Being oversize has its advantages. Just ask researchers at the U.S. Missile Defense Agency, which recently dished out $40 million to arms maker Lockheed Martin to design what could soon be the world's largest pilotless airship. Measuring 500 feet long, with a volume of 5.2 million cubic feet, the prototype high-altitude airship, or HAA, will be 25 times larger than the Goodyear blimp.