Orion helium leak no threat to Artemis II reentry, but will require redesign - Ars Technica

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 on 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.

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 that 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 starting 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 the 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 on 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.

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.