FACTOR, on to Mars — George G. Pinneo

An alien race, the Rasi, reconnoiter on Canth, alarming not only the Canth but humans as well. Once the new threat is partially understood, House Blackman proceeds to build Schrodinger Base on the Lunar far side. The Canth offer to see if they can jointly redirect a nitrogen/water/oxygen comet to impact Mars, releasing it's gases to rebuild the Martian atmosphere. After the new Martian atmosphere clears of comet-impact debris, Geoff Blackmon, and his team begins building a Martian settlement, using a Canth starship and lander to explore the new planet.