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Real-time Graphics Program for Spin-Stabilized Satellite Attitude Analysis

IP.com Disclosure Number: IPCOM000111271D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 122K

Publishing Venue

IBM

Related People

Carey, LI: AUTHOR [+4]

Abstract

Disclosed is a real-time, interactive graphics program for assisting satellite analysts in the planning of attitude maneuvers for spin-stabilized satellites. It displays Quick Look plots of the satellite's attitude state, which enable the user to visually compare a desired attitude with the actual attitude. It also allows the user to vary interactively the desired attitude. The program also displays other plots that show when the satellite's sensors are unusable and when the attitude is not suitable for attitude correction.

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Real-time Graphics Program for Spin-Stabilized Satellite Attitude
Analysis

      Disclosed is a real-time, interactive graphics program for
assisting satellite analysts in the planning of attitude maneuvers
for spin-stabilized satellites.  It displays Quick Look plots of the
satellite's attitude state, which enable the user to visually compare
a desired attitude with the actual attitude.  It also allows the user
to vary interactively the desired attitude.  The program also
displays other plots that show when the satellite's sensors are
unusable and when the attitude is not suitable for attitude
correction.

      The attitude of a satellite is its orientation in space.  Many
satellites are spin-stabilized, which means that they control their
attitude by spinning.  Spin-stabilized satellites gradually lose
their stability due to precession--they begin to wobble like a
spinning top.  Periodically their attitudes must be corrected.  These
attitude corrections are typically planned by ground-based satellite
analysts.  To plan an attitude correction, the analyst must first
determine the attitude error.  Spin-stabilized satellites measure
their attitude indirectly through the use of sun sensors and Earth
horizon sensors.  The sun sensors measure the sun elevation angle
relative to the spin axis of the satellite.  The Earth horizon
sensors provide a measure of the azimuthal angle of the Earth
relative to the sun azimuthal angle in the spin plane of the
satellite.  (This is the angle through which the satellite turns from
the time the sun sensor detects the sun to the time the Earth sensor
detects the Earth.)  These two angles are downlinked to the ground
station as part of the satellite's telemetry.  The attitude of the
satellite cannot always be calculated from these two angles.
However, by plotting the position of these angles on a
sun-elevation-angle-vs-Earth-sun-separation-angle graph, along with
the position that results from the desired satellite attitude, a
measure of the attitude error can be derived.

      Fig. 1 shows such a "Quick Look"  plot.  The cross at the
center indicates the desired attitude, which is derived from orbit
and attitude prediction software, while the other cross indicates the
actual attitude, which is derived from telemetry.  The contour lines
are error curves that mark constant attitude errors.  The task of the
satellite analyst is to determine the correction needed to make the
actual attitude agree with the desired attitude.  To complicate
matters, the satellite may be wobbling, which results in a constantly
changing attitude.  In addition, it may be impossible to calculate
the attitude based only on the sun elevation angle and Earth-sun
separation angle.  The plot of Fig. 1 may look like Fig. 2 during
certain portion...