After months of debate, a NASA spending bill is expected to appear for a vote on the House floor today (Sept. 29).?

House lawmakers are expected to vote on a version of the NASA authorization bill passed by the Senate in August, instead of a compromise bill floated last week by Congressman Bart Gordon (D-Tennessee), who chairs the House subcommittee on science and technology. If no vote occurs, the measure would have to wait until after the Nov. 2 elections.

?I anticipate that the House will consider the Senate version of the NASA reauthorization on Wednesday," Gordon said in a statement released Monday (Sept. 27). [NASA's New Direction: FAQ]

Extra shuttle flight on the table

The Senate approved its version of NASA's authorization bill on Aug. 5. That bill, S. 3729, approved ?$19 billion for NASA in 2011 as part of a three-year budget of nearly $60 billion.

If approved by the House as is, the Senate's NASA bill would officially allow NASA to add one extra space shuttle flight to the two final missions already planned before the shuttle fleet is retired in 2011. But that would not affect the coming Oct. 1 layoffs of nearly 1,400 shuttle workers by NASA contractor United Space Alliance ? a joint venture by Boeing and Lockheed Martin that oversees NASA's shuttle fleet.

USA announced the shuttle worker layoffs in July as part of a workforce reduction plan due to the space shuttle fleet's impending retirement. Those layoffs, which affect workers in Florida, Alabama and Texas, will take effect Friday.

At the time, USA spokeswoman Kari Fluegel told SPACE.com that the layoffs would occur despite the addition by Congress of an extra shuttle flight to NASA's ?schedule.

In addition to the extra shuttle flight, the bill would extend the International Space Station through at least 2020. It also sets aside $1.3 billion over three years to support the development of commercial spacecraft, less than half of the $3.3 billion the White House has requested.?

The Senate bill also directs NASA to begin work on a new heavy-lift rocket in 2011, which would be essential to launch massive components for future deep space missions. The White House's space plan calls for that work to begin later, in 2015.

Supporters of the Senate bill said its passage should clear the way for new jobs among commercial space firms, which NASA plans to rely on to send astronauts into low-Earth orbit as part its new space exploration plan.

"A protracted stalemate over the NASA authorization bill would likely cause continued layoffs and would make it more difficult for commercial companies to ramp up hiring," said Bretton Alexander, president of the Commercial Spaceflight Federation, in a statement. "We cannot afford to delay the creation of new jobs, and the Senate bill, which we support, could be on the President?s desk before the end of the week."

Critical time for NASA

President Obama's new space plan, announced in February, would cancel NASA's moon-oriented Constellation program and replace it with a more ambitious program aimed at deep space missions. The Constellation program called ?for Orion space capsules and Ares rockets to follow the shuttle program.

The new NASA plan, Obama later said in April, should send astronauts to an asteroid by 2025 and then aim for a manned Mars mission in the 2030s.

Obama also tasked NASA to draw on commercial space vehicles to ferry astronauts to and from the International Space Station. Until those commercial vehicles are available, the U.S. would rely on Russian Soyuz craft to fly humans in space and unmanned Russian, Japanese and European freighters to launch cargo.

Gordon said he hopes private companies will succeed with their commercial space vehicles, but he has reservations.

"I am wary of being completely dependent on them, because if they fail, we will be dependent on the Russians for longer than absolutely necessary," he said.

Some lawmakers unsatisfied

In his statement, Gordon said it was clear a compromise bill would not make it through the House and Senate before time ran out. The fiscal year ends Thursday (Sept. 30), leaving little room for more negotiations.

"For the sake of providing certainty, stability, and clarity to the NASA workforce and larger space community, I felt it was better to consider a flawed bill than no bill at all as the new fiscal year begins," Gordon said.

Among Gordon's major concerns is the Senate provision for an extra shuttle flight in 2011, as well as funding to speed up development of a heavy-lift rocket to jump-start NASA's deep space exploration effort. The Senate version, Gordon contends, does not explain how the shuttle program's extension will be paid for. NASA has said it costs $200 million a month to keep the shuttle program going.

"The Senate bill includes an unfunded mandate to keep the Shuttle program going through the remainder of FY 2011, even after the Shuttle is retired, at a cost of $500 million or more without clarifying where the funds will come from, all but ensuring that other important NASA programs will be cannibalized," Gordon said.

NASA officials have said the extra shuttle flight would likely fly sometime around June 2011 and deliver large spare parts and cargo to the space station.

The shuttle Discovery is slated to launch Nov. 1 to deliver a new storage room and humanoid robot prototype to the station. The shuttle Endeavour is slated to fly Feb, 26, 2011 to deliver a nearly $2 billion astrophysics experiment ? called the Alpha Magnetic Spectrometer ? to the space station. After that flight, the $100 billion station will be complete after more than 12 years of construction.