🚀 go-pugleaf

In article <10165@sun13.scri.fsu.edu>, jac@ds8.scri.fsu.edu (Jim Carr) writes:
|>In article <77146@ut-emx.uucp> johncobb@ut-emx.cc.utexas.edu (John W.
Cobb) writes:
|>>     .....      It is a free lunch scenario. The energy is extracted
|>>from the stored energy in the magnetic field structure of the earth.
|>
|>>If this is still counterintuitive, think back to the common sophomore
|>>physics lecture demonstration of a homopolar generator. That is, take
|>>a copper disk and spin it in a magnetic field. You will find a potential
|>>drop between  the center and the edge. 
|>
|>And when you extract the current, the disk slows down.  TANSTAAFL
|>
|>The voltage may be there, but if you want to do work, the work has to 
|>come from somewhere and in this case it comes from the mechanical 
|>energy of the shuttle.

Looking over my postings, I realize that I have been less than crystal
clear. My apologies. Actually, there are two sources of energy that I
have been talking about. The first is the VXB induced electric field.
Here when you draw current, you do pay the price of degrading your orbit.

The second source is actual stored electrical energy in the magnetosphere
itself. As I mentioned before, the effect of a magnetic field is to provide
(partial) electrical insulation. Charged particles are confined to move
only along the magnetic field fields since perpendicular motion is (to
zeroth order) simple Larmor gyration. Now Frist and higher order drifts
allow motion perpendicular to the magnetic field, but at this level it is
possible to set up significant electrical fields. The issue then becomes
one of trying to identify the electrostatic potential on each magnetic
field line of the Earth's magnetosphere. Now in most cases, one talks of the
magnetic field lines terminating in a conduction plate, however, the Earth
is peculiar in this feature. The magnetic field lines terminate through an
insulating medium, the Troposphere. So it is indeed possible to have
electrostatic potentials existing (either in a non-rotating or co-rotating
reference frame). If you position your tether to take advantage of this
energy source, you are essentially powering your spacecraft's electrical
subsystem with energy previously stored electrostatically in the magneto-
sphere. This is what I meant by a free lunch scenario. Now I can't
lay hands on how big this effect is. I know it fluctuates depending
on solar wind variations and the state of the Earth's magnetosphere, but
I just can't get the numbers.

However, looking over the numbers I heard quoted in the popular press,
it seems that they are looking at the first possibility (E=VXB generation).
[Note, the sample numbers I gave before were off by two offseting errors.
The length of the (fully extended) tether was to be 12 miles not 1 or 2,
but I also overestimated the ionospheric field. It should be 0.1-1
Gauss not 10 according to a handy source here, although that still seems
intuitively low to me. Correcting for these two errors implies that most of 
the stated ~10Kv potential should be a result of the VXB potential.]

sorry for the confusion.

john w. cobb
jwc@fusion.ph.utexas.edu