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R: Old (without PC) tracking ?

----- Original Message -----
From: Richard W L Limebear <Richard@g3rwl.demon.co.uk>
To: <amsat-bb@AMSAT.Org>
Sent: Tuesday, December 25, 2001 11:59 AM
Subject: Re: [amsat-bb] Old (without PC) tracking ?

> William, Gang
> "William Leijenaar" writes:
> > I am looking for some way to predict satellite passes without use of an
> > computer system. I have read about some system that worked with pen,
> > (map) and ruler.
> In Britain this is called an OSCARLATOR. It uses a polar projection map
> (thats a great-circle map centred on the pole) and there is a sample map
> inside the back cover of the "Satellite Experimenters Handbook" along with
> a description in one of the chapters.
> You use clear plastic overlays which change for each satellite with one
> (the range circle) centred on your QTH and the other (the orbital path)
> centred on the pole. This works fine for LEO but I'm not aware of one for
> the phase-3 orbits.
> 73 and Seasons Greetings
> Richard W L Limebear G3RWL
> g3rwl@amsat.org
> FOC # 1188
Hello Richard,G3RWL

The use of polar projection map with the clear plastic overly, namely the
range circle,and the orbital path can be used as well for elliptical orbits
provided  some modifications to LEO maps are made.

In LEO orbits the altitude of the satellite is considered constant and every
concentric circle in the range circle means always the same value of
elevation and every radial curve from the center of it means always the same
value of azimuth

In LEO orbit the traking procedure is to set the orbital path in to the
longitude of the equator crossing  for that orbit and take a note of the
time of  the equator crossing.

In order to know the AZ and EL it is only necessary to add every elapsed
minute to the orbital path beginning from the time of equator crossing
given by the satellite efemeridis of the LEO satellite.

In other words,as soon the satellite enters in to your range circle the only
operation needed is to read  the AZ in degrees directly in the radial curve
crossed by the the orbital path and than directly correlate every concentric
circle with the corresponding EL in degrees.

Using elliptical orbit it become more complicated because the altitude of
the satellite changes continuously with the elapsed time from the equator
crossing or from the crossing of perigee.

In order to solve this problem it was necessary to compute a very large
polar projection map including earth areas down to -60 degrees at
South latitude.

In addition,and more important it was necessary to calculate a range circle
considering the satellite at the apogee.

The apogee range circle is very large in diametyer indeed but every
concentric circle has an identification  numbar wich do not means directly
the satellite elevation.

In order to know the satellite elevation every numbar written in each
concentric circle must be correlated to a separate table in wich each numbar
take a different elevation value in degrees depending on the elapsed time
 from the satellite equator crossing or from the perigee crossing depending
 on the type of efemeridis used for it.

This matter become more complicaded considering that the elevation
correlated to the elapsed time from the equator crossing on the concentric
circle is not constant for the life of a satellite in elliptical orbit but
it changes greatly changing  the satellite argument of perigee (W).

It happen that using this system for satellite like  OSCAR-10, OSCAR-13 or
AO40 it where necessary to compute and publish a new concentric circle every
almost tree monts because the inclination is not 63,44 degrees and the
argument of perigee (W) is not steady and constant in the time.

In addition,using this  map system with satellites in elliptical orbits it
would be necessary to use a second polar projection map in order to
know the actual coverage of the satellite.

Before the launch of OSCAR-10 the computer was not so popular in to the HAM
circles and so the above described map was developed for elliptical orbits
and it was  ready to operate using satellite efemeridis at the time of
OSCAR-9 that was unfortunately lost in the Atlantic ocean with ARIANE-4
fligh 06

During the elapsed time between OSCAR-9  expecting  OSCAR-10 the first step
to abandone the use of maps and satellite efemeridis was made by  Dr. Tom
Clark, W3IWI who writted an absolutely  new program using the keplerian
elements instead of the previous satellite efemeridis system

Tom's  program was written in North Star Basic and published in to the
AMSAT ORBIT magazine Nr 6 / 1981

Starting from the W3IWI effort a new era begins for all traking software in
the future and since i was in touch with him at that time i got from him the
honour to receive by letter his absolutely new software prototype with many
notes writtem in it by Tom's pencil and by his hand.

I hope that this note help to know some of the historical  steps made by
amateurs in developing their traking tools and software until the computer
programs took over.

73 de i8CVS Domenico

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