Rockoon
From NewMarsWiki
A rockoon is a rocket powered launch vehicle using a high altitude balloon as a launch platform. This method limits the rocket's size to the payload of the balloon platform and increases the complexity of launch by requiring the balloon's systems to function as well as the rocket's. However, it can lift the rocket above much of the atmosphere (and its consequent drag), and provides considerable potential energy of position to the rocket. Thus, rockoons require less delta v, making them - in priciple - ideal for sounding rockets and orbital launches with very small payloads.
