NASA has named the four astronauts who would fly the last-ever space shuttle mission next summer, should Congress approve the flight.

Officially, the four astronauts announced Sept. 14 are assigned to STS-335, the rescue mission that would fly only if needed to home the members of the Space Shuttle Endeavour’s STS-134 mission in February, currently the final scheduled shuttle flight.

But if Congress directs NASA to add a shuttle flight to the manifest, then the STS-335 crew and the Space Shuttle Atlantis would launch in June carrying supplies and spare parts to the international space station.

Since the 2003 Space Shuttle Columbia accident, NASA has trained a launch on need crew to be ready to fly in the event of irreparable damage to a shuttle while in orbit. Typically, the next crew to fly serves as the rescue crew for the current mission.

“These astronauts will begin training immediately as a rescue crew as well as in the baseline requirements that would be needed to fly an additional shuttle flight,” Bill Gerstenmaier, NASA associate administrator for space operations, said in a statement. “The normal training template for a shuttle crew is about one year prior to launch, so we need to begin training now in order to maintain the flexibility of flying a rescue mission if needed, or alter course and fly an additional shuttle mission if that decision is made.” All four crewmembers have prior space shuttle experience. They are: Chris Ferguson, a retired U.S. Navy captain and two-time space flyer who would serve as commander; Doug Hurley, U.S. Marine colonel, who would serve as pilot; and astronaut Sandy Magnus and retired U.S. Air Force Col. Rex Walheim, who would be the mission specialists.