This story was updated at 4:25 p.m. ET.

A key Senate committee on Thursday approved an authorization bill that would allow NASA to add one more space shuttle mission before retiring the fleet, and press forward with ambitious plans to send astronauts to an asteroid and on to Mars.

After months of debate and criticism, the Senate's Commerce, Science and Transportation committee passed the NASA authorization bill by a unanimous vote. The bill will now move up to the full senate for review.

?NASA is an agency in transition. We?ve had to take a clear, hard look at what we want from our space agency in the years and decades to come," said Sen. John D. Rockefeller, IV (D-West Virginia), who chairs the Senate committee, in a statement. "I?ve made my views on this matter very clear: NASA?s role cannot stay static. It must innovate and move in a new direction."

The extra shuttle mission would fly in 2011, after two more flights currently planned for November 2010 and February 2011.

In addition, the new authorization bill directs NASA to immediately begin work on a huge, heavy-lift rocket ? which would be vital for any asteroid or Mars missions by astronauts ? instead of waiting until 2015 as proposed by President Barack Obama in his initial space vision announced earlier this year.

The bill would also advance the development of spacecraft for deep space missions to as early as 2016, rather than 2025 ? the goal for the first crewed mission to arrive at an asteroid announced by President Barack Obama earlier this year.

It also allows the extension of the International Space Station's program through at least 2020, also as previously proposed by Obama. [FAQ: NASA's New Direction]

Extra shuttle flight, new spacecraft

NASA's new direction has been the focus of much debate, with some critics calling for an extension of the space shuttle program, which has been slated for retirement next year. Originally, NASA's Constellation program to return to the moon was planned to replace the shuttles, but President Obama's new plan called for canceling Constellation. Some lawmakers have argued to keep Constellation, or to replace it instead with a more shuttle-derived alternative.

"For many months, this committee has been working on a bipartisan basis to develop a strong and forward-looking reauthorization bill for NASA," Rockefeller said. "Through this process, I believe we?ve reached a sensible center. This bill offers what I like to call a ?third way? for NASA."

The bill is a compromise of sorts between Obama's plan and its detractors, the committee said.

"It has been a long and very hard road to get here,? said committee member Sen. Kay Bailey Hutchison (R-Texas), who co-sponsored the bill, in a statement. ?We began more than four months ago with a new proposal for NASA introduced by the President which I believe would have ended the era of U.S. dominance in space exploration, threatened the use of the space station, and jeopardized manned spaceflight. This legislation approved today represents a strong balance between the need for investment in new technology and the continued evolution of the commercial market to take an increasing role in supporting our efforts in low Earth orbit."

The authorization bill clears the way for the extra shuttle mission, allowing NASA to press forward with preparations to launch more vital supplies or spare parts to the International Space Station to stock up for the years ahead without the space plane fleet.

NASA's next two shuttle flights will also help complete construction of the International Space Station. The extra space shuttle flight, likely aboard the shuttle Atlantis, would carry a four-astronaut crew to the space station in the summer of 2011, NASA shuttle officials have said.

NASA's space shuttles are the only spacecraft currently capable of hauling huge experiments and spare parts for the space station. Once they retire, the space agency plans to use Russian spacecraft to ferry crews and cargo to the orbiting laboratory until American commercial vehicles become available.

Obama also called for the cancellation of NASA's Constellation program developing new rockets and spacecraft to return astronauts to the moon. In its place, he proposed an ambitious goal of sending astronauts to an asteroid by 2025 and on to Mars in the mid-2030s. A focus on new space technology was key, Obama emphasized.

"In short, this bill provides a blueprint to get our nation?s space program moving forward in a smart, fiscally responsible way, and in a way that will maintain America?s edge in space flight, exploration, science and aeronautics," Rockefeller said.

Commercial spacecraft funding

The NASA authorization bill falls largely in line with the space exploration plan proposed by President Obama in February, but with some differences.

Obama's space vision called for a 2011 budget of $19 billion for NASA (a slight boost from 2010). It also called for $6 billion over the course of five years (with about $3.3 billion of that pegged for the first three years) support the development of commercial spacecraft that could fly American astronauts into space after the shuttle fleet is retired next year.

As approved Thursday, the NASA authorization bill would allocate $1.6 billion of the funds for commercial spaceships over the next three years, according to a statement released by committee member Sen. Bill Nelson (D-Florida), who chairs its space subcommittee and represents the state that is home to NASA's space shuttle launching site.

?The goal was to preserve U.S. leadership in space exploration and keep as much of the rocket-industry talent as possible employed,? Nelson said.

Commercial spaceflight advocates, such as the Space Frontier Foundation, have criticized the new bill because of its drop in funding for private spacecraft development.

The foundation urged support for an amendment, proposed by Sen. Mark Warner (D-Va.) would have added $2.1? billion for commercial spaceflight over the next three years to ensure it was funded at the level requested by President Obama.