Performance Analysis of a Flywheel Microvibration Isolation Platform for Spacecraft

Abstract

A N ULTRAQUIET spacecraft bus is crucial for line-of-sight pointing accuracy of high-precision spacecraft, such as remote sensing satellites and space observatories [1–3]. However, there are plenty of disturbance sources onboard the spacecraft, mainly including but not limited to flywheels (reaction wheels, momentum wheels), solar array drive, and antenna drive [4]. These disturbance sources will induce microvibration of the spacecraft bus and cause deleterious effects on the pointing performance of payloads. Flywheels are common actuators of the spacecraft attitude control system. As the flywheel operates, besides the output of attitude control torque, it also generates speed-related disturbances due to its rotor imbalance and other imperfections of internal structures [5]. The flywheel has been identified as the dominant microvibration source of many spacecraft [6,7], as in the cases of the Chandra Observatory and the James Webb Space Telescope (JWST). Vibration isolation is an effective approach to attenuate microvibration caused by flywheels [8]. Alkhatib and Golnaraghi [9] and Liu et al. [10] reviewed state-of-the-art microvibration isolation and controlmethods, including passive isolation techniques, activevibration control, active–passive hybrid isolation techniques, and semiactive isolation techniques. A reaction wheel isolator made up of machined spring elements with bonded viscoelastic material was designed to reduce the level of flywheel disturbances transmitted to the optical train of the Chandra Observatory [6]. A two-stage vibration isolation system is employed tomeet the stringent requirement of up to milliarcsecond pointing stability of the JWST [7,11]. The first stage is reaction wheel isolators between each reaction wheel and the spacecraft bus. The second stage is a 1 Hz isolator between the spacecraft bus and the optical payload. Makihara et al. studied the techniques for isolating observation devices from disturbances of the momentum wheel using piezoelectric ceramics [12]. Oh et al. investigated the characteristics of two types of isolators for flywheel vibrations [13,14]. The first type used electrorheological fluid to act as agent of semi-active isolation. The second type used a biometal fiber valve-controlled semi-active damper to mitigate the vibrations. Narayan et al. investigated dynamic characteristics of a momentum wheel and reduced its impact on the earth sensor through redesign of the mounting bracket of the momentum wheel [15]. Zhou et al. developed a soft suspension design for a reaction wheel to reduce disturbance output [16]. Kamesh et al. proposed a low-frequency platform to act as a mount for reaction wheels [17,18]. Zhou and Li designed and tested a soft platform for a momentum wheel [19]. Luo et al. proposed a vibration isolation approach for multiple-flywheel system based on Stewart platform [20]. Although lots of efforts have been taken by researchers to study the vibration isolation problem of flywheels, the rotor speed of the flywheel was either ignored or assumed steady in their dynamicmodels; thus, the dynamic characteristics of the flywheel at operation mode were neglected. Besides, whether or not the vibration isolator will affect the normal output of attitude control torque of the flywheel has also not yet been studied and clarified. In this Note, first, a vibration isolation platform for the flywheel is proposed, and a coupled dynamic model of the flywheel and the platform is established. Second, vibration isolation performance of the platform is assessed by comparing the output disturbances both in the cases of without or with the platform when the flywheel is actuated. Then, the influence of the platform on the output of the attitude control torque and rotor speed of the flywheel is examined. Last, the transmissibility of the disturbances from the flywheel to the spacecraft bus is acquired to further verify the effectiveness of the platform.