HELSINKI — Japan’s SLIM lander has been forced to power down on the moon with its solar cells unable to catch sunlight, but hope remains that the spacecraft can be reactivated.
Japan’s Smart Lander for Investigating Moon (SLIM) successfully touched down on the lunar surface, targeting the rim of the small, mid-latitude Shioli crater at 10:20 a.m. Eastern (1520 UTC) Jan. 19.
The Japan Aerospace Exploration Agency (JAXA) confirmed the successful landing just under two hours later. Two small rovers, Lunar Excursion Vehicle 1 and 2 (LEV-1 and 2) were successfully deployed onto the surface of the moon. The achievement proved the technical approach of SLIM and made Japan the fifth country to successfully soft-land on the moon.
SLIM’s solar cells were, however, not generating power. JAXA thus prioritized acquiring data while the spacecraft ran on battery power. While initially not confirmed, it was suspected that the attitude of the lander relative to the sun left its solar cells useless.
In a series of posts on X, formerly known as Twitter, via an official mission account Jan. 22, JAXA stated that SLIM disconnected its battery at 12%, as planned, to prevent over-discharge. SLIM powered down at 12:57 p.m. Eastern (1757 UTC) Jan. 19. Before this, JAXA managed to obtain “a lot of data.”
“Technical and image data acquired during the landing descent and on the lunar surface were successfully transmitted,” according to JAXA. The agency is conducting a detailed analysis of the data.
There remains the possibility of the spacecraft being reactivated later in the lunar day. SLIM’s solar cells are facing west, according to telemetry data. This attitude means the cells are not receiving sunlight and cannot generate electricity to power the spacecraft.
SLIM could receive sunlight and generate power as the sun’s position in the sky changes. The SLIM team is preparing for the recovery of the spacecraft in this event.
Sunset over Shioli crater is expected around early UTC Jan. 31. If it can be reawakened, SLIM will attempt to achieve its “extra” objectives including extended operation and acquiring science data. Its Multi-Band Camera (MBC) will assess the composition near Shioli crater by analyzing the spectra of sunlight reflected off its surface.
JAXA said it will hold a press conference Jan. 25 (12:00 a.m. Eastern (0500 UTC). The event could reveal if the landing achieved its full success according to mission criteria of a high-precision landing with an accuracy of 100 meters or better. The agency may also present any images received from SLIM or its rovers.
“We are preparing to announce the status of SLIM and current results at the end of the week. Although the attitude after landing did not go as planned, we are glad we could achieve so much and are happy to have landed successfully,” the SLIM account stated.
SLIM launched Sept. 6, 2023, and completed a looping, 110-day voyage to the moon Dec. 25, when the spacecraft entered lunar orbit. The flight profile saved the spacecraft propellant and allowed for a higher science payload mass.
The successful landing made Japan only the fifth country to robotically soft-land on the moon. The success follows five months after India became the fourth country to land on the moon with Chandrayaan-3.
Further lunar landing missions are planned for 2024. China is gearing up for an unprecedented lunar far side sample return mission around May. U.S. firm Intuitive Machines is planning up to three landings. The first, IM-1, is currently scheduled to launch in February.
Edited at 5:01 p.m. Eastern to clarify expected landing area.