One cool proposal is StarTram [1], which has a long (100km+) maglev run in an evacuated tunnel to a linear accelerator up the side of a mountain, ending in a ma

One cool proposal is StarTram [1], which has a long (100km+) maglev run in an evacuated tunnel to a linear accelerator up the side of a mountain, ending in a magnetohydrodynamic "window" to keep the atmosphere out, launching out the end fast enough to reach orbit. The acceleration of the first plan (30g) is too much for humans, so it'd initially be for cargo only. The second stage is a crazy-awesome magnetically levitated tube that exits at an altitude of 22km, and gives low enough accelerations that a human could survive. [1] https://en.wikipedia.org/wiki/StarTram https://en.wikipedia.org/wiki/StarTram