Snap dynamics
Computer program calculates normal vibration modes of complex structures elimating excessively large amounts of input data, run time, and core storage. Provision for accuracy improvement is also included.
Kiefling, L.↗
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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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Analysis of fatigue crack propagation
The correlation between fatigue crack propagation and stress intensity factor is analyzed. When determining fatigue crack propagation rate, a crack increment, delta a, and its corresponding increment in load cycles, delta N, are measured. Fatigue crack propagation must be caused by a shear and/or a normal separation mode. Both of these two processes are discrete if one looks at the atomic level. If the average deformation and fracture properties over the crack increments, delta a, can be considered as homogeneous, if the characteristic discrete lengths of sigma a, if the plastic zone size is small, and if a plate is thick enough to insure a plane strain case, da/dN is proportional to delta K squared. Any deviation of empirical data from this relation must be caused by the fact that one or more of these conditions are not satisfied. The effects of plate thickness and material inhomogeneity are discussed in detail. A shear separation mode of fatigue crack propagation is described and is used to illustrate the effects of material inhomogeneity.
Liu, H. W.↗
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.↗
Photometer dewar system for NASA C141 airborne telescope (Kuiper Flying Observatory)
The design, calibration, and testing of a photometer to be used in an airborne telescope is described. A description of the cryogenics of the photometer is given, and photographs and blueprints of the photometer are included. The photometer is designed with a focal plane beam switching system so that the airplane telescope can be used in a normal optical mode at the bent Cassegrain focus and with the photometer operating in the pressurized cabin of the airplane. The concept was to produce a system which could be used in almost the same manner as ground based infrared photometers and dewars of the O'Brien Observatory at the University of Minnesota.
Ney, E. P.↗
Symbol synchronizer assembly instability study, part 2
Data processing to develop a third-order phase model and to translate all such processed data to the frequency realm for further analysis was described. The frequency study yields a long frequency modulation (FM) drift sinusoid (1600-sec period), an impressed secondary drift wave with a period of about 116 sec, and a set of even harmonics of twice the ramp period-the latter arising from, and used to modify, the phase detector model. The result is applied secondarily to estimate the strong-signal SSA phase detector response "out-of-lock." Finally, the main drift components are verified against all available data, and the result is used to estimate minimum lock conditions and the SSA drift effect under normal operating modes. The instability problem appears marginally resolvable if the acquisition technique is modified.
Bunce, R. C.↗
Multi-axis hand controller for the shuttle remote manipulator system
The Shuttle Remote Manipulator System, has a articulated arm of 50 ft. length with six motor-driven joints. The basic purpose is to establish physical contact with various space hardware items and maneuver these to the desired position and attitude with respect to the Orbiter, nulling out relative velocities and stabilizing the free-body system by managing residual energies. The normal operating mode is resolved-motion end-point rate control by man-in-loop command. The translational freedoms are defined so that the End Effector (EEFTR) of the arm will move in planes parallel to the principal translational planes of the Orbiter, at a rate commanded by the displacement of the Translation Hand Controller in the corresponding freedom and direction. The rotational freedoms are rate-controlled by the Rotation Hand Controller about pivot axes parallel to Orbiter roll, pitch and yaw, originating at the EEFTR reference point.
Lippay, A. L.↗
The role of rotor impedance in the vibration analysis of rotorcraft
In an improved method which retains the advantage of separate treatment of rotor and airframe, the rotor impedance is used to correct the input to the airframe. This improved method is illustrated for a strongly idealized case of vertical excitation and then for rolling and pitching moment excitation of a four bladed hingeless rotor on an up-focussing flexible mount. Contrary to the usual approach that represents aeroelastic blade motions by a series of normal blade modes in vacuum, the aeroelastic rotor impedances are computed directly with a finite blade element method that includes aerodynamics. The rotor impedance matrix for three or more blades is determined from the root moment impedance for a single blade by a simple multiblade transformation rule. Force and moment amplitudes transferred from the rotor to the support are found to be critically dependent on the support dynamics.
Hohenemser, K. H.↗
A new battery charger/discharger converter
A new optimum topology dc-to-dc switching converter is extended to provide bidirectional current flow. The resulting two-quadrant converter can be employed to eliminate the discontinuous current mode in normal unidirectional applications, but is especially suited for spacecraft battery conditioning as a charge-discharge regulator in place of the conventional separate converters. Implementation of the control features and the battery charge current and voltage limits are discussed.
Middlebrook, R. D.↗
Torque control for electric motors
Method for adjusting electric-motor torque output to accomodate various loads utilizes phase-lock loop to control relay connected to starting circuit. As load is imposed, motor slows down, and phase lock is lost. Phase-lock signal triggers relay to power starting coil and generate additional torque. Once phase lock is recoverd, relay restores starting circuit to its normal operating mode.
Bernard, C. A.↗
Variable X-ray spectra of BL Lac objects: HEAO-1 observations of PKS 0548-322 and 2A 1219+305
X-ray spectra for the BL Lac objects PKS 0548-322 and 2A 1219+305 measured with the HEAO-1 A2 detectors during pointing maneuvers on September 30, 1978 and May 31, 1978 respectively are presented. Both fit single power law components with low energy absorption. For 2A 1219+305, a thermal bremsstrahlung form gives an unacceptable fit. From a comparison with other statistically poorer observations taken at 6 month intervals while the satellite was in its normal scanning mode, it is found that the sources exhibit spectral variability. A summary of measurements of the 5 BL Lac objects detected with the A2 experiment is presented and it is concluded that X-ray spectral changes in this class of source are common. Their general X-ray spectral characteristics distinguish BL Lac objects from other classes of X-ray emitting active galactic nuclei. Analysis of their total spectra indicates that most of the energy is emitted in the 5 to 100 eV band.
Worrall, D. M.↗
A Digital Program for Calculating the Interaction Between Flexible Structures, Unsteady Aerodynamics and Active Controls
A computer program, ISAC, is described which calculates the stability and response of a flexible airplane equipped with active controls. The equations of motion relative to a fixed inertial coordinate system are formulated in terms of the airplane's rigid body motion and its unrestrained normal vibration modes. Unsteady aerodynamic forces are derived from a doublet lattice lifting surface theory. The theoretical basis for the program is briefly explained together with a description of input data and output results.
Peele, E. L.↗
Directionality effects in the transfer of X-rays from a magnetized atmosphere: Beam pulse shape
A formalism is presented for radiation transfer in two normal polarization modes in finite and semiinfinite plane parallel uniform atmospheres with a magnetic field perpendicular to the surface and arbitrary propagation angles. This method is based on the coupled integral equations of transfer, including emission, absorption, and scattering. Calculations are performed for atmosphere parameters typical of X-ray pulsars. The directionality of the escaping radiation is investigated for several cases, varying the input distributions. Theoretical pencil beam profiles and X-ray pulse shapes are obtained assuming the radiation is emitted from the polar caps of spinning neutron stars. Implications for realistic models of accreting magnetized X-ray sources are briefly discussed.
Meszaros, P.↗
PC-403: Pioneer Venus multiprobe spacecraft mission operational characteristics document, volume 2
The data handling subsystem, command subsystem, communications subsystem, power subsystem, and mission operations of the Pioneer Venus multiprobe are presented. The multiprobe spacecraft performance in normal operating modes that correspond to the performance of specific functions at the time of specific events in the mission is described.
Barker, F. C.↗
Analysis of multispectral data using an unsupervised classification technique: Application to VAS
A statistical classification method based on clustering of multidimensional histograms was applied to several channels of the VAS multispectral imagery. The method automatically discriminates and classifies atmospheric ground features such as cloud types, atmospheric moisture patterns, ocean, or ground. Such a clustering method has the advantage of forming natural data groupings, without a priori classification. Clusters are not limited by straight lines or plane surfaces as is the case in threshold methods. The method was applied to simultaneous full resolution images from channels 8 (11.2 micron), 10 (6.7 micron), and 12 (3.9 micron). Twenty image segments of 64 by 64, 12 image segments of 128 by 128, and 4 image segments of 254 by 254 picture elements were analyzed. In addition, normal VISSR mode images at 1800, 1830, and 2000 GMT were used to identify the classes. The gray levels measured along a scan line and the result of the classification scheme (dashed curves) for the three channels investigated are shown. Each point of the image is affected to a class. Each class is identified by a center of gravity that is represented by a vector in the three dimensional space of gray levels.
Szejwach, G.↗
Quadratic synthesis of integrated active controls for an aeroelastic forward-swept-wing-aircraft
State variable representations of flexible aircraft are obtained using a modeling approach which first defines a mean-reference axis coordinate system. The active system design approach for forward-swept-wing aircraft also expresses structural deformations of the wing in terms of free normal vibration modes relative to this mean reference axis. Calculations which assume quasi-steady incompressible aerodynamics are performed to obtain generalized force expressions for flight conditions. The use of this quadratic synthesis technique shows that increased performance and redundancy over decentralized approaches can be achieved using integrated active longitudinal stability augmentation and aeroelastic stabilization.
Gilbert, M. G.↗
J series thruster thermal test results
Test experience with J series ion thrusters have indicated that the present thruster design may result in excessive temperatures in areas which utilize organic materials such as wire insulation, with the resultant outgassing and potential contamination of insulating materials. Further, it appears that thermal data obtained with earlier thruster designs, such as the 700 series thruster, may not be directly applicable to the J series design. Two J series thrusters were fitted with thermocouples and critical temperatures measured for a variety of configurations and operating parameters. Completely enclosing the thruster to reduce facility contamination significantly increased temperatures prompting the selection of a compromise geometry for life testing. The operating parameter having the largest effect on temperatures was discharge power, while beam power affected little else than extraction system temperatures. Several off-normal operating modes were also investigated. Data believed to be sufficient to effectively modify existing thermal models were obtained from the tests.
Bechtel, R. T.↗
Design Spectrum Analysis in NASTRAN
The utility of Design Spectrum Analysis is to give a mode by mode characterization of the behavior of a design under a given loading. The theory of design spectrum is discussed after operations are explained. User instructions are taken up here in three parts: Transient Preface, Maximum Envelope Spectrum, and RMS Average Spectrum followed by a Summary Table. A single DMAP ALTER packet will provide for all parts of the design spectrum operations. The starting point for getting a modal break-down of the response to acceleration loading is the Modal Transient rigid format. After eigenvalue extraction, modal vectors need to be isolated in the full set of physical coordinates (P-sized as opposed to the D-sized vectors in RF 12). After integration for transient response the results are scanned over the solution time interval for the peak values and for the times that they occur. A module called SCAN was written to do this job, that organizes these maxima into a diagonal output matrix. The maximum amplifier in each mode is applied to the eigenvector of each mode which then reveals the maximum displacements, stresses, forces and boundary reactions that the structure will experience for a load history, mode by mode. The standard NASTRAN output processors have been modified for this task. It is required that modes be normalized to mass.
Butler, T. G.↗
An experimental study of rotor-vortex interactions
A scheme for investigating general blade/vortex interactions (BVIs) has been used to obtain an unusual body of data. The scheme involves locating a vortex generator upstream of a nonlifting rotor so that the vortex interacts with the rotor at any desired forward azimuth. Parallel BVIs produced by this external vortex generator are shown to be nearly identical to those produced by the rotor alone operating in a normal descent mode. The test delineates various generic features of parallel and oblique BVIs. However, the dominant feature is the leading-edge pressure pulse. The effects of blade/vortex angle, and proximity (including head-on interactions) on this pulse are discussed. The effect of Mach number on the leading edge pressure variation is shown to be small even for supercritical interactions.
Caradonna, F. X.↗