After months of rigorous testing, comprehensive data reviews, and thorough deliberations, the agency has decided to rely on SpaceX's Crew Dragon to bring veteran astronauts Suni Williams and Butch Wilmore back home as part of the upcoming Crew-9 mission. Williams and Wilmore will continue their work aboard the ISS as part of Expedition 71-72 before their scheduled return on Crew Dragon in February 2025.

“Spaceflight is risky, even at its safest and even at its most routine, and a test flight is neither safe nor routine. So the decision to keep Butch and Suni aboard the International Space Station and bring the Starliner home uncrewed is the result of a commitment to safety,” said NASA Administrator Bill Nelson during the Starliner update press conference on Saturday, August 24.

The decision to have astronauts return on Dragon instead of Starliner marks one of the most pivotal choices in NASA's human spaceflight history. The choice was unanimous among the agency's senior officials and was officially recommended by the Commercial Crew Program. Nelson emphasized that the difficult lessons learned from the Challenger and Columbia tragedies played a significant role in reaching this conclusion.

“We have had mistakes done in the past, we lost 2 space shuttles as a result of not being a culture in which new information can come forward,” said Nelson.

NASA Astronauts Suni Williams and Butch Wilmore were launched aboard Boeing’s Starliner on June 5, 2024, as a part of the test flight intended to certify the spacecraft for future operational missions. Starliner’s flight was originally scheduled for nine days but its return to Earth was being repeatedly delayed by NASA as the agency meticulously reviewed data from the propulsion system to ensure the spacecraft could support safe undocking and return operations. Prior to launch, NASA was already aware of a helium leak in Starliner’s service module. However, since it was within acceptable safety constraints at the time, Boeing was given the green light to proceed.

During Starliner’s rendezvous maneuver with the International Space Station (ISS), additional helium leaks were detected in the service module. Compounding the issues, Starliner’s first docking attempt was aborted after 5 of its 28 maneuvering thrusters malfunctioned.

Despite the docking success, concerns remained about Starliner’s ability to safely return the crew to Earth due to the ongoing propulsion system issues. To address these concerns, NASA and Boeing conducted ground tests at the White Sands Test Facility in New Mexico. These tests involved firing the engines under conditions similar to those experienced during Starliner’s approach to the ISS, as well as simulating the conditions expected during undocking and the de-orbit burn.

The testing wasn’t limited to the ground. On July 27th, NASA and Boeing performed a hot-fire test of Starliner’s reaction control system jets while it was docked to the ISS. This test involved firing 27 of the spacecraft’s thrusters in short bursts, one at a time, to collect data on their performance and assess the helium leak.

The tests revealed that the valves were operating beyond their intended temperature limits, causing the Teflon-based seals to swell and restrict the flow of oxidizer to the thrusters. This behavior had not been observed by Aerojet during the development and testing phases of the propulsion system, adding a layer of complexity to the challenges faced by the Starliner program.

"I would say the White Sands testing did give us a surprise," NASA Commercial Crew Program Manager, Steve Stitch said in the press conference. "It was this piece of Teflon that swells up and got in the flow path and causes the oxidizer to not go into the thruster the way it needs to. That's what caused the degradation of thrust. When we saw that, I think that's when things changed a bit for us."

Boeing's Starliner teams may have a preliminary understanding of the thruster issue, but the uncertainty with thrusters’ performance outweighed the accepted risk for a crewed return, as Stitch said, “As we got more and more data over the summer and understood the uncertainty of that data, it become very clear to us that the best course of action was to return Starliner uncrewed.” 

“There was just too much uncertainty in the performance of the Starliner thrusters. If they had a better model for the thruster performance, we would’ve taken a different course of action,” he said.

NASA’s Commercial Crew Program is a fixed-price contract, meaning the contractors are only paid when they achieve a set milestone and have to foot the bill for any failures. Boeing is already in a $1.6 billion deficit over delays and cost overruns on the Starliner program. It was just a decade ago when NASA announced that Boeing, one of the agency's most experienced contractors, won the lion's share of money available to end America's reliance on Russia to ferry its astronauts to low-Earth orbit.

At the time, Boeing won $4.2 billion from NASA to complete development of the Starliner spacecraft and fly a minimum of two, and potentially up to six, operational crew flights to rotate crews between Earth and the International Space Station (ISS). SpaceX won a $2.6 billion contract for essentially the same scope of work. Now, the Starliner program finds itself at a crossroads after Boeing learned it will not complete the spacecraft's first Crew Flight Test with astronauts onboard.

Administrator Nelson said that he received assurances from Boeing’s new CEO, Kelly Ortberg, that the company remains committed to flying astronauts to the ISS under the commercial crew program. Boeing will now work with NASA to prepare the Starliner spacecraft for an uncrewed return to Earth which will begin with undocking autonomously from the ISS. Between Starliner's departure and the arrival of Crew-9, Dragon Endeavour, currently docked to the ISS for the Crew-8 mission, will serve as a lifeboat for Suni and Butch in an emergency situation.

NASA Astronauts Zena Cardman, Nick Hague, Stephanie Wilson, and Russian Cosmonaut Aleksandr Gorbunov were initially assigned to fly on Crew-9. However, to accommodate the return of Wilmore and Williams, Dragon will launch with only two astronauts, leaving two seats unoccupied. NASA has yet to decide which two astronauts will command and pilot the Dragon. SpaceX will modify two of the seats to fit Suni and Butch's specifications, as each seat is custom-tailored for the specific astronaut flying on it. Crew-9 will also carry SpaceX’s IVA suits for Starliner's former crew, which they will don during their return to Earth.

Upon Crew-9’s arrival at the ISS, Suni Williams and Butch Wilmore will officially join the Crew-9 team and remain on the ISS, continuing their research and maintenance duties during their extended stay.

For Starliner to fly again, Boeing will need to collaborate with Aerojet and other subcontractors to fully understand the issues with the valves, potentially redesign certain components of Starliner’s propulsion system, and rigorously prove the spacecraft in a comprehensive testing campaign. NASA officials have stated that it is currently too early to determine whether Boeing will be required to conduct another test flight of Starliner, or if the spacecraft could be certified for operational service once the critical issues are resolved.

With a minimum six-month rotation between SpaceX’s Crew Dragon and Boeing’s Starliner, it’s highly likely that Starliner won’t carry astronauts again until at least 2026. Even then, given the ISS is scheduled to be retired in 2030, there may not be enough time left for Starliner to complete all six of its contracted missions, which were originally intended to be flown once per year.