When U.S. space scientists send a $15 million, solar-powered experimental plane into the skies over Hawaii sometime in July, it will achieve top speeds no faster than a bicycle, powered by 14 electric motors not much stronger than hair dryers. But NASA project scientists hope the Helios prototype — which appears to be made of a translucent wing 250 feet long and looking like a flying boomerang — will shatter altitude records, help them understand how to fly on Mars and ultimately pioneer a new era in satellites.