Anika Begay
At a news conference Wednesday, NASA officials publicly discussed for the first time disagreements within the agency about whether the Starliner spacecraft was reliable enough to return two 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, notably that NASA has been quietly working with SpaceX for weeks on a potential rescue mission for Wilmore and Williams, that the launch of the Crew-9 mission has been delayed to Sept. 24 to account for this possibility, and that Starliner is not capable of autonomous undocking with the vehicle’s current software configuration.
NASA’s chief of human spaceflight operations, former astronaut Ken Bowersox, said no final decisions have been made about how Wilmore and Williams will return to Earth. He said there were reasonable disagreements between engineers at NASA, which is the spaceflight customer, and Boeing, which developed and operates Starliner, about the feasibility of the 28 reaction control system thrusters that are used for delicate maneuvering and aiming the vehicle.
“I think it’s been very healthy,” Bowersox said of those internal discussions on a call with reporters Wednesday. “I have to admit, sometimes when you have disagreements, it’s not fun. It can be painful to have those discussions, but that’s what makes us a good organization.”
NASA has explored several options, but officials appear to have settled on two different options for returning the two astronauts to Earth. They could still fly again on the Starliner if NASA engineers become more comfortable with the uncertainty about the thruster’s performance, and if so, they would do so in the second half of this month or early September. Alternatively, NASA could launch the Crew-9 mission with a crew of two instead of four, and Wilmore and Williams would join that “augment” on the space station and return to Earth in February 2025.
Asked if he thought one scenario was more likely than the other, Bowersox said he didn’t know. However, a final decision will be made soon enough. Bowersox said NASA needs to decide on the astronauts’ return path by mid-August.
Propulsion problems
NASA’s concern about the Starliner’s thrusters boils down to the failure of five of them during the vehicle’s ascent to the space station. The Starliner’s flight computer shut down five thrusters, supplied by Aerojet Rocketdyne, during the flight. Four of the five thrusters were recovered after overheating.
Since then, Boeing and NASA have conducted ground and space tests of small thrusters to try to replicate the failure and better understand, fundamentally, what’s happening. By getting to the root cause, engineers will feel confident in their ability to address the problem for Starliner’s return flight to Earth.
In ground tests, engineers were able to demonstrate similar failures. Later inspections showed bulges in a Teflon gasket in an oxidizer valve known as a “poppet,” which could restrict the flow of nitrogen tetroxide propellant. The thrusters consume nitrogen tetroxide and mix it with hydrazine fuel for combustion. Despite the tests, however, engineers still don’t understand exactly why the bulge occurred and whether it will show up during Starliner’s return flight to Earth.
“People really want to understand the physics of what’s going on with the physics of the Teflon, what’s causing it to heat up and what’s causing it to contract,” said Steve Stich, who manages NASA’s Commercial Crew program. “That’s what the team is trying to figure out. I think the NASA community in general would like to understand a little bit more about the root cause.”
