Japan’s iSpace says Hakuto-R crashed because it became confused by crater rim

iSpace has analyzed data from its failed Hakuto-R lunar landing, and it sounds like difficult terrain and a late change in landing site are to blame. Apparently, Hakuto-R was able to complete a full deceleration process in preparation for touching down on the lunar soil. The spacecraft activated its descent sequence when it reached an altitude of about 100 km (62 mi) and was able to slow down until it was moving at only 1 m/s.

However, its software mistakenly estimated its altitude to be zero when it was still hovering about 5 kilometers (3 mi) above the ground. In other words, it thought it had already landed when it had not yet landed, and it descended very slowly near the surface until its propulsion system ran out of fuel. iSpace was never able to establish contact with the spacecraft again, but believes it went on a free fall and eventually crashed on the Moon.

How is it, but what about the why? Well, the company thinks that the most likely reason the Hakuto-R’s software suffered from the altitude estimation issue was that it got confused. As it was flying to its landing site, it passed over a large rock that was determined to be the rim of a crater. The spacecraft’s onboard sensors received an altitude reading of 3 kilometers when it passed through the high-altitude terrain, and this was clearly higher than the estimated altitude already determined by the Hakuto-R team.

The spacecraft’s software mistakenly thought that the sensor had reported an abnormal value, and continued to filter its altitude measurements afterwards. iSpace built the ability to reject abnormal altitude measurements into the lander as a safety measure in the event of a hardware problem with the sensors. However, this backfired for Mission 1 as the simulations of the landing sequence failed to incorporate the lunar environment on the spacecraft’s path. iSpace has decided to change the landing site of Hakuto-R after its critical design review is completed in 2021.

The Hakuto-R mission 1 was set to become the first successful Moon landing by a private company and the first Japanese lunar landing overall. While it did not land on the Moon, iSpace will use data from the mission to design the initial landing sequences for Missions 2 and 3, which are scheduled for launch in 2024 and 2025, respectively.