On Friday evening, Boeing's Starliner spacecraft touched back down at New Mexico—with no people inside. This is particularly concerning given that Starliner took off on the 5th of June with 2 astronauts, Sunita Williams and Butch Wilmore, intending on a test flight that would last a week. Instead, this has evolved into a situation where the capsule has returned unmanned 3 months later, and the two astronauts are stuck on the ISS and planning to only come home in February. So what has happened that has led to this mission ending so catastrophically, and being labeled by Space News as "NASA’s biggest human spaceflight safety crisis" in 20 years?
Background of Starliner
In 2014, NASA selected two companies, SpaceX and Boeing, as part of its Commercial Crew Program to develop spacecraft capable of transporting astronauts to the ISS. SpaceX developed a crew variant of their Dragon capsule, while Boeing worked on the CST-100 Starliner. The aim of this project was to provide NASA with an alternative to relying on Russian Soyuz capsules to transport American astronauts. Given political relations now and back then, this would have obviously been a pretty awkward agreement. While SpaceX completed Crew Dragon and started flights in 2020, Starliner was delayed for 4 years and has continued to be an engineering nuisance.
Sauer's article on Starliner's history details Boeing's prior attempted test flight. After the first one took off in 2019, engineers found that there was a software glitch that put it in the wrong orbit. This meant that it never even reached the ISS and had to return to Earth. Boeing's test flight in 2022 didn't even make it off the ground, with it being pushed back due to valves in the propulsion system being corroded. Since then they have flown some unmanned test flights successfully, but Sauer's article goes in depth into more engineering issues they've faced while preparing for the first manned flight. Despite going into it with positivity, that too went wrong.
The Flight
After having the launch date pushed back twice, Starliner finally launched on June 5th. While it initially looked positive, Lagatta's article details how NASA announced that there were 2 helium leaks shortly before it had reached orbit. By the time it reached docking, there were 5 leaks and 5 of its thrusters had shut down. 4 were restarted for successful docking, but this raised alarm bells at NASA. You may be asking, what is a helium leak? Helium in the Starliner is used for pressurising its reaction control system (RCS) thrusters and allows them to fire. Without these thrusters, Starliner will struggle to dock and more importantly, can't position itself optimally during reentry. While the cause of these helium leaks is uncertain (we'll probably find out more now the craft is on the ground), the current theories are that some seals were degraded due to exposure to propellant vapour, causing the helium leaks. In addition, the thruster problems were caused by separate internal seals being deformed by high temperatures and blocking fuel flow. These high temperatures formed because some flight control tests being ran had the RCS thrusters positioned in direct sunlight for extended periods of time. After a couple of attempts to return with Williams and WIlmore, NASA decided to take the safe route and have the capsule come home alone.
What Next?
Starliner’s return to Earth in New Mexico—three months later than expected—marks an end to a disappointing mission. Although the spacecraft landed safely, the two astronauts remain stranded on the ISS, where they are expected to stay until at least February, when a Crew Dragon capsule is scheduled to bring them home. Boeing will continue to work on the Starliner—relying on SpaceX alone isn't ideal for NASA—however this is yet another major setback and continues to pile onto the public image fiasco Boeing is facing right now. Personally, I'm glad that the astronauts are currently safe and that NASA is prioritising safety in these situations. From an engineering perspective, this mission has exposed several vulnerabilities in the Starliner that will require redesigning. The helium leaks and thruster malfunctions also show the challenges of maintaining complex systems under extreme space conditions—something most people don't really think about when evaluating the risks of space flight. Overall, I'm hoping the return flight goes well and everyone lands safely, but also that Boeing can learn from this mission's failure to make sure Starliner is as safe as possible.
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