[aprssig] Satellite positions: Design Rationale

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Sun Oct 16 15:17:57 CDT 2011

On 10/16/2011 2:00 PM, Greg D wrote:
> I like Bob's suggestion. Well before a pass (longer than an hour is 
> ok), knowing when the pass will be, and how high it will be, are the 
> most useful pieces of information. Shortly before the pass, knowing 
> how many minutes before it starts and how high it will be are most 
> useful. I rarely stalk a satellite, so it's random chance whether it's 
> more or less than an hour away, hence keeping the how high the pass 
> will be is still useful. During a pass, knowing Az, El, and time to 
> end of pass is best.


> Being really clear which of the three cases you are transmitting is 
> also important. Yesterday it was sheer luck that ISS happened to be 
> up. It took me a few minutes to realize that I was in case #3, 
> compared information with my PC in disbelief, and by that time the 
> pass was almost over.

One says "AOS" followed by a time (be it delta or zulu).  The other says 
"LOS" followed by Az: nnn El: nnn.  How much more different do you need 
them to be?  Start with something like "ISS is in view NOW!"?  (I'm 
being completely facetious there).  I believe they're different enough 
(until we muddy the waters by adding the max elevation to AOS) because 
the LOS shows where to point your antenna.

> It occurs to me that the contents of the message you send to "ISS" is 
> ignored. Could it be used as a command autoresponder, indicating what 
> sort of information or format is desired? You could also use it to 
> validate the request, in case there is a collision in the object 
> namespace. You never know if AO51 is a satellite, or an ET visiting a 
> certain place in New Mexico...

They are ignored on purpose, but can optionally be another active APRS 
call-SSID to query the next pass for an alternate station.  I wanted to 
KISS by not requiring any memory of arcane incantations to get the thing 
to give up information.  I personally think that CQSRVR doesn't get much 
use because a) operators can't remember who to send the message to and 
b) they don't remember the syntax to get actions taken.

By only requiring ONE piece of information to be remembered (send a 
message to the satellite name), I'm hoping this won't e a 
flash-in-the-pan idea and may see some long-term activity as people 
figure out how they can effectively use it.

Personally, I don't keep satellite prediction software running at my 
station 24x7, but I DO keep APRS open.  If I'm curious if the ISS is 
going over, that information is now a single message away.  And if the 
pass looks reasonable, I might switch my IGate over to SatGate operation 
for the pass for the benefit of others working ARISS via APRS.  As I've 
said in other messages, it's not just information for the mobile 
operator, it's information at the fingertips of any APRS messaging user.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

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