[amsat-bb] Re: Tracking program performance post chicken little date. (SatPC32 and GPredict)

g0mrf at aol.com g0mrf at aol.com
Thu Oct 13 15:27:54 PDT 2011

 Hi Tom.

Interesting question.

I wonder if running a prediction program forward from a set of 'todays' keps will give a vaild answer for decay date?

Looking at the keps, you have a number for decay rate. I reached the conclusion that this could be a major source of inaccuracy as presumably the value for decay rate will change as the satellite reduces altitude. It maybe the case that decay rate follows a curve which is not replicated by the program. Does anyone know if this is correct as it seems unlikely that software available to us e.g. Nova / GPredict will include algorithms for auto changing decay rate or for including other variables like sunspot cycle. I believe these variables are accounted for in more advanced software like AGI  Satellite tool kit (STK)


David  G0MRF



-----Original Message-----
From: Thomas Doyle <tomdoyle1948 at gmail.com>
To: amsat-bb <amsat-bb at amsat.org>
Sent: Thu, 13 Oct 2011 23:08
Subject: [amsat-bb] Tracking program performance post chicken little date. (SatPC32 and GPredict)

All the hype over the chicken little contest caused me to wonder how
tracking programs will handle it.

I was looked into the Cal Poly CP6  and HAWKSAT1 satellites. The TLE data is
published on both Amsat and Celestrack lists. SatPC32 shows neither of the
satellites as moving. An error is generated when trying to select either of
them. I thought that perhaps they had decayed but had not been removed from
the TLE lists.

GPredict continues to track Az-El for CP6 in real time in the text display
but shows the elevation and altitude as negative and the up/down direction
as D (decayed) - it does not display CP6 on the map. I am assuming that CP6
has decayed. The elevation for CP6 goes up and down and the tracking value
change over time. Since the elevation is always negative perhaps GPredict is
tracking what would have happened if the earth was just a tiny point of mass
and the satellite is able to continue its downward descent. HAWKSAT1 shows
up as above ground and running in GPredict.

Since ARISSAT1 is probably going to decay fairly quickly I took a look at
predicting ahead using the great Preview tracking in SatPC32 to see how
decay is handled. After a couple of really bad years the coverage map for
ARISSAT1 looks better than ever starting just two years from now in 2014.
Unfortunately I could not figure out how to get GPredict to predict more
than 14 days in the future and did not want to fool around changing the
system clock.

I have wondered what the NORAD routines would do after decay and how
tracking programs that use the NORAD model would deal with it. Does the
NORAD model continue to track as if the earth was just a very small very
heavy point in space. A transparent 3D earth display would be very
interesting to use to view the post chicken little results - someone must
have one.  Anyone know for sure ?  HAWKSAT1 is still a bit of a mystery.

73 W9KE tom ...
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