## 4 Verification and Validation
### Mechanical Tests  
It takes several weeks to design and manufacture fixtures. Ideally, developers should start working on the test preparations in parallel to the fabrication of the satellite. Even if test campaigns can be outsourced, developers may still need to provide auxiliary equipment.  
Major mechanical tests can be conducted with one electrodynamic shaker. Figure 10 shows the SE01 CubeSat in a 3U fixture mounted on a shaker through a head adaptor. Since a 3U fixture was available off-the-self, the developers decided to use the product instead of fabricating a 2U fixture in-house. A dummy payload was used to fill in the fixture along with the SE01 CubeSat.  
Programming the shaker to follow all acceleration profiles may take at least one working day. Developers may need to make small modifications to those profiles during the tests, especially at both ends of the frequency range.  
The resonance search test is used to find the lowest resonance frequency. Resonance search tests are performed before and after every major mechanical test. Figure 11 shows the response of a resonance search test for three runs and the control profile for comparison. For the QB50 mission, it was required that the first mode appears above 200 Hz. Additionally, the natural frequency for different runs should not shift more than 5%, otherwise it may indicate a failure during one of the major mechanical tests. On the positive side, a natural frequency shift may indicate internal readjustment, misalignment and/or interference with other components in the fixture. On the negative side, it may indicate loose components, unsecured fastening and/or broken parts.  
The sine vibration test is one of the major mechanical tests, which is performed to confirm that there are no dangerous resonance frequencies in the test range, and the satellite is able to withstand the  
Figure 11: Results of the resonance search tests.  
Figure 10: SE01 in a 3U fixture on the electric shaker facility.  
required load. A quasi-static acceleration test (QAT) is also performed together with the sine vibration test. The QAT emulates the static loads of a rocket during the launch. Static accelerations are usually much higher than dynamic ones. To perform a QAT with an electrodynamic shaker, the acceleration profile should briefly increase to the required amplitude, and come down again for frequencies much lower than the natural frequency. For SE01 in particular, the amplitude of the control signal was increased to 10.8 g between 20 and 21 Hz during the frequency sweep. The results of a sine vibration test with QAT performed on one axis of SE01, shown in Figure 12, illustrate how the response of the satellite increases as it approaches the natural frequency. No unexpected acceleration peaks should be observed, and no damage on the satellite should be noted after the test.  
Random vibrations occur during the launch. Therefore, a random vibration test is used as an accelerated life testing. That is, higher load levels during the test correlate with longer operating times. In a random vibration test all frequency ranges are excited, thus all resonant frequencies are tested simultaneously. In case of SE01, a root-mean-square acceleration of 8.03 g was applied during 120 s for each axis. The results of random vibration test for one of the SE01 axes are shown in Figure 13. The actual root-mean-square acceleration experienced by the satellite was 9.30 g. No damage should be appreciated in the satellite afterwards.  
Figure 12: Results of a sine vibration test and QAT.  
Figure 13: Results of a random vibration test.  
Shock tests emulate rocket stage separation events. Typically, a shock test can be done on an electrodynamic shaker with a half-sine profile. The head of the shaker moves up and down only once in a period of tenths of milliseconds to achieve the required acceleration. Since SE01 was a proto-flight model, a waiver to skip the shock test was granted.