WET MARS: Plentiful, Readily Available Martian Water and Its Implications
Water and its major constituent, oxygen, in large specific quantities are essential for maintenance of human life, and providing them in adequate quantities is widely believed to be a major challenge for human Mars exploration and early settlement. The Martian regolith isn't known to bear either water or hydrogen, the ice-rich Martian polar regions are thermally inhospitable, and the measured water content of Mars' thin atmosphere represents a layer of liquid water of average thickness only about 1% that of the Moon: ~0.001 cm. Crucially, however, this atmospheric Martian water inventory is advected to everyplace on Mars by meteorological phenomena, so that the few cubic kilometers of liquid water-equivalent in the Martian atmosphere are available most anywhere when, merely for the effort of condensing it.
Well-engineered apparatus deployed essentially anywhere on Mars can condense water from the atmosphere in daily quantities not much smaller than its own mass, rejecting into space from radiators deployed over the local terrain the water's heat-of-condensation and the heat from non-ideality of the equipment's operation. Thus, an optimized, photovoltaically powered 0.3 ton water-condensing system could strip 35 tons of water each year from ~104 times this mass of thin, dry Martian air.
Given the 480 sec Isp of H2-O2 propulsion systems exhausting into the 6 millibar Mars-surface atmosphere and the shallow, 5.0 km/s Martian gravity well, 35 tons of water two-thirds converted into 5:1 O2/H2 cryogenic fuel could loft a crew-of-four and their 8-ton ascent vehicle into Earth-return trajectory. The remaining water and excess oxygen would suffice for half-open-cycle life support for a year's stay on Mars. A Mars Expedition thus needs to land only explorers, dehydrated food, habitation gear and unfueled exploration/Earth-return equipment Ð and a modest water/oxygen/fuel plant to operate on Martian atmospheric water. All of the oxygen, water and propellants necessary for life-support, extensive exploration and Earth-return can be provided quite readily by Mars.
The most challenging technical problem with respect to human expeditions to Mars is that of escaping from Earth's deep, 11.2 km/s gravity well. Living on Mars, exploring it extensively and returning to Earth each are technically much less difficult, thanks in no small part to the effective 'wetness' of Mars.