Introduction The fully integrated Advanced Camera for Surveys (ACS) (Ford et al. 1998, SPIE Vol. 3356, 234), suc- cessfully installed in the Hubble Space Telescope (HST) in early March 2002, underwent a series of ground calibration tests at Ball Aerospace and Technologies Corporation (BATC) and at the Goddard Space Flight Center (GSFC) to verify its performance and flight readiness (Hartig et al. 1998, SPIE Vol. 3356, 321). The flight build detectors were installed in late 2000 and the majority of the flight quality data were acquired in the following year. The activities revolved around several major campaigns designed to characterize the flight build detectors and the optical and ultraviolet channels of the instrument and to verify the contract-end-item specifications. In the following, we briefly describe the different ground-based activities.
NASA’s James Webb Space Telescope (JWST) is a 6.5 m diameter, segmented, deployable telescope for cryogenic infrared space astronomy (~40 K). The JWST Observatory architecture includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM) element that contains four science instruments (SIs), including a guider. The SI and guider units are integrated to the ISIM structure and optically tested at NASA Goddard Space Flight Center as an instrument suite using a telescope simulator (Optical Telescope Element SIMulator; OSIM). OSIM is a high-fidelity, cryogenic JWST telescope 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 optomechanical 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. The comprehensive optical test plans include drafting OSIM source configurations for thousands of exposures ahead of the start of a cryogenic test campaign. We describe how we predicted the performance of OSIM light sources illuminating the ISIM detectors to aide in drafting these optical tests before a test campaign began. We also discuss the actual challenges and successes of those exposure predictions encountered during a test campaign to fulfill the demands of the ISIM optical performance verification.
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.
JWST/NIRISS has a non-redundant aperture mask (NRM) for use with its F380M, F430M, F480M and F277W filters. In addition to high-resolution imaging with moderate contrast, the NRM provides better astrometric accuracy over a wide field of view than regular imaging. We investigate the accuracy achievable with the NRM by using an image-plane algorithm to analyze the PSFs of a point source that were obtained at a fixed pixel location with sub-pixel dithers during the second Cryo-Vacuum test campaign of the Integrated Science Instrument Module at NASA’s Goddard Space Flight Center. Astrometry of brown dwarfs with the NRM will be sensitive to the presence of terrestrial planets and can be used to probe the architecture of planetary systems around these objects.
JWST’s Near-Infrared Imager and Slitless Spectrograph (NIRISS) includes an Aperture Masking Interferometry (AMI) mode designed to be used between 2.7μm and 4.8μm. At these wavelengths, it will have the highest angular resolution of any mode on JWST, and, for faint targets, of any existing or planned infrastructure. NIRISS AMI is uniquely suited to detect thermal emission of young massive planets and will permit the characterization of the mid-IR flux of exoplanets discovered by the GPI and SPHERE adaptive optics surveys. It will also directly detect massive planets found by GAIA through astrometric accelerations, providing the first opportunity ever to get both a mass and a flux measurement for non-transiting giant planets. NIRISS AMI will also enable the study of the nuclear environment of AGNs.
The James Webb Space Telescope (JWST) Near IR Imager and Slitless Spectrograph (NIRISS) has a seven hole non-redundant mask (NRM) in its pupil. The interferometric resolution obtained with the NRM provides a reliable measure of the magnification, position, and distribution of the PSF. The NRM image is Nyquist sampled at 4μm and operates with medium-band filters F380M, F430M, and F480M on NIRISS. We discuss cryovac CV1RR early NRM test data on the instrument. An image-plane, point-source model serves as a predictive tool for the NRM PSF, whose fine scale features' relative intensity can be used to measure detector non-linearities and determine its plate scale and rotation. We present a conservative estimate of NRM's wide-field astrometric performance. We present an analysis of the NIRISS plate scale and detector response as well as a prediction for NRM on-sky performance, taking into account measured intrapixel sensitivities, at fields, and detector linearity corrections.
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 Aperture Masked Interferometry (AMI) mode on JWST-NIRISS is implemented as a 7-hole, 15% throughput, non-redundant mask (NRM) that operates with 5-8% bandwidth filters at 3.8, 4.3, and 4.8 microns. We present refined estimates of AMI's expected point-source contrast, using realizations of noise matched to JWST pointing requirements, NIRISS detector noise, and Rev-V JWST wavefront error models for the telescope and instrument. We describe our point-source binary data reduction algorithm, which we use as a standardized method to compare different observational strategies. For a 7.5 magnitude star we report a 10-a detection at between
8.7 and 9.2 magnitudes of contrast between 100 mas to 400 mas respectively, using closure phases and squared visibilities in the absence of bad pixels, but with various other noise sources. With 3% of the pixels unusable, the expected contrast drops by about 0.5 magnitudes. AMI should be able to reach targets as bright as M=5. There will be significant overlap between Gemini-GPI and ESO-SPHERE targets and AMI's search space, and a complementarity with NIRCam's coronagraph. We also illustrate synthesis imaging with AMI, demonstrating an imaging dynamic range of 25 at 100 mas scales. We tailor existing radio interferometric methods to retrieve a faint bar across a bright nucleus, and explain the similarities to synthesis imaging at radio wavelengths. Modest contrast observations of dusty accretion flows around AGNs will be feasible for NIRISS AMI. We show our early results of image-plane deconvolution as well. Finally, we report progress on an NRM-inspired approach to mitigate mission-level risk associated with JWST's specialized wavefront sensing hardware. By combining narrow band and medium band Nyquist-sampled images taken with a science camera we can sense JWST primary mirror segment tip-tilt to lOmas, and piston to a few nm. We can sense inter-segment piston errors of up to 5 coherence lengths of the broadest bandpass filter used ( 250-500 0m depending on the filters). Our approach scales well with an increasing number of segments, which makes it relevant for future segmented-primary space missions.
The Fine Guidance Sensor (FGS) of the James Webb Space Telescope (JWST) features a tunable filter imager (TFI)
module covering the wavelength range from 1.5 to 5.0 μm at a resolving power of ~100 over a field of view of
2.2'×2.2'. TFI also features a set of occulting spots and a non-redundant mask for high-contrast imaging. This paper
presents the current status of the TFI development. The instrument is currently under its final integration and test phase.
In ground testing of the Hubble Space Telescope Wide Field Camera 3 (HST/WFC3), the CCDs of its UV/visible channel exhibited an unanticipated quantum efficiency hysteresis (QEH) behavior. The QEH first manifested itself as an occasionally observed contrast in response across the format of the CCDs, with an amplitude of typically 0.1-0.2% or less at the nominal -83°C operating temperature, but with contrasts of up to 3-5% observed at warmer temperatures. The behavior has been replicated in the laboratory using flight spare detectors and has been found to be related to an initial response deficiency of ~5% amplitude when the CCDs
are cooled with no illumination. A visible light flat-field (540nm) with a several times full-well signal level is found to pin the detector response at both optical (600nm) and near-UV (230nm) wavelengths, suppressing the QEH behavior. We have characterized the timescale for the detectors to become unpinned (days for significant
response loss at -83°C and have developed a protocol to stabilize the response in flight by flashing the WFC3 CCDs with the instrument's internal calibration system.
The Wide-field Camera 3 (WFC3) is a fourth-generation instrument planned for installation in Hubble Space Telescope
(HST). Designed as a panchromatic camera, WFC3's UVIS and IR channels will complement the other instruments onboard
HST and enhance the observatory's scientific performance. UVIS images are obtained via two 4096×2051 pixel
e2v CCDs while the IR images are taken with a 1024×1024 pixel HgCdTe focal plane array from Teledyne Imaging
Sensors. Based upon characterization tests performed at NASA/GSFC, the final flight detectors have been chosen and
installed in the instrument. This paper summarizes the performance characteristics of the WFC3 flight detectors based
upon component and instrument-level testing in ambient and thermal vacuum environments.
Wide Field Camera 3 (WFC3), a panchromatic imager developed for the Hubble Space Telescope (HST), is fully
integrated with its flight detectors and has undergone several rounds of ground testing and calibration at Goddard Space
Flight Center (GSFC). The testing processes are highly automated, with WFC3 and the optical stimulus, which is used to
provide external targets and illumination, being commanded by coordinated computer scripts. All test data are captured
and stored in the long-term Hubble Data Archive. A full suite of instrument characterization and calibration tests has
been performed, including the measurement of key detector properties such as dark current, read noise, flat field
response, gain, linearity, and persistence, as well as instrument-level properties like total system throughput, imaging
quality and encircled energy, grism dispersions, IR thermal background, and image stability. Nearly all instrument
characteristics have been shown to meet or exceed expectations and requirements.
The Advanced camera for Surveys (ACS), installed in the Hubble Space telescope in March 2002, has significantly extended HST’s deep, survey imaging capabilities. ACS comprises three cameras: the Wide Field Camera (WFC) is designed for deep, near-IR survey imaging programs; the High Resolution Camera (HRC) is a high angular resolution imager/coronagraph, which fully samples the HST point spread function in the visible; and the Solar Blind Camera (SBC) is a far-UV imager. ACS has met, or exceeded all of its key performance specification. In this paper we briefly review the in-flight performances of the instrument's CCD detectors. We present an overview of the performance of the ACS CCD detectors, based on the first year of flight science operations.
The Advanced Camera for Surveys (ACS), installed in the Hubble Space Telescope in March 2002, has significantly extended HST's imaging capabilities. We describe the on-orbit optical alignment procedures and results, detailing the excellent image quality performance achieved. Comparison is made with the instrument specifications, ground test results and published performance expectations. The residual aberration content over the field of each channel is described and compared with the optical model, and various other performance measures, including sharpness and encircled energy are treated. The effects of the telescope focus oscillations due to thermal variations ("breathing") and image positional stability are also discussed.
The ACS solar blind channel (SBC) is a photon-counting MAMA detector capable of producing two-dimensional imaging in the UV at wavelengths 1150-1700 Angstroms, with a field of view (FOV) of 31" × 35". We describe the on-orbit performance of the ACS/SBC from an analysis of data obtained from the service mission observatory verification (SMOV) programs. Our summary includes assessment of the point-source image quality and point spread function (PSF) over the SBC FOV, the dark current measurements, the characteristics of the flat fields, fold analysis, throughput, and the UV sensitivity monitor to check for contamination. Where appropriate, a comparison with pre-launch calibration data will also be made.
We present an overview of the Advanced Camera for Surveys (ACS) CCD detectors performance based on the ground testing and the calibration observations taken during the first four months of ACS operation. ACS has been installed into the Hubble Space Telescope in March 2002 and consists of three different cameras. Two of them employ CCD detectors: the Wide Field Camera a mosaic of two 4096 x 2048 CCDs and the High Resolution Camera a single 1024 x 1024 chip. A review of the on-orbit performance is presented here and also comparison is made with the instrument specifications, published performance expectation and ground test results.
We present an overview of the ACS on-orbit performance based on the calibration observations taken during the first three months of ACS operations. The ACS meets or exceeds all of its important performance specifications. The WFC and HRC FWHM and 50% encircled energy diameters at 555 nm are 0.088" and 0.14", and 0.050" and 0.10". The average rms WFC and HRC read noises are 5.0 e- and 4.7 e-. The WFC and HRC average dark currents are ~ 7.5 and ~ 9.1 e-/pixel/hour at their operating temperatures of - 76°C and - 80°C. The SBC + HST throughput is 0.0476 and 0.0292 through the F125LP and F150LP filters. The lower than expected SBC operating temperature of 15 to 27°C gives a dark current of 0.038 e-/pix/hour. The SBC just misses its image specification with an observed 50% encircled energy diameter of 0.24" at 121.6 nm. The ACS HRC coronagraph provides a 6 to 16 direct reduction of a stellar PSF, and a ~1000 to ~9000 PSF-subtracted reduction, depending on the size of the coronagraphic spot and the wavelength. The ACS grism has a position dependent dispersion with an average value of 3.95 nm/pixel. The average resolution λ/Δλ for stellar sources is 65, 87, and 78 at wavelengths of 594 nm, 802 nm, and 978 nm.