A critical malfunction traced back to a single valve within its propulsion unit thwarted Astrobotic’s Peregrine moon lander from accomplishing its lunar objective, a recent mission analysis disclosed on Tuesday. The firm’s executives revealed during a press briefing that this flaw has led to a valve redesign and the incorporation of extra fail-safes within the propulsion mechanism of its subsequent lunar lander, Griffin, to prevent a recurrence of this issue.
The reconsideration of the Peregrine mission was carried out by a committee formed in the mission’s aftermath in January. The mission faced difficulties mere hours following its launch on January 8, marked by the initial activation of its on-orbit propulsion mechanism.
The standard procedure was to pressurize the fuel and oxidizer reservoirs with helium, facilitated by the opening of two pressure control valves, or PCVs. However, uncontrollable helium flow through the second valve into the oxidizer tank was detected, as described by Astrobotic CEO John Thornton at the media briefing.
“The tank experienced swift and severe over-pressurization leading to its rupture and the eventual leaking of oxidizer for the duration of the mission,” he stated.
The failure of the PCV to reseal was likely the result of a mechanical breakdown, attributed to “vibration-induced relaxation” of its internal threaded components, as outlined by the investigation chair, John Horack. The anomaly’s timing and location were pinpointed through telemetry data, corroborating the autonomous sequence of the PCV’s operation and its placement within the propulsion setup. The malfunction was also successfully replicated in terrestrial tests.
Despite the continuous oxidizer leakage, the Astrobotic team managed to stabilize the spacecraft, ensure battery recharge, and maintain payload operation. However, this complication proved to be mission-critical, leading to the spacecraft’s re-entry and disintegration in Earth’s atmosphere after 10.5 days.
The 34-member review panel, composed of 26 internal and eight external individuals, assessed not just the mission data but also the pre-flight qualification and component testing data. They concluded that the malfunction was likely due to the failure of the helium PCV in the propulsion system.
A detailed sequence of the events leading up to the failure, beginning in 2019 when Astrobotic engaged an unnamed contractor for the propulsion feed system’s development, was also provided by the board. The contractor’s challenges with technical and supply chain disruptions during the COVID-19 pandemic led Astrobotic to cancel the contract in early 2022 and take over the system’s assembly in-house.
“By then, we had decided to undertake Griffin’s propulsion mechanism internally, aiming for greater vertical integration,” shared Astrobotic’s mission director Sharad Bhaskaran. “We had cultivated significant propulsion system integration expertise. This strategy also mitigated risks for the more intricate Griffin mission compared to Peregrine.”
Astrobotic engineers faced issues with the PCVs provided by the original vendor, leading to a switch to a new, unnamed PCV provider in August 2022, whose components were subsequently installed onto the lander.
Subsequent tests revealed leaks in one of the PCVs, albeit not the one that would eventually fail in orbit. The troublesome PCV was mended, and despite acknowledging the risk associated with the second valve in their risk register, the engineers believed the malfunction risk was minimal following successful final compliance tests.
Replacing the second problematic PCV was considered too invasive, requiring extensive modification to the lander, thereby nullifying the final test results and introducing new risks from disassembly and reassembly, as Bhaskaran justified the action.
Horack, reflecting on the decision-making process, found the team’s choices to be judicious throughout the mission’s planning and execution phases.
These insights have been channeled into developing the more advanced Griffin lander, slated for a lunar voyage before the close of 2025. This upcoming model features an overhauled valve design, a helium flow regulator for the propellant tanks, and additional backup latch valves to provide redundancy against PCV malfunctioning.
Compiled by Techarena.au.
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