J. Scott Smith
Goddard Space Flight Center
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Featured researches published by J. Scott Smith.
Proceedings of SPIE | 2006
Bruce H. Dean; David L. Aronstein; J. Scott Smith; Ron Shiri; D. Scott Acton
An image-based wavefront sensing and control algorithm for the James Webb Space Telescope (JWST) is presented. The algorithm heritage is discussed in addition to implications for algorithm performance dictated by NASAs Technology Readiness Level (TRL) 6. The algorithm uses feedback through an adaptive diversity function to avoid the need for phase-unwrapping post-processing steps. Algorithm results are demonstrated using JWST Testbed Telescope (TBT) commissioning data and the accuracy is assessed by comparison with interferometer results on a multi-wave phase aberration. Strategies for minimizing aliasing artifacts in the recovered phase are presented and orthogonal basis functions are implemented for representing wavefronts in irregular hexagonal apertures. Algorithm implementation on a parallel cluster of high-speed digital signal processors (DSPs) is also discussed.
Proceedings of SPIE | 2007
Lee D. Feinberg; Bruce H. Dean; David L. Aronstein; Charles W. Bowers; William L. Hayden; Richard G. Lyon; Ron Shiri; J. Scott Smith; D. Scott Acton; Larkin Carey; Adam R. Contos; Erin Sabatke; John P. Schwenker; Duncan Shields; Tim Towell; Fang Shi; Luis Meza
NASAs Technology Readiness Level (TRL)-6 is documented for the James Webb Space Telescope (JWST) Wavefront Sensing and Control (WFSC) subsystem. The WFSC subsystem is needed to align the Optical Telescope Element (OTE) after all deployments have occurred, and achieves that requirement through a robust commissioning sequence consisting of unique commissioning algorithms, all of which are part of the WFSC algorithm suite. This paper identifies the technology need, algorithm heritage, describes the finished TRL-6 design platform, and summarizes the TRL-6 test results and compliance. Additionally, the performance requirements needed to satisfy JWST science goals as well as the criterion that relate to the TRL-6 Testbed Telescope (TBT) performance requirements are discussed.
Proceedings of SPIE | 2012
D. Scott Acton; J. Scott Knight; Adam R. Contos; Stefano Grimaldi; James P. Terry; Paul A. Lightsey; Allison Barto; B. League; Bruce H. Dean; J. Scott Smith; Charles W. Bowers; David L. Aronstein; Lee D. Feinberg; William L. Hayden; Thomas Comeau; Rémi Soummer; Erin Elliott; Marshall D. Perrin; Carl W. Starr
The James Webb Space Telescope (JWST) is a segmented deployable telescope, utilizing 6 degrees of freedom for adjustment of the Secondary Mirror (SM) and 7 degrees of freedom for adjustment of each of its 18 segments in the Primary Mirror (PM). When deployed, the PM segments and the SM will be placed in their correct optical positions to within a few mm, with accordingly large wavefront errors. The challenge, therefore, is to position each of these optical elements in order to correct the deployment errors and produce a diffraction-limited telescope, at λ=2μm, across the entire science field. This paper describes a suite of processes, algorithms, and software that has been developed to achieve this precise alignment, using images taken from JWST’s science instruments during commissioning. The results of flight-like end-to-end simulations showing the commissioning process are also presented.
Proceedings of SPIE | 2009
J. Scott Smith; David L. Aronstein; Bruce H. Dean; D. Scott Acton
The James Webb Space Telescope (JWST) consists of an optical telescope element (OTE) that sends light to five science instruments. The initial steps for commissioning the telescope are performed with the Near-Infrared Camera (NIRCam) instrument, but low-order optical aberrations in the remaining science instruments must be determined (using phase retrieval) in order to ensure good performance across the entire field of view. These remaining instruments were designed to collect science data, and not to serve as wavefront sensors. Thus, the science cameras are not ideal phase-retrieval imagers for several reasons: they record under-sampled data and have a limited range of diversity defocus, and only one instrument has an internal, narrowband filter. To address these issues, we developed the capability of sensing these aberrations using an extension of image-based iterative-transform phase retrieval called Variable Sampling Mapping (VSM). The results show that VSM-based phase retrieval is capable of sensing low-order aberrations to a few nm RMS from images that are consistent with the non-ideal conditions expected during JWST multi-field commissioning. The algorithm is validated using data collected from the JWST Testbed Telescope (TBT).
Proceedings of SPIE | 2009
Lee D. Feinberg; Bruce H. Dean; Tupper Hyde; Bill Oegerle; Matthew R. Bolcar; J. Scott Smith
Future large UV-optical space telescopes offer new and exciting windows of scientific parameter space. These telescopes can be placed at L2 and borrow heavily from the James Webb Space Telescope (JWST) heritage. For example, they can have similar deployment schemes, hexagonal mirrors, and use Wavefront Sensing and Control (WFSC) technologies developed for JWST. However, a UV-optical telescope requires a 4x improvement in wavefront quality over JWST to be diffraction-limited at 500 nm. Achieving this tolerance would be difficult using a passive thermal architecture such as the one employed on JWST. To solve this problem, our team has developed a novel Hybrid Sensor Active Control (HSAC) architecture that provides a cost effective approach to building a segmented UV-optical space telescope. In this paper, we show the application of this architecture to the ST-2020 mission concept and summarize the technology development requirements.
Proceedings of SPIE | 2008
Joseph M. Howard; Kong Q. Ha; Ron Shiri; J. Scott Smith; Gary E. Mosier; Danniella Muheim
This paper is part five of a series on the ongoing optical modeling activities for the James Webb Space Telescope (JWST). The first two papers discussed modeling JWST on-orbit performance using wavefront sensitivities to predict line of sight motion induced blur, and stability during thermal transients. The third paper investigates the aberrations resulting from alignment and figure compensation of the controllable degrees of freedom (primary and secondary mirrors), which may be encountered during ground alignment and on-orbit commissioning of the observatory, and the fourth introduced the software toolkits used to perform much of the optical analysis for JWST. The work here models observatory operations by simulating line-of-sight image motion and alignment drifts over a two-week period. Alignment updates are then simulated using wavefront sensing and control processes to calculate and perform the corrections. A single model environment in Matlab is used for evaluating the predicted performance of the observatory during these operations.
ieee aerospace conference | 2016
David L. Aronstein; J. Scott Smith
Phase retrieval, the process of determining the exit-pupil wavefront of an optical instrument from image-plane intensity measurements, is the baseline methodology for characterizing the wavefront for the suite of science instruments (SIs) in the Integrated Science Instrument Module (ISIM) for the James Webb Space Telescope (JWST). JWST is a large, infrared space telescope with a 6.5-meter diameter primary mirror. JWST is currently NASAs flagship mission and will be the premier space observatory of the next decade. ISIM contains four optical benches with nine unique instruments, including redundancies. ISIM was characterized at the Goddard Space Flight Center (GSFC) in Greenbelt, MD in a series of cryogenic vacuum tests using a telescope simulator. During these tests, phase-retrieval algorithms were used to characterize the instruments. The objective of this paper is to describe the Monte-Carlo simulations that were used to establish uncertainties (i.e., error bars) for the wavefronts of the various instruments in ISIM. Multiple retrieval algorithms were used in the analysis of ISIM phase-retrieval focus-sweep data, including an iterative-transform algorithm and a nonlinear optimization algorithm. These algorithms emphasize the recovery of numerous optical parameters, including low-order wavefront composition described by Zernike polynomial terms and high-order wavefront described by a point-by-point map, location of instrument best focus, focal ratio, exit-pupil amplitude, the morphology of any extended object, and optical jitter. The secondary objective of this paper is to report on the relative accuracies of these algorithms for the ISIM instrument tests, and a comparison of their computational complexity and their performance on central and graphical processing unit clusters. From a phase-retrieval perspective, the ISIM test campaign includes a variety of source illumination bandwidths, various image-plane sampling criteria above and below the Nyquist-Shannon critical sampling value, various extended object sizes, and several other impactful effects.
Integrated Modeling of Complex Optomechanical Systems | 2011
J. Scott Smith; Bruce H. Dean; Alexander Rilee; Thomas P. Zielinski
The James Webb Space Telescope (JWST) is the successor to the Hubble Space Telescope and will be NASAs premier observatory of the next decade. Image-based wavefront sensing (phase retrieval) is the primary method for ground testing and on-orbit commissioning. For ground tests at NASAs Goddard Space Flight Center (GSFC) and Johnson Space Center (JSC), near-real-time analysis is critical for ensuring that pass/fail criteria are met before completion of a specific test. To address this need we have developed a computational architecture for image processing and phase retrieval. Using commercially available off-the-shelf hardware and software, we have designed, implemented, and tested a solution for high-speed parallel computing. The architecture is a hybrid solution utilizing both CPUs and GPUs and exploiting the unique advantages of each. Discussions are presented of the architecture, performance, and current limitations.
Proceedings of SPIE | 2016
Scott Antonille; C. L. Miskey; Raymond G. Ohl; Scott Rohrbach; David L. Aronstein; Andrew Bartoszyk; Charles W. Bowers; Emmanuel Cofie; Nicholas R. Collins; Brian Comber; William L. Eichhorn; Alistair Glasse; Renee Gracey; George F. Hartig; Joseph M. Howard; Douglas M. Kelly; Randy A. Kimble; Jeffrey R. Kirk; David A. Kubalak; Wayne B. Landsman; Don J. Lindler; Eliot M. Malumuth; Michael Maszkiewicz; Marcia J. Rieke; Neil Rowlands; Derek S. Sabatke; Corbett Smith; J. Scott Smith; Joseph Sullivan; Randal Telfer
NASA’s James Webb Space Telescope (JWST) is a 6.5m diameter, segmented, deployable telescope for cryogenic IR space astronomy. The JWST Observatory includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM), that contains four science instruments (SI) and the Fine Guidance Sensor (FGS). The SIs are mounted to a composite metering structure. The SIs and FGS were integrated to the ISIM structure and optically tested at NASAs Goddard Space Flight Center using the Optical Telescope Element SIMulator (OSIM). OSIM is a full-field, cryogenic JWST telescope simulator. SI performance, including alignment and wavefront error, was evaluated using OSIM. We describe test and analysis methods for optical performance verification of the ISIM Element, with an emphasis on the processes used to plan and execute the test. The complexity of ISIM and OSIM drove us to develop a software tool for test planning that allows for configuration control of observations, implementation of associated scripts, and management of hardware and software limits and constraints, as well as tools for rapid data evaluation, and flexible re-planning in response to the unexpected. As examples of our test and analysis approach, we discuss how factors such as the ground test thermal environment are compensated in alignment. We describe how these innovative methods for test planning and execution and post-test analysis were instrumental in the verification program for the ISIM element, with enough information to allow the reader to consider these innovations and lessons learned in this successful effort in their future testing for other programs.
Proceedings of SPIE | 2012
Matthew R. Bolcar; David L. Aronstein; Peter C. Hill; J. Scott Smith; Thomas P. Zielinski
In measuring the figure error of an aspheric optic using a null lens, the wavefront contribution from the null lens must be independently and accurately characterized in order to isolate the optical performance of the aspheric optic alone. Various techniques can be used to characterize such a null lens, including interferometry, profilometry and image-based methods. Only image-based methods, such as phase retrieval, can measure the null-lens wavefront in situ – in single-pass, and at the same conjugates and in the same alignment state in which the null lens will ultimately be used – with no additional optical components. Due to the intended purpose of a null lens (e.g., to null a large aspheric wavefront with a near-equal-but-opposite spherical wavefront), characterizing a null-lens wavefront presents several challenges to image-based phase retrieval: Large wavefront slopes and high-dynamic-range data decrease the capture range of phase-retrieval algorithms, increase the requirements on the fidelity of the forward model of the optical system, and make it difficult to extract diagnostic information (e.g., the system F/#) from the image data. In this paper, we present a study of these effects on phase-retrieval algorithms in the context of a null lens used in component development for the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission. Approaches for mitigation are also discussed.