What is a Hot Air Balloon?

The hot air balloon is the oldest successful human-carrying flight technology.  Hot air balloons that can be propelled through the air rather than simply drifting with the wind are known as thermal airships. A hot air balloon consists of a bag called the envelope that is capable of containing heated air. Suspended beneath is a gondola or wicker basket, which carries passengers and (usually) a source of heat, in most cases an open flame. The heated air inside the envelope makes it buoyant since it has a low density than the relatively cold air outside the envelope. As with all aircraft hot air balloons cannot fly beyond the atmosphere. Unlike gas balloons, the envelope does not have to be sealed at the bottom since the air near the bottom of the envelope is at the same pressure as the air surrounding.