At a press conference on Wednesday, NASA officials publicly discussed for the first time the disagreements within the agency over whether the Starliner spacecraft is really reliable enough to return veteran astronauts Butch Wilmore and Suni Williams to Earth from the International Space Station.
The space agency also confirmed key elements reported exclusively by Ars last week, namely that NASA has been secretly working with SpaceX for weeks on a possible rescue mission for Wilmore and Williams, that the launch of the Crew-9 mission has been postponed to September 24 in light of this possibility, and that Starliner is not capable of undocking autonomously with the spacecraft’s current software configuration.
No final decision has been made about how Wilmore and Williams will return to Earth, said Ken Bowersox, NASA’s human spaceflight operations manager and a former astronaut. He said there had been legitimate disagreements between engineers at NASA, the spaceflight customer, and Boeing, which developed and operates Starliner, about the feasibility of the 28 Reaction Control System thrusters used to delicately steer and redirect the craft.
“I thought it was a very healthy internal debate,” Bowersox said in a conference call with reporters on Wednesday. “I have to admit that sometimes when we have differences of opinion, it’s not fun. Those debates can be painful, but that’s what makes us a good organization.”
NASA has studied a variety of contingencies, but officials appear to have settled on two options for returning the two astronauts to Earth: If NASA engineers are satisfied with the uncertainties surrounding thruster performance, the pair could return aboard Starliner, which would bring them back later this month or early September. Alternatively, NASA could launch the Crew 9 mission with just two astronauts instead of four, with Wilmore and Williams joining the “augmented crew” on the space station to return to Earth in February 2025.
When asked which of the two scenarios he thought was more likely than the other, Bowersox said he couldn’t answer, but a final decision is likely coming soon: NASA has until mid-August to choose a return route for the astronauts, Bowersox said.
Thruster issues
NASA’s concerns about Starliner’s thrusters stem from the failure of five thrusters during the craft’s ascent to the space station. Starliner’s flight computers shut down five of the Aerojet Rocketdyne-supplied thrusters during the flight. Four of the five thrusters were retrieved after overheating.
Since then, Boeing and NASA have been testing the small thrusters on the ground and in space, trying to replicate the failure and get a better understanding of what was going on at the root. Finding the root cause will give engineers more confidence they can address the issue for Starliner’s return flight to Earth.
In ground tests, engineers were able to demonstrate a similar failure. Subsequent inspections found that the Teflon seal on the oxidizer valve, known as the “poppet,” had bulged, which could have blocked the flow of nitrogen tetroxide propellant. The thrusters consume the nitrogen tetroxide, which they mix with hydrazine fuel and burn. But despite the tests, engineers still don’t know exactly why the bulge is happening, or whether it will show up on Starliner’s return to Earth.
“People really want to understand what’s going on relative to the physical properties of Teflon, what’s causing the Teflon to heat up, what’s causing the Teflon to shrink,” said Steve Stich, who manages NASA’s Commercial Crew Program. “That’s really what the team is trying to understand. I think the whole NASA community wants to understand the root cause a little bit more.”
