From the Kennedy Space Center and the Soviet Union's Baikonur Cosmodrome, powerful shuttles and unmanned rockets lift off week after week, bearing construction modules and fuel supplies to a giant space station in earth orbit. There, skilled workers have been assembling the ship that will take the first humans to Mars. After more than a year of construction, the million- pound, ungainly looking spacecraft is ready. With a crew of eight, it separates from the space station and heads for Mars, following the Hohmann ellipse, a space trajectory that may one day be as familiar as a great-circle route over the...

