Re: SPACE: Roton in New Scientist

Michael Lorrey (
Mon, 10 Aug 1998 08:38:34 -0400 wrote:

> It seems a major thing about space travel is the high temperature re-entry.
> Why not not slow the craft down before re-entry? like before we re-enter, use
> a saved amount of fuel and blast in the opposite direction, and just kinna
> free-fall back into earth.

Considering that current rocket technology only allows a mass fraction of around .95, that means that for every ton you put in orbit, you expend 19 tons in fuel and boosters getting it there. In order to cancel all of a spacecraft's velocity so that it can just 'free fall' to earth from altutude, you would essentially need to carry an equal amount of fuel into orbit as you used for the original blastoff. Since you also need to launch that fuel and boosters by the same mass fraction, then you would increase the size, mass and cost of your original launcher by at least 19 while its possible, its not cost effective.