Message-ID: <4B8E6B8E.9080604@nasa.gov>
Date: Wed, 3 Mar 2010 14:00:46 +0000
From: Frank Lemoine <Frank.G.Lemoine@nasa.gov>
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Subject: [ids.analysis.forum] TR: TOPEX and Jason surface forces, again

Forwarded from Luca.Cerri@cnes.fr
==================================


Dear Remko, everybody,
 
thanks for bringing this point to our attention. 
I agree with John remarks concerning SRP modeling. 
I can add that radial differences between orbit solutions 
otained using either UCL or GDR model have negligible mean 
and are within 3 mm RMS over the 10-day cycle. The most signignificant mean 
differences are cross-track. (with max difference at high beta prime, 
as John was pointing out). 

At high beta-prime ±Y radiators are in shadow and facing the along-track direction. 
Also, there is no eclipse for abs(beta)>55° or so. 
Assuming the radiated force as an along-track constant, and this should not 
be that wrong, errors in this force should be compensated
by along track empiricals, however that depends on how constrained is the solution. 

Z radiated fluxes (always radial) should also produce a nearly 
constant force. 

Another point is the Earth thermal emission and albedo. The amplitude of the 
radial force should be stronger when the sun is in the orbit plane 
(low beta) and this force has a mean 60 days pattern. We have not discussed 
about this recently. 

What are the amplitude and phase of the MSL signal that you observe ? 
Is this a globlal MSL signal or are there geographical patterns ? 

Do you observe the same 60 days effect on MSL using JPL orbits ? 
(they use the UCL SRP model and a reduced dynamic approach GDR orbits use 
 CNES box&wing and are more constrained)

Kind regards
Luca
__________________________________
Luca CERRI
Centre National d'Etudes Spatiales
DCT\SB\OR - POD Team
18, av Edouard Belin
31401  Toulouse Cedex 09 - FRANCE
tel.   +33 (0)5 61283549
fax    +33 (0)5 61281855
bpi    1323
email  luca.cerri@cnes.fr


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