In a recent announcement, the Japanese company ispace revealed critical findings regarding the crash of its second lunar lander, the Resilience spacecraft, which occurred on June 5, 2023. During a press briefing held on June 23, company executives shared that a malfunction with the laser rangefinder—an essential device used to gauge altitude during the descent—was likely the culprit behind the failed landing attempt.
ispace officials conducted a thorough review of the failed lunar landing and concluded that the laser rangefinder encountered a hardware issue that prevented it from delivering timely altitude data. This device was supposed to provide critical altitude measurements when the spacecraft was at least three kilometers above the lunar surface, signaling the engines to initiate the final landing burn. Unfortunately, the laser rangefinder only began reporting altitude when the spacecraft was dangerously close to the surface, descending from less than 900 meters.
As a result, the Resilience lander attempted to decelerate rapidly but was traveling at a significantly higher velocity than planned—66 meters per second instead of the intended 44 meters per second. The last telemetry received indicated that at 192 meters altitude, the lander was still descending at 42 meters per second, ultimately leading to the crash.
NASA’s Lunar Reconnaissance Orbiter provided images that pinpoint the probable crash site of the Resilience, located approximately 282 meters south and 236 meters east of the intended landing location. The impact resulted in a crater measuring 16 meters across, underscoring the severity of the landing failure.
Yoshitsugu Hitachi, the executive vice president of the Japan Engineering Office at ispace, stated that the company initially considered both hardware and software issues. However, telemetry data indicated no software malfunctions, and the propulsion system was functioning properly. This led the investigation to focus on the laser rangefinder, which was found to be properly installed but had likely degraded in performance compared to pre-flight tests. Various factors, including lunar surface conditions and the operational environment, could have contributed to this degradation.
Hitachi emphasized that the cause of the Resilience landing failure differed from the issues faced during the company’s first mission in 2023. In that instance, a software error caused the lander to misjudge its altitude, leading to a crash after exhausting its fuel while hovering at five kilometers. He confirmed that the software used in Resilience was functioning effectively, and noted that the first lander had no issues with its laser rangefinder. The Resilience spacecraft utilized a different model, as the original supplier of the device was no longer in operation.
To address the problems encountered during the Resilience mission, ispace is implementing two key strategies. The first involves enhancing the testing protocols for the laser rangefinder and related sensors to better understand their performance under the specific conditions experienced during this mission, such as high lander speed and low surface reflectivity. The second strategy includes evaluating alternative laser rangefinder options, as the unit used on Resilience had not been previously flight-tested.
Additionally, ispace is exploring the integration of supplementary sensors, including lidar and cameras, to improve terrain-relative navigation. The company plans to establish an external review board comprising experts, including former engineers from NASA and the Japanese space agency JAXA, to provide insight and guidance for future missions.
ispace aims to collaborate more closely with JAXA on upcoming missions, leveraging the agency's technical expertise. Despite the setbacks from the recent missions, the schedule for future launches remains intact, with Mission 3, featuring a lander built by ispace U.S. for Draper, and Mission 4, a Japanese-built lander, both slated for launch in 2027.
Chief Executive Takeshi Hakamada expressed the company’s commitment to learning from the failures of its first two lunar missions. “We take it very seriously,” he stated. “However, the important part is that we keep trying. There can be some failures, but we keep improving our systems.” He reassured stakeholders that ispace remains focused on its objectives and is determined to regain their trust through continuous improvement and innovation.
