Landing within 100 metres of its target zone, the craft has pioneered a new image-based automatic navigation system. But its mission might be cut short.
By Ling Xin, 22 January 2024
Japan has become the fifth country to soft-land a spacecraft on the Moon, using precision technology that allowed it to touch down closer to its target landing site than any mission has before. However, the spacecraft might have survived on the lunar surface for just a few hours, owing to a power failure.
Telemetry data showed that the Smart Lander for Investigating Moon (SLIM) touched down in its target area near Shioli crater, south of the lunar equator, early Saturday morning. It landed four months after lifting off from the Tanegashima Space Centre, off the south coast of mainland Japan.
“SLIM has made it to the Moon’s surface. It has been communicating with our ground station and responding to commands from Earth accurately,” Hitoshi Kuninaka, vice president of Kanegawa-based Japan Aerospace Exploration Agency (JAXA), told a press conference after the landing was completed.
“However, it seems that the solar cells are not generating electricity at this point, and the spacecraft is operating solely on its battery,” Kuninaka said. “The battery will last several more hours — those hours will be the remaining life of SLIM.” He said the agency will continue to monitor the lander, because there is still a chance that the panels could start working again.
The successful landing comes around two weeks after the launch of a commercial US spacecraft destined for the Moon — but a propellant problem will prevent it from landing as planned. It’s also been almost a year since a Japanese commercial lander experienced a failure and crashed into the Moon; lunar landings are notoriously difficult to pull off, and a commercial company has yet to do so.
Namrata Goswami, a space-policy researcher at Arizona State University in Phoenix, says the successful landing is “a big win for Asia”. Only China, India and Japan have put a spacecraft on the Moon in the past decade. India successfully landed one last August.
Innovative technology
According to Kuninaka, SLIM has is very likely to have achieved its primary goal — to land on the Moon with an unprecedented accuracy of 100 metres, which is a big leap from previous ranges of a few to dozens of kilometres. SLIM used vision-based navigation technology, which was intended to image the surface as it flew over the Moon, and could locate itself quickly by matching the images with onboard maps.
It remains unclear whether the car-sized, 200-kilogram spacecraft actually touched down in the planned two-step manner. Previous craft landed on four legs simultaneously on a relatively flat area of the Moon. SLIM was designed to hit a 15-degree slope outside Shioli crater first with one leg at the back of the craft before tipping forward and stabilizing on the four front legs.
Observers suggest that SLIM might have rolled during its touchdown, preventing its solar cells from facing the Sun. Kuninaka said that not enough data were available to establish the probe’s posture or orientation. However, if some sunlight reaches the solar cells, SLIM might come back to life.
Two small robots were intended to eject from SLIM before touchdown, says Kuninaka. They were supposed to take images of the lander that they would send back to Earth, but it’s unclear whether they deployed.
If SLIM can come back to life, scientists plan to use a specialized camera — the only scientific instrument onboard — to look for a mineral called olivine in the Moon’s mantle. “If we can detect the olivine’s components and compare it with its counterpart on Earth, it may offer new evidence to support the theory that the Moon was part of Earth long time ago,” says Shinichiro Sakai, the mission’s project manager at JAXA.
The camera would also help to confirm the origin of the Apollo 16 Moon samples. The landing site is about 250 kilometres east of Apollo 16’s 1972 landing site and to the west of an ancient lunar sea called Mare Nectaris. “In Apollo 16 samples, we found exotic basalts, which were most likely ejected from Mare Nectaris,” says Clive Neal, a planetary geologist at the University of Notre Dame, Indiana. By helping to confirm the source, SLIM could tell scientists a lot about impact dynamics and the chemistry of the ancient sea. “It would show that smaller missions can still be very productive and do important science,” Neal says.
Moon rush
Sakai and his team hoped that SLIM’s pinpoint landing technology would give Japan a head-start in the US-led Artemis Program, which aims to return humans to the Moon in 2026. “This technology can be applied to many missions and may constitute a Japanese contribution in international cooperation,” says Sakai.
Although SLIM makes Asia shine in the new Moon race, it might also intensify the competition between spacefaring nations in the region, Goswami says. Now that both India and Japan have created technologies to achieve soft landings on the Moon, their planned joint mission, known as the Lunar Polar Exploration Mission, could rival China’s Chang’e-7 mission, which aims to land in the lunar south pole region in 2026 and will look for ice.
The Moon is experiencing an uptick in visitors. SLIM was the second Moon landing attempt this year, after the ill-fated US Peregrine spacecraft. Next month, the US company Intuitive Machines will continue its attempt to become the first commercial company to land a spacecraft on the Moon. Later this year, China will launch its Chang’e-6 mission to return samples from the far side of the Moon.
(Sources: Nature)
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