HAKUTO-R’s Software Got Confused at the Last Minute, Causing it to Crash into the Moon

On April 26, 2023, people around the world watched as the HAKUTO-R lander made its final approach for a landing on the Moon. It had been “on the road” since December 11, 2022, and completed eight Mission 1 milestones. Numbers 9 and 10 would have been landing and establishing a base on the Moon. As we all know, it reached the lunar surface, but not the way the ispace team expected. NASA images confirmed its final resting place.

HAKUTO-R’s control team just released an error analysis report, showing that software on the lander performed a faulty altitude estimate as the spacecraft was getting ready to settle onto the surface. According to flight data taken as the lander was navigating to its landing site, the onboard sensors sent back altitude data. It passed over the rim of a crater that was higher than expected. That set up a conflict in the software between the actual measured elevation and the estimated elevation provided before landing. The onboard software decided that this was a sensor error and it “filtered out” further measurements from that sensor.

Essentially, the lander estimated its own altitude to be zero, or on the lunar surface. However, it wasn’t. Instead, it was an altitude of about 5 kilometers. When it got to the scheduled landing time, the lander continued to descend slowly until the propulsion system ran out of fuel. At that point, it was still above the surface and fell the rest of the way down.

Programming Changes Doomed HAKUTO-R

As part of the post-crash analysis of the accident, the ispace team traced the crash to a decision made during a critical design review in February 2021. At that time, they changed the landing site location. That necessitated changes in the verification and validation plans controlled by the software. However, mission simulations didn’t have adequate information about the surface environment in the area of the new landing site. That ultimately led to the mismatch between where the lander thought it was versus where it actually flew. So, while the spacecraft did get to the Moon, and was in control most of the way down, it ultimately crashed due to navigation filtering out data it thought was faulty.

The filter function was designed to reject any altitude measurement that was too far off from the lander’s estimate. The idea behind it was to be able to maintain the smooth operation of the lander in the event of a sensor giving an incorrect altitude measurement.

The crash was a tough blow to the ispace team. But, they’ve taken the analysis and incorporated changes into planning for the next missions. The idea is to provide more highly accurate surface terrain data in the landing sequence planning so that future software conflicts can be avoided.

Otherwise, It Really Was a Successful Mission

So, while milestones 9 and 10 were not achieved, and customer payloads were lost, the ispace team demonstrated a remarkable ability to fly the spacecraft on preplanned trajectories and get it to the Moon, according to Takeshi Hakamada, founder and CEO of ispace. “Mission 1 demonstrated a great deal of technical reliability, as our lander reached the lunar surface just prior to landing. Now, we have been able to identify the issue during the landing and have a very clear picture of how to improve our future missions,” he said. “While it is unfortunate that we were not able to fully meet the expectations of all our stakeholders, including our customers, all of us at ispace are proud of what we accomplished in Mission 1 and are very positive about what we can accomplish.”

The milestones for HAKUTO-R were straightforward. They included launch preparations, launch, and orbital deployment. After that, it made the first orbital control maneuver and achieved stable space flight. Then, it performed further orbital control maneuvers and set off for the Moon. Finally, it arrived in the lunar gravitational field and made maneuvers in lunar orbit. Data from all those achievements are already incorporated into the next two ispace missions.

“We have already begun work on Mission 2 and Mission 3,” said Hakamada, noting that the team is prepared to face the challenges and make every effort to improve for future efforts. “We will ensure that the valuable knowledge gained from Mission 1 will lead us to the next stage of evolution. We believe that this is our commitment and our duty to all our stakeholders. ‘Never Quit the Lunar Quest’ In this spirit, we will continue to move forward.”

Future Missions Based on HAKUTO

Ispace began as lunar resource development company in 2010. HAKUTO was originally its entry in the Google Lunar XPRIZE race. The company then worked to develop it for payload delivery to the Moon. Its next missions 2 and 3 should launch in 2024 and 2025. The crashed HAKUTO-R lander carried an interesting set of payloads. The United Arab Emirates supplied the Rashid rover. The Japanese Aerospace Exploration Company (JAXA) supplied a lunar robot called SORA-Q. The agency worked on that in conjunction with the Tomy toy company.

Ispace hopes to provide access to the lunar surface via rovers and other robotic tech demos. Future plans include devices for pharmaceuticals and life sciences projects as well as entertainment and educational programs. In addition, the company sells data services for people and companies who want to enter the lunar exploration market.

For More Information

ispace Announces Results of the “HAKUTO-R” Mission 1 Lunar Landing
Japanese Startup Says Hakuto–R Failed Moon Landing was Caused by Altitude Miscalculation