With Boeing’s Starliner approaching its two-month stay in space, teams spent the weekend conducting high-temperature burn tests of the spacecraft’s thruster performance and helium leaks to help determine when the spacecraft will return and whether it will bring two NASA astronauts aboard.
A test of Starliner’s Reaction Control System (RCS) thrusters was conducted Saturday afternoon while the spacecraft was docked to the International Space Station, Boeing said in a press release. NASA and Boeing teams also monitored the crew flight test mission’s helium system.
“Both teams are very pleased with the results,” Chloe Mehring, NASA’s Starliner flight director, said in a press release.
The spacecraft arrived at the ISS on June 6, a day after it launched aboard a United Launch Alliance Atlas V rocket from Cape Canaveral Space Command Station carrying NASA astronauts Butch Wilmore and Suni Williams. The spacecraft, called the Crew Flight Test Mission, is making its first crewed flight as part of Boeing’s efforts to gain certification to transport astronauts to and from the ISS along with SpaceX’s Crew Dragon spacecraft as part of NASA’s Commercial Crew Program.
The original plan was for Starliner to dock with the ISS for only about eight days, then land with Wilmore and Williams in a desert area in the southwestern US.
However, during the journey to the space station, five of Starliner’s RCS thrusters failed and the spacecraft also experienced several helium leaks in its propulsion system, hardware housed in an attached service module that is scheduled to be separated before re-entry.
However, the Starliner was safely docked and the valves were closed, stopping any further helium leakage, and the team also managed to bring all but one of the thrusters back online, albeit at a reduced power.
Boeing and NASA decided to postpone the return flight while simulating the stress the spacecraft’s thrusters would have experienced during flight in ground tests to determine why some of the thrusters had failed and to further investigate the helium leak problem. Both possible causes were revealed at a press conference last week, setting the stage for a decision on the return flight.
This included high temperature fire testing this weekend.
To check that power, the team sequentially fired a pulse of each of the spacecraft’s 27 RCS thrusters. The rearward-facing thrusters fired for 1.2 seconds, and the remaining thrusters fired for 0.40 seconds, according to Boeing.
“The Starliner and ISS integration teams worked extremely well together this week to finalize and safely execute the docking hot fire sequence,” Mehring said.
Boeing said in a statement that the thrusters “operated between 97 and 102 percent of their peak thrust rating.”
The company said the helium system also remained stable and that the RCS oxidizer shut-off valve, which was not fully installed, was now operating normally after opening and closing several times.
“The last few weeks have been extremely helpful in understanding the helium and thruster anomalies and how to address those issues on future flights,” Mark Nappi, Boeing’s vice president of commercial crewing, said at a press conference last week. “Addressing future flights and gaining the confidence we need was really the goal here.”
Boeing is under contract for six flights to the ISS, but NASA said Friday that the first mission, Starliner 1, won’t occur until August 2025 at the earliest, which will give Boeing time to make modifications to the service module based on findings from this mission.
The high-temperature combustion test follows tests conducted in the weeks following the spacecraft’s arrival at the ISS and will pave the way for a flight test readiness review, likely to be conducted by NASA later this week.
The results of the investigation will determine when Starliner will detach from the station and whether Williams and Wilmore will be on board for the repatriation flight.
Boeing said the undocking date is set for sometime in August, but NASA must decide whether to return the spacecraft or bring home the Crew 8 astronauts, who have been aboard the Crew Dragon spacecraft since March, to make room for Crew 9’s replacement crew to fly on their own Crew Dragon.
Crew 9’s flight is currently scheduled to begin no earlier than Aug. 18. NASA would prefer a handover with Crew 8 and Crew 9 on board at the same time, but the ISS only has two ports that can dock either Dragon or Starliner, so the Starliner would need to clear a parking spot.
Steve Stich, NASA’s commercial crew program manager, said last week that returning Williams and Wilmore aboard Starliner remains the preferred option, but alternatives are also being considered.
“I think we’re getting close to finalizing the basis for the flight to make sure we can get back safely, and that’s our main focus right now,” Stich said. “We have an emergency plan, and we’ve put it into action. NASA always has an emergency plan, and we kind of know what it is, but we haven’t worked on it much yet, but we have a good idea of what it is. But right now we’re really focused on getting Butch and Suni home on Starliner.”
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