This story was updated at 10:28 p.m. ET.

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

Currently, only two shuttle missions remain: the STS-133 mission aboard Discovery, which is scheduled to launch this November, and STS-134 on Endeavour in February 2011. However, NASA approved a final mission, STS-135, which would fly to the International Space Station on Atlantis next June. Congress is still mulling whether to approve the extra flight.

If Congress gives the thumbs-up to STS-135, the shuttle Atlantis would be commanded by Chris Ferguson, a retired U.S. Navy captain and veteran of two previous shuttle missions. Astronaut and U.S. Marine Col. Doug Hurley would serve as pilot, and astronauts Sandy Magnus and retired U.S. Air Force Col. Rex Walheim would be the mission specialists.

Space shuttle fleet retiring

This final shuttle mission would carry supplies and huge spare parts for the space station, pieces that are so large only NASA's space shuttles can carry them.

Atlantis last flew to the space station in May of this year on what NASA planned to be its final mission. If Congress approves one extra space trek for the orbiter, the STS-135 mission would be the 135th flight of NASA's space shuttle fleet, formally known at NASA as the Space Transportation System. The shuttles have been launching into space since April 1981.

NASA is retiring its three-shuttle fleet to make way for a new space exploration plan aimed at sending astronauts to an asteroid by 2025. Plans to retire the space shuttles were initially laid in 2004 by former President George W. Bush in the wake of the tragic 2003 loss of space shuttle Columbia and its seven-astronaut crew.

In August of this year, the Senate approved plans for the additional flight on Atlantis as part of its NASA authorization bill, but a House version of that bill has yet to be finalized.

Rescue mission training

Even if Congress nixes STS-135, the four astronauts will still train for some possible space time.

They'll be the rescue team that brings home Endeavour's STS-134 crew from the space station, should anything go wrong. NASA is calling this possible "launch on need" mission STS-335. The shuttle Atlantis would make that flight as well.

Based on recommendations made after the loss of Columbia, 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, associate administrator for NASA's Space Operations Mission Directorate, 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.

Ferguson flew on STS-115 in 2006 and STS-126 in 2008. Hurley served as the pilot on STS-127 in 2009. Magnus flew on STS-112 in 2002 and launched to the space station in 2008 on STS-126, where she served four and a half months as a flight engineer and science officer before returning to Earth on STS-119 in 2009. Walheim flew on STS-110 in 2002 and STS-122 in 2008.