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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

High Rate User Ka-Band Phased Array Antenna Test Results

The High Rate User Phased Array Antenna (HRUPAA) is a Ka-Band planar phased array designed by the Harris Corporation for the NASA Goddard Space Flight Center. The HRUPAA permits a satellite to downlink data either to a ground station or through the Tracking and Data Relay Satellite System (TDRSS). The HRUPAA is scanned electronically by ground station / user satellite command over a 120 degree cone angle. The phased array has the advantage of not imparting attitude disturbances to the user spacecraft. The 288-element transmit-only array has distributed RF amplifiers integrated behind each of the printed patch antenna elements. The array has 33 dBW EIRP and is left-hand circularly polarized. An engineering model of a partially populated array has been developed and delivered to NASA Goddard Space Flight Center. This report deals with the testing of the engineering model at the Goddard Antenna Range near-field and compact range facilities. The antenna specifications are described first, followed by the test plan and test results.

Caroglanian, Armen↗
NASA NTRS2001

Novel Multiplexing Technique for Detector and Mixer Arrays

Future submillimeter and far-infrared space telescopes will require large-format (many 1000's of elements) imaging detector arrays to perform state-of-the-art astronomical observations. A crucial issue related to a focal plane array is a readout scheme which is compatible with large numbers of cryogenically-cooled (typically < 1 K) detectors elements. When the number of elements becomes of the order of thousands, the physical layout for individual readout amplifiers becomes nearly impossible to realize for practical systems. Another important concern is the large number of wires leading to a 0.1-0.3 K platform. In the case of superconducting transition edge sensors (TES), a scheme for time-division multiplexing of SQUID read-out amplifiers has been recently demonstrated. In this scheme the number of SQUIDs is equal to the number (N) of the detectors, but only one SQUID is turned on at a time. The SQUIDs are connected in series in each column of the array, so the number of wires leading to the amplifiers can be reduced, but it is still of the order of N. Another approach uses a frequency domain multiplexing scheme of the bolometer array. The bolometers are biased with ac currents whose frequencies are individual for each element and are much higher than the bolometer bandwidth. The output signals are connected in series in a summing loop which is coupled to a single SQUID amplifier. The total number of channels depends on the ratio between the SQUID bandwidth and the bolometer bandwidth and can be at least 100 according to the authors. An important concern about this technique is a contribution of the out-of-band Johnson noise which multiplies by factor N(exp 1/2) for each frequency channel. We propose a novel solution for large format arrays based on the Hadamard transform coding technique which requires only one amplifier to read out the entire array of potentially many 1000's of elements and uses approximately 10 wires between the cold stage and room temperature electronics. This can significantly reduce the complexity of the readout circuits.

Karasik, Boris S.↗
NASA NTRS2002

Plasma Interaction with International Space Station High Voltage Solar Arrays

The International Space Station (ISS) is presently being assembled in low-earth orbit (LEO) operating high voltage solar arrays (-160 V max, -140 V typical with respect to the ambient atmosphere). At the station's present altitude, there exists substantial ambient plasma that can interact with the solar arrays. The biasing of an object to an electric potential immersed in plasma creates a plasma "sheath" or non-equilibrium plasma around the object to mask out the electric fields. A positively biased object can collect electrons from the plasma sheath and the sheath will draw a current from the surrounding plasma. This parasitic current can enter the solar cells and effectively "short out" the potential across the cells, reducing the power that can be generated by the panels. Predictions of collected current based on previous high voltage experiments (SAMPIE (Solar Array Module Plasma Interactions Experiment), PASP+ (Photovoltaic Array Space Power) were on the order of amperes of current. However, present measurements of parasitic current are on the order of several milliamperes, and the current collection mainly occurs during an "eclipse exit" event, i.e., when the space station comes out of darkness. This collection also has a time scale, t approx. 1000 s, that is much slower than any known plasma interaction time scales. The reason for the discrepancy between predictions and present electron collection is not understood and is under investigation by the PCU (Plasma Contactor Unit) "Tiger" team. This paper will examine the potential structure within and around the solar arrays, and the possible causes and reasons for the electron collection of the array.

John W. Heard↗
NASA NTRS2003

High Voltage Solar Array ARC Testing for a Direct Drive Hall Effect Thruster System

The deleterious effects of spacecraft charging are well known, particularly when the charging leads to arc events. The damage that results from arcing can severely reduce system lifetime and even cause critical system failures. On a primary spacecraft system such as a solar array, there is very little tolerance for arcing. Motivated by these concerns, an experimental investigation was undertaken to determine arc thresholds for a high voltage (200-500 V) solar array in a plasma environment. The investigation was in support of a NASA program to develop a Direct Drive Hall-Effect Thruster (112HET) system. By directly coupling the solar array to a Hall-effect thruster, the D2HET program seeks to reduce mass, cost and complexity commonly associated with the power processing in conventional power systems. In the investigation, multiple solar array technologies and configurations were tested. The cell samples were biased to a negative voltage, with an applied potential difference between them, to imitate possible scenarios in solar array strings that could lead to damaging arcs. The samples were tested in an environment that emulated a low-energy, HET-induced plasma. Short duration "trigger" arcs as well as long duration "sustained" arcs were generated. Typical current and voltage waveforms associated with the arc events are presented. Arc thresholds are also defined in terms of vo!tage, (current and power. The data will be used to propose a new, high-voltage (>300 V) solar array design for which the likelihood of damage from arcing is minimal.

Schneider, T.↗
NASA NTRS2004

Flexible Microsensor Array for the Monitoring and Control of Plant Growth System

Testing for plant experiments in space has begun to explore active nutrient delivery concepts in which water and nutrients are replenished on a continuous basis for long-term growth. The goal of this study is to develop a novel microsensor array to provide information on the dissolved oxygen environment in the plant root zone for the optimum control of hydroponics and solid substrate plant cultivation systems in the space environment. Miniaturized polarographic dissolved oxygen sensors have been designed and fabricated on a flexible Kapton (trademark) (polyimide) substrate. Two capabilities of the new microsensor array were explored. First, measurements of dissolved oxygen in the plant root zone in hydroponics and solid substrate culture systems were made. The microsensor array was fabricated on a flexible substrate, and then cut out into a mesh type to make a suspended array that could be placed either in a hydroponics system or in a solid substrate cultivation system to measure the oxygen environments. Second, the in situ self-diagnostic and self-calibration capability (two-point for oxygen) was adopted by dynamically controlling the microenvironment in close proximity to the microsensors. With a built-in generating electrode that surrounds the microsensor, two kinds of microenvironments (oxygen-saturated and oxygen-depleted phases) could be established by water electrolysis depending on the polarity of the generating electrode. The unique features of the new microsensor array (small size, multiple sensors, flexibility and self-diagnosis) can have exceptional benefits for the study and optimization of plant cultivation systems in both terrestrial and microgravity environments. The in situ self-diagnostic and self-calibration features of the microsensor array will also enable continuous verification of the operability during entire plant growth cycles. This concept of automated control of a novel chemical monitoring system will minimize crew time required for maintenance, as well as reduce volume, mass, and power consumption by eliminating bulky diagnosis systems including calibrant (fluid and gas) reservoir and flow system hardware.

Kim, Chang-Soo↗
NASA NTRS2002

Ordered nanoparticle arrays formed on engineered chaperonin protein templates

Traditional methods for fabricating nanoscale arrays are usually based on lithographic techniques. Alternative new approaches rely on the use of nanoscale templates made of synthetic or biological materials. Some proteins, for example, have been used to form ordered two-dimensional arrays. Here, we fabricated nanoscale ordered arrays of metal and semiconductor quantum dots by binding preformed nanoparticles onto crystalline protein templates made from genetically engineered hollow double-ring structures called chaperonins. Using structural information as a guide, a thermostable recombinant chaperonin subunit was modified to assemble into chaperonins with either 3 nm or 9 nm apical pores surrounded by chemically reactive thiols. These engineered chaperonins were crystallized into two-dimensional templates up to 20 microm in diameter. The periodic solvent-exposed thiols within these crystalline templates were used to size-selectively bind and organize either gold (1.4, 5 or 10nm) or CdSe-ZnS semiconductor (4.5 nm) quantum dots into arrays. The order within the arrays was defined by the lattice of the underlying protein crystal. By combining the self-assembling properties of chaperonins with mutations guided by structural modelling, we demonstrate that quantum dots can be manipulated using modified chaperonins and organized into arrays for use in next-generation electronic and photonic devices.

Chaperonins/chemistry/ultrastructure↗
NASA NTRS2004

High Voltage Solar Array Arc Testing for a Direct Drive Hall Effect Thruster System

The deleterious effects of spacecraft charging are well known, particularly when the charging leads to arc events. The damage that results from arcing can severely reduce system lifetime and even cause critical system failures. On a primary spacecraft system such as a solar array, there is very little tolerance for arcing. Motivated by these concerns, an experimental investigation was undertaken to determine arc thresholds for a high voltage (200-500 V) solar array in a plasma environment. The investigation was in support of a NASA program to develop a Direct Drive Hall-Effect Thruster (D2HET) system. By directly coupling the solar array to a Hall-effect thruster, the D2HET program seeks to reduce mass, cost and complexity commonly associated with the power processing in conventional power systems. In the investigation, multiple solar array technologies and configurations were tested. The cell samples were biased to a negative voltage, with an applied potential difference between them, to imitate possible scenarios in solar array strings that could lead to damaging arcs. The samples were tested in an environment that emulated a low-energy, HET-induced plasma. Short duration trigger arcs as well as long duration sustained arcs were generated. Typical current and voltage waveforms associated with the arc events are presented. Arc thresholds are also defined in terms of voltage, current and power. The data will be used to propose a new, high-voltage (greater than 300 V) solar array design for which the likelihood of damage from arcing is minimal.

Schneider, Todd↗
NASA NTRS2004

Assessment of High-Voltage Photovoltaic Technologies for the Design of a Direct Drive Hall Effect Thruster Solar Array

A three-year program to develop a Direct Drive Hall-Effect Thruster system (D2HET) begun in 2001 as part of the NASA Advanced Cross-Enterprise Technology Development initiative. The system, which is expected to reduce significantly the power processing, complexity, weight, and cost over conventional low-voltage systems, will employ solar arrays that operate at voltages higher than (or equal to) 300 V. The lessons learned from the development of the technology also promise to become a stepping-stone for the production of the next generation of power systems employing high voltage solar arrays. This paper summarizes the results from experiments conducted mainly at the NASA Marshal Space Flight Center with two main solar array technologies. The experiments focused on electron collection and arcing studies, when the solar cells operated at high voltages. The tests utilized small coupons representative of each solar array technology. A hollow cathode was used to emulate parts of the induced environment on the solar arrays, mostly the low-energy charge-exchange plasma (1012-1013 m-3 and 0.5-1 eV). Results and conclusions from modeling of electron collection are also summarized. The observations from the total effort are used to propose a preliminary, new solar array design for 2 kW and 30-40 kW class, deep space missions that may employ a single or a cluster of Hall- Effect thrusters.

Mikellides, I. G.↗
NASA NTRS2004

The Rossi X-Ray Timing Explorer (XTE) Solar Array Anomaly

The XTE was launched December 30, 1995. Shortly after launch, it become apparent that the solar array was not performing as expected. On leaving shadow, the array exhibited many discontinuous drops in current output. The size of each of these drops was consistent with the loss of a part of a sell. The current decreases could not be caused by the loss of an entire circuit. This meant that the array may have had numerous cracked solar cells that opened as array got warmer. Studies performed on the array's qualification panel suggest that the cell cracks may have been cased by extensive tap testing performed on the array and that these cracks were undetectable at room temperature using usual inspection method.

Gaddy, Edward M.↗
NASA NTRS2004

Design and Fabrication of a Two-Dimensional Superconducting Pop-up Bolometer Array

We have been developing an architecture for producing large format, two dimensional arrays of close-packed bolometers, which will enable submillimeter cameras and spectrometers to obtain images and spectra orders of magnitude faster than present instruments. The low backgrounds achieved in these instruments require very sensitive detectors with NEPs of order 5 x 10(exp -18) W/square root of Hz. Superconducting transition edge sensor bolometers can be close-packed using the Pop-up Detector (PUD) format, and SQUID multiplexers operating at the detector base temperature can be intimately coupled to them. The array unit cell is 8 x 32 pixels, using 32- element detector and multiplexer components. We have fabricated an engineering model array with this technology which features a very compact, modular approach for large format arrays. We report on the production of the 32-element components for the arrays. Planned instruments using this array architecture include the Submillimeter and Far-InfraRed Experiment (SAFIRE) on the SOFIA airborne observatory, the South Pole Imaging Fabry-Perot Interferometer (SPIFI) for the AST/RO observatory, the Millimeter Bolometer Camera for the Atacama Cosmology Telescope (MBC/ACT), and the Redshift (Z) Early Universe Spectrometer (ZEUS j.

Benford, Dominic J.↗
NASA NTRS1999

K-Band Phased Array Developed for Low- Earth-Orbit Satellite Communications

Future rapid deployment of low- and medium-Earth-orbit satellite constellations that will offer various narrow- to wide-band wireless communications services will require phased-array antennas that feature wide-angle and superagile electronic steering of one or more antenna beams. Antennas, which employ monolithic microwave integrated circuits (MMIC), are perfectly suited for this application. Under a cooperative agreement, an MMIC-based, K-band phased-array antenna is being developed with 50/50 cost sharing by the NASA Lewis Research Center and Raytheon Systems Company. The transmitting array, which will operate at 19 gigahertz (GHz), is a state-of-the-art design that features dual, independent, electronically steerable beam operation ( 42 ), a stand-alone thermal management, and a high-density tile architecture. This array can transmit 622 megabits per second (Mbps) in each beam from Earth orbit to small Earth terminals. The weight of the total array package is expected to be less than 8 lb. The tile integration technology (flip chip MMIC tile) chosen for this project represents a major advancement in phased-array engineering and holds much promise for reducing manufacturing costs.

Anzic, Godfrey↗
NASA NTRS2002

High-Temperature Gas Sensor Array (Electronic Nose) Demonstrated

The ability to measure emissions from aeronautic engines and in commercial applications such as automotive emission control and chemical process monitoring is a necessary first step if one is going to actively control those emissions. One single sensor will not give all the information necessary to determine the chemical composition of a high-temperature, harsh environment. Rather, an array of gas sensor arrays--in effect, a high-temperature electronic "nose"--is necessary to characterize the chemical constituents of a diverse, high-temperature environment, such as an emissions stream. The signals produced by this nose could be analyzed to determine the constituents of the emission stream. Although commercial electronic noses for near-room temperature applications exist, they often depend significantly on lower temperature materials or only one sensor type. A separate development effort necessary for a high-temperature electronic nose is being undertaken by the NASA Glenn Research Center, Case Western Reserve University, Ohio State University, and Makel Engineering, Inc. The sensors are specially designed for hightemperature environments. A first-generation high-temperature electronic nose has been demonstrated on a modified automotive engine. This nose sensor array was composed of sensors designed for hightemperature environments fabricated using microelectromechanical-systems- (MEMS-) based technology. The array included a tin-oxide-based sensor doped for nitrogen oxide (NOx) sensitivity, a SiC-based hydrocarbon (CxHy) sensor, and an oxygen sensor (O2). These sensors operate on different principles--resistor, diode, and electrochemical cell, respectively--and each sensor has very different responses to the individual gases in the environment. A picture showing the sensor head for the array is shown in the photograph on the left and the sensors installed in the engine are shown in the photograph on the right. Electronics are interfaced with the sensors for temperature control and signal conditioning, and packaging designed for high temperatures is necessary for the array to survive the engine environment.

Hunter, Gary W.↗
NASA NTRS2005

LEO Download Capacity Analysis for a Network of Adaptive Array Ground Stations

To lower costs and reduce latency, a network of adaptive array ground stations, distributed across the United States, is considered for the downlink of a polar-orbiting low earth orbiting (LEO) satellite. Assuming the X-band 105 Mbps transmitter of NASA s Earth Observing 1 (EO-1) satellite with a simple line-of-sight propagation model, the average daily download capacity in bits for a network of adaptive array ground stations is compared to that of a single 11 m dish in Poker Flats, Alaska. Each adaptive array ground station is assumed to have multiple steerable antennas, either mechanically steered dishes or phased arrays that are mechanically steered in azimuth and electronically steered in elevation. Phased array technologies that are being developed for this application are the space-fed lens (SFL) and the reflectarray. Optimization of the different boresight directions of the phased arrays within a ground station is shown to significantly increase capacity; for example, this optimization quadruples the capacity for a ground station with eight SFLs. Several networks comprising only two to three ground stations are shown to meet or exceed the capacity of the big dish, Cutting the data rate by half, which saves modem costs and increases the coverage area of each ground station, is shown to increase the average daily capacity of the network for some configurations.

Ingram, Mary Ann↗
NASA NTRS2007

Steerable Space Fed Lens Array for Low-Cost Adaptive Ground Station Applications

The Space Fed Lens Array (SFLA) is an alternative to a phased array antenna that replaces large numbers of expensive solid-state phase shifters with a single spatial feed network. SFLA can be used for multi-beam application where multiple independent beams can be generated simultaneously with a single antenna aperture. Unlike phased array antennas where feed loss increases with array size, feed loss in a lens array with more than 50 elements is nearly independent of the number of elements, a desirable feature for large apertures. In addition, SFLA has lower cost as compared to a phased array at the expense of total volume and complete beam continuity. For ground station applications, both of these tradeoff parameters are not important and can thus be exploited in order to lower the cost of the ground station. In this paper, we report the development and demonstration of a 952-element beam-steerable SFLA intended for use as a low cost ground station for communicating and tracking of a low Earth orbiting satellite. The dynamic beam steering is achieved through switching to different feed-positions of the SFLA via a beam controller.

Lee, Richard Q.↗
NASA NTRS2007

Automated Hybridization of X-ray Absorber Elements-A Path to Large Format Microcalorimeter Arrays

In the design of microcalorimeters, it is often desirable to produce the X-ray absorber separately from the detector element. In this case, the attachment of the absorber to the detector element with the required thermal and mechanical characteristics is a major challenge. In such arrays, the attachment has been done by hand. This process is not easily extended to the large format arrays required for future X- ray astronomy missions such as the New x-ray Telescope or NeXT. In this paper we present an automated process for attaching absorber tiles to the surface of a large-scale X-ray detector array. The absorbers are attached with stycast epoxy to a thermally isolating polymer structure made of SU-8. SU-8 is a negative epoxy based photo resist produced by Microchem. We describe the fabrication of the X-ray absorbers and their suspension on a handle die in an adhesive matrix. We describe the production process for the polymer isolators on the detector elements. We have developed a new process for the alignment, and simultaneous bonding of the absorber tiles to an entire detector array. This process uses equipment and techniques used in the flip-chip bonding industry and approaches developed in the fabrication of the XRS-2 instrument. XRS-2 was an X-ray spectrometer that was launched on the Suzaku telescope in July 10, 2005. We describe the process and show examples of sample arrays produced by this process. Arrays with up to 300 elements have been bonded. The present tests have used dummy absorbers made of Si. In future work, we will demonstrate bonding of HgTe absorbers.

Moseley, S.↗
NASA NTRS1993

Differential temperature stress measurement employing array sensor with local offset

The instrument has a focal plane array of infrared sensors of the integrating type such as a multiplexed device in which a charge is built up on a capacitor which is proportional to the total number of photons which that sensor is exposed to between read-out cycles. The infrared sensors of the array are manufactured as part of an overall array which is part of a micro-electronic device. The sensor achieves greater sensitivity by applying a local offset to the output of each sensor before it is converted into a digital word. The offset which is applied to each sensor will typically be the sensor's average value so that the digital signal which is periodically read from each sensor of the array corresponds to the portion of the signal which is varying in time. With proper synchronization between the cyclical loading of the test object and the frame rate of the infrared array the output of the A/D converted signal will correspond to the stress field induced temperature variations. A digital lock-in operation may be performed on the output of each sensor in the array. This results in a test instrument which can rapidly form a precise image of the thermoelastic stresses in an object.

Lesniak, Jon R.↗
NASA NTRS1992

Geometric fiedlity of imaging systems employing sensor arrays

A sensor assembly to be carried on an aircraft or spacecraft which will travel along an arbitrary flight path, for providing an image of terrain over which the craft travels. The assembly includes a main linear sensor array and a plurality of auxiliary sensor arrays oriented parallel to, and at respectively different distances from, the main array. By comparing the image signals produced by the main sensor array with those produced by each auxiliary array, information relating to variations in velocity of the craft carrying the assembly can be obtained. The signals from each auxiliary array will provide information relating to a respectively different frequency range.

Jones, Kenneth L.↗
NASA NTRS2008

Testing Microshutter Arrays Using Commercial FPGA Hardware

NASA is developing micro-shutter arrays for the Near Infrared Spectrometer (NIRSpec) instrument on the James Webb Space Telescope (JWST). These micro-shutter arrays allow NIRspec to do Multi Object Spectroscopy, a key part of the mission. Each array consists of 62414 individual 100 x 200 micron shutters. These shutters are magnetically opened and held electrostatically. Individual shutters are then programmatically closed using a simple row/column addressing technique. A common approach to provide these data/clock patterns is to use a Field Programmable Gate Array (FPGA). Such devices require complex VHSIC Hardware Description Language (VHDL) programming and custom electronic hardware. Due to JWST's rapid schedule on the development of the micro-shutters, rapid changes were required to the FPGA code to facilitate new approaches being discovered to optimize the array performance. Such rapid changes simply could not be made using conventional VHDL programming. Subsequently, National Instruments introduced an FPGA product that could be programmed through a Labview interface. Because Labview programming is considerably easier than VHDL programming, this method was adopted and brought success. The software/hardware allowed the rapid change the FPGA code and timely results of new micro-shutter array performance data. As a result, numerous labor hours and money to the project were conserved.

Rapchun, David↗