Japan’s SLIM robotic spacecraft entered lunar orbit Dec. 25, setting up a moon landing attempt scheduled for Jan. 19. SLIM completed a roughly three-minute-long lunar orbit insertion burn at 2:51 a.m. Eastern (0751 UTC), the Japan Aerospace Exploration Agency (JAXA) announced Christmas Day. SLIM is now in a 600 x 4,000-kilometer polar lunar orbit, as planned. The spacecraft is currently in a normal condition, JAXA stated. It will soon begin gradually lowering its orbit in preparation for landing. The landing attempt is scheduled to begin at 10:00 a.m. Eastern (1500 UTC) Jan. 19, landing around 20 minutes later. The lander will aim to set down within a 100 meters of its target point on the slope of the mid-latitude Shioli crater. SLIM launched Sept. 6 on a H-2A rocket from Japan’s Tanegashima Space Center along with the XRISM space telescope. SLIM spacecraft entered low Earth orbit and began a series of orbit-raising maneuvers as part of its circuitous voyage to the moon. It made a translunar injection burn Sept. 30, making a lunar flyby Oct. 4. This set the spacecraft on a long, looping, propellant-saving journey to the moon, leading to lunar orbit insertion on Christmas Day. SLIM will next gradually lower its apolune, or farthest point from the moon, and enter a circular orbit at an approximately 600-kilometer-altitude in mid-January, according to JAXA.
Perilune will then be lowered, reaching a 15-km-altitude orbit Jan. 19 Japan time, ready for the Jan. 19 landing. SLIM will begin to decelerate from a speed of around 1,700 meters per second at that point.
Five crushable, 3D-printed aluminum lattice landing legs will help the lander absorb the of impact of touch down and settle on the sloped rim of the 300-meters-wide Shioli crater.
A successful SLIM landing would make Japan the fifth country to soft land on the moon. In August India became the fourth nation to achieve the feat with its high latitude Chandrayaan-3 mission landing.
The main objective of SLIM is to demonstrate a highly-accurate lunar soft-landing with a lightweight architecture. It will use a vision-based navigation system and carries observational data from Japan’s SELENE orbiter launched in 2007. This system will be used to identify its landing zone during its autonomous descent and landing. It also carries a laser range finder for the final stages of descent.
Beyond the landing attempt itself, the spacecraft is designed to spend the remainder of the lunar day on the surface conducting experiments. SLIM carries a Multi-Band Camera (MBC) to assess the composition of Shioli crater by analyzing the spectra of sunlight reflected off its surface. Teams are particularly looking for the presence of the mineral olivine, which may have been ejected from beneath the moon’s crust.
SLIM is also carrying a pair of small, innovative rovers. Lunar Excursion Vehicle 1 (LEV-1) uses a hopping mechanism, while LEV-2 is a baseball-sized, spherical rover. Both carry cameras and science payloads.
The mission could lead to lower cost exploration efforts in the future, according to JAXA. The accuracy of landings will be useful for accessing areas of high scientific interest instead of more general, safer landing zones.
The spacecraft has a dry mass of 200 kilograms and 700-730 kg wet mass at launch. The expected development cost was 18 billion yen ($120 million).
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