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An earth chord sensor on board a satellite produces an electrical pulse as the satellite spins and sweeps the sensor across the earth. If the satellite is spinning at a low spin rate or if the sensor is measuring a long earth chord, the sensor produces an irregular pulse with sharp voltage peaks rat

An earth chord sensor on board a satellite produces an electrical pulse as the satellite spins and sweeps the sensor across the earth. If the satellite is spinning at a low spin rate or if the sensor is measuring a long earth chord, the sensor produces an irregular pulse with sharp voltage peaks rather than a near trapezoidal pulse. The present invention digitizes the output of the earth chord sensor and a processor processes the digitized output through a data buffer to detect the leading edge peak and trailing edge peak of the pulse. The processor may detect the peaks through parabolic curve fitting among the digitized data points of the sensor output. The processor calculates the earth chord time as the time width of the pulse between the detected leading edge peak and trailing edge peak of the pulse and transmits, by telemetry, the calculated earth chord time to a ground station for use in satellite positioning.

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[ What is claimed is:] [1.] A system for determining an earth chord time of a satellite, wherein the satellite is spinning at a low spin rate or wherein the satellite is measuring a long earth chord, comprising:an earth chord sensor for generating an electrical pulse;an analog to digital converter f

[ What is claimed is:] [1.] A system for determining an earth chord time of a satellite, wherein the satellite is spinning at a low spin rate or wherein the satellite is measuring a long earth chord, comprising:an earth chord sensor for generating an electrical pulse;an analog to digital converter for digitizing the pulse; anda processor which receives the digitized pulse, detects a leading edge peak and a trailing edge peak of the pulse and calculates a time difference between the leading edge peak and the trailing edge peak.