NASA doesn't know yet where it will get the money, but on Thursday the space agency officially added another space shuttle launch to its schedule — the final one for the fleet.
The space agency set a target launch date of June 28 for the shuttle Atlantis and started preparations for the 135th and last shuttle flight. The four-member crew will take up supplies to the International Space Station, make one spacewalk, and return a faulty pump that has bedeviled engineers.
Now three missions remain before NASA retires its shuttle fleet this year. The shuttle Discovery's last mission is slated for Feb. 24, and Endeavour's is set for April.
Thursday's move allows different parts of the shuttle program to start work on Atlantis' 12-day flight, including astronaut training and mission planning, NASA spokesman Michael Curie said.
Atlantis was originally planned as an emergency-only rescue mission if needed for the Endeavour crew, and it will continue to serve as a backup shuttle for that mission, as "STS-335." But if Endeavour's flight proceeds normally, Atlantis will then be prepared for its own resupply mission, STS-135.
Last year, the Obama administration and Congress clashed over the future of the human space program and came up with a compromise that authorized one extra flight of the shuttle — the Atlantis mission. But Congress never gave NASA the few hundred million dollars needed for the extra flight. That left NASA in a quandary about whether the flight was real or not.
The initial money is coming from the space shuttle program's regular budget, but that can't provide the big dollar amounts needed for a shuttle flight, Curie said.
"We're optimistic that the funding will be there," Curie said, but he couldn't give details about where the money will come from. The current scenario calls for Congress to appropriate the funds in March.
NASA was under the gun to start preparations. Otherwise, the Atlantis mission wouldn't have been able to launch in late June, Curie said.
The final flight will be commanded by Christopher Ferguson and includes Douglas Hurley, Sandra Magnus and Rex Walheim. It's been decades since a four-person crew flew on the shuttle, but STS-135 will have a minimal crew for safety's sake. If Atlantis is unable to return from space for any reason, the crew members would be rescued from the station using Russian Soyuz spacecraft.
The extra flight means that Mark Kelly — the husband of wounded U.S. Rep. Gabrielle Giffords — will not command the final shuttle flight even if he stays on the Endeavour mission. With his wife's expected long rehabilitation, Kelly asked for a backup commander to be named in case he couldn't fly as scheduled in April.
After the fleet's final flight, the shuttles would be retired and distributed to three museums around the country. NASA would have to rely on other countries' spacecraft as well as commercial spacecraft currently under development for its station transport needs. Eventually, NASA would turn to a new generation of spaceships for long-term exploration.
This report was supplemented by msnbc.com.