Japan's "Moon Sniper" touches down

Initial telemetry indicates that Japan's Smart Lander for Investigating Moon (SLIM) touched down at 10:20:03 a.m. ET this morning making Japan the fifth country to soft landing a spacecraft on the Moon after the Soviet Union, United States, China, and India.

But this was not a perfect landing.

The Japan Aerospace Exploration Agency (JAXA) confirmed the landing in a press conference, it shared that the lander was operating on limited battery power because the landing did not orient the solar panels as planned.

SLIM is a demonstration mission launched back on Sept. 6, 2023, aboard a H-IIA rocket from the Tanegashima spaceport in Japan. It is a lightweight spacecraft designed to test precision high-precision landing techniques with the goal of landing 100 meters (330 ft) accuracy using vision-based navigation.

The landing sequence begins as SLIM fires is engines from lunar orbit. It uses vision-based navigation to accurately estimate its own position then navigation, guidance and control, to approach the target location above the lunar surface. From above the target location, SLIM makes constant measures of its altitude and terrain-relative velocity via radar.

As the spacecraft approaches the target autonomous image-based obstacle detection takes over to help ensure a safe landing by avoiding hazardous rocks and other obstacles.

The landing sequence also includes an ambitious plan to hover vertically then set the spacecraft down one leg at a time on the slopped landing site in the "Sea of Nectar" near the Shioli crater about 200 miles southeast of the Apollo 16 landing site.

For comparison, the Viking landers aimed for a 280 by 100 km (175 by 60 miles) target on Mars in the 1970s. Spirit and Opportunity reduced that to 150 by 19 km (93 by 12 miles).

The Mars 2020 mission (Perseverance) shrunk that target to 13 km by 7 km (8 by 4 miles) using similar image mapping technology to pinpoint its landing, achieving an accuracy of about 5 meters (16 feet). The will spend the next few weeks analyzing how the spacecraft they've dubbed their "Moon Sniper" performed.

Engineering bragging rights aside, precise landing is extremely useful. The places on the Moon we want to send future spacecraft, like those in polar regions with sustainable water, are extremely narrow. Setting down as close to the center of the target as possible is even more important for landers like SLIM which cannot adjust their position once on the surface.

Once on the surface, JAXA plans to use a multi band spectral camera aboard SLIM to analyze rocks estimated to come from the lunar mantle. A pair of probes were also deployed to provide images of the scene.

“XRISM will provide the international science community with a new glimpse of the hidden X-ray sky,” said Richard Kelley, the U.S. principal investigator for XRISM at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

XRISM returned its first images in early January.