If everything goes according to plan, China will soon become the third country behind the United States and the Soviet Union to successfully return a sample of lunar material. Their Chang’e 5 mission, which was designed to collect 2 kilograms (4.4 pounds) of soil and rock from the Moon’s surface, has so far gone off without a hitch. Assuming the returning spacecraft successfully renters the Earth’s atmosphere and lands safely on December 16th, China will officially be inducted into a very exclusive club of Moon explorers.
Of course, spaceflight is exceedingly difficult and atmospheric reentry is particularly challenging. Anything could happen in the next few days, so it would be premature to celebrate the Chang’e 5 mission as a complete success. But even if ground controllers lose contact with the vehicle on its return to Earth, or it burns up in the atmosphere, China will come away from this mission with a wealth of valuable experience that will guide its lunar program for years to come.
In fact, one could argue that was always the real goal of the mission. While there’s plenty of scientific knowledge and not an inconsequential amount of national pride to be gained from bringing a few pounds of Moon rocks back to Earth, it’s no secret that China has greater aspirations when it comes to our nearest celestial neighbor. Starting with the launch of the Chang’e 1 in 2007, the Chinese Lunar Exploration Program has progressed through several operational phases, each more technically challenging than the last. Chang’e 5 represents the third phase of the plan, with only the establishment of robotic research station to go before the country says they’ll proceed with a crewed landing in the 2030s.
Which helps explain why, even for a sample return from the Moon, Chang’e 5 is such an extremely complex mission. A close look at the hardware and techniques involved shows a mission profile considerably more difficult than was strictly necessary. The logical conclusion is that China intentionally took the long way around so they could use it as a dry run for the more challenging missions that still lay ahead.
While most people associate Moon rocks with the Apollo program, the Soviet Union also conducted a series of successful robotic sample return missions during the 1970s. The three Luna missions only brought back a small fraction of the material that NASA did with their far larger and more ambitious crewed vehicle, but they proved that even with the relatively primitive technology of the era, lunar sample return could be done at a far lower cost and without risk to human life.
It stands to reason that replicating the Luna missions of the 1970s would still be the fastest and cheapest way to return a sample from the Moon. By today’s standards, the sensors, cameras, and communications equipment used on those early landers are absolutely archaic. Modern materials and battery technology would also allow for a far lighter craft than was possible 50 years ago, though the 5,727 kg (12,626 lb) launch mass of the Luna 16 still would have been within the payload capacity of China’s Long March 5 booster.
Calling it easy would certainly be a stretch. After all, modern technology and materials alone weren’t enough to prevent Israel’s Beresheet lander from crashing into the lunar surface. But China had already placed several robotic craft on the Moon, so adding a Luna-inspired return stage to the Chang’e 5 lander would have been the most expedient way to achieve their goals. Instead, they did something very different.
Echos of Apollo
When referring to Chang’e 5, we aren’t really talking about a single spacecraft, but a “stack” of several distinct vehicles that each have a specific role. Once the craft were in orbit around the Moon, the lander separated and descended independently to the surface. Soil and rock samples were then loaded into a smaller ascent vehicle mounted to the top of it. This diminutive craft took off from the Moon, leaving the lander behind, and docked with the service module that had remained in orbit. The samples were transferred to the orbital module, which then detached from the ascent vehicle and used its engine to leave lunar orbit and begin the return leg of the journey. In the end, only a small capsule will actually make it all the way back and land on Earth.
If that sounds familiar, it’s because this is the same mission architecture used during the manned Apollo missions. Known officially as Lunar Orbit Rendezvous (LOR), this concept was selected by NASA because it allowed for a much smaller booster than would have been required otherwise. A single spacecraft capable of flying to the Moon, landing, and then returning to Earth would be extremely heavy; largely because the propellant necessary for the return to Earth would be nothing more than dead weight on the trip down the lunar surface and back.
With the “nesting doll” LOR approach, each subsequent phase of the mission is accomplished by a smaller and lighter craft. The downside is that it’s operationally far more complex, requiring two spacecraft to rendezvous and dock in lunar orbit. For NASA, that meant years of additional research and development had to take place before Apollo could ever head to the Moon. This lead directly to Project Gemini, a series of missions used to develop the navigational and docking techniques that would eventually be used during Apollo’s lunar rendezvous.
Little is currently known about China’s plans in regards to human exploration of the Moon, but it stands to reason they’ll use the same tested LOR architecture that NASA demonstrated during Apollo and will continue to use during the Artemis program. By testing automated rendezvous and docking techniques during the robotic Chang’e missions, China could potentially avoid spending the time and money required for their own crewed Gemini-style program.
Practice Makes Perfect
The crew of Apollo 10 had the honor of performing the first rendezvous and docking in lunar orbit as part of the “dress rehearsal” for the eventual landing made during the Apollo 11 mission, but Chang’e 5 marks the first time such a feat has been accomplished by a robotic craft. While remotely operated vehicles have previously docked in geostationary orbit, the unique challenges of performing such a delicate operation while in orbit around another body make this a considerable technical achievement.
Which is why China made sure to get some practice runs in first. The Chang’e 5-T1 mission was launched in 2015 to demonstrate some of the techniques that would be required to eventually return from the Moon. This included testing the sample capsule’s ability to safely reenter the Earth’s atmosphere and performing several simulated docking maneuvers.
Even though the vehicle only had a virtual partner to practice with, this experiment could be seen as analogous to the later Gemini missions, which had astronauts dock their spacecraft with the unmanned Agena Target Vehicle while in low Earth orbit. When it came time for the real thing, the rendezvous and capture of the Chang’e 5 ascent vehicle went perfectly on December 5th. There’ll be another opportunity to gather data on autonomous lunar docking during the Chang’e 6 mission to the Moon’s south pole as well, which is currently expected to happen by 2024.
It’s still too early to say how much of an impact these robotic practice runs will have on their crewed counterparts in the 2030s, but one thing is for sure: China now knows a lot more about lunar rendezvous and docking than the United States did before the Apollo program.