WASHINGTON — Astrobotic’s Peregrine lunar lander was unable to make it to the moon because of a failure of a single valve, leading to work to redesign the valve and overall propulsion system on the company’s larger Griffin lander.
Astrobotic released Aug. 27 a report by a failure review board that examined the Peregrine Mission One flight in January. That mission suffered a propellant leak hours after launch that kept the spacecraft from attempting a lunar lander. The spacecraft instead flew through cislunar space for 10 days before reentering over the South Pacific.
The investigation concluded the leak was most likely caused when a pressure control valve (PCV) malfunctioned, allowing the uncontrolled flow of helium pressurant into the spacecraft’s oxidizer tank, rupturing it. The valve, designated PCV2, had worked normally in prelaunch testing but failed after launch.
The valve lost its ability to seal due to “vibration-induced relaxation” in threaded components that caused a mechanical failure in the valve, said John Horack, the Ohio State University professor who chaired the review board, at a briefing about the report.
“If you shake it sufficiently, you can get some changes in the mechanical configuration that will prevent the valve sealing. It’s pretty much no different than when your sink starts to drip,” he said.
As part of the investigation, engineers took a spare PCV and put it through shock and vibration environments like that experienced by the valve on the spacecraft. “We then put helium on it and after a moderate, small, number of cycles, the valve leaked. You could hear it leak from about four feet away,” he said. The report noted the leak rates in those tests were similar to those observed on the spacecraft.
The valve leak came after several twists and turns in the development of Peregrine’s propulsion system. Astrobotic initially decided in 2019 to outsource the development of the propulsion feed system to a supplier, but that company encountered supply chain problems after the pandemic that led Astrobotic to bring that work in-house in early 2022.
Astrobotic then experienced problems with the original PCVs on that system, and it decided in August 2022 to switch vendors. While the oxidizer valve, PCV2, from that new vendor passed acceptance tests, a similar one on a line to pressurize the fuel tank, PCV1, experienced leaks. Astrobotic repaired PCV1 and found it worked normally. The company then put the spacecraft through a series of environmental tests, including vibration and acoustics.
“We still carried PCV2 as a risk” after those prelaunch tests, said Sharad Bhaskaran, Peregrine Mission One director at Astrobotic, because of the repairs to PCV1. The company elected not to make any preemptive repairs to PCV2 because that valve was not leaking and also because its location in the spacecraft was much harder to access.
“To access it to do repairs or replace it would have required extensive surgery on the spacecraft,” he said, and in the process invalidate the just-completed environmental tests. “That, along with the risk of doing some damage if we had de-integrated and reassembled the spacecraft, led us to the conclusion that it was best to proceed to the next stage of the program and not to replace PCV2.”
Horack said the review board did not fault the company for that decision. “I can’t see any decisions made in the flow leading up to the launch where I would have said, ‘Hey, I think you should have done this differently,’” he said. “Those decisions were pretty sound. I think the decision-making of the team was very good.”
Lessons learned for Griffin
Astrobotic is incorporating technical and other changes from Peregrine into its larger Griffin lunar lander, which is set to launch by the end of 2025. Steve Clarke, vice president of landers and spacecraft at Astrobotic, said the company is working with the valve vendor, which the company declined to name, to redesign the valve.
Griffin’s propulsion system will also have a regulator to control the flow of helium used to pressurize the tank as well as backup latch valves should the redesigned PCVs malfunction. “If we did see the same failure mechanism on the pressure control valves, the latch valve would also be a way to control the flow into the oxidizer and fuel tanks,” he said.
Astrobotic is also incorporating other corrective and preventative actions that stemmed from the Peregrine mission. Peregrine suffered 24 inflight anomalies beyond the valve problem, eight of which were deemed “mission critical” but were resolved. Bhaskaran those problems included issues with flight software and guidance, navigation and control systems, as well as one with NASA’s Deep Space Network used for communicating with Peregrine.
“Those were resolved in real time by the flight control team,” he said. “All those lessons learned from those have been infused into GM1 as well.” GM1 is the company’s designation for Griffin Mission One.
That mission was to carry NASA’s Volatiles Investigating Polar Exploration Rover (VIPER) to the south polar region of the moon, but NASA announced in July it was canceling VIPER because of cost and schedule overruns despite the fact that the rover is assembled and going through environmental testing. NASA is retaining the Commercial Lunar Payload Services (CLPS) task order it awarded to Astrobotic for that mission, with plans to replace VIPER with other payloads or ballast.
John Thornton, chief executive of Astrobotic, said in the call that there are a few smaller payloads on GM1 that are still flying, including a small CubeRover the company developed as well as from NASA, ESA and an undisclosed customer.
“We’ve had dozens of conversations with folks that want to fly on Griffin. Some of those are more advanced than others,” he said. “Now that we have the extra payload capacity, we are in conversations with multiple parties.”
He and other company executives said they were optimistic about the prospects for Griffin making a successful landing despite the failure of Peregrine to even attempt a landing. Peregrine’s mission allowed the company to gain flight heritage on many subsystems that will be used on Griffin. The mission also gave company personnel experience in operating a spacecraft and dealing with anomalies.
Thornton added that the CLPS program’s approach to working with new lander companies at price points far less than traditional government missions required a greater acceptance of risk. “We’re trying to do a mission at a price point that has never been possible before, and as such we have decisions on where to focus and how quickly we can get to launch,” he said.
“I think we got really, really close” with Peregrine, he said. “I’m very confident that Griffin is going to hit the right balance and we’re going to stick that landing.”
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