# [amsat-bb] Re: Magnetic Sail

John B. Stephensen kd6ozh at comcast.net
Sat Dec 29 18:22:40 PST 2007

```P3 satellites use magnetorquing for attitude control, but it only works near
perigee.

73,

John
KD6OZH

----- Original Message -----
From: "Mike Lemons" <motie at mindspring.com>
To: <amsat-bb at amsat.org>
Sent: Saturday, December 29, 2007 22:56 UTC
Subject: [amsat-bb] Magnetic Sail

>I was trying to think of an inexpensive way to get from LEO to HEO when
> I came up with the idea of  using electricity to move the satellite like
> an electric motor.  The satellite is moving through the Earth's magnetic
> field, so if you put a big coil on it, you should be able to time the
> current through the coil in order to get the satellite to move in
> whatever direction that you want.
>
> Then, I found that some one had already thought of it:
> http://en.wikipedia.org/wiki/Magnetic_sail
>
> Quoting: "By varying the magnetic sail's field strength over the course
> of its orbit, a magnetic sail can give itself a "perigee kick" raising
> the altitude of its orbit's apogee."
>
> In the simplest mode, you would energize the field to repel from the
> earth's pole as you pass over it.  In this form of magnetic levitation,
> the satellite is going to want to flip over.  You could compensate for
> this by having two coils extended on moment arms in a shallow "V"
> angle.  See http://en.wikipedia.org/wiki/Dihedral  This would prevent
> roll.  You would need two more "wings" at a 90 degree angle to control
> for yaw.  You might be able to get away with only three wings 120
> degrees apart.
>
> I don't know how long it would take to get to HEO.  That would depend on
> how strong of a field you could produce over how big of an area.  It
> would work better with a lighter craft.
>
> This method of propulsion has the potential for reducing the cost of
> getting commercial satellites into higher orbits.  Another advantage is
> that you can reverse the process to de-orbit your satellite at end of
> life.  This method of propulsion might work to take you to another
> planet, too.
>
> It seems to me that NASA would be interested in seeing if this works.  I
> for one wish that NASA would do more proof of concept experiments like
> this with alternate methods of spacecraft propulsion.
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