Originally Posted by
WhatThePhysics
Right, we should be using comets, not asteroids. Comets can be contained in stress resistant polymer shells composed of local chemicals, then redirected with a combination of gravity tractors, thrusters fueled by local chemicals, reflective coatings, and gravitational slingshots assisted by asteroids, planetoids, and other comets. By exploiting cyclical Hohmann transfer orbits, we can set up a comet "railroad" that goes between Venus and Mars, which will provide both planets with useful volatiles, shipping access, and rotation modification. Sure, it'll cost a lot of energy to set this up, but it's a multipurpose system that can help accelerate the development of a stable, interplanetary civilization.
As for whether we can reasonably expect to be doing this in the next 1000 years, I think it's quite possible and worth discussing. Ideas that seem unrealistic today can seem obvious tomorrow, and even the most incredible concepts can add flavor to science fiction, at the very least.