3,971 research outputs found
Optimization of coronagraph design for segmented aperture telescopes
No full textThe goal of directly imaging Earth-like planets in the habitable zone of other stars has motivated the design of coronagraphs for use with large segmented aperture space telescopes. In order to achieve an optimal trade-off between planet light throughput and diffracted starlight suppression, we consider coronagraphs comprised of a stage of phase control implemented with deformable mirrors (or other optical elements), pupil plane apodization masks (gray scale or complex valued), and focal plane masks (either amplitude only or complex-valued, including phase only such as the vector vortex coronagraph). The optimization of these optical elements, with the goal of achieving 10 or more orders of magnitude in the suppression of on-axis (starlight) diffracted light, represents a challenging non-convex optimization problem with a nonlinear dependence on control degrees of freedom. We develop a new algorithmic approach to the design optimization problem, which we call the ”Auxiliary Field Optimization” (AFO) algorithm. The central idea of the algorithm is to embed the original optimization problem, for either phase or amplitude (apodization) in various planes of the coronagraph, into a problem containing additional degrees of freedom, specifically fictitious ”auxiliary” electric fields which serve as targets to inform the variation of our phase or amplitude parameters leading to good feasible designs. We present the algorithm, discuss details of its numerical implementation, and prove convergence to local minima of the objective function (here taken to be the intensity of the on-axis source in a ”dark hole” region in the science focal plane). Finally, we present results showing application of the algorithm to both unobscured off-axis and obscured on-axis segmented telescope aperture designs. The application of the AFO algorithm to the coronagraph design problem has produced solutions which are capable of directly imaging planets in the habitable zone, provided end-to-end telescope system stability requirements can be met. Ongoing work includes advances of the AFO algorithm reported here to design in additional robustness to a resolved star, and other phase or amplitude aberrations to be encountered in a real segmented aperture space telescope
Assessing the performance limits of internal coronagraphs through end-to-end modeling: a NASA TDEM study
No full textAs part of the NASA ROSES Technology Development for Exoplanet Missions (TDEM) program, we are conducting a study of three internal coronagraphs (PIAA, vector vortex, hybrid bandlimited) to understand their behaviors in realistically-aberrated systems with wavefront control (deformable mirrors). This study consists of two milestones: (1) develop wavefront propagation codes appropriate for each coronagraph that are accurate to 1% or better (compared to a reference algorithm) but are also time and memory efficient, and (2) use these codes to determine the wavefront control limits of each architecture. We discuss the results from the study so far, with emphasis on representing the PIAA coronagraph and its wavefront control behavior
Tennessee roads / Jesse Stuart. In Mountain herald / Lincoln Memorial University.
No full textThis picturesque poem was written by then-sophomore (and future celebrated author) Jesse Stuart about the roads of Tennessee
End-to-end simulations of different coronagraphic techniques
No full textThe NASA exoplanet exploration program is dedicated to developing technologies for detecting and characterizing extrasolar planets. In support of that program we have evaluated three different coronagraphic techniques (bandlimited Lyot, optical vortex, and phase-induced pupil apodization) using optical propagation simulations. These utilized a complete hypothetical telescope+coronagraph system with phase and amplitude aberrations. Wavefront control using dual sequential deformable mirrors was performed. We discuss the different computational techniques necessary to accurately simulate each coronagraph
No. 617 Stuart Ruckman
No full textTranscript (12, 40 pages) of two interviews by Matt Driscoll with Stuart Ruckman on April 9, 2010, and July 7, 2011Ruckman (b. 1966) was born in Salt Lake City, Utah. Stuart shares how his family, particularly his father, played a significant role in introducing him to the outdoors. Some of his initial explorations included a hike to the top of Mount Olympus when he was five years old, backpacking trips in the Wasatch and Uinta Mountains, and a successful summit attempt on the Grand Teton when he was twelve. Stuart discovered technical rock climbing due to the influence of his older brother Bret, five years Stuart\u27s senior. Bret learned under Dennis Turville, a well-respected Salt Lake climbing instructor. Stuart shares his observations on the Salt Lake climbing community of the late 1970s and 1980s, noting the intimacy of the community, while also pointing out the significant influence of a handful of climbers, including Merrill Bitter, Les Ellison, and Brian Smoot. He briefly describes the proliferation of new-route development in the Wasatch during his first decade in climbing. In collaboration with his brother Bret, Stuart published comprehensive guidebooks on climbing in the Wasatch Mountains. Stuart\u27s contributions as a first-ascensionist and co-author of Rock Climbing the Wasatch Range attest to his lasting impact on Utah climbing. Interview is part of the Outdoor Recreation History Project. Interviewer: Matt Driscol
HARPS-N @ TNG, two year harvesting data : performances and results
No full textThe planet hunter HARPS-N[1], in operation at the Telescopio Nazionale Galileo (TNG)[13] from April 2012 is a highresolution spectrograph designed to achieve a very high radial velocity precision measurement thanks to an ultra stable environment and in a temperature-controlled vacuum. The main part of the observing time was devoted to Kepler field and achieved a very important result with the discovery of a terrestrial exoplanet. After two year of operation, we are able to show the performances and the results of the instrument
George MacLeod’s open-air preaching: performance and counter-performance
No full textStuart Blythe uses the methodology of performance to analyse George MacLeod’s open-air preaching. He points out that MacLeod’s preaching was derived from a theology of the incarnation, and an understanding of the paradoxes and dichotomies of common human life. This preaching, Blythe suggests, was also a counter-performance in the context of outlooks and ideologies inimical to the gospel. The paper raises interesting issues related to preaching as performance, and the further question as to whether or not the life and work of the Church as a whole might now be better understood as a counter-performance.Publisher PD
The JWST/NIRCam Coronagraph: Mask Design and Fabrication
No full textThe NIRCam instrument on the James Webb Space Telescope will provide coronagraphic imaging from lambda =1-5 microns of high contrast sources such as extrasolar planets and circumstellar disks. A Lyot coronagraph with a variety of circular and wedge-shaped occulting masks and matching Lyot pupil stops will be implemented. The occulters approximate grayscale transmission profiles using halftone binary patterns comprising wavelength-sized metal dots on anti-reflection coated sapphire substrates. The mask patterns are being created in the Micro Devices Laboratory at the Jet Propulsion Laboratory using electron beam lithography. Samples of these occulters have been successfully evaluated in a coronagraphic testbed. In a separate process, the complex apertures that form the Lyot stops will be deposited onto optical wedges. The NIRCam coronagraph flight components are expected to be completed this year
Redemption in the work of Francis Stuart
No full textThe idea of redemption is central to an understanding of the work
of Francis Stuart. Through an examination of its development and
expression, it is possible to demonstrate the integrity of his work and
its distinctive qualities. Such a demonstration is necessary because
Stuart's writing has been subjected to comparatively little scholarly
inquiry, although reviews of his work, especially that produced since
1949, suggest that it is impressive and important.
First, a general background to Stuart's work, a discussion of the
special problems associated with reading it, and a summary of his corpus
is provided. This indicates that the idea of redemption is important to
his earliest writing. The state of redemption is shown to be a
necessary apotheosis for Stuart's outcast heroes; it involves spiritual
suffering through which may be found a sense of reintegration and a
higher reality. This is expressed through interrelated themes such as
those of gambler, artist and ordinary man; mystic and criminal; sacred
and profane love; and spirituality and the mundane. The nature of the
redemptive experience is further elaborated by distinctive, complex
motifs, especially the hare, the ark and the woman-Christ. Their
recurrence provides an important element in the unity of Stuart's work.
Because Stuart's idea of the outcast raises important biographical
questions, an examination of the relationship between Stuart's life and
his work is made. Finally, the way in which the idea of redemption
exists in the language structures of Stuart's novels is examined, with
especial reference to his most recent work, The High Consistory. The
thesis shows that the development of the these of redemption
demonstrates the integrity of Stuart's work
Segmented coronagraph design and analysis (SCDA): an initial design study of apodized vortex coronagraphs
No full textThe segmented coronagraph design and analysis (SCDA) study is a coordinated effort, led by Stuart Shaklan (JPL) and supported by NASA's Exoplanet Exploration Program (ExEP), to provide efficient coronagraph design concepts for exoplanet imaging with future segmented aperture space telescopes. This document serves as an update on the apodized vortex coronagraph designs devised by the Caltech/JPL SCDA team. Apodized vortex coronagraphs come in two flavors, where the apodization is achieved either by use of 1) a gray-scale semi-transparent pupil mask or 2) a pair of deformable mirrors in series. Each approach has attractive benefits. This document presents a comprehensive review of the former type. Future theoretical investigations will further explore the use of deformable mirrors for apodization
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