If the pioneers of the Earth's great age of exploration had had to carry all their supplies upon their backs - food, water and even the air that they breathed - most of our planet would still be an uncharted wilderness. Yet the men and women who will explore the solar system in the 21st century must bear just such a burden, unless, like their predecessors on Earth, they can learn to live off the land.
Fortunately, future astronauts may be able to do exactly that. The solar system is rich in energy and raw materials. If we can learn how to exploit them in situ, we will quite literally take a huge load from the shoulders of our explorers.
Consider, for example, a lunar mission - a possible target of ESA's Aurora programme. For an exploration team to live in long-term comfort on the lunar surface, each person requires around 30 kg of consumables daily - food, water and air. To put a kilogramme of anything on the Moon means launching about 4.5 kg into Earth orbit. The extra mass is simply the rocket propellant needed for the lunar trip and a soft landing at the final destination. Since at current prices it would cost around 100,000 Euros to put those 4.5 kilos into orbit, supplying and resupplying our lunar explorers will rapidly burn a very big hole in the most generous budget.
There is a better, cheaper way to do things. Most of the 30 kg daily allowance consists of oxygen, either in the form of air for breathing or locked into water molecules. Very conveniently, the lunar regolith - the loose, powdery 'soil' that covers the surface of the Moon - is about 45% oxygen.
This indigenous resource could also be used as construction material to shelter humans against the harsh radiation environment, to provide for needed storage facilities, or to extract other material such as metals or silicon for further applications. With the help of some relatively simply technology, the lunar explorers can tap into an almost unlimited supply and they will have a truly unlimited supply of solar energy to power their biochemical 'factories'.
With lunar oxygen available, resupply costs undergo a startling transformation. Not only do the explorers have a homegrown source of breathing air but they need no longer import liquid water, which forms the greater part of their daily allowance. All they need is hydrogen, which is almost non-existent in the lunar rocks. The resupply burden shrinks by 80% and the support costs drop from the fantastic to the feasible.
In principle, similar techniques will allow us to exploit the resources of the moon and Mars. With an abundant supply of locally-produced air and water, astronauts could even grow much of their own food - in greenhouses made from extraterrestrial glass.
In-situ resources will ultimately yield much more than life-support. If astronauts can find - or make - water, they can also make rocket propellant. Better still, robot chemical plants could generate the fuel before the humans arrive: the idea already features in several proposals for manned Mars missions. With no need to haul propellant for a return trip, a Mars ship would be vastly cheaper as well as more comfortable for its crew and much better provided with scientific equipment.