The long-awaited Chang'e-6 is returning to Earth and is not far from home, and is expected to land in Siziwangqi, Inner Mongolia, between 13:41 and 14:11 on June 25. The returner uses a semi-ballistic jump reentry, the trajectory will fly over multiple countries, and in the event of an offset, will the precious lunar back samples be stolen?
Chang'e-6 was launched on May 3 and reached the vicinity of the moon on May 8. After counting the lunar orbit, landing, ascent and rendezvous and docking around the moon, Chang'e-6 stayed on the other side of the moon until June 20. At around 0:00 on June 21, the Chang'e-6 orbital return assembly ignited four 150 N engines again at the perilunar point, completed the second moon-to-earth transfer incidence, and finally left the circumlunar orbit and officially embarked on the journey back to the earth's homeland.
Before landing, the orbital return complex will also undergo 1 to 3 orbital corrections. When Chang'e-6 is about 5,000 kilometers away from Earth, the returner and orbiter will separate. The orbiter then took an evasive maneuver, and the returner re-entered the atmosphere in a semi-ballistic jump, flying over India, Nepal, and other countries before entering the mainland.
The so-called semi-ballistic type means that the spacecraft will use the lift generated by the air when re-entering, which can control the direction and has high landing accuracy. The shape of Chang'e-6's returner is similar to that of the Shenzhou spacecraft, in the shape of a bell, and lift is generated when the spacecraft is traveling in a direction that is not in the same straight line as the axis of symmetry. The semi-ballistic jump re-entry refers to the process of the spacecraft entering the atmosphere twice, which is the legendary water drift.
This is due to the fact that Chang'e-6 is returning from the moon 380,000 kilometers away, and the speed will get faster and faster. When flying near Earth, the relative velocity to Earth is already close to the second cosmic velocity of 11.2 km/s, which is much higher than the reentry velocity of the manned spacecraft, which is less than 7.9 km/s. At such high speeds, if you re-enter directly like a manned spacecraft, the friction with the atmosphere will be extremely intense, and the aerodynamic heating and pressure will be very large, which will bring great challenges to Chang'e-6's heat resistance and anti-ablation ability.
Therefore, Chang'e-6 did not choose to enter the atmosphere directly like the Apollo spacecraft, but adopted a semi-ballistic jump reentry, that is, choosing a suitable angle and attitude to re-enter the atmosphere for the first time at an altitude of 120 kilometers. When the returner descends to an altitude of 60 kilometers, it will bounce upwards under the lift generated by air resistance, and fly out of the atmosphere again at an altitude level, as if playing a "water drift".
After that, the returner will reach an altitude of up to 100-140 km, and then descend again and re-enter the atmosphere for the second time. At this time, the speed of the returner has been greatly reduced, and it has been reduced to about 7.9 km/s in the first universe, and it can enter the atmosphere and land like a manned spacecraft. You should be able to see that the process of semi-ballistic jump reentry is much more complicated than direct reentry, much like the "Sanger ballistic" used in hypersonic weapons, which puts forward higher requirements for the control of spacecraft.
Since Chang'e-6 was originally a backup spacecraft for Chang'e-5 and landed at the same site as Chang'e-5, there is reason to believe that Chang'e-6's re-entry orbit is similar to that of Chang'e-5, both of which start the first re-entry from the skies over the Indian Ocean, and that Chang'e-6 will reach the lowest point (60 km) of the first re-entry over the Arabian Sea between the Arabian Peninsula and India. It then rises in altitude and flies over Indian territory and reaches its highest point near the border between Nepal and the mainland, after which it enters the mainland.
At the time of Chang'e-5's return, the mainland's Yuanwang-3 survey ship was responsible for the first re-entry measurement and control, and now the new generation of Yuanwang-7 survey ship with a displacement of 27,000 tons has entered the Indian Ocean to complete the Chang'e-6 re-entry monitoring and control mission.
After flying over the Tibetan Plateau, Chang'e-6 will re-enter for the second time and land at the Siziwangqi landing site in Inner Mongolia. Since its first entry into the atmosphere, the Chang'e-6 returner has flown more than 6,500 kilometers, passing through India, Nepal and the mainland, and the landing site is only a few hundred kilometers away from Mongolia. This raises the question: if Chang'e-6's re-entry orbit deviates, will it fall into the territory of other countries?
Judging by the re-entry trajectory, it is not without such a possibility. The timing and position of re-entry are determined by the moon-to-Earth transfer orbit parameters of the orbit-return combiner. If there is a deviation in the orbit, the re-entry point will deviate, and the subsequent landing site will deviate very much, thousands of kilometers are possible.
However, there are conditions for the returner to achieve a "drifting" trajectory, and the returner needs to maintain a specific angle in the atmosphere in order to generate sufficient lift. If the attitude is not maintained, the lift cannot be generated, and this becomes a "ballistic" reentry, which will fall directly to the ground. If this happens, there is a possibility that the returner will fall into the territory of India.
The Chang'e-6 returner carried about 2 kilograms of samples from the far side of the moon, and these lunar soil and moon rocks are extremely valuable, and they are the first time that humans have obtained samples from the far side of the moon, even the Americans do not have them, so they have become the dream of scientists all over the world. India is also quite ambitious in lunar exploration, and has launched Chandrayaan-1, 2 and 3, of which Chandrayaan-3 has successfully made a soft landing, although it has only worked for less than 10 days, but it has also completed the expected goal.
India also plans to launch Chandrayaan-4 in 2026 to return lunar samples, just like Chang'e-5. It can be seen that India is quite concerned about the moon, and it must also covet the lunar soil contained in Chang'e-6, and it is eager to get some. If Chang'e-6 accidentally falls on Indian soil, will India take the lunar soil for itself?
India's Chandrayaan-3
In addition to India, another one to note is Mongolia. Although the country is not on the flight path of Chang'e-6, it is only a few hundred kilometers away from the landing site of the Siziwangqi. If Chang'e-6 deviates from its flight direction and the landing site deviates significantly from the intended landing site, it is also possible that it will deviate into Mongolian territory. Although Mongolia does not have a space program of its own, if it really gets such a precious thing, will it also think about it?
It is not unheard of for a spacecraft to deviate from the landing site. In 1965, Soviet cosmonauts Alexei Leonov and Pavel Belyaev took off on the Ascent-2 spacecraft and completed the first human spacewalk. The spacewalk was so thrilling that Leonov almost didn't make it back to the spacecraft. When the spacecraft returned, the positioning system malfunctioned, and the astronauts were forced to use a manual landing, with a deviation of hundreds of kilometers, and finally landed in a primeval forest in Siberia, where they were found 24 hours later.
On January 18, 1969, the Soviet Union's "Soyuz-5" manned spacecraft was forced to enter a ballistic re-entry without lift and deviate by up to 2,000 kilometers when it returned with an improper attitude and a heat-proof outsole that failed to face downward. In 2003, the United States used Russia's Soyuz-TMA1 manned spacecraft to return from the International Space Station for the first time, but it deviated 460 kilometers from the intended landing site and lost contact with the Moscow control center for more than two hours.
In fact, no spacecraft can rule out the possibility of landing deviation, and the mainland's Shenzhou spacecraft has also set up 10 autonomous emergency landing areas around the world, of which 3 are in China and 7 are abroad. Foreign landing areas are distributed in Australia, the United States, South America, North Africa, the Middle East and other regions.
So back to the question: if the Chang'e-6 returner really lands in the territory of another country, will the lunar soil be taken away and forcibly occupied by other countries? You can rest assured that this is theoretically impossible.
In 1967, the Treaty on the Principles to be Followed by the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies, formulated by the United Nations Committee on the Peaceful Uses of Outer Space, entered into force. In 1968, another Agreement on the Rescue of Astronauts, the Return of Astronauts and the Return of Objects Launched into Outer Space entered into force.
In accordance with the provisions of the outer space treaties and rescue agreements, ownership of objects launched into outer space, objects landed or built outside the Earth and their components shall not be affected by their appearance in outer space and extraterrestrial bodies or their return to Earth. If the object or part thereof appears outside the territory of the State from which it was launched, the other States shall return it to the State from which it was launched, and the State launching may request documentation before returning it. Of course, the costs of fulfilling the obligation to locate and return a space object or its component parts should be borne by the launching State.
Therefore, even if Chang'e-6 falls into the territory of another country, the other country cannot take it as its own, and is obliged to return it to the mainland, and the expenses incurred need to be paid by the mainland. If the returner caused damage to the ground, the mainland should compensate for it. Now everyone understands, according to the United Nations convention, lunar soil will not be lost!