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NASA NTRS1984

An improved dual-frequency technique for the remote sensing of ocean currents and wave spectra

A two frequency microwave radar technique for the remote sensing of directional ocean wave spectra and surface currents is investigated. This technique is conceptually attractive because its operational physical principle involves a spatial electromagnetic scattering resonance with a single, but selectable, long gravity wave. Multiplexing of signals having different spacing of the two transmitted frequencies allows measurements of the entire long wave ocean spectrum to be carried out. A new scatterometer is developed and experimentally tested which is capable of making measurements having much larger signal/background values than previously possible. This instrument couples the resonance technique with coherent, frequency agility radar capabilities. This scatterometer is presently configured for supporting a program of surface current measurements.

Schuler, D. L.↗

NASA NTRS1984

Some aerodynamic discoveries and related NACA/NASA research programs following World War 2

The World War 2 time period ushered in a new era in aeronautical research and development. The air conflict during the war highlighted the need of aircraft with agility, high speed, long range, large payload capability, and in addition, introduced a new concept in air warfare through the use of guided missiles. Following the war, the influx of foreign technology, primarily German, led to rapid advances in jet propulsion and speed, and a host of new problem areas associated with high-speed flight designs were revealed. The resolution of these problems led to a rash of new design concepts and many of the lessons learned, in principle, are still effective today. In addition to the technical lessons learned related to aircraft development programs, it might also be noted that some lessons involving the political and philosophical nature of aircraft development programs are worth attention.

Spearman, M. L.↗

NASA NTRS1984

Rotorcraft flight-propulsion control integration

The parallel development of digital engine and flight controls for U.S. Army helicopters has made possible the future derivation of a fully integrated digital flight/propulsion control system. A NASA/Army research program has been undertaken to exploit these possibilities, ultimately yielding a generation of helicopters with exceptional agility and maneuverability in military roles and low pilot workloads in all-weather civil aviation missions. The program's three phases respectively address system modeling and analysis, flight hardware and software development, and flight evaluations aboard a research vehicle.

Mihaloew, J. R.↗

NASA NTRS1985

Evaluation of OMV ranging and docking systems

The Orbital Maneuvering Vehicle (OMV) will serve as a shuttle-based or permanent space station-based vehicle designed to rendezvous and soft dock with various other free-flying space vehicles for purposes of inspection, support, and retrieval. This study is concerned primarily with the eventual need for the OMV to rendezvous and dock softly with the Edwin P. Hubble Space Telescope (ST). Utilizing the available capabilities of the large microwave anechoic chamber facility at Marshall Space Flight Center for simulating docking target vehicle motions in a free-space environment, a program is being devised for benchmark testing of rendezvous and docking sensor systems proposed for use on the OMV. A testing regimen suitable for evaluating the accuracy and tracking agility in sensing range, range rate, and angle information at close ranges (0 R 30m) has been developed.

Mcdonald, M. W.↗

NASA NTRS1985

Large space antenna technology applied to radar-imaging, rain-rate measurements, and ocean wind sensing

During the last decade, the utility of spaceborne microwave remote sensing systems for ocean windspeed measurement, ocean wave imaging and sea ice studies was demonstrated. Development of large space antennas offers some interesting possibilities for rain rate measurements, ocean and ice studies, and radar imaging. The joint use of active and passive sensors using the 15 m antenna for ocean, ice, and soil moisture studies; rain rate measurements; and radar imaging is considered. Verification of the frequency agile rain radar concept with Shuttle offers the possibility of much needed rain rate statistics over the ocean.

Moore, R. K.↗

NASA NTRS1984

Exact nonlinear command generation and tracking for robot manipulators and spacecraft slewing maneuvers

In connection with the current interest in agile spacecraft maneuvers, it has become necessary to consider the nonlinear coupling effects of multiaxial rotation in the treatment of command generation and tracking problems. Multiaxial maneuvers will be required in military missions involving a fast acquisition of moving targets in space. In addition, such maneuvers are also needed for the efficient operation of robot manipulators. Attention is given to details regarding the direct nonlinear command generation and tracking, an approach which has been successfully applied to the design of control systems for V/STOL aircraft, linearizing transformations for spacecraft controlled with external thrusters, the case of flexible spacecraft dynamics, examples from robot dynamics, and problems of implementation and testing.

Dywer, T. A. W., III↗

NASA NTRS1986

High-spectral resolution solar microwave observations

The application of high-spectral resolution microwave observations to the study of solar activity is discussed with particular emphasis on the frequency dependence of microwave emission from solar active regions. A shell model of gyroresonance emission from active regions is described which suggest that high-spectral resolution, spatially-resolved observations can provide quantitative information about the magnetic field distribution at the base of the corona. Corresponding observations of a single sunspot with the Owens Valley frequency-agile interferometer at 56 frequencies between 1.2 and 14 Ghs are presented. The overall form of the observed size and brightness temperature spectra was consistent with expectations based on the shell model, although there were differences of potential physical significance. The merits and weaknesses of microwave spectroscopy as a technique for measuring magnetic fields in the solar corona are briefly discussed.

Hurford, G. J.↗

NASA NTRS1985

Deduction of coronal magnetic fields using microwave spectroscopy

Gyroresonance opacity renders the solar corona optically thick at frequencies which are low integral multiples of the local gyrofrequency. This causes the microwave spectrum of sunspots to be sensitive to the strength of coronal magnetic fields. The concept is illustrated by high spectral resolution observations of a sunspot acquired with the Owens Valley frequency-agile interferometer. The observed spectrum is compared to the results of three-dimensional atmospheric model calculations in which the sunspot field is represented by the potential field of a dipole located beneath the photosphere. The comparison enables the depth, orientation and magnetic moment of the dipole that best fits the observations to be determined. Since such observations require that the microwave emission be resolved spectrally, not spatially, the technique may be applicable to the study of stellar coronal fields.

Hurford, G. J.↗

NASA NTRS1986

High-spatial-resolution microwave and related observations as diagnostics of coronal loops

High spatial resolution microwave observations of coronal loops, together with theoretical models for the loop emission, can provide detailed information about the temperature, density, and magnetic field within the loop, as well as the environment around the loop. The capability for studying magnetic fields is particularly important, since there is no comparable method for obtaining direct information about coronal magnetic fields. Knowledge of the magnetic field strength and structure in coronal loops is important for understanding both coronal heating and flares. With arc-second-resolution microwave observations from the Very Large Array (VLA), supplemental high-spectral-resolution microwave data from a facility such as the Owens Valley frequency-agile interferometer, and the ability to obtain second-of-arc resolution EUV aor soft X ray images, the capability already exists for obtaining much more detailed information about coronal plasma and magnetic structures than is presently available. This capability is discussed.

Holman, Gordon D.↗

NASA NTRS1987

Tracking and pointing maneuvers with slew-excited deformation shaping

It is shown in this paper how it is possible to shape the slew-excited structural response of a deformable vehicle undergoing agile attitude maneuvers, so that the required fully corrected slew torque profiles can be computed on-line in closed form, and with the same bandwidth as required for the rigid body case. This is accomplished by simultaneously applying maneuver-dependent structural force controls of progressively smaller amplitudes, at the cost of progressively higher signal processing complexity of slew torque and structural force command generation.

Dwyer, Thomas A. W., III↗

NASA NTRS1988

Optically interconnected phased arrays

Phased-array antennas are required for many future NASA missions. They will provide agile electronic beam forming for communications and tracking in the range of 1 to 100 GHz. Such phased arrays are expected to use several hundred GaAs monolithic integrated circuits (MMICs) as transmitting and receiving elements. However, the interconnections of these elements by conventional coaxial cables and waveguides add weight, reduce flexibility, and increase electrical interference. Alternative interconnections based on optical fibers, optical processing, and holography are under evaluation as possible solutions. In this paper, the current status of these techniques is described. Since high-frequency optical components such as photodetectors, lasers, and modulators are key elements in these interconnections, their performance and limitations are discussed.

Bhasin, Kul B.↗

NASA NTRS1987

A review of decametric radio astronomy - Instruments and science

The techniques and instruments used in Galactic and extragalactic radio astronomy at dkm wavelengths are surveyed, and typical results are summarized. Consideration is given to the large specialized phased arrays used for early surveys, the use of wideband elements to increase frequency agility, experimental VLBI observations, and limitations on ground-based observations below about 10 MHz (where the proposed LF Space Array, with resolution 0.5-5 arcmin, could make a major contribution). Observations discussed cover the Galactic center, the Galactic background radiation, SNRs, compact Galactic sources, the ISM, and large extragalactic sources.

Erickson, W. C.↗

NASA NTRS1988

Rotorcraft research at NASA

An overview of NASA research in rotorcraft technology is presented. Ten percent of the NASA aeronautics program is made up of rotorcraft research. The aeronautics program conducts research in five areas: aerodynamics, propulsion, materials and structures, information sciences and human factors, and flight systems. The key objectives of NASA research are major reduction in external noise and aircraft vibration, reduction of pilot workload for night, adverse weather and NOE flying, increasing power and reducing fuel consumption in small engines, and identifying and exploiting vehicle characteristics and concepts for triple current speed and improved maneuverability and agility. NASA and Army resources are combined to pursue research at three major centers. The Ames research center conducts research in the physics of transition and turbulent flows, using a new improved wind tunnel and the NAS system. At the Langley Research Center, work is done in noise and vibration reduction, finding lighter and more durable composite structures, and aeroelasticity for tilt motors and X-wing configurations. At the NASA Lewis Research Center, researchers are working on improving helicopter propulsion systems.

Burks, John S.↗

NASA NTRS1987

A new radar technique for satellite rainfall algorithm development

A potential new radar parameter was investigated for measuring rainfall, namely the summation of the phase shifts at horizontal and vertical polarizations due to propagation through precipitation. The proposed radar technique has several potential advantages over other approaches because it is insensitive to the drop size distribution and to the shapes of the raindrops. Such a parameter could greatly assist the development of satellite rainfall estimation algorithms by providing comparative measurements near the ground. It could also provide hydrologically useful information for such practical applications as urban hydrology. Results of the investigation showed that the parameters can not be measured by radar. However, a closely related radar parameter, propagation differential phase shift, can be readily measured using a polarization diversity radar. It is recommended that propagation differential phase shift be further investigated and developed for radar monitoring of rainfall using a polarization agile radar. It is also recommended that a prototype multiple frequency microwave link be constructed for attenuation measurements not possible by existing radar systems.

Jameson, Arthur R.↗

NASA NTRS1989

A variable-gain output feedback control design methodology

A digital control system design technique is developed in which the control system gain matrix varies with the plant operating point parameters. The design technique is obtained by formulating the problem as an optimal stochastic output feedback control law with variable gains. This approach provides a control theory framework within which the operating range of a control law can be significantly extended. Furthermore, the approach avoids the major shortcomings of the conventional gain-scheduling techniques. The optimal variable gain output feedback control problem is solved by embedding the Multi-Configuration Control (MCC) problem, previously solved at ICS. An algorithm to compute the optimal variable gain output feedback control gain matrices is developed. The algorithm is a modified version of the MCC algorithm improved so as to handle the large dimensionality which arises particularly in variable-gain control problems. The design methodology developed is applied to a reconfigurable aircraft control problem. A variable-gain output feedback control problem was formulated to design a flight control law for an AFTI F-16 aircraft which can automatically reconfigure its control strategy to accommodate failures in the horizontal tail control surface. Simulations of the closed-loop reconfigurable system show that the approach produces a control design which can accommodate such failures with relative ease. The technique can be applied to many other problems including sensor failure accommodation, mode switching control laws and super agility.

Halyo, Nesim↗

NASA NTRS1989

Semi-autonomous design concepts for a Mars rover

Studies of rover mobility and surface rendezvous for a Mars Rover/Sample Return (MRSR) mission have been performed. The objective of these efforts has been to identify and address the most challenging issues and develop the most promising design options for the rover mobility and navigation subsystems. A series of trade studies culminated in three candidate design concepts: a large, but otherwise conventional four-wheel drive vehicle; a sophisticated and agile six-legged walking vehicle; and a greatly simplified legged vehicle. This paper summarizes the key design features for these three concepts. For each design, the approaches to vehicle locomotion, sensing and navigation are discussed first. Timelines are developed for the adopted concepts of operation which constrain the range of the remaining parameters. Estimates of rover mass, volume, and power are provided, and performance is projected for vehicle range, terrain traversibility and navigation accuracy.

Spiessbach, Andrew J.↗

NASA NTRS1988

Optically interconnected phased arrays

Bhasin, Kul B.↗

NASA NTRS1989

US/UK Advanced Short Takeoff and Vertical Landing program (ASTOVL)

Both the U.S. and the UK have substantial technology bases from past and current R and D programs, a common background of service experience and, potentially, much common interest in the future use of advanced STOVL combat aircraft. Equally interested in the operational advantages of the short takeoff and vertical landing capability of combat aircraft, combined with supersonic and high agility performance, the U.S. and the UK have agreed to collaborate on ASTOVL research underwritten by a Memorandum of Understanding (MOU) (1986) between the two governments. The paper describes the aims and provisions of the MOU, gives the results of studies, illustrates the technology development underway, and outlines the future ASTOVL technology program. Particular attention is given to concept studies on advanced vectored thrust, the ejector augmentor, the hybrid tandem fan, and the remote augmented lift system.

Levine, J.↗