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NASA NTRS1992

Lidar Measurements of Metallic Species in Mesopause Region

Sodium density distributions were measured over more than 20 nights since Jul. 1991 at Tokyo Metropolitan University. Our sodium lidar specifications are shown. The lidar consists of a dye laser that is pumped by a pulsed Nd:YAG laser. The dye laser is tuned to the D2 resonant absorption line of Na at the wavelength of 589 nm. A small fraction of the output beam is directed to a hollow-cathode lamp. The precise tuning of the Na D2 line is accomplished by monitoring the signal obtained from the hollow-cathode lamp and controlling the grating in the dye laser oscillator cavity. The raw data for each profile were obtained by firing the laser 5000 times for approximately 8.5 minutes. We have observed the sporadic sodium layers three times during the observation period. Recently, lidar measurements of iron atoms were also performed. Other aspects of this investigation are presented.

Nagasawa, Chikao↗

NASA NTRS1992

Tunable Electro-optic modulators for lidar systems and atmospheric applications

In global sensing applications using different types of lidars, the spectral range and fine frequency coverages are often limited because of the finite tunabilities of molecular lasers and the number of molecular species that are available. To overcome the above obstacle, we have proposed new broadband frequency tunable electro-optic (EO) modulators that can cover a wide range from the mid-infrared to the visible as lidar sources in atmospheric sensing applications such as high resolution atmospheric molecular spectroscopy, Differential Absorption Lidar (DIAL), and laser radar imaging. The configuration of the proposed new tunable EO modulators includes an electro-optic active crystal element surrounded by a ferrite tuning element which is placed inside a microwave waveguide. The tuning is provided by an external magnetic field, which is either longitudinal or transverse, and the modulator can be either single sideband type or a double sideband type depending on the application required for the spectral purity of the modulator output.

Eng, R. S.↗

NASA NTRS1992

Acoustophoresis method and apparatus

A method and apparatus are provided for acoustophoresis, i.e., the separation of species via acoustic waves. An ultrasonic transducer applies an acoustic wave to one end of a sample container containing at least two species having different acoustic absorptions. The wave has a frequency tuned to or harmonized with the point of resonance of the species to be separated. This wave caused the species to be driven to an opposite end of the sample container for removal. A second ultrasonic transducer may be provided to apply a second, oppositely directed acoustic wave to prevent undesired streaming. In addition, a radio frequency tuned to the mechanical resonance and coupled with a magnetic field can serve to identify a species in a medium comprising species with similar absorption coefficients, whereby an acoustic wave having a frequency corresponding to this gyrational rate can then be applied to sweep the identified species to one end of the container for removal.

Heyman, Joseph S.↗

NASA NTRS1991

End-loaded crossed-slot radiating elements

Three cavity-backed crossed-slot antenna configurations are described that offer simple design, easy frequency tuning, light weight, low loss, and low cost. These antennas are designed for mobile satellite (MSAT) vehicle phased-array applications. The slots in these antennas are end-loaded. The end loading makes the slots effectively longer, and hence reduces their resonant frequency. Therefore, relatively small radiating elements can be achieved for large-angle-scanning phased-array antennas. These antennas have good RF characteristics and provide a relatively wide bandwidth without needing external tuning circuits for impedance matching. Measurements for the return loss and the far-field pattern of these antennas are presented.

Manshadi, F.↗

NASA NTRS1992

CW dye laser technique for simultaneous, spatially-resolved measurements of temperature, pressure, and velocity of NO in an underexpanded free jet

Gas dynamic quantities within an underexpanded free jet were measured nonintrusively using a rapid-tuning, CW ring dye laser. A nitrogen jet was seeded with 0.5 percent NO in N2, and the conditions were controlled such that a barrel shock formed. The frequency-doubled output of the dye laser was used to spectrally resolve rotational lines in the NO gamma band near 225 nm. With the rapid-tuning capability, these rotational spectra were acquired at a repetition rate of 4 kHz. Spatial resolution was afforded by monitoring the induced fluorescence via a lens and photomultiplier tube. Modeling the spectrally-resolved features with Voigt profiles permitted simultaneous measurements of NO velocity, rotational temperature, and pressure. Expansion of the jet was assumed to be isentropic, and agreement between measured and expected values was typically better than 10 percent over most of the Mach-number range encountered. At high Mach numbers, the measured rotational temperatures systematically departed from the isentropic temperature distribution. Such a measured departure could be ascribed to the onset of a non-Boltzmann distribution of NO rotational states.

Di Rosa, M. D.↗

NASA NTRS1992

Measuring ionospheric electron density using the plasma frequency probe

During the past decade, the plasma frequency probe (PFP) has evolved into an accurate, proven method of measuring electron density in the ionosphere above about 90 km. The instrument uses an electrically short antenna mounted on a sounding rocket that is immersed in the plasma and notes the frequency where the antenna impedance is large and nonreactive. This frequency is closely related to the plasma frequency, which is a direct function of free electron concentration. The probe uses phase-locked loop technology to follow a changing electron density. Several sections of the plasma frequency probe circuitry are unique, especially the voltage-controlled oscillator that uses both an electronically tuned capacitor and inductor to give the wide tuning range needed for electron density measurements. The results from two recent sounding rocket flights (Thunderstorm II and CRIT II) under vastly different plasma conditions demonstrate the capabilities of the PFP and show the importance of in situ electron density measurements of understanding plasma processes.

Jensen, Mark D.↗

NASA NTRS1992

Fully integrated aerodynamic/dynamic optimization of helicopter rotor blades

This paper describes a fully integrated aerodynamic/dynamic optimization procedure for helicopter rotor blades. The procedure combines performance and dynamics analyses with a general purpose optimizer. The procedure minimizes a linear combination of power required (in hover, forward flight, and maneuver) and vibratory hub shear. The design variables include pretwist, taper initiation, taper ratio, root chord, blade stiffnesses, tuning masses, and tuning mass locations. Aerodynamic constraints consist of limits on power required in hover, forward flight and maneuver; airfoil section stall; drag divergence Mach number; minimum tip chord; and trim. Dynamic constraints are on frequencies, minimum autorotational inertia, and maximum blade weight. The procedure is demonstrated for two cases. In the first case the objective function involves power required (in hover, forward flight, and maneuver) and dynamics. The second case involves only hover power and dynamics. The designs from the integrated procedure are compared with designs from a sequential optimization approach in which the blade is first optimized for performance and then for dynamics. In both cases, the integrated approach is superior.

Walsh, Joanne L.↗

NASA NTRS1992

A reinforcement learning-based architecture for fuzzy logic control

This paper introduces a new method for learning to refine a rule-based fuzzy logic controller. A reinforcement learning technique is used in conjunction with a multilayer neural network model of a fuzzy controller. The approximate reasoning based intelligent control (ARIC) architecture proposed here learns by updating its prediction of the physical system's behavior and fine tunes a control knowledge base. Its theory is related to Sutton's temporal difference (TD) method. Because ARIC has the advantage of using the control knowledge of an experienced operator and fine tuning it through the process of learning, it learns faster than systems that train networks from scratch. The approach is applied to a cart-pole balancing system.

Berenji, Hamid R.↗

NASA NTRS1992

How life affects the geochemical cycle of carbon

Developing a quantitative understanding of the biogeochemical cycles of carbon as they have worked throughout Earth history on various time scales, how they have been affected by biological evolution, and how changes in the carbon content of ocean and atmosphere may have affected climate and the evolution of life are the goals of the research. Theoretical simulations were developed that can be tuned to reproduce such data as exist and, once tuned, can be used to predict properties that have not yet been observed. This is an ongoing process, in which models and results are refined as new data and interpretations become available and as understanding of the global system improves. Results of the research are described in several papers which were published or submitted for publication. These papers are summarized. Future research plans are presented.

Walker, James C. G.↗

NASA NTRS1991

A multiple objective optimization approach to quality control

The use of product quality as the performance criteria for manufacturing system control is explored. The goal in manufacturing, for economic reasons, is to optimize product quality. The problem is that since quality is a rather nebulous product characteristic, there is seldom an analytic function that can be used as a measure. Therefore standard control approaches, such as optimal control, cannot readily be applied. A second problem with optimizing product quality is that it is typically measured along many dimensions: there are many apsects of quality which must be optimized simultaneously. Very often these different aspects are incommensurate and competing. The concept of optimality must now include accepting tradeoffs among the different quality characteristics. These problems are addressed using multiple objective optimization. It is shown that the quality control problem can be defined as a multiple objective optimization problem. A controller structure is defined using this as the basis. Then, an algorithm is presented which can be used by an operator to interactively find the best operating point. Essentially, the algorithm uses process data to provide the operator with two pieces of information: (1) if it is possible to simultaneously improve all quality criteria, then determine what changes to the process input or controller parameters should be made to do this; and (2) if it is not possible to improve all criteria, and the current operating point is not a desirable one, select a criteria in which a tradeoff should be made, and make input changes to improve all other criteria. The process is not operating at an optimal point in any sense if no tradeoff has to be made to move to a new operating point. This algorithm ensures that operating points are optimal in some sense and provides the operator with information about tradeoffs when seeking the best operating point. The multiobjective algorithm was implemented in two different injection molding scenarios: tuning of process controllers to meet specified performance objectives and tuning of process inputs to meet specified quality objectives. Five case studies are presented.

Seaman, Christopher Michael↗

NASA NTRS1993

Acoustophoresis separation method

A method and apparatus are provided for acoustophoresis, i.e., the separation of species via acoustic waves. An ultrasonic transducer applies an acoustic wave to one end of a sample container containing at least two species having different acoustic absorptions. The wave has a frequency tuned to or harmonized with the point of resonance of the species to be separated. This wave causes the species to be driven to an opposite end of the sample container for removal. A second ultrasonic transducer may be provided to apply a second, oppositely directed acoustic wave to prevent undesired streaming. In addition, a radio frequency tuned to the mechanical resonance and coupled with a magnetic field can serve to identify a species in a medium comprising species with similar absorption coefficients, whereby an acoustic wave having a frequency corresponding to this gyrational rate can then be applied to sweep the identified species to one end of the container for removal.

Heyman, Joseph S.↗

NASA NTRS1993

Quaternion normalization in spacecraft attitude determination

Attitude determination of spacecraft usually utilizes vector measurements such as Sun, center of Earth, star, and magnetic field direction to update the quaternion which determines the spacecraft orientation with respect to some reference coordinates in the three dimensional space. These measurements are usually processed by an extended Kalman filter (EKF) which yields an estimate of the attitude quaternion. Two EKF versions for quaternion estimation were presented in the literature; namely, the multiplicative EKF (MEKF) and the additive EKF (AEKF). In the multiplicative EKF, it is assumed that the error between the correct quaternion and its a-priori estimate is, by itself, a quaternion that represents the rotation necessary to bring the attitude which corresponds to the a-priori estimate of the quaternion into coincidence with the correct attitude. The EKF basically estimates this quotient quaternion and then the updated quaternion estimate is obtained by the product of the a-priori quaternion estimate and the estimate of the difference quaternion. In the additive EKF, it is assumed that the error between the a-priori quaternion estimate and the correct one is an algebraic difference between two four-tuple elements and thus the EKF is set to estimate this difference. The updated quaternion is then computed by adding the estimate of the difference to the a-priori quaternion estimate. If the quaternion estimate converges to the correct quaternion, then, naturally, the quaternion estimate has unity norm. This fact was utilized in the past to obtain superior filter performance by applying normalization to the filter measurement update of the quaternion. It was observed for the AEKF that when the attitude changed very slowly between measurements, normalization merely resulted in a faster convergence; however, when the attitude changed considerably between measurements, without filter tuning or normalization, the quaternion estimate diverged. However, when the quaternion estimate was normalized, the estimate converged faster and to a lower error than with tuning only. In last years, symposium we presented three new AEKF normalization techniques and we compared them to the brute force method presented in the literature. The present paper presents the issue of normalization of the MEKF and examines several MEKF normalization techniques.

Deutschmann, J.↗

NASA NTRS1993

Adaptive control strategies for flexible robotic arm

The motivation of this research came about when a neural network direct adaptive control scheme was applied to control the tip position of a flexible robotic arm. Satisfactory control performance was not attainable due to the inherent non-minimum phase characteristics of the flexible robotic arm tip. Most of the existing neural network control algorithms are based on the direct method and exhibit very high sensitivity if not unstable closed-loop behavior. Therefore a neural self-tuning control (NSTC) algorithm is developed and applied to this problem and showed promising results. Simulation results of the NSTC scheme and the conventional self-tuning (STR) control scheme are used to examine performance factors such as control tracking mean square error, estimation mean square error, transient response, and steady state response.

Bialasiewicz, Jan T.↗

NASA NTRS1992

Slot antenna SIS mixers for submillimeter wavelengths

We are developing improved versions of a slot antenna SIS mixer which we have previously described. The initial work demonstrated a double sideband noise temperature of 420 K for a 500 GHz quasi-optical SIS mixer employing a twin-slot antenna on a quartz dielectric substrate. A quartz hyperhemispherical lens is used to focus the incoming radiation onto the twin-slot antenna. The advantages of a twin-slot antenna include a low impedance (35 omega) and a clean, symmetric beam pattern into the dielectric with a 70 percent efficiency. In our original mixer, the radiation was coupled from the two slot antennas onto superconducting microstrip lines which fed the SIS junction. By performing an impedance transformation using tapered lines and by feeding the radiation from the two slots to the junction in parallel, the effective (real) impedance seen by the junction was reduced to just 4 omega. This very low impedance allowed a junction area of 2.3 sq micron to be used at 500 GHz, which was manufactured using optical lithography. However, no attempt was made to tune out the junction capacitance. We estimate that this capacitance reduces the impedance coupling efficiency to eta(sub Z) approx. equals 0.23, for our junction with omega R(sub N) C = 5.3 at 500 GHz. The recent development of techniques using electron-beam lithography to manufacture junctions with very small areas (approx. equals 0.1 sq microns) now allows considerably more flexibility in the design of SIS mixer circuits. We have redesigned the slot-antenna mixer to take advantage of this possibility. In particular, we have included a novel circuit which allows the junction capacitance to be tune out over a broad bandwidth. For instance, mixers designed for 800 GHz using NbN/MgO/NbN junctions with realistic parameters achieve a 3 dB impedance bandwidth of nearly 400 GHz. Furthermore, our circuit uses only short lengths of microstrip and should be less sensitive to RF losses than other designs. The improved impedance match should give a large reduction in noise temperature as compared to our previous mixer. The new devices are currently under fabrication. Further details of the design and any available experimental results are discussed.

Zmuidzinas, Jonas↗

NASA NTRS1992

A quasioptical resonant-tunneling-diode oscillator operating above 200 GHz

We have fabricated and characterized a quasioptically stabilized resonant-tunneling-diode (RTD) oscillator having attractive performance characteristics for application as a radiometric local oscillator. The fundamental frequency of the oscillator is tunable from about 200 to 215 GHz, the instantaneous linewidth is between 10 and 20 kHz, and the output power across the tuning band is about 50 micro-W. The narrow linewidth and fine tuning of the frequency are made possible by a scanning semiconfocal open cavity which acts as the high-Q resonator for the oscillator. The cavity is compact, portable, and insensitive to vibration and temperature variation. The total dc power consumption (RTD plus bias supply) is only 10 mW. The present oscillator provides the highest power obtained to date from an RTD above 200 GHz. We attribute this partly to the use of the quasioptical resonator, but primarily to the quality of the RTD. It is fabricated from the In(0.53)Ga(0.47)As/AlAs materials system, which historically has yielded the best overall resonant-tunneling characteristics of any material system. The RTD active area is 4 sq microns, and the room-temperature peak current density and peak-to-valley current ratio are 2.5x10(exp 5) A cm(exp -2) and 9, respectively. The RTD is mounted in a WR-3 standard-height rectangular waveguide and is contacted across the waveguide by a fine wire that protrudes through a via hole in a Si3N4 'honeycomb' overlayer. We estimate that the theoretical maximum frequency of oscillation of this RTD is approximately 1.1 THz, and that scaled-down versions of the same quasioptical oscillator design should operate in a fundamental mode up to frequencies of at least 500 GHz.

Brown, E. R.↗

NASA NTRS1992

Model for the computation of self-motion in biological systems

A technique is presented by which direction- and speed-tuned cells, such as those commonly found in the middle temporal region of the primate brain, can be utilized to analyze the patterns of retinal image motion that are generated during observer movement through the environment. The developed model determines heading by finding the peak response in a population of detectors or neurons each tuned to a particular heading direction. It is suggested that a complex interaction of multiple cell networks is required for the solution of the self-motion problem in the primate brain.

Perrone, John A.↗

NASA NTRS1993

Air-mass flux measurement system using Doppler-shifted filtered Rayleigh scattering

An optical system has been investigated to measure mass flux distributions in the inlet of a high speed air-breathing propulsion system. Rayleigh scattered light from air is proportional to the number density of molecules and hence can be used to ascertain the gas density in a calibrated system. Velocity field measurements are achieved by spectrally filtering the elastically-scattered Doppler-shifted light with an absorbing molecular filter. A novel anamorphic optical collection system is used which allows optical rays from different scattering angles, that have different Doppler shifts, to be recorded separately. This is shown to obviate the need to tune the laser through the absorption to determine velocities, while retaining the ability to make spatially-resolved measurements along a line. By properly selecting the laser tuning and filter parameters, simultaneous density measurements can be made. These properties are discussed in the paper and experiments demonstrating the velocimetry capability are described.

Shirley, John A.↗

NASA NTRS1994

An active antenna for ELF magnetic fields

The work of Nikola Tesla, especially that directed toward world-wide electrical energy distribution via excitation of the earth-ionosphere cavity resonances, has stimulated interest in the study of these resonances. Not only are they important for their potential use in the transmission of intelligence and electrical power, they are important because they are an integral part of our natural environment. This paper describes the design of a sensitive, untuned, low noise active antenna which is uniquely suited to modern earth-ionosphere cavity resonance measurements employing fast-Fourier transform techniques for near-real-time data analysis. It capitalizes on a little known field-antenna interaction mechanism. Recently, the authors made preliminary measurements of the magnetic fields in the earth-ionosphere cavity. During the course of this study, the problem of designing an optimized ELF magnetic field sensor presented itself. The sensor would have to be small, light weight (for portable use), and capable of detecting the 5-50 Hz picoTesla-level signals generated by the natural excitations of the earth-ionosphere cavity resonances. A review of the literature revealed that past researchers had employed very large search coils, both tuned and untuned. Hill and Bostick, for example, used coils of 30,000 turns wound on high permeability cores of 1.83 m length, weighing 40 kg. Tuned coils are unsuitable for modern fast-Fourier transform data analysis techniques which require a broad spectrum input. 'Untuned' coils connected to high input impedance voltage amplifiers exhibit resonant responses at the resonant frequency determined by the coil inductance and the coil distributed winding capacitance. Also, considered as antennas, they have effective areas equal only to their geometrical areas.

Sutton, John F.↗