Kepler is NASA’s first space mission dedicated to the study of exoplanets. The primary scientific goal is statistical—to estimate the frequency of planetary systems associated with sun-like stars, especially the detection of earth-size planets in the habitable zones. Kepler was launched into an Earth-trailing heliocentric “drift-away” orbit (period=372 days ) in March 2009. The instrument detects the faint photometric signals of transits of planets across the stellar disks of those systems with orbital planes fortuitously oriented in our line of sight. Since the probability of such alignments is small, Kepler must observe a large number of stars. In fact, Kepler is monitoring approximately 150,000 stars with a 30-min cadence. The scientific goals led to the choice of a classical Schmidt telescope, and requirements on field-of-view, throughput, spectral bandpass, image quality, scattered light, thermal and opto-mechanical stability, and in-flight adjustment authority. We review the measurement requirements, telescope design, prelaunch integration, alignment, and test program, and we describe the in-flight commissioning that optimized the performance. The stability of the flight system has enabled increasing recognition of small effects and sophistication in data processing algorithms. Astrophysical noise arising from intrinsic stellar variability is now the dominant term in the photometric error budget.
KEYWORDS: Mirrors, Silicon carbide, Solar telescopes, Optical fabrication, Secondary tip-tilt mirrors, Off axis mirrors, Safety, Solar energy, Surface finishing, Control systems
L-3 Integrated Optical Systems (IOS) Division has been selected by the National Solar Observatory (NSO) to design and
produce the Top End Optical Assembly (TEOA) for the 4-meter Advanced Technology Solar Telescope (ATST) to
operate at Haleakalā, Maui. ATST will perform to a very high optical performance level in a difficult thermal
environment. The TEOA, containing the 0.65-meter silicon carbide secondary mirror and support, mirror thermal
management system, mirror positioning and fast tip-tilt system, field stop with thermally managed heat dump, thermally
managed Lyot stop, safety interlock and control system, and support frame, operates in the "hot spot" at the prime focus
of the ATST and so presents special challenges. In this paper, we describe progress in the L-3 technical approach to
meeting these challenges, including silicon carbide off-axis mirror design, fabrication, and high accuracy figuring and
polishing all within L-3; mirror support design; the design for stray light control; subsystems for opto-mechanical
positioning and high accuracy absolute mirror orientation sensing; Lyot stop design; and thermal management of all
design elements to remain close to ambient temperature despite the imposed solar irradiance load.
Polished 1.5m bare beryllium, off-axis aspheric mirror segments, constituting the cryogenic primary
mirror of NASA's ambitious Flagship Mission, James Webb Space Telescope (JWST), have been
successfully completed at L-3 Communications -Tinsley. Tinsley has finished the secondary, tertiary, fine
steering and spare mirrors as well. We will describe both the end results, where it was demonstrated that
visible quality mirror results can be achieved on large extremely lightweighted compliant off-axis mirrors,
and the steps taken at Tinsley to achieve these results. Over 26 square-meters of bare beryllium were
optically processed twice, first for room temperature figure, then for the cryo-null figure for the cryogenic
differences.
We will discuss mid-spatial frequency (MSF) optical surface errors, and how they affect
optical performance of an optical system, including contrast, ensquared energy and pixel cross-talk. MSF
errors will be represented in terms of Power Spectral Density (PSD), and examples will be discussed
where PSD is well controlled and poorly controlled. We will show recent examples of PSDs of aspheric
mirrors, sometimes with very challenging aspheric departure or other attributes, as routinely finished
Tinsley, and suggest ways the designer can effectively specify an optic for smoothness.
KEYWORDS: Mirrors, Space telescopes, Polishing, Telescopes, Zerodur, James Webb Space Telescope, Optical fabrication, Glasses, Magnetorheological finishing, Information operations
Pending critical spaceborne requirements, including coronagraphic detection of exoplanets, require exceptionally
smooth mirror surfaces, aggressive lightweighting, and low-risk cost-effective optical manufacturing methods.
Simultaneous development at Schott for production of aggressively lightweighted (>90%) Zerodur® mirror blanks,
and at L-3 Brashear for producing ultra-smooth surfaces on Zerodur®, will be described. New L-3 techniques for
large-mirror optical fabrication include Computer Controlled Optical Surfacing (CCOS) pioneered at L-3 Tinsley,
and the world's largest MRF machine in place at L-3 Brashear. We propose that exceptional mirrors for the most
critical spaceborne applications can now be produced with the technologies described.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.