Could a single spacecraft’s propulsion system flaws reshape NASA’s crew transport strategy for the rest of the decade? That’s the question now looming large after the agency’s decision to pare Boeing’s Commercial Crew contract from six missions to four, with the next Starliner flight flying uncrewed. The move comes in the wake of the 2024 “Calamity Capsule” incident in which thruster failures and helium leaks during the Crew Flight Test forced NASA to leave astronauts Sunita Williams and Barry “Butch” Wilmore aboard the International Space Station for almost nine months, returning them on a SpaceX Crew Dragon.
The next mission, Starliner-1, targeted for no earlier than April 2026, will carry cargo rather than astronauts. Its primary role will be to validate extensive upgrades to the propulsion system and other hardware before Boeing can attempt operational crew rotations. NASA Commercial Crew Program manager Steve Stich stated, “NASA and Boeing are continuing to rigorously test the Starliner propulsion system in preparation for two potential flights next year. This modification allows NASA and Boeing to focus on safely certifying the system in 2026, execute Starliner’s first crew rotation when ready, and align our ongoing flight planning for future Starliner missions based on station’s operational needs through 2030.”
The propulsion issues that kept Starliner on the ground were serious: during the June 2024 docking attempt, several reaction control system thrusters failed in rapid succession, which could have resulted in a loss of six-degrees-of-freedom control. Mission control took the unusual step of granting a waiver from standard flight rules to remotely reset the thruster system and recover partial maneuvering capability. Post-flight analysis traced the failures to the overheating of Teflon seal components inside thruster valves that deformed under repeated firing and restricted propellant flow. Ground tests at White Sands duplicated the overheating and validated the vulnerability of the seals, leading to consideration of redesigns.
Adding to the failed thrusters were five helium leaks in the service module’s propulsion manifolds: one detected prelaunch and four that developed in orbit. Helium pressurizes propellant tanks, and leaks compromise thrust performance. Engineers suspect seal degradation from long-term propellant vapor exposure and plan to replace the material in future builds. The service module, jettisoned before reentry, cannot be recovered for direct inspection; hence, ground-based analog testing is key.
Certification for Starliner comes courtesy of the requirements laid out by NASA’s Commercial Crew Program, which demand safe and redundant systems to transport crew. Certification depends on the resolution of propulsion anomalies, redesigning the vulnerable components, and verification of the fixes during flight. The unmanned Starliner-1 would serve as its in-flight qualification, similar in purpose and function to the SpaceX Demo-2 mission in 2020, though Boeing’s timeline is far more compressed, considering the ISS is planned for deorbit in 2030.
The competitive contrast with SpaceX is dramatic. Certification of Crew Dragon was completed after a single crewed test flight, and it has since executed more than a dozen NASA crew rotations, plus private missions, at a per-seat cost of about $55 million versus an estimated $90 million for Starliner. SpaceX’s vertically integrated manufacturing and streamlined supply chain have facilitated its rapid iteration and reliability, while Boeing’s program has been afflicted by complexity in its supply chain, workforce attrition, and systemic verification gaps noted in multiple reports from the Aerospace Safety Advisory Panel.
From an engineering point of view, the propulsion architecture is considerably different: Starliner features a service module with several RCS thrusters and orbital maneuvering engines fed by hypergolic propellants pressurized by helium, parachute-assisted landings on land, while Crew Dragon uses integrated Draco thrusters for orbital maneuvering and SuperDraco abort engines with splashdown recovery at sea. Disposability of the service module complicates post-flight failure analysis; the reusable capsule of Crew Dragon allows direct inspection of flight hardware.
NASA’s requirement for “dissimilar redundancy” in crew transport-two different spacecraft designs-remains the primary strategic rationale for continuing to keep Starliner in play. Should anything happen that forces Crew Dragon to be grounded, the availability of Starliner becomes crucial. At only four contracted flights, including one uncrewed, though, Boeing’s margin for error is razor-thin. Any further delays may result in not making the operational ISS window.
The stakes are not just programmatic. Boeing has absorbed more than $2 billion in losses on the fixed-price contract, and the mission cut reduced the current value to $3.732 billion. The Starliner-1 mission will be the testing field for whether Boeing’s engineering fixes can restore sufficient confidence in the safety systems of the spacecraft and its place in the final years of ISS crew transportation.
