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At least 379 records · Page 21

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NASA NTRS1979

Twin jet noise shielding for a supersonic cruise vehicle

An engine arrangement for a supersonic cruise vehicle (SCV) has been developed that shows promise for jet noise reduction without the performance penalties associated with mechanical suppressors and engine oversizing. This arrangement, wherein two engines are placed on top of the wing directly above two similarly-mounted engines below the wing, can produce 3 to 5 dB less noise below the aircraft flight path than when four engines are installed under the wing. This noise reduction is due to acoustic shielding of the upper jets by the lower jets. Test data are reviewed to verify this acoustical shielding phenomenon, and detailed takeoff trajectories are calculated to show the effects of sideline and flyover noise levels on constraining maximum range SCV configurations. Engine placement variation and differential throttling, wherein thrust is unloaded from the lower engine and added to the upper engine, are to be explored as means for maximizing the shielding effect.

Clauss, J. S., Jr.↗

NASA NTRS1979

Magnetic shielding in a low temperature torsion pendulum experiment

A new type of ether drift experiment searches for anomalous torques on a permanent magnet. A torsion pendulum is used at liquid helium temperature, so that superconducting cylinders can be used to shield magnetic fields. Lead shields attenuate the earth's field, while Nb-Sn shields fastened to the pendulum contain the fields of the magnet. The paper describes the technique by which the earth's field can be reduced below 0.0001 G while simultaneously the moment of the magnet can be reduced by a factor 7 x 10 to the 4th.

Phillips, P. R.↗

NASA NTRS1979

Space vehicle meteoroid shielding design

Design principles of spaced, multiwall meteoroid protection are investigated in the light of experimental data generated during the Apollo Program. The outer wall or shield is shown to be the most important element in the meteoroid-spacecraft interaction. The condition of the debris is primarily a function of the shock pressure, the melting points of the meteoroid and the shield, and the length of the meteoroid and thickness of the shield. Spacing between the walls is effective up to approximately 100 times the length of the meteoroid. The required thickness of the second wall is shown to be proportional to the meteoroid mass, velocity, and density, and to the spacing between the walls, taken with exponents dependent upon the condition of the debris. The effects of placing additional elements (insulation or honeycomb cells) between the two walls are discussed, and the efficiency of various protective configurations is presented. An analysis of the meteoroid protection proposed for the Comet Halley probe is included as an appendix.

Cour-Palais, B. G.↗

NASA NTRS1979

Electron, electron-bremsstrahlung and proton depth-dose data for space-shielding applications

A data set has been developed, consisting of depth-dose distributions for omni-directional electron and proton fluxes incident on aluminum shields. The principal new feature of this work is the accurate treatment, based on detailed Monte Carlo calculations, of the electron-produced bremsstrahlung component. Results covering the energy region of interest in space-shielding calculations have been obtained for the absorbed dose (a) as a function of depth in a semi-infinite medium, (b) at the edge of slab shields, and (c) at the center of a solid sphere. The dose to a thin tissue-equivalent detector was obtained as well as that in aluminum. Various results and comparisons with other work are given.

Seltzer, S. M.↗

NASA NTRS1981

Effects of a modified leading edge on noise and boundary-layer transition in a rod-wall sound shield at Mach 5

A version of a rod wall sound shield was tested in the Mach 5 pilot quiet tunnel over a range of unit Reynolds numbers from 10 to 35 million per meter. The model was modified by inclining the leading edge plates to produce an initial 2 deg expansion to ascertain the sensitivity of boundary layer transition to leading edge disturbances. Rod surface pitot pressures, mean free stream pitot pressures, and static pressures on the rods and plenum walls were measured. Hot-wire measurements were also made in the model and nozzle free stream at a unit Reynolds number of 15 million per meter. The surface pitot pressures indicated that transition was much farther forward than for the previous tests due to the leading edge modification and minor fabrication flaws in the model. Early boundary layer transition on the rods was confirmed by hot-wire measurements which showed much higher noise levels in the free stream shield flow when compared with results from previous tests. Mean pitot pressure surveys within the shielded region inside the model indicated that there was an overexpansion and recompression that would limit the streamwise length of undisturbed flow to about 13 cm along the centerline.

Creel, T. R., Jr.↗

NASA NTRS1981

System requirements of Starprobe thermal shield

The mission of the Starprobe Spacecraft is to do in situ exploration of the solar corona to four solar radii. A thermal shield is required to protect the spacecraft equipment from a 3000 sun incident solar energy level caused by this close approach to the sun. The thermal shield requirements discussed include configuration, material requirements, temperature level, penetrations, outgassing and mass loss, and contamination as referenced to spacecraft mission parameters. Further, the size of the spacecraft will be limited by the space transport system orbiter payload bay dimensions, thus defining the upper limit of the relative sizes and locations of the heat shield and spacecraft equipment.

Miyake, R. N.↗

NASA NTRS1980

Analytical study of twin-jet shielding two-dimensional model

The development of an analytical model to estimate the shielding of one jet by an adjacent jet in a twin jet configuration is discussed in relation to aircraft generated noise. The azimuthal redistribution of sound defining the shadow zone is investigated. Wave equations were solved in the plane normal to the jet axis to estimate the diffraction and reflection of sound by a heated, cylindrical jet. Thus, the noise source considered is essentially a line source assumed to emit at discrete frequency and at rest with respect to the shielding jet which is assumed to be a cylinder of heated flow in which the temperature is constant across the jet. Results show that the sound pressure decreases rapidly with frequency beyond the onset of the shielding to a minimum value. Results also show that increasing the spacing between the source and the jet shifts the curves toward higher frequencies.

Gerhold, C. H.↗

NASA NTRS1982

Role of immobilization of irradiated rats in the protective effect of bone marrow shielding

Rats were exposed to X-radiation to study the influence of immobilization and shielding of part of bone marrow during exposure on survival. It is concluded that (1) the beneficial effect of the stress factor (created by the immobilization of rats during exposure) can aggregate with the effect of bone marrow shielding and, under certain conditions, imitate the latter; and (2) the probability of the protective effect of immobilization should be taken into account when assessing the influence of bone marrow shielding.

Gronskaya, N. F.↗

NASA NTRS1981

An investigation of MAGSAT and complementary data emphasizing precambrian shields and adjacent areas of West Africa and South America

Accomplishments with regard to the mapping and analysis of MAGSAT data for the investigation of correlations between the magnetic field characteristics of South American and African shields are reported. Significant results in the interpretation of the global total-field anomalies and the anomaly patterns of Africa and South America are discussed. The central position of the Brazilian shield tends to form a negative total-field anomaly, consistent with findings for shields in equatorial Africa. Sedimentary sequences in the Amazon basin and in the Rio de Janeiro-Sao Paolo areas exhibit positive anomalies, also consistent with equatorial Africa. Results for the Caribbean Sea and Guyana regions are also described.

Hastings, D. A.↗

NASA NTRS1982

Starprobe thermal shield system design concepts

The mission goals, flight trajectory, and material durability requirements for the NASA Starprobe spacecraft are reviewed. The spacecraft will use a Jovian gravity assist to pass within four solar radii of the sun to study fields and particles near the sun, perform experiments dealing with relativity and gravity, and observe the structure of the solar atmosphere from the photosphere to the corona. Constraints on the system size and mass design are given, and the system is noted to be required to withstand 2500 K at perihelion, thermally insulate the instrument payload, have a tube for optical measurements, and provide protection from meteorite damage. A secondary shield is also required to dispense thermal radiation that passes the primary shield and could endanger the payload. Design options are discussed, along with temperature control requirements and a conical carbon-carbon primary shield with mass-loss rate characteristics sufficient to meet a 2.5 mg/sec criterion.

Maag, C. R.↗

NASA NTRS1985

Telescoping Shield for Point-Focusing Solar Concentrators

Telescoping shield normally stowed around solar receiver protects heat engine and supporting structure from overheating when concentrator aimed few degrees away from line to Sun. When extended, shield intercepts off center concentrated solar radiation. Heat spread out over thermally conductive shield and reradiated diffusely not to cause structural damage.

Argoud, M.↗

NASA NTRS1984

Free jet feasibility study of a thermal acoustic shield concept for AST/VCE application: Single stream nozzles

A technology base for the thermal acoustic shield concept as a noise suppression device for single stream exhaust nozzles was developed. Acoustic data for 314 test points for 9 scale model nozzle configurations were obtained. Five of these configurations employed an unsuppressed annular plug core jet and the remaining four nozzles employed a 32 chute suppressor core nozzle. Influence of simulated flight and selected geometric and aerodynamic flow variables on the acoustic behavior of the thermal acoustic shield was determined. Laser velocimeter and aerodynamic measurements were employed to yield valuable diagnostic information regarding the flow field characteristics of these nozzles. An existing theoretical aeroacoustic prediction method was modified to predict the acoustic characteristics of partial thermal acoustic shields.

Majjigi, R. K.↗

NASA NTRS1984

Galactic heavy-ion shielding using electrostatic fields

The shielding of spacecraft against galactic heavy ions, particularly high-energy Fe(56) nuclei, by electrostatic fields is analyzed for an arrangement of spherical concentric shells. Vacuum breakdown considerations are found to limit the minimum radii of the spheres to over 100 m. This limitation makes it impractical to use the fields for shielding small spacecraft. The voltages necessary to repel these Fe(56) nuclei exceed present electrostatic generating capabilities by over 2 orders of magnitude and render the concept useless as an alternative to traditional bulk-material shielding methods.

Townsend, L. W.↗

NASA NTRS1985

Pretinning Nickel-Plated Wire Shields

Nickel-plated copper shielding for wires pretinned for subsequent soldering with help of activated rosin flux. Shield cut at point 0.25 to 0.375 in. (6 to 10 mm) from cut end of outer jacket. Loosened end of shield straightened and pulled toward cut end. Insulation of inner wires kept intact during pretinning.

Igawa, J. A.↗

NASA NTRS1984

Free jet feasibility study of a thermal acoustic shield concept for AST/VCE application-dual flow. Comprehensive data report. Volume 1: Test nozzles and acoustic data

Acoustic and diagnostic data that were obtained to determine the influence of selected geometric and aerodynamic flow variables of coannular nozzles with thermal acoustic shields are summarized in this comprehensive data report. A total of 136 static and simulated flight acoustic test points were conducted with 9 scale-model nozzles The tested nozzles included baseline (unshielded), 180 deg shielded, and 360 deg shielded dual flow coannular plug configurations. The baseline configurations include a high radius ratio unsuppressed coannular plug nozzle and a coanuular plug nozzle and a coannular plug nozzle with a 20-chute outer stream suppressor. The tests were conducted at nozzle temperatures and pressure typical of operating conditions of variable cycle engine.

Janardan, B. A.↗

NASA NTRS1986

Jet shielding of jet noise

An experimental and theoretical study was conducted to develop a validated first principle analysis for predicting the jet noise reduction achieved by shielding one jet exhaust flow with a second, closely spaced, identical jet flow. A generalized fuel jet noise analytical model was formulated in which the acoustic radiation from a source jet propagates through the velocity and temperature discontinuity of the adjacent shielding jet. Input variables to the prediction procedure include jet Mach number, spacing, temperature, diameter, and source frequency. Refraction, diffraction, and reflection effects, which control the dual jet directivity pattern, are incorporated in the theory. The analysis calculates the difference in sound pressure level between the dual jet configuration and the radiation field based on superimposing two independent jet noise directivity patterns. Jet shielding was found experimentally to reduce noise levels in the common plane of the dual jet system relative to the noise generated by two independent jets.

Simonich, J. C.↗

NASA NTRS1986

Topographic evidence for shield volcanism on Io

Similarities between terrestrial shield volcanoes and a volcano on Io observed in Voyager I imagery of the satellite at 30 deg S, 246 deg W are delineated. A photoclinometry model was used to numerically estimate the slope based on the Minnaert photometric function. The slope values are accurate to within 10 deg on the sun-facing slope and 1 deg on the shadow side. As found with shield volcanoes, the feature has a central edifice, 40-50 km in diameter, and a broad, elliptical base, 77 x 90 km across. The summit of the Io volcano is 2.2-2.8 km above the surrounding plane and contains a caldera about 5 km in diameter. The similarity in shape between basaltic terrestrial shield volcanoes and the Io volcano indicates that the Io feature may also be composed of basalt. The composition could be sulfur if the heat flow was under 0.05 W/sq m, as it might have been in later stages of formation.

Moore, J. M.↗

NASA NTRS1988

Flexible Protective Shield For Newly Welded Joints

Simple device promotes defect-free welds in oxidation-prone metals. Welding torch pulls trailing shield behind to provide protective shield of argon gas over hot weld bead. Guide at front of torch holder feeds welding wire to joint. Shield bent or straightened to fit closely against weld joint.

Dyer, Gerald E.↗