Katz.uci-750a%Rand-Relay@sri-unix.UUCP (10/21/83)
Although the chief advantage of rocket alternatives is that you don't have to lift the fuel, energy recycling is another advantage. With two way transfers (i.e. missions which eventually return), some lifting methods can act like an energy bank. You make a withdrawal when going put (up in the gravity well), and you return most of what you withdrew when you return. For a space elevator and some other systems, payloads going down help to supply energy for the payloads going up. Admittedly, some energy is almost always lost and one can't always store up enough between launches. Thus, SSteinberg's summary of Newtonian mechanics of launch are correct, but neglect the change in mass due to fuel burning. You reminded him about the mass change, but neglected energy recycling. Is there anything else we left out?
REM%MIT-MC@sri-unix.UUCP (10/21/83)
From: Robert Elton Maas <REM @ MIT-MC> Indeed, if a space elevator (or rotating skyhook) is designed to recover energy on descending payloads, then it would be self-supporting energywise because when we start processing asteroids for Earth-consumed materials more stuff will be coming to Earth than leaving Earth on the elevator/hook, and with reasonable efficiency the energy recovered from descending materials should exceed the energy needed for ascending people and equipment.
rbc@houxw.UUCP (10/26/83)
You could use the structure of a power evelvator to carry the energy from an SPS to the Earth. In a superconducting cable perhaps. Avoiding all the microwaves from space to ground would cancel a lot of fears for the SPS.