The big problem with rockets is actually that you have to carry your propellant with you, and progressively waste energy accelerating your own propellant. Finit

The big problem with rockets is actually that you have to carry your propellant with you, and progressively waste energy accelerating your own propellant. Finite time or limited thrust don't actually affect this (increasing the exhaust velocity does though -- at the cost of energy efficiency). It's the infamous tiranny of the Rocket equation (https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation) To get near 100% efficiency, it follows from the kinetic energy formula and conservation of momentum the body you're pushing against must have a much larger mass than you[1]. So discounted exotic phenomena, the only way to travel efficiently through space is to push off a very large mass, departing at full velocity, or in the case of near-Earth travel, simply push Earth. The space elevator is essentially an elaborate staircase. It is in a stable equilibrium, and climbing it doesn't steal energy from the counterweight (which in fact doesn't move in fact because it is in constant tension); you're just pushing Earth away. In the grand scheme of things the very low efficiency of maybe 10% (in my guesstimation) to LEO isn't so bad (not even the maybe ~5% interplanetary efficiency); especially considering the costs of space systems in general in comparisson to fuel cost. This small fuel cost makes reusable rockets quite an attractive option near term (as noted by SpaceX). But long term, that's quite a steep inefficiency. If we were to endeavor large scale colonization or exploration of exoplanetary resources it seems to me either a kinetic launch system or at least a space elevator variant would be a necessity. [1] Derivation: M1 v1=M2 v2 => v1^2 = (M2/M1)^2 v2^2; M1 v1^2 + M2 v2^2 = E => M2^2/M1 v2^2 + M2 v2^2 = E; M2 v2^2 (1+M2/M1) = E => K2 = E/(1+M2/M1). As M1->infinity, all the kinetic energy goes to K2 and none to K1 (which is why you don't give Earth any meaningful energy by walking).