WASHINGTON - NASA's human space flight program is too underfunded to fly, an independent panel of experts said Thursday in their final report to US President Barak Obama.

The 155-page document is pretty much along the lines of the review panel's summary report in August. It presents five options for Obama's advisors to choose from to push the space program forward.

"The US human space flight program appears to be on an unsustainable trajectory" due to lack of funds, panel leader Norman Augustine said in the report.

The former president of aerospace giant Lockheed Martin and ex-US Army undersecretary said the goals of the Constellation program launched in 2004 by then president George W. Bush were too much to chew for NASA.

Constellation aims to return to the moon by 2020 and then establish a lunar launchpad for a first human trip to Mars.

The National Aeronautics and Space Administration's yearly budget is about 18 billion US dollars, 10 of which are plowed into the human space flight program, chiefly in developing the successor of the space shuttle: the Ares 1 rocket and the Orion Crew Exploration Vehicle.

The Augustine Committee said an additional three billion US dollars a year are needed for NASA to meet the Constellation program goals or take human space flight the next step beyond the existing International Space Station.

"The committee concludes that the ultimate goal of human exploration is to chart a path for human expansion into the solar system," the report said.

"This is an ambitious goal, but one worthy of US leadership in concert with a broad range of international partners."