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NASA NTRS1988

An approximation theory for the identification of nonlinear distributed parameter systems

An abstract approximation framework for the identification of nonlinear distributed parameter systems is developed. Inverse problems for nonlinear systems governed by strongly maximal monotone operators (satisfying a mild continuous dependence condition with respect to the unknown parameters to be identified) are treated. Convergence of Galerkin approximations and the corresponding solutions of finite dimensional approximating identification problems to a solution of the original finite dimensional identification problem is demonstrated using the theory of nonlinear evolution systems and a nonlinear analog of the Trotter-Kato approximation result for semigroups of bounded linear operators. The nonlinear theory developed here is shown to subsume an existing linear theory as a special case. It is also shown to be applicable to a broad class of nonlinear elliptic operators and the corresponding nonlinear parabolic partial differential equations to which they lead. An application of the theory to a quasilinear model for heat conduction or mass transfer is discussed.

Banks, H. T.↗

NASA NTRS2009

UAVSAR - A New Airborne L-Band Radar for Repeat Pass Interferometry

NASA/JPL has developed a new airborne Synthetic Aperture Radar (SAR) which has become available for use by the scientific community in January, 2009. Pod mounted, the UAVSAR was designed to be portable among a variety of aircraft, including unmanned aerial systems (UAS). The instrument operates in the L-Band, has a resolution under 2m from a GPS altitude of 12Km and a swath width of approximately 20Km. UAVSAR currently flies on a modified Gulfstream-III aircraft, operated by NASA s Dryden Flight Research Center at Edwards, California. The G-III platform enables repeat-pass interferometric measurements, by using a modified autopilot and precise kinematic differential GPS to repeatedly fly the aircraft within a specified 10m tube. The antenna is electronically steered along track to assure that the antenna beam can be directed independently, regardless of speed and wind direction. The instrument can be controlled remotely, AS AN OPTION, using the Research Environment for Vehicle Embedded Analysis on Linux (REVEAL). This allows simulation of the telepresence environment necessary for flight on UAS. Potential earth science research and applications include surface deformation, volcano studies, ice sheet dynamics, and vegetation structure.

Mace, Thomas H.↗

NASA NTRS1988

Mars rover technology development requirements

The technology development requirements for various Mars rover range capabilities are discussed, focusing on local navigation of the rover. The capabilities of two methods are compared. In one method, operators on the earth view stereo pictures sent by the rover and determine short traverse paths which the rover follows. The other method achieves more autonomous capability by using computer vision from orbital imagery with approximate long routes commanded from earth. The locomotion, navigation, ground operations, computation, power, thermal control, communications, sample acquisition, and analysis and preservation requirements are examined.

Bedard, Roger↗

NASA NTRS2012

Design of the PIXIE Adiabatic Demagnetization Refrigerators

The Primordial Inflation Explorer (PIXIE) is a proposed mission to densely map the polarization of the cosmic microwave background. It will operate in a scanning mode from a sun-synchronous orbit, using low temperature detectors (at 0.1 K) and located inside a teslescope that is cooled to approximately 2.73 K - to match the background temperature. A mechanical cryocooler operating at 4.5 K establishes a low base temperature from which two adiabatic demagnetization refrigerator (ADR) assemblies will cool the telescope and detectors. To achieve continuous scanning capability, the ADRs must operate continuously. Complicating the design are two factors: 1) the need to systematically vary the temperature of various telescope components in order to separate the small polarization signal variations from those that may arise from temperature drifts and changing gradients within the telescope, and 2) the orbital and monthly variations in lunar irradiance into the telescope barrels. These factors require the telescope ADR to reject quasi-continuous heat loads of 2-3 millwatts, while maintaining a peak heat reject rate of less than 12 milliwatts. The detector heat load at 0.1 K is comparatively small at 1-2 microwatts. This paper will describe the 3-stage and 2-stage continuous ADRs that will be used to meet the cooling power and temperature stability requirements of the PIXIE detectors and telescope.

adiabatic demagnetization refrigerator↗

NASA NTRS2003

Setting up a Grid: A Guide for Beginners by a Beginner

A simple compute grid can be constructed for under $ 1,000 with 5 computers on a LAN for the purpose of video compression from captured digital video to MPEG file format. The process for setting up this grid will be covered in detail, including the required operating systems and hardware, the required globus software, and the required video capture and compression software. Pitfalls encountered will be discussed, and the approximate timeline for a motivated but uninformed beginner. The installation, configuration, and operation of additional software that is needed test, measure and otherwise verify that the grid components are functioning as "advertised", will also be presented. This is a true life account for setting up a grid based on instructions in Chapters 9 and 10 of Introduction to Grid Computing with Globus.

Welch, Clara↗

NASA NTRS1978

Design and operation of a solar heating and cooling system for a residential size building

The first year of operation of solar house is discussed. Selected design information, together with a brief system description is included. The house was equipped with an integrated solar heating and cooling system which uses fully automated state-of-the art. Evaluation of the data indicate that the solar house heating and cooling system is capable of supplying nearly 100 percent of the thermal energy required for heating and approximately 50 percent of the thermal energy required to operate the absorption cycle air conditioner.

Littles, J. W.↗

NASA NTRS1989

Tilt rotor aircraft aeroacoustics

This paper studies the state of knowledge and the needed improvement in noise methodology and measurements for tilt rotor aircraft. Similarities and differences between tilt rotor aeroacoustic conditions and helicopter and propeller experience are identified. A discussion of the possible principal noise mechanisms throughout the flight envelope shows a need for further experimental and analytical investigations to develop an adequate understanding of the important sources and influencing factors. Existing experimental data from flight tests suggest terminal area noise reduction by operating within certain portions of the conversion flight envelope. Prediction methods are found to provide approximate indications only for low frequency harmonic and broadband noise for several of the tilt rotor's operating conditions. The acoustic effects of the hover case 'fountain' flow are pronounced and need further research. Impulsive noise and high frequency harmonic noise remain problems, as on helicopters, pending major improvements in wake, unsteady aerodynamics, and acoustics methodology.

George, Albert R.↗

NASA NTRS1978

A strictly Markovian expansion for plasma turbulence theory

The collision operator that appears in the equation of motion for a particle distribution function that has been averaged over an ensemble of random Hamiltonians is non-Markovian. It is non-Markovian in that it involves a propagated integral over the past history of the ensemble averaged distribution function. All formal expansions of this nonlinear collision operator to date preserve this non-Markovian character term by term yielding an integro-differential equation that must be converted to a diffusion equation by an additional approximation. In this note we derive an expansion of the collision operator that is strictly Markovian to any finite order and yields a diffusion equation as the lowest non-trivial order. The validity of this expansion is seen to be the same as that of the standard quasi-linear expansion.

Jones, F. C.↗

NASA NTRS2001

Engine With Regression and Neural Network Approximators Designed

At the NASA Glenn Research Center, the NASA engine performance program (NEPP, ref. 1) and the design optimization testbed COMETBOARDS (ref. 2) with regression and neural network analysis-approximators have been coupled to obtain a preliminary engine design methodology. The solution to a high-bypass-ratio subsonic waverotor-topped turbofan engine, which is shown in the preceding figure, was obtained by the simulation depicted in the following figure. This engine is made of 16 components mounted on two shafts with 21 flow stations. The engine is designed for a flight envelope with 47 operating points. The design optimization utilized both neural network and regression approximations, along with the cascade strategy (ref. 3). The cascade used three algorithms in sequence: the method of feasible directions, the sequence of unconstrained minimizations technique, and sequential quadratic programming. The normalized optimum thrusts obtained by the three methods are shown in the following figure: the cascade algorithm with regression approximation is represented by a triangle, a circle is shown for the neural network solution, and a solid line indicates original NEPP results. The solutions obtained from both approximate methods lie within one standard deviation of the benchmark solution for each operating point. The simulation improved the maximum thrust by 5 percent. The performance of the linear regression and neural network methods as alternate engine analyzers was found to be satisfactory for the analysis and operation optimization of air-breathing propulsion engines (ref. 4).

Patnaik, Surya N.↗

NASA NTRS1972

The development of materials capable of operation in an oxidizing atmosphere for extended periods of time

An evaluation is presented of silicon carbide, zirconium diboride, and iridium-coated graphite as materials for construction of furnace cores which could operate under highly oxidizing conditions at temperatures of approximately 2,200 C in the presence of molten aluminum oxide. It was found that silicon carbide and zirconium diboride could not withstand oxidizing atmospheres in the presence of aluminum oxide at temperature 2,200 C. However, graphite furnace cores coated with iridium were found to be useful furnace cores at 2,200 C in an oxidizing atmosphere for reasonably extended periods of time.

Duhamel, A. P.↗

NASA NTRS1972

Design and control of remote manipulators

Results of investigations on vibrational modes of manipulators revealed: (1) any arbitrary manipulator may be analyzed for its small motion compliances; (2) a simulation of the Martin-Marietta shuttle boom with a 65,000 lb. payload attached, indicated three natural frequencies; and (3) simulations can be made of rigid limbs and flexible joints as well as for flexible limbs and locked joints and combinations thereof. Trajectories for arms were determined so that some integral criterion such as integral of kinetic energy or control torque magnitude is minimized over a motion of the arm. Experiments performed to evaluate various TV displays in conjunction with manipulator control modes showed that when mounted directly to the manipulator control arm and arranged to look approximately along the arm to the hand the operator could perform the task almost as quickly as when viewing the task directly.

Whitney, D. E.↗

NASA NTRS1972

Design and performance of a space simulation facility for long-term ion thruster system testing.

An existing space simulation facility was modified to provide the required simulated orbital environment for approximately one year of continuous testing of an operating SERT II mercury ion thruster system. Modifications included a frozen mercury collector system operating at cryogenic temperatures and automatic safety features to permit unattended operation. Special high-voltage insulators and passthroughs were designed to ensure electrical and thermal isolation in the presence of mercury vapor and deposits. The facility performance characteristics which provided the required environment without detrimental effects from mercury during the specialized test are discussed.

Mckinney, H. F.↗

NASA NTRS1973

Pioneer Venus mechanical roots pump test and evaluation

A mechanical pump for use with the Pioneer-Venus probe mass spectrometer inlet system was obtained, and a limited performance testing program, including ultimate/compression ratio tests and throughput tests at three different pump speeds, was performed. Considerable operating experience with the pump was obtained over approximately 200 hours of running. The test results show general agreement with pump specifications.

Thomas, N. C.↗

NASA NTRS1973

A neutral-atmosphere composition experiment for the Atmosphere Explorer-C, -D, and -E.

The neutral-atmosphere composition experiment instrumentation is designed to obtain in-situ measurements of neutral thermosphere composition from Atmosphere Explorer-C, -D, and -E. The system is based on previously flown OGO-6 and San Marco-3 composition instruments. The mass-spectrometer sensor includes a gold-plated thermalizing chamber and ion source, a hyperbolic rod quadrupole analyzer, and an off-axis electron multiplier. Automatic ion-source sensitivity control and pulse-counting techniques provide density measurement capability from approximately 125 to 1000 km altitude. The normal operating mode includes measurement at all masses in the range of 1 to 44 amu, with emphasis on hydrogen, helium, oxygen, nitrogen, and argon.

Pelz, D. T.↗

NASA NTRS1974

Hingeless rotor theory and experiment on vibration reduction by periodic variation of conventional controls

The reduction of the n per rev. pitch-, roll- and vertical vibrations of an n-bladed rotor by n per rev. sinusoidal variations of the collective and cyclic controls is investigated. The numerical results presented refer to a four-bladed, 7.5-foot model and are based on frequency response tests conducted under an Army-sponsored research program. The following subjects are treated: extraction of the rotor transfer functions (.073R hub flapping and model thrust versus servo valve command, amplitude and phase), calculation of servo commands (volts) required to compensate .073R hub flapping (3P and 5P) and model thrust (4P), evaluation of the effect of the vibratory control inputs on blade loads, and theoretical prediction of the root flapbending moments generated by 0 to 5P perturbations of the feathering angle and rotor angle of attack. Five operating conditions are investigated covering advance ratios from approximately 0.2 to 0.85. The feasibility of vibration reduction by periodic variation on conventional controls is evaluated.

Sissingh, G. J.↗

NASA NTRS1974

The response of rotating machinery to external random vibration

A high-speed turbogenerator employing gas-lubricated hydrodynamic journal and thrust bearings was subjected to external random vibrations for the purpose of assessing bearing performance in a dynamic environment. The pivoted-pad type journal bearings and the step-sector thrust bearing supported a turbine-driven rotor weighing approximately twenty-one pounds at a nominal operating speed of 36,000 rpm. The response amplitudes of both the rigid-supported and flexible-supported bearing pads, the gimballed thrust bearing, and the rotor relative to the machine casing were measured with capacitance type displacement probes. Random vibrations were applied by means of a large electrodynamic shaker at input levels ranging between 0.5 g (rms) and 1.5 g (rms). Vibrations were applied both along and perpendicular to the rotor axis. Response measurements were analyzed for amplitude distribution and power spectral density. Experimental results compare well with calculations of amplitude power spectral density made for the case where the vibrations were applied along the rotor axis. In this case, the rotor-bearing system was treated as a linear, three-mass model.

Tessarzik, J. M.↗

NASA NTRS1974

S-193 scatterometer transfer function analysis for data processing

A mathematical model for converting raw data measurements of the S-193 scatterometer into processed values of radar scattering coefficient is presented. The argument is based on an approximation derived from the Radar Equation and actual operating principles of the S-193 Scatterometer hardware. Possible error sources are inaccuracies in transmitted wavelength, range, antenna illumination integrals, and the instrument itself. The dominant source of error in the calculation of scattering coefficent is accuracy of the range. All other ractors with the possible exception of illumination integral are not considered to cause significant error in the calculation of scattering coefficient.

Johnson, L.↗

NASA NTRS1975

Kinesthetic control simulator

A kinesthetic control simulator is reported that has a flat base upon which rests a support structure having a lower spherical surface for rotation on the base plate with columns which support a platform above the support structure at a desired location with respect to the center of curvature of the spherical surface. A handrail is at approximately the elevation of the hips of the operator above the platform with a ring attached to the support structure which may be used to limit the angle of tilt. Five degree freedom-of-motion can be obtained by utilizing an air pad structure for support of the control simulator.

Hill, P. R.↗