Relative Motion Demo

A pass happens when the satellite and the rotating ground station have the same longitude again. The repeat interval is set by the relative angular rate.

Relative-motion demo
A pass happens when the satellite and the rotating ground station have the same longitude again. The key rate is ωrel = ωsat - ωE.
Pass timeline
0 h
4 h
8 h
A new alignment happens at 4 h and again at 8 h, even though the orbital period is not 4 h.
Interpretation
m = 1: the satellite gains 360° on the station in 4 hours.
m = 2: it gains 720° in 4 hours, so it still lines up after 4 hours.
The repeat interval is set by the relative motion, not directly by the orbital period.
Animation speed
Earth rate
Satellite rate
Relative rate
Longitude gap
Why a pass repeats every 4 h
In 4 hours, the satellite must gain an integer number of full turns on the station:
(ωsat - ωE) · 4 h = 360° m
For the selected case, the gain in 4 h is .