Japan’s space agency has confirmed its moon-lander successfully achieved its pinpoint landing on the moon on January 19.
The Japan Aerospace Exploration Agency (JAXA) couldn’t confirm the landing precision on the day after the spacecraft’s solar panels failed to produce power.
JAXA officials knew the lander had performed a controlled descent because none of its other components appeared to have been damaged.
However, a JAXA statement on January 25 said one of the lander’s two main engines failed during its descent.
As the Smart Lander for Investigating Moon (SLIM) touched down near Shioli crater, Japan became the fifth country to soft-land a robotic instrument on the moon, months after India’s Chandrayaan 3 succeeded in August 2023.
JAXA built SLIM to be light and sent it towards the moon on a loopy path that conserved fuel.
The gains were to help SLIM on its primary mission: to land within a small 100 m by 100 m patch on the moon.
So far, spacecraft planning to land on Mars and the moon were allowed to do so within large patches hundreds of metres wide.
In comparison, SLIM’s designated patch is tiny, giving the spacecraft its nickname “moon sniper”.
According to the JAXA statement, SLIM was within 10 m of its designated landing spot until it was 50 m above the surface.
At this stage, SLIM used maps of the moon’s surface in this area acquired by the orbiter of the Chandrayaan 2 mission.
SLIM’s computer overlaid them with images captured by its navigation camera, and used the result to spot obstacles to its descent.
“[It] is highly likely that the main engine was already affected by the loss of function when the second obstacle detection occurred,” the statement added.
This is because SLIM’s positional accuracy had increased from 3-4 m during the first obstacle detection exercise to 10 m in the second.
The engine’s failure eventually caused SLIM to drift to a spot 55 m east, where it landed.
Whether this failure is related to the solar panels’ inability to generate power is under investigation.
When the engine’s thrust was lost, SLIM’s onboard computer attempted to control the lander’s position using the other engine.
“The descent velocity at the time of contact with the ground was approximately 1.4 m/s or less, which was below the design range, but conditions such as the lateral velocity and attitude were outside the design range, and this is thought to have resulted in a different attitude than planned,” according to the statement.
“While more detailed evaluation continues, it is reasonable to mention that the technology demonstration of pinpoint landing within an accuracy of 100 m, which has been declared to be the main mission of SLIM, has been achieved,” the statement added.
The Indian Space Research Organisation (ISRO) launched the Chandrayaan 2 mission in July 2019 with the primary mission of soft-landing a robotic lander on the moon.
While the mission successfully entered into orbit around the moon in August, the soft-landing attempt in September failed when the lander crashed on the surface.
The Chandrayaan 2 orbiter has continued to stay in orbit, studying the moon, including preparing a map of its surface.
ISRO’s Chandrayaan 3 mission successfully soft-landed a lander on the moon, in the natural satellite’s south pole region, also with help from images captured by the Chandrayaan 2 orbiter.
JAXA and ISRO are expected to collaborate in the near future on the Lunar Polar Exploration (LUPEX) mission, which will also be a lunar surface mission.
SLIM’s pinpoint landing will inform the LUPEX lander, which will also be required to soft-land in the relatively highly uneven terrain of the south pole region. Many craters here have permanently shadowed parts where scientists expect to find water ice.
- Japan became the fifth country to soft-land a robotic instrument on the moon, months after India’s Chandrayaan 3 succeeded in August 2023
- ISRO’s Chandrayaan 3 mission successfully soft-landed a lander on the moon, in the natural satellite’s south pole region
- JAXA and ISRO are expected to collaborate in the near future on the Lunar Polar Exploration (LUPEX) mission, which will also be a lunar surface mission
