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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Effectiveness of back-to-back testing

Three models of back-to-back testing processes are described. Two models treat the case where there is no intercomponent failure dependence. The third model describes the more realistic case where there is correlation among the failure probabilities of the functionally equivalent components. The theory indicates that back-to-back testing can, under the right conditions, provide a considerable gain in software reliability. The models are used to analyze the data obtained in a fault-tolerant software experiment. It is shown that the expected gain is indeed achieved, and exceeded, provided the intercomponent failure dependence is sufficiently small. However, even with the relatively high correlation the use of several functionally equivalent components coupled with back-to-back testing may provide a considerable reliability gain. Implications of this finding are that the multiversion software development is a feasible and cost effective approach to providing highly reliable software components intended for fault-tolerant software systems, on condition that special attention is directed at early detection and elimination of correlated faults.

Vouk, Mladen A.↗
NASA NTRS2004

Aerodynamic Characteristics and Glide-Back Performance of Langley Glide-Back Booster

NASA-Langley Research Center is conducting system level studies on an-house concept of a small launch vehicle to address NASA's needs for rapid deployment of small payloads to Low Earth Orbit. The vehicle concept is a three-stage system with a reusable first stage and expendable upper stages. The reusable first stage booster, which glides back to launch site after staging around Mach 3 is named the Langley Glide-Back Booster (LGBB). This paper discusses the aerodynamic characteristics of the LGBB from subsonic to supersonic speeds, development of the aerodynamic database and application of this database to evaluate the glide back performance of the LGBB. The aerodynamic database was assembled using a combination of wind tunnel test data and engineering level analysis. The glide back performance of the LGBB was evaluated using a trajectory optimization code and subject to constraints on angle of attack, dynamic pressure and normal acceleration.

Pamadi, Bandu N.↗
NASA NTRS1992

A new fabrication technique for back-to-back varactor diodes

A new varactor diode process has been developed in which much of the processing is done from the back of an extremely thin semiconductor wafer laminated to a low-dielectric substrate. Back-to-back BNN diodes were fabricated with this technique; excellent DC and low-frequency capacitance measurements were obtained. Advantages of the new technique relative to other techniques include greatly reduced frontside wafer damage from exposure to process chemicals, improved capability to integrate devices (e.g. for antenna patterns, transmission lines, or wafer-scale grids), and higher line yield. BNN diodes fabricated with this technique exhibit approximately the expected capacitance-voltage characteristics while showing leakage currents under 10 mA at voltages three times that needed to deplete the varactor. This leakage is many orders of magnitude better than comparable Schottky diodes.

Smith, R. Peter↗
NASA NTRS1995

Integrated back to back barrier-N-N(+) varactor diode tripler using a split-waveguide block

The back-to-back barrier-N-N(+) (bbBNN) varactor is a nonlinear device being developed for frequency multiplier applications above 100 GHz. Its symmetrical C-V characteristic, low series resistance, freedom from external bias and suitability to planarization make it an ideal choice for high frequency, low power, odd harmonic generation. In this paper, the performance of a 220-GHz waveguide tripler using, for the first time, a planar GaAs bbBNN device integrated on a quartz microstrip circuit is presented. A new split-waveguide block design has been employed to provide the proper embedding impedances to the device at the input and third harmonic output frequencies. A flange-to-flange tripling efficiency of 7% has been obtained at 220 GHz with an output power in excess of 700 mu W. This is believed to be the highest conversion efficiency yet reported for a tripler with an integrated device at this frequency. Theoretical calculations indicate that substantial improvement is possible with modest changes to the device and circuit parameters.

QUARTZ MICROSTRIP CIRCUITS↗
NASA NTRS1990

Back-To-Back, Counterrotating Turbopumps

Pair of counterrotating turbopumps mounted back to back in novel one-piece volute housing. Serves as spool piece into which pumps inserted, one from each end. Includes turbine inlet and outlet volutes. Enables easy replacement of each pump/turbine assembly. Designed to provide fuel and oxidizer to rocket engine at high pressures; modified versions useful in providing other two-fluid high-pressure flows or redundant high-pressure flow of single fluid.

Palgon, Alfred M.↗
NASA NTRS1989

A comparison of the merits of open-back, symmetric sandwich, and contoured back mirrors as light-weighted optics

A parametric study of contoured back mirrors, symmetric sandwich mirrors, and open-back mirrors is presented. Each mirror type is examined with regard to self-weight-induced deflection, efficiency, and fabrication constraints. A chart of fabrication and mounting factors as well as stiffness and weight factors is presented for assistance in choosing an appropriate mirror type in a given application.

Valente, Tina M.↗
NASA NTRS1947

Stability and control characteristics of an airplane model having a 45.1 degree swept-back wing with aspect ratio 2.50 and taper ratio 0.42 and a 42.8 degree swept-back horizontal tail with aspect ratio 3.87 and taper ratio 0.49

Tests were made of an airplane model having a 45.1 degree swept-back wing with aspect ratio 2.50 and taper ratio 0.42 and a 42.8 degree swept-back horizontal tail with aspect ratio 3.87 and taper ratio 0.49 to determine its low-speed stability and control characteristics. The test Reynolds number was 2.87 x 10(6) based on a mean aerodynamic chord of 2.47 feet except for some of the aileron tests which were made at a Reynolds number of 2.05 x 10(6). With the horizontal tail located near the fuselage juncture on the vertical tail, model results indicated static longitudinal instability above a lift coefficient that was 0.15 below the lift coefficient at which stall occurred. Static longitudinal stability, however, was manifested throughout the life range with the horizontal tail located near the top of the vertical tail. The use of 10 degrees negative dihedral on the wing had little effect on the static longitudinal stability characteristics. Preliminary tests of the complete model revealed an undesirable flat spot in the yawing-moment curves at low angles of attack, the directional stability being neutral for yaw angles of plus-or-minus 2 degrees. This undesirable characteristic was improved by replacing the thick original vertical tail with a thin vertical tail and by flattening the top of the dorsal fairing.

Schuldenfrei, Marvin↗
NASA NTRS1994

Improved Fabrication Of Back-To-Back Planar Varactor Diodes

Improved method for fabrication of GaAs-based back-to-back planar varactor diodes simplifies processing and makes fabricated devices less vulnerable to damage at various intermediate process steps. Expected to increase device yields and offers several improvements over older method. Process steps modified and juggled providing simplified processing of devices that are more rugged.

Smith, Richard P.↗
NASA NTRS1995

Back-To-Back Barrier Varactor Frequency Multipliers

Two reports present further detailed information about odd-harmonic frequency-multiplier devices described in "Barrier/n/n+ Varactor Frequency Multipliers" (NPO-18428). Devices comprise Schottky-barrier/n/n+ diodes in planar back-to-back configuration.

Choudhury, Debabani↗
NASA NTRS1994

A Tripler to 220 GHz Using a Back-to-Back Barrier-N-N+ Varactor Diode

The back-to-back barrier-N-N+ (bbBNN) varactor is a nonlinear device being developed for frequency multiplier applications above 100 GHz. Its symmetrical C-V characteristic, low series resistance and suitability to planarization make it ideal choice for high frequency, low power, odd harmonic generation. In this paper, the performance of a 220 GHz tripler using integrated planar bbBNN devices is presented.

frequency multiplier↗
NASA NTRS1993

A Back-To-Back Barrier-N-N+ (bbBNN)Diode Tripler at 200 GHz

This paper describes the performance of planar back-to-back Barrier-N-N+ (bbBNN) devices for mm and submm wave multiplier applications. A technique has been developed for characterizing planar bbBNN devices with Vector Network Analyzer, which gives both the series resistance and voltage dependent capacitance of the device.

Diode Tripler↗
NASA NTRS2000

Magnetic back-to-back locator

A back-to-back locator instrument includes a first portion with an array of two or more magnetic sensors, and an indicator arrangement. A second portion of the instrument includes an array of correspondingly located magnets. Each of the first and second portions includes a marking arrangement, which either allows marking of the underlying surface, or viewing of a mark on the surface for properly locating the instrument portion thereon. When the two portions are congruent or registered, the indicator arrangement gives a maximum indication of corresponding locations. In a particular use, corresponding locations on the inside and outside of a tank are identified. The indicator arrangement may include a separate indicator for each magnetic sensor. A flux concentrator may be associated with each magnetic sensor.

Phillips, Scott G.↗
NASA NTRS1992

Rotary machine having back to back turbines

A rotary machine having a pair of back to back turbines in serial flow relationship is disclosed. Various construction details are developed which permit for a compact design. In one detailed embodiment the turbine has a housing having an inlet manifold and an exit manifold which are disposed between the outlet manifold for an associated turbopump.

Burgy, N. Frank↗
NASA NTRS1994

Integrated Back-to-Back Barrier-N-N + Varactor Diode Tripler Using a Split-waveguide Block

The back-to-back barrier-N-N + (bbBNN) varactor is a nonlinear device being developed for frequency multiplier applications above 100 GHz. Its symmetrical C-V characteristic, low series resistance and suitability to planarization make it ideal choice for high frequency, low power, odd harmonic generation. In this paper, development of an integrated planar multiplier device and its performance as a 220 GHz tripler is presented. A new split-waveguide block design has been used to provide the proper embedding impedances to the device. The performance over 200-240 GHz has been measured and the integrated bbBNN device is shown to provide as much as 734 microwatts output power. A flange-to-flange tripling efficiency of 7% has been obtained. This is believed to be the highest conversion efficiency yet reported for all planar tripler at this frequency. The performance is expected to be improved further with minor changes to the device and circuit parameters.

interstellar↗