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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 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Thermal evaluation of advanced solar dynamic heat receiver performance

The thermal performance of a variety of concepts for thermal energy storage as applied to solar dynamic applications is discussed. It is recognized that designs providing large thermal gradients or large temperature swings during orbit are susceptible to early mechanical failure. Concepts incorporating heat pipe technology may encounter operational limitations over sufficiently large ranges. By reviewing the thermal performance of basic designs, the relative merits of the basic concepts are compared. In addition the effect of thermal enhancement and metal utilization as applied to each design provides a partial characterization of the performance improvements to be achieved by developing these technologies.

Crane, Roger A.↗
NASA NTRS1989

Compatibility of molten salts with advanced solar dynamic receiver materials

Metal-coated graphite fibers are being considered as a thermal conductivity enhancement filler material for molten salts in solar dynamic thermal energy storage systems. The successful metal coating chosen for this application must exhibit acceptable wettability and must be compatible with the molten salt environment. Contact angle values between molten lithium fluoride and several metal, metal fluoride, and metal oxide substrates have been determined at 892 C using a modification of the Wilhelmy plate technique. Reproducible contact angles with repeated exposure to the molten LiF indicated compatibility.

Jaworske, D. A.↗
NASA NTRS1990

Digital Demodulator For Advanced Receiver

Complexity and cost reduced by new design for half-band filters. Digital demodulator designed for use in reception of phase- and amplitude-modulated digital signals of bandwidths up to 15 MHz on microwave carriers. System performs coherent demodulation in phase and in quadrature with carrier locked in phase to intermediate frequency of 10 MHz. Design suitable for fabrication in very-large-scale integrated circuitry. Principal innovative feature of demodulator is design of half-band digital low-pass filters that remove sum-frequency components.

Sadr, Ramin↗
NASA NTRS1988

Resonant-tunneling oscillators and multipliers for submillimeter receivers

Resonant tunneling through double-barrier heterostructures has attracted increasing interest recently, largely because of the fast charge transport it provides. In addition, the negative differential resistance regions that exist in the current-voltage (I-V) curve (peak-to-valley ratios of 3.5:1 at room temperature, and nearly 10:1 at 77 K, were measured) suggest that high-speed devices based on the character of the I-V curve should be possible. For example, the negative differential resistance region is capable of providing the gain necessary for high-frequency oscillations. In the laboratory attempts were made to increase the frequency and power of these oscillators and to demonstrate several different high-frequency devices.

Sollner, T. C. L. Gerhard↗
NASA NTRS1989

Performance of the all-digital data-transition tracking loop in the advanced receiver

The performance of the all-digital data-transition tracking loop (DTTL) with coherent or noncoherent sampling is described. The effects of few samples per symbol and of noncommensurate sampling rates and symbol rates are addressed and analyzed. Their impacts on the loop phase-error variance and the mean time to lose lock (MTLL) are quantified through computer simulations. The analysis and preliminary simulations indicate that with three to four samples per symbol, the DTTL can track with negligible jitter because of the presence of earth Doppler rate. Furthermore, the MTLL is also expected to be large engough to maintain lock over a Deep Space Network track.

Cheng, U.↗
NASA NTRS1990

Performance of a 300 Mbps 1:16 serial/parallel optoelectronic receiver module

Optical interconnects are being considered for the high speed distribution of multiplexed control signals in GaAs monolithic microwave integrated circuit (MMIC) based phased array antennas. The performance of a hybrid GaAs optoelectronic integrated circuit (OEIC) is described, as well as its design and fabrication. The OEIC converts a 16-bit serial optical input to a 16 parallel line electrical output using an on-board 1:16 demultiplexer and operates at data rates as high as 30b Mbps. The performance characteristics and potential applications of the device are presented.

Richard, M. A.↗
NASA NTRS1989

The cavity heat pipe Stirling receiver for space solar dynamics

The receiver/storage unit for the low-earth-orbiting Stirling system is discussed. The design, referred to as the cavity heat pipe (CHP), has been optimized for minimum specific mass and volume width. A specific version of this design at the 7-kWe level has been compared to the space station Brayton solar dynamic design. The space station design utilizes a eutectic mixture of LiF and CaF2. Using the same phase change material, the CHP has been shown to have a specific mass of 40 percent and a volume of 5 percent of that of the space station Brayton at the same power level. Additionally, it complements the free-piston Stirling engine in that it also maintains a relatively flat specific mass down to at least 1 kWe. The technical requirements, tradeoff studies, critical issues, and critical technology experiments are discussed.

Kesseli, James B.↗
NASA NTRS1990

Efficient space propulsion and power using a high-temperature, gaseous radiation receiver

A two-dimensional analysis is carried out for a flowing gas radiation heater, a device whereby focused solar radiation is deposited volumetrically in a gas to produce high temperatures for space power or propulsion. The paper includes radiative losses to the walls of the absorption chamber, and demonstrates that if wall reflectivity exceeds 75 percent, gas temperatures above 3000 K are possible.

Mattick, A. T.↗
NASA NTRS1991

Symbol lock detection in the ARX 2 and Block 5 receivers

The performances of 5 symbol-lock detectors are compared. These detectors are the square-law detector with overlapping (SQOD) and nonoverlapping integrators, the absolute-value detectors with overlapping and nonoverlapping integrators, and the signal-power estimator detector (SPED). The analysis considers various scenarios in which the observation interval is much larger than or equal to the symbol-synchronizer loop bandwidth, and which were not considered in previous analyses. Also, the case of threshold setting in the absence of signal is considered. It is shown, that the SQOD outperforms all others when the threshold is set in the presence of a signal, independent of the relationship between loop bandwidth and observation period. On the other hand, the SPED outperforms all others when the threshold is set in the presence of noise only.

Shihabi, M.↗
NASA NTRS1990

Performance of a 300 Mbps 1:16 serial/parallel optoelectronic receiver module

Optical interconnects are being considered for the high speed distribution of multiplexed control signals in GaAs MMIC-based phased array antennas. This paper describes the performance of a hybrid GaAs optoelectronic integrated circuit (OEIC), along with a description of its design and fabrication. The OEIC converts a 16-bit serial optical input to a 16 parallel line electrical output using an on-board 1:16 demultiplexer and operates at data rates as high as 305 Mbps. The performance characteristics as well as potential applications of the device are presented.

Richard, M. A.↗
NASA NTRS1991

Low noise InP-based MMIC receivers for W-band

A program to develop a monolithic W-band low noise amplifier (a critical element in any W-band communications, sensors, or radar application) is described. Goals of the program include a completely monolithic low noise amplifier, less than a 3.5 dB noise figure, and a monolithic mixer suitable for integration with the LNA.

Leonard, Regis F.↗
NASA NTRS1990

Synchronization techniques for all digital 16-ary QAM receivers operating over land mobile satellite links

The performance of a low bit rate (64 Kb/s) all digital 16-ary Differentially Encoded Quadrature Amplitude Modulation (16-DEQAM) demodulator operating over a mobile satellite channel, is considered. The synchronization and detection techniques employed to overcome the Rician channel impairments, are described. The acquisition and steady state performance of this modem, are evaluated by computer simulation over AWGN and RICIAN channels. The results verify the suitability of the 16-DEQAM transmission over slowly faded and/or mildly faded channels.

Fines, P.↗
NASA NTRS1992

Post-test examination of a pool boiler receiver

A subscale pool boiler test apparatus to evaluate boiling stability developed a leak after being operated with boiling NaK for 791.4 hr at temperatures from 700 to 750 C. The boiler was constructed using Inconel 625 with a type 304L stainless steel wick for the boiler and type 316 stainless steel for the condenser. The boiler assembly was metallurgically evaluated to determine the cause of the leak and to assess the effects of the NaK on the materials. It was found that the leak was caused by insufficient (about 30 pct.) joint penetration in a butt joint. There was no general corrosion of the construction materials, but the room temperature ductility of the Inconel 625 was only about 6.5 pct. A crack in the heat affected zone of the Inconel 625 near the Inconel 625 to type 316 stainless steel butt joint was probably caused by excessive heat input. The crack was observed to have a zone depleted of iron at the crack surface and porosity below that zone. The mechanism of the iron depletion was not conclusively determined.

Dreshfield, Robert L.↗
NASA NTRS1992

A fixed tuned broadband matching structure for submillimeter SIS receivers

We have designed, fabricated, and tested a quasi-optical spiral antenna mixer with a Nb/AlO(x)/Nb tunnel junction. This design incorporates a hybrid antenna fed by a planar logarithmic spiral antenna to couple to the radiation field, as previously done with Pb based devices, as well as a newly designed matching circuit. This matching circuit is a relatively complex structure requiring several layers of photolithographic processing on top of the actual tunneling device. Computer modeling of the device predicted the measured bandwidth to within 8 percent, making scale model measurements unnecessary. We have obtained a good match from 210 GHz to 460 GHz between the antenna and a relatively large area (1.25 by 1.25 sq microns) tunnel junction with omega R(sub N) C approx. = 2 - 4.4. This compares to simple inductive stubs that attain only a few percent of total bandwidth in the submillimeter band or inductively tuned SIS arrays with an upper limit of operating frequencies well below the submillimeter band. Noise temperatures were measured at 345 GHz, 426 GHz, and 492 GHz yielding double sideband noise temperatures at 200 K, 220 K, and 500 K, respectively.

Buettgenbach, Thomas H.↗
NASA NTRS1992

Progress in integrated-circuit horn antennas for receiver applications. Part 1: Antenna design

The purpose of this work is to present a systematic method for the design of multimode quasi-integrated horn antennas. The design methodology is based on the Gaussian beam approach and the structures are optimized for achieving maximum fundamental Gaussian coupling efficiency. For this purpose, a hybrid technique is employed in which the integrated part of the antennas is treated using full-wave analysis, whereas the machined part is treated using an approximate method. This results in a simple and efficient design process. The developed design procedure has been applied for the design of a 20, a 23, and a 25 dB quasi-integrated horn antennas, all with a Gaussian coupling efficiency exceeding 97 percent. The designed antennas have been tested and characterized using both full-wave analysis and 90 GHz/370 GHz measurements.

Eleftheriades, George V.↗
NASA NTRS1992

Progress on ten-meter optical receiver telescope

A ten-meter hexagonally segmented Cassegrain optical telescope is being considered at the Jet Propulsion Laboratory for use as a research and development facility for optical communications technology. The goal of the study is to demonstrate technology which can eventually be used to develop a network of such telescopes to continuously track and communicate with the spacecraft. Hence, the technology has to be economical enough to allow replication for a ground or space based network. As we need to collect signal photons only, the telescope cost can be substantially reduced by accepting lower image quality. An important design consideration for the telescope is its ability to look very close to the sun. The telescope for optical communications must function during the daytime. Indeed, for some planetary missions it may be necessary that the system be capable of looking within a few degrees of the sun. To enable this, a unique sunshade consisting of hexagonal tubes in precise alignment with the mirror segments has been proposed which will also serve as the support for the secondary. Recent progress on the design and analysis of such an optical reception station is discussed here.

Shaik, Kamran↗
NASA NTRS1992

Real-time processor for staring receivers

The design, fabrication, and testing of a state-of-the-art, high-throughput on-focal plane IR-image signal processor is described. The processing functions performed are frame differencing and thresholding. The final focal plane array will consist of a 128 x 128-pixel platinum-silicide detector bump-mounted to an on-chip CCD multiplexer. The processor is in a 128-channel parallel-pipeline format. Each channel consists of a pixel regenerator (charge differencer), 128-pixel frame store CCD memory, pixel differencer, second pixel regenerator, thresholder (analog comparator), and digital latch. Four parallel analog outputs and four parallel digital outputs are included. The digital outputs provide a bit map of the image. All analog clock signals (128 KHz, 256 KHz, and 5 MHz) are generated by on-chip TTL-input clock drivers. TTL clock driver inputs are generated off-chip. The technology is low-temperature surface and buried channel CCD/CMOS/indium bump. The design goal was 8-bit resolution at 77 K and 1000 frames/s. Applications include point- or extended-target motion detection with thresholding. Design trade-offs and enhancements (such as on-chip detector gain compensation and a simple window processor) are discussed.

Hanzal, Brian↗