By December 2021, the Chang'e-5 sample return mission of the mainland lunar exploration project has been successfully implemented for one year.
The Chang'e-5 probe consists of orbiters, landers, ascents and returners, and the team acts like a relay team to send lunar samples back to Earth through a "relay" approach.
Schematic diagram of the Chang'e-5 probe
So why not send a member to complete the "treasure hunting" task alone?
This is because the sample return task is complex and cannot be done by a single member alone. The team members have a clear division of labor, each with their own tasks:
Orbiter
The orbiter is responsible for "flying", that is, after separating from the launch vehicle, it is responsible for sending the lander, ascent and returner to the lunar orbit, and after completing the sampling task, the returner is sent back to the vicinity of the Earth.
Lander
The lander is responsible for "going down", that is, after reaching the lunar orbit and separating from the orbiter-returner assembly (referred to as the "orbital return assembly"), it is responsible for taking the ascender, soft landing on the lunar surface, and together with the ascender, completing the lunar surface sampling.
Ascender
The ascent ascent is responsible for "getting up", that is, after completing the sampling task, it takes off from the lunar surface with the lunar sample, rendezvouss and docks with the orbital return assembly flying in the lunar orbit, and transfers the lunar sample to the returner.
Returner
The returner is responsible for "falling down", that is, when the orbital return assembly returns to the vicinity of the Earth, it is separated from the orbiter, re-entered the atmosphere, and sends the lunar sample back to the Earth.
First of all, the role of the orbiter is equivalent to that of a space shuttle, which plays the role of transporting back and forth between the Earth and the Moon. Due to the long distance between the Earth and the Moon, it is necessary to change orbit many times during the flight, and when it reaches the vicinity of the Moon, it is also necessary to brake and slow down in order to be captured by the Moon; after "taking" the lunar sample, it is then accelerated to get rid of the Moon's gravity and fly back to the Earth. These tasks require the engine and control system of the orbiter to complete. The returner has no engine, does not rely on the orbiter for ferry, and cannot complete the earth-moon round-trip task.
Secondly, since the moon does not have an atmosphere, landing on the lunar surface from the lunar orbit can only achieve a soft landing by pushing back the engine, generating braking force, and reducing the speed of the lander. The re-entry has no engine and cannot achieve a soft landing; although the orbiter has an engine, due to the large mass of the orbital return assembly, about 4.5 tons, the landing lunar surface and the take-off from the lunar surface require the consumption of a lot of propellant, and the orbiter also undertakes the task of sending the returner back to Earth. Therefore, after reaching the lunar orbit, the orbital return assembly performs a lunar flight without consuming propellant, and the lander and ascender (referred to as the "landing assembly") land on the lunar surface and complete the sampling task.
Schematic diagram of the landing lunar surface of the upper assembly
Third, after completing the sampling task, it is necessary to take off from the lunar surface. The lander weighs nearly 3 tons and consumes a lot of propellant to take off from the lunar surface. In order to reduce the take-off weight and reduce propellant consumption, it is necessary to leave the completed lander on the lunar surface as a take-off platform for the ascender, and the ascender weighing about 0.8 tons will take off from the lunar surface and transfer the lunar samples to the returner by rendezvousing and docking with the orbital return assembly remaining in the lunar orbit.
Schematic diagram of the ascender flying away from the lunar surface
Ascender and railback combination
Schematic of rendezvous and docking in lunar orbit
Finally, to send lunar samples back to Earth, they must re-enter the atmosphere. Due to the very high speed of the returner, friction with the atmosphere will generate a lot of heat, and if heat protection measures are not taken in terms of shape design and material selection, the returner will burn out during re-entry. Only a returner with a heat-resistant design can safely re-enter the atmosphere, and because of its small mass (about 0.3 tons), it can be slowed down by parachute and land smoothly on the ground. The orbiter and ascent apparatus without heat-proof design do not have the conditions for re-entry into the atmosphere.
The re-entry returns to the surface with lunar samples
After 23 days of operation, the Chang'e-5 lunar sampling team returned to the ground with the lunar sample; the lander that completed the mission remained on the lunar surface; after the ascender handed over the lunar sample and separated from the orbital return assembly, it was controlled to deorbit according to the ground instructions and landed at the predetermined landing point on the lunar surface; and the orbiter was given a new mission after completing the earth-moon round-trip transport mission, first to explore the L1 point of the Sun-Di Lagrange, and then returned to the moon from the L1 point of the Heli-Di Lagrange, as of the first anniversary of the lunar sampling, It is still in lunar orbit.
Source: Space Exploration, No. 1, 2022
Text/Zhang Tiejun
Editor/Yang Sishuang
Audit/Yang Jie
Executive Producer/Xu Chunmei
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