****************************************************************************** DORISMail 03-Apr-2000 18:40:59 Message No 0090 ****************************************************************************** Author: Jean-Paul Berthias Subject: Caracteristics of the SPOT satellites Dear colleagues, Following a question from Dr R. Govind we have realized that some of you do not have the detailled caracteristics of the SPOT satellites. In addition, we found that some of the values given for SPOT 4 in the DORIS Mail 57 are incorrect. So here are the parameters that we currently use: SPOT 2 SPOT 3 SPOT 4 mass 1827 kg 1875 kg 2738 kg The characteristics of our (very basic!) macro-models are as follows SPOT 2 and SPOT 3 surfaces X+ X- Y+ Y- Z+ Z- SA+ SA- area 3.5 3.5 6.5 6.5 6.7 6.7 19.5 19.5 specular ref. 0.54 0.54 0.54 0.54 0.54 0.54 0.16 0.16 diffuse ref. 0.07 0.07 0.07 0.07 0.07 0.07 0.16 0.16 SPOT 4 surfaces X+ X- Y+ Y- Z+ Z- SA+ SA- area 3.5 3.5 7.7 7.7 9.0 9.0 24.8 24.8 specular ref. 1.00 0.63 0.54 0.56 0.47 0.47 0.10 0.24 diffuse ref. -0.38 0.81 0.50 0.38 0.11 0.25 0.15 0.24 The spacecraft axes are defined by X = - pitch axis Y = - roll axis Z = yaw axis The SPOT satellites all have geocentric attitude control. (the relation between these axes and the spacecraft shape is given below) [Image] velocity vector along -Y For SPOT 2 and SPOT 4 the normal to the solar array is obtained by rotating the +Z axis by 5 degrees around the Y axis in the direction of the +X axis. This angle is 22.5 degrees in the case of SPOT 4. The solar panel rotates around the X axis. The rotation angle of the array around this axis is such that the angle between the normal to the array and the direction of the Sun is minimal. The components of the normal to the array in the spacecraft frame are therefore SPOT 2 and SPOT 3 [ sin(5) sin(omega t)*cos(5) cos(omega t)*cos(5) ] SPOT 4 [sin(22.5) sin(omega t)*cos(22.5) cos(omega t)*cos(22.5)] If you do not want to use the value of the center of phase correction provided with the data, but would rather compute it yourself, here is the offset of the phase center of the 2 GHz DORIS antenna with respect to the center of gravity SPOT2 SPOT3 SPOT4 X 0.842 m 0.814 m 1.131 m Y -0.339 m -0.328 m -0.338 m Z -1.330 m -1.288 m -1.325 m If you experience any problem processing the SPOT data or understanding the spacecraft description, please send us an E-mail and we will do our best to help you. Jean-Paul Berthias (E-mail: jean-paul.berthias@cnes.fr) Alfred Piuzzi (E-mail: alfred.piuzzi@cnes.fr) CNES Precise Orbit Determination Group 18 avenue E. Belin 31401 TOULOUSE Cedex 4 France