China launches Chang’e-4 spacecraft for pioneering lunar far side landing mission


 HELSINKI — China launched its Chang’e-4 moon mission Dec. 7, successfully sending the lander and rover into a lunar transfer orbit ahead of an unprecedented attempt at a landing on the far side of the moon early in the New Year.

Liftoff of the Long March 3B launch vehicle carrying Chang’e-4 occurred at 1:23 p.m. Eastern time Dec. 7 (02:23 a.m. local time Dec. 8) at the Xichang Satellite Launch Center in southwest China.

The timing of the launch was revealed only through airspace closure notices and no official live coverage was available, though a group of spectators streamed the event online from a viewing area.

The China Aerospace Science and Technology Corporation (CASC), the main contractor for China’s space program, officially announced success of the launch following trans-lunar injection, just under an hour after launch. The spacecraft now enters a five-day voyage to the moon before lunar orbit injection.

The Chang’e-4 mission consists of a lander and rover with a combined mass of just under four metric tons, carrying cameras and science payloads to analyze the lunar surface geology and subsurface, solar wind interactions and carry out low-frequency radio observations in the unique radio-quiet environment on the far side of the moon.

No official date has been released for the landing attempt, but CASC announced shortly after launch that the landing will take place in the first days of January 2019, following sunrise over the main candidate landing within the Von Kármán crater in late December.

As the far side of the moon never faces the Earth, communications with the spacecraft will be facilitated by the ‘Queqiao’ relay satellite launched in May and inserted into a halo orbit around the second Earth-moon Lagrange point in June.

From this vantage point between 65,000-85,000 kilometers beyond the moon the Queqiao satellite will have constant line-of-sight with both the Chang’e-4 spacecraft and Chinese ground stations in China, at Kashi and Jiamusi, Namibia and Argentina.

Chang’e-4 was originally planned as a backup to the Chang’e-3 lander and rover mission, which made China the third country to achieve a soft-landing on the lunar surface, and the first since the Soviet Union’s Luna 24 in 1976.

Payload fairing for the Chang'e-4 lunar far side mission. Credit: CASC
Payload fairing for the Chang’e-4 lunar far side mission. Credit: CASC

The spacecraft have been repurposed for a more ambitious landing on the far side of the moon, which poses far greater challenges and requirements but also the promise of great scientific payoffs.

The topography of the far side is far more rugged and variable than the near side, which is marked with vast, smooth basaltic seas or mare, which can be seen from Earth with the naked eye. The far side contains few such maria and the Chang’e-4 mission may bring insight into this mystery.

The expected target landing site selected for Chang’e-4 is thus in the relatively smooth southern portion of the 186-kilometer-diameter Von Kármán crater, though automated hazard avoidance during its descent could make the spacecraft set down elsewhere.

The crater is situated in the South Pole-Aitken Basin (SPA), a 2,500-kilometerwide, 12-kilometer-deep ancient impact crater of intense scientific interest which could contain exposed material from the moon’s upper mantle.

Investigation of the composition of areas of the SPA could reveal clues to the history of the moon and development of the wider solar system.

The lander is equipped with a Low Frequency Spectrometer (LFS) and the German-developed Lunar Lander Neutrons and Dosimetry (LND), as well as a Landing Camera (LCAM) and Terrain Camera (TCAM).

Like Chang’e-3, the rover will carry a Panoramic Camera (PCAM) and Lunar Penetrating Radar (LPR) which will reveal subsurface geological structures to depths of up to 500 meters. A Visible and Near-Infrared Imaging Spectrometer (VNIS) and Advanced Small Analyzer for Neutrals (ASAN)—the latter developed by the Swedish Institute of Space Physics, Kiruna—will also be aboard.

The mission rover, based on the Chang’e-3 Yutu (Jade Rabbit), has also been upgraded for greater longevity and addressing the issue which resulted in Yutu immobilization in its second lunar day on Mare Imbrium.

A mini biosphere experiment designed by 28 Chinese universities, containing potato and Arabidopsis seeds and silkworm eggs, will also be part of the mission to test respiration and photosynthesis in the low-gravity and high-radiation environment on the lunar surface.

A render of the Chang'e-4 lander, released on Aug. 15, 2018. Credit: CASC
A render of the Chang’e-4 lander, released on Aug. 15, 2018. Credit: CASC