Starliner to Return to Flight by January, Fly Crew in 2028

On September 28, NASA and Boeing provided an update on the Starliner spacecraft’s Return to Flight, progress made since the Crew Flight Test (CFT), and the program’s future. Teams have completed the majority of the preparation work for the Starliner-1 uncrewed cargo flight and the spacecraft is fully assembled and awaiting a launch this winter.

Starliner-1 is currently scheduled for a launch in January 2027 using the Calypso crew module that previously flew on the Orbital Flight Test and Crew Flight Test missions. This is likely driven by docking port availability, as SpaceX’s CRS-35 cargo mission is planned to remain at the station until November. Starliner-1 will demonstrate almost all of the upgrades necessary to fly crew, with remaining upgrades for Starliner-2 further increasing reliability and robustness.

With the successful launch of the Amazon Leo 8 mission on July 2nd, all six remaining Atlas V rockets are assigned to Starliner missions. As Atlas V is no longer being produced and the design contains some limited-life components, NASA and Boeing have begun working with United Launch Alliance to certify their Vulcan-Centaur rocket for Starliner. The intent is still to use all six Atlas rockets, but if some end up becoming unusable due to age Vulcan will be able to fill the gap. NASA has also restored the ability to fly the Starliner-5 and 6 missions at a later date. They had been converted into contract options in November 2025, but now Boeing can be authorized to start work and receive funding for those missions once the time to fly them gets closer.

The 2024 Crew Flight Test had three major failures. The most obvious and impactful was the failure of five RCS thrusters on Calypso’s service module during the final approach phase of docking. The thrusters did not physically fail, but exceeded software limits on the combustion chamber pressure and so were disqualified by the guidance and control systems. This resulted in a loss of 6 Degrees of Freedom control, though four were eventually recovered and used in the successful docking.

The primary direct causes of this were a valve component known as a “poppet”. A poppet is similar to the valves inside an automobile engine, and is effectively a rod that carries a series of seals to either prevent or allow fluid flow through the valve. If exposed to certain conditions and not properly held in place, the seals can “extrude”, or physically swell and move outwards, which restricts propellant flow and reduces thrust and chamber pressure.  The physical cause of the CFT thruster fail-offs was concluded to be partial vaporization of oxidizer on its way to the combustion chamber due to high temperatures, as well as poppet extrusion due to a manufacturing and design defect that did not fully hold the seals in place and was exacerbated by the excessive heat. 

Boeing is adding several measures to combat the heat surplus, including thermal barriers to decrease heat flow into the system from the outside, software changes to reduce the thruster pulse rate (and thus the amount of generated heat), and the addition of “thermal shunts”, which are components that rapidly move heat away from a source to a heatsink. In ground testing of the new design, thruster temperatures were reduced by around 100°F. While this will significantly help, the poppet itself will also be redesigned to make the system more robust. This effort has already begun, and will progress through design, fabrication, and extensive testing before Starliner receives its final crew certification ahead of Starliner-2.

The Crew Module RCS thruster failure was caused by corrosion due to residual hydrazine reacting with air, so going forward all CM RCS thrusters will be immediately flushed to vacuum followed by a slow nitrogen purge after landing. The service module helium leaks were due to seals degrading after long term exposure to hypergolic propellants, so the material has been changed and the seals also made slightly larger to improve the seal strength. The flight recorder will be upgraded with a higher recording rate, the batteries will be upgraded, and the parachute design will be updated as well.

While Starliner is making good progress towards return to flight, it must be placed in the context of the many other changes incoming to the ISS and the space industry as a whole. As reported by Ars Technica, SpaceX is planning to retire its Dragon spacecraft no later than 2030, with other outlets reporting that they plan to retire Falcon 9 soon after. 

The latest of NASA’s periodic sole-source justification filings that precede new purchases of Crew Dragon missions, released in late May, allowed for six such missions, accounting for Crew-15 through Crew-20. This was driven both by continued Starliner delays and by the shortening of ISS expedition length from 9 months back to the standard 6 months. The first three missions (Crew-15 through Crew-17) were purchased immediately, with 18 through 20 able to be ordered at a later date. However, unless all Starliner missions after Starliner-2 were deferred to after Crew-20, it is unlikely that all six Dragons could be flown before 2030. Given the evidence that the heating and thruster performance issues will be finally resolved after Starliner-1 and 2, it is more likely that NASA will not order the remaining three Dragon missions and simply alternate Starliner and Dragon until Crew-17 before flying back to back Starliners for the rest of the ISS’s on-orbit life. Given the mid-2028 target date for Starliner-2, this would imply that only three inter-provider handoffs will occur, between Crew-16 and Starliner-2, Starliner-2 and Crew-17, and Crew-17 and Starliner-3. This is a far cry from the dozens originally envisioned, but will mean that all of the original program goals will at last be met.

Another effect of Dragon’s retirement is that, for the first time, there will be only one crew provider in the program at all. While for most of its life Commercial Crew has effectively operated with a SpaceX monopoly, Boeing was still present and working towards flight, which presented some incentive to keep costs down in case of future head-to-head competition. NASA has shown little interest in funding the development of a third crew transportation system, though it is willing to help an industry-developed vehicle obtain certification to carry NASA astronauts. However, with no guaranteed certification or development assistance and a demand of only one flight per year (assuming the continued use of Starliner), privately developing such a vehicle is likely unattractive at best. The nearest such vehicles to flight are the two LEO cargo spacecraft in development for the European Space Agency’s ALADDIN initiative, The Exploration Company’s Nyx and Thales Alenia Space’s unnamed cargo spacecraft. One requirement levied by ESA was that all bids must be able to be evolved into crew spacecraft, but the funding and political will to do this is equally uncertain, even with hiring for Nyx Crew having taken place in the United States already. The cargo spacecraft are due to perform their demonstration missions to the ISS in 2029, so the potential debut of a crew variant is a matter for the second half of the 2030s.

Regardless of what the 2030s hold, Boeing is preparing to return Starliner to flight, hopefully for good. A clean Starliner-1 will set them and NASA up to continue reliable service for the rest of the ISS’s life and show that the vehicle is capable of leading us into the age of commercial space stations. Good luck to Calypso, the NASA and Boeing teams, and everyone involved as Starliner’s story continues.