Despite Engine Malfunction, Powered-down Japanese Moon Lander Achieves Major Goals

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A camera aboard a small micro rover deployed from Japan’s SLIM lunar lander captured an image of the probe resting on one side a few feet away after an engine malfunction during the final stages of descent Jan. 19. Image: JAXA.

One of two engines powering a Japanese moon lander during its descent to the surface Jan. 19 suffered a malfunction of some sort just 160 feet above the lunar surface that sharply reduced its power, the Japanese space agency said Thursday.

The spacecraft touched down at a safe, lower-than-expected velocity, but it was moving too fast sideways because of the unbalanced thrust. As a result, the otherwise-healthy probe apparently tipped over on landing, leaving its solar cells, attached to the upper surface of the craft, pointed to the west, directly away from the sun.

Unable to generate electricity, the spacecraft had only the limited power available in its on-board battery.

After downloading stored images and collecting as much science and engineering data as possible, flight controllers sent commands to shut the probe down 37 minutes after landing, before the battery was completely drained. That should improve the chances it will eventually “wake up” as the 14-day lunar day-night cycle proceeds and the angle to the sun changes.

While the engine problem curtailed post-landing operations, officials with the Japan Aerospace Exploration Agency — JAXA — said the Smart Lander for Investigating (the) Moon, or SLIM, spacecraft successfully demonstrated high-precision landing technology, the primary goal of the mission.

Before the engine malfunction, the craft was descending toward a touchdown within 10 to 13 feet of the planned target, periodically snapping pictures of the surface, comparing them to on-board maps and making adjustments as required.

With the engine problem, the probe ended up landing about 180 feet from the target, still well within the 100-meter (328-foot) goal.

“The pinpoint landing was achieved (with an) accuracy of less than 10 meters, and probably about 3 to 4 meters (10 to 13 feet),” an official said at a JAXA news conference early Thursday. “We believe that this is a great achievement for future exploration.”

The probe also successfully deployed two small micro rovers during the final moments of the descent, one designed to hop about the surface and the other designed to roll. Both appeared functional and one beamed back an image of the SLIM that showed the spacecraft resting on one side a few feet away.

A navigation camera aboard SLIM also worked as planned, capturing images during the descent. After landing, 227 of 233 planned images were beamed back to Earth and assembled into a mosaic showing the rocky terrain where SLIM touched down.

“We are thinking that the solar panels, facing the west, will (eventually) receive sunlight,” a JAXA official said in translated remarks. “There is a possibility that the power generation will be restored and the exploration operation will resume.”

Despite the engine malfunction, SLIM landed on the moon intact and was able to send back science and engineering data before it was shut down. As such, Japan became only the fifth nation to successfully land on the moon after the United States, Russia, China and India.

Three privately-financed robotic moon landing missions have been launched as commercial ventures, but all three failed.

Most recently, the Peregrine lander, built by Pittsburgh-based Astrobotic, was stranded in a highly elliptical Earth orbit after a valve malfunction caused a propellant tank to rupture shortly after launch Jan. 8. Company flight controllers directed the spacecraft to fall back into Earth’s atmosphere where it burned up on Jan. 18.

A second American company, Houston-based Intuitive Machines, plans to launch its own commercial moon lander in mid February.