Re: TRMM orbit

Alan Pickup (alan@wingar.demon.co.uk)
Thu, 19 Mar 1998 22:34:54 +0000

Ralph McConahy <Ralph.Mcconahy@jpl.nasa.gov> writes
>...
>     
>     I have two questions: 
>     
>       1) Why would TRMM be running 2.5 and 2.25 minutes late using fairly 
>          recent elsets?
> 

I am sure that TRMM was manoeuvred between the second and third elsets
in this list of the latest four elsets (day 98073 is March 14):
TRMM             4.0  0.0  0.0  5.6 d            348 x 345 km
1 25063U 97074A   98073.46669167  .00049335  00000-0  32546-3 0  1365
2 25063  34.9955  46.2764 0001896 255.6511 104.4008 15.74467007 16792
TRMM             4.0  0.0  0.0  5.6 d            347 x 345 km
1 25063U 97074A   98074.29093861  .00045098  00000-0  29687-3 0  1374
2 25063  34.9962  40.6753 0001501 261.4931  98.5626 15.74531779 16922
TRMM             4.0  0.0  0.0  5.6 d            348 x 347 km
1 25063U 97074A   98076.06662834  .00038168  00000-0  25673-3 0  1396
2 25063  34.9951  28.6107 0001094 273.8309  86.2800 15.74061226 17207
TRMM             4.0  0.0  0.0  5.6 d            347 x 346 km
1 25063U 97074A   98077.90570401  .00046119  00000-0  30738-3 0  1414
2 25063  34.9954  16.1166 0000714 275.4898  84.5738 15.74244039 17493

The change is most noticeable in the mean motion term which decreases
from 15.74531779 to 15.74061226 when other recent elsets have been
showing the usual drag-induced increase. This is not the first manoeuvre
- there was another decrease in mean motion from 15.74206405 on 98066.11
to 15.73849059 on 98066.23, and there were earlier ones too.

For the week up to (and including) 98074.29, a single orbit can satisfy
all eight elsets with a maximum residual of 0.8 second. Predicting this
forward to the final two epochs above, shows TRMM to be running late by
46 and 109 seconds respectively.

>    
>       2) Since this is such a bright object, why don't many web sites that 
>          have tle's have TRMM in their lists?

Since this is low, manoeuvring and a candidate for decay within a few
month, I include it in my frequently-updated select.tle file, available
via my SatEvo WWW page below. As Jeff Hunt has already posted, other
sites publish elsets for it too.

Alan
-- 
 Alan Pickup | COSPAR site 2707:   55d53m48.7s N   3d11m51.2s W    156m asl
 Edinburgh   | Home:      alan@wingar.demon.co.uk       +44 (0)131 477 9144
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