Astrobotic’s Peregrine lunar lander failed to reach the moon due to a problem with a single valve in the propulsion system, according to a report released by the company. This issue caused the helium to flow uncontrollably into the oxidizer tank, resulting in a rapid overpressurization and subsequent leakage of oxidizer. The failure was likely due to a mechanical issue caused by vibration-induced relaxation between threaded components inside the valve. The spacecraft was stabilized after the leak was discovered, but ultimately returned to Earth after 10.5 days.
A review board consisting of 34 members, including both internal and external experts, determined that the failure of the helium PCV in the propulsion system was the likely cause of the malfunction. The board analyzed data collected from the mission, as well as flight qualification campaign and component testing data. They were able to pinpoint the location and timing of the anomaly, confirming that the valve failure was responsible for the spacecraft’s inability to reach the moon.
The timeline leading to the failure began in 2019 when Astrobotic contracted a vendor for the development of the propulsion feed system. Due to technical and supply chain issues caused by the COVID-19 pandemic, Astrobotic terminated the contract and decided to finish the feed system in-house. This shift in strategy also led to the decision to do the propulsion system for the Griffin lander in-house, aiming for more vertical integration and risk reduction for the upcoming mission.
After encountering issues with the original vendor’s propulsion components, particularly the PCVs, Astrobotic switched to a different supplier in August 2022. Tests on the propulsion system showed leaks in one of the PCVs, but not the one that ultimately leaked on orbit. Despite the identified risk in the risk register, engineers did not replace the second PCV due to the extensive surgery required and the uncertainty of disassembly and reassembly. The decision-making process leading up to the launch was deemed sound by the review board.
The findings from the Peregrine mission failure are now being used to inform the development of the Griffin lander, scheduled to launch before the end of 2025. Engineers have redesigned the valve, added a regulator in the propulsion system to control helium flow, and included backup latch valves for redundancy in case of PCV failure. These changes aim to prevent a similar issue from occurring with the Griffin lander, which is a much more complex mission than the Peregrine.
