Two Chinese astronauts will land on the moon, and the details of China's manned lunar landing program have been unveiled.
On October 31, details of a major milestone China is set to accomplish by 2030 were unveiled at the 7th Manned Spaceflight Academic Conference.
Wang Xiang, Deputy Chief Designer of China Manned Space Engineering and Chief Designer of the Lunar Exploration Engineering, introduced for the first time the crew plan for China's manned lunar exploration mission.
Simply put: Two Long March 10 rockets will be launched in sequence. The Lanyue Lander will take off first and "wait" in the circumlunar orbit; the Mengzhou spacecraft carrying three astronauts will set off afterwards; then the lander will dock with the spacecraft in the circumlunar orbit, two astronauts will transfer to the lander to land on the moon; after completing the mission, they will take off from the lunar surface, dock with the spacecraft and return home.
As netizens summed it up: "Two launches, circumlunar docking; three people go up, two land on the moon." What a surprisingly simple solution!
However, every "simplicity" in a mega engineering project is achieved at the cost of redundancy. Why not build a super-large rocket to finish the mission in one go? We need to calculate every account carefully.
Why two launches?
Two launches reduce the pressure on individual hardware through system design optimization.
When hearing about two launches, the first thought that easily comes to mind is whether the thrust of the rocket is not enough?
Launching the lander and the spacecraft together with one super-heavy rocket means "putting all eggs in one basket". From ignition to orbit insertion, if any link goes wrong, the whole mission chain may be interrupted, with no backup and no second chance.
By splitting into two launches, the risk structure is transformed. The Lanyue Lander will be launched first and wait calmly in the circumlunar orbit; the Mengzhou spacecraft will set off calmly after confirming all its status. With two independent launch chains, if any one encounters an anomaly, the other still has room for adjustment and reorganization, and the time window for lunar landing is more flexible.
Behind this is an easily overlooked engineering common sense: The core contradiction of manned lunar landing has never been "whether we can send enough mass to the moon", but "whether we can leave fault tolerance space for every link". A one-rocket bundled launch seems to have sufficient carrying capacity, but the redundancy at the system level is limited, and the success or failure depends entirely on one single action. Two launches seem to add an extra procedure, but in fact, it turns the risk from "centralized" to "distributed".
Let each machine only do what it is best at
Launching the spacecraft and the lander separately gives full play to their respective strengths.
Mengzhou is a spacecraft, serving as the "long-distance coach" for round trips between the Earth and the moon. It needs to fly from the ground to the circumlunar orbit, then return to the Earth from the circumlunar orbit, and withstand the extreme thermal environment of re-entering the Earth's atmosphere at a speed close to the second cosmic velocity.
Lanyue is a lander, serving as a "shuttle vehicle" for takeoff and landing on the lunar surface. It needs to descend, land, take off and re-dock in the circumlunar orbit, and cope with precise control under the environment of large temperature difference, lunar dust and low gravity on the lunar surface.
Integrating these two major functions into one single aircraft means that it has to meet both the thermal protection and life support requirements for Earth-moon round trips, and possess the structure and propulsion capabilities for lunar surface takeoff and landing. Every kilogram of hardware redundancy has to be carried from the Earth's departure, all the way to the moon.
By developing them separately, Mengzhou does not need to pay the weight cost for the lunar landing and takeoff structure, and Lanyue does not need to carry an extra thermal protection system for re-entering the Earth's atmosphere. Each aircraft only undertakes the tasks it truly needs to complete, and its weight and complexity are both reduced to their respective most economical ranges.
The deeper change lies in the development logic. An aircraft customized for a single mission is rarely applicable to other scenarios; after Mengzhou and Lanyue are separated, both can be developed into serialized products. The near-Earth version of Mengzhou can undertake the round-trip mission for astronauts to the space station, and Lanyue can also provide a platform for subsequent lunar surface cargo transportation and the construction of lunar scientific research stations. The Long March 10 rocket itself also follows a serialized development path, where the derivative versions and the lunar landing version share R&D costs, diluting the overall investment. "Two launches" not only saves the R&D cost of a super-heavy rocket, but also obtains a complete set of reusable transportation systems.
Use on-orbit docking technology to save rocket R&D time
A more subtle perspective comes from the engineering economics interpretation of this solution: China's choice of two launches is essentially using the mature orbital rendezvous and docking capability to replace the R&D time and uncertainty of super-heavy rockets.
From Shenzhou, Tianzhou, the space station to Chang'e-5, from manned rendezvous and docking in near-Earth orbit to unmanned rendezvous and docking in lunar orbit, China's aerospace industry has achieved almost perfect performance in "precisely connecting two spacecraft in orbit". This technical capability does not require new R&D investment for the lunar landing mission, and can be directly applied to the manned lunar landing mission.
However, a super-heavy rocket that can launch the lander and the spacecraft at the same time requires a larger rocket body diameter, more parallel engines, higher structural efficiency, and the subsequent ground tests and flight verification that take years to complete. The advantage of "only one launch" is negligible in the face of these time costs and technical risks.
Two launches transform the problem from "building an unprecedented giant rocket" to "using two rockets with sufficient carrying capacity plus a set of fully verified orbital docking procedures". The Long March 10 has a carrying capacity of no less than 27 tons in the Earth-moon transfer orbit, and the total mass of the Lanyue Lander is about 26 tons, which is a perfect match. Therefore, this is not a passive result of insufficient carrying capacity, but a precise design that limits the carrying capacity demand to a range that is engineering-feasible, serializable and iterable.
Circumlunar docking, the truly hardcore link
Saying that "two launches are smarter" does not mean that it is easier. On the contrary, circumlunar rendezvous and docking is one of the links with the highest technical density in the whole solution, and it is also the necessary cost of "separate launches".
"Circumlunar docking" is the most hardcore part of this solution, and it is also the well-practiced muscle memory of China's aerospace industry.
For rendezvous and docking in Earth orbit, the round-trip communication delay of ground measurement and control is at the millisecond level, and the ground can intervene in real time. In lunar orbit, the one-way communication delay exceeds 1 second, and the round-trip delay can reach more than 2 seconds. This means that ground controllers cannot remotely control the docking process in circumlunar orbit as they do for near-Earth orbit missions. The final approach, alignment and locking must be completed autonomously by the spacecraft. The docking accuracy requirement is at the centimeter level, and the spacecraft will stay behind the moon for a considerable period of time in each circumlunar orbit, "facing the Earth across the moon" with the measurement and control link interrupted.
What is more tricky is the irreversibility of the time window. Circumlunar rendezvous and docking is restricted by multiple constraints including the Earth-moon return window, energy and lighting conditions. If it fails once, reorganization will take several days, and the return window may be missed. This solution distributes the risk from the "launch chain", but raises the difficulty of "on-orbit operation".
Unmanned rehearsal is an important step to deal with circumlunar docking.
The response method of China's aerospace industry is to eliminate risks in advance through "unmanned rehearsal". According to the plan, the Lanyue Lander will first go through the whole process of the manned mission in an unmanned state: launch, circumlunar flight, rendezvous and docking with Mengzhou, lunar landing, stay on the lunar surface, take off, and re-dock, to verify as many key technologies as possible in advance. The difficulty of circumlunar docking is real, but its uncertainty is being gradually eliminated through a series of repeatable and verifiable steps.
The crew member who does not land on the moon acts as the final backup
A question that netizens care about is: what is the person who stays on the spacecraft flying around the moon doing (this is the easiest part, even I can do it)? He is actually the most critical person.
In this solution, Mengzhou is the only channel to return to the Earth from the lunar orbit. After the lander takes off from the lunar surface, it must complete rendezvous and docking with the spacecraft before the astronauts can return home. The responsibility of the remaining crew member is to ensure that this "return channel" is always in an operable, emergency-ready and unobstructed state.
This role itself is the epitome of the "two launches" logic: it does not pursue to let everyone reach the lunar surface, but ensures that every key node on the whole mission chain is guarded, redundant and backed up.
The Saturn V achieved extraordinary results with its powerful thrust, sending the Apollo spacecraft's command module, service module and lunar module all into the trans-lunar orbit in one go. Its romance lies in the ambition of "finishing everything at once". Our calmness, on the other hand, lies in opening a door that can be entered and exited repeatedly, and paving a road that can be traveled back and forth multiple times, from lunar landing to lunar surface stay, from the lunar scientific research station to the deeper deep space.
This article is from the WeChat Official Account "Guokr" (ID: Guokr42), written by Liulang Xingchen, and published with authorization from 36Kr.