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J.D. Phillips, M. Karovska (SAO/CfA)
A space-based imaging interferometer with km-scale baselines will have an angular resolution of ~30 microarcsec at 1500A and will need to keep its pointing direction constant to within a few microarcsec. This task has two components: sensing internal distances between subapertures and from subapertures to the beam-combining hub, and sensing the effective pointing direction with respect to the sky. Monitoring the internal distances will be done with laser distance gauges, and the geometry of those gauges is a critical part of the design of the interferometer. The design should be guided by the following principles: direct relation to the required quantity, precision, stability, minimum laser gauge count, and simplicity. We will describe candidate laser gauge designs and estimate their performance for different configurations. The pointing reference can in some cases be the observed target itself. However, observations of faint or diffuse targets require an approach which does not use light from the observed target. We consider approaches of referencing to other stars, or of ultra-high precision rotation-sensing references, or a combination of both. With the combination, the stellar reference could be of a modest size, and long-term drift could be tolerated in the inertial reference. Important to these studies will be a predicted spectrum of disturbances of the spacecraft orbits. We will discuss the fringe visibility attainable with the candidate pointing and metrology system, and any other measures that may be required to assure adequate visibility.
The author(s) of this abstract have provided an email address for comments about the abstract: jphillips@cfa.harvard.edu
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Bulletin of the American Astronomical Society, 36 #2
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