That same Orion/habitat stack could float in a halo orbit at L2 over the lunar far side while its crew operated robotic rovers on the unexplored surface below to gain experience for Mars (see illustration). Karas says Demos, the smaller of the Martian moons, could be a good choice for a human-exploration base because there is a spot on it that is always in view of Earth and Mars for communications, and the Sun for power. A larger hab could essentially be docked with the low-gravity surface for the 1.5-year stay while the two planets line up again for the return trip, and the crew could use the Orion to move around Demos in the low-gravity environment. The whole process would take six or seven 130-metric-ton SLSs to predeploy the habitat and return stage, and transport the crew there and back.

Karas argues the mission would be affordable, based on NASA funding history. Over the 30-year shuttle era, the U.S. averaged 4.5 missions a year. NASA already has spent more than $5 billion to develop Orion, and the SLS should be cheaper than a shuttle because it uses shuttle-heritage hardware in a simpler configuration.

“Do you think you could afford one or two heavies a year for a couple of years?” Karas asks. “I'm not talking lots and lots of elements like station, so even Mars is less aggressive than station in certain budgetary aspects, as long as you don't land.”