Traveling through time and space & Doing timey wimy stuff.

One year ago today 24th November 2020 Now it’s the 24th November 2021 , the Chang Zheng – Long March Five Carrier Rocket Launched away  in CNSA – China National Space Administration China Wenchang spaceport launch, Change Five  Lunar probe into orbit, opened up towards China – People’s Republic of China’s first celestial bodies sample return trip from Mons Rumker on the Lunar Surface.……  

​​At 23:10 on December 3, 2020, the Chang’e-5 ascender carried a lunar sample to take off from the lunar surface. About 6 minutes later, it entered an elliptical orbit around the moon. At 2:13 on December 6, the ascender accurately reached the scheduled “handover” position 50 kilometers in front of the orbit-return assembly and about 10 kilometers above it. At 5:42, the ascender and the orbit-returning assembly completed the rendezvous and docking. At 6 o’clock, the sample packaging container was transferred from the ascender to the returner. This process of autonomous rendezvous and docking and sample transfer is like the handover process in a 100-meter relay race. It is brilliant and highly technical. Using a lunar orbital rendezvous and docking after take-off from the lunar surface, rather than a direct lunar-to-ground transfer after taking off from the lunar surface, this design is conducive to collecting and carrying more samples back to the earth, and for technical accumulation and verification for subsequent missions.

Aspect 1-chase in space

Both the ascender and the orbit-back assembly fly around the moon, but the orbital heights are different. The ascender runs on the outer track at a height of 210 kilometers, and the orbit-back assembly runs on the inner track at a height of 200 kilometers. The distance on the inner track is short, the track-back assembly runs slightly faster, and the ascender on the outer track runs slower. In order to realize the “transfer bar”, the rail-back assembly needs to raise the rail in the height direction and gradually approach the ascender in the front and rear direction. When approaching a certain distance, the orbit-back assembly will autonomously control the engine to change the direction of travel and take a shortcut to catch up with the ascender. During the entire chase process, multiple anchor points are set up, and the orbit-return assembly stops to keep the relative position unchanged, conducts a state inspection, and ensures that the measurement and control conditions meet the requirements during docking.

Picture: Lunar orbital rendezvous and docking flight phase division. (Source: Xu Yang, Ma Lin, Liu Tao, etc. Chang’e 5 Lunar Orbital Rendezvous and Docking Guidance, Navigation and Control System. Science in China: Technological Sciences, 2021, 51: 788–798)

 Aspect 2-“High-precision measurement” + “Know yourself and the enemy”

During the rendezvous and docking process, it is necessary to make the orbit-return assembly and the ascender know the relative position, speed and attitude of each other. For this reason, a variety of sensors for relative measurement are configured to realize relative navigation. When the distance is 100 kilometers, the microwave radar starts to work. It not only provides the relative motion parameters of the two devices according to the traditional radar “call and answer” mode, but also upgrades to the “dialogue exchange” mode, between the orbital assembly and the ascender. Two-way transmission of remote control commands and telemetry parameters. At a distance of 20 kilometers, lidar “comes on the scene” to provide higher-precision measurement information. At about 100 meters, the optical sensor began to show its talents to achieve close distance and attitude measurement. These sensors are relayed to each other over the working distance and covered and connected, so as to ensure that there are at least two different systems of sensors available at any distance, so that the orbit-back assembly can be seen more accurately, the measurement is more precise, and the system is more reliable. 

Aspect 3-precise “handover baton” from 380,000 kilometers away

The weight of the orbit-return assembly is more than 2 tons, but the mass of the ascender is only one-sixth of its mass. If the traditional collision docking is used, it is very easy to cause the ascender to be knocked into flight. For this reason, a claw-type catching and docking mechanism is specially designed. Each pair of claws is like two arms, which are quickly closed within 1 second to form a closed space, and the passive lock handle of the ascender is firmly restrained inside. Can’t escape. It has to be accurate, and the accuracy requirement after docking is better than 0.5 mm, which is like “threading a needle” in space. The use of 3 sets of claw mechanism star-shaped circumferential layout and self-centering design realizes the automatic centering of the two aircraft after docking, and realizes the lightweight design while ensuring high-precision docking.

The design of the transfer mechanism is also very clever. In order to realize the transfer of long-stroke sample containers of more than six hundred millimeters, the designers found inspiration from the inchworm. Based on the principle of movement stroke amplification + relay transfer, they proposed a relay mechanism for imitating the inchworm. The simple circular expansion and contraction movement of the parallel link can realize the continuous movement of the object. The entire transfer process is like the movement of a caterpillar, stretching and shrinking, continuously advancing.









作者:王琼  胡震宇 于丹 戚铁磊​​​​

Images and visuals are from Weibo and their respectives…. Of CNSA China National Space Administration … 

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