Savvy space writer Oberg (Red Star in Orbit, 1981) lays out current thinking on getting man to Mars and back, perhaps by the turn of the century. And, welcomely, less wish-fulfillment is in evidence than practical planning. Much of the information derives from a 1981 Boulder, Colorado, ""Case for Mars"" colloquium sponsored by university people and private groups, with unofficial NASA participation. The conference touched all bases: propulsion, craft, personnel, landing sites, biological support systems, medical and psychological issues, time and budget. Conjectures are for a 600-day round trip that would include a couple of months on Mars for a handful of astronauts. The upshot (admittedly the consensus of optimists) is that current Apollo and Space Shuttle technology provide sufficient know-how to make the Martian excursion practical. Of course it will take more power, more propellant, more shuttling back and forth to assemble vehicles in beyond-earth orbit. It may not take more money, however, because of existing knowledge and techniques. As for the reasons-why, Oberg sets forth a catalogue of scientific and practical purposes ranging from studies of the origin and history of the solar system to the potential use of Mars as a source of materials or site of human settlements. In that case, the ultimate aim would be ""terraforming""--a sf term for making Mars earth-like by introducing the wherewithal to establish an earth ecosystem. Not touched upon in this otherwise comprehensive survey are complex questions of rights and responsibilities. Does any space-competent country have squatter's rights? Could there be international disputes about prized landing sites or discoveries? One way or other, those who exult in man's destiny in space, or delight in solving engineering problems, will find that Oberg's book provides ample fodder.