18.03.2024

One of the last images returned from Astrobotic’s Peregrine lander was this view showing the crescent Earth as the spacecraft neared reentry. Credit: Astrobotic

THE WOODLANDS, Texas — Despite not making it to the moon, NASA and others flying payloads on Astrobotic’s Peregrine lunar lander say they still got useful data from the mission.

Peregrine launched Jan. 8 on the first flight of United Launch Alliance’s Vulcan Centaur. The spacecraft, though, suffered a propellant leak hours after launch that ruled out any chance of attempting a lunar landing. The spacecraft instead reentered a week and a half after launch.

Although Peregrine did not reach the moon, many of the payloads on board were tested during the flight. “In transit, we were going to keep most of those payloads in a survival mode,” said Dan Hendrickson, vice president of Astrobotic, during a March 11 session about the mission at the Lunar and Planetary Sciences Conference here. “But as our mission deviated, the plan deviated as well, much to the benefit of all the payloads.”

While many of the science payloads on Peregrine weren’t able to collect their intended data from the surface of the moon, they were able to be tested in space and, in some cases, perform some science.

Among them was the Linear Energy Transfer Spectrometer (LETS) instrument, which collected data about the cislunar radiation environment rather than on the lunar surface as intended. “We had to move our operations around to pull data down during the flight,” said Stuart George of NASA’s Johnson Space Center, one of the leaders of the instrument. “The instrument worked perfectly the whole time.”

Another NASA instrument, the Peregrine Ion-Trap Mass Spectrometer (PITMS), also was able to operate during the flight. It detected traces of nitric oxide and nitrogen dioxide that likely was from the lander’s oxidizer that suffered the leak. “That transient atmosphere, if you will, of the oxidizer around the spacecraft, that self-induced environment, persisted,” said Barbara Cohen, principal investigator for PITMS at NASA’s Goddard Space Flight Center.

One of the non-NASA payloads on Peregrine was Iris, a lunar rover built by students at Carnegie Mellon University. “We became a ‘RoverSat’ instead,” said Raewyn Duvall, program manager for Iris. That included testing out many of the rover’s subsystems and even turning some of its wheels to confirm they worked. “Everything that we were allowed to test worked.”

Astrobotic is currently reviewing the Peregrine mission to determine the root cause of the propellant leak and any changes that might be needed for the company’s larger Griffin lander, which is under development to launch NASA’s Volatiles Investigating Polar Exploration Rover (VIPER) mission. Hendrickson said after the presentation that the investigation was going well but did not offer a schedule for completing it.

NASA is following that investigation, said Joel Kearns, deputy associate administrator for exploration in NASA’s Science Mission Directorate, during a NASA town hall at the conference March 11. “Once we have the results of that, NASA will determine what actions we’re going to take in the future,” he said, including any specific changes for VIPER. “We will look at their failure review board findings and determine what steps we need to take for VIPER.”

Griffin and VIPER were set to launch as soon as this November, but Kearns, speaking at a Planetary Science Advisory Committee meeting March 5, said that will likely slip. “It is extremely unlikely they will fly before the end of this year,” he said, because of not just the Peregrine investigation but also other work to prepare the rover and lander for launch. He said NASA would wait to set a new date until after the Peregrine investigation is complete.

Quelle: SN

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Update: 29.08.2024

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Valve problem blamed for Peregrine lunar lander failure

One of the last images returned from Astrobotic’s Peregrine lander was this view showing the crescent Earth as the spacecraft neared reentry. Credit: Astrobotic

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.”

Quelle: SN