[aprssig] Satellite Predictions requires a) Beacon and b) Messaging IGate

Bob Bruninga bruninga at usna.edu
Wed Oct 19 17:55:55 CDT 2011

> I understand the bit about there being so many sats 
> that asking for an estimate of the next few to AOS 
> in my location sounds like a larger programming issue...

Far from it.  ALthough there were as many as 12 interesting AMSATS usable by FM mobiles back in 1998, today there are only 3 or four: ISS, AO51, AO27 and SO50.  

The 0.5% of serious satellite operators that are mobile with a dual band full duplex SSB rig and a beam to work the linear birds are so invested, they will get their tracking from their own laptop or handheld device.  

This APRS satelite info service discussion is for the other 99.5% of APRS mobiles who might want to see what is in range that they can work.

> ... well, an FM sat would also be a good way to 
> "get out", FM sats and those with either mobile 
> or HT capability.

These satelites when they get above about 30 degrees elevation are 6 to 10 dB closer than they are on the horizon and are workable by any FM dual band mobile for a few minutes... IF you know when they are there (2 or 3 times a day each!).
> Also, the "useable part" of the pass is going 
> to be a large variable, so quantifying it for 
> a given user very difficult.

Not it is not.  It is quite well defined.  When it is above 20 or 30 degrees it is 6 to 10 dB stronger and that is when it is useable.  ALL of these satelites have a pass time in this elevation range of only between 3 to 5 minutes.  That's all there is to it.

> If economy of characters is important, then I think 
> MaxEL could be shortened to simply EL, no? 

No, because if we only see EL, then we do not know that it is not some other EL... at some instant in time. MaxEL is a single unchanging quantity for the  pass.

>--- Bob Bruninga wrote:
>>... I'm still a little uncomfortable with the time formats:
>> AOS in 6:45h for 9:50m MaxEL 27
>> ...  So that is kinda unusual to see...
>> 2) No mobile is ever going to see a 9:50 minute pass. 
>>... I'd really like to see that rounded to "9m"
>> Although I do not feel comfortable with 6:45h I am less
>> comfortable with
>> "6.75h" but is more consistent.  If you want to mix
>> minutes and seconds you
>> could use 6h 45m.  Though I don't like that
>> either.  As you know, I like
>> indicating it as a specific TIME if it is more than an hour
>> away or in delta
>> minutes of it is less than an hour.
>> > AOS in 37m for 9m MaxEL 27 (or)
>> > AOS at 1425z for 9m MaxEL 27 (or)
>> Actually, I would make the separation be at 99
>> minutes.   This is because
>> all LEO satellites have periods on the order of 90 to 100
>> minutes, so if it
>> is less than 100 minutes away, then it is the next
>> pass.  If it is more than
>> 99 m inutes away, then it is quite a while.
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