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Sat Tracking By Pencile




(cross-posting to amsat-bb to get more eyeballs on this idea)

On Sun, 22 Jul 2001, James Alderman, KF5WT wrote:

> I have a satellite / education related question.  I use NOVA for locating
> the satellites I'm interested in.  NOVA makes sat tracking easy.  However I
> also like to speak to students and teachers about the educational
> applications of Amateur Radio.  (Some of you may have seen my recent QST
> article in page 57 of the August issue.)
> 
> I wonder if it's possible (or practical) to work satellite formulas on paper
> for instructional purposes.  In other words, take a set of elements, take
> your lat/long and current time, plug the numbers into the formulas, and turn
> the crank to reveal where a satellite will be in the sky at a certain time.
> If this could be done, it would be a wonderful educational activity for
> students.
> 
> Any ideas about whether this could be done?
> 
> 73, James Alderman, KF5WT
> Dallas, Texas

Jim:

Yes, The "Kettering Group" has done this for years, starting with making
orbital estimates using doppler shift and time measurements.  There are
probably some web sites describing the techniques used.  Before home
computers became widespread, ARRL and AMSAT published paper and pencil
methods for tracking low orbit satellites.

Look for references for the "OscarLocator" which was analogous to a
circular slide rule for orbit prediction.

I recall building a tracking system described in an early 1970's QST to
track Oscar 6's 10M beacon.  Given the basic orbit information (mean
motion, eccintricity, inclination), you constructed a template that
followed the motion of the satellite from ascending node to descending
node projected onto a Mercator projection map.  The template was marked
off in minutes after equator crossing time.  You also drew a series of
ellipses on the map around your location to show elevation and azimuth.

To predict a specific pass, you used data broadcast by W1AW for equator
crossing times and longitude.  W1AW would transmit reference data and
there was a formula to propogate the reference times forward (they were
good for about a week).  You calculated when and where the ascending nodes
occurred and use the template to see if the satellite's motion brought it
over your location.  During the actual pass, you used the time tick on the
templtate to see where the satellite was at that moment. The complexity is
appropriate for high school students (one data point - me).

As you can imagine, the workload got a bit much at times, and I was just
receiving.  Makes you appreciate tracking software!  

The Oscarlocator simplifed the process but used, I believe, the same
principles.  It should be possible to build one.

I would look at rigging up a globe to illustrate the orbital principles -
MUCH easier to show it that way in three dimensions.  I've seen Tom Clark,
W3IWI, do something similar at AMSAT meetings using styrofoam balls for
the earth and satellite and cut out pieces of cardboard to show the
orbits. (but how Tom grows a 3rd and 4th hand to keep from dropping
everything is a mystery to me!)

Rather than doing the math entirely by hand, consider the intermediate
stpe of using a spreadsheet and/or symbolic algebra software.  This will
allow the students to see what is going on without making as many
arithmetic errors.

Sounds like a fun project.  Good luck!

73 Steve KA1LM

-------------------------------------------------------------------------
Stephan A. Greene                            sgreene@patriot.net
HAM: KA1LM@amsat.org  QRP-L #232 Grid FM18hx 38 59'83.33"N 77 23'6.15"W
-------------------------------------------------------------------------

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