Asri-unix.903
net.space
utcsrgv!utzoo!decvax!ucbvax!ARPAVAX:C70:sri-unix!Kieran
Fri Mar 5 03:40:32 1982
Gravity-Gradient Stabilization of Satellites
With reference to CARLF@MIT-AI's message (issue 113), there is at least
one reason to use masses on the ends of ropes (or wires, more likely)
to stabilize an orbiting satellite by taking advantage of a gravity-gradient.
This is that you want to avoid deploying any excess structural area
with the stabilization system, since excess area means excess reflection
of solar radiation, which means excess solar-pressure on the structure.
This pressure will increase the disturbance forces acting on the
satellite, tending to modify its orbit (although the effect may cancel
out over a one-year period), which causes an increase in the station-keeping
activity required, and hence the amount of fuel burned by the station-
keeping thrusters--bad news!
A second effect of the solar pressure acting on the wires would be to
bend their tips away from the sun (much like a slender, flexible mast
swaying in a breeze), since ideal wires have no rigidity in the transverse
direction. This could also be undesirable.
True, if you want to deploy ANY mass to stabilize the satellite,
that mass will have some cross-sectional area, and hence will be subject
to these solar pressures. However, a sphere of mass M has a much smaller
surface area than a long, thin wire of mass M; the area of the counter-
weight is reduced by concentrating it into a compact shape.
Of course, the whole idea of the system is to deploy a mass at some
large distance from the satellite, in order to take advantage of the
local gravity-gradient. Hence there is a good reason to put the mass
on the end of a long wire; however, a lumped-mass on the end of a wire
would still be better than a wire alone (I'm pretty sure...).
The length of the wire used, and the size of lumped-mass used, could be
calculated so as to optimize the ratio (stabilizing effect)/(total system
mass), depending on the strength of the local solar radiation, the
amount of stabilizing torque required, the reflectivity of the wire and the
lumped-mass, and various other things. (Spacecraft engineers are
VERY weight-conscious, and just LOVE to optimize systems with respect to
weight)
I'm sorry for flogging what may already be a dead horse, but by the
time the digest eight)
I'm sorry for flogging what may already be a dead horse, but by the
time the digest gets from arpanet to usenet to
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Bruce Jones, Henry Spencer, David Wiseman.
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