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NASA’s James Webb Space Telescope (JWST) is a 6.6m diameter, segmented, deployable telescope for cryogenic IR space astronomy. The JWST Observatory architecture includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM) element which contains four science instruments (SI), including a guider. The SIs and guider are mounted to a composite metering structure with outer envelope approximate measurements of 2.2x2.2x1.7m. These SI units are integrated to the ISIM structure and optically tested at NASA Goddard Space Flight Center as an instrument suite using an Optical telescope element SIMulator (OSIM). OSIM is a high-fidelity, cryogenic JWST simulator that features a ~1.5m diameter powered mirror. The SIs are aligned to the flight structure’s coordinate system under ambient, clean room conditions using opto-mechanical metrology and customized interfaces. OSIM is aligned to the ISIM mechanical coordinate system at the cryogenic operating temperature via internal mechanisms and feedback from alignment sensors and metrology in six degrees of freedom. SI performance, including focus, pupil shear, pupil roll, boresight, wavefront error, and image quality, is evaluated at the operating temperature using OSIM. This work reports on the as-run ambient assembly and ambient alignment steps for the flight ISIM, including SI interface fixtures and customization and kinematic mount adjustment. The ISIM alignment plan consists of multiple steps to meet the “absolute” alignment requirements of the SIs and OSIM to the flight coordinate system. In this paper, we focus on key aspects of absolute, optical-mechanical alignment. We discuss various metrology and alignment techniques. In addition, we summarize our approach for dealing with and the results of ground-test factors, such as gravity.

This paper describes the critical instrument alignment terms associated with the six-degree of freedom alignment of each the Science Instrument (SI) in the James Webb Space Telescope (JWST), including focus, pupil shear, pupil clocking, and boresight. We present the test methods used during cryogenic-vacuum tests to directly measure the performance of each parameter, the requirements levied on each, and the impact of any violations of these requirements at the instrument and Observatory level.

NASA's James Webb Space Telescope (JWST) is a 6.6m diameter, segmented, deployable telescope for cryogenic IR space astronomy (~40K). 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 guider. The SIs are mounted to a composite metering structure. The SI and guider units were integrated to the ISIM structure and optically tested at the NASA Goddard Space Flight Center as a suite using the Optical Telescope Element SIMulator (OSIM). OSIM is a full field, cryogenic JWST telescope simulator. SI performance, including alignment and wave front error, were 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, 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.

The James Webb Space Telescope includes the Integrated Science Instrument Module (ISIM) element that contains four science instruments (SI) including a Guider. We performed extensive structural, thermal, and optical performance(STOP) modeling in support of all phases of ISIM development. In this paper, we focus on modeling and results associated with test and verification. ISIMs test program is bound by ground environments, mostly notably the 1g and test chamber thermal environments. This paper describes STOP modeling used to predict ISIM system performance in 0g and at various on-orbit temperature environments. The predictions are used to project results obtained during testing to on-orbit performance.

Large astronomical missions are usually general-purpose telescopes with a suite of instruments optimized for different wavelength regions, spectral resolutions, etc. Their end-to-end (E2E) simulations are typically photons-in to flux-out calculations made to verify that each instrument meets its performance specifications. In contrast, smaller space missions are usually single-purpose telescopes, and their E2E simulations start with the scientific question to be answered and end with an assessment of the effectiveness of the mission in answering the scientific question. Thus, E2E simulations for small missions consist a longer string of calculations than for large missions, as they include not only the telescope and instrumentation, but also the spacecraft, orbit, and external factors such as coordination with other telescopes. Here, we illustrate the strategy and organization of small-mission E2E simulations using the Galaxy Evolution Spectroscopic Explorer (GESE) as a case study. GESE is an Explorer/Probe-class space mission concept with the primary aim of understanding galaxy evolution. Operation of a small survey telescope in space like GESE is usually simpler than operations of large telescopes driven by the varied scientific programs of the observers or by transient events. Nevertheless, both types of telescopes share two common challenges: maximizing the integration time on target, while minimizing operation costs including communication costs and staffing on the ground. We show in the case of GESE how these challenges can be met through a custom orbit and a system design emphasizing simplification and leveraging information from ground-based telescopes.

A wide array of general astrophysics studies including detecting and characterizing habitable exoplanets could be enabled by a future large segmented telescope with sensitivity in the UV, optical, and infrared bands. When paired with a starshade or coronagraph, such an observatory could enable direct imaging and detailed spectroscopic observations of nearby Earth-like habitable zone planets. Over the past several years, a laboratory-based Visible Nulling Coronagraph (VNC) has evolved to reach requisite contrasts over a ~ 1 nm bandwidth at narrow source angle separation using a segmented deformable mirror in one arm of a Mach-Zehnder layout. More recent efforts targeted broadband performance following the addition of two sets of half-wave Fresnel rhomb achromatic phase shifters (APS) with the goal of reaching 10-9 contrast, at a separation of 2λ/D, using a 40 nm (6%) bandwidth single mode fiber source. Here we present updates on the VNC broadband nulling effort, including approaches to addressing system contrast limitations.

The James Webb Space Telescope's (JWST) end-to-end optical system will be tested in a cryogenic vacuum environment before launch at NASA Johnson Space Center’s (JSC) Apollo-era, historic Chamber A thermal vacuum facility. During recent pre-test runs with a prototype “Pathfinder” telescope, the vibration in this environment was found to be challenging for the baseline test approach, which uses phase retrieval of images created by three sub-apertures of the telescope. To address the vibration, an alternate strategy implemented using classic Hartmann test principles combined with precise mirror mechanisms to provide a testing approach that is insensitive to the dynamics environment of the chamber. The measurements and sensitivities of the Hartmann approach are similar to those using phase retrieval over the original sparse aperture test. The Hartmann test concepts have been implemented on the JWST Test Bed Telescope, which provided the rationale and empirical evidence indicating that this Hartmann style approach would be valuable in supplementing the baseline test approach. This paper presents a Hartmann approach implemented during the recent Pathfinder test along with the test approach that is currently being considered for the full optical system test of JWST. Comparisons are made between the baseline phase retrieval approach and the Hartmann approach in addition to demonstrating how the two test methodologies support each other to reduce risk during the JWST full optical system test.

Measuring the B-mode polarization of the CMB radiation requires a detailed understanding of the projection of the detector onto the sky. We show how the combination of scan strategy and processing generates a cylindrical beam for the spectrum measurement. Both the instrumental design and the scan strategy reduce the cross coupling between the temperature variations and the B-modes. As with other polarization measurements some post processing may be required to eliminate residual errors.

The ATALST (Advanced Technology for Large Aperture Space Telescopes) effort has presented several design incarnations. Here we will compare the 9.2m segmented, the 8m monolithic on-axis and 8m x 6m off-axis concepts.

The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2014. System-level verification of critical performance requirements will rely on integrated observatory models that predict the wavefront error accurately enough to verify that allocated top-level wavefront error of 150 nm root-mean-squared (rms) through to the wave-front sensor focal plane is met. The assembled models themselves are complex and require the insight of technical experts to assess their ability to meet their objectives. This paper describes the systems engineering and modeling approach used on the JWST through the detailed design phase.

We present results of a study of a deployable version of the Advanced Technology Large-Aperture Space Telescope (ATLAST), designed to operate in a Sun-Earth L2 orbit. The primary mirror of the segmented 9.2-meter aperture has 36 hexagonal 1.315 m (flat to flat) glass mirrors. The architecture and folding of the telescope is similar to JWST, allowing it to fit into the 6.5 m fairing of a modest upgrade to the Delta-IV Heavy version of the Evolved Expendable Launch Vehicle (EELV). We discuss the overall observatory design, optical design, instruments, stray light, wavefront sensing and control, pointing and thermal control, and in-space servicing options.

The ATALST (Advanced Technology for Large Aperture Space Telescopes) effort has presented several design incarnations. Here we will discus the design process in detail and compare the design and performance of the 9.2m segmented, the 8m monolithic on-axis and 8m x 6m off-axis concepts.

Design methods are described for unobstructed, plane-symmetric, anamorphic systems composed of three mirrors. Low order imaging constraints are used to reduce the dimensionality of the configuration space. Examples are presented from a specific class of systems with fixed packaging constraints.

The Joint Dark Energy Mission (JDEM) 1,2 is a proposed dark energy space mission that will measure the expansion history of the universe and the growth of its large scale structure. It is intended to provide tight constraints on the equation of state of the universe and test the validity of general relativity. Three complementary observational analyses will be employed: Baryon Acoustic Oscillations, Type 1a Supernovae and Gravitational Weak Lensing. An observatory designed for efficient accommodation of these techniques combines wide-field, diffraction-limited observations, ultra-stable point spread function, and spectroscopy. In this paper we discuss optical configurations capable of simultaneous wide-field imaging and spectroscopy, using either afocal or focal telescope configurations. Spectroscopy may be performed by an integral field unit (IFU), grism or prism spectrometer. We present a flowdown of weak lensing image stability requirements (the most demanding technique optically) to telescope thermo-mechanical stability limits, based on variations in the optical transfer function of combinations of Zernike modes, and the sensitivity of these mode combinations to thermo-mechanical drift of the telescope. We apply our formalism to a representative threemirror anastigmat telescope and find quantitative relations between the second moments of the image and the required stability of the telescope over a typical weak lensing observation.

This is part six of a series describing the ongoing optical modeling activities for the James Webb Space Telescope (JWST). The first two discussed modeling JWST on-orbit performance using wavefront sensitivities to predict line of sight motion induced blur and stability during thermal transients. The third investigates the aberrations resulting from alignment and figure errors after compensation of the controllable degrees of freedom of the observatory (i.e. primary and secondary mirrors). This paper follows the theme of the third, but considers the highly unlikely case where a gross figure error occurs on the secondary mirror. We then compensate for this error using figure control on the primary mirror. The level of compensation as well as the total motions required are evaluated and reported. Impact to image quality over the full field of the observatory is also discussed.

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.

This paper is part four 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. The work here introduces some of the math software tools used to perform the work of the previous three papers of this series. NASA has recently approved these in-house tools for public release as open source, so this presentation also serves as a quick tutorial on their use. The tools are collections of functions written for use in MATLAB to interface with optical design software (CODE V, OSLO, and ZEMAX) using either COM or DDE communication protocol. The functions are discussed, and examples are given.

The Terrestrial Planet Finder-Coronagraph (TPF-C) is a NASA exploration mission to directly detect and characterize terrestrial exoplanets at visible wavelengths. The TPF-C observatory must be able to distinguish a planet that is more than 10 orders of magnitude fainter than its parent star at a separation of 75 milli-arc-seconds (mas). Coronagraphic detection requires a large aperture telescope to resolve the exoplanet from its star, and extreme stability during detection and characterization observations. This paper discusses the requirements and trade studies leading to the current baseline optical design for the TPF-C telescope. The current baseline design is summarized and its prescription is presented.

The Terrestrial Planet Finder Coronagraph (TPF-C) is conducting pre-formulation design and analysis studies based on a 8x3.5m elliptical aperture, light-weight primary mirror feeding an internally occulted (Lyot) coronagraph. The primary mirror has challenging static and dynamic performance requirements. We report on recent trade studies and concepts including open- and closed-back mirror blank designs and comparisons of thermal and mechanical performance; aperture shape alternatives to better match the coronagraph application with weight, packaging, and fabrication constraints; and mirror material trades.

The JWST Observatory currently under development for NASA and it's international partners contains a 6.5 meter diameter cryogenic telescope and a suite of 4 highly sensitive instruments which will collect imagery and spectroscopic data over the spectral range of 0.6 to 30 micrometers. The Observatory architecture contains a number of innovative and aggressive technologies including a light-weight primary mirror made up of 18 individually controllable segments, a large sunshield to permit stable low temperature operation, and a nested multi-loop pointing and tracking subsystem to establish milli-arc second line of sight stability. Detailed analytical models are being developed for each of the individual elements of the Observatory. The work described in this paper draws on these models so as to create a high level end-to-end model for the total Observatory. The principal thrust of this end-to-end model (OPTOOL) is to verify that the Observatory meets its overall image quality requirements. These requirements are codified in terms of Strehl ratio, encircled energy, and image anisotropy, and are applied at wavelengths of 1,2, and 5.6 micrometers. OPTOOL is implemented through Matlab (Version 7.0.1) with a Fourier optics based approach for PSF calculations, and uses a direct integration calculation to permit high spatial sampling of the PSF. Polychromatic PSFs are calculated using the Observatory band pass characteristic and an assumed constant Jansky level target. The focal plane arrays of each of the 4 instruments are also included in the model so that realistic signal with noise imagery can be simulated. Exit pupil optical path difference (OPD) maps can be generated using combinations of Zernike polynomials or shaped power spectral densities. Aberrations can be applied to the entire pupil or to the individual segments which make up the pupil. Global exit pupil OPD maps can also be imported and used to generate predicted Point Spread Functions (PSFs). Sample results are presented.

This is a continuation of a series of papers on the integrated modeling activities for the James Webb Space Telescope(JWST). Starting with the linear optical model discussed in part one, and using the optical sensitivities developed in part two, we now assess the optical image motion and wavefront errors from the structural dynamics. This is often referred to as "jitter: analysis. The optical model is combined with the structural model and the control models to create a linear structural/optical/control model. The largest jitter is due to spacecraft reaction wheel assembly disturbances which are harmonic in nature and will excite spacecraft and telescope structural. The structural/optic response causes image quality degradation due to image motion (centroid error) as well as dynamic wavefront error. Jitter analysis results are used to predict imaging performance, improve the structural design, and evaluate the operational impact of the disturbance sources.

This is the second of a series on the optical modeling activities for the JWST government systems engineering integrated modeling team. Starting with the linear optical model discussed in the first installment, we develop centroid and wavefront error sensitivities for the special case of a segmented optical system such as JWST, where the primary mirror consists of 18 individual segments. Our approach extends standard sensitivity matrix methods used for systems consisting of monolithic optics, where the image motion is approximated by averaging ray coordinates at the image and residual wavefront error is determined with global tip/tilt removed. We develop an exact formulation using the linear optical model, and extend it to cover multiple field points for performance prediction at each instrument aboard JWST. This optical model is then driven by thermal and dynamic structural perturbations in an integrated modeling environment. Results are presented.

This is a continuation of a series of papers on modeling activities for JWST. The structural-thermal- optical, often referred to as "STOP", analysis process is used to predict the effect of thermal distortion on optical performance. The benchmark STOP analysis for JWST assesses the effect of an observatory slew on wavefront error. The paper begins an overview of multi-disciplinary engineering analysis, or integrated modeling, which is a critical element of the JWST mission. The STOP analysis process is then described. This process consists of the following steps: thermal analysis, structural analysis, and optical analysis. Temperatures predicted using geometric and thermal math models are mapped to the structural finite element model in order to predict thermally-induced deformations. Motions and deformations at optical surfaces are input to optical models and optical performance is predicted using either an optical ray trace or WFE estimation techniques based on prior ray traces or first order optics. Following the discussion of the analysis process, results based on models representing the design at the time of the System Requirements Review. In addition to baseline performance predictions, sensitivity studies are performed to assess modeling uncertainties. Of particular interest is the sensitivity of optical performance to uncertainties in temperature predictions and variations in metal properties. The paper concludes with a discussion of modeling uncertainty as it pertains to STOP analysis.

The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2011. System-level verification of critical optical performance requirements will rely on integrated modeling to a considerable degree. In turn, requirements for accuracy of the models are significant. The size of the lightweight observatory structure, coupled with the need to test at cryogenic temperatures, effectively precludes validation of the models and verification of optical performance with a single test in 1-g. Rather, a complex series of steps are planned by which the components of the end-to-end models are validated at various levels of subassembly, and the ultimate verification of optical performance is by analysis using the assembled models. This paper describes the critical optical performance requirements driving the integrated modeling activity, shows how the error budget is used to allocate and track contributions to total performance, and presents examples of integrated modeling methods and results that support the preliminary observatory design. Finally, the concepts for model validation and the role of integrated modeling in the ultimate verification of observatory are described.

The Fourier-Kelvin Stellar Interferometer (FKSI) has been proposed to detect and characterize extra solar giant planets. The baseline configuration for FKSI is a two- aperture, structurally connected nulling interferometer, capable of providing null depth less than lo4 in the infrared. The objective of this paper is to summarize the process for setting the top level requirements and the jitter analysis performed on FKSI to date. The first part of the paper discusses the derivation of dynamic stability requirements, necessary for meeting the FKSI nulling demands. An integrated model including structures, optics, and control systems has been developed to support dynamic jitter analysis and requirements verification. The second part of the paper describes how the integrated model is used to investigate the effects of reaction wheel disturbances on pointing and optical path difference stabilities.

Optical design tools are presented to provide automatic generation of reflective optical systems for educational use. The tools are graphical in nature and use an interactive slider interface with freely available optical design software. Operation of the sliders provides input to adjust first-order and other system parameters (e.g. focal length), while appropriate system construction parameters are automatically updated to correct aberrations. Graphical output is also presented in real-time (e.g. a lens drawing) to provide the opportunity for a truly visual approach to optical design. Available systems include two- and three-mirror telescopes, relays, and afocal systems, either rotationally symmetric or having just a plane of symmetry. Demonstrations are presented.

Challenges in fabrication and testing have historically limited the choice of surfaces available for the design of reflective optical instruments. Spherical and conic mirrors are common, but, for future science instruments, more degrees of freedom will be necessary to meet performance and packaging requirements. These instruments will be composed of surfaces of revolution located far off-axis with large spherical departure, and some designs will even require asymmetric surface profiles. We describe the design and diamond machining of seven aluminum mirrors: three rotationally symmetric, off-axis conic sections, one off-axis biconic, and three flat mirror designs. These mirrors are for the Infrared Multi-Object Spectrometer instrument, a facility instrument for the Kitt Peak National Observatory’s Mayall Telescope (3.8 m) and a pathfinder for the future Next Generation Space Telescope multi-object spectrograph. The symmetric mirrors include convex and concave prolate and oblate ellipsoids, and range in aperture from 92 x 77 mm to 284 x 264 mm and in f-number from 0.9 to 2.4. The biconic mirror is concave and has a 94 x 76 mm aperture, (formula available in paper) and is decentered by -2 mm in x and 227 mm in y. The mirrors have an aspect ratio of approximately 6:1. The fabrication tolerances for surface error are < 63.3 nm RMS figure error and < 10 nm RMS microroughness. The mirrors are attached to the instrument bench using semi-kinematic, integral flexure mounts and optomechanically aligned to the instrument coordinate system using fiducial marks and datum surfaces. We also describe in-process profilometry and optical testing.

Design methods are described for unobstructed, plane-symmetric systems composed of three conic mirrors. Low order imaging constraints (including the requirement of nonanamorphism) are used to reduce the dimensionality of the configuration space. Examples are presented.

Imaging constraints are applied in lens design software macros for automatic generation of Ritchey-Chretien, Three-Mirror-Anastigmat (TMA), and plane symmetric configurations of spherical, conic, and general aspheric mirrors. These tools provide rapid development of telescope and instrument designs by reducing the available degrees of freedom confronting the designer while maintaining the desired set of image properties (e.g. focal length and aberration control). A brief example of a Ritchey-Chretien telescope is presented.

Design methods are presented to facilitate studies of unobstructed afocal systems composed of two and three spherical mirrors. Only unobstructed systems with a plane of symmetry are considered. Low order imaging constraints are determined to eliminate available degrees of freedom and reduce the dimensionality of the configuration space. Example systems are presented.

We investigate unobstructed plane-symmetric imaging systems of two spherical mirrors having three- or four-reflections. Geometry constraints are used to ensure that the odd numbered reflections occur on one spherical mirror, and that even numbered reflections occur on a separate spherical mirror. Imaging constraints are used to ensure appropriate first-order behavior. These geometry and imaging constraints eliminate degrees of freedom from the configuration space, thereby simplifying the design process. For the three-reflection systems, the available degrees of freedom are reduced to four, and for four-reflection systems, they are reduced to five. An alternate method using pickup constraints is discussed. Global optimization using simulated annealing is performed, and example systems are presented.