Japanese space venture: Discrepancy in altitude data led to failed lunar landing

A Japanese space venture says last month's failed moon landing was due to a software glitch that caused the lunar lander to inaccurately estimate its altitude.

The company, ispace, attempted the world's first private-sector lunar landing on April 26. But its craft failed to make a soft landing because of problems in the final stage of descent.

The company's CEO and others explained the results of an analysis of flight data on Friday.

They said that when the lander passed over a roughly three-kilometer-high cliff on the moon, a discrepancy emerged between the altitude measured by onboard sensors and the estimated altitude set in advance.

The company said this caused the lander's software to erroneously determine that the lander was at a lower altitude that it actually was.

This meant that while the vehicle estimated its own altitude as zero, it was actually at a height of about five kilometers above the lunar surface.

The engineers said the lander continued to descend at low speed until the propulsion system ran out of fuel. They said the vehicle went into free-fall about two minutes later.

The firm says it will modify the software and improve its landing sequence simulations. It says it will make a fresh attempt for a moon landing next year.

CEO Hakamada Takeshi said that the final five kilometers are within an acceptable margin of error, compared to the distance between Earth and the moon.

He said reaching the final phase of the landing is a major achievement, and that ispace engineers will ensure that the valuable knowledge gained from the mission will lead them to the next stage of evolution.