ispace Says Software Error Caused HAKUTO-R Lunar Lander to Crash into Moon

A software glitch and a change in destination combined to cause ispace’s commercial HAKUTO-R lunar lander to crash into the Moon last month as it attempted a soft landing on the surface on April 26, according to new details shared by the company on Thursday (May 26).

HAKUTO-R’s descent was going as planned until the lander passed over the rim of Atlas Crater, which towered approximately 1.8 miles (3 km) above the lunar surface. A sensor on board recorded a sharp increase in altitude as the spacecraft headed toward its landing spot inside the crater.

The sensor accurately measured HAKUTO-R’s altitude. However, the onboard software concluded the measurement was in error and ignored it, ispace said in a mission update.

“While the lander estimated its own altitude to be zero, or on the lunar surface, it was later determined to be at an altitude of approximately 5 km [3.1 miles] above the lunar surface,” the company announced. “After reaching the scheduled landing time, the lander continued to descend at a low speed until the propulsion system ran out of fuel. At that time, the controlled descent of the lander ceased, and it is believed to have free-fallen to the Moon’s surface.”

Software written to ensure a safe landing in the event of a sensor malfunction ended up dooming the mission when it misinterpreted accurate data.

“This filter function, designed to reject an altitude measurement having a large gap from the lander’s estimation, was included as a robust measure to maintain stable operation of the lander in the event of a hardware issue including an incorrect altitude measurement by the sensor,” ispace added.

The company said a change in the landing location from Lacus Somniorum, which is a relatively flat plain, to Atlas Crater resulted in insufficient software testing prior to launch.

“One major contributing factor to this design issue was a decision to modify the landing site after critical design review completed in February 2021,” the company announced. “This modification influenced the verification and validation plan despite numerous landing simulations carried out before the landing.”

In a press briefing, company officials said they made the change to maximize the benefits of the mission for ispace as well as its customers who had payloads aboard the HAKUTO-R lunar lander.

ispace said the results of the investigation will assist it with future lunar missions.

“This information will be incorporated into software design, as well as upgrades and expansion of the scope of preparatory simulations of the landing sequence for our future missions, including Mission 2 and Mission 3, to improve the accuracy of landing sequences,” the company said.

“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,” said ispace Founder and CEO Takeshi Hakamada. “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.”

“We have already begun work on Mission 2 and Mission 3. We are prepared to face the challenges and make every effort to improve,” Hakamada continued. “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.”