China will launch one of its most complex and exciting missions so far later this year, when Chang'e-5 attempts to land on and collect samples from the Moon before delivering them to Earth—the first such mission by any country for more than four decades. The mission will be an engineering feat and result in some significant science, but it also has some interesting subplots.
Chang'e-5 marks the third and final stage of the original China Lunar Exploration Program (CLEP) approved in the early 2000s, which set out to first orbit and map the Moon (Chang'e-1 and 2), then land and rove on the lunar surface (Chang'e-3 and Yutu), and finally collect samples and bring them to Earth for analysis.
Following earlier successes and technological breakthroughs, Chang'e-5 is now scheduled to launch in late November from Wenchang on a new Long March 5 heavy-lift rocket.
The last lunar sample return was the Soviet Union's Luna 24 in 1976, so China is clearly still catching up. But rather than merely copying Cold War-era missions, as has often been suggested, this will also provide lessons and experience for more ambitious missions in the future.
The Luna 24 ascent stage returned directly to Earth, but China has decided that the Chang'e-5 mission will rely on a lunar orbit rendezvous similar to that used for the Apollo landings. The 8.2 metric ton Chang'e-5 spacecraft thus consists of a service module, lander, ascent unit, and a return vehicle.
After collecting samples, the ascent module will lift off and dock with the service module in orbit around the Moon, nearly 400,000 kilometers away from Earth. The samples will be transferred to the reentry capsule, which itself will separate from the service module a few thousand kilometers from Earth before reentry and landing.
The lunar orbit rendezvous approach is a very interesting choice we'll look at later, but note for now that this will be the first robotic rendezvous and docking around a planetary body other than the Earth.
Landing sites and science goals
Six Apollo and three Soviet robotic Luna missions brought lunar rocks and regolith back to Earth, but the Moon is a large and diverse body and there is much to be learned. According to a paper recently presented at the 48th Lunar and Planetary Science Conference, a number of target sites near Mons Rümker in the northern Oceanus Procellarum are being considered.
Spectral analysis of craters using imaging data from the Chandrayaan-1 Moon Mineralogy Mapper suggests that material at one candidate area is just 1.33 billion years old, meaning Chang'e-5 could be returning by far the youngest lunar basaltic samples yet (Apollo basalt samples were 3 to 4 billion years old).
Planetary Scientist Phil Stooke, using information from another paper to be presented at the European Geoscience meeting in April, mapped out the region containing seven candidate sites identified by scientists with the Chinese Academy of Sciences. Within this, the 'preferred landing area' box marks the candidate site discussed above.
The Chang'e-5 lander will also be carrying three scientific payloads. The Lunar Regolith Penetrating Radar (LRPR) will investigate the subselenean structure and guide the drilling process, which will penetrate to a depth of around two metres and retrieve around around two kilograms of samples. This is similar to the ground-penetrating radar the Yutu rover employed to uncover the previously unknown complexity beneath the surface of Mare Imbrium.
The Lunar Mineralogical Spectrometer (LMS) will collect in-situ measurements and analyze the mineralogical composition of the sample site, look for water absorption features, and provide comparisons with returned samples.
Last but far from least, a Panoramic Camera (PCAM) with stereo capability will be along for the ride and hopefully return spectacular images like those from the panoramic camera on the Yutu rover. Emily Lakdawalla's blog post on the Chang'e-3 data set is an absolute must.
It is expected that all of this will be attempted within a single lunar day (14 Earth days) to reduce risk, with the reentry capsule scheduled to touch down in the grasslands of Siziwang Banner in Inner Mongolia—the same landing area used for Shenzhou human spaceflight missions—before the end of December.
The samples will then be immediately sent for analysis at a specially built, but unspecified, laboratory headed by Chinese cosmochemist and CLEP chief scientist Ouyang Ziyuan. It is hoped the mission will reveal new information about the Moon's interior, its thermal evolution, and late-stage volcanism.
Long March to the Moon and back
To make a mission of this complexity possible, China has taken a number of incremental and necessary steps to ensure they are ready for the challenge.
The lander and service module are based on successful earlier Chang'e missions, while rendezvous and docking have been proven by Shenzhou missions visiting the Tiangong-1 and 2 space labs.
In 2014, China launched the Chang'e-5 T1 test mission including a reentry capsule nicknamed 'xiao fei' which returned from around the Moon and successfully demonstrated a 'skip reentry'—a maneuver used to help get rid of with the extra energy that comes with high velocity return from the Moon (around 11 km/s compared to 7 km/s from low Earth orbit).
China has also needed to develop a heavy-lift launch vehicle and new launch site to get to this point. The Long March 5 will also be sending an orbiter, lander and rover to Mars in 2020. Another variant, the 5B, will allow the country to begin constructing its Mir-class space station around late 2018.
Space missions are also almost always an international effort. Though not yet confirmed, China may once again receive tracking, telemetry and command (TT&C) support from ESA's European Space Operations Center, as was the case for Chang'e-3. In this case tracking stations in Kourou and Maspalomas would provide crucial assistance for the probe's trip to the Moon.
Human and Martian subplots
The fact that the Chang'e-5 will be carrying out a difficult Lunar Orbit Rendezvous rather than a simpler direct return is an indication that the mission is also a small step towards putting astronauts on the Moon.
The country's government has not officially announced a program for human lunar landings, but this, together with the development of a successor to the Shenzhou crewed spacecraft and preliminary work on a Saturn V-class super-heavy launch vehicle (Long March 9), leaves little doubt that China is targeting the Moon around the 2030s.
Another monumental mission that Chang'e-5 rendezvous approach could prove useful for is a Mars sample return, which the country is planning for around 2030 using the requisite Long March 9. Returning samples from the Red Planet, a mission now being studied, could yield clues or direct evidence for past or even present extraterrestrial life, a moment that would be a clear marker in human history (and 'change the worlds' in the words of Bill Nye). NASA also has plans for such a project, but its future is unclear. While there is no 'space race' between China and the United States, this could be one small arena in which they compete for a potentially seismic 'first'. There's a long way to go before sampling Mars, but Chang'e-5 will hopefully be a step along this road.
The other good news is that Chang'e-5 is far from the end of China's robotic plans for lunar exploration, which are now being expanded. Chang'e-4, the backup to the successful Chang'e-3, is being repurposed for an unprecedented 2018 far side lander and rover mission, involving a relay satellite at Earth-Moon Lagrange Point 2, as Emily Lakdawalla details here.
Should both Chang'e-5 and the slightly confusingly later Chang'e-4 mission come off, the backup sample return probe Chang'e-6 is expected to be used to collect material from the lunar far side or south pole. Following this, the early 2020s will see robotic visits separately to both poles.