Starliner will return from the ISS uncrewed
Boeing’s CST-100 Starliner will return from the International Space Station (ISS) in September without astronauts, reports SpaceNews. NASA has decided against bringing back the astronauts who launched in June due to thruster issues that present significant risks.
NASA's Decision and Rationale
NASA announced on August 24 that astronauts Butch Wilmore and Suni Williams will extend their stay on the ISS until February. Starliner will fly back uncrewed in early September. Agency officials made this call after identifying issues with the reaction control system thrusters that malfunctioned during Starliner’s June approach to the ISS.
Officials discovered that they lacked complete confidence regarding the thrusters’ performance. "That uncertainty remains in our understanding in the physics going on in the thrusters," stated Jim Free, NASA associate administrator. Testing conducted at NASA's White Sands Test Facility replicated the loss of thruster performance caused by a heated Teflon seal. This raised concerns about the mission’s critical thruster burns required for undocking and returning to Earth.
Evaluating Risks and Safety
High uncertainty regarding the thrusters led NASA to prioritize crew safety. Steve Stich, NASA’s commercial crew program manager, explained the difficult choice of returning Starliner uncrewed. "There was just too much risk for the crew," Tinder added that testing revealed unpredictable thruster behavior on return. It became apparent to Ken Bowersox, NASA associate administrator for space operations, that crew return was infeasible only in the last moments of decision-making.
Bowersox emphasized that all NASA representatives unanimously supported this decision. Boeing was agreeable to both uncrewed and crewed options. According to Bowersox, "They believe in their vehicle and they’d be willing to bring a crew home on it."
Moving Forward with the Mission
NASA plans an alternative strategy. Starliner will undock from the ISS uncrewed and will land at White Sands or another southwestern location in the U.S. Crew-9, scheduled for launch no earlier than September 24, will take two of its originally assigned crew, making room for Williams and Wilmore. The Crew Dragon spacecraft is set to return in February 2024.
Norm Knight, director of NASA’s flight operations, confirmed that decisions on the final crew for Crew-9 will be publicized once finalized. Both Wilmore and Williams are prepared for a longer stay, having undergone recent refresher training. Their contributions to the ongoing work at the ISS have been significant.
Modifications for the Return
Changes to Starliner’s departure sequence are underway. Stich stated that modifications would help it separate from the ISS promptly. Additionally, the spacecraft's software configurations will adapt to account for the absence of astronauts during docking. NASA has yet to confirm a precise return date, beyond early September.
Uncertain Future for Starliner
The timeline for future flights of Starliner remains undetermined. Post-uncrewed mission evaluations will guide decisions necessary for the next phases. Factors will influence whether another crewed test flight is required prior to certification for ISS crew rotation missions.
Stich noted, "I don’t think we have decided on the path yet of another crewed flight test." Bowersox added that various options exist for moving forward.
There has been speculation about Boeing’s commitment amid reported losses of $1.6 billion. However, NASA Administrator Bill Nelson received reassurances from Boeing’s leadership that the Starliner program will continue.
"I expect that Starliner will fly again with astronauts aboard," he assured, ending his statement with certainty: "100%." The focus remains on ensuring crew and spacecraft safety as preparations for a safe return continue.
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