KEYWORDS: Diffractive optical elements, Astrobiology, Telescopes, Space observatories, Planets, Space telescopes, James Webb Space Telescope, Space operations, Stars, Satellites, Optical fabrication
We describe progress on the Nautilus Space Observatory concept that is enabled by novel, very large (8.5mdiameter), ultralight-weight, multi-order diffractive lenses that can be cost-effectively replicated. The scientific goal of Nautilus is the rigorous statistical exploration of one thousand potentially life-bearing planets and the assessment of the diversity of exo-earths. Here we review the science requirements and key design features of Nautilus. The new optical technology (MODE lenses) at the heart of the Nautilus telescopes also poses exciting new optical fabrication and metrology challenges. We will summarize these challenges and provide an overview of emerging solutions.
The direct characterization of exoplanetary systems with high contrast imaging is among the highest priorities for the broader exoplanet community. As large space missions will be necessary for detecting and characterizing exo-Earth twins, developing the techniques and technology for direct imaging of exoplanets is a driving focus for the community. For the first time, JWST will directly observe extrasolar planets at mid-infrared wavelengths beyond 5 μm, deliver detailed spectroscopy revealing much more precise chemical abundances and atmospheric conditions, and provide sensitivity to analogs of our solar system ice-giant planets at wide orbital separations, an entirely new class of exoplanet. However, in order to maximise the scientific output over the lifetime of the mission, an exquisite understanding of the instrumental performance of JWST is needed as early in the mission as possible. In this paper, we describe our 55-hour Early Release Science Program that will utilize all four JWST instruments to extend the characterisation of planetary mass companions to ∼15-20 μm as well as image a circumstellar disk in the mid-infrared with unprecedented sensitivity. Our program will also assess the performance of the observatory in the key modes expected to be commonly used for exoplanet direct imaging and spectroscopy, optimize data calibration and processing, and generate representative datasets that will enable a broad user base to effectively plan for general observing programs in future cycles.
The Coronagraphic Debris Exoplanet Exploring Payload (CDEEP) is a Small-Sat mission concept for high contrast imaging of circumstellar disks. CDEEP is designed to observe disks in scattered light at visible wavelengths at a raw contrast level of 10-7 per resolution element (10-8 with post processing). This exceptional sensitivity will allow the imaging of transport dominated debris disks, quantifying the albedo, composition, and morphology of these low-surface brightness disks. CDEEP combines an off-axis telescope, microelectromechanical systems (MEMS) deformable mirror, and a vector vortex coronagraph (VVC). This system will require rigorous testing and characterization in a space environment. We report on the CDEEP mission concept, and the status of the vacuum-compatible CDEEP prototype testbed currently under development at the University of Arizona, including design development and the results of simulations to estimate performance.
We describe a novel space observatory concept that is enabled by very large (8.5m-diameter), ultralight-weight multi-order diffractive lenses that can be cost-effectively replicated. The observatory utilizes an array of identical telescopes with a total combined light collecting area equivalent to that of a 50m-diameter telescope. Here we review the capabilities of a Nautilus unit telescope, the observatory concept, and the technology readiness of the key components. The Nautilus Observatory is capable of surveying a thousand transiting exo-earth candidates to 300 pc for biosignatures, enabling a rigorous statistical exploration of potentially life-bearing planets and the diversity of exo-earths.
KEYWORDS: Point spread functions, Stars, Coronagraphy, Speckle, Sensors, Telescopes, Signal to noise ratio, Space operations, Hubble Space Telescope, Charge-coupled devices
The Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) contains the only currently operating coronagraph in space that is not trained on the Sun. In an era of extreme-adaptive-optics-fed coronagraphs, and with the possibility of future space-based coronagraphs, we re-evaluate the contrast performance of the STIS CCD camera. The 50CORON aperture consists of a series of occulting wedges and bars, including the recently commissioned BAR5 occulter. We discuss the latest procedures in obtaining high-contrast imaging of circumstellar disks and faint point sources with STIS. For the first time, we develop a noise model for the coronagraph, including systematic noise due to speckles, which can be used to predict the performance of future coronagraphic observations. Further, we present results from a recent calibration program that demonstrates better than 10 − 6 point-source contrast at 0.6″, ranging to 3 × 10 − 5 point-source contrast at 0.25″. These results are obtained by a combination of subpixel grid dithers, multiple spacecraft orientations, and postprocessing techniques. Some of these same techniques will be employed by future space-based coronagraphic missions. We discuss the unique aspects of STIS coronagraphy relative to ground-based adaptive-optics-fed coronagraphs.
The EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE) science mission concept uses a visible-wavelength phase-induced amplitude apodization (PIAA) coronagraph to enable high-contrast imaging of circumstellar debris systems and some giant planets at angular separations reaching into the habitable zones of some of the nearest stars. We report on the experimental results obtained in the vacuum chamber at the Lockheed Martin Advanced Technology Center in 10% broadband light centered about 650 nm, with a median contrast of 1×10−5 between 1.2 and 2.0λ/D simultaneously with 3×10−7 contrast between 2 and 11λ/D for a single-sided dark hole using a deformable mirror (DM) upstream of the PIAA coronagraph. These results are stable and repeatable as demonstrated by three measurement runs with DM settings set from scratch and maintained on the best 90% out of the 1000 collected frames. We compare the reduced experimental data with simulation results from modeling observed experimental limits. The observed performance is consistent with uncorrected low-order modes not estimated by the low-order wavefront sensor. Modeled sensitivity to bandwidth and residual tip/tilt modes is well matched to the experiment.
The capabilities of a high (∼10−9 resel−1) contrast narrow-field coronagraphic instrument (CGI) on a space-based WFIRST-C or probe-class EXO-C/S mission are particularly and importantly germane to symbiotic studies of the systems of circumstellar material from which planets have emerged and interact with throughout their lifetimes. The small particle populations in “disks” of co-orbiting materials can trace the presence of planets through dynamical interactions that perturb the spatial distribution of light-scattering debris, which is detectable at visible wavelengths and resolvable with a WFIRST-C or EXO-S/C CGI. Herein, we (1) present the scientific case to study the formation, evolution, architectures, diversity, and properties of the material in the planet-hosting regions of nearby stars; (2) discuss how a CGI under current conception can uniquely inform and contribute to those investigations; (3) consider the applicability of CGI-anticipated performance for circumstellar debris system studies; (4) investigate, through WFIRST CGI image simulations, the anticipated interpretive fidelity and metrical results from specific representative zodiacal debris disk observations; (5) comment on specific observational modes and methods germane to and augmenting circumstellar debris system observations; and (6) present a case for augmenting future CGI instrumentation with the capability to obtain full linear-Stokes imaging polarimetery, which greatly benefits characterization of the material properties of circumstellar dust and exoplanet atmospheres (discussed in other studies).
This paper is the fourth in the series on the technology development for the EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer) mission concept, which in 2011 was selected by NASA's Explorer program for technology development (Category III). EXCEDE is a 0.7m space telescope concept operating with a Phase Induced Amplitude Apodization (PIAA) Coronagraph and a Deformable Mirror (DM) to create a "dark-hole" or a region of high-contrast starlight suppression at the focal plane to allow direct imaging of exoplanets. This will allow fundamental science in the form of direct detection and spatial resolution of low surface brightness circumstellar debris disks, and the direct imaging of giant planets with angular separations as close in as the habitable zone of the host star. Thus, EXCEDE can function as both a scientific and technological precursor for any mission capable of imaging exo-Earths.
Previously, we have reported experimental results on the first milestone, the demonstration of EXCEDE contrast in monochromatic light in air and more recently in vacuum. In this paper, we report on the procedure and the experimental results obtained for our second milestone demonstration of the EXCEDE starlight suppression system carried in a vacuum chamber at the Lockheed Martin Advanced Technology Center. This includes high contrast performance demonstrations at 1.2 λD, which includes a lab demonstration of 1x10-5 median contrast between 1.2 and 2.0 λD simultaneously with 3x10-7 median contrast between 2 and 11 λD in 10% bandwidth polychromatic light centered at 650 nm for a single-sided dark zone. The results are stable and repeatable as demonstrated by three measurement runs with DM settings set from scratch and maintained on the best 90% out of the 1000 collected frames per run. We compare reduced experimental data with simulation results from modeling experimental limits.
In this paper we describe the opto-mechanical design, tolerance error budget an alignment strategies used to build the Starlight Suppression System (SSS) for the Exoplanetary Circumstellar Environments and Disk Explorer (EXCEDE) NASA’s mission. EXCEDE is a highly efficient 0.7m space telescope concept designed to directly image and spatially resolve circumstellar disks with as little as 10 zodis of circumstellar dust, as well as large planets. The main focus of this work was the design of a vacuum compatible opto-mechanical system that allows remote alignment and operation of the main components of the EXCEDE. SSS, which are: a Phase Induced Amplitude Apodization (PIAA) coronagraph to provide high throughput and high contrast at an inner working angle (IWA) equal to the diffraction limit (IWA = 1.2 l/D), a wavefront (WF) control system based on a Micro-Electro-Mechanical-System deformable mirror (MEMS DM), and low order wavefront sensor (LOWFS) for fine pointing and centering. We describe in strategy and tolerance error budget for this system, which is especially relevant to achieve the theoretical performance that PIAA coronagraph can offer. We also discuss the vacuum cabling design for the actuators, cameras and the Deformable Mirror. This design has been implemented at the vacuum chamber facility at Lockheed Martin (LM), which is based on successful technology development at the Ames Coronagraph Experiment (ACE) facility.
For the technology development of the mission EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer)—a 0.7 m telescope equipped with a Phase-Induced Amplitude Apodization Coronagraph (PIAA- C) and a 2000-element MEMS deformable mirror, capable of raw contrasts of 10−6 at 1.2 λ/D and 10−7 above 2 λ /D — we developed two test benches simulating its key components, one in air, the other in vacuum. To achieve this level of contrast, one of the main goals is to remove low-order aberrations, using a Low-Order WaveFront Sensor (LOWFS). We tested this key component, together with the coronagraph and the wavefront control, in air at NASA Ames Research Center and in vacuum at Lockheed Martin. The LOWFS, controlling tip/tilt modes in real time at 1 kHz, allowed us to reduce the disturbances in air to 10−3 λ/D rms, letting us achieve a contrast of 2.8×10−7 between 1.2 and 2 λ/D. Tests are currently being performed to achieve the same or a better level of correction in vacuum. With those results, and by comparing them to simulations, we are able to deduce its performances on different coronagraphs— different sizes of telescopes, inner working angles, contrasts, etc. — and therefore study its contribution beyond EXCEDE.
KEYWORDS: Point spread functions, Stars, Coronagraphy, Databases, Planets, Space telescopes, Telescopes, Image processing, Signal to noise ratio, Target detection
We are currently conducting a comprehensive and consistent re-processing of archival HST-NICMOS coronagraphic surveys using advanced PSF subtraction methods, entitled the Archival Legacy Investigations of Circumstellar Environments program (ALICE, HST/AR 12652). This virtual campaign of about 400 targets has already produced numerous new detections of previously unidentified point sources and circumstellar structures. We present five newly spatially resolved debris disks revealed in scattered light by our analysis of the archival data. These images provide new views of material around young solar-type stars at ages corresponding to the period of terrestrial planet formation in our solar system. We have also detected several new candidate substellar companions, for which there are ongoing followup campaigns (HST/WFC3 and VLT/SINFONI in ADI mode). Since the methods developed as part of ALICE are directly applicable to future missions (JWST, AFTA coronagraph) we emphasize the importance of devising optimal PSF subtraction methods for upcoming coronagraphic imaging missions. We describe efforts in defining direct imaging high-level science products (HLSP) standards that can be applicable to other coronagraphic campaigns, including ground-based (e.g., Gemini Planet Imager), and future space instruments (e.g., JWST). ALICE will deliver a first release of HLSPs to the community through the MAST archive at STScI in 2014.
This paper is the third in the series on the technology development for the EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer) mission concept, which in 2011 was selected by NASA's Explorer program for technology development (Category III). EXCEDE is a 0.7m space telescope concept designed to achieve raw contrasts of 1e6 at an inner working angle of 1.2 l/D and 1e7 at 2 l/D and beyond. This will allow it to directly detect and spatially resolve low surface brightness circumstellar debris disks as well as image giant planets as close as in the habitable zones of their host stars. In addition to doing fundamental science on debris disks, EXCEDE will also serve as a technological and scientific precursor for any future exo-Earth imaging mission. EXCEDE uses a Starlight Suppression System (SSS) based on the PIAA coronagraph, enabling aggressive performance. Previously, we reported on the achievement of our first milestone (demonstration of EXCEDE IWA and contrast in monochromatic light) in air. In this presentation, we report on our continuing progress of developing the SSS for EXCEDE, and in particular (a) the reconfiguration of our system into a more flight-like layout, with an upstream deformable mirror and an inverse PIAA system, and (b) testing this system in a vacuum chamber, including IWA, contrast, and stability performance. Even though this technology development is primarily targeted towards EXCEDE, it is also germane to any exoplanet direct imaging space-based telescopes because of the many challenges common to different coronagraph architectures and mission requirements. This work was supported in part by the NASA Explorer program and Ames Research Center, University of Arizona, and Lockheed Martin SSC.
The detection of extrasolar planets, using both space- and ground-based telescopes, is one of the most exciting fields in astronomy today, with the ultimate goal of the direct direction of earth-like planets in the habitable zone. It is with this vision that the explorer mission EXCEDE selected by NASA for technology development, is designed. EXCEDE (Exoplanetary Circumstellar Environment and Disk Explorer) is composed of a 0.7 m telescope equipped with a Phase-Induced Amplitude Apodization Coronagraph (PIAA-C) and a 2000-element MEMS deformable mirror, capable of raw contrasts of 10-6 at 1.2 λ/D and 10-7 above 2 λ/D. Obtaining these contrasts requires precise wavefront control algorithms used in conjuncture with deformable mirrors. Unlike other optical systems, where the goal is to obtain the best wavefront, we aim at canceling the diffracted light coming from the parent star in a specific region to increase signal-to-noise of the planet. To do so, we use wavefront control techniques, such as Electric Field Conjugation (EFC) and speckle nulling, already developed and soon to be operational on 8-m class telescopes. One caveat is that the demonstration was done at moderate separations (r> 3λ/D).In this paper, we present tricks and techniques to perform high-contrast imaging at 1.2 λ/d using the NASA Ames Coronagraph Experiment testbed.
Coronagraph technology is advancing and promises to enable space telescopes capable of directly detecting low surface brightness circumstellar debris disks as well as giant planets as close as in the habitable zones of their host stars. One mission capable of doing this is called EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer), which in 2011 was selected by NASA's Explorer program for technology development (Category III). EXCEDE is a 0.7m space telescope concept designed to achieve raw contrasts of 10-6 at an inner working angle of 1.2 λ/D and 10-7 at 2 λ/D and beyond. In addition to doing fundamental science on debris disks, EXCEDE will also serve as a technological and scientific precursor for an exo-Earth imaging mission. EXCEDE uses a Starlight Suppression System (SSS) based on the Phase Induced Amplitude Apodization (PIAA) coronagraph to provide high throughput and high contrast close to the diffraction limit, enabling aggressive performance. We report on our continuing progress of developing the SSS for EXCEDE, including (a) high contrast performance demonstrations at 1.2 λD, which includes a lab demonstration of 2x10-7 median contrast between 1.2 and 2.0 λ/D simultaneously with 6.5x10-8 median contrast between 2 and 4 λ/D in monochromatic light at 655nm, meeting a major milestone in our technology development program; (b) the installation of a new Low Order Wavefront Sensor (LOWFS) which enabled achieving deep contrasts at aggressive inner working angles; (c) implementation of more efficient model-based wavefront control algorithms; and (d) a preliminary broadband contrast result of 6x10-6 contrast at 1.2 λ/D in a 10% band.
The mission EXCEDE (EXoplanetary Circumstellar Environments and Disk Explorer), selected by NASA for technology development, is designed to study the formation, evolution and architectures of exoplanetary systems and characterize circumstellar environments into stellar habitable zones. It is composed of a 0.7 m telescope equipped with a Phase-Induced Amplitude Apodization Coronagraph (PIAA-C) and a 2000-element MEMS deformable mirror, capable of raw contrasts of 10−6 at 1.2 λ/D and 10−7 above 2 λ/D. One of the key challenges to achieve those contrasts is to remove low-order aberrations, using a Low-Order WaveFront Sensor (LOWFS). An experiment simulating the starlight suppression system is currently developed at NASA Ames Research Center, and includes a LOWFS controlling tip/tilt modes in real time at 500 Hz. The LOWFS allowed us to reduce the tip/tilt disturbances to 10−3 λ/D rms, enhancing the previous contrast by a decade, to 8×10−7 between 1.2 and 2 λ/D. A Linear Quadratic Gaussian (LQG) controller is currently implemented to improve even more that result by reducing residual vibrations. This testbed shows that a good knowledge of the low-order disturbances is a key asset for high contrast imaging, whether for real-time control or for post processing.
We present an overview of the EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE), selected by
NASA for technology development and maturation. EXCEDE will study the formation, evolution and architectures of
exoplanetary systems, and characterize circumstellar environments into stellar habitable zones. EXCEDE provides
contrast-limited scattered-light detection sensitivities ~ 1000x greater than HST or JWST coronagraphs at a much
smaller effective inner working angle (IWA), thus enabling the exploration and characterization of exoplanetary
circumstellar disks in currently inaccessible domains. EXCEDE will utilize a laboratory demonstrated high-performance
Phase Induced Amplitude Apodized Coronagraph (PIAA-C) integrated with a 70 cm diameter unobscured aperture
visible light telescope. The EXCEDE PIAA-C will deliver star-to-disk augmented image contrasts of < 10E-8 and a 1.2
λ/D IWA or 0.14” with a wavefront control system utilizing a 2000-element MEMS DM and fast steering mirror.
EXCEDE will provide 0.12” spatial resolution at 0.4 μm with dust detection sensitivity to levels of a few tens of zodis
with two-band imaging polarimetry. EXCEDE is a science-driven technology pathfinder that will advance our
understanding of the formation and evolution of exoplanetary systems, placing our solar system in broader astrophysical
context, and will demonstrate the high contrast technologies required for larger-scale follow-on and multi-wavelength
investigations on the road to finding and characterizing exo-Earths in the years ahead.
Coronagraph technology is advancing and promises to enable space telescopes capable of seeing debris disks as well as
seeing and spectrally characterizing exo-Earths. Recently, NASA's explorer program has selected the EXCEDE
(EXoplanetary Circumstellar Environments and Disk Explorer) mission concept for technology development. EXCEDE
is a 0.7m space telescope concept designed to achieve raw contrasts of 1e-6 at an inner working angle of 1.2 λ/D and 1e-
7 at 2 λ/D. In addition to doing fundamental science on debris disks, EXCEDE will also serve as a technological and
scientific precursor for an exo-Earth imaging mission. EXCEDE uses a Starlight Suppression System (SSS) based on the
Phase Induced Amplitude Apodization (PIAA) coronagraph to provide high throughput and high contrast close to the
diffraction limit, enabling aggressive performance on small telescopes. We report on the latest progress in developing
the SSS and present coronagraphic performance results from our air testbed at NASA Ames. Our results include a lab
demonstration of 1e-5 contrast at 1.2 λ/D, 1.3e-6 contrast at 1.4 λ/D and 2e-8 at 2 λ/D in monochromatic light. In
addition, we discuss tip-tilt instabilities, which are believed to be our main limiting factor at present, and ways of
characterizing them.
KEYWORDS: Planets, Signal to noise ratio, Stars, Coronagraphy, Exoplanets, Jupiter, Device simulation, Imaging systems, Space telescopes, Space operations
The Pupil-mapping Exoplanet Coronagraphic Observer (PECO) medium-class mission concept is a 1.4-m space-based
optical telescope with a high-performance Phase-Induced Amplitude Apodization (PIAA) coronagraph. PECO detects
and characterizes exoplanets and their host systems at 2 λ/D (0.15") separation at high contrast (~1e-10). The optical
design images in 16 filter bands from 400-800 nm, producing simultaneous low-resolution target spectra. PECO will
characterize terrestrial planets in the habitable zones of ~20 nearby F, G, K stars at spectral resolution of R~15, as well
as over a dozen radial-velocity planets and over a hundred gas giants and exozodiacal dust disks. We discuss PECO's
expected science performance and simulated data products over its three-year mission lifetime.
The Pupil mapping Exoplanet Coronagraphic Observer (PECO) mission concept is a 1.4-m telescope aimed at
imaging and characterizing extra-solar planetary systems at optical wavelengths. The coronagraphic method
employed, Phase-Induced Amplitude Apodization or PIAA (a.k.a. pupil mapping) can deliver 1e-10 contrast at
2 lambda/D and uses almost all the starlight that passes through the aperture to maintain higher throughput and
higher angular resolution than any other coronagraph or nuller, making PECO the theoretically most efficient
existing approach for imaging extra-solar planetary systems. PECO's instrument also incorporates deformable
mirrors for high accuracy wavefront control. Our studies show that a probe-scale PECO mission with 1.4 m
aperture is extremely powerful, with the capability of imaging at spectral resolution R≈∠15 the habitable zones
of already known F, G, K stars with sensitivity sufficient to detect planets down to Earth size, and to map
dust clouds down to a fraction of our zodiacal cloud dust brightness. PECO will acquire narrow field images
simultaneously in 10 to 20 spectral bands covering wavelengths from 0.4 to 1.0 μm and will utilize all available
photons for maximum wavefront sensing and imaging/spectroscopy sensitivity. This approach is well suited for
low-resolution spectral characterization of both planets and dust clouds with a moderately sized telescope.
We also report on recent results obtained with the laboratory prototype of a coronagraphic low order wavefront
sensor (CLOWFS) for PIAA coronagraph. The CLOWFS is a key part of PECO's design and will enable high
contrast at the very small PECO inner working angle.
HST provides an unparalleled venue for high contrast imaging which has enabled new observational domains in exo-planet and debris disk imaging. Unburdened by atmospheric 'seeing', NICMOS and STIS achieve very low levels of background contamination from the wings of stellar point spread functions (PSF). Coronagraphy provides additional contrast gains approaching an order of magnitude at small angular distances from occulted stars. The stability of the platform allows scattered and diffracted light to be further reduced by two additional orders of magnitude through PSF-subtraction. The non-destructive read-out modes of the NICMOS detectors permit sampling the PSF, with its strong radial brightness gradient, over a dynamic range exceeding 5x107 in a single spacecraft orbit. In H-band, sub-stellar companions of ΔH ~ 8+2 x (angular separation in arcseconds) are unambiguously detected in twenty minutes of integration. Raw sensitivity metrics, such as presumtively static Strehl ratios, are often invoked in comparing the performance of different instrumental systems but belie the true detectability levels which are dominated by systemic non-repeatable PSF variations (not photon statistics). Such variations can give rise to false detections of companions (and circumstellar disks) and introduce very significant photometric errors. The ability to rotate the HST field with high precision about the target axis and acquire temporally stable reference PSFs readily permits the identification and rejection of rotationally-invariant optical artifacts. We discuss the repeatable, quantifiable performance limits routinely reached by HST (currently unachievable on ground-based systems), for which PSF stability is critical.
The Near IR Camera and Multi-Object Spectrometer (NICMOS), installed into the Hubble Space Telescope (HST) in February 1997, incorporates a coronagraphic imaging capability. The coronagraph is comprised of two optical elements. The camera 2 field divider mirror, upon which the HST f/24 input beam is imaged, includes a 170 micrometers diameter hole which contains approximately 93 percent of the encircled energy from a stellar Point Spread Function (PSF) at a wavelength of 1.6 micrometers . The coronagraphic hole lowers both the diffracted energy in the surrounding region by reducing the high spatial frequency components of the occulted core of the PSF< and down stream scattering. The geometrical radius of this occulting spot, when re-imaged through the camera 2 f/45 optics, is approximately 4 pixels at the detector focal plane. An oversized cold pupil-plane mask, with radial structures co-aligned with the HST secondary mirror spider, acts over the whole 19.1 inch by 19.2 field to further reduce the diffracted energy in the direction of the spider vanes. The absolute performance levels of the coronagraph were ascertained during the servicing mission observatory verification program. Using a differential imaging strategy we expect to achieve statistically significant detectors of sub-stellar companions at 1.6 micrometers with a (Delta) H of approximately 10 and separations as close as 0.5 inch. The NICMOS environments of nearby stars programs is exploiting this capability in systematic surveys of nearby, and young stars searching for brown dwarfs and giant planets, and protoplanetary disks around main-sequence stars.
NICMOS, the near IR camera and multi-object spectrometer was placed in the Hubble Space Telescope in February 1997. Since then it has ben carrying out and extensive program of scientific research. This paper presents the current status and performance of the instrument along with a sample of the observations that have been carried out to this date.
KEYWORDS: Sensors, Diodes, Hubble Space Telescope, Spectrographs, Particles, Calibration, In situ metrology, Environmental sensing, Space operations, Space telescopes
The nature of the Hubble Space Telescope's (HST) low Earth orbit imposes scheduling restrictions and interruptions in the data collection periods for it's compliment of scientific instruments. During many of these times the Faint Object Spectrograph (FOS) is in a full operational configuration and is taking detector background measurements which are continually reported in HST's engineering telemetry stream. These data are primarily used to monitor the instrument for changes in behavior resulting, principally, from intermittently noisy diodes in its digicon arrays. These same data may be used to monitor temporal changes in the charged particle environment of HST's near-earth orbit. We present here the results of a study of two years of on-orbit FOS background data obtained serendipitously during periods while the FOS in an operational state, but not exposing on external, or calibration targets. These in situ data, which represent more than 100,000 discrete samples (equivalent to more than 1100 orbits) have allowed us to accurately measure variations in the background proton flux seen by the FOS. An analysis of these variations have permitted us to model the geomagnetic environment of the South Atlantic Anomaly (SAA) as a function of time as well as the change in detector background as a function of geomagnetic latitude.
The Wide Field Planetary Camera (WF/PC) onboard the Hubble Space Telescope contains contaminants which condense on the windows in front of each CCD detector. These contaminants are UV opaque and increase with time to the extent that after several months they block 50% of the flux at 300 nm. Also, when the contaminants are warmed above -40 degree(s)C and then returned to the normal CCD operating temperature of -87 degree(s)C, particles form and severely degrade the image quality. The windows may be temporarily cleaned by raising their temperature to 0 degree(s)C. However, this results in a change in the structure of the flat field due to the partial removal of the UV flood which was applied after launch to suppress Quantum Efficiency Hysteresis in the CCDs. Repeated decontaminations will reintroduce the QEH and necessitate another time consuming UV flood and recalibration of the instrument. After 22 months of on-orbit operation, the contaminants could no longer be fully removed by the decontamination procedure. This paper describes the current state of the contaminants, what has been deduced concerning their properties and sources, the results of our efforts to remove them, and some lessons for future space-based instruments using cryogenic UV sensitive detectors.
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