Strength Analysis - Finite Element Analysis for Satellite Structures - page 195

Table 4.30 Angular positioning deviation angles for precise equipment relative to the star sensor

Equipment Angle before

deformation
h (deg)

Modified angle after
deformation h 0

Angular positioning
deviations angle h dev
(arcmin)

(deg)

Case1 Case 2 Case1 Case 2

MBEI 136 135.9871 135.9955 -0.777 -0.269

AVM, gyro M x 90 89.9982 90.0063 -0.105 0.379

AVM, gyro M y 46 46.0042 46.0117 0.252 0.7002

AVM, gyro M z 44 43.9885 43.9908 -0.691 -0.5512

AVM, skewed gyro 44 44.0233 44.0238 1.3996 1.428

Reaction wheels M x 90 90.0127 90.0068 0.7614 0.40734

Reaction wheels M y -1 134 134.0076 133.9993 0.4549 -0.0395

Reaction wheels M y -2 134 134.0035 133.9959 0.2078 -0.2446

Reaction wheels M z 44 44.0221 44.0202 1.3242 1.2117

Magnetometer 136 135.9947 135.9979 -0.3168 -0.1239

Magnetorquers 44 43.9828 43.9892 -1.0341 -0.6458

Note
Case 1 represents thermal deformation due to on-orbit maximum temperatures
Case 2 represents thermal deformation due to on-orbit minimum temperatures

which is clear from the previous analysis. Therefore, the material can fail in
fatigue from the many cycles of on-orbit thermal deformation loading. The results
data of thermoelastic analysis are used to evaluate the thermal fatigue damage for
the basis unit block.
By reviewing the results data of thermal deformation analysis and the thermal
stress distributions in the basis unit block module under maximum and minimum
temperatures (Figs. 4.75 and 4.78 ), it is found that the maximum thermal stress
occurs at the same location under both cases. This location is specified as ''Point
30'' in Fig. 4.50 . The entire satellite structure is affected by cyclic thermal stresses
along the operation life time of the satellite. However, Point 30 is the location most
severely affected by fatigue damage due to on-orbit thermal cyclic loading.
The total fatigue damage at any point located in the basis unit block module,
including Point 30, is the dynamic fatigue damage due to mechanical vibrations
during transportation and launch plus the thermal fatigue damage due to on-orbit
cyclic thermal stresses. Therefore, to calculate the overall fatigue damage for the
basis unit block, dynamic fatigue damage must be known for Point 30 based on the
fatigue analysis of dynamic vibrations discussed at Sect. 4.12 . Moreover, thermal
fatigue damage must be calculated for the critical points located in the basis plate
module and basis walls module. Points 11 through 18 represent the locations of the
maximum resultant stresses during mechanical loading phases.
By applying the same method used to calculate dynamic fatigue damage in
Sect. 4.12 , the dynamic fatigue damage results for Point 30 are given in
Table 4.31 . For thermal fatigue damage calculation, the maximum and minimum
cyclic thermal stresses for the critical points are taken from the thermoelastic
analysis results. The time life cycles (N th ) corresponding to each given stress ratio