In the Apollo program much was made of the importance of the human involvement. Jim Irwin found the Genesis Rock sitting on top of a grey mound at the Apollo 15 site. Jack Schmitt, the only trained field geologist-astronaut, discovered orange soil underfoot close to Apollo 17. May be robots would have missed these. Apollo 13 showed how humans can react to the unexpected If something breaks they have a chance of being able to mend it. Robots are (as yet) very poor at repairing themselves.

But think of the problems. Humans are big; they use up 30 kg of raw material every day. And they have to be kept in a very precisely controlled environment. Too much heat or too much cold and they die. Very soft landings are required as are very, gentle take offs. Robots are not like that. Initially we humans will also need to take everything with us. In the future we might possibly find some water on Mars and Moon but there is no food and no free oxygen. Humans have to be kept healthy in space, and mentally active. Unlike robots, they cannot be switched off. Even though Valeri Polyakov lived in the Mir space station under zero-gravity conditions for 438 days, prolonged exposure to zero-gravity is still life-threatening. When weightless muscle and bone mass has been found to decrease by 1 % per month. And again, unlike with robots, ethics dictates that you cannot just send someone out there and not bring them back alive. Suicide missions are unthinkable. And to cap it all humans are extremely difficult to sterilise. It is highly likely that we would contaminate Mars when we started to wander over its surface and this could destroy the life-evidence that we are seeking.

The dangers to humans of bringing Mars soil into the landing craft must also not be underestimated. And returning Mars samples to Earth might be life-threatening to our population.

Apart from the rather unexciting low Earth orbit there are only two space places that humans can reasonably go to in the near future, these being the Moon and Mars. The Moon is easy. We have done the hard part; we have already shown it is possible to get there. All we have to do now is to return and stay. But if we stay for a month, near the lunar equator, we know that the ambient temperature will increase at lunar mid-day to a blood boiling 111°C, and then drop fourteen days latter, at lunar midnight to an oxygen-liquefying 170°C. Astronauts will have to dig themselves into lunar caves and insulate themselves from this violent temperature variation by covering their landing craft with deep layers of lunar soil.

Mars is much more difficult to get to than the Moon. This planet never gets closer to Earth than 56 million kilometres, and when it is behind the Sun is a huge 400 million kilometres away. A trip to Mars would take about 180 days, and a similar time is needed to get back. If Mars is visited when near conjunction, i.e. when Mars is on the same side of the Sun as Earth, one would most likely have to wait some 550 days until the next conjunction to come back. In this case the total trip time is about two and a half years. Mars is frosty-cold, the atmosphere is hostile and thin and its lack of oxygen and ozone means that the surface is exposed to dangerous levels of ultra-violet radiation. But at least Mars has a gravitational field that is 38 % of the Earth’s and it does go round every earth day or so. Another problem with the human exploration of Mars is the nagging thought that one could send about a hundred robot probes to Mars for the cost of a single manned mission