## 3 Sinusoidal Vibration Test of the Deployable Reflector Antenna in STM Phase  
Figure 3 shows the test configuration and procedure of the sinusoidal vibration test at the STM phase. The sinusoidal vibration test is to evaluate the structural stability against the sinusoidal load propagated to the payload through launch adaptor during the launch process. Unlike the computer analysis that numerically calculates the acceleration response of each component according to the set test specifications, the test is started at a relatively low-level input load. And then, the input acceleration level is gradually increased to protect the reflector antenna prototype during the environmental test. The sinusoidal vibration test is performed for each of the x, y, and z axes in the test environment of Figure 3a-c, and the test procedure is as shown in Figure 3d. The sinusoidal vibration test starts at 1/3 level of the test specifications and is performed stepwise up to the full level-el test, and a low-level sine sweep test (LLSST) is performed before/after each step of the intermediate level to calculate the frequency and amplitude shift of the fundamental mode frequency. Two shift values are the pass/fail criteria of the sinusoidal vibration test. Generally, if the frequency and amplitude shift of the fundamental mode is more than 5% before/after each test, it is considered that there is a problem, such as a crack, loosening of a bolt or permanent deformation, with the test specimen [13]. The sinusoidal vibration test of the reflector antenna in STM phase was conducted with the dummy structure of X- and S-band antenna assembly located in the top side to express the structural behavior property of the reflector antenna. Figure 4 shows the modal analysis of the deployable reflector antenna in the stowed condition. The antenna developed in this study is mounted to the satellite body using eight bolts on the base plate. As shown in Figure 4a, the analysis model of the reflector antenna connects the eight-bolting hole to a rigid body element, and a fixed boundary condition is imposed to the independent nodes of the rigid body element. Figure 4b,c shows that the vibration modes of the reflector antenna for the x and y directions are 24.6 Hz (2 nd mode) and 24.5 Hz (1 st mode), reflectively. The z-directional mode is 121.1 Hz (160 th mode). Because the modal effective mass fraction of the vibration modes in Figure 4a-c is more than 0.5, three modes represent the dynamic behavior for each direction (inplane/out-of-plane). The out-of-plane vibration mode appears at a higher frequency band than the in-plane mode. It means that the reflector antenna has high dynamic stiffness in the out-of-plane direction. Figure 2: Conceptual diagram of the deployable reflector antenna in STM phase. Figure 4: _Cont._  
Figure 3: Concept of sinusoidal vibration test; the test configuration with vibration zig for (**a**) x, (**b**) y, and (**c**) z-axes and (**d**) test procedure. Before the sinusoidal vibration test, the structural stability of the STM of the reflector antenna was evaluated by using the finite element analysis. Figure 5 shows the sinusoidal test configuration and result for the reflector antenna in STM phase. Figure 5a shows the test configuration of the sine vibration. As mentioned above, the bottom part of the reflector antenna is connected to the satellite body by eight bolts. The excitation forces in the in-plane and out-of-plane directions are as shown in the vibration specification in Figure 5b. As shown in Figure 5c, the test specification relaxation was applied to the sinusoidal vibration test for the in-plane direction. In the sinusoidal vibration test, a tri-axial load cell (Kistler type 9377C) with a calibrated range of \(-30\) kN to \(30\) kN was used at eight interfaces to measure the interface load transmitted from the satellite body [14]. The maximum allowable load of the calibrated load range of the loadcell is \(60\) kN.