B. STEP Cube Lab-II’s Deployable Solar Panel Module
5. Launch Vibration Test
- 140 -
Fig. 72 Time History of the Pogo Pin Current during the SEE Test.
- 141 -
most critical axis as it induces the largest dynamic deflection of the solar panel.
Accelerometers were attached to the test jig and shaker slip table to monitor the input vibration loads. The output acceleration responses of the solar panel were measured using an accelerometer attached near the center of the solar panel. The test was performed at an ambient room temperature of 20 °C. The structural safety of the solar panel module was validated by comparing the variation in the 1st eigenfrequencies of the panel, which were obtained through low-level sine sweep (LLSS) tests performed before and after each vibration test. In order to judge the structural safety of the specimen under the launch load, the 1st eigenfrequency variation in the LLSS should be less than 5%.
After completing all the vibration tests, the release function test was performed on the solar panel to evaluate the reliability of the mechanism.
Fig. 73 Launch Vibration Test Setup Configuration of the Qualification Model of the Solar Panel Module.
A modal survey test was performed before and after each vibration test to verify the
- 142 -
structural safety of the solar panel module. A low-level sinusoidal vibration excitation with an amplitude of 0.5 g was applied to the solar panel module. Figure 74 shows the z-axis low-level sine sweep response of the solar panels in the z-axis excitation performed before the full level vibration tests that determine the natural frequency of the panel. Moreover, that also helps to check natural frequency shift before and after the full-level vibration tests of the panel for the test result evaluation. The results shows that the first eigenfrequency of the VMLSA along the z-axis was 75.0 Hz, which is 1.53 times higher than that of the typical PCB panel. However, the VMLSA first eigenfrequency is 1.25 times lower value compared with the simulation analysis result of 94.4 Hz. This is because of the mechanical holding constraint of the solar panel by the nylon wire was simply modelled by RBE2 rigid body element in the analysis that provided a much stiffer constraint compared to the actual boundary condition applied by nylon wire winding knot. Additionally, the presence of backlash in the torsional hinges also contributed for the reduction of natural frequency of the solar panel module compared with the simulated result.
- 143 -
Fig. 74 Low-level Sine Sweep Results in the z-axis Excitation.
The full-level sine vibration test results of the solar panel module along the x-, y-, and z-axis excitations are presented in Fig. 75. In the figure, only the corresponding axis vibration responses of the solar panel with the excitation axis are presented, as the corresponding axis has a larger dynamic response than the other axis of the panel. In the sine vibration tests, the qualification-level input loads specified in Table 16 were applied to the solar panel along each axis; however, the z-axis was the most critical axis because it induced the largest dynamic deflection of the solar panel. With respect to the maximum 2.5 g sine vibration input load in each axis, the maximum acceleration
0 . 0 1 0 . 1 1 1 0
I n p u t p r o f i l e ( 0 . 5 g @ 2 0 ~ 5 0 0 H z ) T y p i c a l P C B ( m a x . 4 .4 1 g @ 4 8 . 9 H z ) V M L S A ( m a x . 2 .5 1 g @ 7 5 . 0 H z )
2 0 1 0 0
Acceleration (g)
F r e q u e c n c y ( H z )
5 0 0
- 144 -
responses of the corresponding x-, y-, and z-axes with the excitation axes within the input frequency range were 2.5, 2.5, and 10.26 g, respectively. The solar panel’s maximum resonance response of 10.26 g was observed at 75 Hz on the z-axis during the same axis excitation of the panel.
Fig. 75 Sinusoidal Vibration test Results of Solar Panel’s Corresponding Axis in the x-, y-, and z-axis Excitations.
Figure 76 shows the random vibration test results of the solar panel along each
0 . 1 1 1 0 1 0 0
1 0 1 0 0
I n p u t p r o f i l e ( m a x . 2 . 5 g ) x - a x i s r e s . ( m a x . 2 .5 g ) y - a x i s r e s . ( m a x . 2 .5 g ) z - a x i s r e s . ( m a x . 1 0 .2 6 g )
Acceleration (g)
F r e q u e n c y ( H z )
- 145 -
excitation axis with respect to the input level of 14.1 Grms. The corresponding axis Grms
values of the solar panel along the x-, y-, and z-axis excitations, calculated from PSD acceleration profiles, were 16.57, 16.36, and 13.51, respectively. The Grms of the solar panel in the z-axis was lower by a factor of 1.04 than that of the input level.
Fig. 76 Random Vibration Test Results of Solar Panel’s Corresponding Axis in the x-, y-, and z-axis Excitations.
Figure 77 shows the representative modal survey results of the acceleration response
0 . 0 0 1 0 . 0 1 0 . 1 1 1 0
1 0 0 1 0 0 0
I n p u t p r o f i l e ( m a x . 1 4 . 1 G ) x - a x i s r e s . ( m a x . 1 6 .5 7 G ) y - a x i s r e s . ( m a x . 1 6 .3 6 G ) z - a x i s r e s . ( m a x . 1 3 .5 1 G )
PSD Acceleration (g /Hz)2
F r e q u e n c y ( H z )
r m s r m s r m s r m s
- 146 -
measured at the solar panel along z-axis excitation. The result obtained prior to the full level vibration tests indicate that the first eigenfrequency of the panel was 75.0 Hz along the z-axis, which, after the sine and random vibration tests appeared at 74.3 Hz and 70.79 Hz, respectively. The frequency-shifted after exposed in the full level severe launch vibration tests is minimal.
Fig. 77 Low-level Sine Sweep Results in the z-axis Excitation Before and After vibration Tests.
Table 32 summarizes the 1st eigenfrequencies of the solar panel in each axis obtained through the LLSS tests performed before and after each vibration test. The tabulated result shows that the 1st eigenfrequency shift was within 4.85% throughout the
0 . 0 1 0 . 1 1 1 0
2 0 1 0 0
I n p u t p r o f i l e (0 . 5 g @ 2 0 ~ 5 0 0 H z )
z - a x i s r e s . ( b e f o r e te s t , m a x . 2 . 5 1 g @ 7 5 .0 H z ) z - a x i s r e s . ( a f t e r s i n e , m a x . 2 . 4 2 g @ 7 4 . 3 H z ) z - a x i s r e s . ( a f t e r r a n d o m , m a x . 2 . 4 3 g @ 7 0 . 7 9 H z )
Acceleration (g)
F r e q u e n c y ( H z )
5 0 0
- 147 -
test sequences of the panel, which was within the 5% criterion. In addition, after the launch vibration tests have been completed, the solar panel was visually inspected, and no crack, dissociation, or plastic deformation were observed on the laminated stiffeners.
These tests and inspection results indicate that the structural safety of the proposed solar panel module was successfully validated in the qualification-level launch environment tests.
Table 32 LLSS Test Results of the Solar Panels Before and After Full Level Vibration Tests.
Test Axis Status
1st
Eigenfrequency (Hz)
Difference (%)
Sine Vibration
x
Before 835.2
0.19
After 833.6
y
Before 602.4
0
After 602.4
z
Before 75.0
0.93
After 74.3
Random Vibration
x
Before 833.6
0.19
After 832.0
y
Before 602.4
0
After 602.4
z
Before 74.3
4.85
After 70.7
- 148 -
6. Comparison between Simulation and Experimental Dynamic Analysis Results