比如

http://aerospace.vulcan.com/#vision

比如

Airships have been proposed as a potential cheap alternative to surface rocket launches for achieving Earth orbit. JP Aerospace have proposed the Airship to Orbit project, which intends to float a multi-stage airship up to mesospheric altitudes of 55 km (180,000 ft) and then use ion propulsion to accelerate to orbital speed.^[126] At these heights, air resistance would not be a significant problem for achieving such speeds. The company has not yet built any of the three stages.

又比如

Due to the height, more than 90% of atmospheric matter is below the high-altitude platform. This reduces atmospheric drag for starting rockets. "As a rough estimate, a rocket that reaches an altitude of 20 km when launched from the ground will reach 100 km if launched at an altitude of 20 km from a balloon."^[10] Such a platform has been proposed to allow the usage of (long) mass drivers for launching goods or humans into orbit.^[11]