Newsgroups: sci.space
Path: cantaloupe.srv.cs.cmu.edu!das-news.harvard.edu!noc.near.net!howland.reston.ans.net!usc!cs.utexas.edu!utnut!utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: Electrical Spacecraft via Magnetic field of earth?
Message-ID: <C6DF6w.Bur@zoo.toronto.edu>
Date: Sat, 1 May 1993 23:13:39 GMT
References: <1993May1.044441.1@aurora.alaska.edu>
Organization: U of Toronto Zoology
Lines: 39

In article <1993May1.044441.1@aurora.alaska.edu> nsmca@aurora.alaska.edu writes:
>Okay, the earth has a magnetic field ...
>...if you put a object in the earth magnetic field, it produces electricty..

Well, it's not that simple -- you're in Earth's magnetic field, and you
don't generate electricity -- but it can be done.

>Now the question. Can you use electricity to power a space/low earth orbit
>vehicle? and i fyou can, can you use the magnetic field of the earth to power
>it??

The way you power things is with electricity, so the answer to the first
question is definitely yes.  (If you meant to say "propel" rather than
"power", the answer is "sort of".)  Yes, you can use interaction with the
Earth's magnetic field to get electrical power, and there are potential
applications for this.

However, bear in mind that there is no free lunch.  The energy isn't
coming from nowhere.  What such systems do is convert some of the energy
of your orbital velocity into electrical energy.  There are cases where
this is a useful tradeoff.  Using power obtained in this way for propulsion
is useful only in special situations, however.

What you *can* do is get your power by some other means, e.g. solar arrays,
and run the interaction with the magnetic field in reverse, pumping energy
*into* the orbit rather than taking energy out of it.

If you want more information, trying looking up "electrodynamic propulsion",
"tether applications", and "magsails".

>Can the idea of a "dragless" satellite be used in part to create the
>electrical field?

No.  A "dragless" satellite does not magically have no drag; it burns fuel
constantly to fight drag, maintaining the exact orbit it would have *if*
there was no drag.  This is why there are quotes around "dragless".
-- 
SVR4 resembles a high-speed collision   | Henry Spencer @ U of Toronto Zoology
between SVR3 and SunOS.    - Dick Dunn  |  henry@zoo.toronto.edu  utzoo!henry
