Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Case Studies”

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.

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

At least 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Effects of the motions of a platform-mounted payload on the nutational stability of a dual-spin spacecraft - A Galileo case study

In the presence of spacecraft nutation, tracking of an inertially fixed target by the Galileo scan platform requires the use of two control loops to move the scan platform and the stator in such a way as to compensate for spacecraft motion. The effect of these control loops on spacecraft nutational stability is examined using an eigenvalue analysis approach as well as several computer analysis packages. It was found that the actions of these control loops tend to drive nutation to the point of neutralizing, and even overpowering the damping actions of the spacecraft nutation damper, for pointing directions close to the spacecraft's poles. Stable and unstable zones are mapped out for two sets of spacecraft mass properties, and contributions of rotor asymmetry and stator flexibility are also discussed.

Man, G. K.↗
NASA NTRS1984

Case study of sample spacing in planar near-field measurement of high gain antennas

Far field antenna patterns can be reconstructed from planar near field measurements acquired at a sample spacing of lambda/2 or less. For electrically large antennas, sampling at the Nyquist rate may result in errors due to system electronic drift over long acquisition times. The computer capacity may limit the largest size of the near field data set. The requirement to sample at the Nyquist rate is relaxed for high gain antennas which concentrate most of the radiated energy into a small angular region of the far field. The criteria for sample spacing at greater than lambda/e through the use of a priori information of the antenna radiation characteristics are presented. Far field patterns of a 30 GHz dual offset reflector system with a 2.7 m parabolic main reflector are computed from near field data obtained at sample spacings ranging from 0.1 lambda to 10 lambda. The effects of sampling interval and spectrum cutoff on the far field patterns are discussed.

Acosta, R. J.↗
NASA NTRS1984

The near Earth current sheet: ISEE-1 and -2 case studies

Two crossings of the near Earth current sheet are examined using magnetic field and plasma data from ISEE-1 and 2. The current sheet thickness is measured to be 0.9 Re using a 2 satellite technique which greatly reduces the ambiguity of such measurements. Approximate pressure balance is found to exist between the diamagnetically dominated current sheet and surrounding, already high beta, plasma sheet. The accurate calculation of the sheet normal velocity with the two satellite technique allows the calculation of the current density distribution in the sheet. The crosstail current density is found to peak about an ion-gyroradius on both sides of the center of the sheet. A simple model consistent with these results is discussed.

Mccomas, D. J.↗
NASA NTRS1984

Extraction of topography from side-looking satellite systems A case study with SPOT simulation data

Techniques for reconstructing topographic data from side-looking satellite systems have been developed whereby nadir and off-nadir passes are coaligned to calculate the stereo displacement for each pixel in the nadir view by correlating a small subarea to a corresponding subarea in the off-nadir pass. The correlation algorithm was tested on two pairs of data sets consisting of patterns of bars and boxes and then applied to the SPOT simulation data set. The correlation was a maximum in areas where the relief was changing gradually, while in areas of constantly changing topography, the correlation decreased.

Ungar, S. G.↗
NASA NTRS1983

A case study of the energy dissipation of the gravity wave field based on satellite altimeter measurements

Wave breaking is proposed as the primary energy dissipation mechanism for the gravity wave field. The energy dissipation rate is calculated based on the statistical model proposed by Longuet-Higgins (1969) with a modification of the breaking criterion incorporating the surface stress according to Phillips and Banner (1974). From this modified model, an analytic expression is found for the wave attenuation rate and the half-life time of the wave field which depend only on the significant slope of the wave field and the ratio of friction velocity to initial wave phase velocity. These expressions explain why the freshly generated wave field does not last long, but why swells are capable of propagating long distances without substantial change in energy density. It is shown that breaking is many orders of magnitude more effective in dissipating wave energy than the molecular viscosity, if the significant slope is higher than 0.01. Limited observational data from satellite and laboratory are used to compare with the analytic results, and show good agreement.

Huang, N. E.↗
NASA NTRS1984

Comments on 'Comparative diagnostic case study of east coast secondary cyclogenesis under weak versus strong synoptic-scale forcing'

A comment is presented on a recent paper by Pagnotti and Bosart (1984) which contrasted different forcing mechanisms for weak and strong cyclones along the east coast of the U.S., and Bosart replies. The comment argues that the paper did not give a clear definition of 'weak' upper-level forcing and did not provide sufficient evidence to support its claim that the return branch of transverse circulations may be coupled to the middle as opposed to the lower troposphere.

Uccellini, L. W.↗
NASA NTRS1983

Case study of Pampa, Texas, multicell storms

Analysis of the Pampa, TX, multicell storms showed prestorm environmental conditions of a strong horizontal convergence of moisture, mixing ratio 12 g/kg at the 850 mb level in the Texas Panhandle areas and strong winds with shear veering with height. Rapid-scan satellite imagery showed that the clouds penetrated above the tropopause and cloud-top temperatures were at least 4 to 9 C colder than the temperature of the tropopause. This formation and collapsing of high-mass-density overshooting cloud tops above the tropopause is characteristic of tornadoes in the middle portion of the United States.

Hung, R. J.↗
NASA NTRS1984

A case study on the application of geosynchronous satellite infrared data to estimate soil moisture

The use of GOES IR temperature data to estimate soil moisture content is discussed and demonstrated, modifying the procedure proposed by Wetzel et al. (1984) to provide for incorporation of independent measurements of vegetation biomass, geostrophic wind speed, and surface dewpoint. Data acquisition, processing, and the statistical approach employed are described; data for Kansas and Nebraska during a six-day period in July 1978 are analyzed; and a statistical relationship between observed surface temperature and antecedent precipitation index is established. The results are presented in tables, graphs, and maps, and the regression procedure is found to predict antecedent precipitation with statistically significant precision.

Woodward, R. H.↗
NASA NTRS1984

Validation of fault-free behavior of a reliable multiprocessor system - FTMP: A case study

A program of experiments has been conducted at NASA-Langley to test the fault-free performance of a Fault-Tolerant Multiprocessor (FTMP) avionics system for next-generation aircraft. Baseline measurements of an operating FTMP system were obtained with respect to the following parameters: instruction execution time, frame size, and the variation of clock ticks. The mechanisms of frame stretching were also investigated. The experimental results are summarized in a table. Areas of interest for future tests are identified, with emphasis given to the implementation of a synthetic workload generation mechanism on FTMP.

Clune, E.↗
NASA NTRS1985

A case study in R and D productivity: Helping the program manager cope with job stress and improve communication effectiveness

Certain structural changes in the Naval Material Command which resulted from a comparison of its operations to those of selected large-scale private sector companies are described. Central to the change was a reduction in the number of formal reports from systems commands to headquarters, and the provision of Program Management Assistance Teams (at the request of the program manager) to help resolve project problems. It is believed that these changes improved communication and information-processing, reduced program manager stress, and resulted in improved productivity.

Bodensteiner, W. D.↗
NASA NTRS1985

R and D productivity improvement at Honeywell: A case study

The problems encountered when computer-aided-design/documentation was applied to a large design program at Honeywell; how a study team was established to solve the problem; the techniques used by the team and the resulting solutions are described. The techniques used in this instance may be applied to other problem areas in the R&D process to improve productivity.

Lyons, W. E.↗
NASA NTRS1985

A fuelwood plantation site selection procedure using geographic information system technology: A case study in support of the NASA Global Habitability Program

A study undertaken in support of NASA's Global Habitability Program is described. A demonstration of geographic information system (GIS) technology for site evaluation and selection is given. The objective was to locate potential fuelwood plantations within a 50 km radius of Nairobi, Kenya. A model was developed to evaluate site potential based on capability and suitability criteria and implemented using the Environmental Research Institute of Michigan's geographic information system.

Roller, N. E. G.↗
NASA NTRS1985

Magnetic disturbances in the vicinity of synchronous orbit and the substorm current wedge - A case study

It is pointed out that magnetospheric substorms have been referred to as the 'fundamental instability' of the magnetosphere which results from coupling between the solar wind and the earth's magnetic and plasma environment. The present paper is mainly concerned with magnetic observations made by the midlatitude Air Force Geophysics Laboratory (AFGL) Magnetometer Network, the GOES 2 and 3 synchronous satellites, and the near-geosynchronous P78-2 Spacecraft Charging at High Altitudes (SCATHA) satellite. Ground-based Pi 2 and magnetic bay observations are used to detect a clear substorm onset. An idealized model of the substorm current system is utilized to relate the observations to the spatial location and temporal development of the substorm disturbance near synchronous orbit.

Singer, H. J.↗
NASA NTRS1985

Characteristics of Arctic Ocean ice determined from SMMR data for 1979 - Case studies in the seasonal sea ice zone

Sea ice data derived from the Scanning Multichannel Microwave Radiometer are examined for sections of the Arctic Ocean during early summer 1979. The temporary appearance of spuriously high multiyear ice fractions in the seasonal ice zones of the Kara and Barents Seas is a result of surface melt phenomena and the relative responses of the different channels to these effects. These spurious signatures can provide early identification of melt onset and additional information on surface characteristics.

Anderson, M. R.↗
NASA NTRS1985

A case study of the effects of random errors in rawinsonde data on computations of ageostrophic winds

Data input for the AVE-SESAME I experiment are utilized to describe the effects of random errors in rawinsonde data on the computation of ageostrophic winds. Computer-generated random errors for wind direction and speed and temperature are introduced into the station soundings at 25 mb intervals from which isentropic data sets are created. Except for the isallobaric and the local wind tendency, all winds are computed for Apr. 10, 1979 at 2000 GMT. Divergence fields reveal that the isallobaric and inertial-geostrophic-advective divergences are less affected by rawinsonde random errors than the divergence of the local wind tendency or inertial-advective winds.

Moore, J. T.↗
NASA NTRS1985

Engineering challenges of in-flight spacecraft - Voyager: A case study

Some of the engineering problems encountered during the post-launch phase of interplanetary space missions are described, with emphasis given to the Voyager missions. The major in-flight modifications in Voyager spacecraft's operational capability with respect to communications, payload, and navigation systems are discussed. Attention is given to the instances of 'failure workaround' including: recovery from a failed receiver, recovery from a seized scan platform actuator, and modifications to the Attitude Articulation and Control Subsystem (AACS) software during the Saturn encounter. A detailed line drawing of the Voyager spacecraft is provided.

Jones, C. P.↗
NASA NTRS1986

Designing with Ada for satellite simulation: A case study

A FORTRAN-operated and an Ada-oriented design for the same system are compared to learn whether an essentially different design was produced using Ada. The designs were produced by an experiment that involves the parallel development of software for a spacecraft dynamics simulator. Design differences are identified in the use of abstractions, system structure, and simulator operations. Although the designs were significantly different, this result may be influenced by some special characteristics discussed.

Agresti, William W.↗