Strength Analysis - Finite Element Analysis for Satellite Structures - page 190

Fig. 4.76 Temperature distribution for the entire satellite during minimum average surface
temperatures [ 7 ]
minimum average on-orbit surface temperatures are considered. The diagrams of
equivalent stress (10 3 MPa) and displacement (mm) distributions in the basis unit
block module are shown in Figs. 4.77 , 4.78 , 4.79 and 4.80 . The stress values are
determined according to Von Mises criterion. Displacements are relative to the
points of the star sensor attachment to its bracket, which are the fixation points for
the entire model of Small Sat structure during thermoelastic analysis. The maxi-
mum stress values (r e ) in the basis unit block module in each on-orbit thermal case
and their equivalent yield margins of safety (MS y ) are given in Table 4.28 .
4.15 Mounting Accuracy Due to On-Orbit Thermal
Deformation
From the static point of view, the basis unit block module is safe under thermal
loading, because the yield margin of safety has a positive value in both design cases.
But this is not enough to decide that the design is satisfactory. Satisfactory per-
formance of the satellite requires accurate prediction of thermal deformations to
verify pointing and alignment accuracy requirements for sensors (Mounting
Accuracy). Therefore, it is important to calculate the angular positioning deviations
for all high precise equipment (MBEI and ADCS devices) relative to the star sensor
due to on-orbit thermal deformation. These values must not exceed the limiting
deviations specified for mounting precise equipment. Table 4.29 lists the limiting
angular positioning deviations for the most precise equipment relative to the star
sensor, which are derived from the structure requirements [ 7 ].