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Crater confusion caused Japan’s Hakuto lunar mission to fail

Japan’s ispace startup last month very nearly succeeded in becoming the first team to land a privately funded spacecraft on the moon.

But the mission ended in failure when the $90 million lander — Hakuto — lost touch with mission controllers before crash landing on the lunar surface, bringing the endeavor to an abrupt end.

The Tokyo-based team behind ispace remained positive, however, saying that all of the test mission’s stages besides the final one were a success, providing it with plenty of data that will give it a good chance of succeeding next time around.

Some of that data was used in its post-mission analysis, which investigated the precise cause of the crash landing. In a news release from ispace, the company said that an error occurred with the lander’s altitude measurement.

“While the lander estimated its own altitude to be zero, or on the lunar surface, it was later determined to be at an altitude of approximately 5 kilometers (3.11 miles) above the lunar surface,” ispace said.

“After reaching the scheduled landing time, the lander continued to descend at a low speed until the propulsion system ran out of fuel. At that time, the controlled descent of the lander ceased, and it is believed to have free-fallen to the moon’s surface.”

The most likely reason for the lander’s erroneous altitude estimation, ispace said, was a software issue.

It said that as the lander was navigating to the planned touchdown location, the altitude measured by the onboard sensors rose sharply when it passed over a large cliff — believed to be a crater rim — approximately 3 kilometers (1.86 miles) in elevation.

“According to the analysis of the flight data, a larger-than-expected discrepancy occurred between the measured altitude value and the estimated altitude value set in advance,” ispace said. “The onboard software determined in error that the cause of this discrepancy was an abnormal value reported by the sensor, and thereafter the altitude data measured by the sensor was intercepted.”

A complicating factor was the team’s decision to select a new landing site for Hakuto that it thought would be more interesting for scientists. Preparations for the new site failed to adequately take into account the lunar environment on the navigation route, resulting in the software misjudging the lander’s altitude on its final approach, ispace explained.

The company said lessons learned from the mission will be incorporated into its next attempt to successfully land on the lunar surface, though a date has yet to be set for that mission.

Last week, NASA published the first images of what it believes to be parts of the wreckage of the Hakuto lander, captured by the space agency’s Lunar Reconnaissance Orbiter as it passed overhead.

NASA is inking contracts with private firms — ispace among them — to develop landers capable of transporting cargo to the lunar surface as part of its Artemis program.

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Trevor Mogg
Contributing Editor
Not so many moons ago, Trevor moved from one tea-loving island nation that drives on the left (Britain) to another (Japan)…
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