A mile-long hot-air balloon is proposed for space research and solar power generation. The concept is one of a large, manned station-a free-floating, navigable craft-able to ascend to the stratosphere and to remain there for years. Buoyancy would be provided by solar-heated, confined air. The craft would be capable of performing very-long-term monitoring of chemical, physical, electrical, and biological processes. Complementary to satellites, it would be able to carry astrophysical and Earth-sensing instruments. In addition it could be used as a high-power generating station, a power and communications relay station, a high-energy optical and radio astronomical observatory, and even a local weather-modification station. Most of these missions could be conducted simultaneously.