NASA is exploring the possibility of building space-based solar power stations that would produce electricity for use on Earth. A “Sun Tower” design being considered might stretch 22 miles in length with solar collectors 100 to 200 meters in diameter. Each station might beam up to 1.2 billion watts of electricity to ground stations via microwave, enough to power 1.2 million homes. NASA has given out $6.4 million in contracts to companies and universities to develop solar power systems, and the agency hopes to demonstrate by 2015 whether such space-based stations are feasible.