2020-09-06

China X37 where the dragon sees the head but not the tail

By yqqlm yqqlm
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September 4, Long March 2F Send”reusable spacecraft” into space

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It is generally believed that “reusable spacecraft” refers to China’s X-37, which is similar in concept The American X-37 in China is like a small space shuttle

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Long March 2F was used for launching because compared to the usual satellites or spacecraft, the payload wingspan is extra wide, here is still the US X-37

On September 4, China successfully launched a reusable experimental spacecraft with the Long March 2F carrier rocket at the Jiuquan Satellite Launch Center. The experimental spacecraft will be in orbit for a period of time and then return to the scheduled landing site in China. During this period, the verification of reusable technology will be carried out as planned to provide technical support for the peaceful use of space. This is the 14th launch mission of the Long March 2 F carrier rocket.

This is said to be China’s X-37, which may be part of the mysterious”Shenlong” project. It is generally believed that this is a small unmanned space shuttle with a wide range of military applications. Unusually, the Long March 2F is generally dedicated to manned space launches. This is the first time it has been used for unmanned spacecraft. It is generally believed to be because the”reusable spacecraft” has a larger wingspan.

The space shuttle is a significant detour in the history of aerospace. The original intention is to take two steps. In the case of horizontal take-off and horizontal landing, first achieve vertical take-off and horizontal landing. The reusable space shuttle will improve the economy of space launch. However, the cost of the space shuttle is actually higher than that of a single-use launch vehicle. The failure of the”Challenger” further reduced the number of launches, making it impossible to use the number of launches to amortize the cost. The crash of the”Colombia” finally locked the fate of the space shuttle.

But many advanced technologies pioneered by the space shuttle have left a profound impact, X -37 can be regarded as an unmanned and miniaturized space shuttle. But this is not just as simple as a low-cost space shuttle, more importantly, the focus of X-37 is to explore the aerodynamic assisted orbit change capability.

On an orbit without air, the orbit change can only be achieved by starting the orbit-changing rocket engine to eject high-speed gas and using the projected momentum to form a reaction. . Satellites do this, and therefore they have only limited orbital change capabilities, and space-borne fuel is limited. The fuel that X-37 carries is also limited, but with the ability to control hypersonic aerodynamics at the edge of the atmosphere, this is different.

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The space shuttle”sit into” the atmosphere, not one end of it”into” the atmosphere

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The aerodynamic state during reentry is very complicated, but more complicated is the shock wave shape and thermodynamic management

Space Shuttle Return The key technology is to achieve thermal protection through re-entry attitude and re-entry angle. The space shuttle can neither descend too fast to cause the body temperature to rise sharply, nor to glide for too long to cause heat accumulation, both of which will cause the body to overheat and burn. In addition, the actual reentry attitude of the space shuttle is head-up and tail-to-the-earth, which is to”sit into” the atmosphere instead of”penetrating” into the atmosphere. In this posture, the sturdy body bears most of the aerodynamic and thermal loads, and the astronaut’s cockpit is also on the relatively”shady” back. In order to control the sinking rate, the space shuttle must periodically sway from side to side and lose lift during the roll in order to descend to a lower altitude early, so the actual trajectory is an S-shaped descent.

But if the aerodynamic control at the edge of the atmosphere is not used to control the sinking rate, but to control the reentry attitude, the result is different. Before the space shuttle reenters, it must first start the rocket engine before tailing, reduce the speed to below the orbital speed, use gravity to descend naturally, and then adjust its attitude until it reaches its head and prepare for reentry. If appropriate acceleration at the moment of reentry, supplemented by a shallower angle of attack, the air density difference at the edge of the atmosphere can be used to break water drift. Stone flake bleaching uses the density difference interface between air and water. The density difference interface at the edge of the atmosphere is not so clear, so the space shuttle has a certain”descent” when it floats, but the dynamic pressure and buoyancy caused by the final density difference will still”hold up” the space shuttle and bounce back to form water. drift. The mystery is that if the left and right are not horizontal when reentering, but the left is high and the right is low, it will form an upward rebound force while forming a rightward side force, causing the water drift to turn right. Low left and high right are the opposite. In the water drift, you can also hit the water drift with turning like this. In fact, when using rock flakes for water bleaching, if the tilt angle is too large, the rock flakes will only be stroked on the water surface and then directly sink into the water. Because the density difference at the edge of the atmosphere is more gradual, it is relatively easy to hit water drifts with turns, but this is only relative. At that speed, nothing is easy.

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Appropriate control of the left and right inclination of the stone flakes can produce water drift with corners

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Reentry- Pulling up is also the same principle. Accelerating during the floating phase can easily re-enter the orbit; if you have a little heel angle, you can take a turn while drifting.

However, after hitting a water drift with a bend, the space shuttle’s trajectory completely changed, and it accelerates into orbit again. Completed the change of track. Due to the altitude and speed of the sub-orbit, the fuel consumption of re-entry is not large, so the fuel consumption required for aerodynamic orbit change is much lower than that of direct orbit change. Of course, decelerating to re-entry speed and re-accelerating to orbit still consume fuel. It is said that the aerodynamic assisted orbit change only needs to consume 0.5%of the fuel of the conventional orbit change. This is too optimistic, but the savings are still significant. Compared with the conventional satellite orbit change, this is simply the ability to”unlimited orbit change”. This is no longer a space shuttle that can only controllable return, but an orbital plane.

This”unlimited track change” capability of orbital aircraft is very important in the military .

Reconnaissance satellites are the basic reconnaissance methods of modern military powers. The geostationary satellite is”gazing” at the earth, but the distance is too far. In order to obtain the highest resolution for close reconnaissance, reconnaissance satellites generally operate in low orbits and scan the earth’s surface periodically. This determines that it is impossible for the reconnaissance satellite to stay above the target for observation, and it also has a long and relatively fixed revisit period. Therefore, the classic method of anti-satellite reconnaissance is to take time to hide when the satellite is over the top, or to leave the visible area of ​​the reconnaissance satellite in advance.

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The reconnaissance satellite is good, but the orbit is fixed, the revisit period is long, and it is easy to be countered by the opponent’s time.

In orbit, the orbiting aircraft is no different from satellites, but with the ability to”infinitely change orbit”, the orbiting aircraft can adjust its orbit at any time, greatly shortening the revisit period, or The coordination of 2-3 orbital aircrafts and alternate flying over to form a quasi-real-time surveillance is extremely significant for military reconnaissance. This can maintain intensive reconnaissance in key areas during the war, and it can also track enemy aircraft carriers in near real time. Once China has such capabilities, combined with hypersonic reconnaissance aircraft such as Non-Reconnaissance-8, the US aircraft carrier on the Western Pacific will be like a streaking. Orbital changes can also make the revisit cycle unpredictable, making counter reconnaissance almost impossible.

The”infinite change of tracks” also makes the”space fighter” possible. One of the X-37 test items is the”non-cooperative convergence.” To be friendly, this can be approaching and leaning on the disabled satellite to repair or bring it back; more popular, it can be approaching and destroying enemy satellites, the same is true for enemy space stations, or even directly capturing enemy satellites and bringing them back. Earth.

But in the foreseeable future, this capability is only possible for low-orbit satellites. It is possible to return from low orbit to the edge of the atmosphere, change its orbit and re-enter the orbit after the water drift. But returning from mid-orbit and re-orbiting, fuel consumption may be unacceptable. The problem with high orbits is even greater.

High orbits are generally geosynchronous, mainly communication satellites. Medium orbits are mainly navigation satellites, relay communication satellites and other satellites that can accept longer revisit periods. Low orbits are mainly reconnaissance satellites, earth observation satellites, etc. Even if it can only deal with low-orbit satellites, the military significance is still huge.

But you can’t just think about good things. It has been 30 years from the space shuttle to the X-37. It has been 10 years since the first launch of the X-37. There is no report of aerodynamic assisted orbit change. The X-37 project has always been shrouded in high secrecy, but the X-37 in orbit has been tracked by countless astronomy and space enthusiasts around the world day and night, and such a test cannot cover people’s ears. The demons are in the details. The biggest demons are hypersonic flight control and thermal protection.

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The wave rider can be compared to a water ski, and the shock wave caused by the flying body acts as a water ski.

Orbital aircraft is a waverider when flying at hypersonic speeds in the atmosphere. The lift does not come from the wings, but from the shock waves generated by the flying body, just like water skiing on the water. The same board. The difficulty of the waverider is that this is not only a problem of aerodynamics, but also a problem of aerothermal dynamics. The shock wave is not only a phenomenon formed by the highly compressed air, but the shock wave itself is also a heat transfer body, and the thermodynamic phenomena before and after the shock wave are highly complicated. This makes pneumatic control no longer just pneumatic control, so”angled water drift” is just a highly simplified description.

The angled water drift is only turning, and the track change also involves entering the track again, not only aligning the direction , But also stand at the starting point, aim at the angle, and calculate the speed. All of this makes the aerodynamic assisted orbit change technology highly complex and requires a deep technical background in hypersonic flight. This is the forefront of aerospace, and China happens to be in a leading position. Yes, in terms of hypersonic speed, China leads the world, including the United States.

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The United States is simultaneously studying the provolute and waverider superb missiles, but the HTV-2 of the waverider has been dismantled, leaving only the AHW of the provoked body.

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The Dongfeng-17 already installed in China is a wave-riding body like a fake replacement

As far as the hypersonic flying body technology is concerned, the rotating body is the primary stage, and the waverider is the advanced stage. The hypersonic missiles that the United States is developing are basically in the stage of development. It does not have to be a simple cone, it can be a double cone, but it still cannot jump out of the large frame of the cone. This is because the cone is axisymmetric, the aerothermal dynamics are relatively simple, the aerodynamic control is relatively simple, and the addition of small wings is relatively easy to handle. However, the lift and drag of the rotating body is relatively low, and the gliding performance is not good. The flat arrow cluster-shaped wave rider is better, but the wave rider is more technically difficult. The U.S. wave rider HTV-2 did not achieve the expected results, and has been dismounted. Now we are focusing our efforts to get the second best and get the AHW of the body first. X-37 is a more complicated waverider than HTV-2, and it is even more difficult to handle. In the case of HTV-2 failure, it is not surprising that X-37 has not tested the key aerodynamic assisted orbiting technology for a long time.

Another problem is thermal protection. When the orbiter finally returns, the thermal protection problem is the same as that of the space shuttle. When the water is bleached, the pneumatic heating time is shorter and the thermal protection problem is less. But every aerodynamic assisted orbit change is a process of pneumatic heating. The one-time thermal protection problem is relatively easy to solve. As long as you persist until you reach the ground, you will win. The big deal is that the space shuttle is overhauled every time it takes off. Therefore, the launch cost far exceeds expectations. But the orbital plane has no such possibility. It must be able to withstand repeated aerodynamic heating before it can finally return. Under ideal circumstances, the final return should not require major repairs to be dispatched again. This is a much higher thermal protection requirement.

The aerodynamic overload caused by water bleaching is also a severe test of the structure. After several water bleaching, the structure weakens or even falls apart.

China’s Dongfeng-17 is the world’s first hypersonic missile to achieve actual combat conditions. There are also hypersonic missiles with greater range and more advanced technology. Heard. This is a booster-glide bomb, which uses advanced waveriders. The first thing that needs to be solved for long-term hypersonic glide is the thermal protection problem. Therefore, China has the world’s leading technology and experience in this area.

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The typical boost-gliding projectile has an obvious process of leaping up-Zha Mengzi-pull up and level up

But China’s booster-gliding projectile adopts advanced in-atmospheric direct launch technology. When the upper atmosphere reaches the glide height, the rocket engine shuts down and uses gravity to naturally bow its head. , Then the engine ignites again and accelerates horizontally to the starting speed. The traditional boost-gliding has obvious leaping-zhamengzi-pull-up and flattening, and there are outer atmosphere and reentry problems. The direct lift-off in the atmosphere in China is completely different from that. From the trajectory, it almost climbs to After the glide height is changed directly, the trajectory is flatter, the trajectory is more erratic, and it is more difficult to detect and intercept. But this is different from the shallow reentry-floating of an orbital plane.

But Leaping-Zha Mengzi is the basic skill of Dongfeng 21D and Dongfeng 26C. These anti-ship ballistic missiles are not simple reentry, but maneuvering with pneumatic control. Reentry, with limited super gliding ability, otherwise it would not be able to talk about anti-ship. Therefore, China also has a solid technical foundation in re-entry-pull up.

Integrate these technologies and take a higher level of re-entry control, and the Chinese X-37 will be a matter of course. But the fat man is not made in one bite. The first thing that needs to be tested and verified is the autonomous horizontal return and rapid re-launch technology, which is equivalent to the goal that the space shuttle should have achieved. The conventional orbit change on the track must also be tested and verified, and the re-tracking technology is an in-depth development of the conventional orbit change. In long-term use, the repeated and reliable restart of the rocket engine also needs verification. Then it is the turn to verify key technologies such as aerodynamic assisted orbit change and related reusable thermal protection, reusable high overload resistance structure.

X-37 has set a record of 722 days on orbit, which is not as remarkable as it sounds. It’s no problem for a longer time if you just circle the track. The”Dongfanghong-1″ satellite launched by China on April 24, 1970 is still in orbit. If you are not worried about becoming orbital garbage, after being unmanned and using solar power, the life of the orbit is only limited by the number of orbital changes and the amount of fuel carried.

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The space shuttle can release and recover satellites, but for smaller orbiting aircraft, this is not the main purpose and lacks practical value.

It is not the main purpose to release satellites in orbit as a vehicle. Satellites are”going and not returning”. With a large carrier rocket like the Long March 2F, it bears the cost of wasting a large amount of space in the fairing. Just for the orbital aircraft to release satellites in orbit, it is not as good as the launch vehicle to release satellites directly into orbit. The number, weight, and quantity of satellites that can be carried are Larger volume and multiple stars with one arrow are already mature technologies. In fact, the recyclable launch vehicle booster stage is more useful to reduce the cost of satellite launches, as the US Space Exploration Corporation’s”Falcon” series rockets have proven this. The long-distance successive release of satellites after the orbiting plane changes orbit also requires fuel consumption, which can also be done directly by the launch vehicle. There is no reason for the orbiter to wait for the time to release the satellite in orbit. If there is a real need, the payload stage of the launch vehicle to release the satellite at the end of the orbit can become an orbiting body by itself, and then release the satellite according to the instructions.

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The”Keyhole 11″ reconnaissance satellite is in the assembly workshop. The X-37’s small body is impossible to recover satellites of this level, but the recovery of small satellites is of little value

For manned launches, there must be a return. It is reasonable to use a space shuttle as a returnable manned vehicle, but it is unmanned Later, level return is not the main advantage. Bringing satellites back from space is not a big demand. Really expensive and valuable satellites are very large. When the solar panels are retracted, the”keyhole” reconnaissance satellite is 19.5 meters long and 3 meters in diameter. The cargo hold of -37 is only 2.1 meters in length and 1.2 meters in width, which is far worse. To be able to recover”keyhole” satellites, the space shuttle’s cargo compartment is not enough. The space shuttle’s cargo compartment is only 18.3 meters long and 4.6 meters wide. Space must be left for recovery operations, and it is impossible to just fit them in. It is meaningless to enlarge the X-37B to the size of the space shuttle. The space shuttle is too large and the launch cost is too high, so it is technically impossible to quickly relaunch without major repairs.

Using X-37 to launch anti-ship or surface-to-surface missiles in space is actually an old idea. In the early stages of ballistic missile development, there was an idea of ​​some orbital weapons, which was to launch the missile, stand by on the orbit, and re-enter the attack when required. This is technically not difficult to achieve, and it also makes missile early warning almost impossible. However, in violation of international treaties on the demilitarization of outer space, X-37 is not required at all.

The same is true with X-37 anti-satellite. If there is no orbital aircraft’s ability to change orbit, X-37 is not more effective than anti-satellite, which is already in orbit. The killer satellites flying close to each other’s satellites will change their orbits according to the order when necessary, and implement non-cooperative convergence and detonation. This is a mature technology in the Soviet era, and it is also cheaper to use a launch vehicle than to use the X-37. Of course, this is also a violation of the treaty on the demilitarization of outer space, so the Soviet Union has not really deployed it, at least never admitted it.

The biggest reason for the existence of orbital aircraft is the”unlimited orbital change” capability assisted by aerodynamics. X-37 hasn’t done it yet, it depends on China. What’s interesting is that the press release refers to”technical verification” rather than”scientific research.” This generally refers to the final verification stage before practicality, which is just around the corner. Once successful, this will be a milestone achievement in China’s space military technology. Of course, it is also useful for the peaceful use of space.

When the picture of the J-20 was first circulated on the Internet, the official model was not announced. People referred to it as”black silk”. It’s worse now, people don’t even see it, and they can only call it China’s X-37. Too low-key can be maddening sometimes. But when the dragon who sees the head and the tail reveals the truth, it will bring surprises.