Live coverage: SpaceX Falcon Heavy launches NASA’s Psyche on mission to a metal asteroid

A troublesome liquid oxygen valve on the Space Launch System’s first flight-rated core stage will keep NASA from performing a second test-firing of the rocket’s four main engines this week.

Eric Boe, one of three astronauts assigned to the first piloted test flight of a Boeing CST-100 Starliner commercial crew ship later this year has been removed from the mission due to unspecified medical issues, NASA announced Tuesday. He will be replaced by veteran astronaut Mike Fincke.

A 6.6-million-pound Apollo-era crawler-transporter rolled up the ramp to pad 38B on Tuesday and was positioned directly under the 3.5-million-pound Space Launch System rocket and its 11.3-million-pound mobile launch platform.