A key NASA supporter in Congress is beginning a formal push for an extra space shuttle flight, as NASA officials prepare to present options to top Obama administration officials next month.

Sen. Bill Nelson is putting language approving an additional space shuttle mission into the Senate's NASA reauthorization bill this year, the Florida Democrat wrote in a letter to President Obama this week.

NASA is preparing the shuttle Atlantis to fly on a rescue, or "launch on need" flight next year should the final shuttle flight be forced to take refuge on the International Space Station due to heat shield damage.

An external fuel tank and two solid rocket boosters will also be in place to support the rescue mission.

Credit: NASA

Nelson is advocating using those parts to launch one more shuttle flight if the rescue mission is not necessary. The new mission, called STS-135, would launch next summer under Nelson's proposal with a four-person crew and a package of needed supplies for the complex.

The White House is also going through its own decision process for the STS-135 flight.

"That discussion has gone all the way up," NASA chief Charles Bolden told a Senate committee May 12. "I have told people that there is the potential that I would like to fly the launch on need mission, and it would be for logistics reasons."

But the STS-135 mission would be left without its own rescue flight, the first time the shuttle would fly without such a contingency plan since the Columbia accident.

Russian Soyuz capsules, each capable of carrying three people, would be the only way home for stranded shuttle astronauts if STS-135 ran into trouble. That's why the crew on the flight would be limited to four astronauts, the smallest crew possible accomplish key mission objectives.

"It's not an easy decision because I would have no launch on need vehicle to back it up, and that's not trivial," Bolden said.

NASA managers say they need to know by next month whether to execute plans for the mission.

"At some point, we've got to quit working options, write them down on a piece of paper, and get serious and get ready and go execute," said Bill Gerstenmaier, NASA's associate administrator for space operations, in a press conference Wednesday.

STS-134, currently the last planned shuttle flight, is slated to launch late this year or in early 2011 with cargo and an international astrophysics experiment. The STS-133 mission of Discovery is the next scheduled launch this fall.

Space station officials say the best time for an extra shuttle flight would be around June 2011, after the two planned shuttle missions and European and Japanese cargo freighters reach the outpost this winter. That schedule would best ensure the space station has all the supplies it needs after the shuttle's retirement and before unmanned commercial U.S. cargo carriers begin launching.

"It will allow us to more smoothly transition the workforce in Florida and Texas from the shuttle program to the vision you've set for NASA's future," Nelson wrote in the letter to President Obama. "It will also guarantee U.S. access to space for a longer period of time, and thereby help to close the spaceflight gap until a new domestic capability is provided. Last but not least, it will reduce risk to the station should a major component fail and need to be replaced before STS-135 is flown."

The president's budget request for fiscal year 2011 includes $600 million to pay for shuttle operations through Dec. 31, but more money would have to be appropriated to pay for delays into calendar year 2011 or an extra shuttle flight.

Shuttle managers say it will cost between $150 million and $200 million to maintain the program's workforce each month through the final flight, whenever that occurs.