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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Measuring Segmented Primary Mirror WFE in the Presence of Vibration and Thermal Drift on the Light-Weighted JWST

The light-weighted design of the Optical Telescope Element (OTE) of the James Webb Telescope (JWST) leads to additional sensitivity to vibration from the ground - an important consideration to the measurement uncertainty of the wavefront error (WFE) in the primary mirror. Furthermore, segmentation of the primary mirror leads to rigid-body movements of segment areas in the WFE. The ground vibrations are minimized with modifications to the test facility, and by the architecture of the equipment supporting the load. Additional special test equipment (including strategically placed isolators, tunable mass dampers, and cryogenic magnetic dampers) mitigates the vibration and the response sensitivity before reaching the telescope. A multi-wavelength interferometer is designed and operated to accommodate the predicted residual vibration. Thermal drift also adds to the measurement variation. Test results of test equipment components, measurement theory, and finite element analysis combine to predict the test uncertainty in the future measurement of the primary mirror. The vibration input to the finite element model comes from accelerometer measurements of the facility with the environmental control pumps operating. One of the isolators have been built and tested to validate the dynamic performance. A preliminary model of the load support equipment and the OTE with the Integrated Science Instrument Module (ISIM) is complete. The performance of the add-on dampers have been established in previous applications. And operation of the multi-wavelength interferometer was demonstrated on a scaled hardware version of the JWST in an environment with vibration and thermal drift.

Whitman, Tony L.↗
NASA NTRS2008

Optical Coating Performance and Thermal Structure Design for Heat Reflectors of JWST Electronic Control Unit

The James Webb Space Telescope (JWST) consists of an infrared-optimized Optical Telescope Element (OTE) that is cooled down to 40 degrees Kelvin. A second adjacent component to the OTE is the Integrated Science Instrument Module, or ISIM. This module includes the electronic compartment, which provides the mounting surfaces and ambient thermally controlled environment for the instrument control electronics. Dissipating the 200 watts generated from the ISIM structure away from the OTE is of paramount importance so that the spacecraft's own heat does not interfere with the infrared light detected from distant cosmic sources. This technical challenge is overcome by a thermal subsystem unit that provides passive cooling to the ISIM control electronics. The proposed design of this thermal radiator consists of a lightweight structure made out of composite materials and low-emittance metal coatings. In this paper, we will present characterizations of the coating emittance, bidirectional reflectance, and mechanical structure design that will affect the performance of this passive cooling system.

Quijada, Manuel A.↗
NASA NTRS2015

JWST Pathfinder Telescope Integration

The James Webb Space Telescope (JWST) is a 6.5m, segmented, IR telescope that will explore the first light of the universe after the big bang. In 2014, a major risk reduction effort related to the Alignment, Integration, and Test (AI&T) of the segmented telescope was completed. The Pathfinder telescope includes two Primary Mirror Segment Assemblies (PMSA's) and the Secondary Mirror Assembly (SMA) onto a flight-like composite telescope backplane. This pathfinder allowed the JWST team to assess the alignment process and to better understand the various error sources that need to be accommodated in the flight build. The successful completion of the Pathfinder Telescope provides a final integration roadmap for the flight operations that will start in August 2015.

JWST↗
NASA NTRS2016

Status of the JWST Science Instrument Payload

The James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) system consists of five sensors (4 science): Mid-Infrared Instrument (MIRI), Near Infrared Imager and Slitless Spectrograph (NIRISS), Fine Guidance Sensor (FGS), Near InfraRed Camera (NIRCam), Near InfraRed Spectrograph (NIRSpec); and nine instrument support systems: Optical metering structure system, Electrical Harness System; Harness Radiator System, ISIM Electronics Compartment, ISIM Remote Services Unit, Cryogenic Thermal Control System, Command and Data Handling System, Flight Software System, Operations Scripts System.

JWST Payload↗
NASA NTRS2016

Transiting Exoplanet Studies and Community Targets for JWST's Early Release Science Program

The James Webb Space Telescope (JWST) will likely revolutionize transiting exoplanet atmospheric science, due to a combination of its capability for continuous, long duration observations and its larger collecting area, spectral coverage, and spectral resolution compared to existing space-based facilities. However, it is unclear precisely how well JWST will perform and which of its myriad instruments and observing modes will be best suited for transiting exoplanet studies. In this article, we describe a prefatory JWST Early Release Science (ERS) Cycle 1 program that focuses on testing specific observing modes to quickly give the community the data and experience it needs to plan more efficient and successful transiting exoplanet characterization programs in later cycles. We propose a multi-pronged approach wherein one aspect of the program focuses on observing transits of a single target with all of the recommended observing modes to identify and understand potential systematics, compare transmission spectra at overlapping and neighboring wavelength regions, confirm throughputs, and determine overall performances. In our search for transiting exoplanets that are well suited to achieving these goals, we identify 12 objects (dubbed community targets'') that meet our defined criteria. Currently, the most favorable target is WASP-62b because of its large predicted signal size, relatively bright host star, and location in JWST's continuous viewing zone. Since most of the community targets do not have well-characterized atmospheres, we recommend initiating preparatory observing programs to determine the presence of obscuring clouds/hazes within their atmospheres. Measurable spectroscopic features are needed to establish the optimal resolution and wavelength regions for exoplanet characterization. Other initiatives from our proposed ERS program include testing the instrument brightness limits and performing phase-curve observations. The latter are a unique challenge compared to transit observations because of their significantly longer durations. Using only a single mode, we propose to observe a full-orbit phase curve of one of the previously characterized, short-orbital-period planets to evaluate the facility-level aspects of long, uninterrupted time-series observations.

JWST Early Release Science (ERS)↗
NASA NTRS2021

JWST Noise Floor. II. Systematic Error Sources in JWST NIRCam Time Series

The James Webb Space Telescope (JWST) holds great promise for characterizing atmospheres of transiting exoplanets, potentially providing insights into Earth-sized planets within the habitable zones of M-dwarf host stars if photon-limited performance can be achieved. Here, we discuss the systematic error sources that are expected to be present in grism time-series observations with the NIRCam instrument. We find that pointing jitter and high-gain antenna moves in addition to the detectors' subpixel crosshatch patterns will produce relatively small variations (less than 6 parts per million, ppm). The time-dependent aperture losses due to thermal instabilities in the optics can also be kept to below 2 ppm. To achieve these low noise values, it is important to employ a sufficiently large (more than 1farcs1) extraction aperture. Persistence due to charge-trapping will have a minor (less than 3 ppm) effect on the time series 20 minutes into an exposure and is expected to play a much smaller role than it does for the Hubble Space Telescope WFC3 detectors. We expect detector temperature fluctuations to contribute less than 3 ppm. In total, our estimated noise floor from known systematic error sources is only 9 ppm per visit. We urge caution, however, because unknown systematic error sources could be present in flight and will only be measurable on astrophysical sources such as quiescent stars. We find that reciprocity failure may introduce a perennial instrument offset at the 40 ppm level, so corrections may be needed when a multi-instrument multi-observatory spectrum is stitched together over wide wavelength ranges.

Everett Schlawin↗
NASA NTRS2016

Jwst from Below: An Overview of the Construction of the James Webb Space Telescope, Interesting Metrology, and Cryogenic-Vacuum Testing

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 guider. The SIs are mounted to a composite metering structure. The SI and guider units are integrated to the ISIM structure and optically tested at NASA Goddard Space Flight Center as a suite using a telescope simulator (Optical Telescope Element SIMulator; OSIM). OSIM is a full field, cryogenic JWST telescope simulator. SI performance, including alignment and wavefront error, is evaluated using OSIM. This is an overview presentation to undergraduate students and other personnel at the University of Richmond, planned for 12 Oct, 2016. It uses material previously released by NASA on the Internet (e.g., via Flickr) or at engineering conferences (e.g., SPIE). This presentation provides an overview of the status of the project, with an emphasis on optics and measurement.

instrument development↗
NASA NTRS2008

JWST ISIM Harness Thermal Evaluation

The James Webb Space Telescope (JWST) will be a large infrared telescope with a 6.5-meter primary mirror. Launch is planned for 2013. JWST wl1 be the premier observatory of the next decade serving thousands of astronomers worldwide. The Integrated Science Instrument Module (ISIM) is the unit that will house thc four main JWST instruments. The ISIM enclosure passively cooled to 37 Kelvin and has a tightly managed thermal budget. A significant portion of the ISIM heat load is due to parasitic heat gains from the instrument harnesses. These harnesses provide a thermal path from the Instrument Electronics Control (IEC) to the ISIM. Because of the impact of this load to the ISIM thermal design, understanding the harness parasitic heat gains is critical. To this effect, a thermal test program has been conducted in order to characterize these parasitic loads and verify harness thermal models. Recent parasitic heat loads tests resulted in the addition of a dedicated multiple stage harness radiator. In order for the radiator to efficiently reject heat from the harness, effective thermal contact conductance values for multiple harnesses had to be determined. This presentation will describe the details and the results of this test program.

Kobel, Mark↗
NASA NTRS2009

Non-invasive Optical End-to-End Test of a Large TMA Telescope (JWST) from the Intermediate Focus

The James Webb Space Telescope (JWST) requires testing of the full optical system in a cryogenic vacuum environment before launch. Challenges with the telescope architecture and the test environment lead to placing removable optical test sources at the Cassegrain intermediate focus of the Telescope. The Science Instrument suite will be used to align the telescope and to verify the wavefront error. The Science Instruments capture test images that are analyzed using focus diverse phase retrieval. The wavefront sensing algorithms have the large dynamic range required to measure the relatively small wavefronts of interest in the presence of the large aberrations resulting from the off-axis source locations at the intermediate focus. These inherent aberrations of the off-axis design are removed analytically from the measured data. The test design and in-situ wavefront sensing process enables a number of tests to verify the alignment and optical quality of the system.

Whitman, Tony↗
NASA NTRS2018

Developing Controlled Conductive Boundaries for JWST Cryogenic Testing

In 2017, the James Webb Space Telescope (JWST) underwent functional testing and optical metrology verification of the combined Optical Telescope Element and Integrated Science Instrument Module (OTIS) under cryogenic vacuum conditions in Chamber A at the Johnson Space Center. Maintaining flight-like thermal boundary conditions was a critical requirement for optical testing and required unique and challenging Ground Support Equipment (GSE) design solutions. Two such GSE systems, the Integrated Science Instrument Module (ISIM) Precool Straps and the Hardpoint Struts were direct conduction interfaces to the flight hardware. Hardware safety during cooldown required detailed design of their conductivity, and thermal balance testing required "zero-Q" (0-Q) heater implementation to bring the heat flow to zero, thereby cutting off these non-flight conductive links after operating temperatures were achieved. This paper describes the design considerations and approach implemented to achieve the required flight hardware cool down and return to ambient conditions, ensure flight hardware safety, and minimize the non-flight-like heat flows to or from the observatory during cryo-stable testing.

Cooke, D.↗
NASA NTRS2018

Developing Controlled Conductive Boundaries for JWST Cryogenic Testing

In 2017, the James Webb Space Telescope (JWST) underwent functional testing and optical metrology verification of the combined Optical Telescope Element and Integrated Science Instrument Module (OTIS) under cryogenic vacuum conditions in Chamber A at the Johnson Space Center. Maintaining flight-like thermal boundary conditions was a critical requirement for optical testing and required unique and challenging Ground Support Equipment (GSE) design solutions. Two such GSE systems, the Integrated Science Instrument Module (ISIM) Precool Straps and the Hardpoint Struts were direct conduction interfaces to the flight hardware. Hardware safety during cooldown required detailed design of their conductivity, and thermal balance testing required zero-Q (0-Q) heater implementation to bring the heat flow to zero, thereby cutting off these non-flight conductive links after operating temperatures were achieved. This paper describes the design considerations and approach implemented to achieve the required flight hardware cool down and return to ambient conditions, ensure flight hardware safety, and minimize the non-flight-like heat flows to or from the observatory during cryo-stable testing.

Cooke, Dwight A.↗
NASA NTRS2020

Preparing the JWST Observatory for Science Observations

The James Webb Space Telescope (JWST) is a large (6.5 m) near-and mid-infrared telescope scheduled for launch in 2021. JWST will be used to explore fundamental questions in astrophysics and planetary science, including the evolution of galaxies, the first light of stars, the formation of stars and planets as well as the characterization of exoplanets. To achieve these scientific goals, NASA and its international partners, the Canadian Space Agency (CSA) and the European Space Agency (ESA), have developed four science instruments for JWST and have prepared detailed commissioning plans for each. The NASA Project Science team has also outlined activities to characterize the performance of the Observatory as a whole. These activities include: 1) monitoring of the instrument and telescope cooldown for contamination mitigation; 2) measurements of straylight and other backgrounds for validation of the JWST stray light models as well as instrument background subtraction algorithms; 3) characterization of optical thermal distortion between its hot and cold telescope pointings within the observable field of regard and 4) trending of observatory performance parameters. Each of these activities has been planned in close collaboration with the observatory wavefront, commissioning planning, and science instrument teams. Here we present the plans for these activities, the expected results and how they will impact future guest observer (GO) proposals and JWST science community

Erin C Smith↗
NASA NTRS2015

The JWST Science Instrument Payload: Mission Context and Status

The James Webb Space Telescope (JWST) is the scientific successor to the Hubble Space Telescope. It is a cryogenic infrared space observatory with a 25 sq m aperture (6 m class) telescope that will achieve diffraction limited angular resolution at a wavelength of 2 micrometers. The science instrument payload includes four passively cooled near-infrared instruments providing broad- and narrow-band imagery, coronography, as well as multi-object and integral-field spectroscopy over the 0.6 is less than lambda is less than 5.0 micrometers spectrum. An actively cooled mid-infrared instrument provides broad-band imagery, coronography, and integral-field spectroscopy over the 5.0 is less than lambda is less than 29 micrometers spectrum. The JWST is being developed by NASA, in partnership with the European and Canadian Space Agencies, as a general user facility with science observations proposed by the international astronomical community in a manner similar to the Hubble Space Telescope. Technology development and mission design are complete. The science instrument payload is in the final stage of testing ahead of delivery for integration with the telescope during early 2016. The JWST is on schedule for launch during 2018.

narrow-band imagery↗
NASA NTRS2014

The JWST Science Instrument Payload: Mission Context and Status

The James Webb Space Telescope (JWST) is the scientific successor to the Hubble Space Telescope. It is a cryogenic infrared space observatory with a 25 sq m aperture (6 m class) telescope that will achieve diffraction limited angular resolution at a wavelength of 2 microns. The science instrument payload includes four passively cooled near-infrared instruments providing broad- and narrow-band imagery, coronography, as well as multi-object and integral-field spectroscopy over the 0.6 < lambda < 5.0 microns spectrum. An actively cooled mid-infrared instrument provides broad-band imagery, coronography, and integral-field spectroscopy over the 5.0 < lambda < 29 microns spectrum. The JWST is being developed by NASA, in partnership with the European and Canadian Space Agencies, as a general user facility with science observations to be proposed by the international astronomical community in a manner similar to the Hubble Space Telescope. Technology development and mission design are complete. Construction, integration and verification testing is underway in all areas of the program. The JWST is on schedule for launch during 2018.

cryogenic infrared space observatory↗
NASA NTRS2022

How NASA decided Webb was ready: Inside the risk assessment

Every do-it-yourselfer knows how hard it can be to declare a project complete. Will another turn of the bolt or brushstroke make things better or worse? That was roughly the choice NASA faced a year before the Dec. 25 launch of the James Webb Space Telescope. Would more testing close more technical risks in the nearly $10 billion project or create new ones? In the end, NASA decided against more testing. NASA’s Jesse Leitner and Tupper Hyde describe the assessment they performed.

JWST↗
NASA NTRS2016

Characterization of the JWST Pathfinder Mirror Dynamics Using the Center of Curvature Optical Assembly (CoCOA)

The JWST (James Webb Space Telescope) Optical Telescope Element (OTE) consists of a 6.6 meter clear aperture, 18-segment primary mirror, all-reflective, three-mirror anastigmat operating at cryogenic temperatures. To verify performance of the primary mirror, a full aperture center of curvature optical null test is performed under cryogenic conditions in Chamber A at NASA Johnson Space Center using an instantaneous phase measuring interferometer. After phasing the mirrors during the JWST Pathfinder testing, the interferometer is utilized to characterize the mirror relative piston and tilt dynamics under different facility configurations. The correlation between the motions seen on detectors at the focal plane and the interferometer validates the use of the interferometer for dynamic investigations. The success of planned test hardware improvements will be characterized by the multi-wavelength interferometer (MWIF) at the Center of Curvature Optical Assembly (CoCOA).

Wells, Conrad↗
NASA NTRS2016

Characterization of the JWST Pathfinder Mirror Dynamics Using the Center of Curvature Optical Assembly (CoCOA)

The JWST (James Webb Space Telescope) Optical Telescope Element (OTE) consists of a 6.6 meter clear aperture, 18-segment primary mirror, all-reflective, three-mirror anastigmat operating at cryogenic temperatures. To verify performance of the primary mirror, a full aperture center of curvature optical null test is performed under cryogenic conditions in Chamber A at NASA Johnson Space Center using an instantaneous phase measuring interferometer. After phasing the mirrors during the JWST Pathfinder testing, the interferometer is utilized to characterize the mirror relative piston and tilt dynamics under different facility configurations. The correlation between the motions seen on detectors at the focal plane and the interferometer validates the use of the interferometer for dynamic investigations. The success of planned test hardware improvements will be characterized by the multi-wavelength interferometer (MWIF) at the Center of Curvature Optical Assembly (CoCOA).

Wells, C.↗