Article-I.D.: <2517@mordor.UUCP>
Date: Fri, 5-Jul-85 12:46:40 EDT
Article-I.D.: mordor.2517
Posted: Fri Jul  5 12:46:40 1985
Date-Received: Thu, 11-Jul-85 05:25:21 EDT
Sender: daemon@mordor.UUCP
Lines: 32

From: DIETZ@RUTGERS.ARPA


I was wondering if the solar wind might make a better power source than
sunlight, in space.  At first glance this seems silly, since the sun emits
most of its energy as light.  However, it may be possible to extract energy
from the solar wind using much less massive machines.  (Question for
astrophysicists: what fraction of the sun's energy goes into the solar
wind, and how fast does the wind blow?)

The idea is to use magnetohydrodynamic techniques and avoid the need for a
material collector.  The solar wind is a highly conductive plasma moving
at high velocity (100's of km/sec, I think).  If it goes though a transverse
magnetic field a current is induced perpendicular to both.  All one needs
to collect this current are two electrodes, one emitting electrons, the
other either collecting electrons or emitting positive ions.  A wire
connecting the electrodes completes the circuit.

We can generate a magnetic field with a large diameter superconducting loop
at the center of the device.  The other parts of the collector are
essentially one dimensional, and very light.  For example, if the wire
connecting the electrodes is a 10 km long aluminum cable with a cross
section of 10 cm^2, it has a mass of 27 tonnes and a resistance of .28 ohms.

On a grander scale, it may be possible to use the interaction of the solar
wind with the Earth's magnetic field, potentially allowing us to use
the power of the solar wind falling on the entire magnetosphere.  I don't
remember how far out the Earth's magnetic field goes, assuming 40,000 km
from the Earth's center, and assuming the solar wind has 10^-5 times the
power of sunlight, that's about 70 terawatts.  Superconducting cables would
be necessary for these distances, perhaps in geosynchronous orbit.
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Article-I.D.: <2555@mordor.UUCP>
Date: Mon, 8-Jul-85 12:23:54 EDT
Article-I.D.: mordor.2555
Posted: Mon Jul  8 12:23:54 1985
Date-Received: Fri, 12-Jul-85 00:25:52 EDT
Sender: daemon@mordor.UUCP
Lines: 22

From: DIETZ@RUTGERS.ARPA


Looking in the encyclopedia britanica, I get a power level of from .1 to
1 milliwatt per meter^2 (1 to 10 protons per cm^3 at ~500 km/sec), or
roughly 10^-7 to 10^-6 x the intensity of sunlight.  Generating magnetic
fields over sufficiently large areas to make this practical seems
unlikely, unless the Earth's field is used.

The Earth's field may be used as follows: because the solar wind is so
highly conductive, it effectively excludes the earth's magnetic field.
What happens is the boundary layer of the plasma has a current ciculating
so as to neutralize the field at larger distances.  We can tap this
current by stretching a cable from one side of the field to the other
behind the earth.  Current is collected at the ends through some sort of
plasma and/or electron guns (no extensive wire mesh is needed).  Even
at 10^-7 x sunlight intensity this is still ~5 terawatts.

This scheme may significantly modify the earth's magnetosphere.  If so,
pulsed operation may dump the Van Allen belts, reducing radiation hazards
in intermediate orbits.
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