# Re: Decaying Sats

Bjorn Gimle (bjorn.gimle@online.dextel.se)
08 Aug 1995 07:31:06 GMT

```Lutz Schindler,lschindler@assi.s-link.de
asked me about how to observe decaying satellites:

Hello Lutz,

I guess it will depend on what you want to do, what you you
want out of it for yourself, what you want to contribute, and
if you want to observe and/or compute.

Also, which prediction program(s) you use, and if you are willing
to use more programs.

As for observing, my tips are:

1. Inspect your elsets to know well in advance which objects
have old, inaccurate elsets, and which are about to decay.

2. Observe the decay candidates while their elsets are reliable,
so that you know their magnitude and flashing patterns.

3. Use NASA GSFC OIG RBBS (!) to get recent elsets for decay
candidates, if not sufficiently new are obtained here or
other places.

4. When decay closes in (and/or weekends stop the flow of elsets)
make notes of which elset you used for prediction, and how
many seconds before/after prediction your observation is.
Use this for extrapolation, to make it easier to find
the last days.

The effect of elset errors is usually quadratic with respect to
age of elset, perhaps    ndot2 * (day-Epoch)**2 * 2000 seconds,
and the expected decay day = Epoch + 0.08 / ndot2  or later.
Near the decay, the inaccuracy grows faster - I use
time * ln(time) , where time=remaining life time, as a factor.

If you don't know how to find the components of the equations,
let me know, and/or look in a previous mail I wrote July 28 !

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==(Bjorn_gimle@lector.kth.se)==(bjorn.gimle@duesenberg.se)==
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```