A SUBSATELLITE AREA-OF-VIEW CIRCUIT.
NAVAL RESEARCH LAB WASHINGTON D C
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A subsatellite circle circuit is included in the NRL experimental satellite position prediction and display equipment SPAD. The circuit paints, on the expanded display, a circle enclosing the area of view for a selected satellite. A combination of digital and analog techniques is used to generate a polygonal approximation to the ideal circle. Compensation for meridian convergence is provided, so that the resulting error is roughly equal to the degree to which an octagon approximates a circle. With simple circuit changes the polygon could have 12, 16, 20, or more sides. The circle center is defined by the subsatellite position, and the SPAD prediction computer uses the satellite look-cone angle say, that of a cloud-cover camera and the satellite height to generate a circle radius in increments of 8 naut mi up to a maximum radius of 504 naut mi. This limit is determined by the practical requirement of displaying the circle only on the expanded display of limited area for any portion of the earths surface. A duplicate circuit generates a circle about own ships position. The operational significance to be attached to the circles is of no concern in the present study. Rather, the circuit design approach, the design equations, and circuit description at the block-diagram level are the important elements. With suitable modification the circle circuit used for SPAD is applicable to any cathode-ray tube display having either electrostatic or magnetic deflection, providing the entire display surface is scanned by a method involving two orthogonal axes of deflection. Author
- Electrooptical and Optoelectronic Devices
- Unmanned Spacecraft