NASA official acknowledges internal “disagreement” on safety of Starliner return
"We heard from a lot of folks that had concerns."
During a news conference on Wednesday, NASA officials for the first time publicly discussed divisions within the agency about 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 exclusively reported by Ars over the last week, chiefly that NASA has quietly been working for weeks with SpaceX on a potential rescue mission for Wilmore and Williams, that the Crew-9 mission launch has been delayed to September 24 to account for this possibility, and that Starliner is unable to undock autonomously with the current software configuration on the vehicle. The chief of space human spaceflight operations for NASA, former astronaut Ken Bowersox, said no final decisions have been made on how Wilmore and Williams return to Earth. He said there were reasonable disagreements among 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 that are used for delicate maneuvering and pointing of the vehicle. "I think it's been very healthy," Bowersox said of these internal discussions during a call with reporters on Wednesday. "I have to admit that sometimes when we get disagreement, it's not fun. It can be painful having those discussions, but it's what makes us a good organization." NASA has been studying various contingencies, but officials appear to have settled on two different options for bringing the two astronauts back to Earth. They could still fly back on Starliner if NASA engineers become more comfortable with the uncertainty about the thruster 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 rather than 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 could not say. However, a final decision will be made fairly soon. Bowersox said NASA needs to choose the astronauts' return path by mid-August.
Thruster issues
NASA's concern about Starliner's thrusters boils down to the failure of five of them during the vehicle's ascent to the space station. Starliner's flight computer shut off five thrusters, provided by Aerojet Rocketdyne, in flight. Four of the five thrusters were recovered after overheating. Since then Boeing and NASA have conducted ground- and space-based tests of the small thrusters to try to replicate the failure and better understand, fundamentally, what is occurring. By getting to the root cause, the engineers will feel confident in their ability to address the problem for Starliner's flight back to Earth. In ground tests, the engineers were able to demonstrate similar failures. Subsequent inspections showed bulging in a Teflon seal in an oxidizer valve known as a "poppet," which could restrict the flow of nitrogen tetroxide propellant. The thrusters consume the nitrogen tetroxide and mix it with hydrazine fuel for combustion. Despite the tests, however, engineers still don't understand precisely why the bulging is occurring and whether it will manifest on Starliner's flight back to Earth. "People really want to understand the physics of what's going on relative to the physics of the Teflon, what's causing it to heat up and what's causing it to contract," said Steve Stich, who manages the Commercial Crew program for NASA. "That's really what the team is off trying to understand. I think the NASA community in general would like to understand a little bit more of the root cause." Boeing engineers are advocating for flying Starliner as is, that enough is known about the problem that failures will not occur during the vehicle's return to Earth. However, during meetings of key engineers at NASA known as the "Program Control Board" this week, there was no agreement that this so-called flight rationale was enough to fly crew on the vehicle. "We heard from a lot of folks that had concerns," Bowersox said. "We heard enough voices that the decision was not clear at the Program Control Board." Given that NASA will soon decide whether to fly crew on Starliner, the Boeing team has about a week to convince the NASA team of Starliner's safety before a potential switch to Crew Dragon.
Autonomous undock software
Stich also explained why it would take a few weeks to reconfigure the software package on board Starliner to allow for a safe undocking of the spacecraft without crew. This is one reason the Crew-9 mission launch was pushed from August 18 to late September. Although the capability to undock without a crew exists within the flight software on Starliner, it is currently configured for crew operations. That is, during the process of undocking and moving away from the space station, the flight software takes certain actions, and the crew takes certain actions. This configuration change toward integrated operations between software and crew was made after the previous autonomous flight of Starliner in 2022 that flew to the space station and back. "Essentially, what we're asking the team is to go back two years in time and resurrect the software parameters that are required to give automatic responses to breakouts near the ISS should we have a problem in close to ISS, which the software now allows them to do manually," Stich said. "The team is always updating these mission data loads as different things change." No work has been done on the autonomous software package since the flight in 2022. Ars reported it would take about four weeks to complete testing of this configuration change, and Stich confirmed this. "Before we go execute that, it's just smart and responsible to take the software and mission data loads in this configuration, go into the integrated test facility where all the flight software resides, and go run it through some test cases just to make sure we haven't missed anything," Stich said. "That's really what would take the time if we were to pivot to an uncrewed undock."
