Japan Explains How It Made an Upside-Down Moon Landing

Japan Explains How It Made an Upside-Down Moon Landing
Japan Explains How It Made an Upside-Down Moon Landing

Japan’s first lunar lander, SLIM, made history by achieving the most precise landing on the moon ever. But it also faced some unexpected challenges that left it upside-down on the lunar surface. Here’s what happened and why it matters.

The SLIM mission

SLIM, which stands for Smart Lander for Investigating Moon, is a small-scale exploration lander designed by the Japan Aerospace Exploration Agency (JAXA) to demonstrate accurate lunar landing techniques and investigate the moon’s origins. It was launched in September 2023, along with the X-Ray Imaging and Spectroscopy Mission (XRISM), on board the H-IIA rocket¹.

The mission’s main objective was to land within a 100-meter-wide target zone near the Shioli crater, a region covered in volcanic rock. This would require a high level of navigation accuracy and control, as most previous probes have used landing zones about 10 kilometers wide. Improved accuracy would give scientists access to more of the moon, since probes could be placed nearer to obstacles².

SLIM also carried two autonomous probes, LEV-1 and LEV-2, which were released just before landing. LEV-1, a hopping robot equipped with an antenna and a camera, was tasked with recording SLIM’s landing and transmitting images back to Earth. LEV-2, a baseball-sized rover equipped with two cameras, was developed by JAXA together with Sony, toymaker Tomy Co. and Doshisha University. The two probes were designed to frame and select images independently, using LEV-1’s antenna to send them back to base³.

The landing mishap

SLIM’s landing attempt took place on January 15, 2024, after a 20-minute descent from lunar orbit. Everything went according to plan until the final minute, when one of SLIM’s two main engines lost thrust and apparently fell off the spacecraft, leaving the craft’s sole remaining engine to bring the spacecraft in for an off-balance landing⁴.

Despite the engine failure, SLIM managed to hit the tiny patch of the moon’s surface it was aiming for, in a remarkable feat of engineering. Data analysis showed that the spacecraft landed about 55 meters away from its target site, in between two craters. It would have been even closer, within three to four meters, had the engine not malfunctioned⁵.

However, the hard landing caused the spacecraft to topple over, with its nose planted into the lunar regolith and its rear propulsion section pointed toward space. This meant that the spacecraft’s solar panels wound up facing the wrong direction, and it could not generate power. JAXA said it had prioritized transmitting landing data before SLIM’s battery ran out⁶.

The upside-down image

The first image of SLIM on the lunar surface was sent back by LEV-2, the tiny rover, through LEV-1, the hopping robot. The image showed SLIM upside-down, with its four legs sticking up in the air. It was a stunning and somewhat comical sight, capturing the triumph and tragedy of the mission in one frame⁷.

JAXA project manager Shinichiro Sakai said the image was just like he had imagined and seen in computer renderings. He said he almost fell down when he saw it, and that SLIM’s pinpoint landing deserved a “perfect score”. He also said that SLIM had opened the door to a new era of lunar exploration⁸.

JAXA said there was still hope that the probe would be able to recharge once the moon enters its daytime in the coming days. If that happens, SLIM might be able to resume some of its scientific activities, such as measuring the temperature and magnetic field of the landing site, and taking more images with its navigation camera.

The significance of the mission

Despite the landing mishap, SLIM’s mission was a success in many ways. It demonstrated that Japan has the technology and expertise to achieve precise lunar landings, which could pave the way for future missions to explore the moon and other planets. It also showed that small-scale and low-cost landers can perform complex and challenging tasks, such as navigating around obstacles and releasing autonomous probes.

SLIM’s landing site was also of scientific interest, as it was located in a region rich in volcanic rock, which could provide clues about the moon’s formation and evolution. By studying the composition and age of the rocks, SLIM could help answer questions such as how the moon’s crust and mantle differentiated, and how the moon’s volcanism changed over time.

SLIM’s mission was also a testament to the resilience and creativity of the JAXA team, who overcame many difficulties and uncertainties to make the mission possible. SLIM’s upside-down image was a reminder of the risks and rewards of space exploration, and the spirit of adventure and curiosity that drives it.

¹: Live Coverage: Launch of the X-Ray Imaging and Spectroscopy Mission (XRISM) and the Smart Lander for Investigating Moon (SLIM) onboard the H-IIA Launch Vehicle No. 47
²: Japan’s 1st moon lander has hit its target, but it appears to be upside-down
³: JAXA | Smart Lander for Investigating Moon (SLIM)
⁴: A Japanese spacecraft faceplanted on the Moon and lived to tell the tale
⁵: The results of the Moon Landing by the Smart Lander for Investigating Moon (SLIM)
⁶: Japan’s ‘moon sniper’ probe made incredibly accurate landing, but is now upside down
⁷: Image reveals Japan’s historic SLIM spacecraft landed upside down on the moon
⁸: Japan Explains How It Made an Upside-Down Moon Landing
: NASA – NSSDCA – Spacecraft – Details
: Japan’s SLIM spacecraft sticks moon landing – upside-down
: Japan’s 1st moon lander has hit its target, but it appears to be upside-down

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