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Proceedings Paper

Imaging terrestrial planets with a free-flying occulter and space telescope: an optical simulation
Author(s): Alfred B. Schultz; Richard G. Lyon; Mark Kochte; Dorothy A. Fraquelli; Frederick Bruhweiler; Ian J. E. Jordan; Kenneth G. Carpenter; Michael A. DiSanti; Cherie Miskey; Melodi Rodrigue; M. Sami Fadali; Dennis Skelton; Helen M. Hart; Kwang-Ping Cheng
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Paper Abstract

In this manuscript, we further develop our concepts for the free-flying occulter space-based mission, the Umbral Missions Blocking Radiating Astronomical Sources (UMBRAS). Our optical simulations clearly show that an UMBRAS-like mission designed around a 4-m telescope and 10-m occulter could directly image terrestrial planets. Such a mission utilizing existing technology could be built and flown by the end of the decade. Moreover, many of the other proposed concepts for Terrestrial Planet Finder (TPF) could significantly benefit by using an external occulter. We present simultations for an optical design comprising a square aperture telescope plus square external occulter. We show that the entire diffraction pattern, which is propagated from occulter to telescope and through telescope to focal plane, may be characterized by two parameters, the Fresnel number and the ratio of the telescope diameter to the occulter width. Combining the effects of a square occulter with apodization provides a much more rapid roll-off in the PSF intensity between the diffraction spikes than may be achieved with an unapodized telecope aperture and occulter. We parameterize our results with respect to wavefront quality and compare them against other competing methods for exo-planet imaging. The combination of external occulter and apodization yields the required contrast in the region of the PSF essential for exo-planet detection. An occulter external to the telescope (i.e., in a separate spacecraft, as opposed to a classical coronagraph with internal occulter) reduces light scatter within the telescope by approximately 2 orders of magnitude. This is due to less light actually entering the telescope. Reduced scattered light significantly relaxes the constraints on the mirror surface roughness, especially in the mid-spatial frequencies critical for planet detection. This study, plus our previous investigations of engineering as well as spacecraft rendezvous and formation flying clearly indicates that the UMBRAS concept is very competitive with, or superior to, other proposed concepts for TPF missions.

Paper Details

Date Published: 19 November 2003
PDF: 10 pages
Proc. SPIE 5170, Techniques and Instrumentation for Detection of Exoplanets, (19 November 2003); doi: 10.1117/12.506192
Show Author Affiliations
Alfred B. Schultz, Computer Sciences Corp. (United States)
Space Telescope Science Institute (United States)
Richard G. Lyon, NASA Goddard Space Flight Ctr. (United States)
Mark Kochte, Computer Sciences Corp. (United States)
Space Telescope Science Institute (United States)
Dorothy A. Fraquelli, Computer Sciences Corp. (United States)
Frederick Bruhweiler, Catholic Univ. of America (United States)
Ian J. E. Jordan, Computer Sciences Corp. (United States)
Kenneth G. Carpenter, NASA Goddard Space Flight Ctr. (United States)
Michael A. DiSanti, NASA Goddard Space Flight Ctr. (United States)
Cherie Miskey, Catholic Univ. of America (United States)
Melodi Rodrigue, Univ. of Nevada/Reno (United States)
M. Sami Fadali, Univ. of Nevada/Reno (United States)
Dennis Skelton, Orbital Sciences Corp. (United States)
Helen M. Hart, Computer Sciences Corp. (United States)
Johns Hopkins Univ. (United States)
Kwang-Ping Cheng, California State Univ./Fullerton (United States)

Published in SPIE Proceedings Vol. 5170:
Techniques and Instrumentation for Detection of Exoplanets
Daniel R. Coulter, Editor(s)

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