Author: Saito Shin
Reviewed by: Yuandao

  At 4:30 a.m. Beijing time on November 24, 2020, the Long March 5 Y5 launch vehicle successfully lifted off from the Wenchang Spacecraft Launch Site in Hainan carrying the Chang’e 5 probe. CCTV News and the Our Space new-media platform jointly broadcast the entire launch live, demonstrating the confidence of China’s space program in the mission. This time, let us talk about Chang’e 5.

  Many readers may be wondering: what are the technical challenges of the Chang’e 5 mission?

  We will look at them separately, before and after launch.

Before Launch:

  For the prelaunch phase, consider just one example: propellant loading. Chang’e 5 was fueled in its combined-spacecraft configuration. The complete vehicle contains more than 600 units or sets in its propulsion subsystem. When propellant was loaded into more than 200 units or sets of its bipropellant propulsion subsystem, Chang’e 5 was already assembled as a combination of four spacecraft—the ascender, lander, returner, and orbiter. This configuration more closely matched the in-flight state, simplified final assembly, and reduced technical risks in assembly, but made propellant loading far more difficult and dangerous than fueling the spacecraft separately. Hong Xing, deputy chief designer of the Chang’e 5 probe system and chief model designer at the Sixth Academy, described it this way: “Twelve tanks had to be divided into six groups for loading. There were two kinds of tank: metal-diaphragm tanks and surface-tension tanks. Some had to be evacuated, while others remained at atmospheric pressure. Some required the propellant to be cooled, while others needed it kept at room temperature, so the filling method differed in every case. The loading sequence also crossed over: first fuel, then oxidizer, and finally back to fuel. In addition, the pipes were long, with many lines and branches … there were many more points requiring attention.” In his view, fueling Chang’e 5 as a four-spacecraft assembly was the most complex loading operation in the history of China’s spacecraft program. Consider the figures: “Compared with fueling the separate spacecraft, fueling the complete assembly increased the number of interfaces with the probe from five or six to nearly 20, and the number of equipment-side loading lines from five or six to nearly 20. In the combined configuration, many filling ports were higher, making the pipe routes more complex and much longer. Previously, keeping the pipes leak-free meant managing five or six lines totaling several dozen meters. Now, nearly 20 lines totaling about 300 meters had to be managed simultaneously.” Stacked in its four-spacecraft configuration, Chang’e 5 “stood eight or nine meters tall, with many protruding components, such as antennas, already installed. While working, the loading technicians had to lean half their bodies out at height and reach into a jungle of equipment. Besides carrying out their own operations precisely, they could not touch any other component—not even drop a washer.”

After Launch:

  Developed by the China Aerospace Science and Technology Corporation, Chang’e 5 was China’s first lunar probe designed to conduct a robotic surface-sampling and return mission. With a total mass of about 8.2 tonnes, it was also the heaviest and most complex space probe China had developed up to that point. It would collect samples autonomously on the lunar surface. The ascender would then lift off and complete an autonomous rendezvous and docking with the orbiter in lunar orbit, after which the samples would return to Earth. If the mission succeeded, China would become the third country, after the United States and Soviet Union, to bring samples back from the Moon. That would also complete the crucial final step in China’s three-stage lunar-exploration plan: “orbit, land, and return.” Chang’e 5 was additionally expected to achieve four firsts in Chinese spaceflight: the first automated sampling on the lunar surface, the first liftoff from the lunar surface, the first uncrewed rendezvous and docking in lunar orbit 380,000 kilometers from Earth, and the first return to Earth with lunar soil at close to Earth’s escape velocity, also known as the second cosmic velocity.

  Chang’e 5 was expected to collect about two kilograms of material from the Moon, including small rocks from the surface and a core from roughly two meters beneath it. The volcanic plain of Mons Rümker, where Chang’e 5 would land, lies at the western edge of Oceanus Procellarum and may contain basaltic rocks only 1.21 billion years old. By comparison, the lunar soil returned by the Apollo missions had an average age of 3.1 to 4.4 billion years. These younger geological samples could provide valuable information about late volcanic activity on the Moon. In addition to lunar sampling, Chang’e 5 would pursue eleven technical and research objectives, including verification of a heavy-lift launch vehicle, flight along an Earth–Moon transfer orbit, braking near the Moon, lunar-orbit flight, ascent from and descent to the lunar surface, rendezvous and docking in lunar orbit, waiting in lunar orbit, Moon–Earth transfer, and atmospheric reentry at Earth’s escape velocity.