Astrobotic‘s journey to the moon took an unexpected turn when its Peregrine lunar lander didn’t achieve its lunar target, attributed to a glitch in a single valve within the propulsion system, a recent mission report disclosed. In a public revelation, company executives elaborated on the malfunction’s specifics and unveiled enhancements for the propulsion system of their next lunar lander, Griffin, to prevent repeat failures.
The in-depth analysis derived from a review board convened soon after the conclusion of the Peregrine mission earlier in January. This mission encountered challenges mere hours following its January 8 launch, during the initial activation of the spacecraft’s propulsion system while in orbit.
At this critical moment, the spacecraft’s fuel and oxidizer reservoirs were supposed to be pressurized with helium through the opening of two pressure control valves (PCVs). However, an unanticipated “uncontrollable” flow of helium through the second valve into the oxidizer tank was discovered, leading to an abrupt and severe over-pressurization of the tank, Astrobotic CEO John Thornton detailed in a press briefing.
This malfunction caused the tank to rupture, unleashing oxidizer across the mission’s duration, Thornton added. The failure of the problematic PCV to reseal, presumably due to a mechanical fault from “vibration-induced relaxation” among some valve internals, was determined. Evidence from telemetry data aligned with this hypothesis, further corroborated by successful replication of the failure in terrestrial tests.
Despite the continuation of the oxidizer spill, Astrobotic’s crew managed to stabilize the spacecraft, recharge its batteries, and energize its payloads. Nonetheless, the complication was decisive in the mission’s failure, culminating in the spacecraft’s re-entry to Earth’s atmosphere where it was incinerated after over ten days.
The review board, comprising 34 individuals including 26 from within Astrobotic and 8 external experts, concluded that the propulsion system’s single helium PCV fault was the likely root of the malfunction. This intense scrutiny spanned not only mission-specific data but also encompassed comprehensive flight qualification and component testing data.
In addition to uncovering the malfunction’s cause, the board traced its origins back to 2019, marking a series of events leading up to the mishap. Astrobotic’s shift in 2022 towards internalizing propulsion system development for their Griffin project, inspired by challenges encountered with external suppliers, underscored their commitment to enhanced integration and risk mitigation for their subsequent lunar ventures.
Astrobotic’s decision, albeit fraught with immediate hurdles, including component issues with the initial vendor’s propulsion elements, eventually led to switching to a different PCV supplier in August 2022. This pivot, coupled with insights from final system tests that exposed leaks in one of the PCVs, shaped the company’s risk assessment and decision-making approach in the project’s critical stages.
These investigative findings have informed the development strategies for Griffin, Astrobotic’s next venture to the moon. This encompasses a redesigned valve, additional regulatory mechanisms in the propulsion system for controlled helium flow to the fuel and oxidizer tanks, and supplementary backup latch valves for redundancy, ensuring enhanced reliability for future missions.