ispace, the Japanese company, has determined that a malfunctioning laser rangefinder was the cause of the crash of its second lunar lander, Resilience, on June 5th. A press briefing on June 23rd detailed the findings of their investigation. The laser rangefinder, crucial for determining altitude during descent, experienced a hardware problem that prevented it from providing timely altitude data.
The device was designed to provide data from at least three kilometers above the surface, initiating the final landing burn. However, it didn't provide its first measurement until the lander was below 900 meters, already traveling at 66 meters per second – significantly faster than the planned 44 meters per second. The final telemetry, at 192 meters altitude, indicated a descent rate of 42 meters per second.
Images from NASA’s Lunar Reconnaissance Orbiter pinpoint the crash site, roughly 282 meters south and 236 meters east of the planned location, resulting in a 16-meter-wide crater. Yoshitsugu Hitachi, ispace executive vice president, confirmed that software and propulsion systems were ruled out as contributing factors. The investigation focused on the laser rangefinder, concluding that its performance degraded compared to pre-flight tests.
Possible causes of the degradation include lunar surface conditions affecting laser reflection, reduced laser power, decreased performance at higher velocities, or environmental factors like vacuum or radiation. “We are currently unable to further narrow them down,” Hitachi stated, “or whether the anomaly was due to a single factor or a combination of multiple factors.”
This failure differs from their 2023 mission, where a software problem caused the crash. Hitachi noted that Resilience used a different laser rangefinder model due to unavailability of the previous model. Ryo Ujiie, ispace’s chief technology officer, outlined steps to improve future missions, including enhanced testing of the laser rangefinder and consideration of alternative or supplementary sensors like lidar or cameras. A new external review board will aid in this process.
Despite this setback, Takeshi Hakamada, ispace CEO, emphasized the company’s commitment, stating: “We take it very seriously…However, the important part is that we keep trying. There can be some failures, but we keep improving our systems.” He also confirmed that the schedule for Missions 3 and 4 remains unchanged, launching in 2027, with an expected cost increase of 1.5 billion yen ($10.3 million) for improvements.