Despite being a relative latecomer to deep space exploration, China has made quickly established itself as one of the leading nations in the field. Since the launching of the China Lunar Exploration Programme (CLEP), also known as the Chang’e Programme, in 2004, China has successfully sent four robotic probe missions to the orbit and land on the Moon. The upcoming Chang’e 4 mission will attempt to make a soft-landing on the lunar far side – the first in the history of human space exploration. This is to be followed by the Chang’e 5 lunar sample return mission in 2019. The current robotic lunar missions will also pave the way for a future crewed lunar programme.
Although Chinese scientists first envisioned ambitious plan to explore the Moon and other planets in the solar system in the 1970s, a lack of financial funding and political sponsorship meant such a dream could not materialise until three decades later. In 1992, a mission was proposed to use a Long March 3 booster to send a metal emblem to the Moon surface to mark the ending of British colony in Hong Kong in 1997. The project was later abandoned due to a lack of funding.
In 1995, three top Chinese scholars published the concept study of a lunar orbiter based on the DFH-3 communications satellite bus. In April 1997, the Chinese political leadership received a report titled “Suggestions for Developing China’s Lunar Exploration Technology” from the scientific community. In 1998, the Commission of Science Technology and Industry for National Defence (COSTIND) carried out a preliminary study on the robotic lunar exploration programme.
In his speech titled “China’s Space Exploration in the 21st Century” during the 1st International Space Week in May 2000, Luan Enjie, Director of the China National Space Administration (CNSA), revealed that the country was planning to explore the Moon. The Chinese government white paper titled “China’s Space Activities” in November of the same year outlined three key areas in the country’s future space programme development: application satellites, human spaceflight, and deep space exploration. The lunar exploration programme would be the first step in China’s deep space ambition.
COSTIND drew out a three-step plan for its robotic lunar programme:
- Phase-I: To send unmanned missions to survey the lunar surface from orbit.
- Phase-II: To send 1 to 2 missions to land on the Moon surface, where they will deploy unmanned lunar rovers to explore the surrounding areas.
- Phase-III: To send 1 to 2 missions to collect lunar soil samples and return them to Earth.
The China Lunar Exploration Programme (CLEP) was officially created by the Chinese government in 2004. CASC China Academy of Space Technology (CAST) was awarded the contract to develop the robotic lunar exploration probes named Chang’e after the Moon god in ancient Chinese mythology. To support the lunar missions, a deep space tracking network was constructed, with a 50-metre radio antenna in Beijing, and 40-metre radio antennas in Kunming, Shanghai, and Ürümqi, forming a 3,000-km very long baseline interferometry (VLBI) network.
China’s first robotic probe to orbit the Moon, Chang’e 1, was based on the CAST DFH-3 satellite bus. The 2,350 kg cube-shaped spacecraft carried 8 pieces of mission equipment, including a 120-m resolution stereo camera, a laser altimeter, an imaging spectrometer, a Gamma and X-ray spectrometer, a microwave radiometer, a high-energy particle detector, and two solar wind detectors.
Chang’e 1 was launched from the Xichang Satellite Launch Centre (XLSC) by a Long March 3A launcher on 24 October 2007 and the spacecraft entered a 200 km lunar orbit on 5 November. Over the next 12 months, Chang’e 1 surveyed the Moon’s surface from orbit using its mission payload.
The spacecraft transmitted back 1.37TB of data from its onboard CCD camera, allowing the production of a 120 m/pixel resolution image covering the entire lunar surface. The spacecraft’s laser altimeter obtained 9.16 million of terrain measurements, allowing the production of the entire lunar terrain model with 3,000 m accuracy. The Gamma and X-ray spectrometer mapped out the distribution of Uranium, Potassium and Thorium in lunar soils for the entire lunar surface.
The Chang’e 1 mission officially ended in October 2008, though the spacecraft remained in orbit for another four months to conduct further tests. On 1 March 2009, Chang’e 1 carried out a controlled crash into the Moon’s surface under the command of the Mission Control at 08:13:10 UTC, ending its 16-month mission.
Originally built as a backup to the Chang’e 1 mission, Chang’e 2 was similar in size and design to its predecessor, but featured improved X-band telemetry and communications systems, and carried more propellants and new mission payload. The spacecraft used a direct orbit injection removing the need of orbiting the earth before entering the lunar transfer orbit, which reduced the journey time to the Moon from 14 days to 5 days (112 hours).
Chang’e 2 was launched from Xichang by a Long March 3C launcher on 1 October 2010 and the spacecraft settled into a 100 km lunar orbit on 6 October. During its seven-month mission, the spacecraft carried out orbit manoeuvre to enter a 100 x 15 km elliptic orbit, in order to get closer to the lunar surface to obtain higher-resolution images of the planned landing spot.
The Chang’e 2 mission officially ended in June 2011, and the spacecraft left the lunar orbit under the command of the mission control. After 85 days of travel, the spacecraft reached the Earth-Moon Second Lagrangian Point (L2), a stable point on the side of the earth opposite the Sun, on 1 September.
Chang’e 2 spent the next 235 days probing the Sun and the earth’s magnetic field and to chart solar storms near L2, and also tested the two newly constructed deep space communications antennas in Kashgar and Jiamusi, which form part of China’s deep space tracking and communications network.
Chang’e 2 departed from L2 on 15 April 2012 to explore the 10 million kilometres deep space. On 13 December, the spacecraft flew by a small Near Earth Asteroid 4179 Toutatisat a distance about 7 million kilometres away from Earth. While flying by the asteroid at a distance of 770 m and a relative velocity of 10.73 km/s, Chang’e 2 captured the first optical images of the asteroid, which allowed close observation of the asteroid surface and estimation of its size.
By 2014, Chang’e 2 continued to fly away from Earth and had reached a distance of 80 million kilometres to Earth, thus becoming a satellite of the Solar System. The spacecraft had enough propellants left to continue functioning up to a distance of 300 million kilometres according to the estimation of Chinese space engineers.
Chang’e 3 was the first spacecraft to have made a soft-landing on the Moon since the Soviet Union’s Luna 24 mission in 1976. The mission was intended to demonstrate and perfect spaceflight techniques critical for the subsequent lunar missions, including lunar soft-landing, lunar surface exploring, lunar-night survival, and deep-space communications.
The Chang’e 3 spacecraft consisted of two parts: a lunar landing craft (the “Lander”) and a wheeled lunar surface explorer vehicle (the “Rover”, also known as Yutuor Jade Rabbit in its nickname). The 3,700 kg Lander had four landing legs and its body was 0.83 m above the ground when standing on the surface. Scientific instruments carried onboard the spacecraft included landing camera, terrain camera, lunar-based ultraviolet telescope, and extreme-ultraviolet (EUV) camera. Engineering payload included lunar dust monitoring sensor and surveillance camera.
To ensure a successful and precision soft-landing on the lunar surface, the Lander also featured an autonomous landing navigation system, which was designed to measure the craft’s distance and velocity relative to the Moon. The system possessed certain terrain recognition and autonomous terrain avoidance capabilities to guide the Lander during the landing descent without requiring interference from the Mission Control on Earth.
The Chang’e 3 mission was launched atop a Long March 3B launcher on 2 December 2013 from Xichang and the spacecraft entered the 100 km lunar orbit on 6 December. After spending on the lunar orbit for eight days and making several orbit-changing manoeuvres, the Lander touched down on the Moon’s surface at on 14 December, at Mare Imbrium, about 40 km south of the 6 km diameter Laplace F crater.
On 15 December, the Lunar Rover Yutu (Jade Rabbit) was successfully deployed to start its scheduled three-month lunar surface inspection mission. The Automatic Lunar Surface Exploring Vehicle (自动月面巡视器), commonly known as “Lunar Rover” (月球车), is a solar-powered, six-wheeled robotic vehicle capable of autonomously navigating itself around the lunar surface to explore the surrounding areas. The 120-kg vehicle had a designed life of 90 lunar days, and its onboard instruments included a stereo camera, a lunar-ground penetrating radar, an infrared spectrometer, an X-ray spectrometer, and mechanical lunar soil collector.
However, after going into sleep mode to ensure its first lunar night in January 2014, Yutu failed to respond to commands from the mission control. Having failed to transmit any signal after the second lunar night in February, the rover was declared inoperative, though its onboard instruments remained functional. Chinese space engineers admitted that a control circuit malfunction in the rover’s driving unit prevented it from moving or folding its mast and solar panels into an insulating position during lunar night, causing its these instruments to degrade rapidly.
Chang’e 5-T1 was designed as a precursor mission to Chang’e 5, China’s robotic lunar sample return mission scheduled for 2017. The primary objective of the mission was to validate the design of the lunar sample return capsule and to demonstrate high-speed atmospheric re-entry from the translunar flight.
The Chang’e 5-T1 spacecraft consisted of a Service Module that was based on the Chang’e 2 lunar orbiter design, and a Chang’e 5 return capsule that was essentially a scaled-down version of the Shenzhou re-entry module. The launch vehicle also carried a Luxembourg-made experimental radio beacon and a nano-satellite from the virtual organisation Pocket Spacecraft.
Chang’e 5-T1 was launched atop a Long March 3C launcher from Xichang on 24 October 2014. Flying along a circumlunar free-return trajectory around the Moon, the spacecraft reached the 12,000 km perilune point on 28 October. After passing behind the Moon once, the spacecraft began its flight to Earth. During the 4-day journey back to Earth, a series of course correction manoeuvres were conducted to precise targeting of the re-entry trajectory corridor chosen for the mission.
At 05:53 CST on 1 November, the return capsule was separated from the Service Module at about 5,000 km from Earth and its atmospheric re-entry began 20 minutes later. The return capsule performed a skip re-entry, where the craft made an initial entry to slow itself down and then climbed to atmospheric exit for a ballistic exospheric segment (‘skip’), before performing a second re-entry. Such a technique helped create greater entry range and slow the craft down before final entry, but require precision guidance due to its more complex trajectory compared with a conventional ballistic entry. The same technique was used by the Soviet Zond 6, 7 and 8 lunar probes. The Apollo Command Module also made similar pull-up segments (though not leaving the atmosphere) during its re-entry.
Within a period of 15 minutes, the return capsule entered and exited the earth atmosphere, and then made its second entry, travelling over a total distance of 6,000 km, before deploying its main parachute and eventually touching down inside its targeted landing zone in the Siziwang Banner Landing Site in Inner Mongolia.
After the return of the capsule, the Chang’e 5-T1 Service Module remained in orbit for its expanded mission. Under the command of the mission control, the spacecraft flew to the Earth-Moon Second Lagrangian Point (L2) in November 2014. After circling L2 three times, the spacecraft left flew towards the Moon in January 2015 for the second-phase of the expanded mission. The spacecraft first fired its thrusters to slow down and entered into a highly elliptic 5,300 x 200 km lunar orbit. After three retrofire burns the spacecraft eventually settled in a 200 km circular lunar orbit — a manoeuvre to simulate the flight of the future Chang’e 5 Orbiter Module.
During the third phase of the expanded mission in March, the Chang’e 5-T1 Service Module performed three retrofire burns to lower itself to an altitude of 18 km from the lunar surface, and then simulated the flight of the Chang’e 5 Lunar Sample Module taking off from the lunar surface to rendezvous and dock with the Orbiter Module in the lunar orbit.
Originally built as a back-up to the Chang’e 3 mission, Chang’e 4 was later adopted for a new task: to make an unprecedented attempt to soft-land on the lunar far side. Unlike Chang’e 3, which used a slow, arc-shaped descent, Chang’e 4 will attempt a more steep, almost vertical descent onto the Moon’s surface.
The first-stage of the mission involved the placing of a relay satellite named Queqiao to the Earth-Moon Second Lagrangian Point (L2). The 425 kg communications satellite was launched atop a Long March 4C from Xichang on 21 May 2018.
The first lunar sample return mission was scheduled for launch in late 2017, but now postponed to 2018 due to the ongoing issues with the CZ-5 launch vehicle. The robotic spacecraft will first fly to lunar orbit and then deploy a lander to make a soft-landing on the Moon surface. After collecting the lunar soil samples, the ascent module of the lunar lander will take off to fly back to lunar orbit, where it will perform a lunar orbit rendezvous (LOR) to dock with the re-entry module. The re-entry module carrying the lunar soil samples to fly back to Earth orbit, and return the samples inside a re-entry capsule to land on Earth.
A proposed second lunar sample return missions to return lunar soil samples collected from the far side of the Moon in 2023.