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SGP4Standard General Perturbations Satellite Orbit Model 4
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Because of the relatively low fidelity of the TLEs and the lack of transparency of the Analytical Graphics Incorporated special perturbations orbit-determination algorithm and the way it compares to SGP4, though, the causality of the delta between the TLE and the element set created from the test data remains unknown but is probably a mixture of timing accuracy and algorithm mismatch.