Re: TLE with future epoch

From: Marco Langbroek via Seesat-l <seesat-l_at_satobs.org>
Date: Mon, 1 May 2017 11:28:30 +0200
Here are some of my telescopic data on the Chang'e 3 rb in sub-lunar orbit from
2015, i.e. a very long period object:

39459 13 070B   9331 G 20151017125107000 17 75 0122114-193309 56 I+157 01
39459 13 070B   9331 G 20151017125914000 17 75 0122120-193321 56 I+163 01

site 9331 = Warrumbungle, NSW, Australia, 31.27517 S, 149.19453 E, 552 m ASL

Space-track has a TLE for this object, epoch 15295.50000000 which is 5 days in
the future with respect to the obs (interestingly, they don't have a TLE for a
full year before this date).

These fit to the TLE with these residuals (in degrees, and deltaT in seconds):


      STA  YYday HH:MM:SS.sss   XTRK    deltaT     Perr
( 1) 9331  15290 12:51:07.000   0.75   -4740.11    0.837
( 2) 9331  15290 12:59:14.000   0.75   -4731.68    0.838

So almost a degree difference in position between observed and predicted.

I seem to remember, but have to look that up, that at some later point the
residuals went much worse than that.

These are difficult to predict objects in chaotic motion, notably influenced by
solar radiation pressure. Over longer periods these don't integrate well (and
even on shorter periods residuals quickly build up).

- Marco


-----
Dr Marco Langbroek  -  SatTrackCam Leiden, the Netherlands.
e-mail: sattrackcam_at_langbroek.org

Cospar 4353 (Leiden):     52.15412 N, 4.49081 E (WGS84), +0 m ASL
Cospar 4355 (Cronesteyn): 52.13878 N, 4.49937 E (WGS84), -2 m ASL
Station (b)log: http://sattrackcam.blogspot.com
Twitter: _at_Marco_Langbroek
-----
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Received on Mon May 01 2017 - 04:30:07 UTC

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