SLIM — Japan becomes the fifth nation to soft-land on the Moon

Just after midnight Japan time on 20 January 2024 (still 19 January in UTC), the control room at JAXA's Sagamihara campus fell quiet as the Smart Lander for Investigating Moon began its twenty-minute descent toward Shioli crater. The stakes were double: Japan had never soft-landed on the Moon, and no one had ever attempted what SLIM promised, a landing not somewhere safe but somewhere exact. Engineers had nicknamed it the Moon Sniper. Its target was a sloping crater rim that older landers would never have dared approach.

SLIM navigated by sight, photographing the surface during descent and matching craters against onboard maps built from lunar orbiter imagery. Then, at fifty meters altitude, one of its two 500-newton main engines abruptly lost thrust. The guidance software compensated in real time, drifting east as it descended on the surviving engine. SLIM touched down roughly 55 meters east of its aim point, and JAXA later judged its accuracy before the final avoidance maneuver at ten meters or better, possibly three to four. The price was attitude: the lander came to rest nose-down, its solar cells facing west, away from the morning Sun.

Running on battery, SLIM transmitted its precious navigation data and imagery before controllers deliberately shut it down at 2:57 a.m. JST, preserving charge for a possible resurrection. Seconds before touchdown it had ejected two tiny robots, the hopping LEV-1 and the baseball-sized SORA-Q, which photographed the upended lander and radioed the image home. Eight days later, as the Sun swung west, light reached the panels and SLIM woke up. It studied nearby olivine-bearing rocks that the team nicknamed after dog breeds, then survived three frigid two-week lunar nights it was never designed to endure, before JAXA concluded operations on 26 August 2024.