The investigation pinpointed the core problem: the service module's reaction control thrusters — small engines used to steer the spacecraft — were operating outside the conditions they had been qualified for, which led to the loss of control experienced during the flight. Through extensive ground testing and analysis, NASA and Boeing determined that the thruster performance issues stemmed from a combination of factors, including the thermal environment the thrusters experienced and features inherent in their design.

The fixes

Boeing has already made thermal modifications to the service module, which NASA will evaluate for improved performance on Starliner-1. The two organizations have also jointly decided to pursue an additional thruster valve design change as part of the push toward certification and future crewed flights.

That valve modification targets a specific failure mode: poppet seal extrusion, a deformation of the small seals inside the valves that adversely affected thruster performance. Engineers will complete the change after the uncrewed flight.

Boeing will implement other upgrades across the spacecraft as well. These include new crew module thrusters, new batteries, and minor modifications to the parachute system, all intended to improve performance and reliability in support of certification.

The uncrewed Starliner-1 mission will verify the improved thermal environments, collect the performance data needed to formally qualify the propulsion system, and identify any residual risk before astronauts fly again.

"Starliner's next flight is a critical step on the path to achieving full system certification and ensuring a sustained human presence in low Earth orbit," said Dana Weigel, manager of NASA's Low Earth Orbit Program. "With the safety of our space station crew and the public as our highest priority, we will test Starliner's propulsion system through targeted demonstration objectives and disciplined operational controls. These steps are essential to validating Starliner's thermal performance which is a key element for the certification."

Why NASA is sticking with Starliner

NASA's commercial crew program has always aimed to maintain more than one U.S. option for carrying astronauts to orbit, reducing dependence on any single provider. Isaacman framed the decision in historical terms.

"We are living through the most exciting era of space exploration since Apollo," he said. "As this domain continues to open, there will be growing demand for launch vehicles, transfer stages, landers, and, of course, spacecraft that carry astronauts. NASA has been committed to having multiple crew transportation options since the beginning of the Commercial Crew Program. We have worked closely with Boeing to address the issues identified on previous Starliner flights, and we intend to see this vehicle return to flight in support of the International Space Station and future commercial destinations."

The stakes extend beyond a single spacecraft. NASA sees a second operational crew vehicle as essential for responsibly concluding space station operations, transitioning to commercially owned stations, and expanding commercial access to space.

The timeline is ambitious, and the schedule — like the 2028 crewed-flight target — remains a plan rather than a guarantee. Much depends on what the uncrewed Starliner-1 flight reveals about the fixes now in place. But with 61 recommendations from the investigation in hand and a defined sequence of test flights, modifications, and certification work ahead, Starliner now has its clearest path yet back to carrying astronauts.