POINTS, an astrometric optical interferometer with a nominal measurement accuracy of 5 microarcseconds for the angle between a pair of stars separated by about 90 deg. is presently under consideration by two divisions of NASA-OSS. Based on a preliminary indication of the observational needs of the two missions, we find that a single POINTS mission will meet the science objectives of both TOPS-1 and AIM. The instrument detects a dispersed fringe (channelled spectrum) and therefore can tolerate large pointing errors. In operation, the difficult problem of measuring the angular separation of widely spaced star pairs is reduced to two less difficult problems: that of measuring the angle between the two interferometers and that of measuring interferometrically the small offset of each star from the corresponding interferometer axis. The question of systematic error is the central theme of the instrument architecture and the data-analysis methods. Stable materials, precise thermal control, and continuous precise metrology are fundamental to the design of the instrument. A preliminary version of the required picometer laser metrology has been demonstrated in the laboratory. Post-measurement detection and correction of time-dependent bias are the essential elements in data analysis. In that post-measurement analysis, individual star-pair separations are combined to determine both the relative positions of all observed stars and several instrument parameters including overall time-dependent measurement bias. The resulting stellar separation estimates are both global and bias-free at the level of the uncertainty in the reduced (i.e., combined and analyzed) measurements.

Date Published: 10 September 1993
PDF: 18 pages
Proc. SPIE 1947, Spaceborne Interferometry, (10 September 1993); doi: 10.1117/12.155745

Published in SPIE Proceedings Vol. 1947:
Spaceborne Interferometry
Robert D. Reasenberg, Editor(s)