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JAXA's Moon Lander Back to Work After Sunlight Hits Solar Cells

After landing on the moon at an awkward angle due to engine failure, a change in the sun's position has allowed the probe to regain power and send images to Earth.



A photo captured by the lunar robot SORA-Q shows SLIM upside down on the lunar surface. The horizontal lines are capture noise. (Provided by JAXA, Takara Tomy, Sony Group Corporation, and Doshisha University)

On January 29, the Japan Aerospace Exploration Agency (JAXA) announced that its lunar lander had regained power and resumed operations on the moon. This development comes as a relief after JAXA reported on January 25 that the spacecraft's solar panels were not generating power due to the angle at which it had landed.

The Smart Lander for Investigating Moon (SLIM) achieved a momentous lunar landing on January 20, establishing Japan as the fifth country to accomplish this feat. Impressively, the probe landed just 55 meters (180 ft) from its target, marking the world's first "precision landing" within 100 m (328 ft). This was confirmed by flight data and images captured by a lunar robot carried on board SLIM. 

According to JAXA, SLIM touched down on the lunar surface from an altitude of approximately 15 kilometers (9 miles) above the moon. It descended upright towards the sloped ground near a crater while capturing images of the moon's surface. SLIM accurately determined its own position by meticulously comparing the images with a lunar map created using prior observations. Just before landing, SLIM released the ultra-compact robot SORA-Q and the Lunar Excursion Vehicle (LEV-1).

Artist's rendering of exploration lander SLIM's lunar landing. (Provided by JAXA)

Engine Failure

Then, SLIM was supposed to conduct a two-step landing. First, it was to tilt to the side toward the surface's incline so that only its main leg would touch down. Then, the craft was to continue tilting until the front legs also touched down, stabilizing the landing.

However, one of the two engines sustained damage, resulting in the loss of thrust during retro-firing. This caused a disruption in the spacecraft's posture. Flight data and images captured by SORA-Q and transmitted by LEV-1 indicate that SLIM landed upside down. The solar panels faced west, where sunlight couldn't reach at the time. That meant they could not generate power.  

Had there been no problem with the engine, JAXA believes that the lander would have touched down within 10 meters (33 ft) or less of its target. This is suggested by the fact that SLIM autonomously avoided obstacles near the target area. It is unclear what caused the engine to malfunction.

After SLIM transmitted flight data and lunar images to Earth using its internal battery, the engineers turned the spacecraft off. By doing so, they hoped to preserve the minimum remaining power required for a stable system reboot when solar power generation became possible.

SORA-Q before (left) and after changing shape. (Provided by JAXA, Takara Tomy, Sony Group Corporation, Doshisha University)

Sunlight Shines on Probe

When SLIM landed on the southern side of the moon's equator, in the Mare Nectaris in the early hours of January 20, it was still morning on the moon. One lunar day is equivalent to approximately 27 Earth days. Therefore, sunlight did not reach the solar panels on the west side of the spacecraft. Subsequently, as the region entered lunar daytime, the direction of sunlight changed, making power generation possible.

Communication with SLIM was restored on January 28 at 11 pm (JST), according to JAXA. Data received from the spacecraft indicated that a specialized camera for observations has also become operational. The captured images are being sent back to Earth.


However, the lunar surface temperature during the daytime exceeds 100 degrees Celsius (212 degrees Fahrenheit). This will damage the semiconductors, giving only a few days for the prob to conduct activities. Furthermore, capturing images with the specialized camera will become challenging in February as the region transitions into nighttime and becomes dark.

JAXA stated that it will "continue lunar activities as long as possible while monitoring the spacecraft's condition."


(Read the article in Japanese.)

Author: The Sankei Shimbun

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