133 lines
3.6 KiB
Plaintext
133 lines
3.6 KiB
Plaintext
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(word processor parameters LM=8, RM=78, TM=2, BM=2)
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Taken from KeelyNet BBS (214) 324-3501
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Sponsored by Vangard Sciences
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PO BOX 1031
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Mesquite, TX 75150
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August 3, 1990
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Courtesy of NASA BBS at 205 895-0028
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APPLICATIONS
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The most important application of auxiliary-propulsion ion
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thrusters is north-south stationkeeping.
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Gravitational forces of the Sun and Moon tend to increase the
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inclination of the geosynchronous orbit. Through the use of proper
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thrusting, centered about the nodal crossings, the geosynchronous
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orbit will not incline and will remain in the equatorial plane.
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The duration of thrust each day depends on the spacecraft mass
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and thrust level and on how closely the thrusters can be alined with
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respect to a north-south line and still have a thrust direction
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through the center of mass of the spacecraft.
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Three-axis stable-platform spacecraft allow the thrusters to be
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alined directly north-south.
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Effects of solar pressure and the triaxiality (gravitational
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nonuniformity) of the Earth will cause the east-west position of a
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geosynchronous spacecraft to vary unless thrust corrections are
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properly applied.
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The triaxiality of the Earth is a much weaker disturbing force
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than that caused by the Sun and Moon and requires only 1/26 of the
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total impulse for proper correction.
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The thrusters can easily perform east-west stationkeeping
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through the use of the gimbal system; their thrust is deflected in
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the correct direction and they are started simultaneously at
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specific times throughout the orbit.
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Station walking, or changing the east-west location of the
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geosynchronous spacecraft, can also be accomplished.
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Because the center of solar pressure and the center of mass of
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the spacecraft are rarely the same point, the speed of flywheels, or
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momentum wheels, must be gradually increased in order to hold the
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spacecraft in the power orientation.
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Electric thrusters can provide a counter-acting disturbing
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torque, which can be used to dump or reduce the velocity of the
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momentum wheels. This reduction can help lower excessive momentum-
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wheel spin rates.
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--------------------------------------------------------------------
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If you have comments or other information relating to such topics as
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this paper covers, please upload to KeelyNet or send to the Vangard
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Sciences address as listed on the first page. Thank you for your
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consideration, interest and support.
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Jerry W. Decker.........Ron Barker...........Chuck Henderson
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Vangard Sciences/KeelyNet
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--------------------------------------------------------------------
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If we can be of service, you may contact
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Jerry at (214) 324-8741 or Ron at (214) 484-3189
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