As Boeing’s Starliner approaches its two-month mark in space, teams conducted a hot-fire test of thruster performance and helium leaks on the spacecraft over the weekend to help inform the decision on when the spacecraft will return home and whether its two NASA astronaut passengers will accompany it.
Boeing announced in a press release that the test of the Starliner’s reaction control system (RCS) thrusters was conducted Saturday afternoon while the spacecraft was docked with the International Space Station. NASA and Boeing teams also monitored the helium system for the crew flight test mission.
“Both teams were very pleased with the results,” Chloe Mehring, NASA’s Starliner flight director, said in the press release.
The spacecraft arrived at the ISS on June 6, a day after launching from Cape Canaveral Space Force Station aboard a United Launch Alliance Atlas V rocket with NASA astronauts Butch Wilmore and Suni Williams aboard. Dubbed the Crew Flight Test mission, the astronauts are participating in the spacecraft’s first human flight as part of Boeing’s efforts to have it certified for use alongside SpaceX’s Crew Dragon spacecraft to ferry astronauts to and from the ISS as part of NASA’s Commercial Crew Program.
Initial plans called for Starliner to remain docked with the ISS for only about eight days before a scheduled return flight that would take Wilmore and Williams to land at one of several desert sites in the southwestern United States.
But during their journey to the station, five of Starliner’s RCS thrusters failed and several helium leaks were identified in the spacecraft’s propulsion system, housed in the attached service module, a piece of hardware that will be jettisoned before reentry.
The Starliner was able to dock safely, however, and the valves were closed to prevent any further helium leaks. The teams were also able to restart all but one of the thrusters, albeit at reduced power.
Boeing and NASA decided to postpone any return plans while they conducted ground tests to simulate the stresses the spacecraft’s thrusters under during the trip and determine why some of them failed while delving deeper into the helium leak problem. Last week, the probable causes of both failures were revealed at a press conference, and the path to a decision on a return home was mapped out.
This included this weekend’s hot firing test.
The teams successively fired 27 of the spacecraft’s RCS thrusters for one pulse each to confirm their power. The rear-facing thrusters fired for 1.2 seconds while the others fired for 0.40 seconds, according to Boeing.
“The integrated teams between Starliner and the ISS worked extremely well together this week to finalize and safely execute the docked hot-fire sequence,” Mehring said.
Boeing said the thrusters were operating “at maximum thrust values ranging from 97 to 102 percent,” according to the statement.
The company said the helium system also remained stable and noted that an RCS oxidizer isolation valve that was not properly installed was now operating normally after opening and closing several times.
“These last few weeks have been very helpful in understanding the helium and propellant anomalies and how to address those issues for future flights,” Mark Nappi, Boeing’s vice president of commercial crew, said at a news conference last week. “That’s the real goal here, is to be able to handle future flights and gain the confidence that we needed.”
Boeing is under contract to make six trips to the ISS, but NASA revealed Friday that the first mission, Starliner-1, would take place no earlier than August 2025, giving Boeing time to make fixes to the service module based on the results of that mission.
The hot-fire test follows another conducted in the weeks since its arrival at the ISS, and paves the way for NASA to hold a flight test readiness review likely later this week.
The results of the examination will determine when Starliner will undock from the station and whether Williams and Wilmore will be on board when it returns home.
Boeing said undocking dates are available throughout August, but NASA will have to make a decision about whether to return that spacecraft home or send the Crew-8 astronauts who have been on board since March back to their Crew Dragon spacecraft to make room for the Crew-9 replacements who will fly their own Crew Dragon.
Crew-9 is currently scheduled to launch no earlier than August 18. NASA would prefer to conduct a handoff so that Crew-8 and Crew-9 are on board at the same time, which would require Starliner to vacate its parking spot since there are only two ports on the ISS capable of accommodating either Dragon or Starliner.
Steve Stich, NASA’s commercial crew program manager, said last week that Williams and Wilmore’s return to Starliner remained the preferred choice, but that alternatives had also been proposed.
“I think we’re starting to get to the final pieces of the flight logic to make sure we can get home safely, and that’s our priority right now,” Stich said. “We have contingency options. We’ve implemented them. NASA always has contingency options. We know a little bit more about what those options are, and we haven’t worked on them a lot. But we kind of know what those options are. But right now, we’re really focused on getting Butch and Suni home on Starliner.”
Originally published: July 29, 2024 at 11:42 a.m.
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