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NASA NTRS1979

Terrestrial/land mobile satellite considerations, NASA plans and critical issues

This paper briefly reviews the land mobile market and discusses services that might be provided by hybrid terrestrial/land mobile satellite systems (T/LMSS). In view of the expected urban/suburban patterns of planned terrestrial systems it is suggested that a satellite may prove a cost-effective complement to terrestrial systems for serving thinly populated or large geographical areas. A basic Land Mobile Satellite Service (LMSS) is described, example applications are provided, and the status and rationale for LMSS frequencies in the 806-890 MHz band is given. Next, examples are given of NASA supported land mobile satellite experiments and a preliminary T/LMSS work plan, part of an overall Narrowband Program, is presented for structuring future work. The initiation of the T/LMSS plan depends on pending management/budget decisions. The report closes with a listing of issues and potential problem areas, the solutions of which NASA believes are critical to the success of the proposed T/LMSS effort.

Knouse, G. H.↗

NASA NTRS1980

Simultaneous radiation damage and annealing of GaAs solar cells

In this report, concepts and equations are developed to describe the simultaneous radiation damage and annealing of solar cells. The annealing characteristics of three types of defects are employed to study three examples of continuous irradiation and annealing. One example shows that the effective damage could be reduced by a factor of fifty. The difficulty of a laboratory experiment properly simulating the effects in space are discussed. Potential advantages of continuous annealing such as reduction of stable defect formation and omission of radiation cover glasses are presented.

Heinbockel, J. H.↗

NASA NTRS1981

Global patterns in cloud forms on Mars

Mariner 9 images and all Viking orbiter images through July 1979 were searched for cloud forms. A computer-accessible catalog was assembled, consisting of a classification of cloud type (lee wave, for example) and properties (directionality, wavelength, for example). Lee wave directionality shows a pattern and seasonal variation at high latitudes which is consistent with predictions of theoretical modeling. Fog and haze occurrence shows no obvious correlation with water abundance or any other simple causal factor. Lee waves are rare at equatorial latitudes. Plumes (probably dust) occur preferentially at locations where strong boundary layer convection is expected.

French, R. G.↗

NASA NTRS1981

Small velocity changes using a SEP spacecraft

The Solar Electric Propulsion (SEP) system is designed to deliver large payloads using extended thrusting periods. However, for certain classes of missions, it would be desirable to also use the low thrust propulsion system to impart the small velocity changes typically required to control an orbit in the vicinity of the target body. This paper examines the characteristics and capabilities of using an example SEP system to apply small velocity changes in arbitrary directions. Formulas are developed and examples presented for the rotation and translation which results when the ion thrusters are used to make large turns about all three of the spacecraft axes. This data is then used to propose various techniques for achieving arbitrary velocity changes. While still in a formative stage, the results may be useful in both the design of SEP spacecraft and formulation of future missions.

Jones, J. B.↗

NASA NTRS1981

Mission options for the first SEPS application

Missions to comets and asteroids are primary candidates for Solar Electric Propulsion System (SEPS) applications. NASA estimates that the first SEPS mission might be launched as early as 1988. This paper presents mission opportunities available for launches between 1988 and early 1991 and discusses the performance capabilities of the current SEPS. Use of a Shuttle Two-Stage IUS and/or a Shuttle Wide Tank Centaur launch vehicle is assumed in the performance assessment. The list of possible first SEPS missions consists of nine missions to comets of primary interest and examples of multiple asteroid rendezvous missions. Both an earth crossing asteroid and a main belt asteroid are considered as first possible targets in the multiple asteroid rendezvous examples. Mission opportunity and performance maps for Eros and Anteros are presented which provide exact performance data and optimal launch and arrival dates for any launch year.

Yen, C.-W. L.↗

NASA NTRS1980

Progress in passive microwave remote sensing - Nonlinear retrieval techniques

A variety of nonlinear retrieval methods have been applied to passive microwave remote sensing problems. These problems can be characterized in part by the degree to which their underlying physics and statistics can be understood and characterized in a simple way. Four examples of varying complexity are considered here; the simplest problem requires only analytic expressions for retrievals, whereas the most complex problem has been handled only with pattern classification techniques. The four examples are: (1) Doppler measurements of winds at 70 to 100 km, (2) retrieval of atmospheric water vapor profiles using the opaque 183-GHz water vapor resonance, (3) retrieval of snow accumulation rate by means of combined theoretical and empirical procedures, and (4) classification of diverse polar terrain by means of pattern recognition techniques.

Staelin, D. H.↗

NASA NTRS1981

Toward defining good writing: A rhetorical analysis of the words, sentences, and paragraphs in 16 industrial scripts

The assumption that teachers of technical writing agree on a definition of good writing was found to be without basis. Resolution of disagreements arising from close reading and textual analysis is described. Writing samples from corporate sources including IBM, ALCOA, Exxon, Weyerhaeuser, Bell Labs, Underwriters Laboratories, Dow Chemical, and US Steel were requested. A mixture of informative and persuasive examples, and examples directed at lay and specialist audiences were received. Analyses of 16 writing samples are reported. Analysis of word level, sentence level, and paragraph level, was completed. Syllabism, verb selection, nominalizations, vocabulary choices, t-units, subordination, sentence and clause length, syntactic order, patterns, development, topic sentences, propositional order, and transitions were analyzed.

Freisinger, R. R.↗

NASA NTRS1982

Effect of seals on rotor systems

Seals can exert large forces on rotors. As an example, in turbopump ring seals film stiffness as high as 90 MN/m (500,000 lb/in) have been calculated. This stiffness is comparable to the stiffness of rotor support bearings; thus seals can play an important part in supporting and stabilizing rotor systems. The work done to determine forces generated in ring seals is reviewed. Working formulas are presented for seal stiffness and damping, and geometries to maximize stiffness are discussed. An example is described where a change in seal design stabilized a previously unstable rotor.

Fleming, D. P.↗

NASA NTRS1982

A variational approach to the study of capillary phenomena

The problem of determining the free surface of a liquid in a capillary tube, and of a liquid drop, sitting first on a horizontal plane and then on more general surfaces is considered. With some modifications, the method applies to the study of pendent drops and of rotating drops as well. The standard capillary problem, i.e. the determination of the free surface of a liquid in a thin tube of general cross section, which resuls from the simultaneous action of surface tension, boundary adhesion and gravity is discussed. It turns out that in this case the existence of the solution surface depends heavily on the validity of a simple geometric condition about the mean curvature of the boundary curve of the cross section of the capillary tube. Some particular examples of physical interest are also be discussed. Liquid drops sitting on or hanging from a fixed horizontal plane are discussed. The symmetry of the solutions (which can actually be proved, as consequence of a general symmetrization argument) now plays the chief role in deriving both the existence and the regularity of energy-minimizing configurations. When symmetry fails (this is the case, for example, when the contact angle between the drop and the plate is not constant, or when the supporting surface is not itself symmetric), then more sophisticated methods must be used. Extensions in this direction are outlined.

Emmer, M.↗

NASA NTRS1981

Investigation of MAGSAT and TRIAD magnetometer data to provide corrective information on high-latitude external fields

The compilation of a catalog of the MAGSAT-observed high altitude disturbances is discussed and an example of contents and format is given. The graphs allow the investigation of Birkeland current signatures which are superimposed upon the main geomagnetic field. An example of a display of the MAGSAT orbital tracks in a polar geomagnetic coordinate system with the locations, flow directions, and intensities of field aligned currents shown in color is also given. The display was generated using an interactive color graphics terminal.

Potemra, T. A.↗

NASA NTRS1982

Determination of eigenvalues of dynamical systems by symbolic computation

A symbolic computation technique for determining the eigenvalues of dynamical systems is described wherein algebraic operations, symbolic differentiation, matrix formulation and inversion, etc., can be performed on a digital computer equipped with a formula-manipulation compiler. An example is included that demonstrates the facility with which the system dynamics matrix and the control distribution matrix from the state space formulation of the equations of motion can be processed to obtain eigenvalue loci as a function of a system parameter. The example chosen to demonstrate the technique is a fourth-order system representing the longitudinal response of a DC 8 aircraft to elevator inputs. This simplified system has two dominant modes, one of which is lightly damped and the other well damped. The loci may be used to determine the value of the controlling parameter that satisfied design requirements. The results were obtained using the MACSYMA symbolic manipulation system.

Howard, J. C.↗

NASA NTRS1981

Identification and evaluation of software measures

A large scale, systematic procedure for identifying and evaluating measures that meaningfully characterize one or more elements of software development is described. The background of this research, the nature of the data involved, and the steps of the analytic procedure are discussed. An example of the application of this procedure to data from real software development projects is presented. As the term is used here, a measure is a count or numerical rating of the occurrence of some property. Examples of measures include lines of code, number of computer runs, person hours expended, and degree of use of top down design methodology. Measures appeal to the researcher and the manager as a potential means of defining, explaining, and predicting software development qualities, especially productivity and reliability.

Card, D. N.↗

NASA NTRS1982

Aircraft geometry verification with enhanced computer generated displays

A method for visual verification of aerodynamic geometries using computer generated, color shaded images is described. The mathematical models representing aircraft geometries are created for use in theoretical aerodynamic analyses and in computer aided manufacturing. The aerodynamic shapes are defined using parametric bi-cubic splined patches. This mathematical representation is then used as input to an algorithm that generates a color shaded image of the geometry. A discussion of the techniques used in the mathematical representation of the geometry and in the rendering of the color shaded display is presented. The results include examples of color shaded displays, which are contrasted with wire frame type displays. The examples also show the use of mapped surface pressures in terms of color shaded images of V/STOL fighter/attack aircraft and advanced turboprop aircraft.

Cozzolongo, J. V.↗

NASA NTRS1982

Variational methods in simultaneous optimum interpolation and initialization

The duality between optimum interpolation and variational objective analysis, is reviewed. This duality is used to set up a variational approach to objective analysis which uses prior information concerning the atmospheric spectral energy distribution, in the variational problem. In the wind analysis example, the wind field is partitioned into divergent and nondivergent parts, and a control parameter governing the relative energy in the two parts is estimated from the observational data being analyzed by generalized cross validation, along with a bandwidth parameter. A variational approach to combining objective analysis and initialization in a single step is proposed. In a simple example of this approach, data, forecast, and prior information concerning atmospheric energy distribution is combined into a single variational problem. This problem has (at least) one bandwidth parameter, one partitioning parameter governing the relative energy in fast slow modes, and one parameter governing the relative weight to be given to observational and forecast data.

Wahba, G.↗

NASA NTRS1981

Shock-associated low-energy ion enhancements observed by Voyagers 1 and 2

Observations of shock-associated ion enhancements at energies of not less than 30 keV are presented from data gathered by Voyagers 1 and 2. Observations include examples of energetic storm particle events associated with flare-produced shocks and examples of corotating particle events (CPE) associated with forward and reverse shocks that bound corotating interaction regions in the outer heliosphere. Most of the CPE have recurrent double-peaked intensity enhancements showing little or no velocity dispersion at peak intensities, time durations of several days, and soft energy spectra extending up to 5 MeV/nucleon. The lowest energy ion enhancements are confined mainly downstream of the corotating interaction regions with the magnitude and duration of the upstream enhancements increasing with increasing ion energy. The observations are consistent with the dynamical and kinematical effects expected when low energy ions are accelerated at quasi-perpendicular shocks.

Decker, R. B.↗

NASA NTRS1981

Microscopy and microstructure of Shuttle thermal protection system materials

Examples of the contribution of microstructural analysis to the development of the Space Shuttle tile insulation system are presented, with photographic examples of the scanning electron microscope (SEM) investigations. After the basic thermal protection system materials had been selected, it was neccessary to analyze the mechanical responses of the combined materials; which included: (1) the polymer strain isolation pad (SIP), (2) the room temperature-vulcanizing silicone rubber bond, (RTV), and (3) rigid ceramic fiber reusable surface insulation (RSI). Microstructural analysis was used to provide information on deformation and fracture mechanisms, load transfer mechanisms, and structural alterations occurring before final failure. Both quantitative and qualitative information was obtained in the open, three-dimensional fibrous structures of the ceramic tiles by means of novel techniques of encapsulation and dissolution.

Newquist, C. W.↗

NASA NTRS1981

A general purpose computer-to-computer interface Xerox Sigma computer-to-DEC PDP 11 computer

The Sigma/PDP 11 Interface is a general-purpose system for interconnecting a Xerox Sigma series computer and a DEC PDP 11 series computer. Although the unit is designed to operate in a real-time environment, it can be used in nonreal-time modes as well. Several features, designed to facilitate using the system in varied applications are included in the unit; for example, the features can be used to isolate software or hardware faults. This paper contains descriptions of the hardware and software operations of the interface and examples of real-time applications in the research environment at Ames Research Center.

Fetter, J. L.↗

NASA NTRS1981

Molecules in interstellar clouds

The physical conditions and chemical compositions of the gas in interstellar clouds are reviewed in light of the importance of interstellar clouds for star formation and the origin of life. The Orion A region is discussed as an example of a giant molecular cloud where massive stars are being formed, and it is pointed out that conditions in the core of the cloud, with a kinetic temperature of about 75 K and a density of 100,000-1,000,000 molecules/cu cm, may support gas phase ion-molecule chemistry. The Taurus Molecular Clouds are then considered as examples of cold, dark, relatively dense interstellar clouds which may be the birthplaces of solar-type stars and which have been found to contain the heaviest interstellar molecules yet discovered. The molecular species identified in each of these regions are tabulated, including such building blocks of biological monomers as H2O, NH3, H2CO, CO, H2S, CH3CN and H2, and more complex species such as HCOOCH3 and CH3CH2CN.

Irvine, W. M.↗