Japan for at least a few hours a month.
The country’s robotic SLIM spacecraft touched down on the lunar surface this morning (January 19), marking a major achievement for Japan: It became the fifth country to land softly on Earth’s nearest neighbor.
Yamakawa Hiroshi, head of the Japan Aerospace Exploration Agency (JAXA), said at the post-landing press conference today (in Japanese; English translation provided by a translator during the briefing).
Hiroshi added that going forward, “we should be able to access the lunar surface.” “I believe there is now a path to that.”
Other countries in the moon landing club are the Soviet Union and the United States, which made their first trips to the lunar surface during the Cold War space race; China, where the first landing took place in December 2013; and India, whose Chandrayaan-3 lander duo touched down last August.
But that wasn’t all good news for SLIM: The probe’s solar panels were not generating electricity on the lunar surface as planned, JAXA officials said at today’s briefing. If the problem is not resolved soon, SLIM may remain silent forever. Its battery can only support lunar operations for a few hours.
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SLIM (short for “Intelligent Lander for Exploring the Moon”) was launched last September along with an X-ray space telescope called XRISM. The scope launched into low-Earth orbit shortly after liftoff (and recently sent home its first test images), but SLIM is on its way to more distant celestial shores.
The probe followed a long, looping route towards the moon, finally reaching lunar orbit on Christmas Day. Its initial orbit was highly elliptical, taking SLIM 373 miles (600 kilometers) from the lunar surface at its closest point and 2,485 miles (4,000 km) at its farthest point.
Early on Sunday morning, January 14, SLIM performed a significant engine burn, circularizing its orbit at an altitude of 373 miles and setting the stage for descent and landing operations.
These operations were accelerated this morning by another burn that lowered SLIM’s orbit to approximately 9 miles (15 km) above the lunar surface. And they culminated today with a landing attempt that began around 10 a.m. (1500 GMT; midnight Japan time on January 20) and was completed 20 minutes later.
All seemed to be going well: SLIM reached several milestones during the descent, and the lander communicated with its operators throughout and after the historic landing. However, JAXA was not immediately able to confirm the status of SLIM after landing. About an hour later, the agency gave us an update via press conference explaining the probe’s power issues.
JAXA officials said it was unclear why the solar cells were not working. However, they are unlikely to be damaged during landing because the SLIM’s other hardware appears to be good and functional. According to JAXA, it is possible that the lander was not oriented towards the sun as expected.
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SLIM aimed to land within 330 feet (100 meters) of its target site at the rim of Shioli Crater, which explains the probe’s nickname, “Lunar Sniper.”
“While impressive in their own right, this mission’s landing objectives are also key to the future of scientific lunar exploration,” The Planetary Society wrote in a mission statement.
“Global interest in the moon is growing, with many countries and commercial organizations entering the field,” added the nonprofit advocacy group led by former TV “Science Guy” Bill Nye. “As lunar exploration progresses, the need to target specific regions to answer outstanding scientific questions will also increase. SLIM’s mission architecture hopes to change the standards for lunar landing missions from landing exactly where it is easy to land where desired.”
JAXA officials said at the press conference that SLIM achieved the desired landing precision, but it could take about a month for the mission team to confirm this result.
SLIM also aimed to demonstrate that small, relatively inexpensive spacecraft have impressive exploration capabilities. The probe weighs only 440 pounds (200 kilograms) without propellant, and its mission costs about 18 billion yen (US$120 million) to develop, according to The Planetary Society.
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While SLIM is primarily a landing technology demonstrator, it is designed to do some scientific work during the surface mission, which is expected to last a lunar day, or about two Earth weeks. (There are no heaters to protect the SLIM’s electronics against the cold lunar night.)
Using its onboard spectrometer, SLIM aimed to study its surroundings, part of the Mare Nectaris (“Sea of Nectar”) located about 15 degrees south of the lunar equator. The instrument’s data can reveal information about the composition of the region, which can shed light on the formation and evolution of the moon; but SLIM won’t have a chance to do this unless the solar panels are installed and operational.
SLIM also carried two smaller rovers; A small hopper called LEV-1 and a ball-shaped vehicle known as LEV-2. (“LEV” stands for “Lunar Rover.”) These small robots are designed to deploy from the SLIM mothership, collect some data of their own, and take photographs.
Data shows both LEV-1 and LEV-2 were deployed as planned, JAXA officials said in a statement today. And LEV-1 is known to work, contributing to the mission’s accomplishments.
SLIM was not the first Japanese spacecraft to aim for a Moon landing. The country deployed a small lander called OMOTENASHI on NASA’s Artemis 1 mission, which sent an uncrewed Orion capsule into lunar orbit and back in late 2022. However, OMOTENASHI’s managers were unable to communicate with the probe and the landing attempt was aborted.
The private Hakuto-R lander took a major hit in April 2023 but failed. Hakuto-R, built and operated by Tokyo company ispace, managed to reach lunar orbit but crashed during a landing attempt when it became confused by the rim of a lunar crater.
Editor’s Note: This story was updated at 1pm on January 19th with news that SLIM had landed successfully but was dealing with a power issue.