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  • Other Sources  (15)
  • 1980-1984  (15)
  • 1
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    Control of large space structures: Status report on achievements and current problems (1983)
    In:  CASI
    Details
    Publication Date: 2006-04-11
    Description: The objectives, state-of-the-art, and problems of large space structures control are outlined. The general objectives range from basic deployment and maneuvering, where some vibration modes may be suppressed, to disturbance rejection for very high performance imaging applications. The controls selected generally must produce some combination of eigenvalue/eigenvector and loads modification in order to achieve the mission objectives. An experiment illustrating the dynamic control of a suspended circular plate is described. Analysis methods used in system modelling, signal processing, and process control and monitoring are discussed. Sensor and actuator performance are assessed.
    Keywords: LAUNCH VEHICLES AND SPACE VEHICLES
    Type: NASA. Langley Research Center Modeling Analysis, and Optimization Issues for Large Space Struct.; p 55-72
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    NASA TECHNICAL REPORTS
  • 2
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    Rate 3/4 convolutional coding of 16-PSK - Code design and performance study (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Convolutional coding coupled with 16-PSK modulation is investigated for bandwidth efficient transmission. Rate 3/4, small memory codes are found which are optimized in the free-distance sense on the Gaussian channel. These codes provide up to 4.8 dB of coding gain with 32 states over uncoded 8-PSK, a scheme having the same spectral efficiency as the codes described. The performance is compared with earlier findings of Ungerboeck and some recent results on R = 2/3 coded 8-PSK. In addition, results of a channel transmission study to assess the performance of the four-state code on the band-limited nonlinear channel are presented, and it is found that performance of the coded scheme degrades comparably with uncoded 8-PSK, i.e., coding gain is roughly preserved.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-32; 1308-131
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Ring current dynamics and plasma sheet sources (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The source of the energized plasma that forms in geomagnetic storm ring currents, and ring current decay are discussed. The dominant loss processes for ring current ions are identified as charge exchange and resonant interactions with ion-cyclotron waves. Ring current ions are not dominated by protons. At L4 and energies below a few tens of keV, O+ is the most abundant ion, He+ is second, and protons are third. The plasma sheet contributes directly or indirectly to the ring current particle population. An important source of plasma sheet ions is earthward streaming ions on the outer boundary of the plasma sheet. Ion interactions with the current across the geomagnetic tail can account for the formation of this boundary layer. Electron interactions with the current sheet are possibly an important source of plasma sheet electrons.
    Keywords: GEOPHYSICS
    Type: ESA Achievements of the Intern. Magnetospheric Study (IMS); p 233-242
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  • 4
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    Comparison of an analytical approximation for particle motion in a current sheet with precise numerical calculations (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Approximate analytic solutions exist for particle motion in a one-dimensional current sheet with a constant normal magnetic field component. These solutions are tested against precise numerical calculations, and a range of validity of the analytic solutions is inferred. For example, in the geomagnetic tail neutral sheet, for a dawn-dusk electric field of 0.1-1 mV/m, lobe field of 10-40 nT, and sheet thickness of 1000 km, the analytic solutions serve as a good predictor of particle motion when the normal magnetic field component is less than 3 or 4 nT. By using the analytic solutions, initial distribution functions are mapped into final (accelerated) distributions, and the analytic mappings are compared with numerical mappings.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 147-158
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  • 5
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    A source for the geomagnetic storm main phase ring current (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The paper considers a proposed source for the geomagnetic storm main phase ring current. It is shown that the flux increases of trapped ions and electrons observed by Explorer 45 at L below 4 during two large geomagnetic storms can be explained by inward radial displacement of the preexisting trapped particle distribution. The proposed source requires only the acceleration of the previously entrapped particle population by inward displacement under conservation of the first two adiabatic invariants. It is suggested that a significant difference between large geomagnetic storms and typical substorm activity may be the inward convection occurring over a large longitude range during storms, but only over a small longitude range during typical substorms.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 85; Feb. 1
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  • 6
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    STS-1 operational flight profile. Volume 5: Descent, cycle 3 (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The trajectory data presented are to be used for orbiter systems and subsystems evalation, flight and mission control center software verification, flight techniques and timeline development, crew training, and evaluation of operational mission suitability. The entry profile is very similar to cycle 2, however, elevon and body flap temperature margins have increased and the elevon schedule was changed. The terminal area energy management (TAEM) profile was completely reshaped to conform with new angle of attack constraints and left hand turn around the heading alignment cylinder. Also, the entry/TAEM interface was adjusted to minimize guidance induced angle of attack transients across the interface. The approach and landing phase was reshaped for a 20 deg glideslope and reduced velocity at touchdown. The definition of the runway threshold was standardized for all landing sites. This results in a shift at Edwards Air Force Base in aim points and touchdown relative to the threshold of 1000 feet. The rollout remains essentially unchanged with the exception of the speedbrake, which is now deployed to 50 percent at touchdown.
    Keywords: SPACE TRANSPORTATION
    Type: NASA-TM-81077 , JSC-14483 , REPT-78-FM-51-VOL-5-REV-1 , T79-12405
    Format: application/pdf
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  • 7
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    Effect of flameholder pressure drop on emissions and performance of premixed-prevaporized combustors (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Parametric tests were conducted to determine the effects of flameholder pressure drop on the emissions and performance of lean premixed-prevaporized combustors. A conical flameholder mounted in a diverging duct was tested with two values of flameholder blockage. Emissions of nitrogen oxides, carbon monoxide, carbon dioxide, and unburned hydrocarbons were measured for combustor entrance conditions of 600 to 800 K air temperature, 0.3 MPa to 0.5 MPa pressure, and 20 m/sec to 35 m/sec reference velocity. Jet A fuel was injected at flow rates corresponding to an equivalence ratio range from 0.8 down to the lean stability limit. Emission results for the high-blockage flameholder were a substantial improvement over the low-blockage emission results. A correlation of combustion efficiency with flameholder pressure drop was developed for pressure drops less than 9 percent.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-TP-2131 , E-1358 , NAS 1.60:2131
    Format: application/pdf
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  • 8
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    An association between discrete aurora and energetic particle boundaries (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Low-altitude observations of the energy flux carried by precipitating auroral electrons are compared with simultaneous measurements of the more energetic particle population to determine the spatial relationships between discrete auroras and those regions where the ion population exhibits a full loss cone. Discrete auroras are identified as instances where large, spatially structured energy fluxes (in excess of 10 erg per sq cm s) are carried almost exclusively by precipitating electrons. This comparison makes it possible to infer a relation between discrete auroras and earthward streaming ions observed in the tail. Since discrete auroras occur in association with field-aligned currents, an evaluation is made of the suggestion that auroral field-aligned currents map to the outer boundary of the plasma sheet.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 2395-240
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  • 9
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    Effect of fuel-air-ratio nonuniformity on emissions of nitrogen oxides (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The inlet fuel-air ratio nonuniformity is studied to deterine how nitrogen oxide (NOx) emissions are affected. An increase in NOx emissions with increased fuel-air ratio nonuniformity for average equivalence ratios less than 0.7 and a decrease in NOx emissions for average equivalence ratios near stoichiometric is predicted. The degree of uniformityy of fuel-air ratio profiles that is necessary to achieve NOx emissions goals for actual engines that use lean, premixed, prevaporized combustion systems is determined.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-TP-1798 , E-648
    Format: application/pdf
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  • 10
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    Electron energization in the geomagnetic tail current sheet (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Electron motion in the geomagnetic tail current sheet is examined analytically. An estimation of the energization of electrons trapped by the convective field is made independent of a guiding center approximation. The electrons in the energy range 100 eV - 100 keV have their pitch angle scattered and trapped in the current sheet until accelerated by the convective field. Predictions are made for the electrons that escape the current sheet, electron precipitation in diffuse auroral phenomena and current sheet interactions as a source for plasma sheet electrons and ions.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 5479-548
    Format: text
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