On Fri, 5/27/16, Robert Bruninga bruninga@usna.edu wrote:

I understand the curved trace.  It crosses near the pole at the latitude of the inclination of the orbit.  And I understand the circular plot which is angle and elevation from your QTH when placed over your house.  But I do not understand the straight line scale going nearly vertical and labeled RS?  WHy is there no curve to it?

Bob,

If I remember correctly, the RS satellites of that era had orbital inclinations a bit over 90 degrees, thereby causing the ground tracks to appear straighter than satellites having inclinations less than 90 degrees.

The "Satellite Experimenter's Handbook" included an Oscar Locator that when used in conjunction with reference orbit and equator crossing (EQX) data transmitted in CW by W1AW, provided my first exposure to making orbital predictions.

Later on, I wrote some code in BASIC for my Commodore 64 that propagated the EQX reference orbits ahead in time, and eventually added additional code (mostly based on equations in the "Satellite Experimenter's Handbook") that eventually eliminated the need for the Oscar Locator, altogether.

Incidentally, NASA once published a book for educators on the subject of Weather Satellite reception that included a map and overlays very similar to those included with the Oscar Locator. I seem to remember there were versions of the RSGB's "VHF-UHF Manual" that also carried a similar map.

Out of this work, PREDICT was eventually born, which led to the on-line pass predictions provided on the AMSAT-NA website, not to mention gpredict, and other derivatives that live on to this day.

73 de John, KD2BD