Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “IBC”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Nitric oxide gamma band emission in an aurora

Emission of the NO gamma (1,0) band at 2150 A has been observed by a rocket-borne spectrophotometer in an IBC II(+) aurora. The nu-prime progression of the gamma-system does not appear in the spectrum. The observed emission rate of the 2150 A feature increases relative to N2(+) first negative band emission with increasing altitude. We suggest radiative recombination of NO(+) ions with electrons as a possible excitation mechanism compatible with the data.

Feldman, P. D.↗
NASA NTRS1977

Auroral vector electric field and particle comparisons. I - Preliminary convection topology

Data obtained by Polar 3, launched from northern Norway January 27, 1974, are interpreted. The rocket, which traversed nearly 3 deg of latitude, crossed over a stable IBC II auroral arc in the positive bay region and continued north to a convection boundary which has been identified as the Harang discontinuity. Measurements of the complete electric field vector, of energetic electrons, and of auroral emissions were used to study the convection topology in the premagnetic midnight region. The inverted V nature of the electron precipitations at the convection boundary, compared with the lack of such structure over the arc which was within the positive bay region, is thought to indicate that auroral arcs are likely to be associated with inverted V type precipitation only at or poleward of convection boundaries and their eddy structures.

Maynard, N. C.↗
NASA NTRS1977

Auroral recombination of N and O - A possible source for emission in the gamma and delta bands of NO

Radiative recombination of N and O provides a significant source for auroral emission in the gamma and delta bands of NO with selective population of vibrational levels in the A 2 Sigma(+) and C 2 Pi states. This mechanism may account for emissions detected near 2150 A. Models are derived for the auroral ionosphere and include estimates for the concentrations of N and NO. The concentration of NO is estimated to have a value of about 100 million per cu cm near 140 km in an IBC III aurora. The corresponding density for N is about 50 million per cu cm, and the concentration ratio NO(+)/O2(+) has a value of about 5.5.

Wofsy, S. C.↗
NASA NTRS1978

A search for nitric oxide gamma band emission in an aurora

A strong emission feature at 2150 A has been observed by a rocket-borne spectrophotometer in an IBC II(+) aurora. This feature, commonly identified with the NO gamma (1,0) band, is comparable in intensity to the nearby N2 Vegard-Kaplan bands. Comparison of the observed spectra with a theoretically produced synthetic spectrum allows all but this feature to be assigned to N2 transitions. No bands of the v prime = 0 or 2 progressions or any other bands from v prime = 1 appear, casting serious doubt on the identification of this feature as the NO gamma (1,0) band.

Beiting, E. J., III↗
NASA NTRS1978

Auroral excitation of optical emissions of atomic and molecular oxygen

The O I 'green line' (1S-1D) at 5577 A and the O2 (0,0) atmosphere band at 7620 A were measured in a steady IBC II(plus) aurora simultaneously with N2 emissions and the auroral electron flux. An empirical model based on these rocket measurements shows that the principal excitation source of O2(b 1 Sigma g plus) is energy transfer from O(1D), with direct electron impact of O2 contributing less than 5 percent. While the altitude profile of the green line emission resembles that which would be produced by electron impact excitation of O2, a dissociative excitation cross section of 10 to the minus 16th power is required for this interpretation. None of the other known O(1S) excitation mechanisms are thought capable of producing the observed emission rate.

Feldman, P. D.↗
NASA NTRS1979

Ultraviolet spectrum of the Aurora /2000-2800 A/

Ultraviolet spectra between 2000 and 2800 delta-v of an IBC II(+) aurora were obtained by a rocket-borne Ebert-Fastie monochromator at 15-A resolution over Fort Churchill, Manitoba. The v-prime = 0-8 progressions of the N2 Vegard-Kaplan system, the delta-v = 8 sequence of the Lyman-Birge-Hopfield system, and a progression attributed to the Herman-Kaplan system were identified by a synthetic spectrum analysis. Relative populations of the first eight vibrational levels of the A3 Sigma u(+) state at high altitude were obtained from the theoretically generated spectra, and quenching rate coefficients were derived for these eight levels by using an atomic oxygen concentration derived from data from another experiment on board. For v = 0 the quenching rate coefficient was found to be 2.0 times 10 the minus 10th cu cm/sec and was not found to increase for higher vibrational levels. The intensity of the (0,2) band of the Herman-Kaplan system was found to be about 5 times the theoretically predicted value, but even so, the cascade from E3 Sigma g(+) provides less than 2% of the A3 Sigma u(+) state population.

Beiting, E. J., III↗
NASA NTRS1979

N2 vibrational distribution in aurorae

The N2 vibrational distribution is calculated for a specific IBC Class II aurora using as input data obtained from coordinated rocket and satellite observations and currently accepted excitation and quenching rates. The results of the calculations indicate no significant vibrational enhancements for this specific aurora nor for 'upper limit' estimates for more intense aurorae. It is concluded that if significantly larger concentrations of vibrationally excited N2 molecules exist in the aurora, as recent rocket EUV measurements suggest, current concepts of the sources and sinks of N2 vibrational excitation will require significant revision.

Waite, J. H.↗
NASA NTRS1980

The excitation and collisional deactivation of metastable N/2P/ atoms in auroras

The concentration and altitude distribution of metastable N(2P) atoms was measured in a diffuse IBC II(+) auroral arc. The dominant N(2P) source is shown to be the dissociative excitation of N2 by electron impact with a minor contribution from the dissociative recombination of N2(+) ions. The possibility that an ion-molecule process involving atomic oxygen and vibrationally excited N2(+) ions is a significant N(2P) source is examined. Values for the proportional yield of N(+), N(2P), N(2D), and N(4S) atoms from electron-impact dissociation of N2 under optically thick conditions are given.

Zipf, E. C.↗
NASA NTRS1980

Production of nitrous oxide in the auroral D and E regions

A study of nitrous oxide formation mechanisms indicates that N2O concentrations greater than 10 to the 9th per cu cm could be produced in IBC III aurora or by lower-level activity lasting for many hours, and, in favorable conditions, the N2O concentration could exceed the local nitric oxide density. An upper limit on the globally averaged N2O production rate from auroral activity is estimated at 2 x 10 to the 27th per second.

Zipf, E. C.↗
NASA NTRS1984

Periodic control of the individual-blade-control helicopter rotor

Results of an investigation into methods of controller design for an individual helicopter rotor blade in the high forward-flight speed regime are described. This operating condition poses a unique control problem in that the perturbation equations of motion are linear with coefficients that vary periodically with time. The design of a control law was based on extensions to modern multivariate synthesis techniques and incorporated a novel approach to the reconstruction of the missing system state variables. The controller was tested on both an electronic analog computer simulation of the out-of-plane flapping dynamics, and on a four foot diameter single-bladed model helicopter rotor in the M.I.T. 5x7 subsonic wind tunnel at high levels of advance ratio. It is shown that modal control using the IBC concept is possible over a large range of advance ratios with only a modest amount of computational power required.

Mckillip, R. M., Jr.↗
NASA NTRS1985

Periodic control of the individual-blade-control helicopter rotor

This paper describes the results of an investigation into methods of controller design for linear periodic systems utilizing an extension of modern control methods. Trends present in the selection of various cost functions are outlined, and closed-loop controller results are demonstrated for two cases: first, on an analog computer simulation of the rigid out of plane flapping dynamics of a single rotor blade, and second, on a 4 ft diameter single-bladed model helicopter rotor in the MIT 5 x 7 subsonic wind tunnel, both for various high levels of advance ratio. It is shown that modal control using the IBC concept is possible over a large range of advance ratios with only a modest amount of computational power required.

Mckillip, R. M., Jr.↗
NASA NTRS1988

Active control rotor model testing at Princeton's Rotorcraft Dynamics Laboratory

A description of the model helicopter rotor tests currently in progress at Princeton's Rotorcraft Dynamics Laboratory is presented. The tests are designed to provide data for rotor dynamic modeling for use with active control system design. The model rotor to be used incoporates the capability for Individual Blade Control (IBC) or Higher Harmonic Control through the use of a standard swashplate on a three bladed hub. Sample results from the first series of tests are presented, along with the methodology used for state and parameter identification. Finally, pending experiments and possible research directions using this model and test facility are outlined.

Mckillip, Robert M., Jr.↗
NASA NTRS1989

Design of an active helicopter control experiment at the Princeton Rotorcraft Dynamics Laboratory

In an effort to develop an active control technique for reducing helicopter vibrations stemming from the main rotor system, a helicopter model was designed and tested at the Princeton Rotorcraft Dynamics Laboratory (PRDL). A description of this facility, including its latest data acquisition upgrade, are given. The design procedures for the test model and its Froude scaled rotor system are also discussed. The approach for performing active control is based on the idea that rotor states can be identified by instrumenting the rotor blades. Using this knowledge, Individual Blade Control (IBC) or Higher Harmonic Control (HHC) pitch input commands may be used to impact on rotor dynamics in such a way as to reduce rotor vibrations. Discussed here is an instrumentation configuration utilizing miniature accelerometers to measure and estimate first and second out-of-plane bending mode positions and velocities. To verify this technique, the model was tested, and resulting data were used to estimate rotor states as well as flap and bending coefficients, procedures for which are discussed. Overall results show that a cost- and time-effective method for building a useful test model for future active control experiments was developed. With some fine-tuning or slight adjustments in sensor configuration, prospects for obtaining good state estimates look promising.

Marraffa, Andrew M.↗
NASA NTRS1990

Radiation response issues for infrared detectors

Researchers describe the most important radiation response issues for infrared detectors. In general, the two key degradation mechanisms in infrared detectors are the noise produced by exposure to a flux of ionizing particles (e.g.; trapped electronics and protons, debris gammas and electrons, radioactive decay of neutron-activated materials) and permanent damage produced by exposure to total dose. Total-dose-induced damage is most often the result of charge trapping in insulators or at interfaces. Exposure to short pulses of ionization (e.g.; prompt x rays or gammas, delayed gammas) will cause detector upset. However, this upset is not important to a sensor unless the recovery time is too long. A few detector technologies are vulnerable to neutron-induced displacement damage, but fortunately most are not. Researchers compare the responses of the new technologies with those of the mainstream technologies of PV HgCdTe and IBC Si:As. One important reason for this comparison is to note where some of the newer technologies have the potential to provide significantly improved radiation hardness compared with that of the mainstream technologies, and thus to provide greater motivation for the pursuit of these technologies.

Kalma, Arne H.↗
NASA NTRS1991

Report of the direct infrared sensors panel

The direct infrared sensors panel considered a wide range of options for technologies relevant to the science goals of the Astrotech 21 mission set. Among the technologies assessed are: large format arrays; photon counting detectors; higher temperature 1 to 10 micro-m arrays; impurity band conduction (IBC) or blocked impurity band (BIB) detectors; readout electronics; and adapting the Space Infrared Telescope Facility and Hubble Space Telescope. Detailed development plans were presented for each of these technology areas.

Mccreight, Craig↗
NASA NTRS1992

Research on measurement and control of helicopter rotor response using blade-mounted accelerometers 1991-92

Preliminary wind tunnel tests of the hill-size Model 412/IBC rotor at the Ames Research Center, NASA, are described. Blade flapping motion was excited by swash plate oscillation, and the flapping response was measured using blade-mounted accelerometers and compared with flapping motion inferred form blade strain measurements. The recorded open-loop accelerometer signals were used as input to the flapping-IBC system in the laboratory. The resulting controller cyclic pitch outputs are compared with the original cyclic pitch excitation inputs, and the potential effectiveness of the controller in suppressing the original excitation is evaluated. Control of blade flapping excites blade lagging, and vice versa; the paper describes a theoretical investigation of these coupling effects.

Ham, Norman D.↗
NASA NTRS1994

10 and 20 micron imaging with arrays

We discuss imaging with arrays in the thermal IR. Aspects of the design and performance of the 'Golden Gopher', an infrared array camera are presented. This instrument operates in a high-background environment, for ground-based astronomical imaging from 5 to 27 micrometers. It is built around a 20 x 64 element Si:As Impurity Band Conduction (IBC) device manufactured by GenCorp Aerojet Electronic Systems Division, and has a noise-equivalent flux density (NEFD) of 23.5 mJy (min(exp -1/2) (arcsec(exp -2) at lambda = 10 micrometers, delta-lambda = 1 micrometer, on the Mt. Lemmon 1.5m telescope. We present and discuss a sample of the data. In addition we discuss the design and expected performance of the 'Long Wavelength Spectrometer' which is now under construction for the Keck telescope.

Jones, B.↗
NASA NTRS1997

Development of 256 x 256 Element Impurity Band Conduction Infrared Detector Arrays for Astronomy

This report describes the work performed on a one and a half year advance technology program to develop Impurity Band Conduction (IBC) detectors with very low dark current, high quantum efficiency, and with good repeatable processes. The program fabricated several epitaxial growths of Si:As detecting layers from 15 to 35 microns thick and analyzed the performance versus the thickness and the Arsenic concentration of these epitaxial layers. Some of the epitaxial runs did not yield because of excessive residual impurities. The thicker epitaxial layers and the ones with higher Arsenic concentration resulted in good detectors with low dark currents and good quantum efficiency. The program hybridized six detector die from the best detector wafers to a low noise, 256 x 256 readout array and delivered the hybrids to NASA Ames for a more detailed study of the performance of the detectors.

Domingo, George↗