I’m doing a piece for Popular Mechanics on alternatives to rockets, and I was going to cover rail guns, gas guns, space elevators, sky hooks, and perhaps the launch loop. Does anyone have any other suggestions?
[Update a while later]
Folks, when I say alternatives to rockets, I am including all vehicles that employ chemical rocket engines, including airbreathers. As I said, unconventional.
[Update a few minutes later]
OK, I’m thinking of three categories: cannons (whether EM, chemical, whatever), external energy (laser, Orion), and momentum exchange (tethers, space elevators, compression towers). I know the latter isn’t really momentum exchange, but it fits sort of. The former don’t work well for passengers, but are well suited to bulk delivery of low-cost stuff (e.g., propellants), and the latter require very high up-front capital costs, in general. With a lot of tech risk.