President Barack Obama signed a NASA spending bill into law Monday, following last week's approval by Congress. The measure directs NASA to move forward with an additional shuttle flight to the International Space Station, before retiring the fleet.
Sally Ride, the first American woman in space who took part in a White-House ordered review of human spaceflight, said the extra flight represents "an important extension" for supporting the space station.
The orbiting lab is meant to operate until at least 2020, with U.S. astronauts hitching rides on Russian Soyuz capsules until private companies in America can pick up the slack.
During a telephone press conference Monday, Sen. Bill Nelson, D-Fla., said the funding issue should be resolved once Congress returns next month to Washington in a lame duck session. The space agency expects a final decision no later than December.
Only two shuttle launches officially remain, with the next one coming up Nov. 1. The third, yet-to-be-formalized mission would take place next June. Atlantis already is being prepped in case it needs to rescue the crew of Endeavour, set to fly in February.
Only four astronauts -- instead of the usual six or seven -- are assigned to that rescue mission. The crew size will remain the same if NASA gets the third shuttle flight. NASA wants to limit the number of crew members who would need to take refuge at the space station in case Atlantis is damaged at liftoff and couldn't be flown back to Earth.
Those four shuttle astronauts would need to return on Soyuz spacecraft over the course of a year.
The NASA Engineering and Safety Center reported last month that the risks associated with an additional shuttle flight -- with no shuttle backup -- were in line with others accepted by the shuttle and station programs in the wake of the 2003 Columbia disaster.
Nelson said an additional flight will ease the impact of shuttle job cuts.
"Instead of the shuttle work force dropping precipitously off of a cliff, it smooths that transition" as work begins on a new heavy-lift rocket and commercial spacecraft pick up steam, the senator said. He described the post-shuttle period as "the new NASA."
Obama's plan for NASA calls for eventual missions by astronauts to asteroids and Mars, and shelves his predecessor's goal of returning to the moon.