Search

SCDU (Spectral Calibration Development Unit) is a vacuum test bed that was built and operated for the SIM-Planetquest Mission and has successfully demonstrated the calibration of spectral instrument error to an accuracy of better than 20 picometers. This performance is consistent with the 1 micro-arc second goal of SIM. The calibration procedure demonstrated in the test bed is traceable to the SIM flight instrument. This article is a review of all aspects of the design and operation of the hardware as well as the methodology for spectral calibration. Spectral calibration to better than 20 picometers and implications for flight are discussed.

We describe the current performance of an adaptive optics testbed for optical communication. This adaptive optics system allows for simulation of night and day-time observing on a 1 meter telescope with a 97 actuator deformable mirror.

Adaptive optics systems with Shack-Hartmann wavefront sensors require reconstruction of the atmospheric phase error from subaperture slope measurements, with every sensor in the array being used in the computation of each actuator command. This fully populated reconstruction matrix can result in a significant computational burden for adaptive optics systems with large numbers of actuators. A method for generating sparse wavefront reconstruction matrices for adaptive optics is proposed. The method exploits the relevance of nearby subaperture slope measurements for control of an individual actuator, and relies upon the limited extent of the influence function for a zonal deformable mirror. Relying only on nearby sensor information can significantly reduce the calculation time for wavefront reconstruction. In addition, a hierarchic controller is proposed to recover some of the global wavefront information. The performance of these sparse wavefront reconstruction matrices was evaluated in simulation, and tested on the Palomar Adaptive Optics System. This paper presents some initial results from the simulations and experiments.

Control laws for an adaptive optics system for the Palomar Mountain Hale Telescope are described. These are derived using a linear matrix model of the optics, which gives the Hartman-sensor centroids and the science camera wavefront as functions of deformable mirror (DM) commands and atmospheric phase. The matrices defining this system can be directly measured from the optics, some at finer spatial resolution than the wavefront sensor can resolve. A minimum-wavefront compensator feeds back both the wavefront sensor centroids and previous DM commands, using the atmospheric covariance to smooth the response at the finer spatial scale. The DM command feedback provides direct observability of waffle, piston and other modes unobservable in the wavefront sensor. Compensator gains can be updated using Kalman filtering techniques to track the evolution of the atmospheric covariance matrix.