I'm writing a novel that takes place in a future where we've just begun to go interstellar, but the costs are still quite high and the purpose is definitely scientific study, exploration, and so on. FTL is not an option. Within the solar system we are quite advanced in the sense that we have colonized Mars, Venus, a good number of asteroids, various moons of Jupiter, Saturn . . . . not long has passed (a few centuries at the most; still working out the details) so terraforming is in very early stages or not being attempted at all; but asteroid mining is extremely lucrative and humanity is overall very well-established in terms of orbital colonies, space travel, and such.
I'm not sure all that background is helpful, but wanted to give the general picture. My question is what methods of non-rocket spacelaunch are going to be most prominent at various stages of human advancement? I've done a bit of research and it seems like, with the sorts of resources I'm giving my civilization, an orbital ring might be a very strong option . . . . augmented of course by individual projectile launchers and whatnot used by individual corporations and so on . . . . but I'm going after the overall most efficient method, here. I haven't found anything comparing exact building costs and payload capacities and such. Does anyone have a link? If not, any ideas?
As humanity advances of course, we have to assume some degree of technological innovation. So a space elevator might be unfeasible today partly because of technological limitations; but in the future should I assume it will be possible? Probably, at least EVENTUALLY. So at what point in the future will such things become possible enough to make them more cost-effective than, say, a less advanced method that might be more realistic in the near term? Would something like an orbital ring be unfeasible for so long that startrams or mass drivers or guns or whatever would become predominant first? Is my impression that they would be easier correct or totally off?
Does my question make sense? Also, I am asking paticularly about Earth here but any random thoughts on other matters, like Mars' lighter atmosphere making a space elevator more realistic, would be welcome. Thanks!