Improving Control of Remote Manipulators
Advanced theoretical and experimental developments in field of remote manipulators discussed in conference preprint. Report synthesizes number of sensing and control techniques.
Bejczy, A. K.↗
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The report of the Gravity Field Workshop
A Gravity Field Workshop was convened to review the actions which could be taken prior to a GRAVSAT mission to improve the Earth's gravity field model. This review focused on the potential improvements in the Earth's gravity field which could be obtained using the current satellite and surface gravity data base. In particular, actions to improve the quality of the gravity field determination through refined measurement corrections, selected data augmentation and a more accurate reprocessing of the data were considered. In addition, recommendations were formulated which define actions which NASA should take to develop the necessary theoretical and computation techniques for gravity model determination and to use these approaches to improve the accuracy of the Earth's gravity model.
Smith, D. E.↗
Jacchia-Lineberry upper atmosphere density model
A series of increasingly accurate models which are a careful blend of empirical and theoretical formulae were developed. The exospheric temperature is assumed to be a function of: (1) the average and daily variations in the solar flux, (2) the average and three hourly variations in the geomagnetic index, (3) the angle between the position vector and the axis of the unsymmetric atmospheric bulge, and (4) the angle between the position vector and the geomagnetic pole. The exospheric temperature is related to the density by the solution of the diffusion equilibrium equations for the different constituents of the atmosphere as a function of altitude. Other variations are modeled directly as changes in the density. They are: (1) changes due to the semiannual effect, and (2) changes due to the seasonal latitudinal effect. The causes for these variations are not exactly known but may be modeled sufficiently by empirical formulae. The Jacchia model is assumed to be valid over the altitude range of 90 to 2500 km. The residuals between the observed density from satellite drag observations and the computed densities show the mean relative error to be generally less than 10 percent with occasional peak errors near 50 percent.
Mueller, A. C.↗
Improved thermophotovoltaic power system
Improvements in thermophotovoltaic (TPV) system design to ease the geometry and performance requirements are discussed. A TPV system usually consists of a receiver cavity lined with reflective materials and Si solar cells. A suspended central absorber/radiator converter absorbs solar energy and heats to an equilibrium temperature of 2000-23,000 K. Radiant heat at that temperature is well matched to Si solar cell low energy excitation. An elliptical geometry cavity is described which bypasses normal cell mounting problems by having the cells fixed to a plate positioned between the loci of the cavity. Incoming concentrated solar flux is absorbed by the absorber/radiator, which emits the radiation for reflection from the cavity walls to eventually pass through the solar cell wall. Dielectric stack coatings can be used on the walls. A theoretical model was developed for the performance and verified with a laboratory apparatus. Efficiencies of nearly 30% were found practical with existing materials and technologies.
Horne, W. E.↗
Measurement of acoustic modes and wall impedance in a turbofan exhaust duct
Acoustic measurements made with in-duct modal probes show how individual acoustic modes, as generated by fan/stator interaction, interact with a well-characterized liner. This measured attenuation provides a critical test for predicted attenuation as developed from the theoretical analysis of sound propagation in annular ducts with treatment and sheared flow. The primary investigations took place in the exhaust duct of a model fan mounted in an anechoic chamber. The results presented include induct attenuation, sound power attenuation as measured in the far field, and in-situ acoustic impedance measurements of the treated wall sections. Good theory/experiment agreement was found; the differences of treatment suppression between theory and measured values differed at most by 2.7 dB.
Fiske, G. H.↗
SC3 - A wing concept for supersonic maneuvering
A supersonic wing design concept that overcomes the problems associated with nonlinear inviscid pressure distribution is presented together with a summary of the supporting theoretical and experimental development program. The key design feature is a conical panel supporting a controlled supercritical conical camber (SC3) crossflow expansion and recompression which permits lift on the upper surface to be obtained without producing an adverse pressure gradient or crossflow shock wave strong enough to separate the boundary layer. The role of aerodynamics in the design implementation is discussed, as are the concept development, the initial design validation on a fabricated and tested SC3 design, and the body and canard interaction effect. The design and testing of an isolated wing with a planform and thickness distribution representative of a practical application are described. Wind-tunnel results show that significant performance gains can be obtained for fighter aircraft using this concept.
Mason, W. H.↗
Cumulus cloud transport of transient tracers
A theoretical framework is developed for including cumulus cloud transport, rainout of water soluble gases, and aqueous phase chemistry into gas phase photochemical models. Cloud populations are represented as ensemble distributions of individual clouds of various heights. An individual cloud is represented as a one-dimensional, steady state plume with height-independent radius entraining air from the boundary of the cloud. The model is applied to several hypothetical atmospheric tracers to show how clouds may affect the tropospheric distributions of ozone, NO(y), SO2, peroxyacetylnitrate, hydrocarbons, and other gases. Although the numerical experiments were based on cloud mass fluxes from diagnostic studies in the tropics and thus are not representative of the entire globe, it was found that an increasing mixing ratio with height in the free troposphere can be produced for some gases with only a surface source when clouds are present. This suggests that some reactive tropospheric species with primarily surface sources may play a somewhat more important role in tropospheric chemistry than is presently believed depending on the global distribution of cloud mass fluxes. Deficiencies in existing photochemical models due to the way clouds are typically treated are discussed.
Gidel, L. T.↗
Theoretical basis for design of thermal-stress-free fasteners
A theoretical basis was developed for the design of fasteners which are free of thermal stress. A fastener can be shaped to eliminate the thermal stress which would otherwise result from differential thermal expansion between dissimilar fastener and sheet materials for many combinations of isotropic and orthotropic materials. The resulting joint remains snug, yet free of thermal stress at any temperature, if the joint is uniform in temperature, if it is frictionless, and if the coefficients of thermal expansion of the materials do not change with temperature. In general, such a fastener has curved sides; however, if both materials have isotropic coefficients of thermal expansion, a conical fastener is free of thermal stress. Equations are presented for thermal stress free shapes at both initial and final temperature, and typical fastener shapes are shown.
Blosser, M. L.↗
Local effects of partly-cloudy skies on solar and emitted radiations
Atmospheric aerosol and turbidity measurements were analyzed and the results are presented. The correlation of global insolation with cloud cover fractions for the first complete year's data set was completed. A theoretical model was developed to parameterize the effects of local aerosols upon insolation received at the ground using satellite radiometric data and insolation measurements under clear sky conditions. A February data set, composed of one minute integrated global insolation and direct solar irradiances, cloud cover fractions, meteorological data from nearby weather stations, and GOES East satellite radiometric data was collected to test the model and used to calculate the effects of local aerosols.
Whitney, D. A.↗
Multifrequency observations of the BL Lacertae object 0735+178
In each of the present four simultaneous spectra covering the radio-through-X-ray regimes, the IR-UV synchrotron continuum dominates the total observed power and presumably becomes opague between 10 to the 11th and 10 to the 13th Hz. Nonsimultaneous observations were also conducted, over a longer time period, in order to study long- and short-term variability at X-ray, optical, and radio frequencies. These data indicate that the rapid and dramatic variations evident at IR and optical wavelengths are absent at radio and X-ray frequencies, supporting a view of IR-UV flux emanation from a small region, while the X-rays are produced by the inverse Compton process in the radio-emitting region. Particles, photons and magnetic field may not be far from equipartition in this region. Theoretical suggestions are developed regarding the radial behavior of the electron density and magnetic field.
Bregman, J. N.↗
Analyses of processing variables in propellant burn rate and modulus. I - Mixing times
The effect of the final mixing time on quality of smokeless AP/HTPB propellant with bimodal AP was examined. Identical ingredients were mixed for various intervals, cast in a circular tube, then fired in a static test. Mechanical properties were measured and initial moduli were calculated from the initial slope of the S-N curves. A theoretical model was developed using the data to quantitatively configure a quality control procedure. A minimum time for mixing fine and coarse AP particles was identified and was approximated to within a factor of two or three using a viscous dispersion time and the surface areas of the particles. The model could be improved by considering settling time and particle size distribution effects.
Ramohalli, K.↗
Electrocatalysis of fuel cell reactions: Investigation of alternate electrolytes
Oxygen reduction and transport properties of the electrolyte in the phosphoric acid fuel cell are studied. The areas covered were: (1) development of a theoretical expression for the rotating ring disk electrode technique; (2) determination of the intermediate reaction rate constants for oxygen reduction on platinum in phosphoric acid electrolyte; (3) determination of oxygen reduction mechanism in trifluoreomethanesulfonic acid (TFMSA) which was considered as an alternate electrolyte for the acid fuel cells; and (4) the measurement of transport properties of the phosphoric acid electrolyte at high concentrations and temperatures.
Chin, D. T.↗
Study of spectral/radiometric characteristics of the Thematic Mapper for land use applications
Progress during the Environmental Research Institute of Michigan-ERIM's and 5 image data quality assessment program for the thematic mapper is described. Analyses of LANDSAT 5 TM radiometric characteristics were performed. Effects which had earlier been found in LANDSAT 4 TM data were found to be present in LANDSAT 5 data as well, including: (1) scan direction related signal droop; (2) scan correlated level shifts; and (3) low frequency coherent noise. Coincident LANDSAT 4 and 5 raw TM data were analyzed, and band by band relationships between the two sensors were derived. Earlier efforts which developed an information theoretic measure of multispectral information content were continued, comparing TM and MSS information content.
Malila, W. A.↗
An air-breathing ballistic space transporter for Europe
With increasing transport requirements, reusable space transporters again receive serious consideration in Europe as successors to the Ariane family. The paper deals with a hydrogen-ramjet-propelled, 1-1/2-stage reusable ballistic space transporter with vertical take-off and landing and using liquid hydrogen/oxygen rockets. This novel concept was developed in a theoretical study at the University of Stuttgart. The results are compared with recently published studies of several other European space transporter concepts. The data derived for the Istra - concept are: 15.4 Mg payload into low Earth-orbit, 155 Mg gross lift-off mass, 10% payload ratio, which represents a 57% propellant saving, and 44% reduction in dry mass (structure and engines) compared with comparable two-stage pure rocket concepts.
Kramer, P. A.↗
Magnetic fields in the radiative interior of stars. I Thermal shadows and forced convection. II - Forced convection and the Li-7 abundance
A theoretical model is developed for thermal shadows of magnetic inhomogeneities and their effects in the radiative cores of stars such as the sun. It is shown that the shadows cause a slight decrease of gas pressure, thereby lowering the opacity and raising the effective heat transport. The shadows produced by the inhomogeneities induce thermal gradients and therefore forced convection. If the field strength is at least 400,000 gauss partial Li-7 depletion will occur due to destruction in convection-dominated thermonuclear reactions. The scale of the field would need to be 30,000 km.
Parker, E. N.↗
A theoretical model of artificial spread F echoes
A theoretical model is developed for artificial spread F echoes elicited by irradiating the ionospheric F region with signals from ground-based HF transmitters. Account is taken of the irregularity polarizations, scale length and the magnetic dip angle of the echo. Ray tracing equations are defined for wave propagation in a horizontally stratified ionosphere which has been bathed with HF signals and therefore contains wavelike structures. Irregularities polarized within the meridian plane are found to cause the spread F echoes, while perpendicularly polarized irregularities do not. A magnetic dip angle of 5 deg must be exceeded for the spread F to become strong. The irregularities need scale lengths exceeding 100 m. Modes of operation are identified for inducing the required spread F echoes using ground-based radiotelescopes.
Kuo, S. P.↗
The relation of flux transfer events to magnetic reconnection
Preliminary results of a search for heat-transfer signatures in electron data on 31 flux-transfer events (FTEs) are reported. Strong acceleration or deceleration, large parallel pressure anisotropies, and temperatures and densities between those of the magnetosphere and the magnetosheath are commonly observed within the surface of the flux-transfer interval defined by the heat-flow peaks, with some evidence of field-aligned ionospheric electrons. A theoretical model is developed to explain some of the observations and illustrated with diagrams. Dynamical tests on a large well-resolved FTE show that the data are consistent with a one-sided passage of the probe into and out of a rotational shear layer.
Scudder, J. D.↗
Optical technique to study the impact of heavy rain on aircraft performance
A laser based technique was investigated and shown to have the potential to obtain measurements of the size and velocity of water droplets used in a wind tunnel to simulate rain. A theoretical model was developed which included some simple effects due to droplet nonsphericity. Parametric studies included the variation of collection distance (up to 4 m), angle of collection, effect of beam interference by the spray, and droplet shape. Accurate measurements were obtained under extremely high liquid water content and spray interference. The technique finds applications in the characterization of two phase flows where the size and velocity of particles are needed.
Hess, C. F.↗