Astrobotic’s lander didn’t make it to the Moon because of a failed valve

Seven months after its first lunar lander fell short of reaching the Moon, Astrobotic announced Tuesday that the spacecraft was stricken by a valve failure that caused a propellant tank to burst in orbit. The company's next landing attempt, using a much larger spacecraft, will include fixes to prevent a similar failure.

Astrobotic's first Peregrine lander, which the company called Peregrine Mission One, launched January 8 aboard United Launch Alliance's first Vulcan rocket. But soon after separating from the rocket in space, the lander ran into trouble as it stepped through an activation sequence to begin priming its propulsion system.

A review board determined "the most likely cause of the malfunction was a failure of a single helium Pressure Control Calve called a PCV—Pressure Control Valve 2, within the propulsion system," said John Horack, a space industry veteran and professor of aerospace and mechanical engineering at Ohio State University.

Helium was supposed to pressurize Peregrine's propulsion system and force fuel and oxidizer from the lander's onboard storage tanks into the spacecraft's small rocket engines to combust and generate thrust.

"PCV2 suffered a loss of seal capability that was most likely due to a mechanical failure in the valve caused by vibration-induced relaxation between some threaded components that are inside the valve, so a failure deep inside the valve itself," said Horack, who chaired Astrobotic's investigation into the failure of the Peregrine lander.

It didn't take long for the valve malfunction to have catastrophic consequences for Astrobotic's Peregrine lunar lander, which was attempting to become the first US spacecraft since 1972 to achieve a soft landing on the Moon.

"Upon actuating, opening, and closing the PCV2, helium began to flow uncontrollably into the oxidizer tank, and that caused a significant and rapid over-pressurization of the tank," said John Thornton, Astrobotic's CEO. "Unfortunately, the tank then ruptured and subsequently leaked oxidizer for the remainder of the mission.”

Astrobotic's ground controllers, working out of a control center at the company's headquarters in Pittsburgh, acted quickly to stabilize the situation on the spacecraft. The lander's engines used hydrazine fuel mixed with nitrogen tetroxide to generate thrust, but with its diminished supply of nitrogen tetroxide, Peregrine was unable to maneuver into orbit around the Moon and attempt a landing.

But the company kept the lander alive, and ground teams were able to make small adjustments to ensure Peregrine's solar panels pointed toward the Sun to produce power as it arced on a loop that reached approximately the distance of the Moon. Ten-and-a-half days after launch, Earth's gravity pulled it back into the atmosphere, and it burned up over the remote Pacific Ocean.

Astrobotic developed and built the Peregrine lander under contract to NASA, which awarded the company a $108 million contract to deliver a suite of government-sponsored science payloads to the lunar surface. Peregrine Mission One was the first mission launched under the umbrella of NASA's Commercial Lunar Payload Services (CLPS) program, which buys transportation from commercial vendors for science payloads heading to the Moon.

Going to the Moon on a budget

It turns out Astrobotic officials were aware of the risk of a pressure control valve failing on the Peregrine spacecraft. The lander had two of these valves, one controlling the flow of helium into the fuel tank, and another into the oxidizer tank. During ground testing before the mission, the pressure control valve on the fuel side started leaking, so engineers swapped it out for a new one. The similar valve on the oxidizer side, which ended up failing in space, showed no problems during ground tests, according to Sharad Bhaskaran, Astrobotic's mission director for Peregrine Mission One.

Although the pressure control valve on the oxidizer side was the same design, Astrobotic decided not to replace it because doing so would have required disassembling large portions of the Peregrine lander, further delaying the mission's launch, which was already running several years behind schedule.

Tests of a spare pressure control valve that were conducted following the Peregrine mission confirmed it could leak after engineers subjected it to vibrations like those it would experience during a rocket launch.

“You’ve got a threaded component inside the valve," Horack said. "So you can think about a screw and a washer, or any threaded component. And if you shake it sufficiently, you can get some changes in the mechanical configuration that will prevent the valve from seating. And it's pretty much no different than when your sink starts to drip in your kitchen. Water gets through the seal and comes out the other side. In this case, it’s helium and it's high pressure, so it's much harder to confine."

Astrobotic did not identify the third-party vendor who supplied the pressure control valve, but officials said the company is working with its supplier to redesign the component. "It is slightly different than the actual valve that flew on Peregrine, the same vendor, but we worked closely with them to redesign the internal workings," said Steve Clarke, Astrobotic's vice president of landers and spacecraft.

Astrobotic's next lander, named Griffin, is larger and more complex than Peregrine. It will use the redesigned pressure control valves, and Astrobotic will install pressure regulators and so-called latch valves in the helium system on Griffin. These new components would control the flow of helium into the propellant tanks in the event of a similar pressure control valve failure on Astrobotic's next mission, officials said Tuesday.

"We’ve got increased reliability now in the system to mitigate against that single point failure," Clarke said.

Accepting risk

One of the key tenets of NASA's CLPS program is to foster the development of a new commercial industry for transporting instruments and cargo to the Moon. These CLPS missions are precursors to future human lunar landings with the Artemis program, and CLPS contractors are trying to reach the Moon for a fraction of the cost of a typical NASA mission.

Thornton, Astrobotic's CEO, said the company had to make "tough decisions" on the Peregrine mission to keep costs down. NASA set up the CLPS program to use firm fixed price contracts, similar to the contracts the agency uses for commercial crew and cargo services for the International Space Station. This puts Astrobotic and the other CLPS companies on the hook for any cost overruns.

But unlike those programs, NASA didn't offer any of the CLPS contractors up-front money to develop their spacecraft.

"We do have to keep it in context that this is not a multibillion-dollar mission," Thornton said. "These are the first missions. It’s a little bit like the first launch of a new launch vehicle in a commercial paradigm. How many times have we seen a first launch fail? It’s part of the development cycle. It’s part of how we learn. It’s part of how we get better as an industry."

NASA officials have said they're willing to accept risk on the CLPS program. When the agency set up the program in 2018, officials used the sports analogy of taking "shots on goal" for the approach they wanted to take with CLPS.

Intuitive Machines, a Houston-based company, launched the second CLPS mission a month after Astrobotic's failed Peregrine mission. Their Nova-C lander touched down on the Moon on February 22, marking the first successful controlled lunar landing by a US spacecraft in more than 51 years.

Astrobotic currently has one more CLPS contract to use the Griffin lander. NASA originally contracted with Astrobotic to use Griffin to deliver a half-ton rover named VIPER to the Moon's south polar region. But NASA canceled the VIPER rover project in July after it ran over budget and behind schedule. NASA is soliciting ideas from US companies to take over the VIPER rover, which is fully assembled but in need of testing, if the companies can afford to pay the remaining costs to get it to the launch pad.

NASA is keeping its $323 million contract with Astrobotic for the Griffin lander mission, which is now slated to launch in late 2025, but the agency won't have any significant science payloads on the spacecraft. Thornton said Astrobotic is seeking opportunities to fill some of the Griffin lander's excess capacity with payloads from other customers, but time is short, with a launch scheduled for next year.

NASA will provide Astrobotic with a mass simulator to maintain the weight and balance of the Griffin lander without VIPER. The space agency is also flying a laser retroreflector array on Griffin, and Astrobotic will use the mission to deploy its own privately-developed small lunar rover, a fraction of the size of VIPER, on the Moon.

Joel Kearns, deputy associate administrator for exploration in NASA's science directorate, told reporters last month that he wants to see Astrobotic demonstrate the Griffin lander because it can deliver heavier cargo to the lunar surface than most other CLPS providers. Astrobotic says Griffin can deliver nearly 1,400 pounds (625 kilograms) of payload mass to the lunar surface, while Peregrine has a payload capacity of up to 220 pounds (100 kilograms).

Astrobotic doesn't have any more missions on the books with its smaller Peregrine lander, but Bhaskaran said the Peregrine design could be repurposed as a tug or a spacecraft platform for applications other than lunar landings.

Other important systems on the Peregrine lander performed well over the craft's 10-and-a-half days of operations. All of the other anomalies on the spacecraft were either resolved in real-time by Astrobotic's ground team, or were not significant, company officials said.

“I think the decisions that were made at each point in time were sound engineering decisions and sound programmatic decisions," Horack said. "If you're going to ask me what I wish we had, I wish we had a more robust design of the valve. Sometimes hardware just fails."

"We’re trying to do a mission at a price point that has never been possible before, and as such, we have to make decisions on where to focus and how quickly we can get to launch, and we’re trying to balance that," Thornton said. "And I think we got really, really close. I’m very confident that with Griffin, we’re going to hit the right balance, and we’re going to stick that landing and be ultimately successful.”