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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

High power master oscillator power amplifier (MOPA) AlGaAs laser for intersatellite communications

A master oscillator power amplifier (MOPA) configuration has been developed using an anti-reflection-coated AlGaAs semiconductor broad area laser in a reflective amplifier mode. For CW injection, the MOPA produced 340 mW of diffraction-limited power. The semiconductor MOPA configuration also produced peak diffraction-limited powers of 360 mW and 320 mW for quaternary pulse position Q-PPM modulation rates of 50 Mbps and 325 Mbps, respectively, for a peak injected power of 100 mW. Angular beamsteering during modulation was minimized by collimating the injected beam. The diffraction-limited peak power was limited by the frequency chirp of the master oscillator and also by the coupling losses of the injected beam.

Cornwell, Donald M., Jr.↗
NASA NTRS1999

Experimental Cross Sections for Excitation of the 2s S-2 yields 2p P-2 Transition in C(3+)

Experimental cross sections are presented for excitation of the 2s yields 2p transition in C(3+). Use is made of the energy-loss method with merged beams. Also described is use of a multipole "electronic aperture" to discriminate against elastically-scattered electrons. Comparisons are made with previous experimental energy-loss and optical-emission data, and with results of several theoretical calculations.

Chutjian, A.↗
NASA NTRS1984

Refractive turbulence effects on truncated Gaussian beam heterodyne lidar

A monostatic heterodyne lidar performance model is formulated to study the combined effects of beam truncation and refractive turbulence in the weak scintillation regime. The results show that there is a loss of signal power due to beam truncation and coherence loss, but there is also an enhancement of signal power due to log-amplitude covariance in suitable conditions of long paths with weak turbulence.

Murty, R.↗
NASA NTRS2011

The Impact of Return-Current Losses on the Observed Emissions from Solar Flares

Electrons accelerated in solar flares are expected to drive a co-spatial return current in the ambient plasma when they escape the acceleration region. This return current maintains plasma neutrality and the stability of the beam of streaming electrons. The electric field that drives this return current also decelerates the energetic electrons in the beam. The corresponding energy loss experienced by the accelerated electrons can affect the observed properties of the X-ray and radio emissions from flares and the evolution of the thermal flare plasma. I will discuss the properties of the flare emissions expected in a classical, steady-state model. As part of this discussion, I will examine Gordon Emslie's 1980 conjecture that return-current losses result in a maximum brightness for the hard X-ray emission from flares.

Holman, Gordon D.↗
NASA NTRS1999

Vibration Analysis and Control of Flexible Beam by Using Smart Damping Structures

The temperature effects on frequency, loss factor and control of a flexible beam with a constrained viscoelastic layer and shape memory alloy layer (SMA) are discussed. It is shown that the temperature in the SMA (actuation) layer is very important in the determination of frequency and loss factor of such a structure. The effects of damping layer shear modulus and damping layer height as affected by the temperature are also discussed. As temperature plays such an important role, it is, therefore, imperative to evaluate temperature effects on the control of the system as well. Results with and without active control are discussed.

Chen, Q.↗
NASA NTRS2011

Scanning and Defocusing Properties of Microstrip Reflectarray Antennas

A symmetric reflectarray, consisting of variable-size square patch elements with a commonly used mathematical model for the horn in the form of a cosine function, has been designed using the transmit mode technique for different f/D ratios with 10 dB edge taper. Subsequently, the antennas were analyzed for the radiation pattern and gain. The infinite array model was used to determine the reflection phase of each patch element in the design and analysis codes. By displacing the feed laterally, the scan characteristics were obtained, such as the beam deviation factor, gain loss, and pattern degradation. The properties of reflect arrays were compared to those of the conventional paraboloidal reflectors. The same procedure was used to study the scan properties of offset reflectarrays. There is no cross-polarized radiation in the principal planes for a symmetric system. Cross-polarized radiation exists in non-principal planes off broadside in symmetric systems, with greater levels for larger values of subtended angles. Such cross-polarized radiation level increases with subtended angle just as cross-polarization level increases with decreasing values of f/D ratios for symmetric paraboloids in non-principal planes. Pattern distortions and gain loss were found to be more severe in the case of a microstrip reflectarray compared to the conventional parabolic reflector. The scan performance of the reflect arrays was found to improve with f/D ratios as is true for paraboloids. In general, scanning by means of displaced feed is limited to a few beam - widths in reflectarrays. Feed displacement in the axial direction of a symmetric reflectarray was investigated and compared to that of paraboloids. The gain loss due to the defocused feed of a reflectarray was found to be nearly the same as that of a paraboloid of the same subtended angle for larger values of f/D, and for displacements away from the antenna. The gain loss of an axially defocused reflectarray was found to be greater than that of a paraboloid for displacements closer to the antenna, especially for smaller values of f/D. In general, the performance of a defocused reflectarray was found to be poorer than that of a comparable paraboloid reflector.

Rengarajan, Sembiam↗
NASA NTRS1969

A positive taper traveling-wave tube

Synchronism can be maintained between the RF beam current and the circuit electromagnetic waves over substantially the entire length of a traveling-wave tube by increasing the pitch of the last portion of the helical wave structure. There is no loss of linearity or beam conversion efficiency.

Grechberg, R. W.↗
NASA NTRS2008

Quasi-Optical Transmission Line for 94-GHz Radar

A quasi-optical transmission line (QOTL) has been developed as a low-loss transmission line for a spaceborne cloudobserving radar instrument that operates at a nominal frequency of 94 GHz. This QOTL could also readily be redesigned for use in terrestrial millimeter-wave radar systems and millimeter-wave imaging systems. In the absence of this or another lowloss transmission line, it would be necessary to use a waveguide transmission line in the original radar application. Unfortunately, transmission losses increase and power-handling capacities of waveguides generally decrease with frequency, such that at 94 GHz, the limitation on transmitting power and the combined transmission and reception losses (greater than 5 dB) in a waveguide transmission line previously considered for the original application would be unacceptable. The QOTL functions as a very-lowloss, three-port circulator. The QOTL includes a shaped input mirror that can be rotated to accept 94-GHz transmitter power from either of two high-power amplifiers. Inside the QOTL, the transmitter power takes the form of a linearly polarized beam radiated from a feed horn. This beam propagates through a system of mirrors, each of which refocuses the beam to minimize diffraction losses. A magnetically biased ferrite disc is placed at one of the foci to utilize the Faraday effect to rotate the polarization of the beam by 45 degrees. The beam is then transmitted via an antenna system. The radar return (scatter from clouds, and/or reflections from other objects) is collected by the same antenna and propagates through the Faraday rotator in the reverse of the direction of propagation of the transmitted beam. In the Faraday rotator, the polarization of the received signal is rotated a further 45 degrees, so that upon emerging from the Faraday rotator, the received beam is polarized at 90 with respect to the transmitted beam. The transmitted and received signals are then separated by a wire-grid polarizer.

Perez, Raul M.↗
NASA NTRS1992

Measurement of vortex flow fields

A 3-D laser fluorescence anemometer (LFA) was designed, built, and demonstrated for use in the Langley 16 x 24 inch Water Tunnel. Innovative optical design flexibility combined with compact and portable data acquisition and control systems were incorporated into the instrument. This will allow its use by NASA in other test facilities. A versatile fiber optic system facilities normal and off-axis laser beam alignment, removes mirror losses and improves laser safety. This added optical flexibility will also enable simple adaptation for use in the adjacent jet facility. New proprietary concepts in transmitting color separation, light collection, and novel prism separation of the scattered light was also designed and built into the system. Off-axis beam traverse and alignment complexity led to the requirement for a specialized, programmable transverse controller, and the inclusion of an additional traverse for the off-axis arm. To meet this challenge, an 'in-house' prototype unit was designed and built and traverse control software developed specifically for the water tunnel traverse applications. A specialized data acquisition interface was also required. This was designed and built for the LFA system.

Mcdevitt, T. Kevin↗
NASA NTRS2018

3D Simulations of Ion Thruster Accelerator Grid Erosion Accounting for Charge Exchange Ion Space Charge

Accelerator (accel) grid sputtering by ions formed through charge-exchange (CEX) reactions between beam ions and residual neutral gas is a critical life-limiting mechanism for gridded ion thrusters. The three-dimensional ion optics code CEX3D is designed to simulate this grid erosion for a single beamlet, with a particular emphasis on non-axisymmetric features such as the "pits and grooves" erosion commonly observed on the accel grid downstream face in two-grid thrusters. The treatment of CEX ions in the code was recently upgraded with a new particle-in-cell (PIC) module to account for the influence of these ions' space charge on the electrostatic potential downstream of the grids. In order to achieve reasonable computation times while resolving the Debye length near the grids and avoiding gross violations of the Courant-Friedrichs-Lewy (CFL) condition, macroparticle velocities in the PIC calculation are limited through a rescaling procedure that preserves ion trajectories and space charge density. The code accounts for beam divergence, finite momentum transfer in CEX collisions, and radial losses of CEX ions from the beam; these effects are important for determining the CEX ion flux to the accel grid because the calculated potential downstream of the grids can become very flat. The upgraded code has been used to simulate operation of NASA's Evolutionary Xenon Thruster (NEXT) during the 51 kHr Long Duration Test - a selection of results is presented and compared with experimental data.

Chaplin, Vernon H.↗
NASA NTRS1971

The interaction of O(plus) ions with the interior surface of a copper chamber

Modulated beams of 0(+), Ar(+), and Kr(+) in the 100-300 eV range are directed into a copper box simulating the ante-chamber of an orbiting mass spectrometer. An RF quadrupole mass spectrometer and phase sensitive detection extract the component of the internal mass spectrum correlated with the beam. Intense Ar and Kr signals are observed; however, no O or O2 is detectable, indicating loss of the primary O(+) beam to surface interactions. All four primary ions stimulate sizeable signals at masses 26 and 28. The relevance of these experiments to the interpretation of mass spectra obtained by orbiting satellites is discussed.

Siegel, M. W.↗
NASA NTRS1983

A comparison of the thick-target model with stereo data on the height structure of solar hard X-ray bursts

The thick target, hard solar X-ray source height structure is predicted for the case of a beam that is injected vertically downward, having a power law spectrum, being dominated by Coulomb collisional energy losses, and being structurally characterized by the ratio of hard X-ray flux from an upper part of the source to that from the entire source. These predictions are compared with the flux ratios at 150 and 350 keV which were observed by two spacecraft for five events in which the solar limb occults part of the source for one spacecraft. The energy dependence of the occultation ratio is found to be inconsistent with that predicted by the model, and it is concluded that noncollisional losses must be significant in beam dynamics.

Brown, J. C.↗
NASA NTRS2013

Simple Laser Communications Terminal for Downlink from Earth Orbit at Rates Exceeding 10 Gb/s

A compact, low-cost laser communications transceiver was prototyped for downlinking data at 10 Gb/s from Earth-orbiting spacecraft. The design can be implemented using flight-grade parts. With emphasis on simplicity, compactness, and light weight of the flight transceiver, the reduced-complexity design and development approach involves: 1. A high-bandwidth coarse wavelength division multiplexed (CWDM) (4 2.5 or 10-Gb/s data-rate) downlink transmitter. To simplify the system, emphasis is on the downlink. Optical uplink data rate is modest (due to existing and adequate RF uplink capability). 2. Highly simplified and compact 5-cm diameter clear aperture optics assembly is configured to single transmit and receive aperture laser signals. About 2 W of 4-channel multiplexed (1,540 to 1,555 nm) optically amplified laser power is coupled to the optical assembly through a fiber optic cable. It contains a highly compact, precision-pointing capability two-axis gimbal assembly to coarse point the optics assembly. A fast steering mirror, built into the optical path of the optical assembly, is used to remove residual pointing disturbances from the gimbal. Acquisition, pointing, and tracking are assisted by a beacon laser transmitted from the ground and received by the optical assembly, which will allow transmission of a laser beam. 3. Shifting the link burden to the ground by relying on direct detection optical receivers retrofitted to 1-m-diameter ground telescopes. 4. Favored mass and volume reduction over power-consumption reduction. The two major variables that are available include laser transmit power at either end of the link, and telescope aperture diameter at each end of the link. Increased laser power is traded for smaller-aperture diameters. 5. Use of commercially available spacequalified or qualifiable components with traceability to flight qualification (i.e., a flight-qualified version is commercially available). An example is use of Telecordia-qualified fiber optic communication components including active components (lasers, amplifiers, photodetectors) that, except for vacuum and radiation, meet most of the qualifications required for space. 6. Use of CWDM technique at the flight transmitter for operation at four channels (each at 2.5 Gb/s or a total of 10 Gb/s data rate). Applying this technique allows utilization of larger active area photodetectors at the ground station. This minimizes atmospheric scintillation/turbulence induced losses on the received beam at the ground terminal. 7. Use of forward-error-correction and deep-interleaver codes to minimize atmospheric turbulence effects on the downlink beam. Target mass and power consumption for the flight data transmitter system is less than 10 kg and approximately 60 W for the 400-km orbit (900-km slant range), and 12 kg and 120 W for the 2,000-km orbit (6,000-km slant range). The higher mass and power for the latter are the result of employing a higher-power laser only.

Kovalik, Joseph M.↗
NASA NTRS1976

15 cm multipole gas ion thruster

A 15-cm multipole thruster was operated on argon and xenon. The multipole approach used has been shown capable of low discharge losses and flat ion beam profiles with a minimum of redesign. This approach employs low magnetic field strengths and flat or cylindrical sheet-metal parts, hence is suited to rapid optimization and scaling. Only refractory metal cathodes were used in this investigation.

Isaacson, G. C.↗
NASA NTRS1978

Nonlinear stability of solar type 3 radio bursts. 1: Theory

A theory of the excitation of solar type 3 bursts is presented. Electrons initially unstable to the linear bump-in-tail instability are shown to rapidly amplify Langmuir waves to energy densities characteristic of strong turbulence. The three-dimensional equations which describe the strong coupling (wave-wave) interactions are derived. For parameters characteristic of the interplanetary medium the equations reduce to one dimension. In this case, the oscillating two stream instability (OTSI) is the dominant nonlinear instability, and is stablized through the production of nonlinear ion density fluctuations that efficiently scatter Langmuir waves out of resonance with the electron beam. An analytical model of the electron distribution function is also developed which is used to estimate the total energy losses suffered by the electron beam as it propagates from the solar corona to 1 A.U. and beyond.

Smith, R. A.↗
NASA NTRS1978

Up-date of traveling wave tube improvements

A brief survey is presented of areas of progress on traveling wave tube designs. Data demonstrates the effect of multistage depressed collectors, the design of which is made possible by powerful NASA computer programs. Other topics include beam refocusing, RF circuit losses, and cathode testing.

Buck, E.↗
NASA NTRS1979

Nonlinear stability of solar type III radio bursts. I - Theory

A theory of the excitation of solar type III bursts is presented. Electrons initially unstable to the linear bump-in-tail instability are shown to rapidly amplify Langmuir waves to energy densities characteristic of strong turbulence. The three-dimensional equations which describe the strong coupling (wave-wave) interactions are derived. For parameters characteristic of the interplanetary medium the equations reduce to one-dimension. In that case the oscillating two-stream instability (OTSI) is the dominant nonlinear instability. OTSI is stabilized through the production of nonlinear ion density fluctuations that efficiently scatter Langmuir waves out of resonance with the electron beam. An analytical model of the electron distribution function is also developed which is used to estimate the total energy losses suffered by the electron beam as it propagates from the solar corona to 1 AU and beyond.

Smith, R. A.↗