Vibroacoustic launch analysis and alleviation of lightweight, active mirrors

Abstract

Lightweight, active, silicon carbide mirrors can increase the capability of space-based optical systems. However, launch survival is a serious concern for such systems, with the vibrations and acoustics from launch threatening to damage the optics. Therefore, a dynamic, statespace launch model has been developed with which one can quickly analyze the survival probability of many designs and also directly analyze launch load alleviation techniques. This paper discusses the launch model from which launch stress and survival probability are obtained, as well as launch load alleviation techniques that may increase the probability of launch survival. Three launch load alleviation techniques are presented and analyzed: whole spacecraft isolation, passive shunt circuits using the existing embedded actuators, and active damping using the existing actuators. All of the techniques reduce the launch stress, but at the expense of mass and complexity. The launch model allows for early identification of lightweight, active mirror designs which will survive launch, and the alleviation techniques expand the feasible design space by decreasing the launch stress and increasing the probability of launch survival. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

Damping of piezoelectric space instruments: application to an active optics deformable mirror

“…The disturbing vibration is defined in terms of acceleration power spectral density and applied on the active feet of the DM, in the vertical direction. A typical spectrum [10], normalized to 20 g, is used as shown in Fig. 10.…”

“…flexible configurations which would fail a vibration qualification test). A similar study was conducted numerically on a silicon carbide primary mirror (M1) for space telescopes [10]; the authors compared various passive and active vibration alleviation techniques against vibro-acoustic loads and concluded that increasing the damping of the M1 during launch would allow to use better designs of deformable mirrors. Here, we extend these results by implementing numerically and experimentally the piezoelectric resistive and inductive RL shunt on a deformable mirror.…”

Integrated modeling for design of lightweight, active mirrors

“…The model used here is a state-space model derived from finite element normal modes analysis. 4,14 The inputs to the model are random vibration and acoustic spectra from the launch vehicle and the outputs of the model are stresses in the elements, resulting in a stress distribution across the mirror. The total input disturbance is 6.2 g for the random vibrations and 145.2 dB for the acoustics.…”

“…More details about the model and launch disturbances can be found in Cohan. 4,14 The stress outputs from this model are validated to the extent possible. They are compared to available data from multiple similar systems and match within 10% in all cases.…”

“…For example, launch survival is a key challenge in the mirror design. 4 Launch is an extremely harsh environment and silicon carbide is brittle and could break at low areal densities when exposed to the vibrations and acoustics from launch. Yet it is imperative that these fragile optical components arrive on-orbit undamaged.…”