Dr. Dorothy A. Fraquelli Profile

Dr. Dorothy A. Fraquelli

at Computer Sciences Corp

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Author

Publications (6)

Proceedings Article | 12 October 2004 Paper

Apodized square aperture plus occulter concept for TPF

Ian Jordan, Alfred Schultz, Richard Lyon, Helen Hart, Frederick Bruhweiler, Dorothy Fraquelli, Kenneth Carpenter, Mark Kochte, Jan Hollis

Proceedings Volume 5487, (2004) https://doi.org/10.1117/12.553029

KEYWORDS: Space telescopes, Telescopes, Stars, Space operations, Planets, Wavefronts, Diffraction, Optical instrument design, Opacity, Point spread functions

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Proceedings Article | 19 November 2003 Paper

Imaging terrestrial planets with a free-flying occulter and space telescope: an optical simulation

Alfred Schultz, Richard Lyon, Mark Kochte, Dorothy Fraquelli, Frederick Bruhweiler, Ian Jordan, Kenneth Carpenter, Michael DiSanti, Cherie Miskey, Melodi Rodrigue, M. Fadali, Dennis Skelton, Helen Hart, Kwang-Ping Cheng

Proceedings Volume 5170, (2003) https://doi.org/10.1117/12.506192

KEYWORDS: Telescopes, Space telescopes, Planets, Point spread functions, Apodization, Stars, Optical simulations, Coronagraphy, Light scattering, Fourier transforms

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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.

Proceedings Article | 3 March 2003 Paper

UMBRAS: a matched occulter and telescope for imaging extrasolar planets

Alfred Schultz, Ian Jordan, Mark Kochte, Dorothy Fraquelli, Fred Bruhweiler, Jan Hollis, Kenneth Carpenter, Richard Lyon, Mike DiSanti, Cherie Miskey, Jesse Leitner, Richard Burns, Scott Starin, Melodi Rodrigue, M. Fadali, Dennis Skelton, Helen Hart, Forrest Hamilton, Kwang-Ping Cheng

Proceedings Volume 4860, (2003) https://doi.org/10.1117/12.457643

KEYWORDS: Space telescopes, Telescopes, Planets, Stars, Space operations, Exoplanets, Target acquisition, Diffraction, Point spread functions, Coronagraphy

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We describe a 1-meter space telescope plus free-flying occulter craft mission that would provide direct imaging and spectroscopic observations of Jovian and Uranus-sized planets about nearby stars not detectable by Doppler techniques. The Doppler technique is most sensitive for the detection of massive, close-in extrasolar planets while the use of a free-flying occulter would make it possible to image and study stellar systems with planets comparable to our own Solar System. Such a mission with a larger telescope has the potential to detect earth-like planets. Previous studies of free-flying occulters reported advantages in having the occulting spot outside the telescope compared to a classical coronagraph onboard a space telescope. Using an external occulter means light scatter within the telescope is reduced due to fewer internal obstructions and less light entering the telescope and the polishing tolerances of the primary mirror and the supporting optics can be less stringent, thereby providing higher contrast and fainter detection limits. In this concept, the occulting spot is positioned over the star by translating the occulter craft, at distances of 1,000 to 15,000 kms from the telescope, on the sky instead of by moving the telescope. Any source within the telescope field-of-view can be occulted without moving the telescope. In this paper, we present our current concept for a 1-m space telescope matched to a free-flying occulter, the Umbral Missions Blocking Radiating Astronomical Sources (UMBRAS) space mission. An UMBRAS space mission consists of a Solar Powered Ion Driven Eclipsing Rover (SPIDER) occulter craft and a matched (apodized) telescope. The occulter spacecraft would be semi-autonomous, with its own propulsion systems, internal power (solar cells), communications, and navigation capability. Spacecraft rendezvous and formation flying would be achieved with the aid of telescope imaging, RF or laser ranging, celestial navigation inputs, and formation control algorithms.

Proceedings Article | 2 January 2002 Paper

Feedback loops from the Hubble Space Telescope data processing system

Dorothy Fraquelli, Richard Arquilla, Tracy Ellis, Forrest Hamilton, Albert Holm, Mark Kochte

Proceedings Volume 4844, (2002) https://doi.org/10.1117/12.460679

KEYWORDS: Target acquisition, Data processing, Space telescopes, Feedback loops, Hubble Space Telescope, Observatories, Data archive systems, Space operations, Databases, Stars

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Proceedings Article | 15 December 2000 Paper

Imaging planets about other stars with UMBRAS: target acquisition and station keeping

Helen Hart, Ian Jordan, Alfred Schultz, John Hershey, Mark Kochte, Forrest Hamilton, Dorothy Fraquelli, Daniel Schroeder, Fred Bruhweiler, Mike DiSanti, Cherie Miskey, Bruce Johnson, M. Fadali, Melodi Rodrigue, K. Cheng, R. Clark

Proceedings Volume 4087, (2000) https://doi.org/10.1117/12.406339

KEYWORDS: Space telescopes, Telescopes, Target acquisition, Coronagraphy, Stars, Space operations, Planets, Optical instrument design, Sun, Imaging systems

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Proceedings Article | 16 November 2000 Paper

Imaging planets about other stars with UMBRAS II

Alfred Schultz, Ian Jordan, Helen Hart, Fred Bruhweiler, Dorothy Fraquelli, Forrest Hamilton, John Hershey, Mark Kochte, Mike DiSanti, Cherie Miskey, K. Cheng, Melodi Rodrigue, Bruce Johnson, Sami Fadali

Proceedings Volume 4131, (2000) https://doi.org/10.1117/12.406562

KEYWORDS: Space telescopes, Telescopes, Stars, Space operations, Planets, Target acquisition, Sun, Coronagraphy, Image processing, Doppler effect

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