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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.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Solar and stellar radio spikes - Limits on the saturation of the electron-cyclotron maser

The solar millisecond radio 'spikes' have been explained in terms of X-mode radiation generated by a maser near the electron gyrofrequency, acting on fast coronal electrons with a loss cone. This maser is a phenomenon described by quasi-linear theory. It is sensitive to the small first-relativistic correction to the gyrofrequency. Thus, it might be disrupted rather easily by nonlinear effects. The maximum radiation density that can be reached before the radiation entrains (phase-locks) the electrons and saturates the maser is discussed. If the observed durations of solar radio spikes are a measure of the rate of scattering into the loss-cone, then the inferred energy density is at least two orders of magnitude less than the energy density at which entrainment sets in. Also, maser emission from auroral kilometric radiation does not reach wave energies critical for electron entrainment. Maser emissions from flare stars, however, show 3-4 orders of magnitude higher radio fluxes and brightness temperatures than for the solar case and are likely to be saturated by entrainment.

Wentzel, Donat G.↗
NASA NTRS1992

The coevolution of decimetric millisecond spikes and hard X-ray emission during solar flares

Results are presented of an analysis of a comprehensive data set of 27 solar flares with decimetric millisecond spikes between 1980 and 1989, simultaneously observed with the Zuerich radio spectrometers and the Hard X-ray Burst Spectrometer on the SMM spacecraft. Two contradictory relationships of the coevolution of hard X-ray and spiky radio emissions during flares are found: the temporal evolution of both emissions reveals a close functional dependence, but there is a substantial time delay between the two emissions. Five possible scenarios for the hard-X-ray-associated radio spike emission which may account for both their detailed coevolution and their substantial intervening time delay are discussed. All five scenarios are able to explain both the close coevolution of hard X-ray and radio emission as well as their mutual delay to some degree, but none of them can explain all observational aspects in a simple way.

Aschwanden, Markus J.↗
NASA NTRS1955

Preliminary Investigation of a Conical Spike Inlet in Combination with a Vertical-wedge Auxiliary Inlet at Mach Number 1.9

Pressure-recovery characteristics of a nacelle-type-spike inlet in combination with a vertical-wedge auxiliary scoop are presented for a free-stream Mach number of 1.9 at zero angle of attack. The auxiliary scoop provided 17 percent additional air flow with a drop in critical pressure recovery from 0.86 to 0.81. However, in terms of inlet-engine matching, the pressure recovery of the undersized spike inlet operating at a specified corrected air flow increased with the scoop open, for example, from 0.69 to 0.81.

Beke, Andrew↗
NASA NTRS1993

Time-Accurate Unsteady Flow Simulations Supporting the SRM T+68-Second Pressure Spike Anomaly Investigation (STS-54B)

Time-accurate unsteady flow simulations are being performed supporting the SRM T+68sec pressure 'spike' anomaly investigation. The anomaly occurred in the RH SRM during the STS-54 flight (STS-54B) but not in the LH SRM (STS-54A) causing a momentary thrust mismatch approaching the allowable limit at that time into the flight. Full-motor internal flow simulations using the USA-2D axisymmetric code are in progress for the nominal propellant burn-back geometry and flow conditions at T+68-sec--Pc = 630 psi, gamma = 1.1381, T(sub c) = 6200 R, perfect gas without aluminum particulate. In a cooperative effort with other investigation team members, CFD-derived pressure loading on the NBR and castable inhibitors was used iteratively to obtain nominal deformed geometry of each inhibitor, and the deformed (bent back) inhibitor geometry was entered into this model. Deformed geometry was computed using structural finite-element models. A solution for the unsteady flow has been obtained for the nominal flow conditions (existing prior to the occurrence of the anomaly) showing sustained standing pressure oscillations at nominally 14.5 Hz in the motor IL acoustic mode that flight and static test data confirm to be normally present at this time. Average mass flow discharged from the nozzle was confirmed to be the nominal expected (9550 lbm/sec). The local inlet boundary condition is being perturbed at the location of the presumed reconstructed anomaly as identified by interior ballistics performance specialist team members. A time variation in local mass flow is used to simulate sudden increase in burning area due to localized propellant grain cracks. The solution will proceed to develop a pressure rise (proportional to total mass flow rate change squared). The volume-filling time constant (equivalent to 0.5 Hz) comes into play in shaping the rise rate of the developing pressure 'spike' as it propagates at the speed of sound in both directions to the motor head end and nozzle. The objectives of the present analysis are to: (1) capture the dynamic responses of the motor combustion gas flow to correlate with available low-frequency (less than 12.5 sample/sec) data and (2) observe the high-frequency (up to 50 Hz) characteristics of the response to determine any potentials for dynamic coupling.

Dougherty, N. S.↗
NASA NTRS1996

PtSi/Si LWIR Detectors Made With p+ Doping Spikes

PtSi/Si Schottky-barrier devices detecting long-wavelength infrared (LWIR) photons demonstrated. Essential feature of one of these devices is p+ "doping spike"; layer of Si about 10 Angstrom thick, located at PtSi/Si interface, and doped with electron acceptors (boron atoms) at concentration between 5 x 10(19) and 2 x 10(20) cm(-3). Doping spikes extend cutoff wavelengths of devices to greater values than otherwise possible.

Lin, True-Lon↗
NASA NTRS2007

Build-up Approach to Updating the Mock Quiet Spike(TradeMark) Beam Model

A crucial part of aircraft design is ensuring that the required margin for flutter is satisfied. A trustworthy flutter analysis, which begins by possessing an accurate dynamics model, is necessary for this task. Traditionally, a model was updated manually by fine tuning specific stiffness parameters until the analytical results matched test data. This is a time consuming iterative process. NASA Dryden Flight Research Center has developed a mode matching code to execute this process in a more efficient manner. Recently, this code was implemented in the F-15B/Quiet Spike(TradeMark) (Gulfstream Aerospace Corporation, Savannah, Georgia) model update. A build-up approach requiring several ground vibration test configurations and a series of model updates was implemented in order to determine the connection stiffness between aircraft and test article. The mode matching code successfully updated various models for the F-15B/Quiet Spike(TradeMark) project to within 1 percent error in frequency and the modal assurance criteria values ranged from 88.51-99.42 percent.

Herrera, Claudia Y.↗
NASA NTRS2007

F-15B Quiet Spike(TradeMark) Aeroservoelastic Flight-Test Data Analysis

System identification is utilized in the aerospace community for development of simulation models for robust control law design. These models are often described as linear, time-invariant processes and assumed to be uniform throughout the flight envelope. Nevertheless, it is well known that the underlying process is inherently nonlinear. Over the past several decades the controls and biomedical communities have made great advances in developing tools for the identification of nonlin ear systems. In this report, we show the application of one such nonlinear system identification technique, structure detection, for the an alysis of Quiet Spike(TradeMark)(Gulfstream Aerospace Corporation, Savannah, Georgia) aeroservoelastic flight-test data. Structure detectio n is concerned with the selection of a subset of candidate terms that best describe the observed output. Structure computation as a tool fo r black-box modeling may be of critical importance for the development of robust, parsimonious models for the flight-test community. The ob jectives of this study are to demonstrate via analysis of Quiet Spike(TradeMark) aeroservoelastic flight-test data for several flight conditions that: linear models are inefficient for modelling aeroservoelast ic data, nonlinear identification provides a parsimonious model description whilst providing a high percent fit for cross-validated data an d the model structure and parameters vary as the flight condition is altered.

Kukreja, Sunil L.↗
NASA NTRS2007

Build-up Approach to Updating the Mock Quiet Spike(TM)Beam Model

A crucial part of aircraft design is ensuring that the required margin for flutter is satisfied. A trustworthy flutter analysis, which begins by possessing an accurate dynamics model, is necessary for this task. Traditionally, a model was updated manually by fine tuning specific stiffness parameters until the analytical results matched test data. This is a time consuming iterative process. The NASA Dryden Flight Research Center has developed a mode matching code to execute this process in a more efficient manner. Recently, this code was implemented in the F-15B/Quiet Spike (Gulfstream Aerospace Corporation, Savannah, Georgia) model update. A build-up approach requiring several ground vibration test configurations and a series of model updates was implemented to determine the connection stiffness between aircraft and test article. The mode matching code successfully updated various models for the F-15B/Quiet Spike project to within 1 percent error in frequency and the modal assurance criteria values ranged from 88.51-99.42 percent.

Herrera, Claudia Y.↗
NASA NTRS2008

Structure Computation of Quiet Spike[Trademark] Flight-Test Data During Envelope Expansion

System identification or mathematical modeling is used in the aerospace community for development of simulation models for robust control law design. These models are often described as linear time-invariant processes. Nevertheless, it is well known that the underlying process is often nonlinear. The reason for using a linear approach has been due to the lack of a proper set of tools for the identification of nonlinear systems. Over the past several decades, the controls and biomedical communities have made great advances in developing tools for the identification of nonlinear systems. These approaches are robust and readily applicable to aerospace systems. In this paper, we show the application of one such nonlinear system identification technique, structure detection, for the analysis of F-15B Quiet Spike(TradeMark) aeroservoelastic flight-test data. Structure detection is concerned with the selection of a subset of candidate terms that best describe the observed output. This is a necessary procedure to compute an efficient system description that may afford greater insight into the functionality of the system or a simpler controller design. Structure computation as a tool for black-box modeling may be of critical importance for the development of robust parsimonious models for the flight-test community. Moreover, this approach may lead to efficient strategies for rapid envelope expansion, which may save significant development time and costs. The objectives of this study are to demonstrate via analysis of F-15B Quiet Spike aeroservoelastic flight-test data for several flight conditions that 1) linear models are inefficient for modeling aeroservoelastic data, 2) nonlinear identification provides a parsimonious model description while providing a high percent fit for cross-validated data, and 3) the model structure and parameters vary as the flight condition is altered.

Kukreja, Sunil L.↗
NASA NTRS2012

In Situ Potassium-Argon Geochronology Using Fluxed Fusion and a Double Spike

A document highlights an Li-based fluxing agent that enables sample fusion and quantitative Ar-release at relatively low temperatures (900-1,000 C), readily achievable with current flight resistance furnace designs. A solid, double spike containing known quantities of Ar-39 and K-41 was developed that, when added in known amounts to a sample, enables the extraction of a Ar-40/K-40 ratio for age estimation without a sample mass measurement. The use of a combination of a flux and a double spike as a means of solving the mechanical hurdles to an in situ K-Ar geochronology measurement has never been proposed before. This methodology and instrument design would provide a capability for assessing the ages of rocks and minerals on the surfaces of planets and other rocky terrestrial bodies in the solar system.

Hurowitz, Joel A.↗
NASA NTRS2018

MAVEN Case Studies of Plasma Dynamics in Low‐Altitude Crustal Magnetic Field at Mars 1: Dayside Ion Spikes Associated With Radial Crustal Magnetic Fields

We report for the first time, simultaneous ion, electron, magnetic field vector and electric field wave measurements made possible by Mars Atmosphere and Volatile EvolutioN, during ion energy flux spikes in low‐altitude radial crustal magnetic fields on the Mars dayside. Observations show energetic electrons and ions (E > 25 eV) precipitating on magnetic field lines assumed as closed. Ions (E < 1.4 keV) display broad velocity distributions toward Mars, showing ions flowing from higher altitude possibly after magnetic reconnection or loss cone filling from pitch angle scattering effects. Precipitating ions (E < 1.4 keV) show nonadiabatic features depending on ion mass and energy and returning ions (E < 1.4 keV) show evidence of conserving the first adiabatic invariant in a mirror field. We observe magnetic field perturbations up to 60 nT, electric field wave amplitudes up to 38 mV/m, and brief periods of peaked electron spectra. At ∼175 km and at times Mars Atmosphere and Volatile EvolutioN is below the mirroring altitude of electrons, we observe mirroring and transverse heating of H+ ions alongside increased electric field wave amplitude fluctuations. It suggests field aligned potential drops result from different mirror altitudes of ions and electrons. Ions E > 1.4 keV (O+) occur as injected accelerated ion beams and ions heated after energization or deceleration. Energy dispersed kilo‐electron‐volt ions suggest a selection effect in radial magnetic fields for lower‐energy Marsward ions, compared to reflection of higher‐energy anti‐Sunward ions. Precipitating kilo‐electron‐volt ions show energy deposition rates of 3.6 ×10(exp -6) W/sq m and sputtering escape rates from precipitating O+ ions of 1.5 ×10(exp 5)/(sq cm.s) and 2.1 ×10(exp 6)/(sq cm.s) are calculated.

Plasma Dynamics↗
NASA NTRS2020

NASA Engineering and Safety Center Technical Bulletin No. 20-07: Evaluating and Mitigating Liner Strain Spikes in COPV's

Unexpected cracking and leaking in bonded composite overwrapped pressure vessel (COPV) liners occurring in recent test programs have been attributed to liner strain spikes observed through measurement and predicted by analysis. Diminished load transfer between the liner and composite overwrap can lead to localized excessive liner yielding in the dome section. This diminished constraint can occur due to yielding of the adhesive or a manufacturing unbond defect. COPVs should be assessed for susceptibility to this new failure mode.

Evaluating↗
NASA NTRS1957

Performance Comparison at Mach Numbers 1.8 and 2.0 of Full Scale and Quarter Scale Translating-Spike Inlets

The performance of a full-scale translating-spike inlet was obtained at Mach numbers of 1.8 and 2.0 and at angles of attach from 0 deg to 6 deg. Comparisons were made between the full-scale production inlet configuration and a geometrically similar quarter-scale model. The inlet pressure-recovery, cowl pressure-distribution, and compressor-face distortion characteristics of the full-scale inlet agreed fairly well with the quarter-scale results. In addition, the results indicated that bleeding around the periphery ahead of the compressor-face station improved pressure recovery and compressor-face distortion, especially at angle of attack.

Anderson, B. H.↗