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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
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

High Power mm-Wave Transmitter System for Radar or Telecommunications

Future NASA deep space missions able to provide tens of kilo-watts of spacecraft DC power, make it feasible to employ high power RF telecommunications systems. Traditional flight systems (e.g., Cassini), constrained by limited DC power, used a single high-gain 4m Cassegrain reflector fed by a single lower power (20W) transmitter. Increased available DC power means that high power (1000 W) transmitters can be used. Rather than continue building traditional single-transmitter systems it now becomes feasible to engineer and build multi-element active arrays that can illuminate a dish. Illuminating a 2m dish with a spherical wavefront from an offset 1kW active array can provide sufficient ERP (Effective Radiated Power) when compared to a larger Cassegrain dish. Such a system has the advantage of lower mass, lower volume, improved reliability, less stringent pointing requirements, lower cost and risk. We propose to design and build a prototype Ka-band transmit antenna with an active sub-array using 125W TWTAs. The system could be applied to a telecommunications downlink or radar transmitter used for missions such as JIMO.

Stride, S. L.↗
NASA NTRS2024

Demonstration of GaN HEMT MMIC High-Power Amplifier for Lunar Proximity Communications

In this paper, we demonstrate a high efficiency, Ka-band (23.15 to 23.55 GHz) GaN HEMT MMIC based single-ended high power amplifier (HPA). The measured Pout, Gain, PAE, RMS EVM for Offset-QPSK, 8PSK, 16APSK, and 32APSK waveforms, 3rd-order IMD products, noise figure, and phase noise are presented. The results indicate that the saturated output power (P sat ) and the small signal Gain are on the order of 38.8 dBm (7.6 W) and 29.3 dB, respectively. The PAE at Psat is 20.0%. At the 1-dB compression point, the RMS EVM and the out-of-band spectral regrowth are less than 6% and –26 dBc respectively, for all four waveforms. Additionally, the spectrum is in compliance with the NTIA mask requirements for all four waveforms. The output 3rd-order intercept point (OIP3) is on the order of 42 dBm. The noise figure is less than 9.5 dB. The SSB phase noise spectral density is compliant with the envelope defined by the MIL-STD-188-164C. The HPA can enable proximity forward links between the orbiting Gateway/relay satellites and the lunar surface elements and cross links between relay satellites.

Ka-band↗
NASA NTRSDate not supplied

Amplifier Output Power, Gain, Efficiency, and Bandwidth: A Comparative Study of GaN HEMT MMIC Multi-Stage Power Amplifiers versus Distributed Power Amplifiers

In this paper we present first, the results of a study conducted to investigate the microwave performance of a wideband (25-31 GHz) GaN MMIC distributed high power amplifier (HPA). Second, we compare and contrast the above performance with that of an alternate architecture that relies on two HPAs to provide contiguous 25-31 GHz coverage. The two HPAs operate across 25-28 GHz and 27-31 GHz, respectively, and can be switched in and out depending on the need at any given time. The parameters investigated includes the output power, gain, power added efficiency, bandwidth, RMS error vector magnitude for offset-QPSK, 8PSK, 16APSK, and 32 APSK waveforms, 3rd-order intermodulation distortion products, noise figure, and single sideband phase noise.

MMIC↗
NASA NTRS1981

Precise T and F intercomparison via VLF phase measurements

Continuous phase recording of the 16kHz transmission from GBR (UK) are being made and published midday phase data of GBR are received regularly from laboratories in the US, FGR, and UK. The local time scale (UTC, India), at the National Physical Laboratory in New Delhi, and those at the foreign laboratories are intercompared using the VLF phase data. A major factor which limits the accuracy of long term comparison is the seasonal variation in the VLF over delay over long paths. By taking into account the seasonal delay variations in a semiempirical way, the accuracy of time and frequency comparisons can be improved. Over a one year period, accuracy of a few parts in 10 to the 14th power in frequency and 1 to 2 micron sec in time were obtained. The relative frequency offset difference between UTC, (India) and UTC (PTB, Germany) of (7.0 + or - 0.1) x 10 to the -13 power agrees well with that obtained in a satellite experiment.

Gupta, A. S.↗
NASA NTRS1982

Optogalvanic stabilization and offset tuning of a carbon dioxide waveguide laser

A feedback loop employing the change in discharge impedance with output power is used to stabilize the frequency of a CO2 waveguide laser. The relatively high operating pressure of the laser combined with a zero offset feature in the feedback loop allows continuous tuning of the stabilized frequency over a 300-400 MHz range.

Kavaya, M. J.↗
NASA NTRSDate not supplied

Demonstration of a Switched Wideband GaN High-Power Amplifier for Future Space Missions

In this paper, we present the architecture of a Ka-band switched, wideband, high efficiency gallium nitride based high-power amplifier. The architecture is validated by characterizing the driver and power amplifier chain. The measured results include Pout, Gain, PAE, RMS EVM for QPSK, Offset-QPSK, 8PSK, 16APSK, and 16QAM constellations, 3rd order IMD products, and noise figure. The wide bandwidth and high output power of the amplifier will enable future user terminals to interoperate between multiple service provider’s space networks.

high power amplifier↗
NASA NTRS1999

A Preliminary Model for Spacecraft Propulsion Performance Analysis Based on Nuclear Gain and Subsystem Mass-Power Balances

A preliminary model for spacecraft propulsion performance analysis based on nuclear gain and subsystem mass-power balances are presented in viewgraph form. For very fast missions with straight-line trajectories, it has been shown that mission trip time is proportional to the cube root of alpha. Analysis of spacecraft power systems via a power balance and examination of gain vs. mass-power ratio has shown: 1) A minimum gain is needed to have enough power for thruster and driver operation; and 2) Increases in gain result in decreases in overall mass-power ratio, which in turn leads to greater achievable accelerations. However, subsystem mass-power ratios and efficiencies are crucial: less efficient values for these can partially offset the effect of nuclear gain. Therefore, it is of interest to monitor the progress of gain-limited subsystem technologies and it is also possible that power-limited systems with sufficiently low alpha may be competitive for such ambitious missions. Topics include Space flight requirements; Spacecraft energy gain; Control theory for performance; Mission assumptions; Round trips: Time and distance; Trip times; Vehicle acceleration; and Minimizing trip times.

Chakrabarti, Suman↗
NASA NTRS1973

A step in time: Changes in standard-frequency and time-signal broadcasts, 1 January 1972

An improved coordinated universal time (UTC) system has been adopted by the International Radio Consultative Committee. It was implemented internationally by the standard-frequency and time-broadcast stations on 1 Jan. 1972. The new UTC system eliminates the frequency offset of 300 parts in 10 to the 10th power between the old UTC and atomic time, thus making the broadcast time interval (the UTC second) constant and defined by the resonant frequency of cesium atoms. The new time scale is kept in synchronism with the rotation of the Earth within plus or minus 0.7 s by step-time adjustments of exactly 1 s, when needed. A time code has been added to the disseminated time signals to permit universal time to be obtained from the broadcasts to the nearest 0.1 s for users requiring such precision. The texts of the International Radio Consultative Committee recommendation and report to implement the new UTC system are given. The coding formats used by various standard time broadcast services to transmit the difference between the universal time (UT1) and the UTC are also given. For users' convenience, worldwide primary VLF and HF transmissions stations, frequencies, and schedules of time emissions are also included. Actual time-step adjustments made by various stations on 1 Jan. 1972, are provided for future reference.

Chi, A. R.↗
NASA NTRS1984

A low noise synthesizer for autotuning and performance testing of hydrogen masers

A low noise synthesizer has been developed for use in hydrogen maser autotuning and performance evaluation. This synthesizer replaces the frequency offset maser normally used for this purpose and allows the user to maintain all masers in the ensemble at the same frequency. The synthesizer design utilizes a quartz oscillator with a BVA resonator. The oscillator has a frequency offset of 5 X 10 to the minus 8 power. The BVA oscillator is phase-locked to a hydrogen maser by means of a high gain, high stability phase-locked loop, employing low noise multipliers as phase error amplifiers. A functional block diagram of the synthesizer and performance data will be presented.

Cloeren, J. M.↗
NASA NTRS1986

Optical fiber characteristics and standards; Proceedings of the Meeting, Cannes, France, November 25-27, 1985

Papers are presented on outside vapor deposition, the plasma activated CVD process for large scale production of telecommunication fibers, axial lateral plasma deposition technology from plastic clad silica, coatings for optical fibers, primary coating characterization, and radiation-induced time dependent attenuation in a fiber. Topics discussed include fibers with high tensile strength, the characteristics and specifications of airborne fiber optic components, the baseband frequency response of multimode fibers, and fibers for local and broadband networks. Consideration is given to industrial measurements for single mode and multimode fibers, the characterization of source power distribution in a multimode fiber by a splice offset technique, the measurement of chromatic dispersion in a single mode optical, and the effect of temperature on the refracted near-field optical fiber profiling technique.

Bouillie, Remy↗
NASA NTRS1990

Integrated DSP/RF design for an MSAT transmitter

In mobile radio systems, the relatively inefficient use of the spectrum by existing Frequency Modulation (FM) techniques is limiting the available channels. Linear modulation methods are thought to provide the necessary push into more efficient usage of the spectrum. The limitation, to date, of the linear modulation techniques is the fact that the nonlinear power amplifier tends to spread the spectrum and thus offset any spectrum efficiency advantage. Linearization techniques are presently being investigated, in the literature, in order to recover some of the lost spectrum, due to spreading. To this end, digital signal processing (DSP) techniques are thought to provide real time predistortion methods. Some of the complex modulation blocks, normally confined to analog circuitry, are being implemented using DSP circuitry. This paper will address the linearization techniques, for mobile satellite (MSAT) transceivers, that use an integrated DSP/radio frequency design.

Stapleton, S. P.↗
NASA NTRS2006

Hybrid Solid Oxide Fuel Cell/Gas Turbine System Design for High Altitude Long Endurance Aerospace Missions

A system level analysis, inclusive of mass, is carried out for a cryogenic hydrogen fueled hybrid solid oxide fuel cell and bottoming gas turbine (SOFC/GT) power system. The system is designed to provide primary or secondary electrical power for an unmanned aerial vehicle (UAV) over a high altitude, long endurance mission. The net power level and altitude are parametrically varied to examine their effect on total system mass. Some of the more important technology parameters, including turbomachinery efficiencies and the SOFC area specific resistance, are also studied for their effect on total system mass. Finally, two different solid oxide cell designs are compared to show the importance of the individual solid oxide cell design on the overall system. We show that for long mission durations of 10 days or more, the fuel mass savings resulting from the high efficiency of a SOFC/GT system more than offset the larger powerplant mass resulting from the low specific power of the SOFC/GT system. These missions therefore favor high efficiency, low power density systems, characteristics typical of fuel cell systems in general.

Himansu, Ananda↗
NASA NTRS2022

Demonstration of a Switched Wideband GaN High-Power Amplifier for Future Space Missions

In this paper, we present the architecture of a Ka-band switched, wideband, high efficiency gallium nitride based high-power amplifier. The architecture is validated by characterizing the driver and power amplifier chain. The measured results include Pout, Gain, PAE, RMS EVM for QPSK, Offset-QPSK, 8PSK, 16APSK, and 16QAM constellations, 3rd order IMD products, noise figure, and added phase noise. The wide bandwidth and high output power of the amplifier will enable future user terminals to interoperate between multiple service provider’s space networks.

Rainee N. Simons↗
NASA NTRSDate not supplied

Demonstration of a Switched Wideband GaN High-Power Amplifier for Future Space Missions

In this paper, we present the architecture of a Ka-band switched, wideband, high efficiency gallium nitride based high-power amplifier. The architecture is validated by characterizing the driver and power amplifier chain. The measured results include Pout, Gain, PAE, RMS EVM for QPSK, Offset-QPSK, 8PSK, 16APSK, and 16QAM constellations, 3rd order IMD products, noise figure, and added phase noise. The wide bandwidth and high output power of the amplifier will enable future user terminals to interoperate between multiple service provider’s space networks.

High power amplifier↗
NASA NTRS2011

Observations of Energetic High Magnetic Field Pulsars with the Fermi Large Area Telescope

We report the detection of gamma-ray pulsations from the high-magnetic-field rotation-powered pulsar PSR J1119.6127 using data from the Fermi Large Area Telescope. The gamma-ray light curve of PSR J1119.6127 shows a single, wide peak offset from the radio peak by 0.43 +/- 0.02 in phase. Spectral analysis suggests a power law of index 1.0 +/- 0.3(+0.4 -0.2) with an energy cut-off at 0.8 +/- 0.2(+2.0 -0.5) GeV. The first uncertainty is statistical and the second is systematic. We discuss the emission models of PSR J1119.6127 and demonstrate that despite the object's high surface magnetic field--near that of magnetars -- the field strength and structure in the gamma-ray emitting zone are apparently similar to those of typical young pulsars. Additionally, we present upper limits on the gamma-ray pulsed emission for the magnetically active PSR J1846.0258 in the supernova remnant Kesteven 75 and two other energetic high-Beta pulsars, PSRs J1718.3718 and J1734.3333. We explore possible explanations for the non-detection of these three objects, including peculiarities in their emission geometry.

Parent, D.↗
NASA NTRS2003

Next Generation of Hall Thrusters for Space Propulsion

During the previous year, grant activity research focused on demonstrating high thrust/power operation of Hall thrusters. Performance of a low power and a high power Hall thruster was experimentally investigated at discharge voltages from 100 to 150 volts. Discharge efficiencies dropped significantly as discharge voltage was decreased over this range. Reductions in discharge efficiency with decreasing discharge voltage were attributed to reductions in ionization efficiency and/or ion acceleration through a potential less that the applied discharge voltage relative to the performance of state-of-art Hall thrusters operating at discharge voltages of 300 Volts and above. The low power Hall thruster exhibited a more pronounced reduction in discharge efficiency with decreasing discharge voltage. This was attributed to increased electron leakage related to the axial distribution of the radial magnetic field. These data demonstrated that the thrust benefit of operating at discharge voltages below 130 Volts was offset by a corresponding decrease in discharge efficiency for a given input power. Additional activities included continued support of on-going Hall thruster propulsion research within the On-Board Propulsion Branch at NASA Glenn Research Center.

Keith, Theo G., Jr.↗
NASA NTRS1978

Rain-rate estimates for an attenuating radar

An iterative method has been used to produce rain-rate estimates for an attenuating frequency radar. An infinite number of higher-order estimates are shown to converge in the limit to the Hitschfeld-Bordan solution under certain conditions. An error analysis was performed by a model accounting for the randomness of the radar return power, the k-Z, Z-R relations, and offsets in the radar calibration constant. Since the behavior of the estimates strongly depends on system errors, the choice of the best estimate requires a knowledge of the variance and range of offsets in meteorological data and the calibration constant. As the errors increase, the use of the lower orders avoids significant overpredictions. In order to obtain reliable rain-rate predictions in the presence of realistic errors, an antenna pointing angles away from the horizontal at frequencies in the lower end of the X-band may be used. Such antenna configurations insure low attenuation.

Meneghini, R.↗
NASA NTRS1988

Ray tracing optical analysis of offset solar collector for space station solar dynamic system

OFFSET, a detailed ray tracing computer code, was developed at NASA Lewis Research Center to model the offset solar collector for the Space Station solar dynamic electric power system. This model traces rays from 50 points on the face of the Sun to 10 points on each of the 456 collector facets. The triangular facets are modeled with spherical, parabolic, or toroidal reflective surface contour and surface slope errors. The rays are then traced through the receiver aperture to the walls of the receiver. Images of the collector and of the Sun within the receiver produced by this code provide insight into the collector receiver interface. Flux distribution on the receiver walls, plotted by this code, is improved by a combination of changes to aperture location and receiver tilt angle. Power loss by spillage at the receiver aperture is computed and is considerably reduced by using toroidal facets.

Jefferies, Kent S.↗