Astrobotic's Peregrine lunar lander failed to reach the moon because of a problem with a single valve in its propulsion system, according to a mission report released Tuesday. Company executives said in a news conference that engineers have redesigned the valve and added redundancy to the propulsion system of the next lander, Griffin, to prevent the problem from happening again.
The report comes from a review board formed shortly after the Peregrine mission ended in January. The mission ran into trouble just hours after launch on Jan. 8, when engineers were powering up the spacecraft’s propulsion system for the first time in orbit.
At that point, the fuel and oxidizer tanks were supposed to be pressurized with helium when two pressure control valves, or PCVs, were opened. But helium began flowing “uncontrollably” through the second valve into the oxidizer tank, Astrobotic CEO John Thornton explained in a news conference.
“This caused a large and rapid overpressure in the tank,” he said. “Unfortunately, the tank ruptured, releasing oxidizer for the remainder of the mission.”
John Horack, chairman of the review board, said the PCV in question was unable to reseal, likely due to a mechanical failure caused by “vibration-induced loosening” between some threaded components within the valve. Telemetry data pinpointed the exact location and timing of the anomaly, which was consistent with the autonomous sequence of opening and closing the PCV and the valve positioning of the propulsion system. Engineers were also able to replicate the failure in ground tests.
While the oxidizer leak continued, the Astrobotic team was able to stabilize the spacecraft, charge its batteries, and power its payload. But the problem was ultimately fatal to the mission, and 10 and a half days later, the spacecraft returned to Earth and burned up in the atmosphere.
The 34-member review board included 26 from within the company and eight from outside. The board reviewed all data from the flight qualification campaign and component testing, as well as data collected during the mission. Ultimately, it was determined that the cause of the malfunction was actually a failure of a single helium PCV in the propulsion system.
The board also compiled a timeline of events leading up to the failure, dating back to 2019, when Astrobotic contracted with an unnamed supplier to develop the propulsion feed system. When that supplier began experiencing technical and supply chain issues due to the COVID-19 pandemic, Astrobotic decided to terminate the contract in early 2022 and complete the partially assembled feed system in-house.
“By this time, we had already decided to bring Griffin’s propulsion system in-house and had done more vertical integration,” said Sharad Bhaskaran, Astrobotic’s mission director. “We had already developed a lot of the capability to do that propulsion integration… It also took some of the risk out of going into the Griffin program, which was much more complex than Peregrine.”
However, Astrobotic engineers began experiencing problems with the original supplier’s propulsion components, specifically the PCV. In August 2022, they switched to another unnamed PCV supplier, whose valves were installed on the Lander.
During the final set of tests for the propulsion system, one of the two PCVs had a leak, but the PCV that ultimately leaked in orbit was not leaky. That PCV was normal during the test, and the leaky PCV was repaired. Bhaskaran acknowledged that the second PCV was identified as “critical in the risk register” during the test due to a leak in the first PCV, but engineers ultimately determined that the failure was low because the lander passed the final acceptance tests.
He justified his decision not to replace the second PCV by saying that it was located much further inside the spacecraft, requiring “massive surgery” on the lander, invalidating final tests and posing additional risks associated with disassembly and reassembly.
Horack says the team’s decision-making was sound from start to finish. “If you look at the team and what happened, there’s no decision that I see that would lead to a launch where I would say, ‘Hey, I think we should have done this differently.’”
These findings are already beginning to inform the development of the much larger Griffin lander, which is currently scheduled to launch to the moon before the end of 2025. In addition to redesigning the valves, engineers have also introduced regulators into the propulsion system to control the flow of helium to the fuel and oxidizer tanks, and have introduced a backup latch valve for added redundancy in case problems recur with the PCV.
