US President Barack Obama has praised the "heroism¹" of the men who made the first landing on the Moon.

美国总统奥巴马赞扬当年月球首次登录宇航员的“英勇事迹”。

Marking the 40th anniversary of the event, he said Americans continued to draw inspiration from（从……得到启示） Neil Armstrong, Buzz Aldrin and Michael Collins.

"I think that all of us recall the moment in which mankind finally was untethered（解下栓牛马的绳、链） from this planet," he added.

Earlier, Mr Aldrin and Mr Collins called for renewed efforts to send a manned mission to Mars.

Neil Armstrong, the first man on the Moon, said the race to get to the Moon had been the ultimate peaceful contest（竞赛，争论）.

He said it was an "exceptional national investment" for the US and the former USSR.

He spoke² at an event at Washington DC's National Air and Space Museum.

Shortly afterwards, the three astronauts met Mr Obama at the White House.

Mr Obama, who was seven years old when Mr Armstrong and Mr Aldrin took mankind's first steps on the lunar surface, said it was "wonderful" to be in the company of the three history-makers.

"The moment in which we had one of our own step on the Moon and leave that imprint³... is there to this day," Mr Obama said.

He praised the astronauts for the "heroism, the calm under pressure, the grace" with which they operated.

Their achievement, Mr Obama said "was somehow able to lift our sights, not just here in the United States but around the world".

'Great symbol'

The American space industry wants the Obama administration to agree to send Nasa crews back into space, first to the Moon and then to Mars, reports the BBC's Kevin Connolly, in Washington.

A decision could be due later this year, although there is no guarantee Mr Obama will make funds available, our correspondent says.

Speaking at the museum, Mr Armstrong said the Moon race was a "diversion（转移，娱乐活动）" in the Cold War battle between the US and the USSR.

"Eventually, it provided a mechanism⁴（机械，机构） for engendering⁵（产生，引起） co-operation between former adversaries⁶. In that sense, among others, it was an exceptional national investment for both sides."

Fellow astronaut Mr Aldrin praised President John F Kennedy's bold decision to pronounce that the US would land men on the Moon before the end of the 1960s.

"Apollo 11 is a symbol of what a great nation and a great people can do if we work hard, work together and have strong leaders with vision and determination," he said.

But he also pushed for a mission to Mars: "The best way to honour and remember all those who were part of the Apollo programme is to follow in our footsteps; to boldly go again on a new mission of exploration."

Mr Collins, who circled the Moon alone while Mr Armstrong and Mr Aldrin walked on it, said Mars was more interesting than the Moon.

"Sometimes I think I flew to the wrong place. Mars was always my favourite as a kid and it still is today."

He urged further exploration, saying Mars was a "much more worthwhile destination".

Other Nasa astronauts gave a news conference at Nasa headquarters in Washington DC on Monday.

Eugene Cernan, who was the last astronaut to step off the Moon, in 1972, concurred⁷ with the Apollo 11 astronauts and called for a new focus on Mars.

"We need to go back to the Moon, we need to learn a little bit more about what we think we know already, we need to establish bases, put new telescopes there, get prepared to go to Mars. The ultimate goal, truly, is to go to Mars," he told journalists.

"I think the next major goal is not to spend three days, or three weeks or three months on the Moon, but to have you folks, or your kids, or your grand-kids sit here and talk to a group of guys who can tell you what it was like to go to Mars."

But Mr Aldrin disagreed with the view that astronauts should test capabilities⁸ for a long-duration flight on the Moon before attempting a journey to Mars.

"Why go to the most difficult place to do that? Why not do it on the International Space Station," he said.

Mr Aldrin added: "One day, we are going to send some people to the surface of Mars. And if we think we're going to send them there for a year-and-a-half and then bring them back, and then send another group there for a year-and-a-half and bring them back, Washington will find another way to spend that money.

"That's unless we have declared our objective is an increasing, permanent space settlement."

The US space agency's currently stated aim is to return astronauts to the Moon by 2020. But that vision is under review, along with the space vehicles that would get them there.

Nasa is due to retire its space shuttles next year and replace them with the Orion spacecraft, an Apollo-like capsule that would launch on a new rocket called Ares 1.

Another rocket, Ares V, would have the capability⁹ to launch heavy payloads（有效负载） - service and cargo¹⁰ modules¹¹ - that would be needed to service Moon missions.