Investigation of Spacecraft Vibration Subjected to Acoustic Sound Field of Fill Effect

Abstract

Payloads are exposed to severe vibro-acoustic environments during rocket launches as shown in Figure 1-(a). At the same time, fill effect [1-3] occurs in the cavity, which is located in the clearance gap between the inner side of the fairing and the solar paddles of the spacecrafts (Figure 1-(b)). This phenomenon results in a maximum increase in sound pressure level (SPL) by approximately 10 dB [2] and causes the natural frequencies of the solar paddles to shift to the coupling modes as shown in Figure 2. These modes are derived from both the vibrational modes of acoustic sound in the cavity and the solar paddles of the spacecrafts. These coupling modes are different from each vibrational mode in vaco [4, 5]. At the same time, the accelerance level of the solar paddle on the structural vibration modes decreases by delta Hv due to the shifts in natural frequencies. The larger the size of the solar paddles, the lower the natural frequencies. It is important to consider this influence during the development of spacecrafts, because the shifts in natural frequencies can make the accelerance level decreased. However, recent researches on the fill effect focus on the increase of SPL by using FEM: Finite Element Method and BEM: Boundary Element Method. Despite the fact that the shifts in natural frequencies due to the fill effect cannot be neglected, more researches are being carried out on the problems of SPL than the problems of the shifts in natural frequencies.