[AR] Re: Electric Motor Thruster
- From: Norman Yarvin <yarvin@xxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Wed, 6 Jun 2018 13:16:06 -0400
On Mon, Jun 04, 2018 at 03:00:17PM -0700, Monroe L. King Jr. wrote:
Here is a paper on Lorentz force propulsion if you find it interesting.
https://static1.squarespace.com/static/56f67f2820c64796d51b3a33/t/5a79ecece2c48358c68bf6a6/1517939949193/6.2007-6847.pdf
That's a quite different sort of Lorentz force propulsion than the
stuff we've been considering. Instead of generating a magnetic field
via an electrical loop, they propose to charge the whole spacecraft up
electrostatically and let its orbital motion generate the Lorentz
force. Their example is of a circular equatorial orbit: the magnetic
field there is basically horizontal, so v cross B points upwards; the
Lorentz force then works against gravity, raising the orbital
altitude.
Charging up the whole spacecraft isn't so easy, though; the plasma
keeps trying to neutralize it. But it gets easier at smaller sizes:
the capacitance of a sphere (and thus the charge you can put on it for
a given voltage) scales as its radius, while its mass scales as its
radius cubed. So their concept takes it to the extreme: what they
call "Spacecraft-on-Chip".
The paper talks in places about the propulsive force being greater
than drag, giving an indefinite lifetime in LEO, but doesn't include
any calculations to that effect; and given that their main proposed
experiment would be to monitor "differential drag" between a pair of
such chip satellites, I'm not sure if they're really trying to make
that claim or not.
(Drag calculations, incidentally, would be somewhat tricky: their
capacitance calculations include the effect of a "sheath" of charged
particles around the spacecraft, which boosts capacitance -- but if
you're dragging a sheath along with you, that'll probably increase
drag too.)
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