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Proceedings Paper

A balloon-borne stratospheric telescope for Venus observations
Author(s): Eliot F. Young; Mark A. Bullock; Alan Kraut; Graham Orr; Kevin Swartzlander; Tony Wimer; Elton Wong; Patrick Little; Yusuke Nakaya; Russell Mellon; Lawrence Germann
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Paper Abstract

A terrestrial stratospheric telescope is ideally suited for making infrared observations of Venus' night hemisphere during inferior conjunctions. The near-space environment at 35 km altitude has low daytime sky backgrounds and lack of atmospheric turbulence, both of which are necessary for observing Venus' night side at the diffraction limit when Venus is close to the Sun. In addition, the duration of the observing campaign will be around 3 weeks, a time period that is achievable by current long duration flights. The most important advantage, however, will be the ability of a balloonborne telescope to clearly image Venus' night side continuously throughout a 12-hr period (more for certain launch site latitudes), a capability that cannot be matched from the ground or from the Venus Express spacecraft currently in orbit around Venus. Future missions, such as the Japanese Venus Climate Orbiter will also not be able to achieve this level of synoptic coverage. This capability will provide a detailed, continuous look at evolving cloud distributions in Venus' middle and lower cloud decks through atmospheric windows at 1.74 and 2.3 μm, which in turn will provide observational constraints on models of Venus' circulation. The science requirements propagate to several aspects of the telescope: a 1.4-m aperture to provide a diffraction limit of 0.3" at 1.74 μm (to improve upon non-AO ground-based resolution by a factor of 2); a plate scale of 0.1" per pixel, which in turn requires an f/15 telescope for 13 μm pixels; pointing and stability at the 0.05" level; stray light baffling; a field of view of 2 arc minutes; ability to acquire images at 1.26, 1.74 and 2.3 μm; and ability to operate aloft for three weeks at a time. The specific implementations of these requirements are outlined in this paper. Briefly, a 1.4-m Gregorian telescope is proposed, with stray light baffling at the intermediate focus. A three-stage pointing system is described, consisting of a coarse azimuthal rotator, a moderate pointing system based on a star tracker and ALT/AZ gimbals, and a fine pointing system based on analog photodiodes and a fine steering mirror. The science detectors are not discussed here, except to specify the requirement for moderate resolution (R > 1000) spectroscopy.

Paper Details

Date Published: 10 July 2008
PDF: 14 pages
Proc. SPIE 7012, Ground-based and Airborne Telescopes II, 70121S (10 July 2008); doi: 10.1117/12.790032
Show Author Affiliations
Eliot F. Young, Southwest Research Institute (United States)
Mark A. Bullock, Southwest Research Institute (United States)
Alan Kraut, Harvey Mudd College (United States)
Graham Orr, Harvey Mudd College (United States)
Kevin Swartzlander, Harvey Mudd College (United States)
Tony Wimer, Harvey Mudd College (United States)
Elton Wong, Harvey Mudd College (United States)
Patrick Little, Harvey Mudd College (United States)
Yusuke Nakaya, Kogakuin Univ. (Japan)
Russell Mellon, Equinox Interscience, Inc. (United States)
Lawrence Germann, Left Hand Design Corp. (United States)

Published in SPIE Proceedings Vol. 7012:
Ground-based and Airborne Telescopes II
Larry M. Stepp; Roberto Gilmozzi, Editor(s)

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