[amsat-bb] Pass Duration vs Max Elevation

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Fri Oct 14 17:39:37 PDT 2011

Another question from a satellite newbie.

I'm working on a satellite pass information query system via APRS 
messaging and am currently providing future pass duration as a layman's 
indicator of the "quality" of an upcoming pass.  I've been told that 
duration is "of little value" (see below for the full quote) and a max 
elevation is all that matters.

In my (relatively short) time of watching various pass predictions, I've 
found a nearly direct correlation between the duration of a pass and the 
max elevation achieved.  I've not noticed a "longer low pass" nor a 
short high pass for that matter.  Low elevation passes are short, and 
high elevation passes are long.

So, my question, to be answered from the perspective of hoping to get 
more people aware of satellite passes by making it easy to casually 
query their availability while at the same time providing useful 
information to people that frequently "work the birds" (if I've got that 
expression correct) while they're away from their normal prediction 
tools is:

Would a forecast pass duration (expressed as a delta time) be useful in 
this context, or is that truly "of little value" and the Max Elevation 
of a pass should be provided necessitating a potentially greater 
education of the general populace?

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

PS.  Here's my original reasoning for pass duration rather than max 
elevation and the comments I received in reply.  The sender of the 
response is purposely kept anonymous so that I can get independently 
reasoned responses and not just agreements with the quoted source.

>  I went with a pass duration rather than max
>  elevation so novices can better plan their
>  time investment.  They both basically
>  communicate pass "quality" and "ease of
>  working", but everyone understands time, while
>  the experts have a handle on elevation.

Sorry, but time is of little value since it can be a longer low pass that one has no prayer of working from a mobile because it is so low.  So elevation tells it all.  A low max elevation is not worth bothering with no matter how long it is.  A high elevation pass will have a nearly 10 dB advantage to the mobile operator and is very important information.  And also, by definition it is longer.

And satellite operators know the approximate length of a pass.  For a mobile, the shortest is the ISS with about 5 minutes useable.  For PCSAT1, about 10 minutes max.  All other satellites are somewhere in between or are not usually workable from an FM mobile rig with omni antenna.  So the few minutes difference is of little value.

I dont think people are going to arrange their daily schedules around whether a satellite is going to be useable fo 5 minutes or 8 minutes.  But they certainly will change plans for a 60 degree pass compared to a 10 degree pass.

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