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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Screen printing technology applied to silicon solar cell fabrication

The process for producing space qualified solar cells in both the conventional and wraparound configuration using screen printing techniques was investigated. Process modifications were chosen that could be easily automated or mechanized. Work was accomplished to optimize the tradeoffs associated with gridline spacing, gridline definition and junction depth. An extensive search for possible front contact metallization was completed. The back surface field structures along with the screen printed back contacts were optimized to produce open circuit voltages of at least an average of 600 millivolts. After all intended modifications on the process sequence were accomplished, the cells were exhaustively tested. Electrical tests at AMO and 28 C were made before and after boiling water immersion, thermal shock, and storage under conditions of high temperature and high humidity.

Thornhill, J. W.↗
NASA NTRS1985

Processing technology for high efficiency silicon solar cells

Recent advances in silicon solar cell processing have led to attainment of conversion efficiency approaching 20%. The basic cell design is investigated and features of greatest importance to achievement of 20% efficiency are indicated. Experiments to separately optimize high efficiency design features in test structures are discussed. The integration of these features in a high efficiency cell is examined. Ion implantation has been used to achieve optimal concentrations of emitter dopant and junction depth. The optimization reflects the trade-off between high sheet conductivity, necessary for high fill factor, and heavy doping effects, which must be minimized for high open circuit voltage. A second important aspect of the design experiments is the development of a passivation process to minimize front surface recombination velocity. The manner in which a thin SiO2 layer may be used for this purpose is indicated without increasing reflection losses, if the antireflection coating is properly designed. Details are presented of processing intended to reduce recombination at the contact/Si interface. Data on cell performance (including CZ and ribbon) and analysis of loss mechanisms are also presented.

Spitzer, M. B.↗
NASA NTRS2016

Unexpected Nonlinear Effects in Superconducting Transition-Edge Sensors

When a normal metal transitions into the superconducting state the DC resistance drops from a finite value to zero over some finite transition width in temperature, current, and magnetic field. Superconducting transition-edge sensors (TESs) operate within this transition region and uses resistive changes to measure deposited thermal energy. This resistive transition is not perfectly smooth and a wide range of TES designs and materials show sub-structure in the resistive transition (as seen in smooth nonmonotonic behavior, jump discontinuities, and hysteresis in the devices current-voltage relation and derivatives of the resistance with respect to temperature, bias current, and magnetic field). TES technology has advanced to the point where for many applications this structure is the limiting factor in performance and optimization consists of finding operating points away from these structures. For example, operating at or near this structure can lead to nonlinearity in the detectors response and gain scale, limit the spectral range of the detector by limiting the usable resistive range, and degrade energy resolution. The origin of much of this substructure is unknown. This presentation investigates a number of possible sources in turn. First we model the TES as a superconducting weak-link and solve for the characteristic differential equations current and voltage time dependence. We find:(1) measured DC biased current-voltage relationship is the time-average of a much higher frequency limit cycle solution.(2) We calculate the fundamental frequency and estimate the power radiated from the TES treating the bias leads as an antennae.(3) The solution for a set of circuit parameters becomes multivalued leading to current transitions between levels.(4)The circuit parameters can change the measure resistance and mask the true critical current. As a consequence the TES resistance surface is not just a function of temperature, current, and magnetic field but is also a function of the circuit elements (such as shunt resistor, SQUID inductance, and capacitor values). In other words, same device measured in different electrical circuits will have a different resistive surface in temperature, current, and magnetic field. Next we consider that at the transition temperature of a superconductor both the magnetic penetration depth and coherence length are divergent. As a consequence these important characteristic length scales are changing with operating point. We present measurements on devices showing commensurate behavior between these characteristic lengths and the length scale of added normal metal structures. Reordering of proximity vortices leads to discontinuities and irreversibility of the current-voltage curves. Last we consider a weak-link TES including both thermal activated resistance effects and the effect of the magnetic penetration depth being a function of temperature and magnetic field. We derive its impact on the resistive transition surface and the important device parameters a and b.

Superconducting Detectors↗
NASA NTRS2007

Imaging Spectrometer on a Chip

A proposed visible-light imaging spectrometer on a chip would be based on the concept of a heterostructure comprising multiple layers of silicon-based photodetectors interspersed with long-wavelength-pass optical filters. In a typical application, this heterostructure would be replicated in each pixel of an image-detecting integrated circuit of the active-pixel-sensor type (see figure). The design of the heterostructure would exploit the fact that within the visible portion of the spectrum, the characteristic depth of penetration of photons increases with wavelength. Proceeding from the front toward the back, each successive long-wavelength-pass filter would have a longer cutoff wavelength, and each successive photodetector would be made thicker to enable it to absorb a greater proportion of incident longer-wavelength photons. Incident light would pass through the first photodetector and encounter the first filter, which would reflect light having wavelengths shorter than its cutoff wavelength and pass light of longer wavelengths. A large portion of the incident and reflected shorter-wavelength light would be absorbed in the first photodetector. The light that had passed through the first photodetector/filter pair of layers would pass through the second photodetector and encounter the second filter, which would reflect light having wavelengths shorter than its cutoff wavelength while passing light of longer wavelengths. Thus, most of the light reflected by the second filter would lie in the wavelength band between the cutoff wavelengths of the first and second filters. Thus, further, most of the light absorbed in the second photodetector would lie in this wavelength band. In a similar manner, each successive photodetector would detect, predominantly, light in a successively longer wavelength band bounded by the shorter cutoff wavelength of the preceding filter and the longer cutoff wavelength of the following filter.

Wang, Yu↗
NASA NTRS2011

Internal Electrostatic Discharge Monitor - IESDM

A document discusses an innovation designed to effectively monitor dielectric charging in spacecraft components to measure the potential for discharge in order to prevent damage from internal electrostatic discharge (IESD). High-energy electrons penetrate the structural materials and shielding of a spacecraft and then stop inside dielectrics and keep accumulating. Those deposited charges generate an electric field. If the electric field becomes higher than the breakdown threshold (approx. =2 x 10(exp 5) V/cm), discharge occurs. This monitor measures potentials as a function of dielectric depth. Differentiation of potential with respect to the depth yields electric field. Direct measurement of the depth profile of the potential in a dielectric makes real-time electronic field evaluation possible without simulations. The IESDM has been designed to emulate a multi-layer circuit board, to insert very thin metallic layers between the dielectric layers. The conductors serve as diagnostic monitoring locations to measure the deposited electron-charge and the charge dynamics. Measurement of the time-dependent potential of the metal layers provides information on the amount of charge deposited in the dielectrics and the movement of that charge with time (dynamics).

Kim, Wousik↗
NASA NTRS1980

Satellite Power Systems (SPS) concept definition study. Volume 6: In-depth element investigation

The fabrication parameters of GaAs MESFET solid-state amplifiers considering a power added conversion efficiency of at least 80% and power gains of at least 10dB were determined. Operating frequency was 2.45 GHz although 914 MHz was also considered. Basic circuit to be considered was either Class C or Class E amplification. Two modeling programs were utilized. The results of several computer calculations considering differing loads, temperatures, and efficiencies are presented. Parametric data in both tabular and plotted form are presented.

Hanley, G. M.↗
NASA NTRS1996

Air Force NiH2 IPV storage testing

USAF Phillips Laboratory Nickel Hydrogen IPV storage test, performed at the Naval Surface Warfare Center (NSWC) at Crane Indiana, is discussed. The storage tests is just one component of the USAF Phillips Laboratory Nickel Hydrogen IPV Test Program. The plan was to store cells for a defined period and cycle matching cells to determine the effect on cycle life. The storage period was completed in April 95 and the cycling cells have achieved five years of real time LEO cycling. The two main objectives of the storage test are: to investigate various methods on NiH2 cells by using two different manufacturers and two different storage methods or conditions, and to determine the effect of storage method on cycle performance and cycle life by using matching cells cycling at 25% depth of discharge. The comparisons between individual cycle performance as well as cycle life are also reported. During the test the following variables has been considered: constant potential, cell current, open circuit voltage, and temperature. The results of the test are also discussed using charts and tables.

Smellie, Shawn↗
NASA NTRS1977

A gas filter correlation monitor for CO, CH4, and HCl

A fast response instrument for monitoring the atmospheric constituents CO, CH4, and HCl, using a modified nondispersive infrared technique, was designed, assembled, and tested. This gas filter correlation method uses a sample of gas to provide a selective filter for radiation absorbed in a gas mixture containing the specified gas. Depending on the spectral line broadening, temperature, and optical depth of the gas selected, exceptionally high spectral resolution may be attained. A description of the single beam rotating cell system and its specific application is presented along with the signal processing circuit. Calibrations of the instrument show that the technique can be used to measure CO, CH4, and HCl concentrations as small as 5 ppm-m. A field version was employed to measure diurnal variations of CO and CH4 and the interfering effects of other atmospheric gases were analyzed.

Sebacher, D. I.↗
NASA NTRS1984

Equivalent electron fluence for solar proton damage in GaAs shallow junction cells

The short-circuit current reduction in GaAs shallow junction heteroface solar cells was calculated according to a simplified solar cell damage model in which the nonuniformity of the damage as a function of penetration depth is treated explicitly. Although the equivalent electron fluence was not uniquely defined for low-energy monoenergetic proton exposure, an equivalent electron fluence is found for proton spectra characteristic of the space environment. The equivalent electron fluence ratio was calculated for a typical large solar flare event for which the proton spectrum is PHI(sub p)(E) = A/E(p/sq. cm) where E is in MeV. The equivalent fluence ratio is a function of the cover glass shield thickness or the corresponding cutoff energy E(sub c). In terms of the cutoff energy, the equivalent 1 MeV electron fluence ratio is r(sub p)(E sub c) = 10(9)/E(sub c)(1.8) where E(sub c) is in units of KeV.

Wilson, J. W.↗
NASA NTRS2000

Sub-Optical Lithography With Nanometer Definition Masks

Nanometer feature size lithography represents a major paradigm shift for the electronics and micro-electro-mechanical industries. In this paper, we discuss the capacity of dynamic focused reactive ion beam (FIB) etching systems to undertake direct and highly anisotropic erosion of thick evaporated gold coatings on boron-doped silicon X-ray mask membranes. FIB offers a new level of flexibility in micro fabrication, allowing for fast fabrication of X-ray masks, where pattern definition and surface alteration are combined in the same step which eliminates the whole lithographic process, in particular resist, resist development, electro-deposition and resist removal. Focused ion beam diameters as small as 7 nm can be obtained enabling fabrication well into the sub-20 nm regime. In preliminary demonstrations of this X-ray mask fabrication technique 22 nm width lines were milled directly through 0.9 microns of gold and a miniature mass spectrometer pattern was milled through over 0.5 microns of gold. Also presented are the results of the shadow printing, using the large depth of field of synchrotron high energy parallel X-ray beam, of these and other sub-optical defined patterns in photoresist conformally coated over surfaces of extreme topographical variation. Assuming that electronic circuits and/or micro devices scale proportionally, the surface area of devices processed with X-ray lithography and 20 nm critical dimension X-ray masks would be 0.5% that of contemporary devices (350 nm CD). The 20 CD mask fabrication represents an initial effort - a further factor of three reduction is anticipated which represents a further order-of-magnitude reduction in die area.

Hartley, Frank T.↗
NASA NTRS1977

CW ultrasonic bolt tensioning monitor

A CW ultrasonic device is described for measuring frequency shifts of the peak of a mechanical resonance in a body. One application of the device is measuring the strain in a bolt, and other applications such as measuring the thickness of a body, measuring the depth of a flaw in a body, measuring the elongation of a body, and measuring changes in velocity of sound in a body. The body is connected, by means of a CW transducer, to electrical circuit means including a narrow band RF amplifier to form a closed loop feedback marginal oscillator that frequency locks the device to the peak of a mechanical resonance in the body. When the frequency of this peak changes, because of a physical change in the body, the frequency of the oscillator changes. The device includes an automatic frequency resonant peak tracker that produces a voltage that is related to a change in frequency of the oscillator. This voltage is applied to the RF amplifier to change the center of its frequency band to include the frequency of the peak and is a measure of the frequency shift.

Heyman, J. S.↗
NASA NTRS1981

Diagnostic study of BSF silicon solar cells

Solar cells equipped with back surface fields (BSF) were fabricated by means of an aluminum alloy, boron diffusion, and boron ion implantation. The importance of initial thickness, resistivity, orientation, and the crystal growth method were examined. Aluminum in paste form was screen printed on the cell, followed by alloy formation at 800 C for a minute. Application of the BSFs resulted in open circuit voltage improvements dependent on the substrate resistivity, ranging from 10 mV at 0.3 ohm-cm to 50 mV at 15 ohm-cm. The gains in performance were attributed to a longer penetration depth, a heightened concentration profile at the interface, and higher concentrations in the p+ layer.

Yoo, H.↗
NASA NTRS1996

Computational Analysis of Static and Dynamic Behaviour of Magnetic Suspensions and Magnetic Bearings

Static modelling of magnetic bearings is often carried out using magnetic circuit theory. This theory cannot easily include nonlinear effects such as magnetic saturation or the fringing of flux in air-gaps. Modern computational tools are able to accurately model complex magnetic bearing geometries, provided some care is exercised. In magnetic suspension applications, the magnetic fields are highly three-dimensional and require computational tools for the solution of most problems of interest. The dynamics of a magnetic bearing or magnetic suspension system can be strongly affected by eddy currents. Eddy currents are present whenever a time-varying magnetic flux penetrates a conducting medium. The direction of flow of the eddy current is such as to reduce the rate-of-change of flux. Analytic solutions for eddy currents are available for some simplified geometries, but complex geometries must be solved by computation. It is only in recent years that such computations have been considered truly practical. At NASA Langley Research Center, state-of-the-art finite-element computer codes, 'OPERA', 'TOSCA' and 'ELEKTRA' have recently been installed and applied to the magnetostatic and eddy current problems. This paper reviews results of theoretical analyses which suggest general forms of mathematical models for eddy currents, together with computational results. A simplified circuit-based eddy current model proposed appears to predict the observed trends in the case of large eddy current circuits in conducting non-magnetic material. A much more difficult case is seen to be that of eddy currents in magnetic material, or in non-magnetic material at higher frequencies, due to the lower skin depths. Even here, the dissipative behavior has been shown to yield at least somewhat to linear modelling. Magnetostatic and eddy current computations have been carried out relating to the Annular Suspension and Pointing System, a prototype for a space payload pointing and vibration isolation system, where the magnetic actuator geometry resembles a conventional magnetic bearing. Magnetostatic computations provide estimates of flux density within airgaps and the iron core material, fringing at the pole faces and the net force generated. Eddy current computations provide coil inductance, power dissipation and the phase lag in the magnetic field, all as functions of excitation frequency. Here, the dynamics of the magnetic bearings, notably the rise time of forces with changing currents, are found to be very strongly affected by eddy currents, even at quite low frequencies. Results are also compared to experimental measurements of the performance of a large-gap magnetic suspension system, the Large Angle Magnetic Suspension Test Fixture (LAMSTF). Eddy current effects are again shown to significantly affect the dynamics of the system. Some consideration is given to the ease and accuracy of computation, specifically relating to OPERA/TOSCA/ELEKTRA.

Britcher, Colin P.↗
NASA NTRS1981

Life test of a nickel cadmium battery with a protection/reconditioning circuit

Results are discussed for a Ni-Cd battery test over a period of 8 years, 2 months and 44,213 simulated low Earth orbits. The battery cells were protected against overdischarge and reversal at discharge rates up to 25 amperes (1.25C) by a battery protection and reconditioning circuit. The circuit performed flawlessly during the test, and proved its value, both as a battery reconditioner and a cell protection device. Battery cell failures are also discussed. The test demonstrated the viability of using Ni-Cd batteries at depth-of-discharge up to 25 percent for over 5 years in a low Earth orbit.

Lanier, J. R., Jr.↗
NASA NTRS1987

Test results of a 60 volt bipolar nickel-hydrogen battery

In July, l986, a high-voltage nickel-hydrogen battery was assembled at the NASA Lewis Research Center. This battery incorporated bipolar construction techniques to build a 50-cell stack with approximately 1.0 A-hr capacity (C) and an open-circuit voltage of 65 V. The battery was characterized at both low and high current rates prior to pulsed and nonpulsed discharges. Pulse discharges at 5 and 10 C were performed before placing the battery on over 1400, 40% depth-of-discharge, low-earth-orbit cycles. The successful demonstration of a high-voltage bipolar battery in one containment vessel has advanced the technology to where nickel-hydrogen high-voltage systems can be constructed of several modules instead of hundreds of individual cells.

Cataldo, Russell L.↗
NASA NTRS2004

Deep-Sea Video Cameras Without Pressure Housings

Underwater video cameras of a proposed type (and, optionally, their light sources) would not be housed in pressure vessels. Conventional underwater cameras and their light sources are housed in pods that keep the contents dry and maintain interior pressures of about 1 atmosphere (.0.1 MPa). Pods strong enough to withstand the pressures at great ocean depths are bulky, heavy, and expensive. Elimination of the pods would make it possible to build camera/light-source units that would be significantly smaller, lighter, and less expensive. The depth ratings of the proposed camera/light source units would be essentially unlimited because the strengths of their housings would no longer be an issue. A camera according to the proposal would contain an active-pixel image sensor and readout circuits, all in the form of a single silicon-based complementary metal oxide/semiconductor (CMOS) integrated- circuit chip. As long as none of the circuitry and none of the electrical leads were exposed to seawater, which is electrically conductive, silicon integrated- circuit chips could withstand the hydrostatic pressure of even the deepest ocean. The pressure would change the semiconductor band gap by only a slight amount . not enough to degrade imaging performance significantly. Electrical contact with seawater would be prevented by potting the integrated-circuit chip in a transparent plastic case. The electrical leads for supplying power to the chip and extracting the video signal would also be potted, though not necessarily in the same transparent plastic. The hydrostatic pressure would tend to compress the plastic case and the chip equally on all sides; there would be no need for great strength because there would be no need to hold back high pressure on one side against low pressure on the other side. A light source suitable for use with the camera could consist of light-emitting diodes (LEDs). Like integrated- circuit chips, LEDs can withstand very large hydrostatic pressures. If power-supply regulators or filter capacitors were needed, these could be attached in chip form directly onto the back of, and potted with, the imager chip. Because CMOS imagers dissipate little power, the potting would not result in overheating. To minimize the cost of the camera, a fixed lens could be fabricated as part of the plastic case. For improved optical performance at greater cost, an adjustable glass achromatic lens would be mounted in a reservoir that would be filled with transparent oil and subject to the full hydrostatic pressure, and the reservoir would be mounted on the case to position the lens in front of the image sensor. The lens would by adjusted for focus by use of a motor inside the reservoir (oil-filled motors already exist).

Cunningham, Thomas↗
NASA NTRS1987

Test results of a 60 volt bipolar nickel-hydrogen battery

In July 1986, a high-voltage nickel-hydrogen battery was assembled at the NASA Lewis Research Center. This battery incorporated bipolar construction techniques to build a 50-cell stack with approximately 1.0 A-hr capacity (C) and an open-circuit voltage of 65 V. The battery was characterized at both low and high current rates prior to pulsed and nonpulsed discharges. Pulse discharges at 5 and 10 C were performed before placing the battery on over 1400, 40-percent depth-of-discharge, low-earth-orbit cycles. The successful demonstration of a high-voltage bipolar battery in one containment vessel has advanced the technology to where nickel-hydrogen high-voltage systems can be constructed of several modules instead of hundreds of individual cells.

Cataldo, Robert L.↗
NASA NTRS1988

Assessment of the effects of space debris and meteoroids environment on the Space Station solar array assembly

The methodology used to assess the probability of no impact of space debris and meteoroids on a spacecraft structure is applied to the Space Station solar array assembly. Starting with space debris and meteoroid flux models, the projected surface area of the solar cell string circuit of the solar array panel and the mast longeron, and the design lifetime, the possibility of no impact on the solar mast and solar cell string circuits was determined as a function of particle size. The probability of no impact on the cell string circuits was used to derive the probability of no open circuit panel. The probability of meeting a certain power requirement at the end of the design lifetime was then calculated as a function of impacting particle size. Coupled with a penetration and damage models/correlations which relate the particle size to penetration depth and damage, the results of this analysis can be used to determine the probability of meeting the lower power requirement given a degree of redundancy, and the probability of no impact on the solar array mast.

Nahra, Henry K.↗