WASHINGTON — Japanese company ispace says it believes its second lunar lander mission crashed because of problems with a laser rangefinder used to determine altitude during its descent.
At a press briefing late June 23, company executives said a review of the failed landing by its Resilience spacecraft June 5 led it to conclude that the laser rangefinder on the spacecraft suffered a hardware problem of some kind that kept it from providing timely data on the lander’s altitude.
The laser rangefinder was designed to provide altitude data when the spacecraft was at least three kilometers above the surface, triggering engines for the final landing burn. However, the unit did not provide its first altitude measurement until it was less than 900 meters high.
The lander then attempted rapid deceleration, but by that point it was traveling much faster than planned: 66 meters per second versus the 44 meters per second planned. The last telemetry received from the lander, at an altitude of 192 meters, showed it was still descending at 42 meters per second.
Images from NASA’s Lunar Reconnaissance Orbiter, released June 20, show the likely crash site for Resilience, about 282 meters south and 236 meters east of the planned landing location. The impact of the lander made a crater 16 meters across.
Yoshitsugu Hitachi, executive vice president of the Japan Engineering Office at ispace, said at the briefing that the company first examined if hardware or software was to blame. Telemetry revealed no issues with the lander’s software, and also ruled out any issues with its propulsion system.
The company then turned its attention to the laser rangefinder. The reviews found no evidence that the laser rangefinder was improperly installed, he said, leading ispace to conclude that the performance of the unit had degraded in some way compared to pre-flight tests.
Several factors could cause that degradation, including lunar surface conditions that reduced the amount of laser light reflected back to the lander, lower power of the laser, reduced performance at higher velocities or effects from the space environment, such as vacuum or radiation.
“We are currently unable to further narrow them down,” he said through an interpreter of those potential causes, “or whether the anomaly was due to a single factor or a combination of multiple factors.”
Hitachi emphasized that the cause of the Resilience landing was different from the company’s first mission in 2023, when a software problem caused the lander to think it was near the surface when it was in fact at an altitude of five kilometers, hovering until it exhausted its fuel and crashed. That software worked well on Resilience, he said.
The first lander did not have any problems with its laser rangefinder, but he said that Resilience used a different model because the unnamed supplier of the device no longer made the version used on the initial mission.
Ryo Ujiie, chief technology officer at ispace, said the company was taking two major steps to address the problem that caused Resilience to crash. One is to enhance the testing plan for the laser rangefinder and related sensors to better see how they operate in the potential conditions experienced on this mission of high lander speed and low surface reflectivity.
The second is consider a different laser rangefinder, as the unit flown on Resilience was not flight proven. The company will also consider augmenting the laser rangefinder with other sensors, such as lidar or cameras to provide terrain relative navigation.
That will work be supported by a new external review board, which will include people such as former engineers from NASA and the Japanese space agency JAXA. Ispace also plans work more closely with JAXA on future missions tap into its technical expertise.
Those changes will have no impact on the schedule for the next two missions: Mission 3, featuring a lander built by ispace U.S. for Draper flying a NASA mission, and Mission 4, a Japanese-built lander. Both remain scheduled for launch in 2027. Ispace expects to incur about 1.5 billion yen ($10.3 million) in additional costs for those missions from measures like obtaining a better laser rangefinder and improved testing.
“We take it very seriously,” Takeshi Hakamada, chief executive of ispace, said of the failed landings of its first two missions. “However, the important part is that we keep trying. There can be some failures, but we keep improving our systems.”
“Our primary goal today was to convey that ispace, as a challenger, is already moving forward towards its next mission,” he said, vowing to regain trust of its customers and other stakeholders. “We’re committed to demonstrating that ispace will continue to grow undeterred by this setback.”
