Apart from pesky issues with the spacecraft’s toilet and waste disposal system, most of the Artemis II mission has proceeded like clockwork. NASA has made few changes to the flight plan since the launch of the lunar flyby mission April 1.
But ground controllers revamped the timeline Wednesday as the Artemis II astronauts zoomed toward Earth after a close encounter with the Moon earlier this week. The four astronauts were supposed to take manual control of their Orion spacecraft, named Integrity, for a piloting demonstration Wednesday night.
Instead, mission managers canceled the demo to make time for an additional test of the ship’s propulsion system. The goal was to gather data on a “small leak” of helium gas, which Orion uses to push propellant through a series of tanks and pipes to feed the spacecraft’s rocket engines, said Jeff Radigan, NASA’s lead flight director for the Artemis II mission.
The spacecraft burns hydrazine fuel mixed with an oxidizer, nitrogen tetroxide, to power its main engine and thrusters for in-space maneuvers. The leak on Artemis II is in the helium pressure supply to the oxidizer side.
“The leak is not to space. It’s internal to the system across some of our valves, and we really need to characterize that to see what, if any, modifications we might need to make in the future,” Radigan said.
The valves are inside the European-built service module, which the Orion spacecraft will jettison just before reentering the atmosphere Friday evening. The Orion crew module will guide astronauts Reid Wiseman, Victor Glover, Christina Koch, and Jeremy Hansen to a safe splashdown in the Pacific Ocean. The service module will burn up in the atmosphere.
Plenty of margin
The helium leak has not affected the propulsion system’s performance so far. “All of our burns have performed nominally,” Radigan said.
Orion’s trajectory is so close to preflight predictions that NASA has canceled some of the mission’s course correction burns. The midcourse burns that have occurred were all low-impulse maneuvers using the service module’s smaller jets, which don’t require the helium system to recharge pressure.
Amit Kshatriya, NASA’s associate administrator, said mission managers were aware the Orion spacecraft had a “low leak rate” of helium before launch. Engineers also observed a helium leak during the unpiloted flight of the Orion spacecraft on the Artemis I mission in 2022.
Officials decided to proceed with the launch because the spacecraft did not need the full capability of its propulsion system on Artemis II, which followed a “free return trajectory” using the Moon’s gravity to slingshot the capsule back to Earth. This mission required no complex maneuvers to enter orbit around the Moon.
As of Wednesday, nearly 80 percent of the way through the Artemis II mission, the spacecraft had consumed just 40 percent of its fuel. “Clearly, we had put a lot of margin into this mission to make sure we could fly it properly,” said Debbie Korth, NASA’s deputy Orion program manager.
The only burn of the mission to use the service module’s larger main engine was the trans-lunar injection maneuver, or TLI burn, on the second day of the flight. This engine firing propelled the Orion spacecraft out of Earth orbit on a path around the Moon. That’s when the ground teams noticed the helium leak rate start to rise.
Speaking with reporters Thursday, NASA officials said the leak is not a concern for the mission’s return to Earth because the Orion crew module has an independent set of tanks, valves, and thrusters to steer the spacecraft through reentry. The leaky valves will be discarded with the rest of the service module around 20 minutes before Artemis II hits the atmosphere.
But unlike crew module, the service module won’t be recovered. This means engineers won’t have a chance to inspect the valves, so Mission Control ran the propulsion system through a series of checks Wednesday, in lieu of the manual piloting demo. Officials wanted to assess how thermal effects from flying the spacecraft in different orientations—such as pointing toward or away from the Sun—might affect the leak, according to Branelle Rodriguez, NASA’s Orion vehicle manager for the Artemis II mission.
Production risk
Artemis II is, first and foremost, a test flight. It is only the second time an Orion spacecraft has flown to deep space, and the first time it has carried humans. The primary goal of the mission is to learn about the spacecraft’s performance.
“We knew that we have leaky valves to begin with, and we want to make sure that we’re characterizing that leak rate as well as we can,” said Kshatriya, a former NASA flight director. “The leak rate we saw in flight is now an order of magnitude higher than what we saw on the ground. It’s still acceptable, but that will lead us to probably an extensive redesign of that valve system.”
The next flight of an Orion spacecraft will be on the Artemis III mission. Under a new plan announced earlier this year, Artemis III will not travel to the Moon but will fly closer to Earth, either in low-Earth orbit or to a somewhat higher altitude. There, the Orion spacecraft will rendezvous with one or both commercial lunar landers selected by NASA for future voyages to the Moon’s surface. The tests in Earth orbit will pave the way for Artemis IV, NASA’s first attempt to put humans on the lunar surface since 1972.
Artemis IV is when Kshatriya said NASA must have new helium valves ready to go. “I don’t need those valves to hold pressure in the same way for a LEO [low-Earth orbit] orbiting mission, but for a lunar orbit mission, I do.”
NASA’s schedule currently puts the launch of Artemis III in 2027 and Artemis IV in 2028. Kshatriya said he was confident NASA, working the European Space Agency and Airbus, which builds the service module, will be able to fix the valve problem in time for Artemis IV. Manufacturing of the Artemis IV service module is largely complete.
“I’m pretty sure we’re going to need to, at a minimum, tweak the design to prevent the leak rate that we have, if not fundamentally change the way the valve works,” he said.
Valves are a common bugaboo on rockets and spacecraft. Nearly every US human spaceflight program has dealt with malfunctioning or leaky valves. Boeing’s Starliner crew capsule suffered helium leaks in its propulsion system, along with other issues, during a test flight to the International Space Station in 2024. Helium valves on the Space Launch System rocket had to be replaced in the run-up to the Artemis I and Artemis II launches. SpaceX, too, has scrubbed launches due to valve problems. The list goes on.
“There are a lot of options for how to take care of this problem,” Kshatriya said of the issue on the Orion spacecraft. “If anything, I’d characterize it as a production redesign risk for the Artemis IV mission, which I think we can get in front of, and which is why we put so much attention on it during this mission to make sure [we understand] what we’re seeing.”
The big lesson NASA learned on Artemis I involved the capsule’s heat shield. The ablative thermal barrier burned away unevenly as the craft reentered the atmosphere, but Orion still made it to a safe, on-target splashdown. NASA officials said they are confident the heat shield will hold up on Artemis II after adjusting the path Orion will take through the upper atmosphere. A new heat shield design will debut on Artemis III.
NASA engineers spent two years investigating the heat shield issue after Artemis I. Kshatriya does not expect the valve redesign to take as long.
“It’s not a safety of flight, safety of crew, must-work function like the heat shield investigation sent us down,” he said. “It’s going to take work to get it right, but it’s not of that magnitude.”
