January 19, 2024

— Japan has become the fifth country to successfully land a spacecraft on the moon, although a power issue has cut short the robotic probe's projected lifetime on the lunar surface.

The Smart Lander for Investigating Moon (or SLIM) touched down near Shioli crater on Friday (Jan. 19) at 10:20 a.m. EST (1520 GMT or 12:20 a.m. Japan Standard Time on Jan. 20). Japan has joined Russia, the United States, China and India as the only nations to have reached the surface of the moon.

"We believe that the soft landing itself was successful," said Hitoshi Kuninaka, director general of the Japan Aerospace Exploration Agency (JAXA). "The major reason is because the spacecraft was able to send communications to Earth, which means that most of the equipment on the spacecraft is functional and is working properly."

The feat, which was overseen by JAXA, came after a 110-day journey from Earth. The 18 billion yen ($120 million) small-scale exploration lander lifted off atop an H-IIA Launch Vehicle from the Tanegashima Space Center in Japan on Sept. 7, 2023 (Japan Standard Time; Sept. 6 EDT) together with an X-ray space telescope that is a joint mission by JAXA and NASA.

Since then, SLIM gradually raised its orbit around Earth before performing a lunar orbit insertion burn on Dec. 25. The probe then used its thrusters to lower its path over the moon, arriving at about 9 miles (15 kilometers) over the surface after one last burn on Friday morning to set up its approach.

SLIM moon landing. Click to enlarge video in a new pop-up window. (JAXA)

The landing sequence took about 20 minutes to complete. During the first phase, the lander adjusted its cameras ("smart eyes") to point down at the moon, which it used to estimate its position and speed. Arriving at about 2 miles (3.5 km) above its landing site, SLIM entered a vertical descent, using radar to gauge its altitude.

As SLIM neared 165 feet (50 meters) above the lunar surface, it began identifying potential obstacles and refined its direction to avoid any hazards that could pose a threat to a safe touchdown. Finally, at about 10 feet (3 meters), the lander cut off its main engine and fell the rest of the way to the surface.

Five crushable, 3D-printed aluminum lattice landing legs were developed to help SLIM survive the drop and the lander was designed to topple over and lay on its side by design. Communications with SLIM were established after landing, which revealed that the spacecraft's solar panels were not generating electricity.

More time is needed to verify if SLIM earned its nickname of "Moon Sniper" by achieving a pin-point landing within 330 feet (100 meters) of its target site on the slope of Shioli crater in the Sea of Nectar (Mare Nectaris), south of the Apollo 11 landing site in the Sea of Tranquility.

SLIM was designed to operate for one lunar day (about 14 Earth days), but with the lack of solar power, its batteries are expected to be deleted within several hours of the landing.

"it seems that the the solar cells are not generating electricity at this point in time and since we are not able to generate electricity, the operation [of the spacecraft] is being done using the batteries on board," said Kuninaka.

The abbreviated operational lifetime will cut short the lander's ability to collect data about the composition of its surroundings, especially the presence of olivine, which may have been ejected from under the crust of the moon. Finding the green mineral along the slope of the crater could have helped confirm the theory that the moon was formed by a giant impact.

Just before it landed, SLIM deployed two small rovers. Lunar Excursion Vehicle 1 (LEV-1) was designed to hop to record temperatures and radiation levels in the area around the lander. LEV-2 or SORA-Q, which was made by the Japanese toy company TOMY of "Transformers" fame, was programmed to change its shape from a sphere to expose its cameras and ultilize its two hemispheres as wheels.

SLIM's successful landing came on Japan's third attempt to reach the surface. In November 2022, JAXA launched a cubesat with NASA's Artemis I mission that was aimed at performing a hard landing on the moon. The agency declared the OMOTENASHI probe a loss after it was unable to establish communications with the small spacecraft.

Five months later, the Japanese company ispace, inc. attempted a landing with its commercial HAKUTO-R lunar lander, but contact with it was lost as it descended.

The SLIM landing comes on the heels of a failed attempt by Astrobotic Technology to become the first U.S.-based mission to touch down on the moon since the last Apollo mission in 1972. The company's Peregrine lander suffered a propulsion anomaly soon after its launch and, after reaching lunar distance, fell back to Earth for a controlled, destructive reentry over the Pacific Ocean on Thursday (Jan. 18).

Another U.S.-based moon mission and part of NASA's Commercial Lunar Payload Services (CLPS) program, Intuitive Machines' Nova-C IM-1, is scheduled to launch and attempt a landing at the lunar south pole in February.

SLIM is the 150th attempt at a moon mission since 1958, including flybys, orbiters, impactors and landers. The Japanese lander is the 25th spacecraft to successfully touch down on the lunar surface.