Independent explainer. Starliner.net is an independent space publication. We are not Boeing, we are not NASA, and nothing on this page is an official statement from either. For official information, use NASA's Commercial Crew pages and Boeing's own Starliner pages.
Boeing's CST-100 Starliner is one of the two crew capsules NASA paid to develop under its Commercial Crew Program. Its first and so far only crewed flight, the Crew Flight Test (CFT), launched on 5 June 2024 with NASA astronauts Butch Wilmore and Suni Williams. Thruster failures and helium leaks led NASA to send the capsule home empty in September 2024, and the two astronauts returned on a SpaceX Crew Dragon in March 2025. This page sets out what Starliner is, what happened, and what has been announced since.
What Starliner Is
Starliner is a capsule-shaped spacecraft built to carry crew and cargo between Earth and low Earth orbit, primarily to the International Space Station. It has two parts:
- The crew module — the pressurised capsule, about 4.6 m in diameter, designed to seat up to seven people (NASA missions plan for four astronauts plus cargo). Boeing designed it to be reused up to ten times. Unlike Crew Dragon, which splashes down at sea, Starliner lands on land under parachutes, with airbags cushioning the touchdown; White Sands Space Harbor in New Mexico has been the landing site for every flight so far.
- The service module — an unpressurised, expendable section carrying propellant, power, radiators and most of the thrusters: four launch-abort engines, twenty orbital manoeuvring and attitude control (OMAC) thrusters and twenty-eight smaller reaction control system (RCS) thrusters, grouped in four "doghouse" pods. It is discarded before re-entry.
Starliner launches on United Launch Alliance's Atlas V in its N22 configuration (no payload fairing, two solid boosters, and a dual-engine Centaur upper stage), from Space Launch Complex 41 at Cape Canaveral.
Why NASA Wanted Two Capsules
After the Space Shuttle retired in 2011, the only way to get astronauts to the ISS was to buy Soyuz seats from Russia. In September 2014 NASA awarded fixed-price Commercial Crew Transportation Capability contracts to both Boeing (about $4.2 billion) and SpaceX (about $2.6 billion). The idea was dissimilar redundancy: two independent vehicles on two different rockets, so a grounding of one would not leave the station without crew access. SpaceX's Crew Dragon flew its crewed test (Demo-2) in May 2020 and has been flying operational crews since November 2020. Starliner took far longer.
Starliner Timeline
- September 2014 — NASA selects Boeing and SpaceX for Commercial Crew contracts.
- 4 November 2019 — Pad abort test at White Sands. The capsule landed safely, but only two of its three main parachutes deployed because a rigging pin had not been properly connected.
- 20–22 December 2019 — Orbital Flight Test (OFT), uncrewed. A mission elapsed timer error put the spacecraft in the wrong orbit and it could not reach the ISS. It landed at White Sands two days later. Reviews found further software problems, and Boeing chose to repeat the flight at its own expense.
- August 2021 — The repeat flight, OFT-2, was called off on the pad when several oxidiser isolation valves in the service module would not open. The spacecraft went back to the factory.
- 19–25 May 2022 — OFT-2 flies, docks with the ISS and lands at White Sands. A few thrusters failed during the flight, an early hint of later problems.
- June 2023 — The crewed test is delayed again after problems are found with parachute "soft links" and with flammable tape wrapped around wiring in the cabin.
- May–June 2024 — Launch attempts on 6 May and 1 June are scrubbed (an Atlas V valve issue, then a ground-computer fault). A small helium leak in the service module is assessed and accepted before launch.
- 5 June 2024 — The Crew Flight Test launches with Butch Wilmore (commander) and Suni Williams (pilot).
- 6 June 2024 — Several RCS thrusters drop offline during the approach to the station. Most are recovered and Starliner docks; more helium leaks are found.
- 24 August 2024 — After weeks of ground testing, NASA decides to bring Starliner home without crew. Wilmore and Williams will stay on the ISS and return on a Crew Dragon.
- 6–7 September 2024 — Starliner undocks on the evening of 6 September (US Eastern time) and lands uncrewed at White Sands just after midnight Eastern time on 7 September (late on 6 September local time).
- 28 September 2024 — SpaceX Crew-9 launches with only two people aboard, Nick Hague and Roscosmos cosmonaut Aleksandr Gorbunov, leaving two seats for Wilmore and Williams.
- 18 March 2025 — Wilmore and Williams splash down off Florida aboard the Crew-9 Dragon. They were in space for about 286 days on a mission that had been planned to last about eight.
- November 2025 — NASA announces that the Starliner contract has been changed. The next flight, Starliner-1, is to carry cargo but no crew to the ISS, with a target of no earlier than April 2026. The change was reported to reduce the number of flights NASA has committed to buy from six to four, with later flights depending on certification.
What Went Wrong on the Crew Flight Test
The thrusters
During rendezvous, Starliner fires its small aft-facing RCS thrusters many times in quick succession. On CFT, five of them were automatically switched off by the flight software when their performance fell outside limits. Four were brought back before docking. Ground tests later run at NASA's White Sands Test Facility pointed to heat: repeated firing inside the enclosed doghouse pods heated Teflon seals in the thruster valves, which swelled and restricted the flow of oxidiser. The behaviour could be reproduced but not modelled with enough confidence to guarantee safe control during undocking and the deorbit burn.
The helium leaks
Helium is used to push propellant from the tanks to the thrusters. One leak was known before launch. Several more appeared in flight, also linked to seals in the helium system. The leak rates were small compared with the helium on board, but they added to doubts about the propulsion system as a whole.
Why the crew did not ride it home
NASA's engineers and Boeing disagreed about the risk. Boeing argued the spacecraft could bring its crew home safely. NASA concluded there was too much uncertainty about thruster behaviour during the critical departure and deorbit phases, and that the agency had a safer alternative in Crew Dragon. The uncrewed return worked: Starliner undocked, made its deorbit burn and landed normally, though some thrusters again misbehaved on the way.
Were the Astronauts "Stranded"?
Not in the sense often reported. A spacecraft was docked to the station the whole time that could have taken them home in an emergency, first Starliner itself and then the Crew-9 Dragon, which carried two extra seats for them. What changed was the length of the mission: instead of about a week, Wilmore and Williams joined the station crew as full long-duration members (Williams took command of the ISS in autumn 2024). Their return was tied to the normal crew rotation. That rotation slipped when the brand-new Dragon capsule planned for Crew-10 needed more processing time; NASA switched Crew-10 to a previously flown capsule, Endurance, and it launched on 14 March 2025. Crew-9, with Wilmore and Williams aboard, came home four days later.
Starliner Compared With Crew Dragon
- Rocket: Starliner flies on ULA's Atlas V; Crew Dragon on SpaceX's Falcon 9.
- Landing: Starliner lands on land with parachutes and airbags; Crew Dragon splashes down at sea.
- Docking: both dock to the ISS's International Docking Adapters on their own, without the station's robotic arm.
- Track record: Crew Dragon has flown about a dozen NASA crew flights plus several private missions since 2020. Starliner has flown one crewed test flight.
For more on the SpaceX side, see Falcon 9 and Dragon; for the Russian vehicle that was the only option for most of the 2010s, see Soyuz.
What Comes Next for Starliner
The publicly announced plan, as of NASA's November 2025 update, is:
- Starliner-1 — an uncrewed cargo flight to the ISS, initially targeted for no earlier than April 2026, to demonstrate the changes made after CFT (including thruster and seal modifications) before astronauts fly again.
- Crewed rotation flights — to follow only after NASA certifies the vehicle. The number of flights NASA intends to buy has been cut, and the ISS itself is scheduled to retire around 2030, which limits how many flights Starliner can make to it.
Starliner's schedule has moved many times since 2019, so treat any date as a target rather than a forecast. If you are reading this after April 2026, check NASA's Commercial Crew updates for whether Starliner-1 has flown and what was decided afterwards. We update this page when we review it; the date at the bottom shows when that last happened.
Frequently Asked Questions
What is Boeing Starliner?
Starliner (CST-100) is a reusable crew capsule built by Boeing under NASA's Commercial Crew Program to carry astronauts to and from the International Space Station. It launches on a ULA Atlas V and lands on land under parachutes and airbags.
When did Starliner's crewed test flight launch?
The Crew Flight Test launched on 5 June 2024 from Cape Canaveral with NASA astronauts Butch Wilmore and Suni Williams, and docked to the ISS on 6 June 2024.
Why did Starliner come back without its crew?
Several thrusters dropped out during the approach to the station and the propulsion system developed helium leaks. NASA judged that thruster behaviour during undocking and deorbit could not be predicted with enough confidence, so Starliner returned uncrewed, landing at White Sands on 7 September 2024 (Eastern time).
How did Butch Wilmore and Suni Williams get home?
They returned aboard SpaceX's Crew-9 Dragon, which splashed down off Florida on 18 March 2025, after about 286 days in space.
What is Starliner's next mission?
NASA announced in November 2025 that the next flight, Starliner-1, would be an uncrewed cargo mission to the ISS, targeted for no earlier than April 2026. Check NASA's Commercial Crew updates for its current status.
Is Starliner.net affiliated with Boeing?
No. Starliner.net is an independent space publication with no connection to Boeing, NASA or any space agency.