Starlight pointing subsystem for the formation interferometer testbed (FIT)

Abstract

Abstruct-StarLight is a NASA\JPL sponsored mission that will be the first spacebom stellar interferometer. The objective of the mission is to develop and test technologies for performing interferometric observations in space and for the extremely precise formation flying required to make the instrument work. The Formation Interferometer Testbed (FIT) is a ground based prototype of the two spacecraft StarLight instrument.In this paper a complete model of the FIT pointing system is characterized that includes backlash in the siderostat (SD), hysteresis in the PZT actuators of the fast steering mirrors (FSM), time delays, and air path disturbances. Based on this model, a dual stage pointing controller is designed that achieves a bandwidth sufficient to satisfy the pointing requirement. Simulated and experimental results are given that validate the performance of the pointing system.

Modeling of Piezoceramic Actuators for Control

“…Unique experiments were designed to determine the transducer constant and capacitances of the model. The hysteretic capacitance was fit with backlash basis functions which was proposed by the first author in [15]. This hysteresis model is numerically efficient and captures the multivalued behavior of hysteresis as well as the curvature of the hysteresis loops.…”

“…Each backlash output is weighted with a gain k i which changes the slope of the backlash operator when the deadband is engaged. Details of fitting the parameters of this model to experimental data are given in [5,15] but, to summarize, the gains k i are used to fit the curvature of the hysteresis data, the schedule of deadband widths, w i , are used to accurately capture regions of the hysteresis that have high curvature and the initial conditions are used to capture the uniqueness of the initial loading curve. A diagram of the hysteresis model is provided in Figure 8.…”

Asynchronous Control of a Prototype Inchworm Actuator: Control Design and Test Results

“…PZT ceramics suffer from a significant amount of hysteresis which effects the scale factor of the FIA mechanism. To capture this effect, we used the approach discussed in [17] with a hysteresis model developed in various publications including [7,19,20]. The structure of this model is shown in the control block diagram in Figure 4.…”

“…The voltage is generated as a consequence of the charge feedback and capacitance of the PZT, C, since Q = C • V. Figure 4 also illustrates that PZT hysteresis is an electrical domain phenomenon that maps voltage to charge [17]. Backlash basis functions are fit to this input output data using techniques developed in [7,19,20]. The voltage and charge data for this fitting process is generated from low frequency amplifier voltage and PZT displacement data (Data taken without the flexure or environmental impedance active.)…”

Multi-Mode Synchronized Control for Formation Flying Interferometer

“…Two spacecrafts, collector and combiner, form the Starlight space interferometer (Fig. 1) [ 1,2]. Control for combining the light in proper phase (optical pathdfringes control) is multilevel: control of the two spacecraft relative position (3 DOFs), inertial attitude of each spacecraft (6 DOFs), and vernier control of the optical elements placed on each spacecraft, namely, motor, voice coil and piezo-element for the optical delay line actuation [3], and siderostats.…”