After months of consideration, NASA said Thursday that it will finally decide the fate of two astronauts on board the International Space Station, Butch Wilmore and Suni Williams, by this weekend. As soon as Saturday, the two crew members will learn whether they’ll return on a Starliner spacecraft in early September or a Crew Dragon vehicle next February.

On the eve of this fateful decision, the most consequential human spaceflight safety determination NASA has had to make in more than two decades, Ars has put together a summary of what we know, what we believe to be true, and what remains yet unknown.

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For a long time, I was pretty confident that Butch and Suni would come back to Earth on Starliner. I trusted NASA and Boeing officials when they said they just needed to test the vehicle a bit more and become confident enough in the data and analysis to clear the crew to come home on the original spacecraft. … However, as of Friday, my best information continues to point toward a Crew Dragon return as the most likely outcome.