During a news conference Wednesday, NASA officials publicly discussed for the first time divisions within the agency over whether the Starliner spacecraft is really reliable enough to return two veteran astronauts, Butch Wilmore and Suni Williams, back to Earth from the International Space Station.
The space agency also confirmed key elements reported exclusively by Ars over the past week, primarily that NASA has I’ve been working quietly for weeks with SpaceX on a possible rescue mission for Wilmore and Williams, that the launch of the Crew-9 mission has been delayed until September 24 to account for this possibility, and that Starliner cannot undock autonomously with the vehicle’s current software configuration.
NASA’s chief of manned space 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 customer for the spaceflight, and Boeing, which developed and operates Starliner, about the viability of the 28 reaction control system thrusters used to delicately maneuver and aim the vehicle.
“I think it’s been very healthy,” Bowersox said of these internal discussions during a call with reporters Wednesday. “I have to admit that sometimes when there are disagreements, it’s not fun. It can be painful to have those discussions, but it’s what makes us a good organization.”
NASA has been studying several contingencies, but it appears officials have settled on two different options for bringing the two astronauts back to Earth. They could still fly back on the Starliner if NASA engineers become more comfortable with the uncertainty about the booster’s performance — and if so, they would do so during the second half of this month or the first part of September. Alternatively, NASA could launch the Crew-9 mission with a complement of two instead of four astronauts, and Wilmore and Williams would join that “increment” on the space station and fly back to Earth in February 2025.
Asked if he thought one of the two scenarios was more likely than the other, Bowersox said he couldn’t say. However, a final decision will be made fairly soon. Bowersox said NASA needs to choose the astronauts’ return route by mid-August.
Problems with the propeller
NASA is concerned about Starliner’s thrusters because five of them failed during the vehicle’s ascent to the space station. Starliner’s flight computer shut down five thrusters, provided by Aerojet Rocketdyne, mid-flight. Four of the five thrusters recovered after overheating.
Since then, Boeing and NASA have conducted ground and space-based tests of the small boosters to try to reproduce the failure and better understand, in essence, what is 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 testing, engineers were able to demonstrate similar flaws. Subsequent inspections showed a bulge in a Teflon seal on an oxidizer valve known as a “poppet,” which could restrict the flow of nitrogen tetroxide propellant. Thrusters consume nitrogen tetroxide and mix it with hydrazine fuel for combustion. Despite the testing, however, engineers still don’t understand exactly why the bulge occurs and whether it will manifest itself on Starliner’s return flight to Earth.
“People want to really understand the physics of what’s happening in relation to the physics of 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 really what the team is trying to understand. I think the NASA community at large would like to understand a little bit more of the root cause.”