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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

ATS-6 - Radio Frequency Interference Measurement Experiment

The frequency band from 5.925 to 6.425 GHz is served by fixed satellites and by terrestrial microwave links. There is a possibility of microwave links pointed at the horizon causing interference to the uplinks of domestic and international communications satellites sharing the same frequency band. A mathematical model has been derived for predicting the fields at geostationary orbit based on the known characteristics and known distribution of the terrestrial microwave relay system. The Applications Technology Satellite-6 (ATS-6) is sensitive to signals in the range of 10 dBW radiated in the direction of the satellite. Signals in the range of 10-30 dBW have been recorded over various parts of the United States.

Henry, V. F.↗
NASA NTRS1976

Wind tunnel wall interference effects on a supercritical airfoil at transonic speeds

Wind tunnel tests of a 10% supercritical airfoil have been conducted in the Lockheed Compressible Flow Facility at transonic speeds to determine the effects of varying wind tunnel wall porosity on airfoil performance. Wall configurations ranging in porosity from 1.3% to 10% were investigated at Reynolds numbers of 7 to 30 million. Experimental data presented to show the effect of varying wall porosity include airfoil surface pressures, airfoil forces, and wind tunnel wall pressures. Utilizing the experimental results, an assessment of the applicability of current subcritical theoretical methods to predict wall interference corrections in subsonic and transonic flows is made.

Blackwell, J. A., Jr.↗
NASA NTRS1976

Application of the nonlinear vortex-lattice concept to aircraft-interference problems

A discrete-vortex model was developed to account for the hazardous effects of the vortex trail issued from the edges of separation of a large leading wing on a small trailing wing. The model is divided into three main parts: the leading wing and its near wake, the near and far wakes of the leading wing, and the trailing wing and the portion of the far wake in its vicinity. The normal force, pitching moment, and rolling moment coefficients for the trailing wing are calculated. The circulation distribution in the vortex trail is calculated in the first part of the model where the leading wing is far upstream and hence is considered isolated. A numerical example is solved to demonstrate the feasibility of using this method to study interference between aircraft. The numerical results show the correct trends: The following wing experiences a loss in lift between the wing-tip vortex systems of the leading wing, a gain outside this region, and strong rolling moments which can change sign as the lateral relative position changes. All the results are strongly dependent on the vertical relative position.

Kandil, O. A.↗
NASA NTRS1977

Radio frequency interference from near-earth satellites

A pessimistic statistical model was developed for predicting the extent of radio frequency interference (RF1). Based on the assumptions underlying the model, DSN S-band operations can expect one RF1 interruption every 4.1 days, with the average incident lasting 24 s. This implies that 52 or more such satellites, with uncorrelated orbital trajectories, will cause in excess of 5 min of RF1 per day at a DSN station.

Levitt, B. K.↗
NASA NTRS1976

Interference in astronomical speckle patterns

Astronomical speckle patterns are examined in an atmospheric-optics context in order to determine what kind of image quality is to be expected from several different imaging techniques. The model used to describe the instantaneous complex field distribution across the pupil of a large telescope regards the pupil as a deep phase grating with a periodicity given by the size of the cell of uniform phase or the refractive index structure function. This model is used along with an empirical formula derived purely from the physical appearance of the speckle patterns to discuss the orders of interference in astronomical speckle patterns.

Breckinridge, J. B.↗
NASA NTRS1977

An experimental investigation of airframe component interference noise

Measurements of noise produced by a model of a wheel well (rectangular cavity), landing gear (wheel and strut), and flap at Mach numbers of 0.18 and 0.40 have been made in an anechoic flow facility. Individual component noise and component interference noise are described in terms of the OASPL, spectra, and streamwise or flyover directivity patterns. Areas of significant sound generation are illuminated and causes of these noise sources are suggested. Results from an acoustic imaging technique are used to point out other source regions not discernible by simple far-field measurements.

Block, P. J. W.↗
NASA NTRS1977

Problems in the use of interference filters for spectrophotometric determination of total ozone

An analysis of the use of ultraviolet narrow-band interference filters for total ozone determination is given with reference to the New Zealand filter spectrophotometer under the headings of filter monochromaticity, temperature dependence, orientation dependence, aging, and specification tolerances and nonuniformity. Quantitative details of each problem are given, together with the means used to overcome them in the New Zealand instrument. The tuning of the instrument's filter center wavelengths to a common set of values by tilting the filters is also described, along with a simple calibration method used to adjust and set these center wavelengths.

Basher, R. E.↗
NASA NTRS1978

A parametric experimental study of the interference effects and the boundary-condition coefficient of slotted wind-tunnel walls

An experimental study of slotted upper and lower walls in a two-dimensional transonic wind tunnel with solid sidewalls is reported. Results are presented for several slot spacings and slot openness ratios. The experimental data are pressure measurements which were made on an airfoil model and on a sidewall near one of the slotted walls. The slotted-wall boundary-condition coefficient, which relates the pressure and streamline curvature near the wall, is determined from the wall pressure measurements. The measured wall-induced interference is correlated with the experimental values for the boundary-condition coefficient. This correlation is compared with theory.

Everhart, J. L.↗
NASA NTRS1978

Systems and methods for determining radio frequency interference

The presence, frequency and amplitude of radio frequency interference superimposed on communication links originating from a terrestrial region and including a relay in a geostationary spacecraft are determined by pointing a narrow beam antenna on the satellite at the terrestrial region. The level of noise radiated from the region to the antenna is measured at a terrestrial station that is usually remote from the region. Calibrating radio signals having a plurality of predetermined EIRP's (Effective Isotropic Radiated Power) and frequencies in the spectrum are transmitted from the region through the spacecraft narrow beam antenna back to the station. At the station, the levels of the received calibrating signals are separately measured for each of the frequency bands and EIRP's.

Johannsen, K. G.↗
NASA NTRS1979

Interference effects of aircraft components on the local blade angle of attack of a wing-mounted propeller

The aerodynamic interference effects on a propeller operating in the presence of different wing-body-nacelle combinations was studied. The unsteady blade angle of attack variation with azimuth angle by varying the pitch and yaw of the nacelle was minimized. Results indicate for the particular configuration of interest the minimum blade angle of attack variation occurred with the nacelle pitched downward 4.5 deg and yawed inward 3.0 deg.

Mendoza, J. P.↗
NASA NTRS1979

Wind tunnels with adapted walls for reducing wall interference

The basic principle of adaptable wind tunnel walls is explained. First results of an investigation carried out at the Aero-Space Institute of Berlin Technical University are presented for two dimensional flexible walls and a NACA 0012 airfoil. With five examples exhibiting very different flow conditions it is demonstrated that it is possible to reduce wall interference and to avoid blockage at transonic speeds by wall adaptation.

Ganzer, U.↗
NASA NTRS1978

Cochannel interference analysis between spaceborne and terrestrial radars

An analysis of cochannel interference between spaceborne and terrestrial radars is presented. A generic modeling methodology is applied, which, it is felt, will represent the worst-case situation. In order to account for Doppler shifts, auto- and cross-ambiguity functions have been developed for determining matched filter outputs. The results support the ability of such radar systems to coexist relatively harmoniously utilizing currently accepted assignment procedures.

Nicholas, J. J., Jr.↗
NASA NTRS1978

Postperihelion interference filter photometry of the 'annual' Comet P/Encke

Interference filter photometry was taken of Comet Encke on June 14, 1974 (1.07 AU heliocentric distance, postperihelion) at the CTIO (Cerro Tololo Interamerican Observatory) 150-cm reflector. Production rates were calculated as 4.1 x 10 to the 23nd power mol/sec for CN, 5.3 x 10 to 23nd power mol/sec for C3, and 4.3 x 10 to the 24th power mol/sec for C2. These are about three times smaller than at comparable heliocentric distance preperihelion, assuming a value of 100 for the ratio H2O/(C2 + C3 + CN). An upper limit was placed on the production of nonvolatiles at about one-third that of volatiles in mass by assuming a bulk density of 1 g/cu cm, a particle geometric albedo of 0.1, and a phase function of 0.2.

Newburn, R. L., Jr.↗
NASA NTRS1977

Bit timing with pulse distortion and intersymbol interference

Pulse distortion and intersymbol interference due to insufficient filtering in PCM and PSK channels cause performance degradation in terms of both bit error probabilities and timing errors. This paper reports the results of a study analyzing these effects on bit timing subsystems. Consideration is given to both the filter-rectifier and transition tracking type of timing subsystem. Although both these systems perform similarly in high SNR and ideal pulse models, pulse distortion and intersymbol affects each differently. The primary effects in both systems is to cause the presence of an irreducible mean squared timing error due to the intersymbol which limits the ultimate performance. Design procedures to minimize the anomalies of both systems are presented, and indicate modifications of the standard timing subsystems. It is found that specific design directions depend on whether the intersymbol or the receiver noise tends to dominate.

Gagliardi, R. M.↗
NASA NTRS1979

Electromagnetic interference assessment of an ion drive electric propulsion system

The electromagnetic interference (EMI) form elements of an ion drive electric propulsion system was analyzed, and the effects of EMI interaction with a typical interplanetary spacecraft engineering and scientific subsystems were predicted. SEMCAP, a computerized electromagnetic compatibility assessment code, was used to analyze the impact of EMI noise sources on 65 engineering/telemetry circuits and 48 plasma wave and planetary radio astronomy channels measuring over the range of 100 Hz to 40 MHz in a spacecraft of the Voyager type; manual methods were used to evaluate electrostatics, magnetics, and communications effects. Results indicate that some conducted and radiated spectra are in excess of electromagnetic compatibility specification limits; direct design changes may be required for filtering and shielding of thrust system elements. The worst source of broadband radiated noise appears to be the power processor. The magnetic field necessary to thruster operation is equivalent to about 18 amp-sq m per amp of beam current at right angles to the axis caused by the neutralizer/plume loop.

Whittlesey, A. C.↗
NASA NTRS1980

Velocity servo for continuous scan Fourier interference spectrometer

A velocity servo for continuous scan Fourier interference spectrometer of the double pass retroreflector type having two cat's eye retroreflectors is described. The servo uses an open loop, lead screw drive system for one retroreflector with compensation for any variations in speed of drive of the lead screw provided by sensing any variation in the rate of reference laser fringes, and producing an error signal from such variation used to compensate by energizing a moving coil actuator for the other retroreflector optical path, and energizing (through a highpass filter) piezoelectric actuators for the secondary mirrors of the retroreflectors.

Schindler, R. A.↗
NASA NTRS1980

TWINTAN: A program for transonic wall interference assessment in two-dimensional wind tunnels

A method for assessing the wall interference in transonic two dimensional wind tunnel test was developed and implemented in a computer program. The method involves three successive solutions of the transonic small disturbance potential equation to define the wind tunnel flow, the perturbation attriburable to the model, and the equivalent free air flow around the model. Input includes pressure distributions on the model and along the top and bottom tunnel walls which are used as boundary conditions for the wind tunnel flow. The wall induced perturbation fields is determined as the difference between the perturbation in the tunnel flow solution and the perturbation attributable to the model. The methodology used in the program is described and detailed descriptions of the computer program input and output are presented. Input and output for a sample case are given.

Kemp, W. B., Jr.↗
NASA NTRS1980

Low-pass interference filters for submillimeter astronomy

Low-pass (long-wave transmitting) interference filters, suitable for broadband photometric observations, previously have been constructed from series of capacitive grids stretched on thin Mylar. These filters have the desired optical properties of high transmission, sharp cut-ons, and good blocking at short wavelengths. Their designs, however, do not scale from one wavelength to another and their performance can deteriorate at low temperatures due to differential contraction of the dielectric backing and the supporting structure. The deviation of these early filters from the predicted scaling was due primarily to the difference in refractive index between the backing material and the medium between the grids. In the present paper, filters are described in which dielectric spacers are used, instead of air, as the medium between the grids. This technique has improved the scaling and has reduced the distortion from differential contraction.

Whitcomb, S. E.↗