In 1972, when humans last visited the surface of the moon, the bulky, stiff legs of spacesuits made the "moonwalk" more of a swaying hop. Since then, manned missions to space have stayed in Earth orbit, where astronauts mostly use their arms to get around. But when explorers get back to the moon, or if they ever get to Mars, these old spacesuits aren't going to cut it, scientists say. Both destinations, in fact, are in NASA's long-range plans. Last month, the agency announced an ambitious plan to return to the moon by 2018 as a launching pad for a mission to Mars. If they pull it off, astronauts will need added mobility and dexterity for the next stage of modern experiments, exploration, and construction. "We need to design some pretty revolutionary spacesuits if we're really going to realize human exploration of other [planetary] bodies," says Dava Newman, a researcher at Massachusetts Institute of Technology. By combining an old idea with the latest technology, Dr. Newman and her team are trying to build a better spacesuit: the BioSuit, a form-fitting "second skin," designed for lunar and Martian living.The proposed BioSuit will consist of a skintight body suit, a hard torso and backpack for life-support systems and equipment, and a domed helmet. The conceptual images for the project look like science fiction: sleek, color-coded spacemen and spacewomen climbing Martian windmills, whacking red rocks with hammers, and casually shaking hands.Much of the technology needed to make the BioSuit practical may be decades away - just like a Mars mission - but the idea behind it was dreamed up decades ago.