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Re: ka0yos wrong again! Phase / MA



> From: "Gary \"Joe\" Mayfield" <gary_mayfield@hotmail.com>
> Subject: [amsat-bb] ka0yos wrong again!  Phase / MA
> Date: Wed, 9 May 2001 07:19:44 -0500
> 
> It seems I was wrong again!  Yesterday, I explained to someone who asked a
> very legitimate question that phase and MA were two ways to measure the same
> thing.  I said phase was the orbit divided into 256 parts and MA was the
> orbit divided into 360 parts.  Please disregard this misleading explanation.
> It is not correct!
> 
> Phase and MA are the same.   Both are the orbit divided into 256 (0-255)
> parts.  There is no conversion factor.  If the transponder is to be switched
> on at MA 135 it is the same as being switched on at Phase 135.  I apologize
> to anyone I confused or mislead.  I am also a little surprised no one
> corrected me.

I believe that the term "mean anomaly" is often misused by amateurs.

Note that the mean anomaly term in NORAD two-line elements is measured
in degrees (as in 360).  See for example:

	http://celestrak.com/NORAD/documentation/tle-fmt.shtml

Amaterur's regular misuse of the term is noted in the AMSAT Keplerian
elements tutorial (http://www.amsat.org/amsat/keps/kepmodel.html):

	"... Mean anomaly is simply an angle that marches uniformly in
	time from 0 to 360 degrees during one revolution. It is defined
	to be 0 degrees at perigee, and therefore is 180 degrees at apogee."

	"... It has become common practice with radio amateur satellites to
	use Mean Anomaly to schedule satellite operations. Satellites
	commonly change modes or turn on or off at specific places in
	their orbits, specified by Mean Anomaly. Unfortunately, when
	used this way, it is common to specify MA in units of 256ths
	of a circle instead of degrees! Some tracking programs use the
	term "phase" when they display MA in these units. It is still
	specified in degrees, between 0 and 360, when entered as an
	orbital element. ..."

-tjs

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