United States space officials have welcomed President George W Bush's desire to send Americans to Mars and back to the Moon.
The Mars mission will not take place for 10 years
Nasa chief spokesman Glenn Mahone said the agency was "excited" about the news and its implications.
But some critics of the plan have objected to the high costs involved.
Mr Bush will announce the proposals next week, which will include plans for the construction of a permanent lunar space station.
Officials say Mr Bush intends to reinvigorate the US space programme following setbacks such as the Columbia shuttle disaster.
The manned mission to Mars - where Nasa successfully just landed a probe - is not expected for at least 10 years. Correspondents say Mr Bush had been expected to propose a bold new space mission as part of his re-election campaign.
Mr Mahone did not give any details of the forthcoming announcement, but said it would be good for the US space agency.
"We're not going to pre-empt the president," he said. "But we're excited about the news of the announcement next week and what it means for the future direction of Nasa."
The National Space Society in Washington was also celebrating.
"This is probably the most excited I've been about our prospects for a long time," said executive director Brian Chase.
Experts say, however, that the costs and commitment required to get people to Mars, or even back to the Moon, should not be understated.
"The cost of a manned enclave on the Moon, I think, is going to make the space station look cheap. That's the only good thing about it," Stanford University's Douglas Osheroff told AP.
Howard Dean, Mr Bush's likely Democrat challenger in November's presidential elections, said the US simply might not be able to afford a new space programme.
"I'm very much in favour of space exploration," he said. "Where is the tax increase to pay for it?
"We already have a
half-a-trillion-dollar deficit. It is not worth bankrupting the
country if that's what's going to happen.
"This president needs
to be serious about the budget deficit."
Lunar testing ground
The president's father proposed men be sent to Mars when he was in office in 1989 but the project went nowhere due to cost.
Sources say George W Bush will encourage scientists to prepare for the mission in a decade's time, allowing the costs to be spread over a number of years.
The last time the US had men on the Moon was more than 30 years ago.
As the Moon is just three days away, while Mars is at least six months away, it is thought the former could become a testing ground for space equipment.
As part of the Bush space initiative, there will reportedly be more exchanges of technology between (Nasa) and the Pentagon.
It is hoped the exploration could lead to new technologies and potential new energy supplies.
Wholly new rocket and capsule systems would have to be developed.
Although the Moon is relatively close at a distance of 385,000 kilometres, a mission to Mars would require astronauts to live off Earth for several years.