Aeronautics and astronautics – Spacecraft – Attitude control
Patent
1995-08-23
1998-05-12
Barefoot, Galen L.
Aeronautics and astronautics
Spacecraft
Attitude control
B64G 124
Patent
active
057495459
DESCRIPTION:
BRIEF SUMMARY
Invention relates to astronavigation and satellite angular orientation control and is designed for using at autonomously functioning satellite. Satellite, moving in three-dimensional space has six degrees of freedom. In these environment satellite guide control is performed by navigation and orientation system with the determination of three coordinates of location point: flight longitude, latitude and altitude and three angular orientation coordinates: pitch, roll and yaw.
Active control orientation system of the geostationary satellite, being foreseen as analog, is known.(patent of France N 2637565, 1988).
Mentioned orientation control system of the satellite is characterised by the following. System includes the Earth sensor, Sun sensors, sensor of the Pole star, processing and calculation units, drive motors. System provides three-axis satellite stabilization: east-west, north-south and geocentric. The following sensors are used while orientation control:
These different sensors give the output signals, going into data processing networks, that are designed for correction manoeuvres amplitude determination according to this data; manoeuvres are executed by drivers of any known corresponding type (reactive flywheels, inertial flywheels and nozzles). Three satellite orientation angles, including yaw, are being constantly controlled in the working mode.
Errors of the Earth sensor could be used for pitch and roll control without preliminary processing. Angular deviations, corresponding to pitch and roll channels during measurements by the Earth sensor are considered to be equal. System is characterised also by the fact,that in its composition there is a unit, containing the Pole star location evolution model, and this unit is connected with the telemetry unit. Hence, this model parameters are being renewed periodically, basing on the information, receiving from the Earth. In order to control yaw angle, it is necessary to execute the following operations: location in the inertial coordinate system is calculated; Pole star in the star sensor field of view are to be calculated, while this is assumed, that the satellite has ideal orientation (pitch, yaw and roll are equal to zero), the difference of the Pole star location coordinates in the two-dimensional field of view, and basing on this error, yaw control amplitude is to be calculated in order to delete having shift.
Mentioned system has the following, similar to invention,indications while the working mode providing: the Pole star, computer, actuator organs; the Earth sensor, on yaw channel--by star sensor. Foreseen as analog, mentioned system has the following demerits in the satellite angular position determining relatively to north-south axis (the Earth latitude plane): position evolution model; receiving from the Earth; calculate the difference between real and theoretical Pole star position coordinates in the star sensor field of view.
Autonomous on-board system of orbit determination (article "Autonomous on-board orbit determination systems", Astrodynamics Conference. Aug. 20-22, 1984, Seattle, Wash.), being foreseen as a prototype, is known.
Mentioned system includes the Earth sensor, Sun sensors, the Pole star sensor,computer, mass memory device, actuator organs. The Earth sensor is pointed into nadir and it forms errors on pitch and roll for orientation control system,that keeps this direction in the limits of the central zone of non-sensitivity. Error signals are proportional to the Earth angular deviations from sensor line of sight on two across directions. Angle between the Earth sensor line of sight and the Sun sensor line of sight directions is measured by potenciometrical sensor of the panel drive-motor, installed on the panel. Angle "the Sun--object--the Earth" is the best observation for orbit determination. Information about the Sun location relatively to the Earth is taken from a file with ephemerides.
The Sun ephemerides are put into the computer as a complicated time functions. If the Sun is in the satellite orbital plane, then angle "
REFERENCES:
patent: 5108050 (1992-04-01), Maute
patent: 5204818 (1993-04-01), Landecker
patent: 5277385 (1994-01-01), Flament
patent: 5452869 (1995-09-01), Basuthakur et al.
patent: 5508932 (1996-04-01), Achkar et al.
"Autonomous On-Board Orbit Determination Systems" Astrodynamics Conference, Aug. 20-22, 1984, Seattle, WA.
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