# Parallel Load-Bearing and Damping System Design and Test for Satellite Vibration Suppression
## 1 Introduction  
Satellites are subjected to a complex vibration environment during launch [1]. Vibrations are transmitted through the interface of the rocket and the satellite, which includes high-frequency and low-frequency vibrations. The high-frequency random vibration is mainly produced by noise excitation [2, 3]. The low-frequency vibration is generally under 100 Hz, which is mainly caused by two sources: (1) the free vibration decay from the transient excitations, such as the rocket engine's ignition/shutdown, the inter-stage separations, and the booster separations; and (2) unstable vibrations from the intercoupling between the liquid rocket propulsion system and the structure system [4, 5]. The fundamental frequency of a satellite structure is usually under 100 Hz, which is near the low-frequency vibration environment. Therefore, there is vibration amplification in flight and ground tests, which might cause serious consequences such as structural damage. In order to protect satellites dynamically in the launch environment, a series-type vibration isolation technology was proposed. CSA Engineering Inc. has been working on the concept of the whole-spacecraft vibration isolation system since 1993 for The Air Force Research Laboratory. Its typical product is SoftRide, which includes Uniflex for axial vibration attenuation [6] and MultiFlex for both axial and lateral vibration attenuation [7]. Later, [PERSON] improved the CSA passive system by usingactive components to adapt to the dynamic environment during the launch with both broadband and narrowband attenuation [8]. [PERSON] developed the EVLIS (Evolved Launch Vibration Isolation System) prototype, implementing integrated active and passive vibration control [9]. [PERSON] et al. proposed whole-spacecraft disk vibration isolators based on a reliability method, which have a great impact on medium-high frequency [10]. [PERSON] designed a negative resistance electromagnetic shunt damper aimed at the micro vibration [11]. [PERSON] advanced a method using a metal robber damping rod, which isolates high-frequency vibration as well as restraining the resonant peak effectively [12]. [PERSON] established some principles for the vibration isolation design, and they could be adopted to restrain the resonance and isolate the response in a higher frequency domain [13]. [PERSON] developed an octo-strut vibration isolation platform based on the Stewart platform and improved the reliability and load capacity of the original platform [14]. [PERSON] designed a vibration isolation system with magnetic suspension, which can provide a greater restoring force for better dynamic performance [15]. [PERSON] added a metal-rubber shock absorber on the satellite to improve the space camera's image quality [16]. [PERSON] showed that the dynamic features are not affected by the stiffness of viscoelastic material of the vibration control system [17]. However, the principle of traditional series-type whole-spacecraft vibration isolation is changing the frequency and reducing the amplitude. As a result, in practical engineering problems, the satellite branch frequency significantly decreases after introducing the vibration isolation system. This leads to the instability of the attitude. To solve this problem, [PERSON] came up with a new scheme. Constrained damping layers are attached to the main load-carrying structure like the payload adapter. With this scheme, the damping of the whole structure increases, while the stiffness is maintained [18; 19]. [PERSON] also adopted a constrained damping layer on a spacecraft instrument installation board [20]. [PERSON] studied semi-active vibration isolation technology, making use of the high reliability of magnetorheological damper [21]. The two schemes adopt the concept of a parallel system, which has good performance on vibration suppression. Based on previous research, this article presents the design of a parallel damping scheme for a satellite's vibration isolation.