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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Calorimeter probes for measuring high thermal flux

The paper describes expendable, slug-type calorimeter probes developed for measuring high heat-flux levels of 10-30 kW/sq cm in electric-arc jet facilities. The probes are constructed with thin tungsten caps mounted on Teflon bodies; the temperature of the back surface of the tungsten cap is measured, and its rate of change gives the steady-state, absorbed heat flux as the calorimeter probe heats to destruction when inserted into the arc jet. It is concluded that the simple construction of these probes allows them to be expendable and heated to destruction to obtain a measurable temperature slope at high heating rates.

Russell, L. D.↗
NASA NTRS1981

Lower-curing-temperature PMR polyimides

Studies were performed to achieve a lower-curing-temperature PMR polyimide. The use of m-aminostyrene as the end-cap instead of the monoalkyl ester of 5-normbornene-2,3 dicarboxylic acid was investigated in typical PMR formulations. Model compound studies were also performed. Differential scanning calorimetry studies were performed on model compounds and neat resins to establish their melting and curing characteristics. The elevated temperature weight loss characteristics of neat resins and graphite fiber composites were determined. The room temperature and short-time 260 C (500 F) mechanical properties of the composites were also determined. The use of m-aminostyrene end-caps reduced the final cure temperature of PMR resins by about 55 C (100 F), but the composites prepared with these resins are limited to use temperatures of about 260 C (500 F).

Serafini, T. T.↗
NASA NTRS1978

Space fabrication demonstration system

The lower right aluminum beam cap roll forming mill was delivered and installed in the beam builder. The beam was brought to full operational status and beams of one to six bay lengths were produced to demonstrate full system capability. Although the cap flange waviness problem persists, work is progressing within cost and schedule.

Source record↗
NASA NTRS1980

Structural attachments for large space structures

The feasibility of fabricating beams in space and using them as components of a large, crew assembled structure, was investigated. Two projects were undertaken: (1) design and development of a ground version of an automated beam builder capable of producing triangular cross section aluminum beams; and (2) design and fabrication of lap joints to connect the beams orthogonally and centroidal end caps to connect beams end to end at any desired angle. The first project produced a beam building machine which fabricates aluminum beams suitable for neutral buoyancy evaluation. The second project produced concepts for the lap joint and end cap. However, neither of these joint concepts was suitable for use by a pressure suited crew member in a zero gravity environment. It is concluded that before the beams can be evaluated the joint designs need to be completed and sufficient joints produced to allow assembly of a complex structure.

Pruett, E. C.↗
NASA NTRS1981

Icing tunnel tests of a glycol-exuding porous leading edge ice protection system on a general aviation airfoil

A glycol-exuding porous leading edge ice protection system was tested. Results show that the system is very effective in preventing ice accretion (anti-ice mode) or removing ice from an airfoil. Minimum glycol flow rates required for anti-icing are a function of velocity, liquid water content in the air, ambient temperature, and droplet size. Large ice caps were removed in only a few minutes using anti-ice flow rates. It was found that the shed time is a function of the type of ice, size of the ice cap, angle of attack, and glycol flow rate. Wake survey measurements show that there is no significant drag penalty for the installation or operation of the system tested.

Kohlman, D. L.↗
NASA NTRS1981

Ellipsoidal corrections for geoid undulation computations

The computation of accurate geoid undulations is usually done combining potential coefficient information and terrestrial gravity data in a cap surrounding the computation point. In doing this a spherical approximation is made that can cause the errors that were investigated. The equations dealing with ellipsoidal corrections developed by Lelgemann and by Moritz were used to develop a computational procedure considering the ellipsoid as a reference surface. Terms in the resulting expression for the geoid undulation are identified as ellipsoidal correction terms. These equations were developed for the case where the Stokes function is used, and for the case where the modified Stokes function is used. For a cap of 20 deg the correction can reach -33 cm.

Rapp, R. H.↗
NASA NTRS1981

Electromagnetic cascades in pulsars

The development of pair photon cascades initiated by high energy electrons above a pulsar polar cap is simulated numerically. The calculation uses the energy of the primary electron, the magnetic field strength, and the period of rotation as parameters and follows the curvature radiation emitted by the primary, the conversion of this radiation e(+) - e(-) pairs in the intense fields, and the quantized synchrotron radiation by the secondary pairs. A recursive technique allows the tracing of an indefinite number of generations using a Monte Carlo method. Gamma ray and pair spectra are calculated for cascades in different parts of the polar cap and with different acceleration models. It is found that synchrotron radiation from secondary pairs makes an important contribution to the gamma ray spectrum above 25 MeV, and that the final gamma ray and pair spectra are insensitive to the height of the accelerating region, as long as the acceleration of the primary electrons is not limited by radiation reaction.

Daugherty, J. K.↗
NASA NTRS1980

Status of high-temperature laminating resins and adhesives

High-temperature polymers now being developed as adhesives and composite matrices are reviewed, including aromatic polyimides, polybenzimidazoles, polyphenylquinoxalines, nadic end-capped imide oligomers, maleimide end-capped oligomers, and acetylene-terminated imide oligomers. The mechanical properties of laminates based on these resins are reported together with preliminary test results on the adhesive properties for titanium-to-titanium and composite-to-composite lap shear specimens.

Hergenrother, P. M.↗
NASA NTRS1980

The astronomical theory of climatic change on Mars

The response of Martian climate to changes in solar energy deposition caused by variations of the Martian orbit and obliquity is examined. A systematic study is presented of the seasonal cycles of carbon dioxide, water, and dust to provide a complete picture of the climate for various orbital configurations. A new theory for the formation of the polar laminae is developed on the basis of this systematic examination. For the present orbital configuration and climate of Mars, it is shown that regolith damping of the seasonal CO2 cycle is unlikely; the mean atmospheric pressure is probably in equilibrium with the regolith; the low albedo of the north H2O polar cap can be explained by an admixture of 85% ice and 15% dust; and the albedo of the polar caps and the polar heat budget are very sensitive to small variations in dust deposition.

Toon, O. B.↗
NASA NTRS1981

Modifying Stokes' function to reduce the error of geoid undulation computations

Errors in computations of the geoid undulation, which determines the position of the geoid with respect to a reference ellipsoid, introduced by various modifications of the Stokes' function in the Stokes integral formula for the undulation are examined in light of currently available harmonic coefficients. The variants considered include the conventional Molodenskii truncation theory, in which integration is limited to a spherical cap, and the variations suggested by Molodenskii (1958) and Meissl (1971). In computations of the undulation from gravity anomalies in a spherical cap and terrestrial and satellite harmonic potential coefficients (GEM 9 and GEM 10B), it is shown that either of the modifications to the conventional Molodenskii theory results in substantial reductions in truncation errors, with the simpler modification of Meissl even providing superior results in certain circumstances.

Jekeli, C.↗
NASA NTRS1982

"Sandwich" Stiffener for Composite Structural Panels

Concept uses commercial titanium honeycomb core brazed to cap material and panel skin. In fabrication of stringers, large sheets of cap material are brazed to pieces of honeycomb core of desired height. After brazing, individual stringers are cut by electrical-discharge machining, and stringers are subsequently brazed to skin. Sandwich beam stringer is light-weight, structurally-efficient, low-cost stiffener for metal-matrix composite structural panels.

Mcwithey, R. R.↗
NASA NTRS1983

Pressure Relief Valve

Valve cap seated on an O-ring lifts to relieve positive pressure. Is attached to vacuum system by screw-on housing. Caps are loosely tied to pipe with twine or thin wire to make recovery simple.

Brabbs, T. A.↗
NASA NTRS1981

On the dust zoning of rapidly rotating cometary nuclei

The effects of nuclear rotation on the surface of a cometary nucleus (a comet at 1 AU that is H2O dominated and has a radius of 1 km) are considered. It is shown that this dust does not accumulate uniformly on the surface, which here is considered spherical. While dust particles in the two polar cap regions and an equatorial belt remain at rest on the surface, those in two midlatitude bands migrate toward the equator, stopping at the two low latitudes to form dust ridges. As the nucleus spins up, both the polar caps and the equatorial belt shrink in size, and the dust ridges move toward the equator, eventually spinning off the dust from the nucleus when the nuclear rotation period is less than about 3.3 hr. For larger particles for which the gas buoyancy is negligible, migration takes place only if the rotation period is not significantly larger than the critical value of 3.3 hr or if the surface friction is abnormally small.

Houpis, H. L. F.↗
NASA NTRS1982

Electromagnetic cascades in pulsars

The development of pair-photon cascades initiated by high energy electrons above a pulsar polar cap is simulated numerically. The calculation uses the energy of the primary electron, the magnetic field strength, and the period of rotation as parameters, and follows the curvature radiation emitted by the primary, the conversion of this radiation to e(+)e(-) pairs in the intense fields, and the quantized synchrotron radiation by the secondary pairs. A recursive technique allows the tracing of an indefinite number of generations using a Monte Carlo method. Gamma-ray and pair spectra are calculated for cascades in different parts of the polar cap and with different acceleration models. It is found that synchrotron radiation from secondary pairs makes an important contribution to the gamma-ray spectrum above 25 MeV, and that the final gamma-ray and pair spectra are insensitive to the height of the accelerating region, as long as the acceleration of the primary electrons is not limited by radiation reaction.

Daugherty, J. K.↗
NASA NTRS1982

Thermospheric winds at high latitudes from chemical release observations

The considered investigation takes into account wind measurements conducted with the aid of 39 sounding rocket chemical release payloads. Attention is given to the geomagnetic dependence, winds and ion convection patterns, subauroral dayside measurements, evening auroral belt measurements, evening polar cap measurements, postmidnight polar cap measurements, midnight and early morning auroral belt measurements, late evening auroral belt measurements, and anomalous winds. The prevailing theme in presenting and interpreting the wind measurements between 160 and 320 km has been that the gross characteristics of the high-latitude wind system can be readily understood in terms of the pattern distribution of electric fields when the inertial properties of the neutral atmosphere and Coriolis forces are taken into account.

Heppner, J. P.↗
NASA NTRS1982

Addition polyimide adhesives containing various end groups

Addition polyimode oligomers have been synthesized from 3,3 prime, 4,4 prime-benzophenone tetracarboxylic acid dianhydride and 3,3 prime-methylenedianiline using a variety of latent crosslinking groups as end-caps. The nominal 1300 molecular weight imide prepolymers were isolated and characterized for solubility in amide, chlorinated and ether solvents, melt-flow and cure properties, glass transition temperature, and thermal stability on heating in an air atmosphere. Adhesive strengths of the polyimides were obtained both at ambient and elevated temperatures before and after aging at 232 C. Properties of the novel addition polyimides were compared to a known nadic end-capped adhesive, LARC-13.

Saint Clair, A. K.↗
NASA NTRS1982

The polar ionosphere as a source of energetic magnetospheric plasma

Data are presented on an additional ionospheric source composed of ions flowing upward out of the high latitude polar cap with energies in the range of approximately 10 eV to more than about 100 eV. The data are from the energetic ion composition spectrometer (EICS) on board the Dynamics Explorer-1 satellite, launched in August 1981. It is noted that the results presented are not inconsistent with the existence of a polar wind of the type predicted by Axford (1968) since ions with energies less than about 1 eV would have been excluded from the instrument by the generally positive vehicle potential. The results suggest that the polar wind is either modified in mass composition and energy by some as yet unidentified process or is supplemented by a new unrelated source of plasma. What is more, owing to the higher energies, the energetic polar cap ions described here enter the plasma sheet at greater distances than Cowley (1980) estimated and probably represent a significant source of plasma for the maintenance of the plasma sheet.

Shelley, E. G.↗
NASA NTRS1982

Lower-curing-temperature PMR polyimides

Partial substitution of a p-aminostyrene end-cap for the monomethyl ester of 5-norbornene-2, 3-dicarboxylic acid lowered the final cure temperature of typical PMR resins from 600 F to 500 F. The weight loss characteristics of neat resins and graphite fiber composites prepared by using the mixed end-cap approach were determined at 600 F. The room temperature and short-time elevated temperature mechanical properties of the composites at 550 F and 600 F were determined. The mechanical property retention characteristics of the composites at 550 F and 600 F are discussed.

Delvigs, P.↗