BBC News, San Francisco
Lord Rees thinks the UK should focus attention on unmanned spaceflight
Europe should give up on sending men and women into space and concentrate on unmanned projects, according to one of the world's leading astronomers.
The future lies in using advanced robotics, miniaturisation and fabrication, said Lord Martin Rees, the president of the Royal Society.
Europe "should try and get a world lead in unmanned exploration", he said.
Spending funds on manned spaceflights "was not a very good use of money", that should be left to the US, he said.
Three-quarters of Nasa's money was spent "going round and round the Earth 35 years after people had already walked on the Moon", Lord Rees said.
Nasa has a budget this year of more than $17bn (£9bn; 11bn euros), in contrast to the UK's annual civil space budget of £220m ($430m; 270m euros) and the European Space Agency's (Esa) expenditure of 3bn euros (£2.5bn; $5bn).
Steal a march
Speaking to the BBC during a week-long trip to California to promote the Royal Society, Lord Rees said manned missions were largely irrelevant.
These days, no-one gets excited in the way they once did over the early Apollo programme, he added.
"The space shuttle only really makes headlines when there has been a disaster," he said. "Routine shuttle launchings don't make headlines.
"What actually makes the newspaper headlines are the marvellous pictures from the Hubble telescope and those of the surface of Mars and Jupiter and Titan, all obtained robotically."
Lord Rees, the professor of Cosmology and Astrophysics at Cambridge's Institute of Astronomy, said the unmanned part of Nasa's project was - like Europe's - hugely successful.
This, he said, was where the UK should concentrate its energies.
"If I was an American, I would be opposed to a return to the Moon and going to Mars," he said.
"We in Europe should try and get a world lead in space exploration and applications," said the Royal Society president, who also holds the position of English Astronomer Royal.
"Manned missions are hugely more expensive and the practical case for sending people weakens with every advance in robotics and miniaturisation."
Despite his views, though, Europe is pursuing a vigorous human spaceflight policy and has so far spent 5bn euros ($8bn; £4bn) on the space station.
Just last week, Esa unveiled a campaign to recruit the European astronauts of tomorrow.
Britain has also hinted at a change in its long-standing opposition to human space activities following several high-profile reports.
One, a specially convened government advisory panel, suggested the UK's policy has damaged the country both scientifically and economically.
While the notion of a Briton in space could be inspirational for young people, it could also present all sorts of opportunities for business.
In the past, British companies have been denied the chance to bid for high-profile contracts in the human spaceflight arena. That looks set to change.
But Lord Rees remains adamant there is only one path to take and that the UK and Europe are wasting time trying to best the US or Russia in human spaceflight.
"For historical reasons connected with superpower rivalry, space is one of the arenas where America and Russia have a bigger budget for space than Western Europe," he said.
"Whereas in everything else, Western Europe is fully a match for the US. We can be more effective in space if we focus all our budget on miniaturisation, robotics, and fabricators and avoid manned spaceflight."