Demonstration of pathlength feed-forward for precision dim-star astrometry

Abstract

The Space Interferometry Mission (SIM) is a high precision, space-based interferometer designed to achieve micro- arcsecond astrometric resolution. Many of the interesting science targets for SIM astrometry are dim enough that neither the pointing nor the pathlength control necessary for observing fringes can be performed using the usual closed-loop control techniques. The strategy in these cases is to feed forward the required control signals for the dim- star interferometer using other information, including two other interferometers operating simultaneously and locked on bright `guide' stars. The STB-3 testbed at the Jet Propulsion Laboratory, composed of three optical interferometers with a common baseline, is designed to develop these technologies for SIM. In its first phase, to be completed by spring 2000, STB-3 is expected to demonstrate pathlength feed-forward on an optical bench. Here we describe the technique used and the status of this experiment.