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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Performance of 75-millimeter bore arched outer-race ball bearings

An investigation was performed to determine the operating characteristics of 75-mm bore, arched outer-race bearings, and to compare the data with those for a similar, but conventional, deep groove ball bearing. Further, results of an analytical study, made using a computer program developed previously, were compared with the experimental data. Bearings were tested up to 28,000 rpm shaft speed with a load of 2,200 N (500 lb). The amount of arching was 0.13, 0.25, and 0.51 mm (0.005, 0.010, and 0.020 in). All bearings operated satisfactorily. The outer-race temperatures and the torques, however, were consistently higher for the arched bearings than for the conventional bearings

Coe, H. H.↗
NASA NTRS1978

Predicted and experimental performance of jet-lubricated 120-millimeter-bore ball bearings operating to 2.5 million DN

Bearing inner- and outer-race temperatures and friction power losses were calculated using two computer programs. The values obtained were compared with previously reported experimental data for 120 mm bore bearings which operated at thrust loads to 22 240 N (5000 lb), shaft speeds to 20 800 rpm, and with two lubricant flow rates. One program severely underestimated the power loss, while the other, called SHABERTH, provided a good prediction of both race temperatures and power losses.

Coe, H. H.↗
NASA NTRS1978

Research in millimeter wave techniques

During the past six months, efforts on this project have been devoted to: (1) continuation of construction and testing of a 6 GHz subharmonic mixer model with extension of the pumping frequency of this mixer to omega sub s/4, (2) construction of a 183 GHz subharmonic mixer based on the results of tests on this 6 GHz model, (3) ground-based radiometric measurements at 183 GHz, (4) fabrication and testing of wire grid interferometers, (5) calculations of reflected and lost power in these interferometers, and (6) calculations of the antenna temperature due to water vapor to be expected in down-looking radiometry as a function of frequency. Significant events during the past six months include: (1) Receipt of a 183 GHz single-ended fundamental mixer, (2) attainment of 6 db single sideband conversion loss with the 6 GHz subharmonic mixer model by using a 1.5 GHz (omega sub s/4) pump frequency, (3) additional ground-based radiometric measurements and (4) derivation of equations for reflection and loss for wire grid interferometers.

Mcmillan, R. W.↗
NASA NTRS1978

Millimeter wave propagation modeling of inhomogeneous rain media for satellite communications systems

A theoretical propagation model that represents the scattering properties of an inhomogeneous rain often found on a satellite communications link is presented. The model includes the scattering effects of an arbitrary distribution of particle type (rain or ice), particle shape, particle size, and particle orientation within a given rain cell. An associated rain propagation prediction program predicts attenuation, isolation and phase shift as a function of ground rain rate. A frequency independent synthetic storm algorithm is presented that models nonuniform rain rates present on a satellite link. Antenna effects are included along with a discussion of rain reciprocity. The model is verified using the latest available multiple frequency data from the CTS and COMSTAR satellites. The data covers a wide range of frequencies, elevation angles, and ground site locations.

Persinger, R. R.↗
NASA NTRS1978

The phase of the crosspolarized signal generated by millimeter wave propagation through rain

Proposed schemes for cancelling rain-induced crosstalk in dual-polarized communications systems depend upon the phase relationships between the wanted and unwanted signals. This report investigates the phase relationship of the rain-generated crosspolarized signal relative to the copolarized signal. Theoretical results obtained from a commonly accepted propagation model are presented. Experimental data from the Communications Technology Satellite beacon and from the Comstar beacon are presented and the correlation between theory and data is discussed. An inexpensive semi-adaptive cancellation system is proposed and its performance expectations are presented. The implications of phase variations on a cancellation system are also discussed.

Overstreet, W. P.↗
NASA NTRS1978

1 millimeter continuum observations of extragalactic objects

Continuum observations of 23 extragalactic objects have been made at a wavelength of 1 mm; nine of the 23 have been definitely detected at this wavelength. The sources detected include seven from which the 1-mm emission appears to be nonthermal, and two from which the emission appears to be thermal radiation from dust. Repeated observations of the brightest nonthermal sources permitted a search for 1-mm variations on time scales of one month to three years. BL Lac was observed to vary by more than a factor of 2 in flux, and 3C 84, 3C 120, and 3C 273 showed possible variations; 3C 279 showed no variations greater than + or - 30%. The 1-mm variations of BL Lac appear to be correlated with variations at radio wavelengths. The other sources with nonthermal spectra detected were 3C 111 and M87; the two thermal sources detected were NGC 253 and M82. Comparison of the latter two 1-mm measurements with 2.6-mm CO measurements suggests that the CO line in these galaxies is not heavily saturated.

Elias, J. H.↗
NASA NTRS1977

Infrared and millimeter wave techniques for the Cosmic Background Explorer Satellite

The Cosmic Background Explorer Satellite will employ infrared and microwave techniques to gain information about the very early universe. Three instruments will cover the spectral range from 8 microns to 13 mm, determining both the spectrum and angular distribution of the large scale background radiation fields. A cryogenic polarizing Michelson interferometric spectrometer will measure the spectrum of the 3 deg K relic radiation from the big bang with precision. Four differential microwave radiometers will map the sky from 23 to 90 GHz in a search for anisotropy of the universe. A broadband cryogenic IR photometer will map zodiacal dust emission, galactic dust, and an extragalactic residual component.

Mather, J. C.↗
NASA NTRS1978

On the detectability of millimeter wavelength spectral lines from planetary atmospheres

This paper adopts a simple line-formation model to estimate detection limits on the fractional absorption produced by molecular lines in the spectra of the planets, when observed with the 14-m antenna and low-noise receivers of the Five College Radio Astronomy Observatory. The results, which can readily be adjusted for receiver and telescope characteristics of other observatories, indicate that three kinds of observing programs may prove fruitful: (1) programs to monitor temporal variations of the strong CO absorption in the spectrum of Venus and Mars; (2) searches for weak absorption lines of other molecules, which are particularly promising for Venus: and (3) efforts to measure broad features in the continuous spectra of Venus, and possibly Jupiter, produced by molecules deep in the planetary atmospheres. Except for delineation of broad features of NH3 and possibly H2O near 25 GHz, hardly any useful observations can be made at frequencies less than 60 GHz.

White, R. E.↗
NASA NTRS1979

Millimeter wavelength spectroscopy and continuum studies of the planets

Careful observations were made at 86.1 GHz to derive the absolute brightness temperatures of the Sun (7914 + or - 192 K), Venus (357.5 + or - 13.1 K), Jupiter (179.4 + or - 4.7K), and Saturn (153.4 + or - 4.8 K) with a standard error of about 3%. This is a significant improvement in accuracy over previous results. A stable transmitter and novel superheterodyne receiver were constructed and used to determine the effective collecting area of the MWO 4.9 m antenna relative to a previously calibrated standard gain horn. The thermal scale was set by calibrating the radiometer with carefully constructed and tested hot and cold loads. The brightness temperatures may be used to establish an absolute calibration scale and to determine the antenna aperture and beam efficiencies of other radio telescopes at 3.5 mm wavelength.

Vandenbout, P. A.↗
NASA NTRS1979

Research in millimeter wave techniques

The following technical developments are described: (1) a reliable 183 GHz subharmonic mixer, (2) a precision noise figure test setup, (3) the successful deposition of SiO2 on a noncontacting backshort, and (4) sturdier whisker points used for diode contacting.

Forsythe, R. E.↗
NASA NTRS1979

Comparison of predicted and measured elastohydrodynamic film thickness in a 20-millimeter-bore ball bearing

Elastohydrodynamic film thicknesses were measured for a 20-mm bore ball bearing using the capacitance technique. The bearing was thrust loaded to 90, 445, and 778 N (20, 100, and 175 lb). The corresponding maximum contact stress on the inner race was 1.28, 2.09, and 2.45 GPa (185 000, 303,000, and 356, 000 psi). Test speeds ranged from 400 to 15,000 rpm. Measurements were taken with four different lubricants: (1) synthetic paraffinic; (2) synthetic paraffinic with additives; (3) synthetic type II aircraft oil; and (4) synthetic cycloaliphatic hydrocarbon traction fluid. The test bearing was mist lubricated. Test temperatures were 27, 65, and 121 C (80, 150, and 250 F). The measured results for the various test parameters were compared to theoretical predictions from computer programs. Also the data were plotted on dimensionless coordinates and compared to several classical isothermal theories.

Coy, J. J.↗
NASA NTRS1979

Correlation of asperity contact-time fraction with elastohydrodynamic film thickness in a 20-millimeter-bore ball bearing

Elastohydrodynamic film thicknesses and asperity contact-time fractions were measured for a 20 mm bore ball bearing by using the capacitance and conductance techniques. The bearing was thrust loaded to 90, 445, and 778 N. The corresponding maximum stresses on the inner race were 1.28, 2.09, and 2.45 GPa. The test speed ranged from 400 to 15,000 rpm. The test bearing was mist lubricated with a MIL-L-23699A turbine oil. The temperature was 27 C. The experimental results were correlated to give the percent film (no-contact-time fraction) as a function of measured film thickness. Measurements were made for three test series that represented the test bearing in various conditions of run-in. The measurements show that the percent film changes with bearing run-in time. The experimental results agreed well with theoretical predictions based on surface trace analysis for a new bearing. For the run-in state, they agreed with previously reported experimental results. The results show that asperity contact existed at a film thickness-roughness ratio lambda of 6.0 or less for a new bearing. After run-in, no asperity contact occurred at a lambda of 3.5 or greater.

Coy, J. J.↗
NASA NTRS1978

One-millimeter brightness temperatures of the planets

Results are reported for a bolometric determination of the relative brightness at a wavelength of 1 mm of Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune. The relative measurements are converted to absolute temperatures by using a thermal model for Mars, which was checked by observations of Mars and Jupiter at two different epochs. The mean planetary disk temperatures are found to be 320 + or 16 K for Mercury, 276 + or - 14 K for Venus, 145 + or - 7 K for Saturn, 168 + or - 8 K for Jupiter, 87 + or - 7 K for Uranus, and 96 + or - 10 K for Neptune. These results are compared with previous determinations at other wavelengths, and some aspects of the observations of the individual planets are briefly discussed.

Werner, M. W.↗