We are developing imaging Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CZT) pixel detectors with potential applications in hard X-ray astrophysical NASA Explorer and Probe-class missions, utilizing wide field and focusing instruments. Our hybrid sensor consists of a CdTe and a CZT detector with segmented anode contacts directly bonded to an ASIC. We have utilized a custom low-noise, low-power ASIC developed for NuSTAR mission. While NuSTAR employed eV Products CZT detectors, for this study, we used a CdTe detector by Acrorad and a CZT detector by Redlen. Both detectors have anode pixels with a 604-micron pitch in a 32 x 32 array. The CdTe detectors have segmented Schottky blocking contacts, whereas the CZT detectors have plain contacts. Understanding the charge sharing and charge loss behavior between the pixels is crucial to achieve good energy resolutions. In this paper, we report on the study of charge sharing and charge loss effects between the pixels. We will compare the behavior among eV CZT, Redlen CZT, and Acrorad CdTe detectors. Furthermore, we will discuss how these effects might influence smaller pixel pitch detectors for our next-generation prototype ASIC.
HEX-P is a probe-class mission concept that combines the power of high angular resolution with broad bandpass coverage to provide the necessary leap in capabilities to address the important astrophysical questions of the next decade. HEX-P achieves its breakthrough performance by combining technologies developed by experienced partners and international collaborations. HEX-P will be launched into L1 for a high observing efficiency, and to meet the science goals the payload consists of a suite of three co-aligned X-ray telescopes designed to cover the 0.2 - 80 keV bandpass where accretion is at its peak. The High Energy Telescope (HET) has an effective bandpass of 2-80 keV, and the Low Energy Telescope (LET) an effective bandpass of 0.2-20 keV. The combination of bandpass and high observing efficiency delivers a powerful General Observer platform for a broad science that services a wide community base. The baseline mission is 5 years, with 30% of t
The Ultraviolet Explorer (UVEX) mission is built on three scientific pillars: (I) Exploring the low-mass, low-metallicity galaxy frontier; (II) Providing new views of the dynamic universe, and (III) Leaving a broad legacy of modern, deep synoptic surveys. The deep, synoptic all-sky survey includes the Galactic Plane and Magellanic Clouds and achieves depths and resolution matching modern optical/IR surveys with Rubin, Roman, and Euclid. UVEX will follow up the aftermath of GW-detected NS mergers and provide the first rapid UV spectroscopic follow-up of transients. The UVEX payload consists of a single instrument with simultaneous FUV and NUV imaging over a wide (12 deg2) FOV and sensitive R>1000 spectroscopy over a broad band from 1150 – 2650 Å. Placed in a highly elliptical, TESS-like orbit, UVEX achieves low background and high observing efficiency. Frequent ground contacts and rapid slew capability enable UVEX to promptly follow up targets of opportunity, providing the first rapid, deep UV imaging and spectroscopic follow-up capability.
The large side aperture of the Nuclear Spectroscopic Telescope Array (NuSTAR) telescope for unfocused photons (so-called stray light) is a known source of rich astrophysical information. To support many studies based on the NuSTAR stray light data, we present a fully automatic method for determining detector area suitable for background analysis and free from any kind of focused x-ray flux. The method’s main idea is “á trous” wavelet image decomposition, capable of detecting structures of any spatial scale and shape, which makes the method of general use. Applied to the NuSTAR data, the method provides a detector image region with the highest possible statistical quality, suitable for the NuSTAR stray light studies. We developed an open-source Python nuwavdet package, which implements the presented method. The package contains subroutines to generate detector image region for further stray light analysis and/or to produce a list of detector bad-flagged pixels for processing in the NuSTAR Data Analysis Software for conventional x-ray analysis.
HEX-P is a probe-class mission concept that will combine high angular resolution (⪅ 5 ′′ at 6 keV) x-ray imaging and broad energy sensitivity (0.2 − 80 keV) to enable revolutionary new insights into black holes, neutron stars, and other extreme environments powering the high energy universe. HEX-P prioritizes broad band imagery and high resolution simultaneously, providing a wealth of information not possible with any other planned or operating observatory. HEX-P achieves its breakthrough performance by combining technologies developed by experienced partners: high resolution low energy imagery with silicon segmented mirrors provided by the Goddard Space Flight Center (GSFC, Greenbelt, MD); state of the art high energy imagery from nickel shell mirror technology developed by Media Lario (Bosisio Parini, Italy) and the National Institute for Astrophysics (INAF, Merate, Italy) through a contribution from the Italian Space Agency (ASI, Rome, Italy); high speed, high resolution Depleted P-Channel Field Effect Transistor (DEPFET) detectors through a contribution from the Max Planck Institute for Extraterrestrial Physics (MPE, Garching, Germany); photon counting high energy detectors from the NuSTAR team at the California Institute of Technology (Caltech, Pasadena CA); and a spacecraft and payload structure with a 20 m deployable boom developed by Northrop Grumman (Falls Church, VA).
HEX-P is an x-ray probe-class mission concept that will combine high angular resolution (⪅15 arcsec) with broad band spectral coverage (0.2 - 80 keV) to enable revolutionary new insights into the important astrophysical questions of the next decade identified by the 2020 Decadal Survey. Sensitivity is key to the instrument performance and estimating the background a crucial step in the development of the design and prediction of the instrument performance. The HEX-P orbit is at L1, and since L1 has hosted no prior missions with x-ray coverage that can be used to estimate the background level, the particle background has to be simulated. We present here the simulations done to evaluate the contribution to the background from charged particles, which show that the high energy background is dominated by hadronic activation in the detector mass and prompt leptons. To reduce the additional Cosmic X-ray Background (CXB), which is non-charged, the instruments are fitted with apertures and blocking plates of a graded-Z material to attenuate the CXB to a level an order of magnitude below the requirement.
We report on the development of metal-dielectric bandpass filters that can be integrated with back-illuminated CMOS imaging sensors for operation at far ultraviolet wavelengths (FUV, 90-200 nm). These coatings utilize previous developments in atomic layer deposition (ALD) processes for transparent dielectric materials which are combined with evaporated aluminum layers in multilayer structures. Planar coatings can produce an FUV bandpass response that allows broadband silicon imaging sensors to operate with visible and solar blindness. We describe the fabrication and optical characterization of these coatings, and describe the development of delta-doped detectors integrating these coatings that are motivated by the performance requirements of the NASA astrophysics mission Ultraviolet Explorer (UVEX), currently undergoing a Phase A concept study. We also describe the extension of this concept to include graded thickness dielectric layers deposited by ALD. We show that a graded lateral thickness can be engineered in a variety of thermal ALD processes by depositing into a shallow horizontal cavity. This allows for the fabrication of detector-integrated filter coatings with a spatially-varying response that can be matched to the spectral dispersion of the planned UVEX spectrograph channel. Prototype graded coatings are demonstrated over areas up to 4 x 4 cm, and characterized for optical performance and environmental stability.
We present a study of a sample pixelated cadmium zinc telluride (CZT) detector using CZT purchased from Redlen Technologies. We demonstrate that the material shows good uniformity across the 2 cm × 2 cm × 3 mm crystal in terms of leakage current, gain, and spectral resolution. We find that the detector produces very good spectral resolution for energies up to at least 105 keV, achieving a full-width at half-maxima of 450 eV at 14 keV up to 880 eV at 105 keV using only single-pixel events. Though our analysis of spectra including multiple-pixel events is somewhat limited, we also produce a spectrum including events in which photon energy is deposited across two adjacent pixels. We find that this degrades the energy resolution by up to 30%, but this result can likely be improved using more rigorous calibrations. Additionally, we investigate depth-of-interaction effects, showing that spectral resolution can be improved by 3% to 7% for energies between 86 and 105 keV by removing events beyond a certain depth. Performing this cut reduces efficiency, removing 13% to 21% of photons from the resulting spectral lines.
We present an overview of the NuSTAR non x-ray background. This is dominated by proton scattering in the detector and surrounding material as well as activation lines from of material in the detector and its housing. We also discuss contributions from the solar component (when the Sun is active), and the impact of short-lived radiation belts on the NuSTAR background and activation in the detectors.
We present here the updated calibration of the Nuclear Spectroscopic Telescope Array, which was performed using data on the Crab accumulated over the last nine years in orbit. The basis for this new calibration contains over 250 ks of focused Crab observations (imaged through the optics) and over 500 ks of stray-light (SL) Crab observations (not imaged through optics). We measured an epoch averaged spectrum of the SL Crab data and define a canonical Crab spectrum of Γ = 2.103 ± 0.001 and N = 9.69 ± 0.02 keV − 1 cm − 2 s − 1 at 1 keV, which we use as our calibration standard. This calibration released in the Calibration Data Base update 20211020 provides significant updates to: (1) the detector absorption component, (2) the detector response function, and (3) the effective area vignetting function. The calibration improves agreement between FPMA and FPMB across detectors with a standard deviation of 1.7% for repeat observations between off-axis angles of 1′ to 4′. As a consequence of the measured SL observations, the absolute flux of the instrument has increased by 5% to 15%, with 5% below 1′ off-axis angle, 10% between 1 and 2′, and 15% above 4′.
KEYWORDS: Signal to noise ratio, High dynamic range imaging, Sensors, CMOS sensors, Point spread functions, Astronomy, High dynamic range image sensors, CMOS devices, Detection and tracking algorithms, Signal detection
We present an approach for improving the effective well depth of a CMOS detector for use on a UV space telescope by using a combination of two techniques: a dual-gain readout mode and the use of a multi-exposure HDR algorithm. Non-destructive readout of the detector in a high-gain and a low-gain mode optimizes the dynamic range of a single exposure by taking advantage of the low read noise of the first mode and the high well depth of the second. The dynamic range can be further extended by the addition of a second, shorter exposure to probe the saturated regions of the initial exposure. We find that, for simulations of an SRI CMOS imager we are testing, its initial sensitivity to ~3 orders of magnitude in flux can be improved to a dynamic range of over 5.5 orders of magnitude (equivalent to a difference of ~14 AB magnitudes) by the combination of a 300 second dual-gain exposure and a 3 second low-gain exposure, with a low overhead in additional read time and computational complexity.
CMOS detectors offer many advantages over CCDs for optical and UV astronomical applications, especially in space where high radiation tolerance is required. However, astronomical instruments are most often designed for low light-level observations demanding low dark current and read noise, good linearity and high dynamic range, characteristics that have not been widely demonstrated for CMOS imagers. We report the performance, over temperatures from 140 - 240 K, of a radiation hardened SRI 4K×2K back-side illuminated CMOS image sensor with surface treatments that make it highly sensitive in blue and UV bands. After suppressing emission from glow sites resulting from defects in the engineering grade device examined in this work, a 0.077 me−/s dark current floor is reached at 160 K, rising to 1 me−/s at 184 K, rivaling that of the best CCDs. We examine the trade-off between readout speed and read noise, finding that 1.43 e− median read noise is achieved using line-wise digital correlated double sampling at 700 kpix/s/ch corresponding to a 1.5 s readout time. The 15 ke− well capacity in high gain mode extends to 120 ke− in dual gain mode. Continued collection of photo-generated charge during readout enables a further dynamic range extension beyond 106 e− effective well capacity with only 1% loss of exposure efficiency by combining short and long exposures. A quadratic fit to correct for non-linearity reduces gain correction residuals from 1.5% to 0.2% in low gain mode and to 0.4% in high gain mode. Cross-talk to adjacent pixels is only 0.4% vertically, 0.6% horizontally and 0.1% diagonally. These characteristics plus the relatively large (10μm) pixel size, quasi 4-side buttability, electronic shutter and sub-array readout make this sensor an excellent choice for wide field astronomical imaging in space, even at FUV wavelengths where sky background is very low.
Complementary metal-oxide semiconductor (CMOS) detectors offer many advantages over charge-coupled devices (CCDs) for optical and ultraviolet (UV) astronomical applications, especially in space where high radiation tolerance is required. However, astronomical instruments are most often designed for low light-level observations demanding low dark current and read noise, good linearity, and high dynamic range, characteristics that have not been widely demonstrated for CMOS imagers. We report the performance, over temperatures from 140 to 240 K, of a radiation hardened SRI 4k × 2k back-side illuminated CMOS image sensor with surface treatments that make it highly sensitive in blue and UV bands. After suppressing emission from glow sites resulting from defects in the engineering grade device examined, a 0.077 me − / s dark current floor is reached at 160 K, rising to 1 me − / s at 184 K, rivaling that of the best CCDs. We examine the trade-off between readout speed and read noise, finding that 1.43 e − median read noise is achieved using line-wise digital correlated double sampling at 700 kpix / s / ch corresponding to a 1.5 s readout time. The 15 ke − well capacity in high gain mode extends to 120 ke − in dual gain mode. Continued collection of photogenerated charge during readout enables a further dynamic range extension beyond 106 e − effective well capacity with only 1% loss of exposure efficiency by combining short and long exposures. A quadratic fit to correct for non-linearity reduces gain correction residuals from 1.5% to 0.2% in low gain mode and to 0.4% in high gain mode. Cross-talk to adjacent pixels is only 0.4% vertically, 0.6% horizontally, and 0.1% diagonally. These characteristics plus the relatively large (10 μm) pixel size, quasi 4-side buttability, electronic shutter, and sub-array readout make this sensor an excellent choice for wide field astronomical imaging in space, even at far-UV wavelengths where sky background is very low.
We describe a method by which the metrology system of the Nuclear Spectroscopic Telescope Array (NuSTAR) X-ray space observatory, which uses two lasers to characterize the relative motion of the optics and focal plane benches, can be approximated should one laser fail. The two benches are separated by a 10-m-long rigid mast that undergoes small amounts of thermal flexing that needs to be compensated for to produce a nonblurred image. We analyze the trends of mast motion by archival observation parameters to discover whether the mast motion in future observations can be predicted. We find that, using the solar aspect angle, observation date, and orbital phase, we can simulate the motion of one laser by translating the track produced by the other and applying modifications to the resulting mast aspect solution, allowing for the reconstruction of a minimally distorted point spread function in most cases. We will implement the generation of simulated mast files along with the usual NuSTAR data reduction pipeline for contingency purposes. This work has implications for reducing the risk of implementing laser metrology systems on future missions that use deployable masts to achieve the long focal lengths required in high-energy astronomy by mitigating the impact of a metrology laser failure in the extended phase of a mission.
We present the results of ongoing characterization of Cadmium Zinc Telluride (CZT) semiconductors produced by Redlen Technologies. In particular we hope to determine their viability for future X-ray astronomy missions such as the High Energy X-ray Probe (HEX-P). The fully fabricated hybrid detectors consist of CZT crystals with a collecting area of 2 cm × 2 cm and thickness of 3 mm mounted on a custom pixelated ASIC originally designed for the Nuclear Spectroscopic Telescope Array (NuSTAR) mission, which launched in 2012. We present the results of inter-pixel conductance and leakage current tests as well as spectral characterization using an 241Am source. Although further calibration and testing is necessary to determine the capabilities of these detectors, preliminary results indicate that Redlen CZT will be able to achieve spectral resolution and noise levels comparable to those of the CZT detectors currently in use aboard NuSTAR.
KEYWORDS: Sensors, Calibration, Electronics, X-ray telescopes, X-ray optics, Hard x-rays, Signal to noise ratio, Space operations, Spectroscopes, Telescopes
NuSTAR (the Nuclear Spectroscopic Telescope ARray) is a NASA Small Explorer (SMEX) mission launched in June of 2012. Since its launch, NuSTAR has been the preeminent instrument for spectroscopic analysis of the hard X-ray sky over the 3-80 keV bandpass. The low energy side of the bandpass is limited by the absorption along the photon path as well as by the ability of the pixels to trigger on incident photons. The on-board calibration source does not have a low-energy line that we can use to calibrate this part of the response, so instead we use the "nearest-neighbor" readout in the NuSTAR detector architecture to calibrate the individual pixel thresholds for all 8 flight detectors on both focal plane modules (FPMs). These threshold measurements feed back into the quantum efficiency of the detectors at low (<5 keV) energies and, once well-calibrated, may allow the use of NuSTAR data below the current 3 keV limit.
We present the results of ongoing characterization of Cadmium Zinc Telluride (CZT) semiconductors produced by Redlen Technologies for use in X-ray astronomy. The fully fabricated hybrid detectors consist of CZT crystals with a collecting area of 2 cm x 2 cm and thickness of 3mm mounted on a custom ASIC originally designed for the Nuclear Spectroscopic Telescope Array (NuSTAR) mission, which launched in 2012. We present the results of electronic noise, inter-pixel conductance, and leakage current tests as well as spectral calibration using an 241Am source. Despite high electronic noise due to errors in fabrication, we are able to compare characteristics of the Redlen CZT detectors to those of the CZT detectors produced by eV Products aboard NuSTAR.
The High-Energy X-ray Probe (HEX-P) is a probe-class mission concept that will extend the reach of broadband (2-200 keV) X-ray observations, with 40 times the sensitivity of any previous mission in the 10-80 keV band and 10,000 times the sensitivity of any previous mission in the 80-200 keV band. HEX-P addresses key NASA science goals and is an important complement to ESA's L-class Athena mission. Working in coordination with Athena HEX-P will provide continuum measurements that are essential for interpreting Athena spectra. With angular resolution improved by more than an order of magnitude relative to NuSTAR, HEX-P will carry out an independent program aimed at addressing questions unique to the high energy X-ray band, such as the nature of the source that powers Active Galactic Nuclei, the evolution of black holes in obscured environments, and understanding of how compact binary systems form, evolve and influence galactic systems. With heritage from NuSTAR, HEX-P can be executed within the next decade with a budget less than double that of a Medium class Explorer (MIDEX) mission.
The High-Energy X-ray Probe (HEX-P) is a probe-class next-generation high-energy X-ray mission concept that will vastly extend the reach of broadband X-ray observations. Studying the 2-200 keV energy range, HEXP has 40 times the sensitivity of any previous mission in the 10-80 keV band, and will be the first focusing instrument in the 80-200 keV band. A successor to the Nuclear Spectroscopic Telescope Array (NuSTAR), a NASA Small Explorer launched in 2012, HEX-P addresses key NASA science objectives, and will serve as an important complement to ESA’s L-class Athena mission. HEX-P will utilize multilayer coated X-ray optics, and in this paper we present the details of the optical design, and discuss the multilayer prescriptions necessary for the reflection of hard X-ray photons. We consider multiple module designs with the aim of investigating the tradeoff between high- and low-energy effective area, and review the technology development necessary to reach that goal within the next decade.
The Nuclear Spectroscopic Telescope ARray (NuSTAR) has been in orbit for 6 years, and with the calibration data accumulated over that period we have taken a new look at the effective area calibration. The NuSTAR 10-m focal length is achieved using an extendible mast, which flexes due to solar illumination. This results in individual observations sampling a range of off-axis angles rather than a particular off-axis angle. In our new approach, we have split over 50 individual Crab observations into segments at particular off-axis angles. We combine segments from different observations at the same off-axis angle to generate a new set of synthetic spectra, which we use to calibrate the vignetting function of the optics against the canonical Crab spectrum.
The Nuclear Spectroscopic Telescope Array (NuSTAR) launched in June 2012, flies two conical approximation Wolter-I mirrors at the end of a 10.15-m mast. The optics are coated with multilayers of Pt/C and W/Si that operate from 3 to 80 keV. Since the optical path is not shrouded, aperture stops are used to limit the field of view (FoV) from background and sources outside the FoV. However, there is still a sliver of sky (∼1.0 deg to 4.0 deg) where photons may bypass the optics altogether and fall directly on the detector array. We term these photons stray light. Additionally, there are also photons that do not undergo the focused double reflections in the optics, and we term these ghost rays. We present detailed analysis and characterization of these two components and discuss how they impact observations. Finally, we discuss how they could have been prevented and should be in future observatories.
Pixelated Cadmium Zinc Telluride (CdZnTe) detectors are currently flying on the Nuclear Spectroscopic Telescope ARray (NuSTAR) NASA Astrophysics Small Explorer. While the pixel pitch of the detectors is ≈ 605 μm, we can leverage the detector readout architecture to determine the interaction location of an individual photon to much higher spatial accuracy. The sub-pixel spatial location allows us to finely oversample the point spread function of the optics and reduces imaging artifacts due to pixelation. In this paper we demonstrate how the sub-pixel information is obtained, how the detectors were calibrated, and provide ground verification of the quantum efficiency of our Monte Carlo model of the detector response.
The Nuclear Spectroscopic Telescope Array (NuSTAR) is the first focusing high energy (3-79 keV) X-ray observatory operating for four years from low Earth orbit. The X-ray detector arrays are located on the spacecraft bus with the optics modules mounted on a flexible mast of 10.14m length. The motion of the telescope optical axis on the detectors during each observation is measured by a laser metrology system and matches the pre-launch predictions of the thermal flexing of the mast as the spacecraft enters and exits the Earths shadow each orbit. However, an additional motion of the telescope field of view was discovered during observatory commissioning that is associated with the spacecraft attitude control system and an additional flexing of the mast correlated with the Solar aspect angle for the observation. We present the methodology developed to predict where any particular target coordinate will fall on the NuSTAR detectors based on the Solar aspect angle at the scheduled time of an observation. This may be applicable to future observatories that employ optics deployed on extendable masts. The automation of the prediction system has greatly improved observatory operations efficiency and the reliability of observation planning.
The Nuclear Spectroscopic Telescope Array (NuSTAR) is the first focusing high energy (3-79 keV) X-ray observatory. The NuSTAR project is led by Caltech, which hosts the Science Operations Center (SOC), with mission operations managed by UCB Space Sciences Laboratory. We present an overview of NuSTAR science operations and describe the on-orbit performance of the observatory. The SOC is enhancing science operations to serve the community with a guest observing program beginning in 2015. We present some of the challenges and approaches taken by the SOC to operating a full service space observatory that maximizes the scientific return from the mission.
The Nuclear Spectroscopic Telescope Array (NuSTAR) satellite is a NASA Small Explorer mission designed to operate the first focusing high-energy X-ray (3-79 keV) telescope in orbit. Since the launch in June 2012, all the NuSTAR components have been working normally. The focal plane module is equipped with an 155Eu radioactive source to irradiate the CdZnTe pixel detectors for independent calibration separately from optics. The inflight spectral calibration of the CdZnTe detectors is performed with the onboard 155Eu source. The derived detector performance agrees well with ground-measured data. The in-orbit detector background rate is stable and the lowest among past high-energy X-ray instruments.
The Nuclear Spectroscopic Telescope Array (NuSTAR) mission was launched on 2012 June 13 and is the first focusing high-energy X-ray telescope in orbit operating above ~10 keV. NuSTAR flies two co-aligned Wolter-I conical approximation X-ray optics, coated with Pt/C and W/Si multilayers, and combined with a focal length of 10.14 meters this enables operation from 3-79 keV. The optics focus onto two focal plane arrays, each consisting of 4 CdZnTe pixel detectors, for a field of view of 12.5 arcminutes. The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than 100-fold improvement in sensitivity, and with an effective point spread function FWHM of 18 arcseconds (HPD ~1), NuSTAR provides a leap of improvement in resolution over the collimated or coded mask instruments that have operated in this bandpass. We present in-orbit performance details of the observatory and highlight important science results from the first two years of the mission.
The capability of NuSTAR to detect polarization in the Compton scattering regime (>50 keV) has been investigated. The
NuSTAR mission, flown on June 2012 a Low Earth Orbit (LEO), provides a unique possibility to confirm the findings of
INTEGRAL on the polarization of cosmic sources in the hard X-rays. Each of the two focal plane detectors are high
resolution pixellated CZT arrays, sensitive in the energy range ~ 3 - 80 keV. These units have intrinsic polarization
capabilities when the proper information on the double events is transmitted on ground. In this case it will be possible to
detect polarization from bright sources on timescales of the order of 105 s
The Nuclear Spectroscopic Telescope Array (NuSTAR) will be the first space mission to focus in the hard X-ray
(5-80 keV) band. The NuSTAR instrument carries two co-aligned grazing incidence hard X-ray telescopes. Each
NuSTAR focal plane consists of four 2 mm CdZnTe hybrid pixel detectors, each with an active collecting area of
2 cm x 2 cm. Each hybrid consists of a 32x32 array of 605 μm pixels, read out with the Caltech custom low-noise
NuCIT ASIC. In order to characterize the spectral response of each pixel to the degree required to meet the
science calibration requirements, we have developed a model based on Geant4 together with the Shockley-Ramo
theorem customized to the NuSTAR hybrid design. This model combines a Monte Carlo of the X-ray interactions
with subsequent charge transport within the detector. The combination of this model and calibration data taken
using radioactive sources of 57Co, 155Eu and 241Am enables us to determine electron and hole mobility-lifetime
products for each pixel, and to compare actual to ideal performance expected for defect-free material.
The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing hard X-ray (6 - 80 keV) telescope to orbit. NuSTAR will offer a factor 50 - 100 sensitivity improvement compared to previous collimated or coded mask imagers that have operated in this energy band. In addition, NuSTAR provides sub-arcminute imaging with good spectral resolution over a 12-arcminute eld of view. After
launch, NuSTAR will carry out a two-year primary science mission that focuses on four key programs: studying the evolution of massive black holes through surveys carried out in fields with excellent multiwavelength coverage, understanding the population of compact objects and the nature of the massive black hole in the center of the Milky Way, constraining the explosion dynamics and nucleosynthesis in supernovae, and probing the nature of particle acceleration in relativistic jets in active galactic nuclei. A number of additional observations will be included in the primary mission, and a guest observer program will be proposed for an extended mission to expand the range of scientic targets. The payload consists of two co-aligned depth-graded multilayer coated grazing incidence optics focused onto a solid state CdZnTe pixel detectors. To be launched in early 2012 on a Pegasus rocket into a low-inclination Earth orbit, NuSTAR largely avoids SAA passage, and will therefore have low and
stable detector backgrounds. The telescope achieves a 10.14-meter focal length through on-orbit deployment of an extendable mast. An aspect and alignment metrology system enable reconstruction of the absolute aspect and variations in the telescope alignment resulting from mast exure during ground data processing. Data will
be publicly available at GSFC's High Energy Archive Research Center (HEASARC) following validation at the science operations center located at Caltech.
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