# What is the Mystery Effect?

• Subject: [amsat-bb] What is the Mystery Effect?
• From: "Stacey E. Mills" <w4sm@xxxxxxxxxx>
• Date: Sat, 22 Dec 2001 00:12:24 -0500

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stabilized; it's a gyroscope.  When you spin a gyroscope and gently apply
upward force on one end of the axis,  the axis moves 90 degs to your
efforts, either left or right depending on the direction of spin.  The spin
of AO-40 is such that to move the spin (Z) axis "left", decreasing ALON as
we observe, there must be a force trying to rotate the + end of the  Z-axis
upward (northward).  If this force originates off-center to the Z-axis,  it
must be "despun".  That is, as AO-40 rotates, the sum of the force must not
equal zero.  Any mechanical effect  due to something hanging off the
satellite is not despun, and the sum of the effect goes to zero during each
rotation.  Forces can be despun electrically, and this is what is done to
magnetorque.  Despinning for magnetorquing depends on the sun as a fixed
reference.  Theories about currents from the solar panels causing the
mystery effect are intriguing because they are, in effect, despun by the
sun.  However, the wiring is such that we believe insufficient magnetic
force can be generated by these currents to cause the effect.  More
importantly, we currently have perigee eclipses which would completely
eliminate this effect, and yet the observed mystery effect is completely
unchanged.

Any net force/field moving through the center of the Z-axis is by
definition despun.  The momentum wheels contain permanent magnets and the
fields of these magnets are not completely closed.  We believe that the
magnets in all three orthogonal wheels are oriented in the same way.  This
creates a net magnetic field along the Z-axis.  Imagine that the south pole
of this magnetic field emerges from the +Z axis.  The earth's magnetic
field will interact with this field, trying to pull it upward to align with
the earth's north pole.  By gyroscopic effect, this will move the Z-axis
"leftward" decreasing ALON. ... precisely what we see.

The mystery effect  appears to have changed (decreased) somewhat as we have
increased perigee, and the amount of change is consistent with an
interaction with the earth's magnetic field. Althought drag was initially
considered when the perigee was rather low, our current 1000+ km perigee
completely excludes that possibility.  If the solar panels were opened we
would be able to tell by changes in the solar panel current patterns,
changes in magnetorquing efficiency, changes in center of gravity as seen
in the photos, changes in temperatures of the panels and objects shaded by
them, etc.  There is no evidence for any of these things so it is clear
that the panels remain closed.   (Even if one were open, any effect from
this would not be "despun" as discussed above.)

If the mystery effect is due to AO-40 having a net Z-axis magnetic field,
then aligning that field with the earth's magnetic field, should cause the
magnetic force and resultant mystery effect to disappear.  This is one
approach we are considering for counteracting the ME during perigee under
3-axis control.

--
_______________________________________________________________________
Stacey E. Mills, W4SM    WWW:    http://www.cstone.net/~w4sm/ham1.html
Charlottesville, VA     PGP key: http://www.cstone.net/~w4sm/key
_______________________________________________________________________

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