when returning from the Moon, it would require a very narrow entry corridor (maximum and minimum height between which you need to get for a successful landing) would create an overload of more than 12 g, and the landing area would be measured in tens, if not hundreds, of kilometers. The conical descent vehicle created lift during braking in the atmosphere and, turning, changed its direction, controlling the flight. When returning from the earth's orbit, the overload decreased from 9 to 3-5 g, and when returning from the moon - from 12 to 7-8 g. The controlled descent significantly expanded the entry corridor, increasing the reliability of the landing, and greatly reduced the size of the landing area, facilitating the search and evacuation of astronauts.

Calculation of an asymmetric flow around a cone during braking in the atmosphere

Soyuz and Apollo descent vehicles

The diameter of 4 m, chosen for the Apollo, made it possible to make a cone with a half-angle of 33°. Such a descent vehicle has an aerodynamic quality of about 0.45, and its side walls practically do not heat up during braking. But its disadvantage was two points of stable equilibrium - Apollo had to enter the atmosphere with its bottom oriented in the direction of flight, because if it entered the atmosphere sideways, it could roll over into the "nose forward" position and kill the astronauts. A diameter of 2.7 m for the Soyuz made such a cone irrational - too much space was wasted. Therefore, a descent vehicle of the "headlight" type was created with a half-angle of only 7°. It uses space efficiently, has only one point of stable equilibrium, but its lift-to-drag ratio is lower, on the order of 0.3, and thermal protection is required for the side walls.

Already mastered materials were used as a heat-shielding coating. In the USSR, fabric-based phenol-formaldehyde resins were used, and in the USA, epoxy resin on a fiberglass matrix. The mechanism of operation was the same - the thermal protection burned and collapsed, creating an additional layer between the ship and the atmosphere, and the burnt particles took on and carried away thermal energy.

Thermal protection material "Apollo" before and after the flight

Propulsion system

Soyuz-19 feed, engine nozzles are clearly visible

Apollo attitude thrusters close-up

landing system

Apollo landing pattern

In the USSR, they traditionally landed a ship on land. Ideologically, the landing system develops the parachute-jet landing of Voskhodov. After dropping the lid of the parachute container, the exhaust, braking and main parachutes are fired in succession (a spare is installed in case of system failure). The ship descends on one parachute, at an altitude of 5.8 km the heat shield is dropped, and at a height of ~1 m, soft landing jet engines (SLL) are activated. The system turned out to be interesting - the work of the DMP creates spectacular shots, but the comfort of landing varies in a very wide range. If the astronauts are lucky, then the impact on the ground is almost imperceptible. If not, then the ship can hit the ground sensitively, and if you are not at all lucky, then it will also capsize on its side.

Landing pattern

Perfectly normal operation of the DMP

The bottom of the descent vehicle. Three circles from above - DMP, three more - from the opposite side

Emergency Rescue System

From left to right SAS "Apollo", SAS "Soyuz", various versions of SAS "Soyuz"

Thermoregulation system

Means of providing EVA

EVA "Apollo 9"

Docking system

Docking mechanism "Apollo". By the way, it was also used in the Soyuz-Apollo program, with its help the command module docked with the airlock

Scheme of the Soyuz docking mechanism, first version

"Soyuz-19", front view. The docking station is clearly visible

Cabin and equipment

Control panel, view from the left seat

Control Panel. On the left are the flight controls, in the center - attitude control engines, emergency indicators on top, communications below. On the right side are fuel, hydrogen and oxygen indicators and power management

Even though the equipment of the Soyuz was simpler, it was the most advanced for the Soviet ships. The ship was the first to have an on-board digital computer, and the ship's systems included equipment for automatic docking. For the first time in space, multifunctional cathode ray tube indicators were used.

Soyuz spacecraft control panel

Power supply system

Conclusion

But a very high price was paid for this success. Both Soyuz and Apollo were the first ships in which people died. What is even sadder, if the designers, engineers and workers were in less hurry and after the first successes would not cease to be afraid of space, then Komarov, Dobrovolsky, Volkov, Patsaev, Grissom, White and Cheffy

So, the descent vehicle, descending under the influence of the Earth's gravity, gradually enters the increasingly dense layers of the atmosphere. The lower, the greater the air resistance, the more it slows down the descent vehicle, the lower the speed becomes, the steeper the trajectory of its descent becomes.

However, what does “the slower the speed becomes” mean? This means that the kinetic energy of the apparatus decreases. And we know that energy does not disappear and does not appear - it can only pass from one form to another. In this case, the kinetic energy of the descent vehicle is converted into thermal energy, that is, it is spent on heating the oncoming air and the descent vehicle itself.

How the transfer and transformation of energy takes place, we will not consider here. Now it is important for us that this kinetic energy is huge - the same as that of a heavily loaded railway train rushing at a speed of 100 km / h! And almost all of this huge energy must be converted into thermal energy. If special measures are not taken, then one third of it will be enough to turn the entire descent vehicle into steam.

As a result of deceleration, the front surface of the descent vehicle heats up to a temperature of about 6000°. The air at the front wall of the descent vehicle will have such a temperature. This is no longer the usual air, consisting of molecules of nitrogen, oxygen and carbon dioxide, but a plasma consisting of nitrogen, oxygen and carbon atoms, ions and electrons.

Remember the table of melting points various substances. Is there at least one material in it that at this temperature will remain in a solid state? No. All materials known to us at this temperature turn into a liquid or even into a vapor. And even if we had a material that would not melt at such a temperature, this is not enough. After all, the most important thing is that the huge amount of heat that occurs during braking is not transferred inside the descent vehicle. Whatever the temperature outside the descent vehicle, in the crew compartment it should be normal, room temperature. To do this, the walls of the descent vehicle must be well protected from heat, that is, have low thermal conductivity. But that's not all. They must be very strong - after all, when braking in dense layers, the descent vehicle is subjected to enormous pressure. In addition, it is necessary that the walls of the ship have as little weight as possible, because on a space ship every gram of weight counts.

So, the material must have a high melting point, and low thermal conductivity, and high strength, and besides, a low specific gravity. And although in our time scientists have created and are creating a wide variety of artificial materials, none of them can satisfy all these requirements at the same time.

How to be? When this question arose, scientists and engineers began an intensive search for a way out of the situation. Maybe cover the entire descent vehicle with copper cladding? Copper has very good thermal conductivity, and due to this, heat from the front surface will be removed to the side and rear walls of the descent vehicle (only the front, frontal surface of the ship heats up strongly).
But such a skin will weigh a whole ton, which means that the launch weight of the launch vehicle and, consequently, the thrust of the engine will have to be increased by 50 tons. In addition, in this case, almost all the heat will still remain on the ship and gradually pass into the descent vehicle.

There was a proposal to make the front surface of the apparatus porous (that is, having many tiny holes) and through these pores during the descent to push cold liquid or blow out gas from inside the ship. This idea is actually not bad, but it is difficult to implement it, since at high temperatures and pressures that arise on the front surface of the descent vehicle, the pores will become clogged, melted, etc.

The most effective method was proposed by Soviet scientists. Now this method is used when returning to Earth all descent vehicles - both Soviet and American.

Scientists argued something like this. There are currently no materials that meet all four requirements, and it is unlikely that they will be created in the coming years. There is not even a material that would satisfy only the first requirement, that is, would have sufficiently high melting and evaporation temperatures. But after all, the main task is to ensure that the temperature in the crew compartment remains at room temperature, that is, that as little heat as possible passes into the ship. And this can be achieved in the following way.

Let us cover the front wall of the descent vehicle with a material that, although it melts or evaporates at this temperature, requires for its melting and evaporation a large number heat (or, as scientists say, it has large latent heats of phase transitions), and in the molten state it has low viscosity (it flows easily). Then, during the descent, this material will heat up, melt and evaporate, and as soon as it melts, drops and vapors of the material will be blown away from the surface of the descent vehicle by a counter flow of air. In this case, the heat that has accumulated in drops and vapors during heating, melting and evaporation of the material will be carried away from the apparatus along with drops and vapors instead of being transferred from them inside the ship.

To reduce heat transfer into the apparatus, a layer of material with a very low thermal conductivity must be placed under a layer of this material. The strength of the structure can be ensured by making the third layer - a frame made of light titanium alloys, and attaching a “carrying away” shell of a low-heat-conducting material to it. This method is called "thermal protection due to mass entrainment".

It is this method that is currently used on all descent vehicles. Thus, during the descent in the dense layers of the atmosphere, the descent vehicle rushes, surrounded by a veil of hot plasma and drops of heat-shielding material. This veil envelops the ship's antennas, and since the plasma does not transmit radio waves, communication with the Earth is terminated. But it only lasts a few minutes. The air slows down the ship so much that while it descends from 100 kilometers to 30 kilometers, its speed decreases by 56 times! Now it is already possible to produce a stabilizing parachute with a dome diameter of several meters, and at an altitude of 10 kilometers - the main one, with a diameter of several tens of meters. Designers very simply and witty came up with how to do what

the ship would meet the surface of the Earth gently, without any impact (without a push). To do this, a pin about one meter long is produced from the bottom side of the apparatus. When this pin is inserted into the Earth's surface, it automatically turns on the soft-landing solid-propellant thrusters, whose nozzles are directed downwards. As a result, the rest of the speed is extinguished.

Why is such a complex system of descent and landing used? Why not slow down the descent vehicle from beginning to end with the help of a rocket engine? The answer is simple: it is unprofitable, and for a sufficiently heavy descent vehicle it is simply impossible.

The point is this. To launch a satellite, that is, to accelerate it to the first cosmic speed, a launch vehicle is required, the weight of which at the start should be approximately 50 times greater than the weight of the satellite. If we want to launch a satellite weighing 5 tons, then we need a rocket weighing 250 tons. If we want to return a satellite to Earth, we must decelerate it from first space velocity to zero - to ensure a soft landing. And this will require the same rocket - weighing 200 tons. We must take it with us when the ship starts from Earth. But then we have to put into orbit not 5 tons of cargo, but already 255 tons. And to do this, you need to take a rocket weighing 12,700 tons. In order to lift a rocket off the surface of the Earth, its thrust at the start must be at least a little more than its starting weight, that is, in this case, approximately 13,000 tons. But there are no such missiles yet - the most powerful modern rocket while it has a thrust of approximately 3500 tons.

It is also clear that the cost of such a flight increases many times over.

Thus, it is much more profitable to use air resistance for the main braking during landing on the Earth. This also applies to landing on other planets with an atmosphere, such as Venus, Mars, Jupiter, etc. Landing on celestial bodies without an atmosphere, such as the Moon, is another matter. There's nothing you can do about it - you can only slow down the engines.

Let's return to the descent of the ship to the Earth (or to another planet with an atmosphere), namely, to the moment when the descent vehicle had just deorbited and went towards the Earth. It is very important how steep the trajectory of its flight will be. Even the most trained astronauts will die if their body weight becomes ten to thirteen times more than on Earth. Indeed, imagine that a load of ten times your own weight is heaped on you - you will be crushed by it. The astronauts will find themselves in the same position.

But too flat trajectory should not be either. Otherwise, the ship will fly to Earth for a very long time, as a result of which it will heat up too much and the temperature inside it will become more than the astronauts can withstand.

What determines the steepness of the trajectory? If the braking engine is turned on longer than necessary, the descent vehicle will go too steeply. Exactly the same result will be obtained if the traction force is greater than necessary. The steepness of the trajectory also depends on the direction of the engine nozzle during deceleration.

This is especially important in the case of uncontrolled—ballistic—descent. If the descent vehicle has the shape of a ball, then such a ship does not have an aerodynamic quality (lifting force). This means that during its descent, even in dense layers of the atmosphere, astronauts have no way to change the trajectory. The descent takes place along the so-called ballistic trajectory (a stone will fall along such a trajectory if you throw it from the top of the mountain in a horizontal direction) and is called ballistic, or uncontrolled, descent. The entire trajectory of such a descent, including the landing site, is determined already at the moment the braking engine stops working, when the ship has just left orbit. If the steepness is set incorrectly (for example, due to the fact that the brake motor has worked for a few seconds more or less than required), the descent vehicle will land several tens and even hundreds of kilometers closer or farther than expected. And this means that the ship can land in the mountains, in the taiga or at sea, and not in the flat steppe. Of course, the descent vehicle will not sink and the cosmonauts will not die, even if the ship sank into the water or into the taiga—the cosmonauts have a walkie-talkie, flares, food supplies, etc. with risk, and with additional difficulties. Imagine, for example, what would happen if they landed on the side of a high and steep mountain.

These difficulties and troubles can be avoided if the descent vehicle is given a shape that has a lifting force. To do this, the shape of the apparatus must be asymmetrical with respect to the direction of flight. It is this shape, called segmental-conical, that modern descent vehicles have.

When the axis of the descent vehicle coincides with the direction of flight (the angle of attack is zero), the lift force is zero. By changing the angle of attack, that is, the inclination of the descent vehicle relative to the flight axis, the cosmonauts thereby increase or decrease the lift force and, due to this, can change the descent trajectory and choose the landing site. In addition, overloads can also be regulated in this way.

Such a descent vehicle flies with a segmental part forward. In this position, the air resistance is much greater than if it were flying conically forward. And the greater the resistance, the faster the ship slows down. If the craft were to fly conically forward, it would approach the Earth's surface at too high a speed.

Segmental-conical descent vehicles from a height of 20-30 kilometers descend by parachute, just like spherical ones.

The launches of the first spacecraft, first into the orbits of artificial satellites of the Earth, and then for the study of the Moon and planets, became the first stage in practical astronautics. However, in connection with the forthcoming manned flight into space, the return of the spacecraft (or part of it) to Earth was required. In turn, the flights of spacecraft for the study of the Moon and planets required to solve the problem of landing on the studied celestial body. The solution of these problems was complicated by the presence of high speeds of spacecraft. Spacecraft flight velocities relative to the Earth and other bodies solar system range from 2.4 km/s for the Moon to 60 km/s for Jupiter. And this is subject to the initial zero speed far from the planet (as experts say, speeds at infinity). At high initial speeds, i.e., different from zero, the meeting speed will be even greater.

Even if the spacecraft is put into orbit artificial satellite of a celestial body, the speed relative to this body will be only about 1.4 times less (for example, for the Moon - 1.7 km / s, for Jupiter - about 43 km / s). A direct collision of a spacecraft with a celestial body leads at such speeds to the complete destruction and annihilation of the apparatus. Therefore, in order to land on Earth or another planet, it was necessary to reduce the speed of the spacecraft to an acceptable value. Moreover, the decrease in this speed should be quite smooth in order to ensure the safety of astronauts when returning to Earth, but it can also be sharp for interplanetary stations when landing on other planets and for the return of automatic compartments from orbiting scientific stations ...

In radio broadcasts and newspapers, there is an expression "After the successful completion of work in outer space in orbit of an artificial satellite of the Earth, the astronauts in the descent vehicle returned safely to Earth." Why, then, in the descent vehicle, and not in the Soyuz spacecraft, into which the cosmonauts transferred from Salyut?

The concept of "descent vehicle" appeared only at a certain stage in the development of astronautics. This concept is not characteristic of previously invented, more familiar species. land transport: road and rail, sea and air liners. All these types of land transport arrive at their destination in the form in which they set off. We did not see or hear that the passenger, having boarded the train, arrived at the destination station in a separate compartment without a train. Yes, and the plane will put the passenger, descending entirely, in its original form, on the runway of the airfield.

What is the matter here? Why are separate parts usually used to land spacecraft?

Before answering these questions, let's consider and compare the speeds with which the types of land transport familiar to us, as well as spaceships and automatic stations, move. Sea and river vessels have a maximum travel speed of 10–20 m/s (36–72 km/h), cars - 20–40 m/s (72–144 km/h), fast trains - up to 60 m/s (about 200 km / h), passenger aircraft - 80-250 m / s (300-900 km / h). Spacecraft fly at speeds 2–3 orders of magnitude higher. In order for a body to become an artificial satellite of the Earth, it is necessary to inform it of a speed of about 8000 m/s, for interplanetary stations like "Venus" and "Mars" - more than 11500 m/s. In the case of a flight to even more distant planets, even greater speeds are required.

Note that the speed of an artificial Earth satellite of about 8 km/s is 10 times greater than the speed of a bullet fired from a gun. Approximately at the speed of a bullet, only one Baron Munchausen flew, riding a cannonball, and even then it was in a fairy tale. And now the typical speeds of a spacecraft in orbit of an artificial satellite of the Earth are 10–20 times greater than those of a cannonball. And inside the spaceship and orbital station astronauts live and work.

The kinetic energy of spacecraft motion is very high. If, for example, already at lower velocities, a bullet strongly deforms and heats up when it hits an obstacle, then what will happen to a spacecraft with tremendous speed when it hits the surface of the Earth or another body in the solar system?

There are a great many such "experiments" in nature. On the surface of the Moon and some other bodies of the solar system there are many craters of various sizes - from meters to 200 kilometers or more. On the Moon, they can already be seen with a small telescope; the surface of other bodies in the solar system became visible with the same clear clarity after the flight of spacecraft to them. These craters are of impact origin due to the fall of meteoroids and other celestial bodies of relatively small mass. There are such craters on Earth. These include the famous Arizona crater, as well as more recent small craters from the fall of the Sikhote-Alin meteorite and others.

In addition to destruction, the falling body is heated to monstrous temperatures due to the conversion of huge kinetic energy into heat. So, for example, an artificial Earth satellite flying at a speed of 8 km / s has an energy of 32 MJ per kilogram of mass, and a cosmic body flying relative to Jupiter at a second cosmic velocity (60 km / s) has an energy of 1800 MJ per kilogram of mass . If, for example, ice is melted, and then the resulting water is heated until it evaporates completely, then only more than 3 MJ will be required for each kilogram of mass. When metals are heated to melting, followed by their boiling until complete evaporation, for each kilogram of mass, 8 MJ for iron, 6.5 MJ for copper, 7.16 MJ for magnesium, 11.6 MJ for aluminum will be required.

Consequently, if all the kinetic energy, even in the case of an artificial satellite of the Earth, is converted into heat, then it will all evaporate, no matter what material it is made of. For comparison, we note that if the entire kinetic energy of a fast train racing at a speed of 60 m / s (200 km / h) turns into heat and goes entirely to heat the train, then it, made of aluminum-magnesium alloys, will heat up only by 1°C. Such a difference in heating is determined by the fact that the kinetic energy of a moving body does not increase linearly with an increase in speed, but in proportion to the square of the speed.

All these estimates demonstrate what an important and responsible task the designers of spacecraft faced in ensuring the safe return of astronauts to Earth, and at the same time show what gigantic energies they had to deal with. In this case, there were two ways: deceleration of the spacecraft, expending considerable energy, and ensuring sufficiently effective thermal protection of the spacecraft from heating during deceleration in the planet's atmosphere. The natural desire here was to reduce the amount of energy expended on deceleration or, in connection with large energy flows, to provide thermal protection for a relatively small mass, but, of course, not at the expense of reducing the safety of the astronauts' flight during descent to Earth.

This problem is easily solved if we confine ourselves to the task of saving not the entire spacecraft, but only its part, which is called the descent vehicle. In this separate compartment it is quite possible to place the necessary equipment for the study of other planets, as well as astronauts and materials delivered to Earth after a manned flight.

So, descent vehicles are designed to deliver a research cosmonaut to Earth or scientific equipment to another planet for research in its atmosphere or on its surface.

PURPOSE OF THE Descent Vehicle

Under conditions of near-Earth flight, the descent vehicle is designed to deliver an astronaut to the Earth after completing the research program in orbit of an artificial Earth satellite, as well as the materials of these studies in the form of photographic and film films, the results of technological experiments, etc. The descent vehicle of an automatic space station, designed for studies of the bodies of the solar system, serves to deliver a complex of scientific equipment to the surface of the planet. With the help of this equipment, the landing site is photographed and the image is transmitted to the Earth, the chemical and mechanical properties of the soil are studied. The chemical composition of the atmosphere (if any), illumination in the atmosphere and on the surface, wind speed, the presence of aerosols, and much more are determined.

The descent vehicles can deliver cosmonaut-researchers to other bodies (in particular, to the Moon), and then, with the help of a part of the descent vehicle, determine the launch into orbit of an artificial satellite of the planet for docking with the main ship. And the descent vehicle of the main ship then delivers the astronauts to Earth. Descent vehicles without a cosmonaut, equipped with automatic equipment, may also contain a return stage.

For example, the Luna-16 station, which landed on the surface of the Moon, included a return stage. After loading the descent vehicle with lunar soil, the return rocket was launched from the base of the descent vehicle located on the Moon. The launch was carried out upward along the local vertical, without entering the orbit of an artificial satellite of the Moon, and a small descent vehicle arrived on Earth along a flight trajectory. In its composition, the return stage had a rocket unit (propulsion system with fuel tanks), an instrument compartment and a descent vehicle designed for landing on Earth. The descent vehicle delivered samples of lunar soil to Earth, which were transferred to scientific institutes for research.

The descent vehicles of spacecraft form two large groups by their design. These are descent vehicles for landing on planets with an atmosphere of the Earth type and denser, and descent vehicles designed for landing on bodies of the solar system that do not have an atmosphere. The composition of the former includes, as a prerequisite, a heat-shielding coating to preserve the descent vehicle from overheating during braking in the upper layers of the atmosphere. As a rule, a parachute system is used in the final section of deceleration to make a soft landing of the descent vehicle.

The second group of descent vehicles does not require a heat-shielding coating that protects them during braking in the atmosphere, because there is no atmosphere itself. A parachute is also useless in a vacuum, since there is nothing to fill its canopy with. The main element of the descent vehicle on a non-atmospheric body is rocket engines, capable of reducing the approach speed from space to an insignificant value of the order of 1 -10 m / s during relatively long work. For landing on a planet with a rarefied atmosphere (for example, on the planet Mars), both methods are used in succession: aerodynamic braking in the atmosphere with a parachute descent and final braking due to the operation of the propulsion system.

So, a descent vehicle is a device designed to make a soft landing on the Earth or another body in the solar system in order to protect a person or scientific equipment from large overloads and heat flows during atmospheric braking.

BRAKING IN THE ATMOSPHERE

So far, descent vehicles for planets with an atmosphere of the Earth type or denser have been used for landing spacecraft on Earth and Venus. Chronologically descent vehicles designed to land on planets with an atmosphere appeared earlier than descent vehicles for non-atmospheric planets. The first landing of the descent vehicle on Earth was carried out in May 1960. It was an unmanned satellite designed to work out all stages of a manned flight into space. The very first landing of a spacecraft on a non-atmospheric body (the Moon) was carried out on February 3, 1966 (“Luna-9”).

True, a spacecraft hit the Moon as early as 1959, but this happened in the absence of a descent vehicle, and the impact on the Moon's surface ended in the complete destruction of the spacecraft. However, the special (volumetric) arrangement of pennants allowed some of them to be undamaged.

As already mentioned, there are two main ways to reduce the flight speed of a spacecraft: using a propulsion system similar to that used to put a satellite into orbit, and braking in the planet's atmosphere. The first method requires a large amount of fuel to extinguish the gigantic speed, and at present, for planets with an atmosphere, when chemical fuel is used, it is considered uneconomical.

Braking in the atmosphere of cosmic bodies is a common phenomenon in nature. Thanks to the presence of an atmosphere, we find fallen "heavenly rocks" on Earth called meteorites. They are stone, iron and intermediate type. Meteorites that fell to Earth are the remains of msteoroids that flew in their orbits and collided with the Earth. Passing through the atmosphere with a colossal initial flight speed is costly for the celestial guest. Most of it is molten, evaporated and dispersed in the atmosphere. But, fortunately, not all, otherwise we would not have to find meteorites.

The thing is that the released thermal energy is not completely used to heat the meteoroid or the spacecraft (therefore, the estimates given earlier about the conversion of the entire kinetic energy of the falling body into heat were exaggerated). The nature of thermal energy is such that it tends to spread in all directions with varying intensity. And when braking in the atmosphere, thermal energy (and, as a rule, most of it) is transferred to the atmosphere.

And yet, the speed of the meteoroid when it meets the Earth is very high - from 11.2 to 72 km / s. Theoretical calculations and observational data indicate that at meeting speeds of more than 22 km/s, meteoroids are completely destroyed in the Earth's atmosphere. It is interesting to note that on June 30, 1908, eyewitnesses saw a trace of the "Tunguska meteorite" flying from the northwest to the southeast. Consequently, he flew at a large angle towards the Earth, and maybe perpendicular to its movement. Thus, the speed of the meeting was more than 30 km/s, which could cause the complete destruction of the celestial body.

But let us return to the problem of deceleration of the spacecraft. Note that even if we use its natural braking in the atmosphere for this, we still cannot do without a propulsion system. Free descent from orbit due to deceleration in a rarefied atmosphere cannot be considered acceptable, since this causes difficulties in predicting the time and place of landing. The propulsion system creates a braking impulse in order to transform the orbit in such a way that its perigee part is precisely in the dense layers of the atmosphere. In this case, the greater the braking impulse, the steeper the entry of the spacecraft into the dense layers of the atmosphere and the more intense its deceleration.

However, the intensity of deceleration should be limited by the overloads allowed for the crew and instruments, as well as the design of the descent vehicle. For these reasons, the steepness of the entry into the atmosphere must be created smaller. Most of the descent vehicle's kinetic energy, converted into heat during atmospheric deceleration, must be dissipated in the external environment, and only a small part of it can be absorbed by the structure's mass or perceived by the vehicle's heat-shielding systems. With gentle descent trajectories in the atmosphere, the level of overloads and the intensity of heating are lower, however, due to the increase in the duration of the descent, the total fraction of thermal energy supplied to the surface of the apparatus increases.

The nature and intensity of the interaction of the descent vehicle with the air during deceleration is affected by atmospheric parameters, such as density, pressure, temperature, molecular mean free path, propagation velocity of disturbances (speed of sound), molecular mass etc. But even these parameters are not constant, but fluctuate depending on the time of year and day, on changes in solar activity, on climatic factors, wind changes, etc.

The huge speed of entry of the descent vehicle into the atmosphere causes great perturbations in it. Ahead in the direction of flight, the gas of the atmosphere begins to compress, but not gradually, but with a blow, and a seal occurs - the so-called shock wave. The latter moves somewhat ahead of the descent vehicle at the same speed. The temperature in the front of the shock wave reaches several thousand Kelvin. The heat flows go in all directions, including the descent vehicle. In this case, the heat flux falling on the descent vehicle depends on the composition of the atmosphere and its thermodynamic characteristics.

At large entry angles, the flow rises and falls as a result of sharp deceleration in a peak-like manner. It turns out a powerful thermal and dynamic shock and the rapid removal of a solid amount of thermal protection. At small entry angles, the heat flux growth curve is flatter, and the time of its action is longer and the coating is less carried away, but, of course, there is a large heating of the entire thermal protection system.

During the deceleration of the spacecraft, thermal energy enters the atmosphere from its surface in two main ways - due to covective heat transfer in the boundary layer and due to the radiation of the shock wave front. At high flight speeds, the process of convective heat transfer is complicated by gas ionization, non-equilibrium of the boundary layer, and when mass is carried away from the skin surface (burning of the coating, evaporation of thermal protection, etc.) - by mass transfer and chemical reactions in the boundary layer. Shock wave radiation - radiant heat transfer - becomes significant at flight speeds of 6–8 km/s, and becomes decisive at high speeds.

The thermal energy supplied from the outside to the descent vehicle skin is partially dissipated due to radiation from the heated surface, partially absorbed or carried away (during cooling with mass removal) by thermal protection systems, partially accumulated due to the heat capacity of the descent vehicle structure, causing an increase in the temperature of the power elements. A complete study of the thermal regimes at various points of the shell of a descent vehicle of a real configuration, which requires a sufficiently detailed consideration of heat and mass transfer near the cooled surface and the study of temperature fields in the structure, is a very difficult task. Approximate relations are usually used to estimate the heating intensity for some typical sections of the surface of the descent vehicle. Then these estimates are refined on the basis of experimental studies. Thus, the creation of descent vehicles for specific planets with an atmosphere is a laborious and very complicated task, even only in terms of thermal protection, but it is successfully solved in design bureaus.

APPARATUS FOR DESCENT IN THE ATMOSPHERE

Let's look at the existing and already used descent vehicles from the point of view of the distribution of heat flows. The kinetic energy of the descent vehicle, although very large, is easily calculated. The energy released during the deceleration of the descent vehicle in the atmosphere is used only in a small part (1–2%) to heat it, while most of this energy heats the surrounding air and is dissipated in the atmosphere. Practically, these 1–2% of the energy available to the descent vehicle should be used to calculate the thermal protection created.

Generally speaking, in astronautics energy is spent wastefully. When a spacecraft is launched, only 1–2% of the energy of the fuel burned in the propulsion system is used to increase the kinetic energy of the spacecraft. The rest is spent on losses during heating of gases and their outflow into the atmosphere, on moving and increasing the kinetic energy of the first stages of the launch vehicle, on increasing the potential energy of the spacecraft, etc. (Apparently, these percentages are often found in nature. Even, as shown Academician I. V. Petryanov-Sokolov, the efficiency in the processing of minerals on Earth is only 1–2%, but these coincidences are probably a topic for another conversation.)

Both the duration of the heat flux and the magnitude of the drag depend on the angle of entry into the atmosphere. At large entry angles, the resistance increases so sharply that the magnitude of the overload reaches several hundreds of g. This was typical for the interplanetary stations "Venus" of the first generation (up to and including "Venera-8"). Their atmospheric entry angles reached 62–65°, while the g-forces were up to 450 g. This means that each device, each element of the descent vehicle became 450 times heavier and put the same amount of pressure on the support where it was fixed than at the time of installation in the descent vehicle in the assembly shop.

For a long time, the spacecraft "Venus" is in weightlessness in an interplanetary orbit from Earth to Venus, when the descent vehicle does not experience force loads for four months. And only when meeting with the atmosphere of Venus, suddenly, suddenly, a huge force falls on the body and shell of the descent vehicle - the force of atmospheric resistance, which, like a powerful press, tends to crush the descent vehicle. At the same time, it is subjected to the onslaught of two influences simultaneously: the drag force of the atmosphere and a powerful flow of thermal energy. This happens with any descent vehicle that is part of both the interplanetary station and the spacecraft when astronauts return to Earth.

The frontal outer layers of thermal protection sublimate, i.e. evaporate, and are carried away by the air flow, creating a luminous trace in the atmosphere. The high temperature in the shock wave ionizes the air molecules in the atmosphere - a plasma is formed. The plasma blanket covers a large part of the descent vehicle and, like a screen, covers the descent vehicle borne in the atmosphere and thereby deprives the cosmonauts of communication with the astronauts or with the radio complex of the automatic vehicle during landing. Moreover, under terrestrial conditions, ionization is formed, as a rule, at altitudes of 120–15 km, with a maximum in the range of 80–40 km.

Forms of descent vehicles. First of all, we note that descent vehicles intended for planets with an atmosphere can be created either for descent without control - along a ballistic trajectory, or for descent with a motion control system capable of performing a maneuver in the atmosphere. Naturally, even more advanced descent vehicles equipped with a control system can also descend along a ballistic trajectory.

The first descent vehicles used for artificial Earth satellites were made in the form of a ball. These are descent vehicles of satellite ships, Vostok and Voskhod spacecraft, as well as biosatellites. Their descent took place along a ballistic trajectory, no different from natural "descent vehicles" - meteorites. The shape of the ball is the simplest and most widespread in nature. This is the shape of stars, planets, small water droplets, etc.

The spherical structure, except for drag, is not subject to the action of any other forces, except for the force of attraction. Aerodynamics say that the ball has zero quality, i.e., the lifting force when the atmosphere flows around the ball is zero. For a spherical structure, the magnitude of the overload depends on the flight speed and the angle of entry into the atmosphere. For an artificial satellite of the Earth, whose orbital speed is somewhat less than 8 km/s, the entry angle must be small, on the order of one or several degrees, so that the overloads do not exceed 10 g, which is very important for de-orbiting a descent vehicle with a crew .

What is required for comfortable conditions during the descent of astronauts from orbit, i.e., for deceleration to occur with the acceleration of the earth's gravity (i.e., almost 10 m/s 2)?

Firstly, the stopping distance must be 3200 km long. Secondly, if nothing interfered, that is, if we did not count the atmosphere, then we would have to descend for 800 s with the engine turned on. And under terrestrial conditions, the air shell cannot slow down so smoothly during a ballistic descent, and braking occurs more sharply, with large overloads.

In other words, to reduce the magnitude of the overload, it is necessary to carry out a descent not along a ballistic trajectory, but using a lifting force. In this case, it is necessary to use a descent vehicle with an aerodynamic quality. The ball, as already mentioned, does not have aerodynamic quality, but already the plate, if placed obliquely in the air stream, shows the presence of lift. crew compartment - turned out to be a descent vehicle in the form of a headlight.

This design has an aerodynamic quality of up to 0.35, or, in other words, in motion at a certain inclination of the front wall of the headlight, a lifting force arises that reaches a value of 35% of the drag force. The lifting force makes it possible to carry out the descent along a more gentle trajectory, with less overloads. This shape is typical for the descent vehicles of the Soyuz, Mercury, Jsmini and Apollo spacecraft. True, the ship "Mercury" could not use its shape to create lift. The design solution of the ship did not allow this, and the descent of the vehicle always took place along a ballistic trajectory.

What needs to be created to tilt the front wall of the headlight when the air flows around it?

Rice. 1. Displacement of the center of mass of the descent vehicle: 1 - lifting force; 2 - flight direction; CM - center of mass; CD - center of pressure; the place of the most massive equipment is shaded

In principle, this could be done using an orientation system. True, the fuel consumption in this case would reach very large values: after all, it was necessary to create significant control moments to compensate for the moments arising under the action of aerodynamic forces. And from the point of view of the cost of huge masses of fuel, this path is unacceptable.

A simpler solution is to shift the center of mass relative to the axis of symmetry. At the headlight, the front wall is used as the main bearing surface - the bottom, which has the shape of a segment of a sphere of relatively small curvature. The lateral surface of the descent vehicle is made either in the form of a cone or a combination of a cone and part of a sphere. The descent of the apparatus is carried out bottom first. Since in appearance the descent vehicle is a body of revolution, its center of pressure (the resulting force of aerodynamic action) is located on the axis of symmetry. So the mixed center of mass is located between the bottom and the center of pressure.

Such centering provides a stable position of the descent vehicle in the air flow (bottom forward), as well as an asymmetric flow around the descent vehicle. Thanks to the latter, a lifting force appears, which is perpendicular to the oncoming flow (Fig. 1).

Descent from the orbit of an artificial Earth satellite can be successfully carried out in a wide range of initial conditions with acceptable overload and thermal loads both during ballistic descent and during descent using the aerodynamic quality of the descent vehicle. At the same time, a motion control system during descent is widely used, based on the method of controlling the descent vehicle by its programmatic turn along the angle of roll (at a constant angle of attack), which during the flight ensures a change in the effective force - the projection of the lift force on a vertical plane. This method requires rather small control torques, due to the so-called static neutrality in the angle of roll and the invariance of the pattern of air flow around the control process.

But already during the return of the spacecraft after the flight to the Moon, when the speed of its entry into the earth's atmosphere is close to the second cosmic velocity, the problem of descent becomes more complicated due to the increase in overloads and the increase in the intensity of the heat flow. In order to successfully solve the problem of descent, it is necessary in this case to very accurately maintain the "corridor" of atmospheric entry, which determines the boundaries by the angle of entry into the atmosphere. In the case of large angles, large overloads occur, and vice versa, at very small angles, the atmosphere may not "capture" the descent vehicle due to the insignificance of its resistance to its movement. It should be noted that the boundaries of the entry corridor depend both on the aerodynamic characteristics of the descent vehicle and on how the aerodynamic quality of the vehicle is used in the initial segment of immersion into the atmosphere. In addition, with an increase in flight speed, the width of the reentry corridor also decreases, and this leads to an increase in the accuracy of the navigation and correction system in the approach section of the trajectory.

For a descent vehicle with a motion control system, the return from the Moon can be solved in another way. With a sufficiently steep entry into the atmosphere, when the entry angle is greater than 2°, the trajectory of the descent vehicle, even at small constant values ​​of the angle of attack and a small quality factor (within 0.2–0.3), contains ascending sections, i.e., the vehicle may ricochet . In this case, a double immersion of the descent vehicle into the atmosphere is acceptable (Fig ... 2). When approaching the Earth with the second cosmic velocity at an entry angle of 3°, the descent vehicle, after the first immersion, exits the atmosphere into an elliptical orbit and then re-enters the atmosphere, but already at a distance of 10,000 km from the exit point.

Rice. 2. Double immersion into the atmosphere: 1 - the first entry into the atmosphere; 2 - exit from the atmosphere; 3 - second entry into the atmosphere; 4 - landing; 5 - conditional boundary of the atmosphere; 6 - entry corridor

However, it is difficult to provide an exact landing site in this case, since, if the speed deviates by 0.001 (about 8 m/s) from the calculated one, it leads to a deviation in the range of the secondary atmospheric entry point by 300 km, and a deviation in the trajectory inclination angle by 0.1 ° - to range deviation by 180 km. To reduce this uncertainty, the trajectory should have the largest possible angle of inclination at the point of departure from the atmosphere. True, the value of this angle is limited by the margin of the descent vehicle's aerodynamic quality, as well as the permissible limit of maximum overloads (otherwise, there will be deeper immersions into the atmosphere in the first section). On the intermediate flight segment, the control of the device is impossible, and therefore the accumulated deviation in range can only be compensated for on the segment of the second immersion into the atmosphere.

We emphasize that, considering the capabilities of the descent vehicle during the return from orbit and from lunar trajectories, we provided for the software control of the vehicle's motion. However, when returning from orbit, situations may also arise when it becomes impossible to control the descent trajectory using aerodynamic forces. For example, if suddenly the descent vehicle failed to orient itself before entering the atmosphere or, say, to prepare the control system. In these situations, it is necessary to carry out a ballistic descent along the trajectory, which is formed without the use of the lifting and lateral aerodynamic forces of the apparatus.

In this case, a trajectory is selected that provides a much smaller spread of landing sites and avoids unacceptably large overloads. And large overloads are quite possible if the descent vehicle, say, enters the atmosphere inverted by 180°, i.e., when the lifting force does not push the vehicle up, but makes it sink into even denser layers of the atmosphere and makes the descent steeper. However, it is quite simple to organize the necessary ballistic descent - it is enough to tell the device to rotate about an axis coinciding with the direction of flight. With this rotation, the effect of transverse aerodynamic forces is minimized.

Thermal protective coating. As already mentioned, almost all the energy communicated by the launch vehicle to the spacecraft must be dissipated in the atmosphere during its deceleration. However, a certain part of this energy leads to heating of the descent vehicle during its movement in the atmosphere. Without sufficient protection, its metal structure burns out upon entry into the atmosphere and the apparatus ceases to exist. Thermal protection must be a good insulator of thermal energy, i.e., have a low heat transfer capacity and be heat resistant. Such requirements are met by certain varieties of artificial materials - plastics.

The descent vehicle is covered with a heat shield, usually made of these artificial materials, consisting of several layers. Moreover, the outer layer usually consists of relatively strong plastics with graphite filling as the most refractory material, and the next thermal insulation layer is most often made of plastic with fiberglass filling. To reduce the mass of thermal insulation, as a rule, individual layers are made honeycomb, porous, but with a sufficiently high strength.

The thickness of the thermal coating depends on the type of descent vehicle and its purpose. For example, for the descent vehicle of the Venera-14 station, the loss of the heat-shielding coating during the passage of the atmosphere of Venus was about 30–70 mm across the thickness of the protective screen. Therefore, the heat-shielding coating must be thick enough to preserve the metal structure of the descent vehicle. And this is already a significant percentage of the mass of the allowable value for the descent vehicle. So, for the descent vehicle of the Vostok spacecraft, which had a mass of 2460 kg, the mass of the spherical thermal protection was 800 kg.

So, when exposed high temperature the heat-shielding coating, starting from the surface, heats up strongly and then evaporates, thereby carrying away with it excess thermal energy from the descent vehicle. To reduce the mass of the heat-shielding coating, its maximum thickness falls only on the places that are most exposed to the heat flux. For headlight-type descent vehicles, this is the bottom, and the side surfaces, which are subject to less heat, have heat protection of insignificant thickness. Moreover, for individual descent vehicles, after passing through the largest deceleration section and after the termination of the thermal loads, the massive heat shield from the frontal part (from the bottom) is dropped.

parachute system. After the end of intense aerodynamic deceleration, the movement of the descent vehicle becomes relatively uniform. The speed of its decline for various structures in the atmosphere near the Earth is set in the range of 50 - 150 m/s. To save the descent vehicle and ensure the safety of the crew, landing speeds must be much lower. So, for example, the speed when landing on water should not exceed 12–15 m/s, on land (on hard ground) - 6–9 m/s. For comparison, we note that an athlete-parachutist lands at a speed of 5–8 m/s. To reduce the speed of the descent vehicle falling to the Earth, various parachute systems are used.

The mass of these systems also makes up a certain part of the mass of the descent vehicle, and, as a rule, with an increase in the mass of the apparatus, the mass of the parachute system also increases proportionally. The introduction of the parachute system into the air tray and the deployment of the canopy, although not a simple task, is successfully solved in practical astronautics. At relatively high flight speeds, the introduction of a large canopy of the main parachute leads to large loads that the parachute material may not withstand. In this case, large loads will also affect the crew of the apparatus. Structurally, this problem is solved with the help of a parachute system.

First, together with the parachute cover that is being fired, a pilot chute with a small working area of ​​​​the dome is pulled out. This pilot chute introduces the canopy of the drag chute into the oncoming air flow. As a result, the rate of descent of the descent vehicle is almost halved, and then the main parachute is introduced with the help of a braking parachute. And most often, not the full canopy of the main parachute is introduced, but part of it. With a further decrease in the speed of the descent vehicle, the cord, with which the main canopy is reefed, is cut and then the canopy of the main parachute opens completely.

The main parachute canopy has a large working area, which makes it possible to reduce the rate of descent to values ​​that are safe for the crew and the descent vehicle itself. However, it is fundamentally impossible to completely slow down the descent vehicle using only one such parachute. Therefore, the main parachute, depending on the mass of the descent vehicle, can be with one dome or with several. Sometimes, instead of a cascade of brake and main parachutes, a reefed main parachute is used at first, but with a decrease in the speed of descent, the reefing in one or two stages is removed.

Final braking is conveniently carried out using powder engines. These engines turn on just before touching the earth's surface, and they dampen the descent speed to 2–4 m/s. Note that the descent vehicles of the American spacecraft "Mercury", "Gemini" and "Apollo" were equipped only with a parachute system and soft landing powder engines were not used on them, since these descent vehicles landed in the ocean - on the water.

DESCENT VEHICLE OF VOSTOK AND VOSHOD SHIPS

One of the very first descent vehicles successfully returned to Earth was the descent vehicle of the Soviet satellite, made in the form of a ball. This satellite ship was designed to work out all the elements and stages of a manned flight into space. Its descent vehicle practically did not differ from the descent vehicle of the Vostok spacecraft. The latter structurally consisted of two main compartments: the descent vehicle and the instrument compartment. The descent vehicle also included the astronaut's cabin.

During the descent from orbit, after the deceleration impulse was delivered, the descent vehicle separated from the instrument compartment and landed on the Earth, while the instrument compartment entered the dense layers of the atmosphere and ceased to exist there. The mass of the descent vehicle was 2460 kg, its body had the shape of a ball with a diameter of 2.3 m and was made of aluminum alloys. Outside, the entire hull, except for the windows, was covered with a heat shield, on top of which a layer of thermal insulation was applied, which was necessary for the normal functioning of the ship during the orbital flight.

The astronaut's cabin contained a chair and instruments for controlling the spacecraft. Ensuring normal health and maintaining normal human performance in the cosmonaut's cabin was determined by two main systems: life support and thermal control. They maintained the normal composition of the air in the cabin by absorbing the carbon dioxide released by the astronaut during breathing and ensuring a constant oxygen content in the air, as well as removing excess moisture from the air and creating normal temperature conditions within 20–25 °C. In the cabin, the pressure was maintained within the range of 755-775 mm Hg. Art.

In order to evenly mix the atmosphere in the cabin, which did not have convective flows under weightless conditions, a fan was installed. The thermal control system, common to two compartments, was made in a liquid version. To ensure the normal operation of the equipment located in the descent vehicle, there was a rechargeable battery. The cosmonaut's control panel contained a spacecraft attitude control knob with three degrees of freedom, as well as an optical device for the attitude control system.

Before separation, the spacecraft was oriented in a strictly specified direction, and at the calculated time the propulsion system was switched on, imparting a braking impulse to the spacecraft. The engine developed a thrust of 17.5 kN, while the speed decreased by 150–200 m/s. The orbit became elliptical with perigee below 100 km above the Earth's surface. As a result, the descent vehicle entered the dense layers of the atmosphere and slowed down.

At an altitude of about 7 km, the astronaut could eject - through the opening of a special hatch, he, along with the chair, was fired along special guides. Some time later, a braking parachute opened over the seat, and after a few tens of seconds at an altitude of 4 km, when the cosmonaut separated from the seat, the cosmonaut's main parachute opened; the astronaut's landing speed was 5–6 m/s. At the same time, the descent vehicle descended on its own parachute. It was possible to land without leaving the cabin - in the descent vehicle, which descended at a speed of about 10 m/s.

The descent vehicles of the Soviet artificial Earth satellites used to date for conducting biological experiments are in principle not much different from the descent vehicles of the Vostok spacecraft, and therefore we will not dwell on them separately. We only note that they go through all stages of descent, except for ejection, since there is no astronaut's chair here. Various representatives of the animal and plant world are placed inside the descent vehicle, as well as equipment is installed that provides feeding animals and watering plants.

The Voskhod ships, unlike the Vostok ships, were multi-seat. The placement of several cosmonauts at once required a reconfiguration of the cosmonaut's cabin. Three chairs with individual cradles were installed in it, i.e. they were made in size and taking into account the characteristics of the body of each cosmonaut. Since the landing could only be carried out with astronauts in the cabin of the descent vehicle, non-ejection seats were equipped with additional shock absorbers. The main stages of descent from orbit were similar to those for the Vostok spacecraft. But for greater reliability of the descent from orbit, the propulsion system on this ship was duplicated: in addition to the liquid propulsion system, a solid propellant brake engine was placed above it.

In order to reduce the impact on the earth's surface, the descent in the parachuting section was carried out on two parachutes, which were attached not directly to the descent vehicle, but to the soft landing engine housing using pyrolocks. After landing, the pyro-locks worked and the parachute strands were thrown away from the descent vehicle, so that in a strong wind the parachute could not drag the apparatus with the astronauts along the ground.

The powder engine of a soft landing was switched on by a tubular rod, lowered below the descent vehicle by about 3 m. The rod was formed by winding a spring tape from the coil and folding it into a tube. When the rod came into contact with the Earth's surface, the contact was closed and the propulsion system was turned on, which halved the rate of descent, bringing it to 2–4 m/s.

DESCENT VEHICLES FOR THE RETURN OF LUNAR "GEOLOGISTS"

The descent vehicles of the Luna-16, -20 and -24 automatic spacecraft, intended for landing on Earth after taking lunar soil, had the shape of a ball with a diameter of 0.5 m. This shape does not require the creation of a special orientation system necessary for the descent vehicle, with aerodynamic quality. The descent in the atmosphere took place along a ballistic trajectory. The main thing here was the requirement to limit the mass for the descent vehicle. The absence of the cosmonaut removed the obstacles imposed by large overloads.

The landing stage of these automatic stations "Luna", which was a descent vehicle for landing on the moon, also served as a launching device for the "Luna - Earth" space rocket. The latter included a liquid-propellant rocket engine with spherical tanks for propellant components, as well as an instrument compartment with four whip antennas and a descent vehicle attached to the instrument compartment with tie-down straps. The instrument compartment served as the installation site for the instruments of the control system, radio complex, battery and on-board automation.

After the Luna-16 station had drilled the lunar surface with the help of a soil-taking device, the drill with soil was inserted inside the container of the descent vehicle, after which the container was sealed, and after the preparatory operations for checking the readiness, the control system, on command, turned on the propulsion system of the lunar rocket , and it started vertically upwards. At the end of the propulsion system, the rocket had a speed of 2708 m / s, sufficient to overcome the lunar attraction.

The flight of the rocket to the Earth passed along a ballistic trajectory, for which correction was not required and was not provided for (the flight to the Earth lasted about 3 days). Three hours before entering the Earth's atmosphere, the descent vehicle was separated from the rocket by means of pyrotechnics. The entry into the earth's atmosphere was made at a speed of more than 11 km/s.

At the stage of aerodynamic deceleration, the descent vehicle, under the influence of the oncoming air flow, turned its frontal part in the direction of movement, and the damping device stably held it in this position. Further, the landing process was carried out by means of onboard automation. Due to the large angle of entry into the Earth's atmosphere, the descent vehicle experienced an overload of 350 g, and its thermal protection was exposed to a temperature of more than 10,000 K. Upon reaching an altitude of 14.5 km, the speed of the descent vehicle decreased to 300 m/s.

At this moment, on command from the g-force sensor, the cover of the parachute compartment was fired and a brake parachute was introduced into the air stream. At an altitude of 11 km, at the signal of the barometric sensor, the brake parachute was unhooked and the main parachute was introduced. Landing was carried out on solid ground, although the descent vehicle could also descend into the water. To increase buoyancy in the upper part of the descent vehicle, after shooting off the parachute cover, two flexible cylinders were inflated with compressed air.

Figure 3. The descent vehicle of the Luna-16 station on Earth

The descent vehicle of this lunar station (Fig. 3) was a sealed metal ball, the outer surface of which had a heat-shielding coating, which ensured the preservation of the vehicle in the aerodynamic braking region during entry into the Earth's atmosphere. The heat-shielding coating had a variable thickness: in the frontal part, the largest (up to 35 mm), and on the opposite side, only a few millimeters. Structurally, the descent vehicle consisted of three compartments: an instrument compartment, a parachute compartment, and a cylindrical container for lunar soil samples. The instrument compartment housed direction-finding transmitters, batteries, automation elements and a software device. The parachute compartment contained (folded) a parachute, four direction-finding transmitter antennas and two elastic balloons used after landing and inflating them to fix the position of the descent vehicle, as well as to create buoyancy when landing on water.

This descent vehicle had a relatively small size, the spread of the landing site in a given area reached hundreds of square kilometers, and therefore there was a problem with finding the device after landing. In this connection, the direction-finding transmitters installed in it continuously transmitted signals at a strictly fixed frequency, allowing it to be easily located and determine the landing site. A damper was installed from below inside the hull in the frontal part of the descent vehicle, which made it possible to dampen the oscillations of the apparatus during the passage - the stage of aerodynamic braking.

DESCENT VEHICLE OF THE SOYUZ SHIP

This vehicle became the first Russian descent vehicle to perform a controlled descent in the atmosphere. The bottom and ceiling of the descent vehicle are in the form of spherical segments, and its side walls are in the form of a truncated cone. The cosmonauts sit in shock-absorbing seats, installed in such a way that the direction of the action of g-forces during launch into orbit and descent is optimal from the point of view of their tolerance.

Sometimes it is expedient to entrust part of the descent control functions to the crew. In these cases, it should be borne in mind that under the conditions of the action of overloads, human capabilities are reduced. The g-force is most difficult to tolerate when it is directed from the legs to the head, and it is easiest when it acts at angles of 10–15 ° to the chest-back direction and in such a way that there is a small component from the head to the legs. But even under these conditions, already with three or four times overloads, the range of motion in the joints of the hands is significantly reduced, and with overloads of 8 g and more, only movements in the wrist joints remain free.

This is taken into account when designing controls. For better tolerance of G-forces, the cosmonaut needs to maintain muscular composure in the descent section, and for this it is best to use handles. Therefore, the ship's motion control knob is installed on the pilot's seat. In front of the astronauts there is a control panel and an optical sight, which is used when performing rendezvous control orientation. Behind the seats are containers with parachute systems. Instruments and equipment controlled remotely are located in the lower part of the compartment under the seats. There are portholes on the side walls to the right and left of the astronauts.

Outside, a heat-shielding coating is installed on the body of the descent vehicle. The part that is located on the bottom side is made in the form of a separate shield. During parachute descent, the shield is dropped. Under the drop shield of the heat-shielding coating there are four soft-landing powder engines, which are activated by a signal from a gamma-ray altimeter.

On the outer side of the surface of the descent vehicle, there is a board with connectors for electrical communications that provide communication with other compartments. Before splitting the ship, the connectors are automatically undocked.

After aerodynamic braking in the descent section, barometric sensors measure the pressure overboard the descent vehicle. At atmospheric pressure corresponding to an altitude of 9.6 km, a program-time device is launched, which generates a command to shoot the cover of the container of the main parachute system and to put pilot chutes into action. After 16.5 s after that, a command is generated to enter the main parachute. At an altitude of 5.5 km, the main parachute, subject to normal opening, should ensure a steady descent of the descent vehicle.

To check the health of the parachute, the actual rate of descent is monitored for 50 s. If the speed exceeds the maximum permissible value, then a command is formed to shoot the main parachute and put the reserve parachute system into action.

75 s after reaching an altitude of 5.5 km, at the command of the time program device, the frontal heat shield is separated, and the operation of the separation sensors removes the blocking for starting the soft landing engines. In addition, the program-temporary device issues a command to reattach the parachute to a symmetrical harness, turns on the gamma-ray altimeter and cocks the seat cushioning system. At the signal of the altimeter at a height of about 1 m from the earth's surface, the soft landing engines are switched on. According to special shock sensors that register the landing of the device, the blockage for shooting the parachute strands is removed.

As an example, consider the flight of the descent vehicle of the Soyuz T-12 spacecraft. Before performing the landing operation, the spacecraft was oriented to deceleration. Over the southern region of the Atlantic Ocean, a propulsion system with a thrust of 4 kN was turned on. Having worked for 800 s, the engine reduced the orbital velocity by 115 m/s - the orbit became elliptical. Over the Mediterranean Sea at an altitude of 130 km, the spacecraft was set to its original position for separation.

This position is chosen in such a way that by the moment of separation the longitudinal axis of the spacecraft is deviated from the direction of flight by an angle close to 90°. In this case, after separation, the aerodynamic forces cannot again cause repeated approach and collision of the compartments. After separation, only the descent vehicle, protected by a heat-shielding coating, resists and resists high temperatures and atmospheric resistance. Other compartments are not designed for such severe tests and therefore burn up in the atmosphere. The controlled descent began over eastern part Turkey.

During a flight with a controlled descent, the astronauts note that the flight is similar to driving on a cobblestone pavement from the resulting vibrations and shaking. These phenomena have probably been experienced by each of us when flying on high-speed passenger aircraft. During the period of aircraft descent during landing approach, especially when passing through dense clouds, in which there are turbulent ascending air currents, vibration occurs. In the upper layers of the atmosphere, too, there are always currents up and down, winds blow, there are separate areas of low pressure, others of high pressure. When flying a glider at low speed, these irregularities roll up smoothly and slowly and smoothly raise and lower the glider. With a significant increase in speed, these inhomogeneities occur and alternate more often, one might say, they flicker and shake the aircraft with small blows.

DESCENT VEHICLE OF THE SHIP "ZOND"

The descent vehicle of this spacecraft differed little from the descent vehicle of the Soyuz spacecraft; it enters the Earth's atmosphere at the second cosmic velocity. Therefore, its heat-shielding coating is more powerful, and the equipment is designed for flight to the Moon and back.

It is only necessary to note that the descent vehicle of the Zond-5 spacecraft landed after the lunar region in the Earth's atmosphere along a ballistic trajectory in the area indian ocean, and the ship's descent vehicle, Zond-6, landed on the territory of the Soviet Union using a controlled descent system. The first dive into the atmosphere was at a distance of about 10,000 km from the landing site. During the first dive in the atmosphere, the speed of the descent vehicle was reduced to 8 km/s, during the second - to 220 m/s. All stages of further landing on the Earth's surface were similar to the landing of the descent vehicle of the Soyuz spacecraft.

DESCENT VEHICLES OF AMERICAN SHIPS

The descent module of the ship "Mercury". If in automatic spacecraft American specialists used ball-shaped descent vehicles to return to Earth, which descended along a ballistic trajectory, then for manned spacecraft the shape of the descent vehicle for all types of ships differs from the ball. For the Mercury spacecraft, a descent vehicle was developed in the form of a truncated cone on the side of a smaller base connected to the cylindrical part of the body. On the other side of the cone there was a bottom in the form of a spherical segment.

Almost almost the entire ship "Mercury" consisted of a descent vehicle, from which, after launching into orbit, a farm with emergency rescue engines was dropped, and in the deceleration section, after the end of the propulsion system, its separation took place. The braking propulsion system was attached to the bottom of the descent vehicle, which could only descend along a ballistic trajectory with its bottom forward. The bottom of the apparatus experienced the greatest heating from the front of the shock wave during the descent. The side surfaces of the conical and cylindrical shapes were subjected to less heating.

The parachute system of the ship "Mercury" was two-stage, consisting of the main and braking parachutes (the latter also served as a pilot chute). A relatively thick heat shield was installed on the bottom, which, after the introduction of the main parachute, was separated and hung on shock absorbers. When hitting the water surface, the shock absorbers absorbed the impact energy and thereby reduced the overloads experienced by the descent vehicle. It should be noted that all American descent vehicles with astronauts landed on water (with the exception of the MTKK).

There is another feature that distinguishes descent vehicles American ships. If in our manned spacecraft the atmosphere in the astronauts' cabin has an air composition reminiscent of the Earth's atmosphere in terms of physical and chemical parameters, then on the Mercury, Gemini and Apollo spacecraft it is purely oxygen at a pressure of 1/3 of normal (at sea level ).

The descent module of the Gemini spacecraft. The Gemini program was intended to study the problems associated with long-term space flights, rendezvous and docking in orbit, spacewalks, entry of the descent vehicle into the atmosphere and descent to Earth using lift, etc. The results of the work carried out under the program Gemini used for the Apollo program.

The Gemini was the first American spacecraft to be built using a controlled descent system for the descent vehicle (crew compartment). The shape of the descent vehicle was made in the form of a headlight. The entry into the Earth's atmosphere was carried out bottom first, and due to the shifted center of mass relative to the longitudinal axis, the flight in the atmosphere occurred with a constant angle of attack. The controlled flight was performed by rotating the descent vehicle along the roll angle. The descent vehicle of the Gemini spacecraft is two-seat, which made it possible to perform a spacewalk. At the same time, the entire atmosphere of the astronauts' cabin, consisting of oxygen, was released into space, and after the hatch was closed, it was restored due to the stored oxygen in the cylinders.

The descent module of the Apollo spacecraft. This vehicle, which American experts called the crew compartment, was included as an integral part of the main unit, consisting of the descent vehicle and the engine compartment. The main block and the lunar cabin were actually the Apollo spacecraft. In further consideration, we will focus only on the descent vehicle designed to deliver three cosmonauts to a selenocentric orbit and return them to Earth.

The mass of the descent vehicle of the Apollo spacecraft was 5.56 tons, it had the shape of a cone with a rounded top, a base diameter of 3.84 m, a height of 3.4 m, and a cone angle of 66°. The uppermost conical part served as a parachute hatch cover, which was separated before the deployment of parachutes. The hull of the descent vehicle was steel, assembled from laminated panels, the honeycombs of which were made of stainless steel and were enclosed between two steel sheets. The bottom part of the apparatus is made in the form of a spherical segment.

Inside the descent vehicle there was a crew cabin made of aluminum alloys and also had a layered structure with honeycomb filling. The honeycombs had different densities (from 0.07 to 0.114 g/cm 3 ) to ensure a given location of the center of gravity of the entire descent vehicle. In the cockpit, three chairs for astronauts were suspended on special shock absorbers, and the seats of the chairs could be installed at different angles to the back. The cockpit also contained control panels, navigation system equipment, and scientific equipment.

All equipment of the descent vehicle was placed in such a way that the center of gravity of this compartment was located at a certain distance from the longitudinal axis. As a result, when the descent vehicle entered the atmosphere, a certain angle of attack was created and a lifting force arose. With the help of the engines of the orientation system, the angle of roll, and, consequently, the lift force during flight in the atmosphere, could be regulated, which made it possible to carry out a controlled descent.

According to the program, the descent vehicle was lowered into the water. However, measures were taken in case it landed on land. On one side of the compartment there were four special protrusions (shelter with a thin outer screen along the contour of the cone), which, when hitting the surface, were supposed to collapse and thereby dampen shock loads. To ensure the fall of the compartment on the ledges, the parachute lines were attached to the descent vehicle asymmetrically.

The entire surface of the descent vehicle was protected by heat shields, which had a thickness of 8 - 44 mm on the conical part, and 63 mm on the bottom. The screens were made of fiberglass with honeycomb filling. An ablative material served as a filler: a phenol-epoxy resin, into which hollow glass beads were introduced.

After the completion of aerodynamic braking in the atmosphere, the parachute system was activated, which included two braking, three exhaust and three main parachutes. Brake parachutes with a diameter of 5 m were introduced into the air stream at an altitude of 7.6 km - they reduced the speed from 120 to 60 m/s. Pilot parachutes with a diameter of 3 m were introduced at an altitude of 4.5 km, a few seconds later, at an altitude of 4–4.2 km, reefed main parachutes were introduced, each of which had a dome diameter of 26.8 m.

The deployment of the main parachutes was carried out in three stages. When entering the stream, they were reefed, after 5 s they partially opened, after another 3 s they opened more, and finally, after a few more seconds, they unfolded completely. At the moment of splashdown, the speed was 8 m / s, and with one failure, i.e., when one of the parachutes did not open, it was 10.5 m / s (which happened in one of the flights of the Apollo spacecraft).

Reusable spaceships. In modern cosmonautics, in orbits of artificial satellites of the Earth, with rare exceptions ("Space Shuttle"), as a rule, disposable spacecraft are used, a characteristic feature of which is that they do not return to Earth entirely after a space flight. Normal conditions descents are provided only for one of the compartments - the descent vehicle. Design studies have shown that such ships have a number of advantages over ships returned in full force. They are technically simpler and require less material costs for their creation and launch.

The fact is that the salvation of the entire ship is associated with the solution of many additional problems. First, to ensure a controlled descent in an atmosphere with an acceptable temperature regime, the ship must have a streamlined shape with specified aerodynamic characteristics. This means that the ship should either not have protruding elements at all, or before launching they should be removed into the internal volume. Secondly, in order to prevent overheating of the structural elements and the atmosphere of the living compartments, it is necessary to cover the entire outer surface of the ship with thermal protection. This leads to a significant increase in the total mass.

On the Space Shuttle, out of a total spacecraft mass of 111 tons, the mass of thermal protection is about 9 tons, which is almost 10% of the total mass. The landing system turns out to be more complex and heavy. Descent control requires more fuel. As a result, the entire ship becomes more complex and expensive, and a more powerful launch vehicle is required to put it into orbit.

It should be noted that in disposable vehicles, all equipment used to control the descent and landing, as well as for the stay of the crew from the moment of landing to evacuation, is placed in the descent vehicle. Here, in order to ensure the convenience of the crew, in preparation for the descent, they install means for manually controlling the movement of the spacecraft in orbit and means for controlling on-board systems. In the same place, in the descent vehicle, places are provided for packing materials with the results of research and equipment returned to Earth.

DESCENT VEHICLES AMS "VENERA"

The descent vehicles of automatic space stations intended for the exploration of the planet Venus are structurally different from the descent vehicles of spacecraft. The planet Venus has a fairly powerful atmosphere: the atmospheric pressure on the planet's surface is more than 90 times higher than the earth's. The surface temperature is almost 500 °C (about 770 K). This left its mark on the creation of a descent vehicle for Venus.

The first flights to the planet Venus, in addition, were planned in such a way that the descent vehicles would fall approximately into the center of the disk of the planet Venus facing the Earth. This condition was necessary to create radio communication with the descent vehicle, whose antenna with a relatively narrow radiation pattern practically looked at the zenith during descent. But this also imposes special requirements on the angle of entry into the atmosphere of the planet when the station approached it, they turned out to be about 62–65 ° relative to the local horizon.

At an entry speed of more than 11 km/s, this circumstance led to large overloads, reaching up to 450 g. Therefore, it was necessary to think about creating a durable case and equipment capable of withstanding such strong overloads.

The descent vehicles of the first stations that flew to Venus had a shape close to a ball. At the same time, the sensors of scientific instruments could be placed only in the upper part of the descent vehicle, on the cut that opens after the parachute compartment cover is dropped. Initial ignorance of the exact conditions on the planet Venus, contradictory results of various observations led to the creation of relatively strong spherical descent vehicles that can withstand only up to 20 atm. Outside, they were protected by a heat-shielding shell of considerable thickness.

To refine the parameters inherent in the atmosphere of Venus, scientific instruments at the first stations were installed only to determine the temperature, pressure, chemical composition of the atmosphere and its illumination, as well as an altimeter to link data by height above the planet's surface. Such first reconnaissance stations of the planet Venus include the Venera-4 station, which flew in 1967, Venera-5 and Venera-6 - in 1969, Venera-7 - in 1970 and "Venera-8" - in 1972.

As a result of changing views on the physical conditions existing on the planet, as data were received from the descent vehicles, the design of the descent vehicles themselves underwent changes. The strength of the hull had to be increased so that it could withstand external pressure from 10 atm for Venera-4 to 120 atm for Venera-8. As a result, the mass of the descent vehicle increased, and if for the first of them it was 383 kg with a total mass of the station of 1106 kg, then for Venera-7 and Venera-8 the mass of the descent vehicle was already 500 kg with the mass of the station 1200 kg.

At an atmospheric reentry velocity of about 11 km/s, overloads reached 450 g, and the gas temperature in the shock wave front reached 11,000 K. At such high temperatures, the surface of the descent vehicle does not even burn, but simply evaporates.

The descent vehicles of the Venera-4 - Venera-8 stations, close in shape to a ball, had a diameter of about 1 m. The outer surface of the ball, especially its lower frontal part, was supplied with a powerful heat-shielding shell. The latter also delayed the influx of heat into the hermetic container from the surface of the ball during the movement of the descent vehicle in Veper's atmosphere.

The descent vehicles were separated from the automatic space stations when they were still 20,000 to 40,000 km from the planet Venus. With this maneuver, they tried to protect the descent vehicle from damage during entry into the atmosphere. In this case, there will be no collisions between the station compartments and, as a consequence, no damage to the descent vehicle. The orbital compartment did its job - it delivered the descent vehicle to the planet and now it can be destroyed when it enters the atmosphere of Venus, since it does not have an appropriate heat-shielding coating.

However, during the entire flight for 4 months from the Earth to Venus, the orbital compartment provided the temperature regime for its own needs and for the needs of the descent vehicle. Before separation, the thermal control system of the orbital compartment cooled the descent vehicle, which was necessary to extend its performance in the hot conditions of the Venusian atmosphere. The orbital compartment also provided electrical energy for the operation of various systems, drawing it from the Sun with the help of solar panels. Using this compartment, the position of the station in space was determined and the necessary flight correction was carried out to direct the descent vehicle to a given impact zone in the region of the planet Venus.

But, despite such important functions, the orbital compartment was actually only a means for delivering the descent vehicle to the planet Venus in working condition.

Structurally, the descent vehicle itself consisted of two isolated compartments: the lower - instrumental and upper - parachute. In the parachute compartment under the cover, which was dropped after passing through the aerodynamic braking section, there were sensors for scientific instruments, antennas of the radio complex and altimeter, as well as a two-stage parachute system (from the braking and main parachutes). The parachute fabric retained the required strength at temperatures up to 500 °C. Remote antennas of the radio complex for the last two stations from this series were also located here.

After intense aerodynamic deceleration, when a speed of about 200–250 m/s was reached, a command was formed from barometric sensors (at a pressure of 0.6 atm) to shoot off the cover of the parachute compartment and a braking parachute with an area of ​​2.2 m 2 was introduced into the air flow. In the course of a further decrease in speed, the program-time device issued a command to separate the braking parachute and introduce the main one.

The area of ​​the main parachute at Venera-4 was 55 m2, but after the flight of this station, the descent vehicle of which descended in a very "inhospitable" atmosphere for almost 1.5 hours, the characteristics of the main parachute had to be revised. When it was introduced at an altitude of about 70 km, the operation of the descent vehicle stopped already at an altitude of about 30–40 km when the atmospheric level reached a pressure of more than 20 atm. Moreover, a too long descent time led to a strong heating of the equipment in a hot atmosphere.

To speed up the descent, the area of ​​the main parachute for the descent vehicles of the Venera-5 and Venera-6 stations was reduced to 12 m 2 . As a result, the descent speed increased, and the descent itself lasted 51–53 minutes. These descent vehicles descended to the level of altitudes with a pressure of 27–28 atm., and the descent by parachute was already carried out to altitudes of 36 and 38 km. The descent vehicles of the Venera-7 and Venera-8 stations reached the surface of the planet with the operating equipment.

Rice. 4. The descent vehicle of the Venera-8 station: 1 - parachute; 2 - transmitting antenna; 3 - cover of the parachute compartment; 4 - radio transmitter; 5 - damper; 6 - thermal protection; 7 - body; 8 - heat exchanger

The lower instrument compartment of the descent vehicle of the first generation Venera stations (Fig. 4) housed an onboard radio transmitter, a time program device, automation units, a telemetry system, a radio altimeter, a storage battery, a thermal control system, and scientific equipment. A special mechanical damper was installed at the bottom of the descent vehicle, which served to increase the stability of the descent vehicle's motion in the atmosphere of Venus and to reduce the amplitude of its oscillations. The smaller the amplitude, the smaller the lateral overloads, which, added to the axial overload, worsen the impact on the descent vehicle.

After obtaining data on the actual characteristics of the atmosphere of Venus, the designers were able to begin designing and building a new generation of descent vehicles designed for extensive studies of the physical and chemical properties of the atmosphere and surface of this planet. Landing vehicles of the second generation were designed to perform many scientific tasks, including the purpose of "examining" the surface of the planet. Therefore, photographic and television equipment was installed on the descent vehicles. To carry out chemical analysis, a soil sampling device was developed and placed on the descent vehicle, and inside the descent vehicle there was a complex complex for conducting chemical analysis of the collected soil. Antennas, sensors for determining wind speed, illumination, etc. were placed on the rods.

Most of the scientific equipment had to be placed outside the descent vehicle, however, if it was forced to slow down in the atmosphere in this form, then all protruding parts with scientific equipment would be destroyed by a fiery tornado during aerodynamic braking. Therefore, the original descent vehicle was called a landing vehicle, a ball with a heat-shielding coating was put on top of it, and as a result, a new descent vehicle was obtained, but already much larger. The diameter of the ball was 2.4 m, and it consisted of two hemispheres, separated when pyrotechnics were detonated (Fig. 5).

The stations themselves "Venus" have also undergone changes. The launch of automatic interplanetary stations was carried out by a more powerful launch vehicle, and therefore the mass of the stations reached 4.5–5 tons. as a repeater of radio signals coming from the descent vehicle.

To do this, it was necessary to transfer it from the trajectory of hitting the planet to the flyby trajectory. Consequently, in advance of the flight to the planet, it was necessary to separate the descent vehicle, having previously cooled it to increase its survivability in the hot breath of the atmosphere, and then, with the help of the propulsion system, already transferred the station to the flyby trajectory. As a rule, the separation of the descent vehicle and the station is carried out two days before the approach.

Rice. 5. The descent vehicle of the Venera-10 station: 1 - parachute; 2 - scientific equipment operating in the atmosphere in the cloud layer; 3 - telephotometer; 4 - durable case; 5 - thermal protection; 6 - damper; 7 - landing gear; 8 - heat-shielding housing; 9 - brake shield; 10 - antenna

Why two days and not one or ten and not 27 or 59 hours?

For the descent vehicle, the later the separation, the better, since it uses the station's thermal control system and its equipment is checked for operability using the station's systems. And for the station, an earlier separation is necessary in order to create a lower energy impulse for a confident transition from an incoming trajectory to a flyby trajectory. A compromise decision predetermined the separation 48 hours, or two days, before approaching the planet. After separation before the introduction of the parachute system, the descent vehicle moves "silently", the Earth cannot control it. Exactly two days are required for the separation session to be carried out during the time when the ground-based radio tracking facilities located on the territory of the USSR are turned towards the planet Venus. And the session of arrival and landing on the planet of the descent vehicle (which was chosen in advance) should also fall within the period of radio visibility from the territory of our country. Naturally, these periods of radio visibility are multiples of 24 hours - the period of the daily rotation of the Earth.

After separation, the Venera station can be transferred to the orbit of an artificial satellite of Venus (as was the case with the Venera-9 and Venera-10 stations) or to a flyby trajectory with further flight around the Sun in an orbit located between the orbits of the Earth and Venus. The possibility of using the station as a repeater made it possible to significantly reduce the strength characteristics of the descent vehicle, since the harsh conditions for descent to the center of the planet's disk facing the Earth were eliminated.

Thus, it became possible to significantly reduce the angle of entry into the atmosphere. True, due to the permissible deviations of the trajectory from the calculated one, extremely small entry angles cannot be realized, since the atmosphere in this case may not capture the device. The entry angles of 20–23° were taken as the calculated ones for the Venera stations of the second generation. At the same time, maximum overloads reach only 170 g.

Landing of the descent vehicle can now be carried out practically anywhere on the planet, even on its opposite side not visible from the Earth. After all, now the radio signals from the descent vehicle were received by the spacecraft flying past the planet. The signals were received and relayed by him through a highly directional antenna to Earth, but could also be recorded on board the station, and then, as needed, repeatedly reproduced and transmitted to Earth.

Descent vehicles "PIONEER-VENERA"

To conduct research in the atmosphere of Venus, in 1978, American specialists launched the Pioneer-Venus-2 station, weighing 885 kg, which included four descent vehicles. Of these, one had the largest mass of 350 kg with a diameter of 1.5 m, and the other three had a mass of 86 kg with a diameter of 71 cm. Small devices were intended for descent in the atmosphere on the day and night sides of the planet, as well as towards the north pole of Venus.

The descent vehicles were made of titanium in the form of a ball so that they could withstand pressures up to 100 atm. From the outer surface, the ball was protected by a thermal screen, which had thermal protection from a fsnol-carbon coating in the frontal part. In the bottom part there was a coating of foamed elastomeric material.

24 days before approaching the planet, at a distance of about 12 million km, a large descent vehicle separated from the station, and after another 5 days, small vehicles separated at intervals of several minutes. The entry of the descent vehicles into the planet's atmosphere occurred at a speed somewhat greater than 11 km/s. At the same time, braking was aerodynamic.

This section of entry and intense deceleration lasted about 30 s, then the screen of heat-shielding material was dropped near the large descent vehicle and for 17 minutes it descended by parachute (small descent vehicles did not have parachutes). After this time, the parachute was dropped to speed up the passage of the atmosphere up to its surface. Communication with this descent vehicle lasted 1 hour 19 minutes until it hit the surface.

Small descent vehicles, after dropping their heat shields, also conducted radio transmissions before hitting the surface of Venus. The “daytime” descent vehicle (one of the three small ones) after hitting the surface continued to send radio signals for another 68 minutes. The Pioneer-Venera-2 station itself, similarly to the Venera-4 station, burned down in the planet's atmosphere.

In fact, these descent vehicles, not intended for a soft landing on the planet, only served as probes, collecting data on the atmosphere in the process of falling. Only one small vehicle that remained operational after hitting the surface can actually be called a descent vehicle.

Its preservation can be explained by the high density of the atmosphere of Venus, which can reduce the rate of fall, and, consequently, the magnitude of the overload upon impact with the surface.

Why, then, did the descent vehicles intended for landing on Venus have only the shape of a ball, and therefore their descent took place only along a ballistic trajectory?

Firstly, not a person descended to Venus, but scientific instruments that are capable of withstanding overloads of 100 g or more. Secondly, the shape of the ball is the simplest and for it it is not necessary to create a special descent control system. In the case of using a descent vehicle with an aerodynamic quality, such as a headlight, it becomes necessary to use a complex orientation system that determines the entry into the atmosphere and the direction of the lifting force, and also makes it possible to control the lifting force when the vehicle turns in a roll. In any case, the main role in choosing the shape of the descent vehicle for landing on Venus, of course, was played by the simplicity and relatively low cost of creating such a vehicle.

DESCENT WITHOUT ATMOSPHERE

At state of the art cosmonautics have so far carried out practically soft landings in the absence of an atmosphere only on the moon. But in principle, such descent vehicles can be delivered to Mercury, to the satellites of Mars, non-atmospheric satellites of other planets, as well as to asteroids. Note that the smaller the mass of the body of the solar system, the less fuel is possible to land on its surface.

Descent vehicles designed for a soft landing in the absence of an atmosphere are not covered with a heat-shielding layer, but, as a rule, they are dressed only in a “fur coat” of screen-vacuum thermal insulation to protect against the radiant energy of the Sun and protect against deep cooling in space from the shadow side of the device. A parachute for this type of descent vehicle is also not applicable, since there is nothing to fill the dome with in a vacuum. Therefore, to prevent an impact on the surface of the planet, the only means is used - a rocket engine that can extinguish a high speed to insignificant values, on the order of several meters per second.

In this case, the landing of the spacecraft resembles the launch of a rocket, only everything happens in the reverse order. Engines that emit flames from nozzles do not increase the speed of movement, but reduce it, and for this purpose the engine nozzle is turned towards the direction of movement. Moreover, the operation of the propulsion system provides not only a decrease in the speed of the descent vehicle to zero relative to the target, but also compensates for the force of attraction of the body of the solar system.

The braking engine must reduce the speed of the apparatus to a value of several meters per second, and the end of braking must coincide with the moment of approach to the surface of the planet, otherwise the descent vehicle will again develop a high speed as a result of free fall. An analysis of various braking schemes showed that for the first experiments, the most reliable option is braking with a vertical descent of the station, which makes it possible to simplify the landing system.

Theoretically, this problem is easy to solve: using the known values ​​of the planet's attraction force, the thrust force of the engine and the speed of the spacecraft before braking, the distances to the planet's surface are calculated, upon reaching which the spacecraft must turn on the propulsion system. But in practice, determining when to turn on the propulsion system for braking is not easy. How many kilometers are left to fly to the planet - there is no one to ask, milestones in space have not been set. We have to put an altimeter on the spacecraft, in other words, a radar with which you can determine the distance to the surface of the planet.

In accordance with the program calculated in advance and stored in the memory of the spacecraft, upon reaching the desired height above the surface, a command comes from the altimeter to turn on the propulsion system. However, before turning on the propulsion system, it is necessary to direct the engine with the nozzle down. True, there are no concepts of “up” and “down” in outer space. Usually for large celestial bodies, such as stars, planets, "bottom" is associated with their center, but for small bodies, such as asteroids, "bottom" and "top" are determined only from the direction to the center of attraction.

Therefore, to land on a body that does not have an atmosphere, it is necessary to turn the nozzle of the propulsion system in the direction of the gravity force and turn on the installation at such a moment that when it comes into contact with the surface, the speed is close to zero. It is possible to deploy the spacecraft in the direction of the gravity force only by determining the position of the spacecraft relative to the target and the direction of its movement. Only then is the magnitude of the necessary momentum determined to carry out the correction in order to correctly execute the trajectory of descent. The use of the laws of celestial mechanics and the necessary correction of the flight trajectory make it possible to direct the spacecraft to the center of the visible disk of the body or to any other specified landing point.

Turning the descent vehicle in the required direction for braking can be done using the orientation system. With the help of optical sensors of this system, the direction to the Sun or to the reference star is determined. Solving the trigonometric problem, they then find the direction to the center of the planet relative to the direction to the Sun and the direction to the star. Finally, the control system rotates the apparatus to the desired position.

The time interval from turning on the engine to landing is calculated in advance when designing the spacecraft, and the distance to the planet is determined using a radio altimeter. Depending on the mass of the apparatus, both the value of the engine thrust force and the height at which it should be turned on are selected. As for descent vehicles carrying out descent in the atmosphere, in this case, not the entire spacecraft is saved, but only part of it. At the moment the propulsion system is turned on, the extra compartments, i.e., no longer needed on the landing site, are discarded. These are blocks of the astro-orientation system, necessary only for the flight from the Earth to the body under study, as well as used chemical current sources, etc. For example, we note that in Luna-9 the mass of these discharged compartments was commensurate with the mass of the automatic lunar station that landed on the Moon .

All this is done in order to reduce the amount of fuel needed to decelerate the spacecraft. But to control the motion of a spacecraft, it is necessary to periodically determine its speed. Inertia speed cannot be measured. However, when the spacecraft engine is turned on, acceleration appears. In this case, using a gyroscopic integrator, it is possible to measure the speed of movement by integrating linear accelerations. True, in this case, it is not the true speed of the spacecraft that is recognized, but only the magnitude of the change in speed arising from the operation of the propulsion system.

To solve this problem, an electronic computer, by interrogating the altimeter, receives data on height, and from the integrator receives the values ​​of the speed increment at the moments corresponding to the determination of the distance to the planet's surface by the altimeter. Then, according to the programmed program, the electronic brain develops recommendations for throttling or boosting the propulsion system, if the actual speed values ​​differ from the calculated value stored in the computer memory.

Landing of the descent vehicle on the surface after the end of the operation of the propulsion system is carried out by falling from a small height under the influence of the planet's gravity. Impact damping against the surface in order to reduce the overload on the vehicle, as a rule, is carried out on all descent vehicles with the help of three or four supports with individual shock absorbers.

Only the first lunar vehicles Luna-9 and Luna-13 carried out the landing of the descent vehicle in a different way.

DESCENT VEHICLES OF LUNA-9 AND LUNA-13 STATIONS

Before the landing of the spacecraft on the lunar surface, there was the most contradictory information about its properties. According to some sources, the lunar surface was a rocky mountain desert, according to others, the “seas” and continents of the Moon were considered to be covered with a thick layer of dust, in which any spacecraft that dared to land on this surface could drown.

Rice. 6. Scheme of soft landing of the station "Luna-9"

The original solution for a soft landing on the Moon was proposed by S.P. Korolev. At first, the flight of the lunar station had to be slowed down with the help of the propulsion system to a speed of several meters per second, and then the automatic lunar station could be dropped from the propulsion system, and on the Moon there was a descent vehicle packed in soft and elastic cylinders inflated with compressed gas (Fig. 6 ). With a small mass (about 100 kg) and a relatively large bearing surface of the cylinders (about 1.5 m 2), the specific pressure on the ground is negligible. The landing system was designed in such a way that, under any soil (whether it be a hard rocky surface or loose, dispersed soil), a reliable lunar landing of the station was ensured.

The descent vehicle for the Luna-9 station can actually be called an automatic lunar station weighing about 100 kg. Everything else was either destroyed or damaged upon contact with the surface. The body of the descent vehicle, spherical in shape with a diameter of about 50 cm, with closed petals, took an ovoid shape. The station flew up to the Moon at a speed of 2.6 km / s. The astro-orientation system turned and fixed the station in a certain direction in such a way that the nozzle of the propulsion system was directed towards the lunar surface.

48 s before approach, when 75 km remained to the Moon, two compartments with equipment, which had become unnecessary, were separated from the station at the signal of an autonomous altimeter, and the braking propulsion system was switched on. (Its more correct name was the corrective-braking propulsion system, since on the Earth-Moon flight route it was used to correct the flight trajectory to the Moon.) The operation of the propulsion system was controlled according to the program laid down and the station's memory. The engine had the ability to control thrust in a relatively wide range.

Since the beginning of the operation of the propulsion system, two elastic cylinders were pressurized, inside which there was an automatic lunar station. Cylinders, holding the descent vehicle, firmly connected to each other, forming a large elastic ball. Near the lunar surface, the engine was turned off and the section of its nozzle turned around and formed a tubular probe from a flat spring band. In contact with the surface, the probe gave a signal to shoot the descent vehicle with cylinders. In this case, the connection with the station was practically broken, and the separation occurred due to the force of elasticity of the cylinders initially pressed to the support of the station.

The surface to which the cylinders were pressed was somewhat beveled to the side in order to separate the automatic lunar station not vertically, so that the fall would not occur on the propulsion system, but somewhat to the side. The ball with the station made several jumps and stopped. On a signal from the time program device, the connections between the cylinders were broken, and they, like two balls, bounced off the station. The descent vehicle from a small height gently descended to the surface.

Thanks to the egg-shaped shape and the low position of the center of mass, the device could take a predetermined position. 4 minutes after landing, the program-time device issued a command to open the pyro-lock, and the petal antennas opened, simultaneously releasing the whip antennas. Lobe antennas during the flight played the role of receiving-transmitting antennas, and after opening they switched to work as transmitting antennas, while whip antennas served as receiving antennas.

A rigid frame with radio equipment, electronic program-time devices and automation devices, telemetry and scientific equipment was installed inside the descent vehicle body. A telephotometer was located on top, which made it possible to see and transmit to Earth a panorama of the surrounding area. For uninterrupted operation of the equipment in lunar conditions, the required temperature regime was maintained. This was achieved by the device of external thermal insulation of the body, as well as the operation of the thermal control system. The latter included a water tank, a pyro valve, an evaporator valve, a fan, and a piping system.

After landing on the moon, the pyrovalve exploded, the water evaporation system was turned on, and the fan began to work, which ensured the transfer of heat from the device to the gas. The evaporator valve was the sensitive element of the system, the water supply regulator and the evaporator. Water came to him from a tank under pressure and the more intense, the higher the temperature of the valve. In the valve, it evaporated and took away heat from the gas blown through the valve.

The automatic space station "Luna-13" in design and mass was close to the station "Luna-9", only additional scientific equipment was installed on it, as well as instruments for direct study of the lunar soil. These were the mechanical soil sr-penetromstr, which made it possible to determine the mechanical properties of the outer layer of lunar matter, and the radiation densitometer to determine the density of the outer layer of lunar soil. The devices were mounted on mechanisms that ensured the removal of devices fixed on the outer case of the station. The removal mechanisms made it possible to install these devices on the lunar surface at a distance of up to 1.5 m from the automatic lunar station.

After the flight of the Luna-9 and Luna-13 stations, basic data on the properties of the lunar soil were obtained. Since that time, there has been no need to design descent vehicles capable of landing both on rocky soils and on a surface covered with a thick layer of dust. All subsequent lunar landers have already used other methods of soft landing. As a rule, landing devices with leg-shaped supports began to be used. Such a landing gear is capable of withstanding and absorbing the impact of the station with the ground at vertical speeds of 6–8 m/s and at a horizontal velocity component of up to 3–4 m/s and ensure stability when landing on slopes with a steepness of 15–20°.

DESCENT VEHICLES FOR LUNA-16 TYPE STATIONS

The descent vehicle of a new generation of Soviet lunar explorers was developed as a landing stage in the form of an independent multi-purpose rocket unit. This block had a liquid-propellant rocket engine, a system of tanks with propellant components, instrument compartments and shock absorber supports for landing on the lunar surface. Antennas of the onboard radio complex and executive bodies of the attitude control system were also installed on the landing stage.

The instrument compartments housed electronic computing and gyroscopic devices of the control and stabilization system, electronic orientation devices, on-board radio receivers and transmitters of the radio-measuring complex, a program-time device that automatically controls the operation of all systems and assemblies, chemical batteries and current converters, elements of the thermal control system, autonomous means for measuring altitude, horizontal and vertical speed components during landing, and other equipment, including scientific equipment.

The landing stage propulsion system was used not only for braking during landing, but also for orbit correction during the flight from the Earth to the Moon. The propulsion system also included two low-thrust engines, which were switched on at the final stage of landing. The main engine of the landing stage had the possibility of reusable launch.

Landing on the Moon, in contrast to the first descents to the lunar surface, was carried out not directly from the flight tractor, but with the preliminary launch of the spacecraft into the orbit of an artificial satellite of the Moon. By carrying out maneuvers performed with the help of a propulsion system, a pre-landing orbit was formed, which is necessary to create optimal conditions for an accurate landing in a given area of ​​the lunar surface.

A feature of such an orbit is the low altitude of the orbit at the periapsis above the surface of the Moon - only about 15 km. The pericenter in this case is organized over a given landing area. Note that such a height is due to the presence of mountains up to 9 km high on the Moon, the remaining distance of 5-6 km just ensured the permissible errors in the formation of the orbit.

Before turning on the propulsion system for landing, the operations of orientation and program turn of the station were carried out in order to ensure the movement of the engine nozzle forward. The length of the flight path with the engine running from the deorbit point to the lunar landing site was 250 km. The position of the station was strictly stabilized throughout the entire descent segment. Altitude and vertical rate of descent were continuously monitored by the onboard Doppler speed meter and altimeter. All operations during the descent were carried out by automatic devices of the station without the intervention of the Earth.

Upon reaching setpoints altitude above the lunar surface and the vertical components of the velocity, the engine turned off and on again, and at an altitude of 20 m, low-thrust engines began to work instead. Before turning on the engine for braking, two compartments with empty fuel tanks (the fuel was used during the correction and braking near the Moon to create the orbit of an artificial satellite of the Moon), as well as with astronavigation equipment and other instruments not used for the landing, were dropped, and onto the Moon a lightweight landing stage with a payload was lowered (Fig. 7). As the latter, Luna-16, Luna-20 and Luna-24 used the Luna-Earth return rocket, and for Luna-17 and Luna-21, the Lunokhod self-propelled vehicle.

Rice. 7. The descent vehicle of the Luna-16 station: 1 - antenna; 2 - soil intake device; 3 - control system compartment; 4 - fuel side; 5 - support; 6 - engine

The landing stage after turning off the propulsion system descended to the surface. The impact on the ground was softened by four supports with shock absorbers. Moreover, the impact energy was spent on stretching the metal rods located in the pillars of the supports, and on crushing the dish-shaped supports made with honeycomb filling.

DESCENT VEHICLE OF "SURVEYER" STATION

The Surveyor program was intended to study the characteristics of the lunar soil and conditions on the lunar surface to ensure the success of the Apollo program. Structurally, the Surveyor apparatus consists of a frame made of aluminum pipes, to which three landing gear supports and a mast for installing solar cell batteries and a highly directional antenna were attached. On the frame were two sealed containers with electronic. equipment, propulsion system, television camera, navigational and scientific equipment.

With a launch mass of the Surveyor of about 1 ton, a descent vehicle weighing about 280 kg descended to the Moon after the fuel was used up and part of the equipment that was not needed during landing was dropped.

The main spherical brake engine ran on solid fuel. The small thrust engines installed on the apparatus were liquid. The apparatus included a solar sensor and a sensor for the reference star Kapopus, as well as several radars used to determine the rate of descent and the distance to the lunar surface. The radio altimeter gave a signal to turn off the brake engine. Another altimeter, with the help of an onboard computer, controlled small thrust engines.

The landing gear of the spacecraft was in a folded state at launch and deployed only after the spacecraft had entered the flight path to the Moon. The supports had racks with aircraft-type shock absorbers. Aluminum honeycomb shock absorbers were hinged to the bottom of the supports. Shock-absorbing blocks made of aluminum honeycombs were attached to the lower part of the frame of the apparatus, designed to soften the impact of the frame on the ground at the time of the deflection of the main supports.

APOLLO DESCENT VEHICLE

The descent vehicle of this spacecraft was named by American specialists the lunar cabin. It was intended to deliver two cosmonauts from a selenocentric orbit to the surface of the Moon, to ensure their stay on the surface and delivery from the surface of the Moon to a selenocentric orbit. The lunar cabin consisted of landing and takeoff stages. When launching from the Moon, the landing stage remained on the Moon. The lunar cabin was a complex engineering structure that housed a life support system, a guidance and navigation system, a power plant, communications equipment, onboard engines, and scientific equipment.

After separating the lunar cabin from the Apollo spacecraft and reaching a distance of 18 m between them, the lunar cabin turned around to inspect it in order to search for possible damage. Then, for 32 s, the main engine of the landing cabin was turned on, which transferred the descent vehicle to an elliptical orbit with a periapsis height of 15 km above the lunar surface. The descent of the lunar cabin to the lunar surface took place in three stages: deceleration, withdrawal to the landing area, and landing.

Upon reaching the periapsis, the engine of the landing stage of the lunar cabin was switched on, which, when operating at full thrust, created a deceleration lasting 8 minutes. During this time, the cabin traveled about 400 km and descended to a height of 2.6 km. There was still about 15 km to the landing area. Here the stage of launching to the landing area began, for this the lunar cabin was deployed in such a way that the astronauts could see the selected area. At this stage, the landing stage engine operated at 60% of full thrust and in less than 1.5 minutes reduced the flight speed of the cabin from 137 to 15 m/s.

At the end of this stage, the height above the surface was 150 m, and the distance from the landing site was approximately 360 m. At the final stage of the landing, the astronauts were in full control of the flight. The orientation of the lunar cabin, a gradual decrease in engine thrust, and a vertical descent from a height of 30 m were provided. The minimum landing time was 75 s, but in practice it lasted longer, since it took time to inspect the landing area and select a more suitable landing site.

To ensure a soft landing, the landing stage was equipped with a special landing gear. At launch, the landing gear was folded, the telescopic struts were pressed against the body of the landing stage. The landing gear turned around only after the astronauts moved to the lunar cabin. Cup-shaped supports made of aluminum honeycombs were attached to the landing gear on a hinge. To absorb shock loads, a collapsible aluminum alloy honeycomb core was used, which was available in the telescopic legs of the landing gear. The rack was able to be shortened by 0.8 m.

It was envisaged that at a height of about 1 m, the cosmonauts would turn off the engine of the landing stage in order to prevent overheating of the bottom of the descent vehicle from the outflowing jet reflected from the ground. They also feared an engine explosion if it touched the ground while it was running. But in practice, already during the first landing, cosmonaut N. Armstrong forgot to turn off the engine, but the lunar cabin at the moment of touching the ground had almost zero speed. The engine was turned off from the probe located on the landing gear.

The return of astronauts from the moon was carried out using the takeoff stage. The launch was carried out similarly to the launch of a rocket on Earth, but instead of a launch device, a landing stage was used here. The takeoff stage entered the orbit of an artificial satellite of the Moon, and then docked with the main block of the Apollo spacecraft. After the transition of the astronauts from it and the transfer from there necessary equipment and materials, it undocked from the main unit. Subsequently, the takeoff stage either remained in a selenocentric orbit, or it was directed to the lunar surface.

Descent in a rarefied atmosphere

In the practice of space flights, such descent vehicles were used only for flights to the planet Mars. The atmosphere of this planet is very rarefied. Atmospheric pressure on the surface here is from 1/160 to 1/100 of the normal atmospheric pressure on Earth. But, despite such rarefaction, the entry into the atmosphere at cosmic velocities is accompanied by phenomena similar to those of the Earth's atmosphere. To decelerate and reduce the speed from the space speed of several kilometers per second to about 200–300 m/s, an aerodynamic force sufficient for this arises in the Martian atmosphere.

The whole difficulty of descent in the Martian atmosphere lies in the fact that reaching a speed of 200–250 m/s can occur either near the surface or just before impact into it. There is practically no time left for the introduction of the parachute system, and the descent vehicle can be destroyed upon impact with the surface before effective braking with the help of the parachute occurs. Therefore, it is necessary to introduce a parachute not at flight speeds of 200-250 m / s, but much earlier - even at hypersonic speeds of the order of 2 M (about 650 m / s).

This raises the problem of introducing parachutes into a hypersonic flow. For the manufacture of parachutes, it is necessary to use extra-strong material that is able to withstand heavy loads that develop when the parachute is opened. To reduce the load on the parachute, it is necessary to introduce several parachute cascades one after the other with increasing canopy areas. In this case, the load increases slowly. Another way to reduce overloads is to introduce a reefed parachute system with a gradual opening of the main parachute in several stages.

The parachute system under the conditions of Mars effectively reduces the flight speed only to a few tens of meters per second (about 100 m/s). To extinguish the speed to acceptable values, about 10 m / s, a parachute system of reasonable size in the atmosphere of Mars cannot. Therefore, there is a need to use a combined system: together with a parachute system, use a propulsion system. The entire braking stage in this case first proceeds as for planets with an atmosphere, with preliminary use of aerodynamic braking, and then with the help of a parachute system, but at the final stage, as for planets without an atmosphere, a propulsion system is used. The vehicles that made such a landing on the planet Mars include the Soviet stations of the Mars series and the American Viking stations.

DESCENT VEHICLES OF MARS STATION

When deciding which scheme to give preference to: use a propulsion system or a parachute system after aerodynamic braking, and only at the final stage a propulsion system for a soft landing on the surface, the second scheme won, and this victory was due to the best mass characteristics for the descent vehicle. Indeed, in the first scheme, the mass of the braking system, as calculations show, would be 70% of the mass of the descent vehicle, in the second scheme, only 50%. Thus, the use of the parachute system as one of the components of the entire process of deceleration of the descent vehicle gives a gain in the mass of the scientific apparatus and other equipment used.

Since the atmosphere of Mars is very rarefied, and the greater the possibility of aerodynamic deceleration, the larger the midsection of the descent vehicle at a constant mass, an aerodynamic braking cone with a diameter of 3.4 m was put on the descent vehicle. lift-to-drag ratio and, consequently, the movement on the descent section will occur along a ballistic trajectory. Consequently, it was not necessary to install descent motion control systems on the descent vehicle.

During the flight of the second and third automatic station "Mars", it was planned to carry out a soft landing of the descent vehicle on the surface of the planet and transmit signals to the station flying in orbit around the planet. In order to create an artificial satellite of Mars, it was necessary to bring the station to the area of ​​the planet Mars in such a way that its movement was carried out not along an incoming trajectory, but along a flyby, and at a relatively small distance from the surface.

But for a descent vehicle, such a trajectory is unacceptable; for it, the flight trajectory must end with a hit, if not in the planet itself, then at least in the atmosphere. However, due to the rarefaction of the atmosphere and, consequently, in order to increase the path of the apparatus in it for the most effective aerodynamic braking, the flight of the descent vehicle must occur almost tangentially to the surface of the planet. True, due to considerations of the reliability of the task, it was assumed that the entry angle was at least 10°. At smaller entry angles, the atmosphere could not capture the descent vehicle, since in this case there would be no effective deceleration and the descent vehicle, ricocheting, would go away from the planet.

The solution of all these problems led to the fact that the flight of the Mars station was planned along a flyby trajectory, but at a distance of about 40 thousand km from the planet it was planned to separate the descent vehicle from the station and direct it along a new trajectory into the planet's atmosphere. To make it possible to change the flight path, a descent system was installed on the descent vehicle, consisting of a farm with a solid fuel propulsion system and a control system.

Before the separation of the station and the descent vehicle, the Mars station was oriented in a certain way so that the descent vehicle would be directed in the required direction at the moment of separation. 15 minutes after separation, the solid-propellant withdrawal engine was turned on. Having received an additional speed equal to 120 m/s, the descent vehicle headed for the estimated point of entry into the atmosphere. Then the control system, located on the farm, deployed the descent vehicle with an aerodynamic braking cone forward in the direction of travel, which. to ensure the correct oriented entry into the atmosphere of the planet.

To maintain the descent vehicle in this orientation during the flight to the planet, which lasts almost 4 hours, gyroscopic stabilization was carried out. The spin-up of the apparatus along the longitudinal axis was carried out using two small solid-propellant engines installed on the periphery of the aerodynamic brake cone. The farm with the control system and the withdrawal engine, now unnecessary, was separated from the descent vehicle.

Before entering the Martian atmosphere, on command from the time program device, two other solid-propellant engines, also located on the periphery of the brake cone, were turned on, after which the rotation of the descent vehicle ceased. We note that the following circumstance was also taken into account. After the escape system was reset, the moment of inertia and the mass of the descent vehicle decreased, so the engines designed to stop the spin created less momentum than the gyroscopic stabilization engines.

The rotation was stopped mainly so that when the parachute system was introduced, the lines were not whipped.

The descent vehicle entered the atmosphere at a speed of 5600 m/s, but it was protected from thermal impact by an aerodynamic braking cone, the outer surface of which was covered with a heat-shielding shell (Fig. 8). Braking by the atmosphere continued when the speed decreased to 2M. Entering a parachute at such speeds requires a lot of effort. When the descent vehicle moves in the atmosphere at high speeds, a rarefaction is formed behind it, into which a parachute that has not yet had time to open can be drawn (especially with a sluggish introduction). For the forced entry of the parachute, a solid propellant engine was used, located on the cover of the pilot chute compartment.

Rice. 8. The descent vehicle of the station "Mars-2": 1 - aerodynamic cone; 2 - radio altimeter antenna; 3 - parachute container; 4 - pilot chute input engine; 5 - descent vehicle withdrawal engine; 6 - instruments and equipment of the control system; 7 - main parachute; 8 - automatic Martian station

At the end of the aerodynamic braking section, at the command that followed from the overload sensor, even at supersonic flight speed, a pilot chute was introduced with the help of a powder engine. After 1.5 s, with the help of an elongated charge, the torus-shaped parachute compartment was cut, and the upper part of the compartment (lid) was taken away from the descent vehicle by a pilot chute. The cover, in turn, introduced the main parachute with a reefed dome. The lines of the main parachute were attached to a bunch of solid propellant engines, which were already attached directly to the descent vehicle.

When the device slowed down to transonic speed, then, on a signal from the program-time device, a reefing was carried out - the main parachute canopy was fully opened. After 1–2 s, the aerodynamic cone was dropped and the radio altimeter antennas of the soft landing system were opened. During the descent on a parachute for several minutes, the speed of movement decreased to about 60 m / s.

At an altitude of 20-30 m, on command received from the altimeter, the solid-propellant braking engine of a soft landing was turned on and the upper solid-propellant escape engine was uncoupled along with the main parachute. The latter pulled the parachute aside so that the descent vehicle would not be covered by its dome. After some time, the soft landing engine turned off, and the descent vehicle, separated from the parachute container, sank to the surface. At the same time, a parachute container with a soft landing engine was moved aside with the help of low-thrust engines. At the time of landing, a special shock-absorbing coating reliably protected the descent vehicle from possible damage.

During this space experiment, an original communication system was used for the first time. The signal from the descent vehicle, located on the surface of the planet, went to the artificial satellite of Mars - the Mars-3 station, which, after separation from the descent vehicle and turning on the engine, went into orbit around Mars. The satellite memorized the signals transmitted from Mars. Then, after some time, these signals went to Earth.

DESCENT VEHICLE OF VIKING STATION

The Viking automatic space stations were designed to study the planet Mars both from the orbit of an artificial satellite of Mars and with the help of a descent vehicle delivered to the surface of the planet. The mass of each of the two stations was 3620 kg, of which the descent vehicle accounted for 1120 kg. After approaching Mars, the Viking space station with the help of a propulsion system was transferred to the orbit of an artificial satellite of Mars in order to study the planet and select a landing site for the descent vehicle.

Following the adoption on Earth of a decision on the choice of a landing site, the biological envelope of the descent vehicle was dropped. The device in this shell was after sterilization in preparation for launch even in terrestrial conditions. Such measures were taken to exclude the introduction of terrestrial microorganisms to Mars. 1.5 hours after the release of the biological envelope, the descent vehicle separated from the station.

The descent vehicle was oriented, and after 30 minutes 8 liquid-propellant rocket engines were switched on for braking. The descent vehicle's orbit became elliptical, descending at the periapsis into the depths of the planet's atmosphere. The entry velocity into the atmosphere was 4.6 km/s at an entry angle of 16.5°. The frontal screen, which protected the descent vehicle from high temperatures, was designed and fixed on the descent vehicle in such a way as to create an aerodynamic quality of 0.18.

After aerodynamic braking at an altitude of 6 km at a speed of 1.9 M (slightly more than 600 m / s), a parachute system was introduced. Its input, as in the Soviet stations "Mars", was carried out using a powder engine. After 15 seconds, the frontal screen was fired at an altitude of about 4.4 km. Upon reaching a height of 1.2 km and a speed of about 113 m / s, the parachute was separated. This ended the deceleration section using the atmosphere and the deceleration section using the propulsion system began.

The propulsion system with a thrust of 270 kg/s was turned on for 25–40 s, and when a height of 15 m was reached, the thrust was throttled (decreased). With reduced thrust, the descent continued up to a height of 3 m. At this height, the propulsion system was switched off and the descent vehicle fell freely onto the surface of Mars. The impact velocity was 1.5 - 3.3 m/s. From 1120 kg of mass separated from the station, an apparatus weighing 577 kg descended to the surface. The final damping of the velocity occurred with the help of supports similar to those used for vehicles descending to the lunar surface.

HARD LANDING RESEARCH

Such spacecraft, of course, are not intended for a soft landing on the planet under study and study the planet from a short distance when flying to it. At the initial stage of cosmonautics, when descent vehicles were only being developed or found their first use on spacecraft intended for returning to Earth, it was already possible to study other bodies in the solar system from an approach. The first such devices were Luna-1 and Luna-2.

The Luna-3 and Zond-3 stations were used to photograph the Moon at close range. Subsequently, such stations were Luna-12 and a number of apparatuses of the Zond series.

In the American program for exploring the moon from an approach trajectory, the Ranger spacecraft was used, which made it possible to obtain images of the lunar surface from altitudes from 1800 km to 480 m 0.12 s before the impact and death of the apparatus. The transfer of pictures taken with the help of six television cameras was carried out using two transmitters.

CONCLUSION

In the initial period of space exploration, relatively simple descent vehicles were created, for braking and reducing the speed of which the atmosphere of the planets was used, without the use of lifting force, i.e., while the descent was not controlled. These were descent vehicles of a spherical or other shape with a center of mass located on the longitudinal axis. The accumulated experience made it possible to complicate the descent vehicles both constructively and from the point of view of saturation with descent control systems.

At present, in terrestrial conditions, to ensure the landing of a person returning from a space flight, more advanced descent vehicles are used using lift to control the descent. For space exploration of other planets with an atmosphere not yet visited by man, automatic stations with descent vehicles that descend along a ballistic trajectory are still used (with rare exceptions).

Such an uncontrolled descent is used to reduce the cost of creating descent vehicles. In addition, this is done because such descent vehicles are more reliable in operation than controlled descent descent vehicles, on which additional systems and controls must be installed. True, in this case one has to put up with large overloads, reaching 100 g or more.

In the future, with the development of astronautics, during manned flights to other planets, it will become necessary to create descent vehicles with controlled descent for this purpose. And even in the case of only a flyby of these planets with a subsequent return to Earth, the creation of new descent vehicles will be required. At atmospheric reentry velocities of more than 17 km/s, it is almost impossible to provide acceptable g-forces for approaching reentry corridors with a width of about 12–16 km.

The width of the atmospheric reentry corridor decreases significantly with an increase in the approach speed, which, among other things, requires an increase in the accuracy of the orientation and navigation system, as well as high accuracy when making corrections in the approach area. For example, it can be pointed out that, according to some calculated flight trajectories, when returning from the planet Mars (or from its environs), the speed of approach to the Earth increases to approximately 20 km/s. In this case, the use of existing types of descent vehicles cannot ensure the safety of the crew during descent in the atmosphere.

To solve this problem, you need to apply other landing methods. First, it is necessary to reduce the speed of approach to the Earth, i.e., to decelerate to the atmospheric area with the help of a propulsion system. Moreover, the speed must be reduced to a value of the order of 11 km / s - the second space velocity. This path is currently unacceptable in terms of high fuel consumption. Only with the creation and application of new, non-chemical fuels, this method is likely to become an achievable reality.

Second, to expand the lift-to-drag ratio of the descent vehicle in order to increase the entry corridor. However, increasing the quality over 1.0–1.2 to expand the entrance corridor is ineffective and leads to a significant increase in the mass of the heat-shielding coating.

Thirdly, the development of control systems for the movement of the descent vehicle should make rational use of its aerodynamic characteristics. Management only on the angle of roll at a constant angle of attack in this case is not enough. There is a need to control both the angle of attack and the angle of roll. The angle of attack must be controlled by adjusting the center of gravity of the descent vehicle. Of course, if during the angle of attack control it turns out that the vector of the total aerodynamic force varies with respect to the axes of the descent vehicle over a wide range, then it is necessary to provide a system for orienting the crew seats to ensure the optimal impact of the overload.

Regulation, descent at two angles of roll and attack should be carried out according to the programs incorporated in the control system. The descent vehicles used by the Soyuz or Apollo spacecraft are ineffective for controlling the aerodynamic braking at two angles. The most acceptable in this case are descent vehicles made in the form of a semi-cone with a flat top. When using such a descent vehicle, landing on the Earth can be direct, from an approach trajectory, or with a double immersion into the atmosphere.

In the latter case, after the first dive, the descent vehicle exits the atmosphere into an elliptical transfer orbit. At the same time, it is necessary to form the trajectory of the descent vehicle in the first dive section and take into account the restrictions on overloads for the crew, the flight altitude and the values ​​for thermal loads, so that the speed at the exit from the atmosphere does not exceed the second space one.

Landers for non-atmospheric planets for the near future probably will not undergo significant changes. The descent to the Moon has already been quite recently carried out using the orbit of an artificial satellite of the Moon with the aim of reaching the area planned for landing with high accuracy. But this is only from the point of view of the concept of landing. Increasing the comfort and convenience for astronauts, the use of new, more advanced instruments of the orientation and control system will continue.

Table - Chronicle of manned flights

UPK-8, Krasnokamsk

Quiz

1. Why do designers propose to cover the descent compartments of a spacecraft with a layer of fusible material?

This is done for safety so that the compartment does not overheat. There is a so-called ablation protection (from the English ablation - ablation; mass removal) - a technology for protecting spacecraft.

The temperature of the ship upon entering the dense layers of the atmosphere reaches several thousand degrees, the ablative protection under such conditions gradually burns out, collapses, and is carried away by the flow, thus removing heat from the body of the device.

Spacecraft protection technology, thermal protection based on ablative materials, structurally consists of a power set of elements (asbestos textolite rings) and a "coating" consisting of phenol-formaldehyde resins or materials similar in characteristics.

Ablative thermal protection has been used in the designs of all descent vehicles since the early years of the development of cosmonautics (the Vostok, Voskhod, Mercury, Gemini, Apollo, TKS series of ships), continues to be used in the Soyuz and Shenzhou.

An alternative to ablative thermal protection is the use of heat-resistant heat-shielding tiles ("Shuttle", "Buran").

2. Can pendulum clocks be used on the space station?

The pendulum works due to gravity, but there is no gravity on the space station, here the state of weightlessness. Pendulum clocks won't work here. The space station will operate a mechanical (spring) clock.

The first watch to fly into space belonged to Yuri Alekseevich Gagarin. These were Soviet "Navigators". Since 1994, the Swiss watch Fortis has become the official watch of the Cosmonaut Training Center. In the early 2000s, the Cosmonavigator orbital clock, developed by cosmonaut Vladimir Dzhanibekov, was tested on the ISS. This device made it possible at any time to determine over which point on the Earth the ship is located. The first dedicated watch for use in outer space is the Japanese Spring Drive Spacewalk. Electronic clocks did not take root in orbit. The spacecraft is pierced by high-energy particles that disable unprotected circuits

Is it possible to drink water from a glass in zero gravity?

Before the first flights into space, it was largely a mystery to scientists how to organize a meal in a state of weightlessness. It was known that the liquid would either gather into a ball or spread over the walls, wetting them. So, it is impossible to drink water from a glass. It was proposed to the astronaut to suck it out of the vessel.

Practice basically confirmed these assumptions, but also made some significant amendments. It turned out to be convenient to eat from tubes, but, being careful, you can eat food in its earthly form. The astronauts took with them fried meat, slices of bread. Four meals a day were organized for the crew on the Voskhod ship. And during the flight of Bykovsky, viewers saw how he ate green onion, drank water from a plastic bottle and ate vobla with particular pleasure.

We saw on the website http://www. /watch? v=OkUIgVzanPM how American astronauts drink coffee. But the glass there is also plastic, its shape can be changed. You can squeeze liquid out of it. This means that it is almost impossible to drink the water from their usual solid glass cup.

Today, each member of the crew of the International Space Station (ISS) has an individual mouthpiece for drinking, which is mounted on the syringes of the branched onboard water supply systems "Rodnik". The water in the "Spring" system is not simple, but silver-plated. She is passed through special silver filters, which protects the crew from the possibility of a variety of infections.

But perhaps in the near future astronauts will easily be able to drink water from an ordinary glass. Large-scale studies of the behavior of liquids and gases in weightlessness are planned on a platform independent of the ISS. Design work is currently underway, in which teachers and students of the Department of General Physics of the Perm University are participating. Research in this direction has been carried out in Perm for more than 30 years.

4. Which of the astronauts was the first to visit outer space?

Soviet cosmonaut Alexei Arkhipovich Leonov was the first to go into outer space on March 18, 1965 from the Voskhod-2 spacecraft using a flexible airlock. 1 hour 35 minutes after the launch (at the beginning of the 2nd orbit), Alexei Leonov was the first in the world to leave the spacecraft, which was announced to the whole world by the ship's commander Pavel Belyaev: "Attention! A man went into outer space! A man went into outer space! " The television image of a hovering in the background was broadcast on all television channels. At this time, he moved away from the ship at a distance of up to 5.35 m. His spacesuit consumed about 30 liters of oxygen per minute with a total supply of 1666 liters, designed for 30 minutes of work in outer space. It was very difficult for him to return to the ship. He speaks about this in an interview from the pages of the General Director magazine (No. 3, 2013): “Due to the deformation of the spacesuit (it swelled up), the phalanxes of the fingers came out of the gloves, so it was very difficult to wind the halyard. In addition, it became impossible to enter the ship's airlock feet first, as it should be. ... There was no time to panic: there were only five minutes left before entering the shade, and it was impossible to wind the halyard in the shade. ... I kept thinking about what would happen in five minutes, and what would happen in thirty. And acted on the basis of these considerations.

The total time of the first exit was 23 minutes 41 seconds (of which 12 minutes 9 seconds were outside the ship). He conducted medical and biological research, helped in solving problems of space navigation. Based on the results of the exit, a conclusion was made about the possibility of working in open space.

Due to an emergency, the ship landed in the Perm Territory, near the village of Kurganovka, on the border of the Usolsky and Solikamsky regions on March 19, 1965. They were not immediately found in the remote Ural taiga. In memory of this event, the streets of Belyaev, Leonov, and the highway of Cosmonauts appeared in Perm. Three years later, the astronauts visited here again. A stele was erected at the landing site. Alexei Leonov has been a guest of Perm more than once.

The cosmonauts became honorary citizens of Perm. In general, more than a third of the honorary citizens of Perm are connected with the space industry. After all, the road to space begins with us. In March 1958, the government of the USSR decided to expand the production of rockets and rocket engines at Perm enterprises. 19 largest factories and design bureaus worked for space. Rockets equipped with Perm engines launched hundreds of spacecraft into space. Today in Perm, there are three enterprises that assemble individual components or entire engines of space rockets. Proton-PM manufactures liquid-propellant engines for Proton launch vehicles. NPO Iskra produces solid-propellant rocket engines, and the Perm plant Mashinostroitel manufactures various rocket mechanisms.

Perm universities graduate specialists for the aerospace industry, and also conduct research programs on space topics.

In 2013, the team of scientists from the Department of General Physics, Faculty of Physics, Perm State Research University was again invited to participate in the implementation of the Federal Space Program of Russia. Together with specialists from the Energia Rocket and Space Corporation, physicists from Perm State University will develop scientific equipment and an applied research program for the newest OKA-T spacecraft.