CAPE CANAVERAL, Fla. (AP) — NASA has replaced an astronaut assigned to Boeing's first launch with a crew.

Astronaut Eric Boe was pulled Tuesday from the upcoming test flight for unspecified medical reasons, after more than three years of training. Taking his seat will be Mike Fincke, a former space station commander.

Boeing plans to launch its first Starliner capsule without a crew this spring, followed by a launch with astronauts this summer to the International Space Station.

SpaceX — NASA's other commercial crew partner — could launch its Dragon capsule, minus a crew, next month. The capsule and Falcon rocket were on the launch pad Wednesday for a test engine firing.

Boe and three other NASA astronauts were chosen in 2015 as the first commercial crew members. They were assigned to either an initial Dragon or Starliner mission last year.

Boeing astronaut Chris Ferguson, who commanded the final space shuttle flight in 2011 before leaving NASA, said it would have been "an honor" to fly with Boe again to the space station. They were on the same shuttle flight in 2008 during station construction.

"The #Starliner team is bummed that he isn't making this trip," Ferguson said via Twitter, while noting Fincke "brings years of experience." Ferguson said he and NASA astronaut Nicole Mann, who's also on the first Starliner crew, are glad to have Fincke on board.

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