Chang’e 2

Chang'e 2

Other name: CE-2. Type: Robotic lunar orbiting / interplanetary probing. Programme: CLEPAgency: CNSA/SASTIND. Spacecraft family: Chang’e 1. Orbit: Lunar/interplanetary. Mass (gross): 2,480 kg. Launch site: Xichang. Launch complex: LC2. Launch vehicle: CZ-3CLaunch date: 2010-10-01. Lift-off time: 18:59 CST. Ending: n/a. Duration: On-going.

Chang’e 2 was originally built as a backup to Chang’e 1. After the success of the Chang’e 1 mission, Chang’e 2 was turned into a precursor for the subsequent lunar landing mission to test the integrity of the new technologies to be used on Chang’e 3, including direct injection of the spacecraft onto the lunar-transfer path and X-band telemetry. The spacecraft also carried out detailed survey of the potential landing spots and demonstrated the flight in a 100 x 15 km lunar orbit.

The objective of the Chang’e 2 mission was to test and perfect six key technologies:

  • The direct injection of the spacecraft onto the lunar-transfer path without first settling into an Earth orbit;
  • The insertion of the spacecraft on the 100 km lunar orbit;
  • The flight on the 100 x 15 km lunar orbit;
  • The control of the spacecraft through X-band communications;
  • The high-speed (12 mbps download) Lunar-Earth data transmission;
  • The capture of high-definition images of the landing area in the Sinus Iridum (Bay of Rainbows, 43°N 31°W)

The Spacecraft

Chang’e 2 is similar to Chang’e 1 in design, but featuring improved performance, additional propellants, and new mission payload. The spacecraft had a launch mass of 2,480 kg, including 1,300 kg propellants, 136 kg scientific mission payload and 30 kg engineering mission payload. It was designed to operate in a 100 km lunar orbit.

The spacecraft is fitted with a new high-speed (12 mbps download) Lunar-Earth data transmission system, allowing communications over a distance of above 20 million kilometres. The spacecraft’s stabilisation system was also improved for higher control accuracy.

Scientific payloads included a new CCD camera with higher resolution (10 m) than that of Chang’e 1 (120 m resolution), and a new laser rangefinder with higher-accuracy (5 m) for more precise survey of the lunar surface. Engineering mission payload included a X-band transponder and a miniaturised CMOS camera.

The increased mass of the spacecraft and the direct insertion into the lunar transfer orbit required a more powerful CZ-3C launcher, a derivation of the CZ-3A with the assistance of two additional liquid rocket boosters.

Lunar Orbiting Mission

Chang’e 2 was launched from the Xichang Satellite Launch Centre (XLSC) atop the CZ-3C launcher at 18:59:57 Beijing Time (10:59:57 GMT) on 1 October 2010. The spacecraft was placed directly into the lunar transfer orbit (perigee: 200 km; apogee: 380,000 km) without circling the Earth first like its predecessor did. This reduced the total journey time to the Moon from 14 days to less than 5 days (112 hours).

At 03:06 GMT on 6 October, under the command of the Beijing Aerospace Control Centre (BACC), Chang’e 2 fired its thrusters to slow down. The retrofire lasted for 32 minutes and settled the spacecraft into a 12-hour lunar orbit. After three further retrofires, the spacecraft settled into its final orbiting pattern, circling at 100 km above the Moon’s surface once every 118 minutes.

On 26 October, Chang’e 2 carried out an orbit manoeuvre to enter a 100 x 15 km elliptic orbit, so that the spacecraft could get closer to the lunar surface to obtain higher-resolution images of the landing spot. China published the first high-resolution image from Chang’e 2 on 8 November. At 02:34 GMT on 29 October, the spacecraft restored its trajectory to the 100 km circular lunar orbit.

Expanded Mission

The Chang’e 2 mission officially ended seven months after its departure from the Earth. Under the commands of the mission control, the spacecraft left the lunar orbit on 9 June 2011 to fly to the Lagrangian Point (L2), a stable point on the side of the Earth opposite the Sun.

Chang’e 2 reached L2 after 85 days of flight and settled into a parking orbit circling around L2 on 1 September 2011. At this point, the spacecraft was about 1.5 million km away from the Earth, the furthest point any Chinese spacecraft had ever reached.

New tasks for Chang’e 2 included to study the sun and Earth’s magnetic field and to chart solar storms, and to be used to test the two newly constructed deep space communications antennas in Kashgar and Jiamusi, which would form part of China’s deep space tracking and communications network.

After spending 235 days at L2, Chang’e 2 departed on 15 April 2012 to explore the 10 million kilometres deep space. At 16:30:09 CST (08:30:09 GMT) on 13 December, the spacecraft flew by a small Near Earth Asteroid 4179 Toutatis at a distance about 7 million kilometres away from the Earth. Chang’e 2 flew by the asteroid at a distance of 770 m and a relative velocity of 10.73 km/s. It also captured the first optical images of the asteroid, which allowed close observation of the asteroid surface and estimation of its size (4.75 km x 1.95 km [+/-10%]).


Image of Toutatis captured by Chang’e 2

By 2014, Chang’e 2 continued to fly away from the Earth and reached a distance of 80 million kilometres, 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.

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