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ASE 370L Take Home Test 3
April 29, 2010
Drew Rosecrans
DCR544
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View Full Document Satellite Attitude Controller with Control Moment Gyros
It is necessary to control the attitude of a satellite in space. Based on what the satellites’ purpose is, it
may be useful to keep the satellite pointed toward Earth or out into space. There are several ways to
control the attitude of an object in space, but for this problem a control moment gyro (CMG) is to be used.
In this problem it is important to consider gravity gradient torques due to the variation of the earth’s
gravitational field over the satellite. Also aerodynamic disturbances due to the atmosphere need to be
accounted for. The simplified model of the spacecraft is given by
=
=

θsUs Gs 1Iys2 3n2Δ
Where
θs
is the pitch angle,
Us
is the CMG input torque,
= .
Iy 0 2 kg∙m2
,
= 
Δ Iz Ix
,
= .
Ix 0 1 kg∙m2
,
= .
Iz 0 01 kg∙m2
, and
= .
/
n 0 0011 rad sec
is the orbital angular velocity. For this problem it is desired
that the satellite be pointed toward Earth, that occurs when
θs
=
0
, thus the desired pitch angle
θds
=
0
.
Now the gravity gradient term is taken care of in the plant model
Gs
, it is represented by
=
Tgg
3n2Δθs
The CMG is a constantrate flywheel mounted on a set of gimbals that is controlled by actuators. The
simplified model for the CMG is
=
+
Gas 15s 15
The aerodynamic disturbance is due to atmospheric drag acting on the satellite and creating a torque. We
can view this torque as a disturbance because it is generally much smaller than the gravity gradient
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This note was uploaded on 09/18/2011 for the course ASE Controls taught by Professor Bishop during the Spring '10 term at University of Texas at Austin.
 Spring '10
 Bishop

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