Subject: Correct SPOT-3 Offset Values
From: "Lemoine, Frank G. (GSFC-698.0)" <[email-masked]>
To: <[email-masked]>
Date: Fri, 12 Sep 2008 15:24:56 -0500

Dear Colleagues-

I provide below a copy of a message sent by Laurent Soudarin
 of the IDS Central Bureau, following an inquiry into what
 values of OFFSET and Center of Gravity should be used
 for that spacecraft.

Please be careful *not* to use the erroneous values
 in the files at
 
ftp://ftp.cls.fr/pub/ids/satellites/macromodels/spot3mod.pdf
ftp://ftp.cls.fr/pub/ids/satellites/sp3mass.txt

And at the corresponding CDDIS locations until these files
 are corrected.

Best Regards,

Frank Lemoine
NASA Goddard Space Flight Center
=========================================================

Dear Frank,

The reference document is
ftp://ftp.cls.fr/pub/ids/satellites/DORIS_instrument_modelling_1G_envisat_2460_15.pdf

The values for SPOT-3 are given page 30.

*DORIS antenna reference point in the platform reference frame:
XB=     -0.770 m
YB=     -0.330 m
ZB=     -0.950 m

*Satellite centre of gravity
XC=     -1.584 m
YC=     -0.002 m
ZC=     +0.023 m

*Distance between antenna origin and phase center: h2 GHz = -0.315 m (Z axis)

*The components of the centre of gravity - 2 GHz phase centre vector in a
platform reference frame are thus:

X (m) = xB (m) - xC (m)         =       +0.814 (m)
Y (m) = yB (m) - yC (m)         =       -0.328 (m)
Z (m) = zB (m) - zC (m) - h2 GHz (m)    =       -1.288 (m)

*Satellite mass (on orbit): 1875.2 kg (values after manoeuver 10/09/96)

These values above are also the ones used in GINS
...
Spot-3
     x_masse = 1875.2_S ! au 10/09/96
   orig_cdm    = 0._S
     orig_cdp(:,1) = -(/+1.288_S,-0.328_S,-0.814_S/)

avec X_GINS=N , Y_GINS=-T, Z_GINS=R
...

The values in the documents
ftp://ftp.cls.fr/pub/ids/satellites/macromodels/spot3mod.pdf
ftp://ftp.cls.fr/pub/ids/satellites/sp3mass.txt
seem to be obviously erroneous
and will be corrected as soon as possible.

Bon week-end
Laurent