Four NASA satellites that will create a constellation of formation-flying spacecraft were placed aboard their shared United Launch Alliance Atlas 5 rocket Friday.

NASA’s ICESat 2 satellite has been bolted atop a United Launch Alliance Delta 2 rocket at Vandenberg Air Force Base in California as ground teams prepare for the final liftoff of the workhorse launcher Sept. 15.

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.