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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Feasibility of inertialess conscan utilizing modified DSN feedsystems

The closed-loop conical-scan (conscan) technique has proven to be a useful method for pointing the DSN antennas more accurately than is possible by open-loop methods. As presently implemented, the antenna beam is scanned about the received signal direction by physical movement of the antenna. While straightforward, this approach has at least two disadvantages. Firstly, because of structural distortions, finite angle encoder resolution, and drive servo response, the actual antenna beam direction only approximates the commanded beam direction. Secondly, because of the large mass moved during scan, the rate of scan is severely restricted. If there are significant gain or signal level variations during a scan period, the conscan system interprets these variations as antenna pointing error. Both of these disadvantages would be alleviated in an inertialess conscan system in which the beam scanning was performed electronically. Recently, standard JPL antenna feedhorn software was upgraded to calculate, among other things, asymmetric corrugated horn radiation patterns of the type that would be needed for electronic beam scan. The required horn excitation is discussed and the results were described.

Potter, P. D.↗
NASA NTRS1978

Simple torsion test for shear moduli determination of orthotropic composites

The shear moduli G13 and G23 for two different composites (AS/3501 and T300/5209) of uniaxial and cross-ply fiber orientations were determined by torsion testing of flat specimens of rectangular cross section. Torsion tests were run under controlled angle of twist in an electro-hydraulic servo-controlled test system. Both laser and potentiometer methods of measuring the angle of twist were used. The in-plane shear modulus was calculated with a formula for transversally isotropic materials and a formula for orthotropic materials, while the out-of-plane shear modulus was calculated from the orthotropic material formula. Neither the uniaxial nor the angle-ply composite materials studied were transversely isotropic. The degree of anisotropy for the angle-ply materials was several times greater than that of the uniaxial composites. For specimens of uniaxial fiber orientation, the in-plane shear moduli could be calculated to a good approximation by using the isotropic formula and test machine deflection data.

Sumsion, H. T.↗
NASA NTRS1978

Ground-to-space optical power transfer

Using laser radiation as the energy input to a rocket, it is possible to consider the transfer of large payloads economically between low initial orbits and higher energy orbits. In this paper we will discuss the results of an investigation to use a ground-based High Energy Laser (HEL) coupled to an adaptive antenna to transmit multi-megawatts of power to a satellite in low-earth orbit. Our investigation included diffraction effects, atmospheric transmission efficiency, adaptive compensation for atmospheric turbulence effects, including the servo bandwidth requirements for this correction, and the adaptive compensation for thermal blooming. For these evaluations we developed vertical profile models of atmospheric absorption, strength of optical turbulence (CN2), wind, temperature, and other parameters necessary to calculate system performance. Our atmospheric investigations were performed for CO2, 12C18O2 isotope, CO and DF wavelengths. For all of these considerations, output antenna locations of both sea level and mountain top (3.5 km above sea level) were used. Several adaptive system concepts were evaluated with a multiple source phased array concept being selected. This system uses an adaption technique of phase locking independent laser oscillators. When both system losses and atmospheric effects were assessed, the results predicted an overall power transfer efficiency of slightly greater than 50%.

Mevers, G. E.↗
NASA NTRS1979

Scientific and technical applications of a tethered satellite system

A Shuttle-borne tether system capable of deploying a tether to radial distances as great as 100 km was described by Rupp and Laue (1978). The system as discussed by Rupp and Laue would have a total mass of 700 kg and would be mounted on one Shuttle pallet. It would consist of a tether reel mechanism complete with a servo drive motor and control sensors, a boom with docking probe used for initial deployment and subsequent retrieval, some type of satellite weighing 175 kg, up to 100 km of synthetic or metallic tether approximately 1 mm in diameter, a digital control computer, and a control and display panel on the Orbiter aft flight deck for crew operation. The primary use of a tether system for geological applications would be in the measurement of those magnetic and gravitational fields associated with geological structures. The major appeal in connection with atmospheric applications is the system's ability to extend instrumentation down into the lower thermosphere and possibly the mesosphere.

Snoddy, W. C.↗
NASA NTRS1979

Automated vehicle guidance using discrete reference markers

Techniques for providing steering control for an automated vehicle using discrete reference markers fixed to the road surface are investigated analytically. Either optical or magnetic approaches can be used for the sensor, which generates a measurement of the lateral offset of the vehicle path at each marker to form the basic data for steering control. Possible mechanizations of sensor and controller are outlined. Techniques for handling certain anomalous conditions, such as a missing marker, or loss of acquisition, and special maneuvers, such as u-turns and switching, are briefly discussed. A general analysis of the vehicle dynamics and the discrete control system is presented using the state variable formulation. Noise in both the sensor measurement and in the steering servo are accounted for. An optimal controller is simulated on a general purpose computer, and the resulting plots of vehicle path are presented. Parameters representing a small multipassenger tram were selected, and the simulation runs show response to an erroneous sensor measurement and acquisition following large initial path errors.

Johnston, A. R.↗
NASA NTRS1978

The application of hydraulics in the 2,000 kW wind turbine generator

A 2000 kW turbine generator using hydraulic power in two of its control systems is being built under the management of NASA Lewis Research Center. The hydraulic systems providing the control torques and forces for the yaw and blade pitch control systems are discussed. The yaw-drive-system hydraulic supply provides the power for positioning the nacelle so that the rotary axis is kept in line with the direction of the prevailing wind, as well as pressure to the yaw and high speed shaft brakes. The pitch-change-mechanism hydraulic system provides the actuation to the pitch change mechanism and permits feathering of the blades during an emergency situation. It operates in conjunction with the overall windmill computer system, with the feather control permitting slewing control flow to pass from the servo valve to the actuators without restriction.

Onufreiczuk, S.↗
NASA NTRS1979

Optokinetic motion sickness - Attenuation of visually-induced apparent self-rotation by passive head movements

An experimental study was conducted on seven normal subjects to evaluate the effectiveness of passive head movements in suppressing the optokinetically-induced illusory self-rotation. Visual simulation was provided by a servo-controlled optokinetic drum. Each subject participated in two experimental sessions. In one condition, the subject's head remained stationary while he gazed passively at a moving stripe pattern. In the other, he gazed passively and relaxed his neck muscles while his head was rotated from side to side. It appears that suppression of optokinetically-induced illusory self-rotation with passive head movements results from the operation of a spatial constancy mechanism interrelating visual, vestibular, and kinesthetic information on ongoing body orientation. The results support the view that optokinetic 'motion sickness' is related, at least in part, to an oculomotor disturbance rather than a visually triggered disturbance of specifically vestibular etiology.

Teixeira, R. A.↗
NASA NTRS1979

A summary of spectral synthesis procedures for multivariable systems

A new approach to the eigensystem assignment problem is presented. The approach utilizes a null-space formulation of the eigenvalue/eigenvector assignment problem to simultaneously realize arbitrary eigenvalue specifications, approximate desired modal behavior, and achieve low eigensystem sensitivity with respect to plant parameter variations. The methods are applied to the design of regulator and integral plus proportional servo control systems.

Liberty, S. R.↗
NASA NTRS1979

Report of the Electromechanical Subsystems Panel

Deficiencies in electromechanical flight technology are evaluated and development recommendations are made. Specific items discussed include magnetic bearings, lubrication for long life, signal and power transfer devices, servo sensing devices, deployment/retraction devices, cryogenic devices, data storage, and ordnance substitutes.

Source record↗
NASA NTRS1980

Solar maximum mission panel jettison analysis remote manipulator system

A study is presented of the development of the Remote Manipulator System (RMS) configurations for jettison of the solar panels on the Solar Maximum Mission/Multimission Satellite. A valid RMS maneuver between jettison configurations was developed. Arm and longeron loads and effector excursions due to the solar panel jettison were determined to see if they were within acceptable limits. These loads and end effector excursions were analyzed under two RMS modes, servos active in position hold submode, and in the brakes on mode.

Bauer, R. B.↗
NASA NTRS1979

Magnetic suspension system for an Annular Momentum Control Device (AMCD)

A technique to control a rim suspended in a magnetic field was developed. A complete system was developed, incorporating a support structure, magnetic actuators, a rim drive mechanism, an emergency fail-safe system, servo control system, and control electronics. Open loop and closed loop response of the system at zero speed and at 500 revolutions per minute (r/min) of the rim was obtained and analyzed. The rim was then dynamically balanced and a rim speed of 725 r/min was achieved. An analog simulation of the hardware was developed and tested with the actual control electronics connected to the analog computer. The system under development is stable at rim speeds below 700 r/min. Test results indicate that the rim under test is not rigid. The rim has a warp and a number of binding modes which prevented achievement of higher speeds. Further development efforts are required to achieve higher rim speeds.

Source record↗
NASA NTRS1979

T and F comparisons via broadcasting satellite and navigation technology satellite

The preliminary time/frequency dissemination experiments were made using the BSE. In order to establish the technique of the doppler shift canceling, the phase control servo including the satellite link and the precompensating frequency control using the measured values or using the orbital data of the satellite are tested. The amount of the residual doppler shift at the control station can be reduced to the order of 1 part in 10 to the 12th power or less by use of the first and the second methods. The method using the orbit data is expected to give a control capability of a few parts in 10 to 11th power. Thus, the maximum value of the doppler shift at the farther most place of the country is estimated to be + or - 2 x 10 to the -10 power without any correction. The experiment of the international time comparison via the NTS 1 was made for about one year since October 1978. The data of time difference between UTC(USNO) and UTC(RRL) are in good agreement with those via the portable clock of the USNO. By applying the correction for ionospheric delay the standard deviation of the data can be reduced to about one-half.

Saburi, Y.↗
NASA NTRS1980

Dual-spin spacecraft nutation control using articulated payloads

A technique is presented for achieving active control of nutation on a dual-spin spacecraft with an articulated payload through use of the payload's control system. Using the Orbiting Solar Observatory (OSO)-8 as an illustration, the closed-form solution to the nutation/control system dynamic interaction is presented. Control system design criteria are developed which establish the basic stability of the interaction. Design procedures are described to achieve the most effective nutation damping. Limitations on the amount of damping which can be achieved are characterized as functions of spacecraft and payload mass properties and servo-design parameters. The design techniques presented are verified through a series of on-orbit tests recently conducted on the OSO-8 spacecraft.

Slafer, L. I.↗
NASA NTRS1980

Bennett ion mass spectrometers on the Pioneer Venus Bus and Orbiter

Identical Bennett radio-frequency ion mass spectrometer instruments on the Pioneer Venus Bus and Orbiter have provided the first in-situ measurements of the detailed composition of the planet's ionosphere. The sensitivity, resolution, and dynamic range are sufficient to provide measurements of the solar-wind-induced bow-shock, the ionopause, and highly structured distributions of up to 16 thermal ion species within the ionosphere. The use of adaptive scan and detection circuits and servo-controlled logic for ion mass and energy analysis permits detection of ion concentrations as low as 5 ions/cu cm and ion flow velocities as large as 9 km/sec for O(+). A variety of commandable modes provides ion sampling rates ranging from 0.1 to 1.6 sec between measurements of a single constituent. A lightweight sensor and electronics housing are features of a compact instrument package.

Taylor, H. A., Jr.↗
NASA NTRS1979

A small, passively operated hydrogen maser

The paper describes a compact passive hydrogen maser with unique features including a reduction in size. It uses a passive operation mode, permitting the use of a small microwave TE(011) cavity dielectrically loaded by a low loss alumina. The Teflon coated quartz bulb common in other masers has been replaced by a Teflon coating on the inside wall of the cavity producing a simpler designed and a more rugged H-maser package. The cavity and the attached endcaps comprise the vacuum envelope, allowing the use of a single vacuum system. The dimensional stability of the ceramic cavity under barometric changes is sufficiently within the range of the electronic cavity servo so that a second vacuum system is not required. For temperature control, a single oven is located in the magnetic shield nest.

Howe, D. A.↗
NASA NTRS1980

The dynamic F2-layer over Arecibo

The idealized 'servo' model of the ionospheric F2-layer of Rishbeth et al. (1978) is used to simulate the observed behavior of the daytime Fe-peak at Arecibo at sunspot minimum. The meridional pressure-gradient force associated with the meridional neutral-air wind is determined empirically. The local time variation during the day is found to be consistent with the semidiurnal variation given by the MSIS atmospheric model of Hedin et al. (1977). The values of the F2-layer loss and diffusion coefficients needed to match the data are broadly consistent with the MSIS model.

Ganguly, S.↗
NASA NTRS1980

An Imaging Infrared (IIR) seeker using a microprogrammed processor

A recently developed Imaging Infrared Seeker uses a microprogrammed processor to perform gimbal servo control and system interface while performing the seeker functions of automatic target detection, acquisition, and tracking. The automatic detection mode requires up to 80% of the available capability of a high performance microprogrammed processor. Although system complexity was increased significantly, this approach can be cost effective when the basic computation capacity is already available.

Richmond, K. V.↗
NASA NTRS1980

A microprocessor application to a strapdown laser gyro navigator

The replacement of analog circuit control loops for laser gyros (path length control, cross axis temperature compensation loops, dither servo and current regulators) with digital filters residing in microcomputers is addressed. In addition to the control loops, a discussion is given on applying the microprocessor hardware to compensation for coning and skulling motion where simple algorithms are processed at high speeds to compensate component output data (digital pulses) for linear and angular vibration motions. Highlights are given on the methodology and system approaches used in replacing differential equations describing the analog system in terms of the mechanized difference equations of the microprocessor. Standard one for one frequency domain techniques are employed in replacing analog transfer functions by their transform counterparts. Direct digital design techniques are also discussed along with their associated benefits. Time and memory loading analyses are also summarized, as well as signal and microprocessor architecture. Trade offs in algorithm, mechanization, time/memory loading, accuracy, and microprocessor architecture are also given.

Giardina, C.↗