By the time of the first Case for Mars conference in 1981, development of the shuttle was complete and NASA was attempting to obtain funds for a follow-on manned project. S Fred Singer proposed a $10 billion program to send humans to Mars. Deimos would be used as an orbital base; no manned landing would be attempted. Instead the 6 to 8 man crew would guide the surface activities of 10 to 20 Mars surface rovers. The spacecraft would be propelled by solar-electric propulsion on its 700 day mission. The engine would be operated at full thrust throughout the long trip to Mars and back. To prevent the crew from having to endure long months in the acceleration spiral out of earth orbit, much of it in the radiation belts, they would be brought up to rendezvous with the main spacecraft just before it reached escape velocity. These considerations kept the spacecraft mass down to 270 metric tons, A launch in the 1990-1999 period was proposed, with a Venus swing-by to reduce return velocity.
PH-D Proposal Mission Summary:
Crew Size: 6.
Gross mass: 270,000 kg (590,000 lb).