Japan’s SLIM Moon Lander Overcomes Lunar Night Challenges
In a surprising turn of events, Japan’s Smart Lander for Investigating Moon (SLIM) spacecraft made unexpected contact despite not being expected to function after the lunar night. The Japan Aerospace Exploration Agency (JAXA) announced the reestablishment of contact with SLIM on Sunday, February 25, through its dedicated SLIM account on X, formerly known as Twitter.
The communication equipment of the spacecraft experienced extremely high temperatures due to the sun being high over the landing area. As a result, communication was terminated after only a short period of time. However, the SLIM team is now preparing to conduct observations with SLIM’s multiband spectroscopic camera (MBC) later in the lunar day. The MBC is designed to ascertain the composition of the lunar surface and could provide valuable insights into the moon’s history.
SLIM’s ability to survive the deep cold of the lunar night was not part of its design. Temperatures during the roughly 14-Earth-day lunar nighttime fall below minus 130 Celsius, which can damage electronics. Other spacecraft have used radioisotope heater units to provide heating during lunar nights to allow prolonged operations.
The historic landing of SLIM, also known as “Moon Sniper” for its objective of making a precise landing, took place on January 19. With this achievement, Japan joined an exclusive club that includes the United States, the former Soviet Union, China, and India in making successful robotic lunar soft landings. Intuitive Machines has since become the first private entity to land on the moon, although their Nova-C lander, named Odysseus, likely tipped over on its side during landing.
SLIM’s operations on the lunar surface have been limited due to the unintended attitude of the spacecraft after landing. Shinichiro Sakai, SLIM project manager, provided an update on this matter to the Space Development and Utilization Subcommittee of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT). Sakai explained that the landing was hampered by the failure of one of two engines, resulting in uncontrolled lateral movement and the lander ending up on its nose with the main engine pointing upwards.
The spacecraft was planned to tip onto its side, cushioned by five crushable, 3D-printed aluminum lattice landing legs. However, due to SLIM’s solar cell facing away from the sun, the spacecraft was forced to power down just over two hours after landing. Communication with the spacecraft was established on the night of January 28th once sufficient power was obtained from the solar cells.
Sakai mentioned that the team is currently conducting a detailed investigation into the cause of the engine malfunction and will consider future countermeasures. SLIM’s precision landing technology could prove valuable for future missions, allowing teams to target very specific locations of interest instead of general areas.
In addition to its main mission, SLIM also carried a pair of small rovers. The Lunar Excursion Vehicle 1 (LEV-1), weighing 2.1 kilograms, uses a hopping mechanism, while LEV-2 is a 0.25-kilogram, baseball-sized, spherical rover. LEV-1 transmitted an image of SLIM taken by LEV-2 directly to Earth, demonstrating inter-robot radio wave data transmission and revealing the landing state of the main spacecraft. LEV-1 performed seven autonomous hops across 107 minutes.
Despite the challenges faced by SLIM during its mission on the lunar surface, the unexpected contact made during the lunar night provides a glimmer of hope for future exploration and scientific discoveries. The SLIM team’s dedication and determination to overcome obstacles highlight Japan’s commitment to advancing space exploration and pushing the boundaries of what is possible in lunar missions. As scientists continue to analyze the data collected by SLIM, the moon’s mysteries may soon be unraveled, paving the way for further exploration and understanding of Earth’s closest celestial neighbor.