Astrobotic knew its first space mission would be rife with risks. After all, the company’s Peregrine spacecraft would attempt something never done before—landing a commercial spacecraft on the surface of the Moon.
The most hazardous part of the mission, actually landing on the Moon, would happen more than a month after Peregrine’s launch. But the robotic spacecraft never made it that far. During Peregrine’s startup sequence after separation from its United Launch Alliance Vulcan rocket, one of the spacecraft’s propellant tanks ruptured, spewing precious nitrogen tetroxide into space. The incident left Peregrine unable to land on the Moon, and it threatened to kill the spacecraft within hours of liftoff.
“What a wild adventure we were just on, not the outcome we were hoping for,” said John Thornton, CEO of Astrobotic.
Astrobotic’s control team, working out of the company’s headquarters in Pittsburgh, swung into action to save the spacecraft. The propellant leak abated, and engineers wrestled control of the spacecraft to point its solar arrays toward the Sun, allowing its battery to recharge. Over time, Peregrine’s situation stabilized, although it didn’t have enough propellant remaining to attempt a descent to the lunar surface.
Peregrine continued on a trajectory out to 250,000 miles (400,000 kilometers) from Earth, about the same distance as the Moon’s orbit. Astrobotic’s original flight plan would have taken Peregrine on one long elliptical loop around Earth, then the spacecraft would have reached the Moon during its second orbit.
On its way back toward Earth, Peregrine was on a flight path that would bring it back into the atmosphere, where it would burn up on reentry. That meant Astrobotic had a decision to make. With Peregrine stabilized, should they attempt an engine burn to divert the spacecraft away from Earth onto a trajectory that could bring it to the vicinity of the Moon? Or should Astrobotic keep Peregrine in line to reenter Earth’s atmosphere and avoid the risk of sending a crippled spacecraft out to the Moon?
Making lemonade out of lemons
This was the first time Astrobotic had flown a space mission, and its control team had much to learn. The malfunction that caused the propellant leak appears to have been with a valve that did not properly reseat during the propulsion system’s initialization sequence. This valve activated to pressurize the fuel and oxidizer tanks with helium.
When the valve didn’t reseat, it sent a “rush of helium” into the oxidizer system, Thornton said. “I describe it as a rush because it was very, very fast. “Within a little over a minute, the pressure had risen to the point in the oxidizer side that it was well beyond the proof limit of the propulsion tank. We believe at that point the tank ruptured and led to, unfortunately, a catastrophic loss of propellant … for the primary mission.”
Thornton described the glum mood of Astrobotic’s team after the propellant leak.
“We were coming from the highest high of a perfect launch and came down to the lowest low, when we found out that the spacecraft no longer had the helium and no longer had the propulsion needed to attempt the Moon landing,” he said. “What happened next, I think, was pretty remarkable and inspiring.”
In a press briefing Friday, Thornton outlined the obstacles Astrobotic’s controllers overcame to keep Peregrine alive. Without a healthy propulsion system, the spacecraft’s solar panels were not pointed at the Sun. With a few minutes to spare, one of Astrobotic’s engineers, John Shaffer, devised a solution to reorient the spacecraft to start recharging its battery.
As Peregrine’s oxidizer tank lost pressure, the leak rate slowed. At first, it looked like the spacecraft might have only hours of propellant remaining. Then, Astrobotic reported on January 15 that the leak had “practically stopped.” Mission controllers powered up the science payloads aboard the Peregrine lander, proving the instruments worked and demonstrating the spacecraft could have returned data from the lunar surface if it landed.
The small propulsive impulse from the leaking oxidizer drove Peregrine slightly off course, putting it on a course to bring it back into Earth’s atmosphere. This set up Astrobotic for a “very difficult decision,” Thornton said.
Nudging Peregrine off its collision course with Earth would have required the spacecraft to fire its main engines, and even if that worked, the lander would have needed to perform more maneuvers to get close to the Moon. A landing was still out of the question, but Thornton said there was a small chance Astrobotic could have guided Peregrine toward a flyby or impact with the Moon.
“The thing we were weighing was, ‘Should we send this back to Earth, or should we take the risk to operate it in cislunar space and see if we can send this out farther?'” Thornton said.
NASA steps in
Astrobotic asked NASA, the primary customer on the Peregrine mission, for some advice on what to do with the spacecraft. The lander carried five NASA-sponsored science instruments, and Astrobotic’s mission was the first Moon delivery NASA booked through its Commercial Lunar Payload Services (CLPS) program.
NASA set up the CLPS program in 2018 to purchase transportation services for scientific payloads to the lunar surface aboard an emerging fleet of commercial Moon landers. The space agency takes a hands-off approach with the program, allowing contractors to design, build, and fly the missions with little government oversight. These uncrewed flights are precursors to future human landing missions with NASA’s Artemis program.
According to Thornton, NASA was concerned that firing Peregrine’s engines with the oxidizer leak might cause an explosion, littering the region around the Moon with space junk.
“What they were pointing out, and what were also concerned about, was the engines and the fuel systems were not in a nominal condition,” Thornton said. “Because the oxidizer, the pressure was so high and it was in an uncontrolled state, if we burned those engines at any significant length, as the engineers were describing to me, it’s basically like an ‘oxy-acetylene torch’ that is more or less going to burn a hole through those engines.
“So we were concerned about the small but possible probability that (the risk) would be more than just missing a trajectory, more than just missing the Moon itself, it could have possible caused a catastrophic situation that could potentially create more debris,” Thornton said.
Joel Kearns, deputy associate administrator for exploration in NASA’s science mission directorate, said agency officials shared their view of the risks of sending Peregrine toward the Moon.
“Based on everything that Astrobotic had communicated very openly and transparently every step through the mission, we had told them … how we viewed the risks of going ahead and having this Earth-based entry burn-up and disposal versus extending the mission,” Kearns said.
Astrobotic took NASA’s recommendation, and the Peregrine spacecraft plunged into the atmosphere over the South Pacific Ocean on January 18. Nearly all of the spacecraft should have burned up during reentry.
Given the perilous condition of Peregrine’s propulsion system, this was the safest fate for the spacecraft. “We wanted to make sure that we protected cislunar space,” Thornton said.
Ars asked Thornton what Peregrine might have accomplished if the spacecraft steered clear of Earth and head back toward the Moon.
“To venture into that hypothetical that we did not end up doing, if, if, we were successful with that maneuver, theoretically we could have maybe made it around the Earth and potentially could have come back out to the Moon,” he said. “At that point, it would have been anybody’s guess of what could have happened next.
“Maybe we could get an impact, maybe we would have missed the Moon, maybe we could have, maybe, had enough fuel to get into lunar orbit,” Thornton said. “It’s really the hypothetical world at that point because we just don’t really know what would have happened next. But that was part of the challenge and part of the risks that we were weighing, ‘What’s the responsible way to act here?'”
Thornton said it was important to set a responsible precedent for future commercial lunar missions, since Astrobotic was first the first one from the United States.
The NASA science payloads aboard the Peregrine lander were valued at approximately $9 million, according to Kearns. NASA’s contract with Astrobotic to deliver the payloads to the Moon was worth $108 million. The agency has already paid most of that money to Astrobotic as the company achieved developmental milestones with Peregrine, but the final 10 percent of the award was contingent upon success criteria. Kearns said NASA has not yet assessed whether Astrobotic is eligible for any portion of the final payment.
NASA has awarded contracts for seven more CLPS missions in the next few years. Next will be the first flight of the Nova-C lander built by Intuitive Machines. Like Astrobotic, Intuitive Machines’ primary business focus is developing commercial Moon landers. The first Intuitive Machines mission, named IM-1, is scheduled for launch in mid-February.
Later this year, Firefly Aerospace could launch its first robotic Moon lander on a CLPS mission. Intuitive Machines also has a shot at launching a second Nova-C lander this year. Astrobotic is developing a much larger spacecraft, called Griffin, to ferry a NASA rover called VIPER to the Moon’s south pole. This mission is significantly more expensive and complex than Peregrine.
Kearns said NASA will wait to see the results from Astrobotic’s formal investigation into the problems with the Peregrine lander before making any decisions on the Griffin mission with VIPER.
“VIPER is a very visible, very sophisticated, and costly payload that’ll be brought down by CLPS, so we want to make sure we really understand the root cause and the contributing factors of what happened on Peregrine, and if we have to modify our plans for Griffin… we will,” Kearns said.
Thornton said his engineers at Astrobotic have proven they can handle the stresses of spaceflight.
“Even though we had that anomaly right out of the gate, it felt like we were so close,” he said. “That’s why I really feel confident that the next mission will be successful. We know what this anomaly is, we have the mission control team that can basically handle any stressful situation. And if we get a good spacecraft built up, I think we’re going land late this year for the VIPER program.”