Those advocating a return to the moon on economic grounds should read 'Mining the sky' by John Lewis, a professor at the University of Arizona who specialises in Space Development. He says that the argument for mining Helium 3 on the moon is a red herring because the quantities per ton of lunar soil are so small that it will be economically unviable to collect (assuming we ever develop He 3 fusion - it's hard enough developing deuterium fusion). Furthermore, it would be much more cost effective to send an unmanned probe to one of the outer planets where huge amounts of He 3 can be mined directly from their atmospheres.

The science per dollar from manned space exploration is very poor, I am not against human spaceflight but it should be ring-fenced from the science budget. The best strategy would be to use taxpayers money to push for cheap (sub $100/kg) spaceflight and give private companies the incentives (prizes, tax-breaks) to lead space development.

Phil Uttley, Southampton, UK

In economic and intellectual firepower, Europe is fully a match for the US? Hardly.

William Worsley, Arlington, Virginia

Umm Europeans where the reason the US space race got to where it was... almost all the rocket scientists came from europe..

Darren , London,

You all do realize that NASA has performed many of the smaller "bite-sized" missions in addition to the larger manned missions right? NASA has rovers on Mars and spacecraft orbiting Mars, probes on their way to Pluto, and others orbiting the Sun, and another just past Mercury. And those I mentioned are only the tip.

Justin, Orangevale, California/United States

In economic and intellectual firepower, Europe is fully a match for the US? Hardly.

William Worsley, Arlington, Virginia

Manned exploration and robotic exploration can complement each other. A manned mission to the moon is within our technological and physical realm. Further to Gareth Roberts point, can I suggest a book called " Return to the Moon" by Apollo 17 astronaut/scientist Harrison Schmitt that goes into the subject of Helium-3 and the benefits such a mission might bring.

Michael, London, England

Professor Rees, it would perhaps have been wiser for you to write a column in the national paper about the failings of our astronomical funding, rather than that of another nation. As our funding body is currently 80 million GBP in debt, and is considering leaving a number of prestigous and important telescope sites (sites we are likely never to return to due to political and cost pressures), now is not the time to crow about the straightjackets the Americans have put themselves in.

David Hill, St Andrews,

"Everyone has heard of Nasa, many have heard of ESA, but few have heard of BNSC"

Says it all really. Manned space exploration captures the minds of ordinary people. Tinkering with clever robotic probes captures the minds of geeks and boffins. Lord Rees sits firmly in the latter camp. I sit firmly in the former.

G, London,

The real reason why we should invest in space exploration and going back to the moon is because scientists believe the moon contains large deposits of an extremely rare gas called Helium-3 which be mined and used to achieve nuclear fusion. The same process which powers the sun and would be a new source of almost inexhaustible, clean and pollution-free energy on Earth.

Surely a goal worth reaching for the stars for.

Gareth Roberts, Birmingham,

There's enough good science to be done to attack pressing problems to make wasting money on manned spaceflight look ridiculous. The manned lunar programme was a political gesture and vacuous in scientific terms. Lets's do the important stuff now and leave this stuff another few decades at least. It's irrelevant.

caffeineman, newcastle, uk

Not my words but true nonetheless.

"The earth is too fragile a basket for the human race to keep all its eggs in"

The ISS is also, perhaps, our first faltering step to a permanent location outside the hole In the end, clever folk programming remote sensors, and second guessing them when the communications lag is of the oorder of hours, will never have that edge of flexibility granted to the "man on the spot".

Andrew Fanner, Cowplain, UK

Manned space travel under current energy requirements is unjustifiable. In order for one man to travel to Mars and return would take the financial and resource requirements of millions.
The problem is that in order to develop any alternative 'space' delivery/propulsion system does require exploration as this is extending our understanding of gravity, a key to further exploration along with fundamental particle/energy research the sort due to take place at CERN.
A catch 22 situation, but, unfortunately private (excluding show ponies like Virgin Galactic) can neither afford or assume the risks.

Joe, Geelong, Australia, Victoria

Exploration isn't just discovering what you don't know, it's also, importantly, discovering you don't know what. We humans are peculiarly well equipped for this latter task. Neither NASA waste nor the associated American pork-barrel politics should be allowed to stop us.

Noel Falconer, COUIZA, France

"I hope, nonetheless, that some people now living will walk on Mars - though they will be adventurers, perhaps sponsored privately or commercially, accepting extreme cost-cutting and much higher risks than it is politically acceptable for Nasa to impose on publicly funded civilian astronauts."

But this same argument can be used against unmanned space exploration. Private companies can sponsor robots with "extreme cost-cutting" and "much higher risks" than government-funded robots.

So manned space exploration should be conducted by private firms only, and unmanned space exploration should be done by governments? This is inconsistent. Either both manned and unmanned space exploration should be funded privately, or both should be funded by governments.

Arguing that one should be funded privately and one funded publicly is clearly a double standard.

David Bourke, Sydney, Australia

It was a precious Astronomer Royal who suggested that, "Space travel is utter bilge." It is interesting to see that the current Astromomer Royal seems to share that sentiment. His suggestion that expeditions to Mars should be best done by the private sector is interesting, though more than a little unrealistic. A private company, even if it could devote the resources necessary for such an undertaking, would only do so if it could find some way to make a profit. Large, national projects, such as going to Mars or colonizing the Moon, are best done by governments that can devote the resources necssary. The private sector can and should certainly be made partners in such efforts. But waiting for the private sector alone to send people to Mars is a sure way to make sure that the first person to do so will be a Chinese military officer. Neither Lord Rees nor anyone else would very much enjoy a future in which the Chinese are dominate in space.

Mark R. Whittington, Houston, USA