Getting there has always been viewed as the largest obstacle to a significant presence in space. The cost of launching payloads into Earth orbit had always been prohibitively expensive, in the order of $10,000 per pound. The cost to launch an early 21st-century Space Shuttle was $450,000,000. Research efforts on rockets were significant, but the science of escape velocities and orbital mechanics put up walls that seemed insurmountable. A number of different methods for propelling spacecraft beyond conventional rockets had their hopeful proponents, for example, ion propulsion and antimatter/matter collisions.
KeywordsRadiation Belt Science Fiction Solar Sailing Orbital Ring Lunar Material
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