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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 73 records · Page 4

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NASA NTRS1976

Research and development for improved lead-salt diode lasers

A substantial increase in output power levels for lead-salt diode lasers, through the development of improved fabrication methods, as demonstrated. The goal of 1 mW of CW, single-mode, single-ended power output, was achieved, with exceptional devices exhibiting values greater than 8 mW. It was found that the current tuning rate could be controlled by adjusting the p-n junction depth, allowing the tuning rate to be optimized for particular applications. An unexpected phenomenon was encountered when crystal composition was observed to be significantly altered by annealing at temperatures as low as 600 C; the composition was changed by transport of material through the vapor phase. This effect caused problems in obtaining diode lasers with the desired operating characteristics. It was discovered that the present packaging method introduces gross damaging effects in the laser crystal through pressure applied by the C-bend.

Butler, J. F.↗

NASA NTRS1979

Low cost cylindrical converter for measuring lead efficiency

A low cost cylindrical thermionic converter has been designed, fabricated, and tested for use in a NASA-JPL program to directly measure converter lead efficiencies using various electrode materials and surfaces. Efficiency measurements are made using input emitter heater power, output power at the leads, and calculated values of the parasitic losses that would not be present in the application configuration. This information can be used to predict the performance characteristics of the advanced converters currently under development. A series of five converters has been tested. Both structured and smooth molybdenum collectors have been used. Emitters included smooth molybdenum, smooth rhenium, and microstructured rhenium. Cesium pressure families of current-voltage curves are presented for emitter temperatures of 1600, 1700, and 1800 K, along with measured efficiencies as a function of converter current densities for each temperature.

Hatch, G. L.↗

NASA NTRS1980

Electrochemical Orbital Energy Storage (ECOES) technology program

The versatility and flexibility of a regenerative fuel cell power and energy storage system is considered. The principal elements of a Regenerative Fuel Cell System combine the fuel cell and electrolysis cell with a photovoltaic solar cell array, along with fluid storage and transfer equipment. The power output of the array (for LEO) must be roughly triple the load requirements of the vehicle since the electrolyzers must receive about double the fuel cell output power in order to regenerate the reactants (2/3 of the array power) while 1/3 of the array power supplies the vehicle base load. The working fluids are essentially recycled indefinitely. Any resupply requirements necessitated by leakage or inefficient reclamation is water - an ideal material to handle and transport. Any variation in energy storage capacity impacts only the fluid storage portion, and the system is insensitive to use of reserve reactant capacity.

Mcbryar, H.↗

NASA NTRS1981

Jet impingement heat transfer enhancement for the GPU-3 Stirling engine

A computer model of the combustion-gas-side heat transfer was developed to predict the effects of a jet impingement system and the possible range of improvements available. Using low temperature (315 C (600 F)) pretest data in an updated model, a high temperature silicon carbide jet impingement heat transfer system was designed and fabricated. The system model predicted that at the theoretical maximum limit, jet impingement enhanced heat transfer can: (1) reduce the flame temperature by 275 C (500 F); (2) reduce the exhaust temperature by 110 C (200 F); and (3) increase the overall heat into the working fluid by 10%, all for an increase in required pumping power of less than 0.5% of the engine power output. Initial tests on the GPU-3 Stirling engine at NASA-Lewis demonstrated that the jet impingement system increased the engine output power and efficiency by 5% - 8% with no measurable increase in pumping power. The overall heat transfer coefficient was increased by 65% for the maximum power point of the tests.

Johnson, D. C.↗

NASA NTRS1983

Test results and description of a 1-kW free-piston Stirling engine with a dashpot load

A 1 kW (1.33 hp) single cylinder free piston Stirling engine was installed in the test facilities at the Lewis laboratory. The engine was designed specifically for research of the dynamics of its operation. A more complete description of the engine and its instrumentation is provided in a prior NASA paper TM-82999 by J. G. Schreiber. Initial tests at Lewis showed the power level and efficiency of the engine to be below design level. Tests were performed to help determine the specific problems in the engine causing the below design level performance. Modifications to engine hardware and to the facility where performed in an effort to bring the power output and efficiency to their design values. As finally configured the engine generated more than 1250 watts of output power at an engine efficiency greater than 32 percent. This report presents the tests performed to help determine the specific problems, the results if the problem was eliminated, the fix performed to the hardware, and the test results after the engine was tested. In cases where the fix did not cause the anticipated effects, a possible explanation is given.

Schreiber, J.↗

NASA NTRS1983

Test results and description of a 1 kW free-piston Stirling engine with a dashpot load

Schreiber, J.↗

NASA NTRS1983

A 20 GHz, 75 watt, helix TWT for space communications

A space-qualified, helix-type traveling wave tube is being developed for satellite communication systems in the frequency band of 17.7 to 21.2 GHz. The design approach stresses very high efficiency operation, but with very low distortion. The tube provides multi-mode operation, permitting CW saturated power output levels of 75, 40, and 7.5 W. Operation is also anticipated at 5 dB below these saturation levels to achieve the required low distortion levels. Advanced construction features include a five-stage depressed collector, a diamond supported helix slow-wave circuit, and a type M dispenser cathode. High reliability and long life (10 yr) are objectives of the tube design. Preliminary test results on early developmental models of this tube are very encouraging. An output power of 75 to 90 W has been achieved over the full bandwidth with about 40 dB of saturated gain. More importantly, the basic electronic efficiency of the interaction process has been increased from about 7.5-11 percent by the use of the diamond helix support compared to earlier tubes using BeO support rods. This effort is supported by NASA Lewis Research Center and is aimed toward application in the NASA Advanced Communications Satellite Technology Program.

Heney, J. F.↗

NASA NTRS1988

Performance of efficient Q-switched diode-laser-pumped Nd:YAG and Ho:YLF lasers for space applications

Solid-state lasers pumped by continuous-wave diode lasers can be Q-switched to obtain high peak power output pulses. The dependence of laser-pulse energy, average output power, peak power, and pulse width on pulse-repetition frequency in Q-switched Nd:YAG and Ho:YLF lasers is determined and compared. At low pulse repetition rates, the much longer upper-stage lifetime in Ho:YLF gives a distinct advantage. At higher pulse rates, the overall laser efficiency and the stimulated emission cross section are more important parameters, leading to an advantage for Nd:YAG. The results are of significance for designing lasers for use in space optical communications and remote sensing systems.

Marshall, W. K.↗

NASA NTRS1990

A model for a continuous-wave iodine laser

A model for a continuous-wave (CW) iodine laser has been developed and compared with the experimental results obtained from a solar-simulator-pumped CW iodine laser. The agreement between the calculated laser power output and the experimental results is generally good for various laser parameters even when the model includes only prominent rate coefficients. The flow velocity dependence of the output power shows that the CW iodine laser cannot be achieved with a flow velocity below 1 m/s for the present solar-simulator-pumped CW iodine laser system.

Hwang, In H.↗

NASA NTRS1995

Space qualified hybrid superconductor/semiconductor planar oscillator circuit

We report on the space qualification of a hybrid superconductor/semiconductor planar local oscillator (LO) at 8.4 GHz. This oscillator was designed, fabricated, and tested as a component for the High Temperature Superconductivity Space Experiment 2 (HTSSE-2). The LO consisted of a GaAs MESFET and microstrip circuitry patterned onto a YBa2Cu3O(7-delta) high temperature superconducting (HTS) thin film on a 1.0 x 1.0 sq cm lanthanum aluminate (LaAlO3) substrate. At 77 K, this oscillator achieved power output levels up to 10 dBm into a 50 Ohm load. When incorporated into a full cryogenic receiver, the LO provided output powers within 0.0-3.0 dBm with less than 50 mW of dc power dissipation. Space qualification data on the sensitivity of the HTS films to the processing steps involved in the fabrication of HTS-based components are presented. Data on ohmic contacts, strength of wire bonds made to such contacts, and aging effects as well as vibration test results are discussed.

Miranda, F. A.↗

NASA NTRS2006

Tunable Fiber Bragg Grating Ring Lasers using Macro Fiber Composite Actuators

The research reported herein includes the fabrication of a tunable optical fiber Bragg grating (FBG) fiber ring laser (FRL)1 from commercially available components as a high-speed alternative tunable laser source for NASA Langley s optical frequency domain reflectometer (OFDR) interrogator, which reads low reflectivity FBG sensors. A Macro-Fiber Composite (MFC) actuator invented at NASA Langley Research Center (LaRC) was selected to tune the laser. MFC actuators use a piezoelectric sheet cut into uniaxially aligned rectangular piezo-fibers surrounded by a polymer matrix and incorporate interdigitated electrodes to deliver electric fields along the length of the piezo-fibers. This configuration enables MFC actuators to produce displacements larger than the original uncut piezoelectric sheet. The FBG filter was sandwiched between two MFC actuators, and when strained, produced approximately 3.62 nm of wavelength shift in the FRL when biasing the MFC actuators from 500 V to 2000 V. This tunability range is comparable to that of other tunable lasers and is adequate for interrogating FBG sensors using OFDR technology. Three different FRL configurations were studied. Configuration A examined the importance of erbium-doped fiber length and output coupling. Configuration B demonstrated the importance of the FBG filter. Configuration C added an output coupler to increase the output power and to isolate the filter. Only configuration C was tuned because it offered the best optical power output of the three configurations. Use of Plastic Optical Fiber (POF) FBG s holds promise for enhanced tunability in future research.

Geddis, Demetris L.↗

NASA NTRS1995

High Power Amplifier Harmonic Output Level Measurement

A method is presented for the measurement of the harmonic output power of high power klystron amplifiers, involving coherent hemispherical radiation pattern measurements of the radiated klystron output. Results are discussed for the operation in saturated and unsaturated conditions, and with a waveguide harmonic filter included.

klystron amplifiers harmonic output power measurem↗

NASA NTRS1989

Space Power Free-Piston Stirling Engine Scaling Study

The design feasibility study is documented of a single cylinder, free piston Stirling engine/linear alternator (FPSE/LA) power module generating 150 kW-electric (kW sub e), and the determination of the module's maximum feasible power level. The power module configuration was specified to be a single cylinder (single piston, single displacer) FPSE/LA, with tuning capacitors if required. The design requirements were as follows: (1) Maximum electrical power output; (2) Power module thermal efficiency equal to or greater than 20 percent at a specific mass of 5 to 8 kg/kW(sub e); (3) Heater wall temperature/cooler wall temperature = 1050 K/525 K; (4) Sodium heat-pipe heat transport system, pumped loop NaK (sodium-potassium eutectic mixture) rejection system; (5) Maximum power module vibration amplitude = 0.0038 cm; and (6) Design life = 7 years (60,000 hr). The results show that a single cylinder FPSE/LA is capable of meeting program goals and has attractive scaling attributes over the power range from 25 to 150 kW(sub e). Scaling beyond the 150 kW(sub e) power level, the power module efficiency falls and the power module specific mass reaches 10 kg/kW(sub e) at a power output of 500 kW(sub e). A discussion of scaling rules for the engine, alternator, and heat transport systems is presented, along with a detailed description of the conceptual design of a 150 kW(sub e) power module that meets the requirements. Included is a discussion of the design of a dynamic balance system. A parametric study of power module performance conducted over the power output range of 25 to 150 kW(sub e) for temperature ratios of 1.7, 2.0, 2.5, and 3.0 is presented and discussed. The results show that as the temperature ratio decreases, the efficiency falls and specific mass increases. At a temperature ratio of 1.7, the 150 kW(sub e) power module cannot satisfy both efficiency and specific mass goals. As the power level increases from 25 to 150 kW(sub e) at a fixed temperature ratio, power module efficiency is seen to increase slightly, but at the expense of increased specific mass. An empirical equation relating power module thermal efficiency as a function of power module specific mass, power output, and temperature ratio is developed. Alternative configurations to the single cylinder, direct coupled linear alternator approach are also evaluated, but are shown to have technical drawbacks that lessen their attractiveness. The dynamic balance assembly mass (moving mass and structure) represents 20 to 30 percent of the total single cylinder power module mass. Joining two modules in a balanced opposed configuration eliminates the need for the balancer, and a hot end junction can be made without significant addition of structural mass. Recommendations are made for evaluation of advanced heat pipe concepts, tests of radial flow heat exchangers, and evaluation of high temperature alternator materials.

Jones, D.↗

NASA NTRS1987

Overview of free-piston Stirling engine technology for space power application

An overview is presented of free-piston Stirling engine activities, directed toward space power applications. One of the major elements of the program is the development of advanced power conversion. Under this program the status of the 25 kWe opposed-piston Space Power Demonstrator Engine (SPDE) is presented. Initial differences between predicted and experimental power outputs and power output influenced by variations in regenerators are discussed. Technology work was conducted on heat-exchanger concepts to minimize the number of joints as well as to enhance the heat transfer in the heater. Design parameters and conceptual design features are also presented for a 25 kWe, single-cylinder free-piston Stirling space power converter. Projections are made for future space power requirements over the next few decades along with a recommendation to consider the use of dynamic power conversion systems, either solar or nuclear. A cursory comparison is presented showing the mass benefits of a Stirling system over a Brayton system for the same peak temperature and output power. A description of a study to investigate the feasibility of scaling a single-cylinder free-piston Stirling space power module to the 150 kWe power range is presented.

Slaby, Jack G.↗

NASA NTRS2004

Probabilistic Physics-Based Risk Tools Used to Analyze the International Space Station Electrical Power System Output

This paper describes the methods employed to apply probabilistic modeling techniques to the International Space Station (ISS) power system. These techniques were used to quantify the probabilistic variation in the power output, also called the response variable, due to variations (uncertainties) associated with knowledge of the influencing factors called the random variables. These uncertainties can be due to unknown environmental conditions, variation in the performance of electrical power system components or sensor tolerances. Uncertainties in these variables, cause corresponding variations in the power output, but the magnitude of that effect varies with the ISS operating conditions, e.g. whether or not the solar panels are actively tracking the sun. Therefore, it is important to quantify the influence of these uncertainties on the power output for optimizing the power available for experiments.

Patel, Bhogila M.↗

NASA NTRS1988

Ku-band high efficiency GaAs MMIC power amplifiers

The development of Ku-band high efficiency GaAs MMIC power amplifiers is examined. Three amplifier modules operating over the 13 to 15 GHz frequency range are to be developed. The first MMIC is a 1 W variable power amplifier (VPA) with 35 percent efficiency. On-chip digital gain control is to be provided. The second MMIC is a medium power amplifier (MPA) with an output power goal of 1 W and 40 percent power-added efficiency. The third MMIC is a high power amplifier (HPA) with 4 W output power goal and 40 percent power-added efficiency. An output power of 0.36 W/mm with 49 percent efficiency was obtained on an ion implanted single gate MESFET at 15 GHz. On a dual gate MESFET, an output power of 0.42 W/mm with 27 percent efficiency was obtained. A mask set was designed that includes single stage, two stage, and three stage single gate amplifiers. A single stage 600 micron amplifier produced 0.4 W/mm output power with 40 percent efficiency at 14 GHz. A four stage dual gate amplifier generated 500 mW of output power with 20 dB gain at 17 GHz. A four-bit digital-to-analog converter was designed and fabricated which has an output swing of -3 V to +/- 1 V.

Tserng, H. Q.↗

NASA NTRS1980

Sub mm laser local oscillators: Design criteria and results

Diagnostic results are given of the spectral features and the power conversion efficiency of submillimeter (SMM) laser local oscillators. Several criteria are obtained for the design of frequency stable and efficient smm lasers for local oscillator applications. Finally, a design is described and results on the power output and power and frequency stability are given. The mode pattern is very close to a Gaussian profile so that efficient coupling to a quasioptical mixer is possible. The laser provides sufficient output power at a large number of lines to drive the mixer into the low conversion loss regime. Radiometric integration times of several minutes with a spectral resolution of 1 MHz will be possible. With present state-of-the-art Schottky mixers and low noise preamplifiers a radiometric temperature resolution of a few K can be expected over a spectral range from 500to 900 GHz.

Koepf, G. A.↗

NASA NTRS1978

Power Coupling Alternatives for the NEP Thermionic Power System

Three output power coupling methods which can eliminate the high temperature insulator from the Nuclear Electric Propulsion (NEP) power system are described and estimates of their effects on the NEP system masses and cooling requirements are presented. Nominal 400 kWe power systems using push-pull and flux reset inductive output coupling are shown to have specific masses of 22.2 kg/kWe and 18.8 kg/kWe, respectively. Series connected heat pipe systems, which use the heat pipe-to-heat pipe resistance to isolate converters on adjacent heat pipes, are shown to have specific masses 0.5 to 1.4 kg/kWe lower than the NEP baseline system. Increasing the number and temperature of the heat pipes in the system without changing the electric output reduces the calculated system specific mass only slightly, whereas increasing the output power significantly reduces the specific mass. Estimates of cooling requirements indicate that 11-45 sq m of power conditioning radiator are needed. A possible location for the power conditioning radiator may be in the present location of the kapton sputter shield.

Manda, M. L.↗