Japan explains how it made a reverse moon landing
Japan became the fifth country to land on the moon on Saturday, but the spacecraft ended up in an awkward position, with the engine nozzle pointed towards space.
The Japanese spacecraft, known as Smart Lander for Investigating Moon, or SLIM, was planned to land on its side, a strategy to avoid tipping over on the landing site's sloping terrain.
But about 50 meters above the ground, one of SLIM's two main engines appears to have failed, officials from JAXA, the Japanese space agency, said Thursday.
While the onboard computer tried to compensate for the sudden loss of half of the thrust, the spacecraft was still able to hit the ground at a modest vertical speed of about three miles per hour. But the SLIM's horizontal speed and orientation upon landing were beyond the range for which it was designed.
As a result, the spacecraft rolled upside down. It escaped the fate of some other recent robotic missions, which disintegrated on the moon, and its systems worked and communicated with Earth. But the solar panels ultimately faced west, away from the lunar morning sun, and could not generate electricity. With the battery largely depleted, mission controllers on Earth sent an order to shut down the spacecraft less than three hours after landing.
Despite the stumbles, the mission achieved its primary goal: a soft landing on rugged terrain on the moon, within 100 meters of an intended landing site, far more accurate than the uncertainty of kilometers that most landers aim for.
“It has successfully achieved the controlled landing,” Hitoshi Kuninaka, director general of JAXA's Institute of Space and Astronautical Science, said in Japanese at a news conference. “We confirmed that the landing position was 55 meters away from the original target. So we concluded that we had achieved an accurate landing at 100 meters.”
During its brief operation, an instrument on the lander captured low-resolution black-and-white images of the surrounding landscape. SLIM team members gave dog breed nicknames to rocks that caught their interest.
Two small rovers that ejected from SLIM just before landing both moved around the moon's surface, and one of them took a photo of the inverted lander.
JAXA officials remain optimistic that SLIM can come back to life in about a week, when the sun will shine from the west and illuminate the solar panels during the two-week lunar afternoon.
“We will try to establish communication as SLIM will automatically come into operation when power generation starts,” which could allow operations to resume, Shinichiro Sakai, SLIM's project manager, said at the press conference.
When SLIM comes back to life, the lander's instrument will take detailed measurements of the composition of the rocks and soil.
Dr. Sakai said he had “mixed feelings” about the direction the spacecraft ended up. “If the solar cells were face down on the surface, there would be no chance of receiving sunlight, so I feel so relieved. remained as it is,” he said.
Dr. Sakai said photos taken by SLIM during its descent, before and after the partial loss of thrust, indicate that one of the engine jets fell off. JAXA officials are investigating what went wrong.