KSC Next Gen Site
The Highly Reusable Space Transportation (HRST) Study
A rocket works by combining fuel with an oxidizer, with all the oxygen carried aboard the rocket, unlike with airplanes. Most of a rocket at lift off is propellant. Most of a rocket's weight is not rocket, or structure holding the propellant, or engines, or other parts of the rocket. By weight, a rocket at liftoff is mostly it's own propellant.
By weight a typical passenger jet may be 30% propellant, in this case jet fuel, and 70% aircraft. In contrast, a rocket may be about 85% propellant and 15% rocket, worse than reversed. The 15% that's rocket does not make it easy to achieve the design life and robustness of an aircraft-like design, one that can focus more easily on affordability, ease of turnaround operations, reliability or safety.
Now imagine some of the oxidizer was taken from the air as the rocket traveled through the atmosphere. These Rocket-Based Combined Cycle systems were explored in the HRST study. Potentially, such technology using SCRAM cycles, if the barrier of thermal management and materials both external and internal could be overcome, could get to where aircraft-like spaceships, taking off vertically or horizontally, would be as much as 35% "ship" and *the rest propellant, vs. 15% "ship" today. The possibilities are explored here in the broader context of the effect such technology could have on creating routine, affordable access to space.