Single Stage to Orbit
A Single-Stage-To-Orbit launcher is a launch system, which reaches at least low earth orbit with only a single stage. This definition does not even allow booster stages, which are called one-and-a-half stage launchers (eg. Atlas, R7). In Orbiter the Delta-glider is an example of a SSTO vessel.
- Phil Bono Designs
Current SSTO designs
Why is there no SSTO?
Regardless of the amount of historic SSTO designs, no SSTO design ever reached production stage. The reasons are not only of economic nature, there are also engineering problems:
- Fuel tanks - The biggest problem for all SSTO designs lies in the ratio between launch mass and payload mass. In the rocket equation, this parameter is part of the mass ratio. Because SSTOs can't drop construction mass during launch, they have to carry the large fuel tanks into orbit, even when they are almost empty. When multistage launchers simply drop a stage and reduce the construction mass during ascent, a multistage rocket has to accelerate the whole structure until orbit.
- Engine performance - The engines on a SSTO have to work from launch at sea level until reaching orbit in vacuum. While multistage rockets simply use optimized engines for each phase of the ascent, SSTO designs rely often on complex and often unrealistic engine designs.
- Recovery - A SSTO launcher makes only sense when it can be reused. This increases structure and fuel mass and with it: Launch mass.
Many past SSTO designs had been multimillion kilogram vehicles, standing taller as the Saturn V.
EADS Bremen currently developes a Single-Stage-To-Suborbital launch vehicle, with a reuseable winged first stage. This approach needs significantly less fuel for ascent and landing. Similar approaches had been followed by the USA until the mid 90ies, but had been stopped during times of budget cuts.