Monday, May 20, 2024

Japan’s Lunar Lander Wakes Up (Again!) – Sky & Telescope

AstronomyJapan's Lunar Lander Wakes Up (Again!) - Sky & Telescope


Updates:

February 26, 2024: JAXA’s SLIM lander is proving to be “hard-to-kill.” The lunar lander has actually woken up after lunar sunrise (which occurred mid-month)! It has survived the cold, two-week lunar night. It even sent us a new image of its Shioli Crater home.

January 31, 2024: The lander once again fell silent on January 31st, this time owing to the declining angle of sunlight as lunar sunset approached. There’s still a possibility that the lander might survive the lunar night, and the team plans to try to reestablish contact in mid-February. This is the (for now) final photo from the lander:


SLIM on the lunar surface, snapped by the LEV mini-rover.
JAXA

JAXA’s plucky lunar lander is proving hard to kill. Over the past weekend, word came out the Smart Lander for Investigating the Moon (SLIM) managed to charge its solar-powered batteries enough to power back on and resume operations.

“We have already conducted scientific observations with MBC (SLIM’s Multiband Spectroscopic Camera)” says Yusuke Nasu (JAXA) of the SLIM team. “However, it is uncertain how many more days we can continue these observations until sunset.” A lunar day is two weeks long, and the next lunar sunset for the site will occur on January 31st.

SLIM launched along with the X-ray Imaging Spectroscopy Mission (XRISM) observatory last September, and entered lunar orbit on December 25, 2023. The mission was designed to test the “smart eyes” automated landing system and was successful at carrying out a pinpoint (within less than 10 meter) landing on the slope of Shioli Crater. The objective was to land within 100 meters of the target, and JAXA estimates the final landing occurred 55 meters east of the target.

A sequence of images taken from SLIM show nearer and nearer views of the Moon's surface
SLIM on approach to landing, as seen from the onboard navigation camera. You can see Shioli Crater looming large in the view, right before landing.
JAXA

After the landing, it soon became apparent that SLIM was orientated in such a way that it could not charge its systems properly, and was operating on batteries only. An image from the baseball-sized Lunar Excursion Vehicles (LEV-2/SORA-Q) rover jettisoned during landing confirmed that SLIM was indeed tipped over nose first on the surface of the Moon.

Artistic rendering of SLIM on the lunar surface. SLIM is covered in gold foil and reflects sunlight. The surrounding surface and more distant crater walls are gray. The sky is black, with no stars appearing due to the brightness of the foreground.
A rendering of SLIM on the lunar surface, based on the above photo taken by a mini-rover deployed upon landing, shows the orientation of the lander with respect to the surrounding crater.
JAXA

Still, the lander managed to return several images before its batteries drained 157 minutes after landing on January 19th, with rocks named after different dog breeds to denote their relative size.

Side-by-side images of the landing site, with the right image containing labels of various rocks
SLIM’s view of the slopes of Shioli Crater
JAXA / University of Aizu/Ritsumeikan University

On restarting this week, researchers posted an image of the nearby “Toy Poodle” rock in SLIM’s field of view:

Fuzzy grayscale image of a rock's surface
A recent image of the “Toy Poodle” rock near SLIM.
JAXA

Now, researchers must scramble to get what remaining science they can out of the mission. Sunset over the site is today, and the next sunrise isn’t until two weeks from now on February 14th. It’s unlikely that SLIM will survive the long cold lunar night. China’s Yutu rover did so, but it was equipped with small radioisotope heater units; SLIM has no such provision for survival.

NASA’s Lunar Reconnaissance Orbiter (LRO) snapped an image of SLIM in Shioli Crater five days after the lander came down:

Blinking gif showing SLIM landing site
SLIM appears as a dot in the center of this image of the Shioli Crater region, imaged before and after the lander came down.
NASA / LRO

While SLIM struggled, the Lunar Exploration Vehicles (LEV-1 and -2) it brought with it to the surface worked remarkably well. LEV-1 performed planned leaping movements, and LEV-2 returned data from near SLIM, including images of the lander’s orientation and status. Often, we’re left guessing after a lander falls silent, so those images were vital to understanding the technical issues the spacecraft faced. Small, separate, imaging-capable vehicles might become standard to aid and evaluate the success of future missions.



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