Already strapped into their capsule, the four astronauts awaited a final decision, which came down with less than an hour remaining in the countdown. SpaceX canceled for the day. The company did not immediately announce a new launch date, but noted the next try could be as early as Thursday night.

Once at the space station, the U.S., Japanese and Russian crew will replace Wilmore and Williams, who have been up there since June. The two test pilots had to move into the space station for an extended stay after Boeing’s new Starliner capsule encountered major breakdowns in transit.

Starliner’s debut crew flight was supposed to last just a week, but NASA ordered the capsule to return empty and transferred Wilmore and Williams to SpaceX for the return leg.

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an astronaut launch for NASA on Wednesday night.