(41C) Tracking Satellites in Elliptical Orbits

[SlideRule]

An extract from Computer program and sample problem for tracking OSCAR, Ham Radio magazine, MAR 1981 {volume 14, number 3}, pgs 46-50

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… This article contains information to enable an Amateur, with the aid of a computer or calculator, to track, in azimuth and elevation, a satellite in an elliptical orbit.
  The altitude and velocity of a satellite in a circular orbit are nearly constant. However, both altitude and velocity are always changing during an elliptical orbit. Communication range is greatest at the apogee: the point of maximum altitude. This condition corresponds to the point of minimum velocity with respect to an observer on earth. A low velocity means low Doppler shift; it also means that the satellite will remain in view for a longer time and will not demand rapid antenna tracking.
  The spot on the earth surface directly beneath the satellite is called the subsatellite point. A plot of the path of this point is the ground track and must include the effects of earth rotation. If the altitude and subsatellite point are known at a given time, the azimuth and elevation can be found using the same equations as for circular orbits.
  Ground station latitude, δ_g, and longitude, λ_g, will be considered positive if the latitude is in the northern hemisphere and the longitude is west of the prime meridian. South latitude and east longitude must be entered as negative numbers.
sample program
  A program for the HP-41C programmable calculator and printer was written to test the equations and to learn more about elliptic orbits …
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ps:url was posted in reply to HP Forums / HP Software Libraries / General Software Library v / (25) Satellite Orbit Predicting using a pocket calculator and is posted here for ease in dedicated/narrow searches.