However, when Boeing’s CST-100 Starliner spacecraft finally set off on its maiden fully crewed flight in June of 2024, the plan was expected to be relatively simple: an eight-day sojourn at the International Space Station, after which the spacecraft would return the astronauts safely to Earth. Unfortunately, a series of glitches, starting with issues in the spacecraft’s propulsion system and the leakage of helium gas, caused the NASA astronauts Butch Wilmore and Suni Williams to dock for what would prove to be months. The spacecraft returned to Earth empty.
The next mission is Starliner-1, which will fly without any astronauts. This is expected to happen no earlier than April 2026. In this mission, cargo to the ISS along with the orbital testing of propulsion changes to its propulsion system are involved. Under the Commercial Crew Transportation Capability contract, Boeing now has four definitely contracted missions instead of six. There are two optional missions left. The contract cost is now lower by $768 million to a total of $3.732 billion.
At the focal point of this makeover is the Starliner service module propulsion system, which combines 28 reaction control system thrusters, 20 orbital maneuvering and attitude control thrusters, and four RS-88 launch abort engines. In the Crew Flight Test, five of the Starliner’s reaction control system thrusters failed due to overheating of the small Teflon poppet seals in the oxidizer valves. These seals had been deformed due to firing cycles and exposure to the direct rays of the sun. This problem was recreated at the NASA White Sands Test Facility to see if it had been remedied during the design phases.
To make matters worse, five helium leaks were discovered in the RCS helium system, one before launch and the others in orbit. The RCS relies on the helium to pressurize its propellant lines, although enough was present to enable a return, the risk involved with re-entry was not acceptable. The fact that the service module was disposable indicated that components could not be inspected after orbit, which led to the requirement for pre-flight checks on the ground before human certification.
Such propulsion problems are a symptom of a broader pattern of gaps in the verification process for the development of the Starliner spacecraft. Previous tests have already discovered problems with software glitches, corroded parts for valves, the strength of parachutes, and the use of flammable tape. There appears to be an ongoing concern from NASA’s Aerospace Safety Advisory Panel regarding “process escapes” in the testing and verification process for the development of the Starliner spacecraft by Boeing. In contrast, the competition, Crew Dragon developed by SpaceX, has completed 11 successful missions with astronauts on board with little propulsion problems, utilizing an integrated capsule design where the spacecraft’s hardware can be inspected after the mission for any problems with the propulsion system.
The cargo mission Starliner-1 will fly with only cargo and will test the “doghouse” thruster assemblies, helium plumbing, and procedures to prevent overheating of the system. This mission is considered by NASA to be a high-risk systems test, with success paving the way for a crew rotation mission by the end of 2026, while failure will question the relevance of Starliner to ISS operations prior to the ISS’s scheduled retirement in 2030. The Starliner spacecraft is being built by Boeing Company. From the strategy point of view, NASA is still following the strategy of “dissimilar redundancy” for crew transport. However, with the number of crew missions being reduced to two a year and the shortening ISS schedule, the shorted manifest further limits the operational use of Starliner.
Further delay may imply that SpaceX will become the only way to transport crews to the ISS for the rest of the life of the station. However, the risk is the same for Boeing as well. The firm already has a loss of over $2 billion on the fixed-price contract since 2016. Any changes to the design, not to mention the test flights, would further add to the loss. However, for NASA, the approval of the Starliner spacecraft is more than the agreement on the contract. The approval is necessary for the independence of the space agency within low Earth orbit. This is not a cargo transport mission, but rather a test of the functionality of the spacecraft within the market.”
