White Light Modeling, Algorithm Development, and Validation on the Micro-arcsecond Metrology Testbed

The Space Interferometry Mission (SIM) scheduled for launch in early 2010, is an optical interferometer that will perform narrow angle and global wide angle astrometry with unprecedented accuracy, providing differential position accuracies of 1uas, and 4uas global accuracies in position, proper motion and parallax. The astrometric observations of the SIM instrument are performed via delay measurements provided by three Michelson-type, white light interferometers. Two 'guide' interferometers acquire fringes on bright guide stars in order to make highly precise measurements of variations in spacecraft attitude, while the third interferometer performs the science measurement. SIM derives its performance from a combination of precise fringe measurements of the interfered starlight (a few ten-thousandths of a wave) and very precise (tens of picometers) relative distance measurements made between a set of fiducials. The focus of the present paper is on the development and analysis of algorithms for accurate white light estimation, and on validating some of these algorithms on the MicroArcsecond Testbed.