For all the attention focused on how hard it will be to keep astronauts alive while they fly from Earth to Mars, the challenge of setting them safely down on the Martian surface will be just as difficult.

Entry-descent-and-landing (EDL) experts who spoke at a Humans To Mars symposium here say the “sky crane” that landed the robotic Curiosity rover on Mars last year will not scale to the huge sizes need for humans. And even if it did, the “seven minutes of terror” controllers at the Jet Propulsion Laboratory experienced at a distance during the first sky-crane landing may be a little too tame for a human mission.

“While the Curiosity rover has been described as a small nuclear-powered car on the surface of Mars, what we're really talking about here today is landing a two-story house, and perhaps landing that two-story house right next to another two-story house that has been autonomously prepositioned and has fuel for the astronauts when they get there,” says Robert Braun, a Georgia Tech space-engineering professor who was NASA's chief technologist.

To read more, click here.