NASA has decided the Boeing Starliner pilots stuck on the International Space Station will return to Earth in a SpaceX Crew Dragon pod next year - after the US agency's engineers could not clear the Starliner's thrusters for the return trip.

To recap: Boeing flew its Starliner capsule with two pilots onboard to the orbiting space station in June for what was expected to be a mission lasting about a week. The pair of astronauts, Butch Wilmore and Suni Williams, were supposed to return home in that capsule. They were expected to be back by now.

But their journey home was put on hold by NASA due to concerns over the Calamity Capsule's thrusters and helium leaks, leaving the duo stuck on the ISS with its other crew.

After much deliberation, with Boeing insisting its equipment was safe enough, the official plan now, announced over the weekend by NASA, is to return the Starliner pod without its crew to Earth in early September.

A SpaceX Crew Dragon capsule will arrive shortly after, more or less as planned, in a mission dubbed Crew-9. That mission was supposed to bring four more astronauts to the space station, though now it will only bring two, and the Starliner 'nauts will then become part of Crew-9.

Crew-9 is not due to return until February next year at the earliest, meaning the Starliner pair will have to stay on the station for months longer.

NASA has yet to confirm which of the four astronauts originally due to fly on Crew-9 will have to give up their seats.

As well as a black eye for Boeing, the decision also means the existing Crew-8 capsule will have to temporarily act as a lifeboat for six rather than four astronauts until Crew-9 arrives. According to NASA, the cargo area of the capsule will be adapted to provide space for the Starliner duo in the event of an emergency.

During a briefing on August 25, NASA said the decision to return the crew in a SpaceX vehicle was unanimous within the American agency. However, Boeing reckoned a crew would be perfectly safe in its capsule.

Ultimately, it's a question of known and unknown risks. The issues that have bedeviled the Starliner's thrusters have proven too great a risk for NASA to accept. According to NASA, the pod's thrusters are running hotter than expected, which could cause performance problems during the de-orbit burn and maneuvering. Ultimately, the NASA team opted not to take the risk of sending a crew back in Starliner.

The US space agency did not disclose if the failure to return the crew would constitute a loss of mission. The question of whether it would go ahead and certify Starliner for operational use or require another test mission was also described as "premature." It seems highly unlikely that the next crewed launch of Boeing's Starliner will occur before 2026.

At first glance, the decision to return the Starliner uncrewed appears to be evidence of a change of process and management style at NASA following the Challenger and Columbia tragedies, where concerns and dissent over risk and safety were stifled with catastrophic consequences.

However, questions must be asked of the agency as well as Boeing. Starliner was launched with known issues - the helium leaks. Anomalous thruster behavior had also been observed on earlier uncrewed flights.

Despite the problems, NASA went ahead with the launch.

Could the agency have done things differently? Hindsight is a wonderful thing, particularly considering engineers' difficulty in recreating the problems seen in space on the ground. However, it is also difficult not to wonder if some personnel had been affected a little by launch fever as the long-delayed crewed launch date finally rolled around.

As it stands, NASA's decision is a blow for Boeing. The US space agency remains determined to have two operational US crew transportation systems, but there is now a real chance that the ISS might be in its twilight years before Boeing's Starliner is finally certified. ®

https://www.theregister.com//2024/08/25/nasa_spacex_starliner/