SLIM Sleeps in this Month

Japan’s Smart Lander for Investigating Moon did not wake up when JAXA sent a signal yesterday (EDT). The sturdy lander has surprised everyone by continuing to operate after repeated long, cold lunar nights that doom other landers that have only solar cells for power.  JAXA has not given up on SLIM and will try again next month when the Sun returns to the landing site.

Launched in September 2023, SLIM demonstrated its resilience during landing on January 19, 2024 EST (January 20 in Japan).  One of the two engine nozzles fell off and SLIM landed upside down with most of its solar cells pointing away from the Sun as shown in an image taken by a tiny baseball-sized “rover” ejected just before landing.

Nonetheless, JAXA engineers managed to get some data and a partial image back. They held out hope that when the Sun angle changed days later, enough power might be generated to collect more. Sure enough, by the end of its first sunlit period SLIM had sent back a panorama of the landing site and other science data.

The big surprise, however, was when contact was reestablished in February, again in March, and yet again in April.

JAXA tried again last night (Japan time), but reported in a series of posts on X there was no reply. They hope the lander may reboot itself and will try again next month.

来月も太陽電池による発電が十分に得られると見込まれる頃に再度運用を試みる予定です。夜の間に電源がOFFされているので全体がリセットされて再起動することを期待しています。#SLIM #JAXA

— 小型月着陸実証機SLIM (@SLIM_JAXA) May 28, 2024

We tried again on the night of the 27th, but there was no response from #SLIM. As the sun went down around SLIM on the night of the 27th, it became impossible to generate electricity, so unfortunately this month’s operation will end. Thank you very much for the overwhelming support you have shown us since the previous day’s post.

“We plan to try operating it again next month when we expect to be able to generate sufficient solar power. Since the power was turned off overnight, we hope that the whole system will be reset and restarted.” Translated by Google

SLIM is one of a new generation of comparatively inexpensive lunar landers that rely only on solar cells, not radioistopes, for power and warmth. The trade-off for the lower cost is a short lifetime since batteries and electronics are not designed to survive 14 days of frigid cold about -250°C (-418°F).

Two other new-generation spacecraft have successfully landed on the Moon in the past year. As expected, India’s Chandrayaan-3 and the U.S. Odysseus, or Odie, built by Intuitive Machines as part of NASA’s Commercial Lunar Payload Services (CLPS) program, did not wake up after their lunar nights.

Lunar landers sent to the Moon by the Soviet Union and the United States in the 1960s and 1970s, and by China more recently, have radioisotope power supplies that keep the spacecraft warm.

China has two landers on the Moon right now, Chang’e-3 on the nearside and Chang’e-4 on the farside, that have been operating for years. China returned samples from the near side of the Moon with Chang’e-5 in 2020. Chang’e-6 is orbiting the Moon right now and about to descend and return samples from the farside.

China is the only country to send landers to the farside that always faces away from Earth. Despite widespread misunderstanding, the farside of the Moon is not dark. There is no dark side of the Moon. The nearside that faces Earth and the farside that faces away each experience 14 days of sunlight and 14 days of darkness. The waxing and waning of the Moon that we see is the same on the other side.