After nearly half a century of space flight, the cost of putting payloads in orbit hovers around $4000 per pound for commercial launchers and about $10,000 per pound for the Space Shuttle. Such high costs are the single most important limiting factor to expanded business and exploitation of space. 1 Because of the history of difficulties in reducing the cost of rocket launch, researchers have been investigating alternative methods using hypervelocity gun launch systems. The idea goes all the way back to Isaac Newton in his Principia, and was later popularized in a fictional account by Jules Verne in 1865 in his novel "From the Earth to the Moon." While Verne took some literary license in launching people with his gun, technology has now progressed to the point where launch of more robust payloads to orbit is technically feasible. Gun launches of fuel, water, food, solar panels, building materials and other supplies, and even constellations of small robust satellites, could be accomplished, saving not only billions of dollars, but enabling near term industrialization of space by reducing launch costs of such payloads by one to perhaps two orders of magnitude. A brief review of the major gun launch systems under consideration is presented with primary attention to two likely candidates, distributed hydrogen side injection and ram accelerators. Gun Launch to Space (GLTS) has great promise for reducing launch costs, but some technical issues still need to be resolved, and demonstrations of the technologies at a scale size beyond the laboratory is required before significant private investment seems likely.
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