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I. J. E. Jordan (CSC/STScI), P. Henze, G. Sauter (WASI), H. M. Hart (CSC/JHU/FUSE), P. Chen (GSFC), B. Eney (WASI), A. B. Schultz (CSC/STScI), E. Bender (WASI), M. Kochte (CSC/STScI), R. G. Lyon (GSFC), D. Fraquelli (CSC/STScI), F. Bruhweiler (IACS/CUA), C. Roelle, R. Smith, I. Slepian (WASI), Computer Sciences Corporation Collaboration, Goddard Space Flight Center Collaboration, Westminster Astronomical Society, Inc. Collaboration, Institute for Astrophysics and Computational Sciences Collaboration
Results of an optical ground test for an external occulter are presented. External occulter spacecraft designed to be flown with a large space based telescope have been proposed as a technique to enable direct study of exosolar planets. Space-based external occulters have been used for solar coronal studies, where the occulter is positioned tens of meters from the telescope, but for exosolar planet studies the occulter must be positioned thousands of kilometers from the telescope. While the exoplanet design has been modeled, it has never, to our knowledge, been field tested.
The occulter field test design is an optically scaled model of a workable space-based configuration. The telescope aperture diameter, occulting screen diameter, and telescope-occulter separation were chosen to achieve the same system Fresnel number as a space-based configuration. The final ground test configuration consists of a square opaque occulter screen 25-50 mm on a side, enclosed in a large tube to control stray light and positioned about 100 meters from a small telescope with a 9-25 mm aperture mask. Polaris was the test target star, and a tenth-wave 9-inch circular flat was used to redirect star light to the telescope.
The occulter screen could be removed from the light path for initial alignment and calibration, then replaced for occultation tests. Images were taken with a low-noise CCD camera. Preliminary analysis of the August 2004 data suggests that the occulter performed as expected with regard to starlight suppression, and suggests that the occulted PSF could be used by a space-based system to perform real-time alignment sensing between spacecraft at ranges of tens of thousands of kilometers. The optical scaling arguments and analysis of the test images will be presented, along with a discussion of the alignment procedure and photos of the test rig.
We would like to thank CSC, AURA, GSFC, and WASI for research and equipment support surrounding this field demonstration.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.