The main barrier to colonising space is the horrendous amount of energy needed to overcome the gravity well of this planet. No way are we going to do it with rockets, far too primitive and expensive. are elegant in theory, but horribly difficult in practice -even carbon nano tubes are not strong enough.
A much better solution is a, well within the reach of current technology and materials. If re-entering space craft land on it, as well as take off, electrodynamic regenerative braking could capture a large part of re-entry energy, now wasted as heat, so make the economics look even better.

Problems:
- needs to be tethered at two points 2000 km apart, ideally near the equator, and for safety reasons over the ocean. That only leaves a few sites over the Pacific and Atlantic which are suitable, but such is the capacity of the system that is all that would be needed. Suggests these would have to be internationally co-operative projects.
- more worryingly, you cannot build a small test one easily. Not good for learning curve.
- it's going to be fun making sure that (terrestrial) aircraft don't collide with those tethering cables.
Pessimism is the soft option.