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- A rocket sled launch, also known as ground-based launch assist, catapult launch assist, and sky-ramp launch, is a proposed method for launching space vehicles. With this concept the launch vehicle is supported by an eastward pointing rail or maglev track that goes up the side of a mountain while an externally applied force is used to accelerate the launch vehicle to a given velocity. Using an externally applied force for the initial acceleration reduces the propellant the launch vehicle needs to carry to reach orbit. This allows the launch vehicle to carry a larger payload and reduces the cost of getting to orbit. When the amount of velocity added to the launch vehicle by the ground accelerator becomes great enough, single-stage-to-orbit flight with a reusable launch vehicle becomes possible. For hypersonic research in general, tracks at Holloman Air Force Base have tested, as of 2011, small rocket sleds moving at up to 6453 mph (10,385 km/h; Mach 8.5). Effectively a sky ramp would make the most expensive, first stage of a rocket fully reusable since the sled is returned to its starting position to be refueled, and may be reused in the order of hours after use. Present launch vehicles have performance-driven costs of thousands of dollars per kilogram of dry weight; sled launch would aim to reduce performance requirements and amortize hardware expenses over frequent, repeated launches. Designs for mountain based inclined-rail sleds often use jet engines or rockets to accelerate the spacecraft mounted on it. Electromagnetic methods (such as Bantam, Maglifter, and StarTram) are another technique investigated to accelerate a rocket before launch, potentially scalable to greater rocket masses and velocities than air launch. (en)
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