During a news conference Wednesday, NASA officials publicly discussed for the first time divisions within the agency over whether the Starliner spacecraft is actually 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 that Ars has exclusively reported on over the past week, mainly that NASA I worked quietly for weeks with SpaceX regarding a potential rescue mission for Wilmore and Williams, that the launch of the Crew-9 mission has been delayed until September 24 to accommodate this possibility, and that Starliner cannot undock autonomously with the current software configuration in the vehicle.
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 legitimate disagreements between engineers at NASA, the spaceflight customer, and Boeing, which developed and operates Starliner, about the feasibility of the spacecraft’s 28 reaction control system engines, which are used to delicately maneuver and steer the vehicle.
“I think it was very healthy,” Bowersox said of those internal discussions during a call with reporters Wednesday. “I have to admit, sometimes when we have disagreements, it’s not pleasant. Those discussions can be painful, but that’s what makes us a good organization.”
NASA has been exploring various eventualities, but officials have apparently settled on two different options for bringing the two astronauts back to Earth. They could still fly back on the Starliner if NASA engineers feel more comfortable with the uncertainties about engine performance, and if so, they would do so in the second half of this month or the first part of September. Alternatively, NASA could launch the Crew 9 mission with two astronauts rather than four, with Wilmore and Williams joining that “surge” on the space station and flying 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 must choose a return route for astronauts by mid-August.
Engine problems
NASA’s concerns about Starliner’s engines stem from the failure of five of them during the spacecraft’s ascent to the space station. Starliner’s onboard computer shut down five of the engines, supplied by Aerojet Rocketdyne, during the flight. Four of the five engines were recovered after overheating.
Since then, Boeing and NASA have conducted tests of compact engines on the ground and in space to try to replicate the failure and better understand what was happening. By getting to the root cause, engineers will have confidence in their ability to fix the problem as Starliner flies back to Earth.
During ground tests, engineers were able to demonstrate similar failures. Later inspections revealed a bulge in a Teflon seal in the oxidizer valve known as a “poppet,” which could restrict the flow of nitrogen tetroxide fuel. Jet engines consume nitrogen tetroxide and mix it with hydrazine fuel for combustion. Despite testing, engineers still don’t understand exactly why the bulge occurs or 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 respect to the physics of Teflon, what causes it to heat up and what causes it to shrink,” said Steve Stich, who manages NASA’s Commercial Crew program. “That’s what the team is trying to understand. I think the NASA community in general would like to understand a little more about why.”