YYou wouldn’t board a plane if your chances of coming home alive were only 1 in 270. But that probability is what NASA considers an acceptable LOC, or crew loss, projection for a 210-day stay aboard the International Space Station (ISS). Beating that mortal bill was a major concern for NASA officials at an Aug. 14 press conference where they discussed the agency’s efforts to ensure the survival of Butch Wilmore and Suni Williams, the two astronauts currently stranded aboard the ISS.

Wilmore and Williams left Earth on June 5, aiming to complete just an eight-day flight of Boeing’s new Starliner spacecraft – a brief stay at the ISS that would certify the craft for future missions and give the U.S. a much-needed additional option if SpaceX’s Crew Dragon spacecraft, which has been carrying astronauts to the ISS since 2020, ever needs to go offline. Before the Starliner crew reached the ISS, however, five of the spacecraft’s engines began firing, and the supply of the gaseous helium that keeps the engines pressurized had five leaks.

Crew and craft arrived at the station unscathed, but the eight-day mission has now stretched to more than eight weeks while Boeing and NASA troubleshoot the problem and determine whether the Starliner is safe enough to bring Wilmore and Williams home. Last week, NASA announced it was considering a contingency plan that would involve flying the Starliner home empty. A SpaceX Crew Dragon spacecraft, scheduled to carry four people for a five-month stay at the station starting in September, would instead launch with just two crew members, leaving the other two seats empty to bring Williams and Wilmore home in February.

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“We continue to believe in the capabilities and flightworthiness of Starliner,” Boeing said in an August 7 statement after the possible plan was announced.

A week later, at the Aug. 14 press conference, it became clear that NASA may not have quite as much confidence in the new spacecraft’s capabilities. Instead, Ken Bowersox, deputy director of NASA’s Directorate of Space Operations, announced that NASA would conduct a high-level flight readiness review before the end of August to make a final decision on the Starliner’s fate. This compressed timeline is due in part to the limited lifespan of the Starliner’s batteries. They are designed to provide power for only 45 days. Since that six-plus-week deadline has passed, the station has been recharging them, but they can only withstand so much of that power before they fail altogether.

“It’s a pretty big decision whether we’re going to have a crew on board for a return of the Starliner,” Bowersox said at the press conference. “We still have time before we bring the Starliner home, and we want to use that time wisely. We expect to have data analysis ready for a … flight readiness review by the end of next week, possibly early the following week.”

Meanwhile, Boeing is in a bind. The Starliner’s first flight took place seven years after the launch originally promised for 2017 and cost $1.5 billion more than the original $4.2 billion contract NASA had given the company.

“We’ve had very honest conversations with each other,” Bowersox said of NASA and Boeing. “They have confidence in their vehicle. That’s what we expect from them. But … what the NASA team thinks is important, and when we come to a decision, we’ll go through it together.”

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One reason NASA is using every one of the few remaining days to make this decision has to do with the Starliner’s limited reusability. The crew capsule itself is designed to be recovered and redeployed, but the faulty engines are housed in a section called the service module, which is jettisoned before reentry and burns up in the atmosphere. That makes it impossible to conduct engineering forensics after the spacecraft returns, so NASA is trying to learn as much as it can from telemetry and data monitoring before the service module is lost forever.

At the August 14 press conference, a reporter asked if it would be possible for an astronaut from the station to do a spacewalk to check the health of the engines – a suggestion that Joe Acaba, ESA’s chief astronaut, quickly dismissed. “We are not planning a spacewalk,” he said. “The way the system is currently designed, we just don’t get that hardware back and can’t do much in real time.”

In the past, NASA might have been willing to push the crew a little harder, overcome those 1-in-270 odds, and fly Wilmore and Williams home in a less-than-perfect craft. Astronauts have returned safely to Earth in far more damaged spacecraft in the past — notably Apollo 13, which suffered a near-catastrophic explosion en route to the moon in 1970, and Gemini VIII, which spun out of control in orbit in 1966, nearly costing the lives of astronauts Neil Armstrong and Dave Scott before Armstrong got the craft back under control and then brought it home. But the twin losses of the shuttles Challenger in 1986 and Columbia in 2003 have made the agency much more risk-averse, and led to institutional changes designed to encourage mission managers to raise concerns long before such tragedies occur.

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“Personally, I’ve been very focused lately on the concept of combating organizational silence,” said Russ DeLoach, NASA’s safety and mission assurance branch chief. “Unfortunately, when you look at both Challenger and Columbia, you see cases where people could put forward the right data or a valid position, but the environment just didn’t allow it.” Challenger launched during a Florida freeze – which contributed to its predictable explosion – and Columbia was flown home when it couldn’t reenter the atmosphere. A rescue shuttle might have helped save the crew.

This new caution has left Wilmore and Williams stuck. Their original work plan for their eight-day mission was to spend most of their time checking the Starliner’s systems. They have long since finished that work, and in the months that followed they have pitched in, conducting experiments and maintenance on the ISS, just as they have done during their previous assignments aboard the station.

“I spoke to both of them a few days ago,” said Acaba. “They have fully integrated into the … crew. But we are only human, and it is hard on the crew members and their families, and we take that into account.” Still, Acaba said, Wilmore and Williams will only be able to accommodate so much in the extra months they will spend in the air: “They will do what we ask of them; that is their job as astronauts.”