The Japan Aerospace Exploration Agency (JAXA) is hoping to end the pattern of failed lunar landings this week. The agency's SLIM mission has reached lunar orbit and is preparing for its descent on Friday morning. This spacecraft will test a new landing system, which could drop the lander with unparalleled precision—and hopefully in one piece.
SLIM (Smart Lander for Investigating Moon) is headed for Shioli crater, which is believed to be a relatively new feature on the Moon. Previous orbital observations suggest there is ejecta from the impact strewn around the rim, and it may contain olivine and other minerals from the Moon's crust. SLIM hopes to get close enough to this debris to conduct analysis, something that other landers would not be able to do safely.
The SLIM probe will demonstrate the new landing system designed to set it down at a precise location, earning it the extremely cool nickname "Moon Sniper." Most lunar landers target a landing zone the size of a football field or larger—the Peregrine lander, which failed to reach the Moon due to a fuel leak last week, was aiming for a landing zone of several square kilometers. SLIM will continuously scan the surface with cameras. It has a detailed map of the lunar surface, allowing it to match what it sees to determine its location accurately. This process takes just five seconds, ensuring the probe can find its landing zone without zipping past.
JAXA is aiming for an area just 100 meters across, on the slope of Shioli crater, where the lander should have access to impact ejecta. Simply spotting the landing zone is an important first step, but the lander has a few more tricks up its sleeve to touch down safely on a 6-7-degree slope.
SLIM uses its onboard gyroscope, star tracker, and sun sensor to guide it toward the surface. At an altitude of 50 meters, SLIM will switch to a more accurate radar and optical range finder system. The cameras will continue snapping photos to search for possible hazards, allowing the lander to adjust its final target. At an altitude of three meters, the main engines will cut off, and the auxiliary thrusters will tip the spacecraft forward so the main legs will touch down first, followed by the legs at the opposite end. JAXA manager Kushiki Kenji referred to this process as "20 minutes of terror," echoing NASA's description of Curiosity's landing on Mars in 2012.
Japan is among several countries designing new Moon landers, but the lessons of the past have been largely squandered. The decades-long gap between the US and Soviet landings in the 20th century and this new interest in the Moon means that everyone is essentially starting from scratch. Landing on the Moon isn't easy even with experience, but it's even harder when none of the hardware we're sending has actually been tested in space. That's why Japan, the US, Russia, and Israel have all seen recent Moon landers fail. SLIM could be the start of safer, more reliable lunar landings. The landing is set for 10 a.m. ET on Jan. 19. If SLIM misses the landing window, it will have another opportunity in February.
