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nec208
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<p><br />A single-stage-to-orbit (or SSTO) vehicle reaches orbit from the surface of a body without throw away hardware, expending only propellants and fluids. The term usually, but not exclusively, refers to reusable vehicles.</p><p>No Earth-launched SSTO launch vehicles have ever been constructed. Current orbital launches are either performed by multi-stage fully expendable rockets, or by the Space Shuttle which is multi-stage and partially reusable. Several research spacecraft have been designed and partially or completely constructed, including the DC-X, the X-33, and the Roton SSTO. However, none of them has come close to achieving orbit.</p><p>Single-stage-to-orbit has been achieved from the moon by the Apollo program's Lunar Module; the lower lunar gravity and absence of any significant atmosphere makes this much easier than from Earth.</p><p>For rocket-powered SSTO, the main challenge is achieving a high enough mass-ratio to carry sufficient propellant to achieve orbit, plus a meaningful payload weight.</p><p>An SSTO vehicle has one major problem: it needs to lift its entire structure into orbit. To reach orbit with a useful payload, the rocket requires careful and extensive engineering to save weight. This is much harder to design and engineer. A staged rocket greatly reduces the total mass that flies all the way into space; t<strong>he rocket is continually shedding fuel tanks and engines that are now dead weight</strong>.</p> <div class="Discussion_UserSignature"> </div>