A single-stage-to-orbit (or SSTO) vehicle reaches orbit from the surface of a body without jettisoning hardware, expending only propellants and fluids. The term usually, but not exclusively, refers to reusable vehicles. No Earth-launched SSTO launch vehicles have ever been constructed. To date, orbital launches have been performed either by multi-stage fully or partially expendable rockets, or by the Space Shuttle which was multi-stage and partially reusable. Several research spacecraft have been designed and partially or completely constructed, including Skylon, the DC-X, the X-33, and the Roton SSTO. However, despite showing some promise, none of them has come close to achieving orbit yet due to problems with finding the most efficient propulsion system.

Single-stage-to-orbit has been achieved from the Moon by both the Apollo program's Lunar Module and several robotic spacecraft of the Soviet Luna programme; the lower lunar gravity and absence of any significant atmosphere makes this much easier than from Earth.

Read more about Single-stage-to-orbitHistory, Approaches To SSTO, Features of SSTO, Dense Versus Hydrogen Fuels, One Engine For All Altitudes, Airbreathing SSTO, Launch Assists, Nuclear Propulsion, Beam-powered Propulsion, Comparison With The Shuttle, Examples, Alternative Approaches To Cheap Spaceflight

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Single-stage-to-orbit - Alternative Approaches To Cheap Spaceflight
... Using this concept, some aerospace analysts believe the way to lower launch costs is the exact opposite of SSTO ... Whereas reusable SSTOs would reduce per launch costs by making a reusable high-tech vehicle that launches frequently with low maintenance, the "mass production" approach views the technical advances as a source of the cost problem in the first place ...