[aprssig] Satellite positions: Design Rationale

Bob Bruninga bruninga at usna.edu
Sun Oct 16 07:35:33 CDT 2011

> But, I believe I'm going to stick with 
> the objects, because I've got a better 
> way to deliver (most of, outside of 
> QSY tuning) Bob's ACTUAL desired information 
> instead of the station posit that he 
> was asking for.

I think you are making the wrong decision.  It is inconsistent for you to generate a message from "ISS" and then be so stubborn about not originating the POSITION from "ISS" as well.  It violates the principle of least astonishment.

Further there is NO BETTER way to deliver the info.  We have tens of thousands of radios that will compute AND DISPLAY the DIRECTION, DISTANCE to the symbol on the front panel of the radio in a universally consistent manner.  There is no reason to try a "better way" that ignores the receiver display system.  Do you even have an APRS Mobile radio?

This feature you are writing is for the APRS RADIO user.  There is a well defined human inteface and therefor expectations.  Please do not ignore this display!

>> "%AOS:2:27m+8:53m"
>> "AOS:2:27m+8:53m"

Both of those are gyberish, and meaningless without a priori knowledge of what it means.  A fundamental ANATHMA to APRS.

The best format of the email should be along the lines of:

AOS in XXm  MaxEL:YY 


THe difference being whether it is less than one hour away or more.  And the format for the complementary POSITION of the satellite injected into the APRS-IS once a minute should be:


1) It gives a delta reference if the pass is soon.

2) It captures the time if the  pass is later

3) It gives Max Elevation which is the single most important parameter for the mobile operator to visualize the value/quality of the pass.

4) It causes the POSITION to be passed via IGates back to the requester.  And this position SERVES everyone in range of that IGate, not just the requester.

5) It is a legal RF packet because the ham radio callsign of the source "de KJ4ERJ" is included in the standard format for tactical calls.

It is a well designed combination of MESSAGE response and complementary POSITION providing exactly the intended user display on the front panels of all APRS mobile radios and APRS HT's.  And it takes advantage of all the known operational limitations of the APRS-IS and RF system.

Bob, WB4APR.

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