The Fine Guidance Sensor (FGS) is one of the four science instruments on board the James Webb Space Telescope (JWST). FGS features two modules: an infrared camera dedicated to fine guiding of the observatory and a science camera module, the Near-Infrared Imager and Slitless Spectrograph (NIRISS) covering the wavelength range between 0.7 and 5.0 μm with a field of view of 2.2' X 2.2'. NIRISS has four observing modes: 1) broadband imaging featuring seven of the eight NIRCam broadband filters, 2) wide-field slitless spectroscopy at a resolving power of rv150 between 1 and 2.5 μm, 3) single-object cross-dispersed slitless spectroscopy enabling simultaneous wavelength coverage between 0. 7 and 2.5 μm at Rrv660, a mode optimized for transit spectroscopy of relatively bright (J > 7) stars and, 4) sparse aperture interferometric imaging between 3.8 and 4.8 μm enabling high contrast ("' 10-4) imaging of M < 8 point sources at angular separations between 70 and 500 milliarcsec. This paper presents an overview of the FGS/NIRISS design with a focus on the scientific capabilities and performance offered by NIRISS.

The JWST Fine Guidance Sensor (FGS) and Near-Infrared Imager and Slitless Spectrograph (NIRISS)

This review paper addresses topics of fabrication, testing, alignment, and as-built performance of reflective space optics for the next generation of telescopes across the x-ray to far-infrared spectrum. The technology presented in the manuscript represents the most promising methods to enable a next level of astronomical observation capabilities for space-based telescopes as motivated by the science community. While the technology to produce the proposed telescopes does not exist in its final form, the optics industry is making steady and impressive progress toward these goals across all disciplines. We hope that through sharing these developments in context of the science objectives, further connections and improvements are enabled to push the envelope of the technology.

Optics technology for large-aperture space telescopes: from fabrication to final acceptance tests

We present a process for characterizing the correlation properties of the noise in large two-dimensional detector arrays, and describe an efficient process for its removal. In the case of the 2k × 2k HAWAII-2RG detectors (H2RG) detectors from Teledyne which are being used on the Near Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST), we find that we can reduce the read noise by thirty percent. Noise on large spatial scales is dramatically reduced. With this relatively simple process, we provide a performance improvement that is equivalent to a significant increase in telescope collecting area for high resolution spectroscopy with NIRSpec.

Reducing the Read Noise of H2RG detector arrays: Eliminating Correlated Noise with Efficient Use of Reference Signals

In 2017, the James Webb Space Telescope Optical Telescope Element and Integrated Science Instrument Module (OTIS) underwent cryogenic optical testing at the Johnson Space Center. In this paper, we summarize the successful execution and results of this 100-day test, which was a major program milestone. We summarize the as-run test configuration and provide a top-level as-run timeline. We also provide the top-level functional, optical, thermal, and operational results from the test. We summarize the key technical issues encountered and the resolution of those issues. The results of the OTIS test indicate that the payload should be fully capable of delivering on JWST's exciting scientific potential.

/pdf/james-webb-space-telescope-jwst-optical-telescope-element-1fqeracc44.pdf

James Webb Space Telescope (JWST) optical telescope element and integrated science instrument module (OTIS) cryogenic test program and results

In late 2015/early 2016, a major cryo-vacuum test was carried out for the Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST). This test comprised the final cryo-certification and calibration test of the ISIM, after its ambient environmental test program (vibration, acoustics, EMI/EMC), and before its delivery for integration with the rest of the JWST observatory. Over the 108-day period of the round-the-clock test program, the full complement of ISIM flight instruments, structure, harness radiator, and electronics were put through a comprehensive program of thermal, optical, electrical, and operational tests. The test verified the health and excellent performance of the instruments and ISIM systems, proving the ISIM element's readiness for integration with the telescope. We report here on the context, goals, setup, execution, and key results for this critical JWST milestone.

Cryo-vacuum testing of the JWST Integrated Science Instrument Module (SPIE)

The James Webb Space Telescope (JWST) is frequently referred to as the follow-on mission to the Hubble Space Telescope (HST) The “Webb”, as it is often called, will be the biggest space telescope ever built and it will lead to astounding scientific breakthroughs The observatory is currently scheduled for launch in 2020 from Kourou, French Guyana by an ESA provided Ariane 5 rocket The Observatory houses four scientific instruments One of them is NIRSpec, the multi-object Near Infrared Spectrograph, built for ESA by Airbus Defence and Space in Germany After the JWST Optical telescope Element (OTE) integration and testing was completed in early 2016, the Integrated Science Instruments Module (ISIM) was integrated to the OTE in May 2016 The complete system of OTE and ISIM, now called OTIS, then successfully went through an acoustic and vibration test campaign at NASA Goddard Space Flight Center (GSFC) After this, the OTIS system was shipped to the Johnson Space Center (JSC) in Houston, TX, where a final 100+ days lasting cryogenic vacuum test was conducted inside the famous Thermal Chamber A This paper presents NIRSpec’s hardware status and some preliminary test results from the OTIS test campaign

JWST's near infrared spectrograph status and first OTIS test results

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.

/pdf/optical-testing-and-verification-methods-for-the-james-webb-3hhti0kaph.pdf

Optical Testing and Verification Methods for the James Webb Space Telescope Integrated Science Instrument Module Element

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JWST's near infrared spectrograph status and first OTIS test results

Optical Testing and Verification Methods for the James Webb Space Telescope Integrated Science Instrument Module Element