A plan to return US astronauts to the moon "is dead," a White House adviser on space issues said Friday, confirming reports that NASA will instead focus on developing commercial space transport.

"Constellation is dead," the adviser told AFP on condition of anonymity, referring to a program that envisioned returning to the moon by 2020 and using Earth's nearest neighbor as a base for manned expeditions to Mars.

Florida Today newspaper first reported the demise of the program Thursday, saying the plan was doomed by financial constraints in the 2011 budget which President Barack Obama is to present to Congress on Monday.

Reports added that the US space agency will work on finding a commercial solution to ferrying US astronauts to the International Space Station after the scheduled end of NASA's shuttle program in September 2010.

Only five more shuttle flights, including a mission by the Endeavor set for a February 7 launch, are planned.

Astronauts will be able to hitch rides aboard Russian Soyuz spacecraft, but the United States will need a commercial alternative if Congress approves White House plans to scrap development of a successor to the shuttle program.

The administration reportedly plans to hike NASA's budget by 5.9 billion dollars over five years to boost commercial development, with the goal of a first commercial flight to the ISS launching by 2015, the source said.

The Constellation program was launched in 2004 by then-president George W. Bush.

Space expert John Logsdon said the abandonment of the program did not spell the end for US ambitions in space.

"While Constellation is dead, it does not mean human space exploration is also dead," said Logsdon, former director of the Space Policy Institute at George Washington University.

He said NASA would probably start to plan with the private sector and international partners for the future of the ISS past 2020.

Getting the cancellation through Congress would be "tough," he added, as lawmakers from Florida and other states with close ties to the space program would oppose anything that threatened local jobs.

News of Constellation's cancellation came as NASA marked its day of remembrance, honoring astronauts who died in the Apollo 1, Challenger and Columbia space missions.

President Obama released a statement paying tribute to those "who lost their lives supporting NASA's mission of exploration and study of the Earth, the planets and the stars."

"All of humanity has benefited from their courage and devotion," he said.

"We mourn their loss while celebrating their spirit of discovery. May their sacrifice be an inspiration as we continue our nation's work to explore our universe."