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# Re: how abt ao-40 beacon on mode-S?

• Subject: Re: [amsat-bb] how abt ao-40 beacon on mode-S?
• From: Roy Welch <rdwelch@xxxxxxxxxx>
• Date: Wed, 29 Nov 2000 19:07:19 +0000

```True Mean Anomaly is measured from zero to 360 degrees from Perigee.  The
zero to 256 degree measurement is also measured from Perigee, but has been
referred historically as Phase.  I believe this Phase measurement
originally came about because of the binary convienience of the early on
board or ground tracking computers.  The Mean Anomaly stated in the
Keplerian elements is measured 0-360 degrees.

It might be less confusing to continue to call the 0-256 measurement,
Phase.  However, it might really be better to switch to the 0-360 MA usage
in determining the satellite schedule and let the old 0-256 Phase
measurement die an honored death.  This would require a minor change in one
or two tracking programs to switch to the MA designation.

Achim Vollhardt wrote:
>
> Hi folks,
> MA means Mean Anomaly.. this determines the position of the satellite on
> the orbit.
> If you take the orbit period and divide it by 256, you have the time,
> the sat takes for 1 MA unit (right now AO-40 has a period of roughly
> 11.5 hours, that means one MA unit is 2.7 minutes). MA 0 is defined as
> pergee.. that means that MA 128 is the apogee . And MA 20-26 is 54-70
> minutes after perigee.. note that the distance AO-40 travels in one MA
> unit depends on the MA value itself: at apogee (MA 128) the sat is slow,
> so one MA unit is a small amount of distance, at perigee (MA 0) the sat
> is fast and one MA is some already distance..
>
> MA 20-26 has been chosen because of the flight attitude of nearly
> alon/alat 270/0. that means in perigee (or MA 0) the motor is pointing
> opposite flight direction(backwards), so at MA 20-26 the motor (and so
> the hi gain antennas, because they are mounted on the same side) are
> pointing to earth. Remember, AO-40 is still spin stabilized, so its axis
> remains fixed. This is why MA20-26 is a good position for listening to
> any hi gain antenna right now.. I wouldn't be surprised if there were
> any tests with the 70cm TX..
>
> 73s Achim, DH2VA
>
> Jon Ogden wrote:
> >
> > on 11/29/00 9:54 AM, Achim Vollhardt at avollhar@physik.unizh.ch wrote:
> >
> > > Hi folks,
> > > seems, the 'mode-s beacon for testing' - idea wasn't so bad at all..
> > > live telemetry(29.11.00, 15:47 UT) announces the Mode-S general beacon
> > > to be turned on between MA 20 and MA 26. So anybody with mode-s equip:
> > > start listening, but beware of doppler, which will be huge at MA20-26,
> > > calculations for my qth say about 25 khz down the announced 2400.200
> > > MHz! Happy hunting..
> >
> > What does the term "MA" mean?  Right now MA is at 166.  When does it
> > change....and what is it?
> >
> > 73,
> >
> > Jon
> > NA9D
> >
> ----
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--
73, Roy

Internet: w0sl@amsat.org