SEARCH · Engineering Papers

Results for “Frequency control”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41

All sources NASA NTRS DOE OSTI

NASA NTRS1978

Titanium/beryllium laminates - Fabrication, mechanical properties, and potential aerospace applications

The paper describes an investigation to assess the fabricability, mechanical properties, and possible aerospace applications of adhesively-bonded titanium/beryllium Tiber laminates. The results of the investigation indicate that structural laminates can be made which have: a modulus of elasticity comparable to steel, fracture strength comparable to the yield strength of titanium, density comparable to aluminum, impact resistance comparable to titanium, and little or no notch sensitivity. These laminates can have stiffness and weight advantages over other materials, including advanced fiber composites, in some aerospace applications where buckling resistance, vibration frequencies, and weight considerations control the design.

Chamis, C. C.↗

NASA NTRS1980

Standing Alfven wave current system at Io: Voyager 1 observations

The enigmatic control of the occurrence frequency of Jupiter's decametric emissions by the satellite Io is explained theoretically on the basis of its strong electrodynamic interaction with the corotating Jovian magnetosphere leading to field aligned currents connecting Io with the Jovian ionosphere. Direct measurements of the perturbation magnetic fields due to this current system were obtained by the magnetic field experiment on Voyager 1 on 5 March 1979 when it passed within 20,500 km south of Io. An interpretation in the framework of Alfven waves radiated by Io leads to current estimates of 2.8 million amps. A mass density of 7400 to 13600 proton mass units per Cu cm is derived which compares very favorably with independent observations of the torus composition characterized by 7-9 proton mass units per electron for a local electron density of 1050 to 1500 per cu cm. The power dissipated in the current system may be important for heating the Io heavy ion torus, inner magnetosphere, Jovian ionosphere, and possibly the ionosphere or even the interior of Io.

Acuna, M. H.↗

NASA NTRS1982

LORAN-C prediction problems

Control of time and frequency at remote stations and the maintenance of a constant time scale for LORAN-C chains are problems of practical importance. The stability of stations monitoring a LORAN-C chain is analyzed, in particular, those stations monitoring the Northwest Pacific chain. Individual determinations of the quantity, U.S. Naval Observatory Master lock are compared with an averaged value and monitored data.

Lukac, C. F.↗

NASA NTRS1982

Design concepts and cost studies for magnetic suspension and balance systems

The application of superconducting magnets for suspension and balance of wind tunnel models was studied. Conceptual designs are presented for magnetic suspension and balance system (MSBS) configurations compatible with three high Reynolds number cases representing specified combinations of test conditions and model sizes. Concepts in general met initially specified performance requirements such as duty cycle, force and moment levels, model angular displacement and positioning accuracy with nominal design requirements for support subsystems. Other performance requirements, such as forced model sinusoidal oscillations, and control force magnitude and frequency, were modified so as to alleviate the magnitude of magnet, power, and cryogenic design requirements.

Bloom, H. L.↗

NASA NTRS1981

Standing Alfven wave current system at Io - Voyager 1 observations

The enigmatic control of the occurrence frequency of Jupiter's decametric emissions by the satellite Io has been explained theoretically on the basis of its strong electrodynamic interaction with the corotating Jovian magnetosphere leading to field-aligned currents connecting Io with the Jovian ionosphere. Direct measurements of the perturbation magnetic fields due to this current system were obtained by the Goddard Space Flight Center magnetic field experiment on Voyager 1 on March 5, 1979, when it passed within 20,500 km south of Io. An interpretation in the framework of Alfven waves radiated by Io leads to current estimates of 2.8 x 10 to the 6th A. A mass density of 7400-13,600 proton mass units/cu cm is derived, which compares very favorably with independent observations of the torus composition characterized by 7-9 proton mass units per electron for a local electron density of 1050-1500/cu cm. The power dissipated in the current system may be important for heating the Io heavy ion torus, inner magnetosphere, Jovian ionosphere, and possibly the ionosphere or even the interior of Io.

Acuna, M. H.↗

NASA NTRS1981

Measured transonic unsteady pressures on an energy efficient transport wing with oscillating control surfaces

Highlight results are presented from subsonic and transonic pressure measurement studies conducted in the Langley Transonic Dynamics Tunnel on a supercritical wing model representative of an energy efficient transport design. Steady- and unsteady-pressure data were acquired on the upper and lower wing surface at an off-design Mach number of 0.60 and at the design Mach number of 0.78, for a Reynolds number of 2.2 x 10(6) (based on the wing average chord). The model configuration consisted of a sidewall-Mounted half-body fuselage and a semi-span wing with an aspect ratio of 10.76, a leading-edge sweepback angle of 28.8 degrees, and supercritical airfoil sections. The wing is instrumented with 252 static pressure orifices and 164 dynamic pressure gages. Model test variables included wing angle of attack, control-surface mean deflection angle, control-surface oscillating deflection angle and frequency, and phasing between oscillating leading-edge and trailing-edge controls when used together.

Cazier, F. W., Jr.↗

NASA NTRS1984

Dynamics and control of large space structures

An attempt is made to gather data useful to investigators in the fields of large space structure dynamics and control modeling, design and testing. Attention is given to structural dynamics and its relationship to such allied engineering fields as flutter analysis, as well as to problems in the prediction of atmospheric density at orbital altitude. The first challenge posed by large space structure control is the design of control systems with natural frequencies above several major structural frequencies. The establishment of a sufficiently accurate structural model, plant excitation, and shape maintenance, are noted to be additional problems.

Nurre, G. S.↗

NASA NTRS1984

New features of different frequency generating systems due to the use of electrodeless rigidly mounted VBA quartz crystal resonator

The BVA 5 MHz crystal equipped frequency sources exhibit a new blend of performances such as 10 to 11 daily stability, 5x10-13 short term stability (1 to 30 s time intervals) and close to the carrier low phase noise (1 Hz : -120 dBc, 10 Hz : -140 dBc), whereby retaining the customary crystal oscillator benefits of small volume, high reliability and low price, as opposed to more sophisticated frequency generators which would be required to achieve comparable performances. Examples illustrating the impact of the Oscilloquartz BVA oven-controlled crystal oscillator in different frequency generating systems are presented: cesium frequency standards; hydrogen frequency standard; a precision distribution sub-system for satellite ground stations; and high hierarchy exchanges of digital networks, synchronized by the master-slave method are discussed.

Jendly, A.↗

NASA NTRS1983

Satellite communication antenna technology

A general overview of current technology in the field of communication satellite antennas is presented. Among the topics discussed are: the design of multiple beam systems; frequency reuse; and polarization control of antenna measurements. Consideration is also given to: contour beam synthesis; dual shaped reflector synthesis; beam shaping; and offset reflector design. The applications of the above technologies to present and future generations of communications satellites is considered, with emphasis given to such systems as: the Intelsats; the Defense Satellite Communications System, (DSCS-III); Satellite Business System (SBS), and Comstar.

Mittra, R.↗

NASA NTRS1985

Objectives and first results of the NASA SETI Sky Survey field tests at Goldstone, California

The objectives and preliminary results of the initial field tests of the prototype hardware and software for the NASA SETI program are reviewed with emphasis on the Sky Survey component of the NASA search strategy. In particular, attention is given to field test instrumentation, sky pixelation, sky survey field tests, baseline tests, antenna control tests, and radio frequency interference survey. The test results and observational experience will be used to finalize the design of the SETI Sky Survey processing system and to optimize the observational strategy and procedures in time to begin a full-scale Microwave Observing Program in 1990.

Gulkis, S.↗

NASA NTRS1986

PACOSS program overview and status

Many future civilian and military large space structures (LSS) will have as performance objectives stringent pointing accuracies, short settling times, relatively fast response requirements, or combinations thereof. Many of these structures will be large, light weight, and will exhibit high structural modal density at low frequency and within the control bandwidth. Although it is possible in principle to achieve structural vibration control through purely active means, experience with complex structures has shown that the realities of plant model inaccuracies and sensor/actuator dynamics frequently combine to produce substandard performance. A more desirable approach is to apply passive damping technology to reduce the active control burden. Development of the technology to apply this strategy is the objective of the PACOSS (Passive and Active Control OF Space Structures) program. A key element in the PACOSS program is the Representative System Article (RSA). The RSA is a generic paper system that serves as a testbed for damping and controls studies. It also serves as a basis for design of the smaller Dynamic Test Article (DTA), a hardware testbed for the laboratory validation of analysis and design practices developed under PACOSS.

Rogers, L. C.↗

NASA NTRS1987

Programmable electronic synthesized capacitance

A predetermined and variable synthesized capacitance which may be incorporated into the resonant portion of an electronic oscillator for the purpose of tuning the oscillator comprises a programmable operational amplifier circuit. The operational amplifier circuit has its output connected to its inverting input, in a follower configuration, by a network which is low impedance at the operational frequency of the circuit. The output of the operational amplifier is also connected to the noninverting input by a capacitor. The noninverting input appears as a synthesized capacitance which may be varied with a variation in gain-bandwidth product of the operational amplifier circuit. The gain-bandwidth product may, in turn, be varied with a variation in input set current with a digital to analog converter whose output is varied with a command word. The output impedance of the circuit may also be varied by the output set current. This circuit may provide very small ranges in oscillator frequency with relatively large control voltages unaffected by noise.

Kleinberg, Leonard L.↗

NASA NTRS1986

Automation software for a materials testing laboratory

A comprehensive software system for automating much of the experimental process has recently been completed at the Lewis Research Center's high-temperature fatigue and structures laboratory. The system was designed to support experiment definition and conduct, results analysis and archiving, and report generation activities. This was accomplished through the design and construction of several software systems, as well as through the use of several commercially available software products, all operating on a local, distributed minicomputer system. Experimental capabilities currently supported in an automated fashion include both isothermal and thermomechanical fatigue and deformation testing capabilities. The future growth and expansion of this system will be directed toward providing multiaxial test control, enhanced thermomechanical test control, and higher test frequency (hundreds of hertz).

Mcgaw, Michael A.↗

NASA NTRS1988

Real-time flight test analysis and display techniques for the X-29A aircraft

The X-29A advanced technology demonstrator flight envelope expansion program and the subsequent flight research phase gave impetus to the development of several innovative real-time analysis and display techniques. These new techniques produced significant improvements in flight test productivity, flight research capabilities, and flight safety. These techniques include real-time measurement and display of in-flight structural loads, dynamic structural mode frequency and damping, flight control system dynamic stability and control response, aeroperformance drag polars, and aircraft specific excess power. Several of these analysis techniques also provided for direct comparisons of flight-measured results with analytical predictions. The aeroperformance technique was made possible by the concurrent development of a new simplified in-flight net thrust computation method. To achieve these levels of on-line flight test analysis, integration of ground and airborne systems was required. The capability of NASA Ames Research Center, Dryden Flight Research Facility's Western Aeronautical Test Range was a key factor in enabling implementation of these methods.

Hicks, John W.↗

NASA NTRS1987

Recent developments in the experimental identification of the dynamics of a highly flexible grid

Control effectiveness tests of reaction wheel actuators attached to a highly flexible grid are reported. Analytic determination of actuator control effectiveness is accomplished with finite-element modeling. Experimental determination is done with a least-square parameter identification algorithm that identifies the control coefficients of the second-order difference equation model of each vibration mode. The algorithm assumes a model with frequency and damping predetermined from free-decay tests for each mode. Accounting for the difference in forced and resonant frequency was necessary to produce control effectiveness estimates that are in reasonable agreement with the analytic predictions. The average error for control effectiveness coefficients greater than 5/sq sec was 6.384 percent.

Montgomery, Raymond C.↗

NASA NTRS1989

Real-time flight test analysis and display techniques for the X-29A aircraft

Hicks, John W.↗

NASA NTRS1990

Electromechanical propellant control system actuator

New control mechanism technologies are currently being sought to provide alternatives to hydraulic actuation systems. The Propulsion Laboratory at Marshall Space Flight Center (MSFC) is involved in the development of electromechanical actuators (EMA's) for this purpose. Through this effort, an in-house designed electromechanical propellant valve actuator has been assembled and is presently being evaluated. This evaluation will allow performance comparisons between EMA and hydraulics systems. The in-house design consists of the following hardware: a three-phase brushless motor, a harmonic drive, and an output spline which will mate with current Space Shuttle Main Engine (SSME) propellant control valves. A resolver and associated electronics supply position feedback for the EMA. System control is provided by a solid-state electronic controller and power supply. Frequency response testing has been performed with further testing planned as hardware and test facilities become available.

Myers, W. Neill↗

NASA NTRS1991

STARS: An integrated general-purpose finite element structural, aeroelastic, and aeroservoelastic analysis computer program

The details of an integrated general-purpose finite element structural analysis computer program which is also capable of solving complex multidisciplinary problems is presented. Thus, the SOLIDS module of the program possesses an extensive finite element library suitable for modeling most practical problems and is capable of solving statics, vibration, buckling, and dynamic response problems of complex structures, including spinning ones. The aerodynamic module, AERO, enables computation of unsteady aerodynamic forces for both subsonic and supersonic flow for subsequent flutter and divergence analysis of the structure. The associated aeroservoelastic analysis module, ASE, effects aero-structural-control stability analysis yielding frequency responses as well as damping characteristics of the structure. The program is written in standard FORTRAN to run on a wide variety of computers. Extensive graphics, preprocessing, and postprocessing routines are also available pertaining to a number of terminals.

Gupta, Kajal K.↗