Enlarge / NASA astronauts Suni Williams and Butch Wilmore, seen in their Boeing flight suits. (credit: NASA/Francisco Martin)

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.

Why has NASA taken so long?

Wilmore and Williams arrived at the International Space Station 11 weeks ago. Their mission was supposed to last eight days, but there was some expectation that they might stay a little longer. However, no one envisioned the crew remaining this long. That changed when, during Starliner's flight to the space station, five of the 28 small thrusters that guide Starliner failed. After some touch-and-go operations, the astronauts and flight controllers at Johnson Space Center coaxed the spacecraft to a safe docking at the station.