NASA and Boeing Extend Starliner's Stay at ISS to Address Thruster and Helium Leak Issues

NASA has announced another extension for the CST-100 Starliner's stay at the International Space Station (ISS) due to ongoing analysis of thruster problems and helium leaks. Initially scheduled to return on June 22, the spacecraft is now set to undock at 10:10 p.m. Eastern on June 25 and land in White Sands, New Mexico, at 4:51 a.m. Eastern on June 26.

Thruster and Helium Leak Issues

During its flight to the ISS nearly two weeks ago, Starliner encountered two significant issues: thruster malfunctions and helium leaks in its propulsion system.

NASA and Boeing engineers have been conducting thorough analyses, including brief firings of several aft-facing reaction control system (RCS) thrusters. Notably, five of these thrusters were shut down by Starliner's computer as it approached the station, but four were restored to allow docking to proceed.

One thruster, however, was not restored before docking due to what Steve Stich, NASA's Commercial Crew Program Manager, described as a “strange signature” producing almost no thrust. Consequently, this thruster will not be used during the undocking and deorbiting maneuvers.

The remaining thrusters, including both those that malfunctioned during the approach and others that behaved normally, performed as expected during subsequent brief burns. This reassured engineers about their functionality.

“Coming out of that, we feel very confident in the thrusters and the team is just making sure to go look at the thrusters in detail across the whole flight,” - Steve Stich, NASA's Commercial Crew Program Manager

Engineers are investigating the cause of the thruster malfunctions, hypothesizing that heavy use and high temperatures might prevent proper mixing of fuel and oxidizer. Additionally, the thruster tests helped monitor five helium leaks in the propulsion system. Stich noted that in every case, leak rates had decreased, in one instance by 50%.

The demand on the thrusters is much, much less in the later phases of flight.

Extended Analysis and Safety Assurance

NASA and Boeing will continue analyzing Starliner until June 22, focusing then on undocking and return preparations.

This extended stay provides a unique opportunity to thoroughly understand the spacecraft’s performance without schedule pressures.

“We don’t get the service module back, so this is an opportunity to fully understand the system’s performance.” - Mark Nappi, Boeing's Vice President and Commercial Crew Program Manager

Of the 87 flight test objectives set out before launch, the CFT mission has already achieved 77, with the remainder associated with undocking and landing. Additional test objectives have been included to capitalize on the extra time at the station, such as filming Starliner’s hatch operations and collecting more cabin air temperature measurements.

Both Stich and Nappi stressed that they believe Starliner is safe for NASA astronauts Butch Wilmore and Suni Williams to use for their return to Earth. The extra time allows engineers to study the vehicle’s performance further, including in a powered-down state for future long-duration stays at the station.

“We’re taking a little extra time to review all the data and also learn as much as we can while we have the service module in orbit,” - Steve Stich, NASA's Commercial Crew Program Manager

Wilmore and Williams have been actively involved at the station, helping test Starliner systems. They have also contributed to other station activities, including research. On June 13, they assisted NASA astronauts Tracy C. Dyson and Matt Dominick in preparing for a spacewalk that was called off due to a “spacesuit discomfort issue.”

As NASA and Boeing continue their meticulous work, the extended stay of the CST-100 Starliner at the ISS underscores their commitment to safety and thorough analysis, ensuring the spacecraft's readiness for future missions.