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RE: How often do I need to update Keps for STSORBITPLUS?



There are a number of variables involved.  The major variables are:

1.  Whether the satellite has propulsion or not.  If it does, the keps will
need to be updated more frequently to ensure any orbital adjustments are
taken into consideration.  The Space Shuttle is a classic example of an
object of this type.

2.  Altitude and orbit.  Some satellites (e.g. very low orbiting satellites,
such as Mir) are more susceptible to orbit changes caused by atmospheric
expansion during solar flares (this causes more drag than predicted).
Higher orbiting satellites can be unduly influenced by solar and lunar
gravity (That's what caused AO-13 to re-enter).

3.  Tracking software and orbital models.  The more accurate your software
is, the longer it can accurately predict where a given satellite will be
before the keps need updating (assuming the first 2 factors haven't
significantly influenced the satellite's orbit).

The answer is the classic "How long is a piece of string" question, and my
answer would be "You need to update the keps before the predictions become
too inaccurate" :-)

In practice, I update mine every week, which isn't strictly necessary, as I
find pass predictions of LEO birds are within a few dozen km for passes
predicted 2 weeks in advance.  Mi high frequency of updating is for 2
reasons:

1.  Because the keps are there (I get them emailed to me via the KEPS list).
If you've already got them, might as well use them! :) 

2.  I do a lot of forward pass predictions for SO-35, UO-14 and RS-13, up to
3 weeks in advance (for web publication purposes), so getting the latest
keps is more important for me to minimise any inaccuracies.

Tony Langdon.
Systems Development and Support.
ATC Training Australasia.  Level 2 321 Exhibition St Melbourne  3000.
Phone:  1300 13 1983     WWW:  http://www.atctraining.com.au


> -----Original Message-----
> From: Docfester [mailto:docfester@mindspring.com]
> Sent: Friday, 14 April 2000 15:05
> To: Amsat-Bb; Frank Grossman
> Subject: RE: [amsat-bb] How often do I need to update Keps for
> STSORBITPLUS?
> 
> 
> 
> 
> 
> 
> 
> I update at least once a week on the birds that are not in 
> the Clark Orbit
> (Geosynch.) It also depends on how you list the sats, as Real Time or
> Static.  Ransom states to update every 10 days on Real Time 
> and 90 days on
> Static sats.  If you cant do that, just do when you can!!!!
> 
> 
> 73's
> Les Alverson KD4SFD
> 
> I will not be pushed, filed, stamped, indexed, briefed, debriefed, or
> numbered"  -- The Prisoner
> 
> -----Original Message-----
> From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
> Behalf Of Frank Grossman
> Sent: Thursday, April 13, 2000 23:53
> To: AMSAT-BB@AMSAT.Org
> Subject: [amsat-bb] How often do I need to update Keps for 
> STSORBITPLUS?
> 
> 
> I make most of my satellite contacts on the "FM birds" using 
> a five watt HT
> and 19 in. "rat tail," with tracking information from 
> STSPLUS.  Under these
> conditions how often do I need to download updated kep files 
> for adequate
> orbital predictions?
> 
> The most important thing is to identify the overhead, or 
> nearly overhead,
> passes since these are the ones I have the best chance of 
> working on the HT.
> 
> BTW, I've at least heard myself on most of the direct 
> overhead passes I've
> attempted on UO-14, and on a few occasions made several 
> contacts in a row
> before being clobbered by stations with "real" antennas.
> 
> Thanks!
> Frank
> ----
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> 
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