After a four-and-half-day flight to the moon, the Chang’e-4 lander and rover spacecraft from China successfully entered lunar orbit on Wednesday.
At 3:45 a.m. Eastern (08:45 UTC) on December 12th, Chang’e-4 entered an elliptical lunar polar orbit with a perilune of 100 kilometres after a lunar orbit insertion burn.
Chang’e-4 single main variable thruster fired at 129 kilometres distant from the moon after the Beijing Aerospace Command and Control Center (BACC) issued the order at 03:39 Eastern.
The China Lunar Exploration Project (CLEP) revealed the success of this critical braking maneuver within minutes and confirmed that the spacecraft was working correctly and will begin preparations for communications tests with a relay satellite and refining its orbit.
Chang’e-4 was deployed by a Long March 3B carrier rocket from the Xichang Satellite Launch Center, southwest China, at 1:23 p.m. Eastern on December 7th for a 110-hour voyage to the moon.
There were three trajectory correction maneuvers planned for the lunar transfer orbit phase. However, only one was performed on December 9th because the first and final maneuvers were deemed unnecessary and were cancelled.
The spacecraft is made up of a lander and a rover, and it will attempt the first-ever soft landing on the far side of the moon in 2019, which never faces the Earth because of tidal locking.
The lander and rover are outfitted with cameras and science payloads to evaluate 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.
Communications with the spacecraft will be made possible by the ‘Queqiao’ relay satellite deployed in May and subsequently inserted into a halo orbit around the second Earth-moon Lagrange point, approximately 65,000-85,000 kilometres beyond the moon.
The landing will aim for candidate landing sites in the South Pole-Aitken Basin (SPA). Although it has not been officially announced, it is believed that the selected location is the 186-kilometer-diameter Von Kármán crater.
The South Pole-Aitken Basin is a 2,500-kilometer-wide, 12-kilometre-deep ancient impact crater with enormous scientific interest because it could hold exposed material from the moon’s upper mantle and clues to the history and development of the moon.
James Head, a planetary scientist at Brown University’s Department of Earth, Environmental and Planetary Sciences in Providence, Rhode Island, explained to SpaceNews that tools like the Lunar Penetrating Radar, also on board Chang’e-3, will offer images of the structure of the lunar soil layers and any subsurface lava flow units, and any interbedded soils. Moreover, it will assist scientists in learning more about the three-dimensional nature and extent of subsurface units.
Head also explained that the Visible and Near-Infrared Imaging Spectrometer (VNIS) payload is very intriguing because it will enable comparisons between the mineralogy of the floor of the South Pole-Aitken basin to nearside units and help answer questions including did the South Pole-Aitken Basin impact penetrate to the lunar mantle?
As of now, there is no official date for the powered descent landing attempt, but the China Aerospace Science and Technology Corporation (CASC), the main contractor for the Chinese space program, suggested shortly after launch that the landing will happen in the first days of January 2019, following sunrise over the main candidate landing site within the Von Kármán crater late this month.
Chang’e-4 was originally intended 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, in December 2013, and the first since the Soviet Union’s Luna 24 in 1976.
The lander has a dry mass of 1,200 kilograms and holds the 140-kilogram mission rover. At launch when loaded with propellant the spacecraft weighed about 3,800 kilograms.
China’s first sample return mission will follow the Chang’e-4 mission, and then Chang’e-5 could launch in late 2019 on a Long March 5 rocket.
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