I sort of remember in the 1980s there being a mention that perhaps some skyscrapers will extend into outer space and could be used as launch platforms
I still think that using a type of balloon would be the most cost effective launch platform , you could reuse the gas used to lift the platform by pumping the lifting gas into tanks to lower the platform , kind of like a submarine in reverse.
the payload would be the space shuttle minus the main rocket engines , the two booster rockets , and the main hydrogen tank
the payload could then be further lifted by the iss or a similar orbiting platform using carbon nano ribbons.
you would have a completely reuseable payload delivery system that would direct much more time , effort , funds into the actual construction of a mars mission vehicle.
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