“Just one more thruster failure and we’d have lost six-degrees-of-freedom control.” That stark recollection from astronaut Butch Wilmore during Boeing’s Crew Flight Test in June 2024 encapsulates the engineering urgency behind NASA’s latest decision: Starliner-1 will launch without astronauts, carrying only cargo to the International Space Station no earlier than April 2026.
The pivot marks a major reshaping of Boeing’s role in the Commercial Crew Program. Under the original 2014 Commercial Crew Transportation Capability contract, Boeing was slated for six operational crew rotation missions following certification. Now, NASA has reduced its obligated flights to four, with two additional missions held as options. The revised plan means that, at most, three future Starliner flights will carry astronauts before the ISS retires in 2030.
The change is rooted in unresolved propulsion system anomalies from the 2024 Crew Flight Test. During approach to the ISS, numerous reaction control system thrusters in Starliner’s service module failed in rapid succession. The first two were aft-facing units, then a third and fourth eliminated forward translation capability and caused severe impairment to attitude control. Standard flight rules called for an abort, but mission control waived them, remotely resetting the thruster system to recover partial control. Post-flight analysis traced the failures to overheating of small Teflon seal components poppets within the thruster valves. Prolonged firing under direct sunlight caused the seals to deform, restricting propellant flow.
These thrusters are installed in the service module in four “doghouse” compartments, with seven RCS units in each compartment. The service module is jettisoned before reentry, which precludes recovery of failed components for post-flight inspection. Integrated firings of thrusters within a single doghouse are now underway at White Sands Test Facility to validate thermal models and explore possible design changes or operational mitigations. The CFT mission also experienced five helium leaks in the propulsion system, one that was detected pre-launch and four that developed in flight, which brought up concerns regarding propellant pressurization for critical burns.
The thruster and leak issues are part of a broader pattern of Starliner development challenges. The first uncrewed Orbital Flight Test in 2019 failed to reach the ISS due to software errors, which prompted 80 corrective actions. OFT-2 in 2022 succeeded but still experienced thruster anomalies. In 2021, corroded oxidizer valves delayed launch for months, requiring a redesign. And in 2023, Boeing discovered flammable tape on wiring harnesses and parachute components with insufficient strength margins, forcing further remediation. These “process escapes,” as NASA’s Aerospace Safety Advisory Panel termed them, highlighted weaknesses in Boeing’s systems engineering and integration discipline.
After the tragedies of Challenger and Columbia, NASA rebuilt its safety governance structure to include independent input from Technical Authorities in the domains of safety, engineering, and medicine. Russ DeLoach, Chief of Safety and Mission Assurance, underscored that the agency is “hyper-focused on the concept of combating organizational silence” to ensure that dissenting technical opinions are heard. The deliberate pace intentionally means that certification will not be hurried, despite the pressure, to restore Starliner’s crew capability.
Meanwhile, as Boeing works towards certification, SpaceX’s Crew Dragon remains a reliable method of crew transportation. Since the Demo-2 mission in 2020, Dragon has flown 12 NASA crew rotations and multiple private ones with no similar propulsion failures. The operational record of Dragon has enabled NASA to sustain uninterrupted US crew access to the ISS during Starliner’s delays.
The roster of astronauts for Starliner’s eventual first operational crew flight is uncertain. Scott Tingle, once named Starliner-1 commander, has become chief of NASA’s Astronaut Office. Mike Fincke and JAXA’s Kimiya Yui, once assigned to Starliner-1, flew on SpaceX Crew-11. Canadian astronaut Joshua Kutryk’s status remains unclear and Luke Delaney was reassigned to Crew-13. Even veteran Starliner-trained astronauts like Nicole Mann and Sunita Williams have constraints Williams could reach NASA’s limits on radiation exposure before flying another mission on Starliner. The stakes are high for Boeing. So far, it has absorbed more than $2 billion in losses on its fixed-price contract, now valued at $3.732 billion with the reduction in flights.
NASA’s objective is to have two dissimilar US crew transportation systems so that when one vehicle type is grounded, the other can continue to fly astronauts. But before Starliner can join Dragon in that role, its propulsion vulnerabilities must be resolved and it must earn certification a process now riding on the performance of an uncrewed cargo flight in 2026.
