The Japanese private lunar lander Hakuto-R crashed in late April during its historic landing attempt because its onboard altitude sensor was mistaken for the rim of a lunar crater.
After completing its analysis of the data from Hakuto-R’s failed lunar landing, ispace has concluded that difficult terrain and a last-minute disruption to the landing site are to blame. Evidently, Hakuto-R was able to finish the entire delay procedure to prepare for a lunar landing. When the spacecraft reached an altitude of around 100 km (62 mi), it began its descent procedure and was able to slow down until it was only moving less than 1 m/s.
However, its software mistakenly estimated its altitude to be zero while it was still hovering about 5 kilometers (3 miles) above the ground. That is, it thought it had already landed when it hadn’t yet, and it continued to descend at a very low speed near the surface until its propulsion system ran out of fuel. ispace was unable to re-establish contact with the spacecraft but believes it free-failed and eventually crashed on the moon.
Why The Japanese private lunar lander Hakuto-R crash?
That’s the how, but what about the why? Well, the company believes that the most likely reason Hakuto-R crashed is that its software suffered from an altitude estimation problem because it got confused. As it flew towards its landing site, it passed over a large cliff which was determined to be the rim of a crater. The sensor on board the spacecraft got an altitude reading of 3 kilometers as it passed over the high ground, and it was apparently higher than the estimated altitude value that the Hakuto-R team set beforehand.
The spacecraft software mistakenly thought the sensor was reporting an abnormal reading and then continued to filter out the altitude readings. ispace has built-in the ability to reject abnormal height readings on the lander as a failsafe in the event of a hardware problem with the sensor. However, it failed on mission 1 because the landing sequence simulations did not include the lunar environment in the spacecraft’s trajectory. ispace made the decision to change Hakuto-R’s landing site after the critical design review was already completed in 2021.
The Hakuto-R Mission 1 was about to become the first successful moon landing by a private company, and the first Japanese moon landing overall. While it did not actually land on the moon, ispace will use the mission data to design preparatory landing sequences for Missions 2 and 3, which are scheduled to launch in 2024 and 2025, respectively.
