Line-of-nodes Question

From: Jonathan T Wojack (
Date: Tue May 07 2002 - 14:17:34 EDT


I've been studying _Fundamentals of Astrodynamics_ and have a question on
the material that is on pp. 156-159.  Specifically, concerning the
regression of the line-of-nodes due to the oblate shape of the Earth.  It
says that prograde (west-to-east) orbits will have westward nodal
regression, whereas for retrograde (east-to-west) orbits, it is eastward
nodal regression.

Is the following correct:

The line-of-nodes is a point on the Earth surface at an inclination of 0d
where a satellite's orbital path intersects the equator.  For a prograde
orbit, as the low-altitude satellite approaches the equator, the small
(but definite) equatorial bulge of the Earth pulls on the satellite,
causing the satellite's flight path to intersect the equator at a
slightly earlier time (i.e., further west than without the equatorial

Jonathan T. Wojack       
39.706d N   75.683d W            4 hours behind UT (-4)

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