The Gen1 Enterprise can arrive at Mars within 90 days of leaving earth's orbit. This is derived from various analyses sponsored by NASA that show that with mass to engine power ratios within our reach, a 90 day travel time is possible.
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How big is the Gen1 Enterprise? Pretty big. In fact it will be the largest vessel or building ever built by humans.
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The Gen1 Enterprise will be powered by three ion propulsion engines. These will provide constant acceleration, and versions of this technology are already used in spacecrafts. These engines are powered by electricity, and thus using nuclear reactors to generate this electricity is a natural fit.
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