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.
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.
2020年12月3日23时10分，嫦娥五号上升器携带月球样品从月面点火起飞，约6分钟后，进入环月椭圆轨道。12月6日2时13分，上升器准确到达轨返组合体前方50公里、上方约10公里的预定“交班”位置。5时42分，上升器与轨返对合体完成交会对接，6时，样品封装容器从上升器转移到返回器中。这个自主交会对接和样品转移过程就好像百米接力赛中的交接棒过程，精彩纷呈，技术含量极高。采用从月面起飞后进行一次月球轨道交会对接，而不是从月面起飞后直接月地转移，这样的设计有利于采集和携带更多样品返回地球，并为后续任务进行技术积累和验证。
看点1——太空中的追逐
上升器和轨返组合体都在环月飞行，但轨道高度不同，上升器在210公里高的外道跑，轨返组合体在200公里高的内道跑。内道路程短，轨返组合体跑得稍快一些，外道的上升器则跑得要慢一点。为了实现“交接棒”，轨返组合体需要在高度方向上抬高轨道，并且在前后方向上逐渐逼近上升器。当接近到一定距离时，轨返组合体会自主控制发动机来改变行进方向，抄近道赶上上升器。整个追逐过程设置多个停泊点，轨返组合体停下来保持相对位置不变，进行状态检查，并确保对接的时候测控条件满足要求。
看点2——“高精测量”+“知己知彼”
在交会对接过程中，需要让轨返组合体和上升器清楚彼此的相对位置、速度和姿态，为此配置了多种进行相对测量的敏感器，用来实现相对导航。在相距100公里的时候，微波雷达开始工作，既按照传统雷达的“点名答到”模式提供两器的相对运动参数，还升级到“对话交流”模式，在轨返组合体和上升器之间双向传输遥控指令和遥测参数。在相距20公里的时候，激光雷达“登场”，提供更高精度的测量信息。而到了100米左右，光学敏感器开始大显身手，实现近距离的距离和姿态测量。这些敏感器在作用距离上彼此接力又有覆盖衔接，从而确保在任意距离上至少有两种不同体制的敏感器可用，使得轨返组合体看得更准，测得更精，系统更加可靠。
看点3——38万公里之外的精准“交接棒”
轨返组合体重达2吨多，上升器质量却只有它的六分之一，如果采用传统的碰撞式对接，极易导致上升器被撞飞。为此，专门设计了抱爪式抓捕对接机构，每对抱爪犹如两只手臂，在1秒内快速合拢形成闭合空间，将位于上升器的被动锁柄牢牢地约束在内部，再也无法逃脱。对得上还得对得准，对接后的精度要求优于0.5毫米，好比在太空“穿针引线”。采用3套抱爪机构星型周向布局、自定心设计，实现了两飞行器对接后的自动对准中心，在保证高精度对接的同时实现了轻量化设计。
转移机构的设计也很巧妙。为了实现六百多毫米的长行程样品容器转移，设计师们从尺蠖的身上找到了灵感，基于运动行程放大+接力转移的原理，提出了一种仿尺蠖大展收接力式机构，通过多级并联连杆的简单循环展收运动，就可以实现物体的连续移动。整个转移过程如同毛毛虫的运动，一伸一缩、不断前进。
作者：王琼 胡震宇 于丹 戚铁磊
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