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NASA NTRS2000

The CHANDRA X-Ray Observatory: Thermal Design, Verification, and Early Orbit Experience

The CHANDRA X-ray Observatory (formerly AXAF), one of NASA's "Great Observatories" was launched aboard the Shuttle in July 1999. CHANDRA comprises a grazing-incidence X-ray telescope of unprecedented focal-length, collecting area and angular resolution -- better than two orders of magnitude improvement in imaging performance over any previous soft X-ray (0.1-10 keV) mission. Two focal-plane instruments, one with a 150 K passively-cooled detector, provide celestial X-ray images and spectra. Thermal control of CHANDRA includes active systems for the telescope mirror and environment and the optical bench, and largely passive systems for the focal plans instruments. Performance testing of these thermal control systems required 1-1/2 years at increasing levels of integration, culminating in thermal-balance testing of the fully-configured observatory during the summer of 1998. This paper outlines details of thermal design tradeoffs and methods for both the Observatory and the two focal-plane instruments, the thermal verification philosophy of the Chandra program (what to test and at what level), and summarizes the results of the instrument, optical system and observatory testing.

Boyd, David A.↗
NASA NTRS2003

Hypergravity Stimulates the Extracellular Matrix/Integrin-Signaling Axis and Proliferation in Primary Osteoblasts

We set out to determine the molecular mechanisms involved in the proliferative response of primary rat osteoblasts to mechanical stimulation using cell culture centrifugation as a model for hypergravity. We hypothesized that this proliferative response is mediated by specific integrin/Extracellular Matrix (ECM) interactions. To investigate this question we developed a cell culture centrifuge and an automated system that performs cell fixation during hypergravity loading. We generated expression vectors for various focal adhesion and cytoskeletal proteins fused to GFP or dsRed and visualized these structures in transfected (or infected) osteoblasts. The actin cytoskeleton was also visualized using rhodamine-phalloidin staining and Focal Adhesion Kinase (FAK) levels were assessed biochemically. We observed that a 24 hour exposure to 50-g stimulated proliferation compared to the 1-g control when cells were plated on fibronectin, collagen Type I , and collagen Type IV, but not on uncoated tissue culture plastic surfaces. This proliferative response was greatest for osteoblasts grown on fibronectin (2-fold increase over 1-g control) and collagen Type I (1.4 fold increase over 1-g control), suggesting that specific matrices and integrins are involved in the signaling pathways required for proliferation. Exposing osteoblasts grown on different matrices to 10-g or 25-g showed that effects on proliferation depended on both matrix type and loading level. We found that osteoblasts exposed to a short pulse of hypergravity during adhesion spread further and had more GFP-FAK containing focal adhesions compared to their 1-g controls. While overall levels of FAK did not change, more FAK was in the active (phosphorylated) form under hypergravity than in the 1-g controls. Cytoskeletal F-actin organization into filaments was also more prominent after brief exposures to hypergravity during the first five minutes of adhesion. These results suggest that specific integrins sense hypergravity and activate distinct matrix-dependent FAK signaling pathways that can enhance proliferation. Our results also imply that brief exposures to hypergravity accelerate cell adhesion and spreading processes via the focal adhesion-signaling axis. These results support the role of the ECM/integrin-signaling axis in osteoblast response to hypergravity loading.

Parra, M.↗
NASA NTRS2003

Search for Near-Earth Objects with Small Aphelion Distances

An essential component of our ability to efficiently find NEOs at small solar elongation is a focal reducer, whose construction is being separately funded by a grant from NSF. This focal reducer will increase the field of view of the 8k CCD mosaic camera from 19 arc min to about 32 arc min at the Cassegrain focus of the University of Hawaii 2.24-m telescope. As of January, all but one of the lenses for the focal reducer were in hand. The final lens had been delayed due to problems with the availability of the rather exotic material out of which the manufacturer was to fabricate the lens. Perhaps as a result of their rush to deliver that final lens, it developed a crack during the annealing process at the manufacturer, thus they had to start over. The total delay in delivery of that last lens was nearly ten months, and therefore the focal reducer was not completed on schedule and could not be used on the telescope this semester. A postdoctoral research associate was recruited to handle the day-to-day operations. The closing date for applications was 2002 December 3 1, and seven were received. One applicant was not qualified, and two were marginal. Of the four qualified candidates, Fabrizio Bernardi stood out as being best qualified. He was a student of Andrea Carusi and had worked on the CINEOS project in Italy, which includes a component of searching for NEOs at small solar elongations.

Tholen, David J.↗
NASA NTRS2005

Method and structure for minimizing error sources in image and position sensing detectors

A method and structure for minimizing one or more non-uniformities in image and position sensing detectors are provided. The structure is directed to a focal plane processor for removing non-uniformities which distort the computation of a desired property of an object of interest in an image field. The focal plane processor is capable of selectively disconnecting one or more rows and/or columns from further processing in the imaging array for those rows and/or columns which contribute to the presence of at least one non-uniformity in a video image generated by the focal plane processor. In one embodiment, the disconnection means is embodied as pre-processing circuitry which includes row and column shift registers which provide control signals to area-of-interest (AOI) switches. In another embodiment, the pixels which comprise the focal plane array are constructed in a manner which facilitates their individual isolation.

Strohbehn, Kim↗
NASA NTRS2009

Metrology System for a Large, Somewhat Flexible Telescope

A proposed metrology system would be incorporated into a proposed telescope that would include focusing optics on a rigid bench connected via a deployable mast to another rigid bench holding a focal-plane array of photon counting photodetectors. Deformations of the deployable mast would give rise to optical misalignments that would alter the directions (and, hence, locations) of incidence of photons on the focal plane. The metrology system would measure the relative displacement of the focusing- optics bench and the focal-plane array bench. The measurement data would be used in post-processing of the digitized photodetector outputs to compensate for the mast-deformation-induced changes in the locations of incidence of photons on the focal plane, thereby making it possible to determine the original directions of incidence of photons with greater accuracy. The proposed metrology system is designed specifically for the Nuclear Spectroscopic Telescope Array (NuSTAR) a proposed spaceborne x-ray telescope. The basic principles of design and operation are also applicable to other large, somewhat flexible telescopes, both terrestrial and spaceborne. In the NuSTAR, the structural member connecting the optical bench and the photodetector array would be a 10-m-long deployable mast, and there is a requirement to keep errors in measured directions of incidence of photons below 10 arc seconds (3 sigma). The proposed system would include three diode lasers that would be mounted on the focusing-optics bench. For clarity, only one laser is shown in the figure, which is a greatly simplified schematic diagram of the system. Each laser would be aimed at a position-sensitive photodiode that would be mounted on the detector bench alongside the aforementioned telescope photodetector array. The diode lasers would operate at a wavelength of 830 nm, each at a power of 200 mW. Each laser beam would be focused to a spot of .1-mm diameter on the corresponding position-sensitive photodiode. To reduce the effect of sunlight on the measurements, a one-stage light baffle and an 830-nm transmission filter of 10-nm bandwidth would be placed in front of the position- sensitive photodiode. For each metrology reading, the output of the position-sensitive detector would be sampled and digitized twice: once with the lasers turned on, then once with the lasers turned off. The data from these two sets of samples would be subtracted from each other to further reduce the effects of sun glints or other background light sources.

Liebe, Carl Christian↗
NASA NTRS2007

Optimal Calibration of the Spitzer Space Telescope

A document discusses the focal-plane calibration of the Spitzer Space Telescope by use of the instrument pointing frame (IPF) Kalman filter, which was described in Kalman Filter for Calibrating a Telescope Focal Plane (NPO-40798), NASA Tech Briefs, Vol. 30, No. 9 (September 2006), page 62. To recapitulate: In the IPF Kalman filter, optimal estimates of both engineering and scientific focal-plane parameters are obtained simultaneously, using data taken in each focalplane survey activity. The IPF Kalman filter offers greater efficiency and economy, relative to prior calibration practice in which scientific and engineering parameters were estimated by separate teams of scientists and engineers and iterated upon each other. In the Spitzer Space Telescope application, the IPF Kalman filter was used to calibrate 56 frames for precise telescope pointing, estimate >1,500 parameters associated with focal-plane mapping, and process calibration runs involving as many as 1,338 scientific image centroids. The final typical survey calibration accuracy was found to be 0.09 arc second. The use of the IPF Kalman filter enabled a team of only four analysts to complete the calibration processing in three months. An unanticipated benefit afforded by the IPF Kalman filter was the ability to monitor health and diagnose performance of the entire end-to-end telescope-pointing system.

Bayard, David↗
NASA NTRS2007

Delta-Doped CCDs as Detector Arrays in Mass Spectrometers

In a conventional mass spectrometer, charged particles (ions) are dispersed through a magnetic sector onto an MCP at an output (focal) plane. In the MCP, the impinging charged particles excite electron cascades that afford signal gain. Electrons leaving the MCP can be read out by any of a variety of means; most commonly, they are post-accelerated onto a solid-state detector array, wherein the electron pulses are converted to photons, which, in turn, are converted to measurable electric-current pulses by photodetectors. Each step in the conversion from the impinging charged particles to the output 26 NASA Tech Briefs, February 2007 current pulses reduces spatial resolution and increases noise, thereby reducing the overall sensitivity and performance of the mass spectrometer. Hence, it would be preferable to make a direct measurement of the spatial distribution of charged particles impinging on the focal plane. The utility of delta-doped CCDs as detectors of charged particles was reported in two articles in NASA Tech Briefs, Vol. 22, No. 7 (July 1998): "Delta-Doped CCDs as Low-Energy-Particle Detectors" (NPO-20178) on page 48 and "Delta- Doped CCDs for Measuring Energies of Positive Ions" (NPO-20253) on page 50. In the present developmental miniature mass spectrometers, the above mentioned miniaturization and performance advantages contributed by the use of delta-doped CCDs are combined with the advantages afforded by the Mattauch-Herzog design. The Mattauch- Herzog design is a double-focusing spectrometer design involving an electric and a magnetic sector, where the ions of different masses are spatially separated along the focal plane of magnetic sector. A delta-doped CCD at the focal plane measures the signals of all the charged-particle species simultaneously at high sensitivity and high resolution, thereby nearly instantaneously providing a complete, high-quality mass spectrum. The simultaneous nature of the measurement of ions stands in contrast to that of a scanning mass spectrometer, in which abundances of different masses are measured at successive times.

Nikzad, Shouleh↗
NASA NTRS2007

Broadband Achromatic Telecentric Lens

A new type of lens design features broadband achromatic performance as well as telecentricity, using a minimum number of spherical elements. With appropriate modifications, the lens design form can be tailored to cover the range of response of the focal-plane array, from Si (400-1,000 nm) to InGaAs (400-1,700 or 2,100 nm) or InSb/HgCdTe reaching to 2,500 nm. For reference, lenses typically are achromatized over the visible wavelength range of 480-650 nm. In remote sensing applications, there is a need for broadband achromatic telescopes, normally satisfied with mirror-based systems. However, mirror systems are not always feasible due to size or geometry restrictions. They also require expensive aspheric surfaces. Non-obscured mirror systems can be difficult to align and have a limited (essentially one-dimensional) field of view. Centrally obscured types have a two-dimensional but very limited field in addition to the obscuration. Telecentricity is a highly desirable property for matching typical spectrometer types, as well as for reducing the variation of the angle of incidence and cross-talk on the detector for simple camera types. This rotationally symmetric telescope with no obscuration and using spherical surfaces and selected glass types fills a need in the range of short focal lengths. It can be used as a compact front unit for a matched spectrometer, as an ultra-broadband camera objective lens, or as the optics of an integrated camera/spectrometer in which the wavelength information is obtained by the use of strip or linear variable filters on the focal plane array. This kind of camera and spectrometer system can find applications in remote sensing, as well as in-situ applications for geological mapping and characterization of minerals, ecological studies, and target detection and identification through spectral signatures. Commercially, the lens can be used in quality-control applications via spectral analysis. The lens design is based on the rear landscape lens with the aperture stop in front of all elements. This allows sufficient room for telecentricity in addition to making the stop easily accessible. The crucial design features are the use of a doublet with an ultra-low dispersion glass (fluorite or S-FPL53), and the use of a strong negative element, which enables flat field and telecentricity in conjunction with the last (field lens) element. The field lens also can be designed to be in contact with the array, a feature that is desirable in some applications. The lens has a 20deg field of view, for a 50-mm focal length, and is corrected over the range of wavelengths of 450-2,300 nm. Transverse color, which is the most pernicious aberration for spectroscopic work, is controlled at the level of 1 m or below at 0.7 m field and 5 m at full field. The maximum chief ray angle is less than 1.7 , providing good telecentricity. An additional feature of this lens is that it is made exclusively with glasses that provide good transmission up to 2,300 nm and even some transmission to 2,500 nm; thus, the lens can be used in applications that cover the entire solar-reflected spectrum. Alternative realizations are possible that provide enhanced resolution and even less transverse color over a narrower wavelength range.

Mouroulis, Pantazis↗
NASA NTRS2010

Spheres of Earth: An Introduction to Making Observations of Earth Using an Earth System's Science Approach. Student Guide

Scientists from the Image Science and Analysis Laboratory (ISAL) at NASA's Johnson Space Center (JSC) work with astronauts onboard the International Space Station (ISS) who take images of Earth. Astronaut photographs, sometimes referred to as Crew Earth Observations, are taken using hand-held digital cameras onboard the ISS. These digital images allow scientists to study our Earth from the unique perspective of space. Astronauts have taken images of Earth since the 1960s. There is a database of over 900,000 astronaut photographs available at http://eol.jsc.nasa.gov . Images are requested by ISAL scientists at JSC and astronauts in space personally frame and acquire them from the Destiny Laboratory or other windows in the ISS. By having astronauts take images, they can specifically frame them according to a given request and need. For example, they can choose to use different lenses to vary the amount of area (field of view) an image will cover. Images can be taken at different times of the day which allows different lighting conditions to bring out or highlight certain features. The viewing angle at which an image is acquired can also be varied to show the same area from different perspectives. Pointing the camera straight down gives you a nadir shot. Pointing the camera at an angle to get a view across an area would be considered an oblique shot. Being able to change these variables makes astronaut photographs a unique and useful data set. Astronaut photographs are taken from the ISS from altitudes of 300 - 400 km (~185 to 250 miles). One of the current cameras being used, the Nikon D3X digital camera, can take images using a 50, 100, 250, 400 or 800mm lens. These different lenses allow for a wider or narrower field of view. The higher the focal length (800mm for example) the narrower the field of view (less area will be covered). Higher focal lengths also show greater detail of the area on the surface being imaged. Scientists from the Image Science and Analysis Laboratory (ISAL) at NASA s Johnson Space Center (JSC) work with astronauts onboard the International Space Station (ISS) who take images of Earth. Astronaut photographs, sometimes referred to as Crew Earth Observations, are taken using hand-held digital cameras onboard the ISS. These digital images allow scientists to study our Earth from the unique perspective of space. Astronauts have taken images of Earth since the 1960s. There is a database of over 900,000 astronaut photographs available at http://eol.jsc.nasa.gov . Images are requested by ISAL scientists at JSC and astronauts in space personally frame and acquire them from the Destiny Laboratory or other windows in the ISS. By having astronauts take images, they can specifically frame them according to a given request and need. For example, they can choose to use different lenses to vary the amount of area (field of view) an image will cover. Images can be taken at different times of the day which allows different lighting conditions to bring out or highlight certain features. The viewing angle at which an image is acquired can also be varied to show the same area from different perspectives. Pointing the camera straight down gives you a nadir shot. Pointing the camera at an angle to get a view across an area would be considered an oblique shot. Being able to change these variables makes astronaut photographs a unique and useful data set. Astronaut photographs are taken from the ISS from altitudes of 300 - 400 km (approx.185 to 250 miles). One of the current cameras being used, the Nikon D3X digital camera, can take images using a 50, 100, 250, 400 or 800mm lens. These different lenses allow for a wider or narrower field of view. The higher the focal length (800mm for example) the narrower the field of view (less area will be covered). Higher focal lengths also show greater detail of the area on the surface being imaged. There are four major systems or spheres of Earth. They are: Atmosphere, Biosphere, Hydrosphe, and Litho/Geosphere.

Graff, Paige Valderrama↗
NASA NTRS2000

Pulmonary Toxicity of Simulated Lunar and Martian Dusts Intratracheally Instilled into Mice

The National Aeronautics and Space Administration (NASA) is contemplating sending humans to Mars and to the Moon for further exploration. Equipment designated for these extraterrestrial bases will require testing in simulated Martian or lunar environments. The properties of Hawaiian and San Francisco Mountain volcanic ashes make them suitable to be used in these test environments as Martian and lunar dust simulants, respectively. The present toxicity study was conducted to address NASA's concern about the health risk of dust exposures in the test facilities. In addition, the results obtained on these simulants can be used to design a toxicity study of actual moon dust and Martian dust, which will probably be available in a few years. Respirable portions of lunar soil simulant (LSS) and Martian soil simulant (MSS) were separated from their respective raw materials. These soil simulants, together- with fine titanium dioxide (negative control for fibrogenesis in mice), and crystalline silica (positive control) were each intratracheally instilled in saline to groups of 4 male mice (C57BL/6J, 2-3 months old) at 0.1 mg/mouse (LD) or lmg/mouse (HD). The lungs were harvested 7 or 90 days after the single dust treatment for histopathological examination. Lungs of the LSS-LD groups on either the 7- or 90-day study showed no evidence of inflammation, edema, or fibrosis. Clumps of particles and an increased number of macrophages, visible in the lungs examined after 7 days, were absent after 90 days. The LSS-HD-7d group showed mild to moderate alveolitis with neutrophilic and lymphocytic infiltration, and mild perivascular and peribronchiolar inflammation. The LSS-HD-90d group showed signs of chronic inflammation: septal thickening, mild perivascular and peribronchiolar inflammation, mild alveolitis and some fibrosis. Foci of particle-laden macrophages (PLMs) were still visible. Lungs of the MSS-LD-7d group revealed mild focal intraalveolar inflammation with neutrophilic and lymphocytic infiltration, and mild perivascular and peribronchiolar inflammation. The MSS-LD-90d group showed PLMs and scattered foci of mild fibrosis. The MSS-HD-7d group showed large foci of PLMs, intraalveolar debris, mild to moderate focal alveolitis, and mild to moderate perivascular and peribronchiolar inflammation. The MSS-HD-90d group showed focal chronic mild to moderate alveolitis and fibrosis. To mimic the oxidative and reactive properties of Martian surface dust in the test animals, groups of 4 mice were exposed to ozone (0.5 ppm for 3 hours) prior to instillation of the MSS. Lung lesions in the MSS groups were more severe with the ozone pretreatment. The O3-MSS-HD-90d group had wide spread intraalveolar debris, focal moderate alveolitis and fibrosis. The results for the titanium dioxide and quartz controls were consistent with the known pulmonary toxicity of these compounds. The overall severity of toxic injury to the lungs was TiO2<LSS<MSS<MSS+O3<quartz. In general, the toxic responses increased with the increase of dust burden in the lung. Except for TiO2, the increased duration of dust presence in the lung from 7 to 90 days transformed the acute inflammatory response to a chronic inflammatory lesion.

Lam, Chiu-Wing↗
NASA NTRS2006

Coherent Detection of High-Rate Optical PPM Signals

A method of coherent detection of high-rate pulse-position modulation (PPM) on a received laser beam has been conceived as a means of reducing the deleterious effects of noise and atmospheric turbulence in free-space optical communication using focal-plane detector array technologies. In comparison with a receiver based on direct detection of the intensity modulation of a PPM signal, a receiver based on the present method of coherent detection performs well at much higher background levels. In principle, the coherent-detection receiver can exhibit quantum-limited performance despite atmospheric turbulence. The key components of such a receiver include standard receiver optics, a laser that serves as a local oscillator, a focal-plane array of photodetectors, and a signal-processing and data-acquisition assembly needed to sample the focal-plane fields and reconstruct the pulsed signal prior to detection. The received PPM-modulated laser beam and the local-oscillator beam are focused onto the photodetector array, where they are mixed in the detection process. The two lasers are of the same or nearly the same frequency. If the two lasers are of different frequencies, then the coherent detection process is characterized as heterodyne and, using traditional heterodyne-detection terminology, the difference between the two laser frequencies is denoted the intermediate frequency (IF). If the two laser beams are of the same frequency and remain aligned in phase, then the coherent detection process is characterized as homodyne (essentially, heterodyne detection at zero IF). As a result of the inherent squaring operation of each photodetector, the output current includes an IF component that contains the signal modulation. The amplitude of the IF component is proportional to the product of the local-oscillator signal amplitude and the PPM signal amplitude. Hence, by using a sufficiently strong local-oscillator signal, one can make the PPM-modulated IF signal strong enough to overcome thermal noise in the receiver circuits: this is what makes it possible to achieve near-quantum-limited detection in the presence of strong background. Following quantum-limited coherent detection, the outputs of the individual photodetectors are automatically aligned in phase by use of one or more adaptive array compensation algorithms [e.g., the least-mean-square (LMS) algorithm]. Then the outputs are combined and the resulting signal is processed to extract the high-rate information, as though the PPM signal were received by a single photodetector. In a continuing series of experiments to test this method (see Fig. 1), the local oscillator has a wavelength of 1,064 nm, and another laser is used as a signal transmitter at a slightly different wavelength to establish an IF of about 6 MHz. There are 16 photodetectors in a 4 4 focal-plane array; the detector outputs are digitized at a sampling rate of 25 MHz, and the signals in digital form are combined by use of the LMS algorithm. Convergence of the adaptive combining algorithm in the presence of simulated atmospheric turbulence for optical PPM signals has already been demonstrated in the laboratory; the combined output is shown in Fig. 2(a), and Fig. 2(b) shows the behavior of the phase of the combining weights as a function of time (or samples). We observe that the phase of the weights has a sawtooth shape due to the continuously changing phase in the down-converted output, which is not exactly at zero frequency. Detailed performance analysis of this coherent free-space optical communication system in the presence of simulated atmospheric turbulence is currently under way.

Vilnrotter, Victor↗
NASA NTRS2011

Two-Arm Flexible Thermal Strap

Airborne and space infrared cameras require highly flexible direct cooling of mechanically-sensitive focal planes. A thermal electric cooler is often used together with a thermal strap as a means to transport the thermal energy removed from the infrared detector. While effective, traditional thermal straps are only truly flexible in one direction. In this scenario, a cooling solution must be highly conductive, lightweight, able to operate within a vacuum, and highly flexible in all axes to accommodate adjustment of the focal plane while transmitting minimal force. A two-armed thermal strap using three end pieces and a twisted section offers enhanced elastic movement, significantly beyond the motion permitted by existing thermal straps. This design innovation allows for large elastic displacements in two planes and moderate elasticity in the third plane. By contrast, a more conventional strap of the same conductance offers less flexibility and asymmetrical elasticity. The two-arm configuration reduces the bending moment of inertia for a given conductance by creating the same cross-sectional area for thermal conduction, but with only half the thickness. This reduction in the thickness has a significant effect on the flexibility since there is a cubic relationship between the thickness and the rigidity or bending moment of inertia. The novelty of the technology lies in the mechanical design and manufacturing of the thermal strap. The enhanced flexibility will facilitate cooling of mechanically sensitive components (example: optical focal planes). This development is a significant contribution to the thermal cooling of optics. It is known to be especially important in the thermal control of optical focal planes due to their highly sensitive alignment requirements and mechanical sensitivity; however, many other applications exist including the cooling of gimbal-mounted components.

Urquiza, Eugenio↗
NASA NTRS2012

Development of Thermal Infrared Sensor to Supplement Operational Land Imager

The thermal infrared sensor (TIRS) is a quantum well infrared photodetector (QWIP)-based instrument intended to supplement the Operational Land Imager (OLI) for the Landsat Data Continuity Mission (LDCM). The TIRS instrument is a far-infrared imager operating in the pushbroom mode with two IR channels: 10.8 and 12 m. The focal plane will contain three 640 ~512 QWIP arrays mounted onto a silicon substrate. The readout integrated circuit (ROIC) addresses each pixel on the QWIP arrays and reads out the pixel value (signal). The ROIC is controlled by the focal plane electronics (FPE) by means of clock signals and bias voltage value. The means of how the FPE is designed to control and interact with the TIRS focal plane assembly (FPA) is the basis for this work. The technology developed under the FPE is for the TIRS focal plane assembly (FPA). The FPE must interact with the FPA to command and control the FPA, extract analog signals from the FPA, and then convert the analog signals to digital format and send them via a serial link (USB) to a computer. The FPE accomplishes the described functions by converting electrical power from generic power supplies to the required bias power that is needed by the FPA. The FPE also generates digital clocking signals and shifts the typical transistor-to-transistor logic (TTL) to }5 V required by the FPA. The FPE also uses an application- specific integrated circuit (ASIC) named System Image, Digitizing, Enhancing, Controlling, And Retrieving (SIDECAR) from Teledyne Corp. to generate the clocking patterns commanded by the user. The uniqueness of the FPE for TIRS lies in that the TIRS FPA has three QWIP detector arrays, and all three detector arrays must be in synchronization while in operation. This is to avoid data skewing while observing Earth flying in space. The observing scenario may be customized by uploading new control software to the SIDECAR.

Shu, Peter↗
NASA NTRS2011

Superlattice Barrier Infrared Detector Development at the Jet Propulsion Laboratory

We report recent efforts in achieving state-of-the-art performance in type-II superlattice based infrared photodetectors using the barrier infrared detector architecture. We used photoluminescence measurements for evaluating detector material and studied the influence of the material quality on the intensity of the photoluminescence. We performed direct noise measurements of the superlattice detectors and demonstrated that while intrinsic 1/f noise is absent in superlattice heterodiode, side-wall leakage current can become a source of strong frequency-dependent noise. We developed an effective dry etching process for these complex antimonide-based superlattices that enabled us to fabricate single pixel devices as well as large format focal plane arrays. We describe the demonstration of a 1024x1024 pixel long-wavelength infrared focal plane array based the complementary barrier infrared detector (CBIRD) design. An 11.5 micron cutoff focal plane without anti-reflection coating has yielded noise equivalent differential temperature of 53 mK at operating temperature of 80 K, with 300 K background and cold-stop. Imaging results from a recent 10 ?m cutoff focal plane array are also presented.

superlattice↗
NASA NTRS2011

High-Performance LWIR Superlattice Detectors and FPA Based on CBIRD Design

We report our recent efforts on advancing of antimonide superlattice based infrared photodetectors and demonstration of focal plane arrays based on a complementary barrier infrared detector (CBIRD) design. By optimizing design and growth condition we succeeded to reduce the operational bias of CBIRD single pixel detector without increase of dark current or degradation of quantum efficiency. We demonstrated a 1024x1024 pixel long-waveleng thinfrared focal plane array utilizing CBIRD design. An 11.5 micrometer cutoff focal plane without anti-reflection coating has yielded noise equivalent differential temperature of 53 mK at operating temperature of 80 K, with 300 K background and cold-stop. Imaging results from a recent 10 micrometer cutoff focal plane array are also presented. These results advance state-of-the art of superlattice detectors and demonstrated advantages of CBIRD architecture for realization of FPA.

infrared↗
NASA NTRS2011

Nearby Exo-Earth Astrometric Telescope (NEAT)

NEAT (Nearby Exo ]Earths Astrometric Telescope) is a modest sized (1m diameter telescope) It will be capable of searching approx 100 nearby stars down to 1 Mearth planets in the habitable zone, and 200 @ 5 Mearth, 1AU. The concept addresses the major issues for ultra -precise astrometry: (1) Photon noise (~0.5 deg dia field of view) (2) Optical errors (beam walk) with long focal length telescope (3) Focal plane errors , with laser metrology of the focal plane (4) PSF centroiding errors with measurement of the "True" PSF instead of using a "guess " of the true PSF, and correction for intra pixel QE non-uniformities. Technology "close" to complete. Focal plane geometry to 2e-5 pixels and centroiding to approx 4e -5 pixels.

exoplanets↗
NASA NTRS2013

Cobra Fiber-Optic Positioner Upgrade

A prime focus spectrometer (PFS), along with corrective optics, will mount in place of the secondary mirror of the Subaru telescope on Mauna Kea, Hawaii. This will allow simultaneous observations of cosmologic targets. It will enable large-scale galactic archeology and dark energy surveys to help unlock the secrets of the universe. To perform these cosmologic surveys, an array of 2,400 optical fibers needs to be independently positioned within the 498-mm-diameter focal plane of the PFS instrument to collect light from galaxies and stars for spectrographic analyses. To allow for independent re-positioning of the fibers, a very small positioner (7.7 mm in diameter) is required. One hundred percent coverage of the focal plane is also required, so these small actuators need to cover a patrol region of 9.5 mm in diameter. To optimize the amount of light that can be collected, the fibers need to be placed within 5 micrometers of their intended target (either a star or galaxy). The Cobra Fiber Positioner was designed to meet the size and accuracy requirements stated above. Cobra is a two-degrees-of-freedom mechanism that can position an optical fiber in the focal plane of the PFS instrument to a precision of 5 micrometers. It is a theta-phi style positioner containing two rotary piezo tube motors with one offset from the other, which enables the optic fibers to be placed anywhere in a small circular patrol region. The patrol region of the actuator is such that the array of 2,400 positioners allows for full coverage of the instrument focal plane by overlapping the patrol areas. A second-generation Cobra positioner was designed based on lessons learned from the original prototype built in 2009. Improvements were made to the precision of the ceramic motor parts, and hard stops were redesigned to minimize friction and prevent jamming. These changes resulted in reducing the number of move iterations required to position the optical fiber within 5 micrometers of its target. At the time of this reporting, there are still many tests to be performed that will validate system level performance, but on an individual level, the Cobra positioner demonstrates excellent performance and will enable the PFS instrument to make unprecedented measurements of the universe. What is unique about the upgrades made to the Cobra positioner is the improved performance due to the design changes in the hard stops and the ceramic end caps of the motors. Other changes were made to reduce the unit cost of a Cobra positioner without affecting the performance, since thousands of these devices will have to be built for the PFS instrument.

Fisher, Charles D.↗
NASA NTRS2011

High-Performance LWIR Superlattice Detectors and FPA Based on CBIRD Design

We report our recent efforts on advancing of antimonide superlattice based infrared photodetectors and demonstration of focal plane arrays based on a complementary barrier infrared detector (CBIRD) design. By optimizing design and growth condition we succeeded to reduce the operational bias of CBIRD single pixel detector without increase of dark current or degradation of quantum efficiency. We demonstrated a 1024x1024 pixel long-wavelength infrared focal plane array utilizing CBIRD design. An 11.5 micrometer cutoff focal plane without anti-reflection coating has yielded noise equivalent differential temperature of 53 mK at operating temperature of 80 K, with 300 K background and cold-stop. Imaging results from a recent 10 micrometer cutoff focal plane array are also presented. These results advance state-of-the art of superlattice detectors and demonstrated advantages of CBIRD architecture for realization of FPA.

heterostructure↗