Launching a rocket from a balloon
A rockoon is a rocket that is launched from a high-altitude balloon (further HAB). The HAB, typically filled with hydrogen or helium, lifts a special launch platform with the rocket up to an altitude of 20-30 km. As higher levels of the atmosphere get significantly less dense, even a rather small rocket can achieve meaningful altitudes due to reduced friction. If the ascent is nominal and the HAB is within its corridor of maximum height, the rocket is launched. After launching, both the rocket and the HAB are recovered.