Space News Jeff Foust May 26, 2023
A software glitch kept a lunar lander from properly determining its altitude, leading to a crash on its landing attempt last month, Japanese company ispace announced May 26.
The Tokyo-based company said its investigation into the failed landing of its HAKUTO-R M1 lander April 25 concluded that the onboard computer disregarded altitude information from a laser rangefinder on the lander as it passed over a crater rim, leading the lander to conclude it was on the surface when it was still five kilometers above it.
During an online briefing, ispace executives said the landing was going as planned through its initial phases. The altitude, as calculated by an inertial measurement unit, had converged with measurements from the laser rangefinder. The readings diverged, though, once the lander passed over the rim of Atlas Crater as it approached its landing site within it, with the measured altitude increasing by three kilometers.
Ryo Ujiie, chief technology officer of ispace, said that the onboard computer was not programmed to expect that change and ignored the data from the laser rangefinder on the assumption that the instrument had malfunctioned. That was a deliberate choice, he said, “to make our control system more robust against a sensor hardware failure.”
The sensor had not failed, though, and accurately showed the lander was still about five kilometers above the surface when the lander’s computer believed it was on the surface. The lander continued to descend at a slow rate of about one meter per second under its thrusters until it exhausted its propellant. The lander then went into freefall, crashing into the surface at a speed of more than 100 meters per second.
More:
https://spacenews.com/software-problem-blamed-for-ispace-lunar-lander-crash/
