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Johnson, F. S.

Publications and source records attributed to Johnson, F. S..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Composition and physics of the lunar atmosphere.

The existence in the lunar atmosphere of helium, neon, argon, and possibly molecular hydrogen has been confirmed by the Apollo 17 mass spectrometer. The observed helium concentrations and distribution agree closely with model predictions for a non-condensable gas based on a solar wind source, thermal escape and a Monte Carlo random walk calculated longitudinal distribution. Heavier gases are lost by photoionization and subsequent sweeping away by the solar wind electric field. The observed nighttime neon concentration of 80,000 molecules per cu cm is consistent with expected amounts. Argon, however, is adsorbed on the lunar surface late at night when the surface temperature is lowest. It shows the expected predawn enhancement exhibited by condensable gases released into the atmosphere at the sunrise terminator. Hydrogen appears to exist in the molecular rather than atomic state. Its observed concentration is less than a factor of 3 higher than that predicted by a model similar to that used for helium.

Hoffman, J. H.↗
NASA NTRS1973

Variations in density and chemical composition at 120 km from chemical and dynamical processes.

Atmospheric parameters show both systematic and random patterns of behavior at 120 km altitude. Variations in density, temperature, pressure, and especially atomic oxygen concentration are important. The variations are particularly significant because constant boundary conditions at this altitude have commonly been assumed in atmospheric model making. It is surprising how well the assumption of constant boundary conditions has served over the past decade. However, their use has probably introduced erroneous concepts into the field of atmospheric structure, or at least held off the recognition and introduction of important new concepts. The variations at 120 km are caused by changes in energy input into the upper atmosphere, including internal gravity waves and tidal energy from below, and changes in the transport processes within the atmosphere.

Johnson, F. S.↗
NASA NTRS1973

Composition and dynamics of lunar atmosphere

The model of lunar atmosphere is updated to take into account new information on the dynamics and amounts of H2, He-4, Ne-20, Ar-36, and Ar-40. Helium and neon appear to be in close balance with the solar wind, although Ar-36 is depleted in the atmosphere, suggesting that surface materials are not saturated with argon. Atmospheric carbon compounds, which should result from the solar wind influx of carbon, remain undetected, as do nitrogen compounds. However, evidence of a volcanic gas release is presented, which suggests the transient presence of these elements.

Hodges, R. R., Jr.↗
NASA NTRS1973

Lunar atmospheric composition results from Apollo 17

The Apollo 17 mass spectrometer has confirmed the existence of helium, neon, argon, and possibly molecular hydrogen in the lunar atmosphere. Helium and neon concentrations are in agreement with model predictions based on the solar wind as a source and their being noncondensable gases. Ar-40 and Ar-36 both exhibit a predawn enhancement which indicates that they are condensable gases on the nightside and are re-released into the atmosphere at the sunrise terminator. Hydrogen probably exists in the lunar atmosphere in the molecular rather than atomic state, having been released from the surface in the molecular form. Total nighttime gas concentration of known species in the lunar atmosphere is 200,000 molecules/cu cm.

Hoffmann, J. H.↗
NASA NTRS1972

Vacuum measurements on the lunar surface.

Results of measurements of neutral gas pressure on the lunar surface made with a cold cathode ionization gauge carried to the moon by Apollo 14. The vacuum quality at the landing site is much influenced by the adsorption of rocket gases and their later release. During surface operations by the astronauts, the pressure was near 10 to the minus 8th torr. No data were obtained between the time of the surface operations and lunar sunset about 12 days later, at which time the temperature fell rapidly to the vicinity of 100 K. The pressure was about 10 to the minus 12th torr shortly after sunset, but intermittent releases of gas, perhaps from within the moon itself, occasionally raised the pressure by less than an order of magnitude for as long as a day or two at a time and on one occasion to about 10 to the minus 10th torr for about an hour. At lunar sunrise, as the surface was warmed rapidly to about 300 K, the pressure rose rapidly to about 10 to the minus 10th torr, most likely due to the release of absorbed gases in the immediate landing area or on the landing module itself. For comparison with interplanetary vacuum conditions, the directed pressure of the solar wind is usually less than 10 to the minus 11th torr and the pressure of random gas motion within the solar wind, less than 10 to the minus 13th torr.

Johnson, F. S.↗
NASA NTRS1972

Cold cathode gage experiment (lunar-atmosphere detector)

A preliminary evaluation of the cold cathode gage experiment which was included in the ALSEP to determine the amount of gas present on the lunar surface is reported. The instrument, electronic circuitry, and deployment are described. The preliminary results are summarized and include temperature history, and variations in gas concentration detected after deployment.

Johnson, F. S.↗
NASA NTRS1972

Transport processes in the thermosphere.

Description of two different approaches which have been undertaken to consider horizontal transport in the upper atmosphere by large-scale circulation. First and most direct, the horizontal wind field in the middle and upper thermosphere was calculated based on the pressure distributions derived from satellite orbital decay observations. The continuity conditions were used to calculate the vertical motions. The second approach was to evaluate the energy deficits or surpluses as a function of altitude and latitude and to assume the presence of vertical motions sufficient to balance these deficits or surpluses by compressional heating or cooling. Then continuity conditions were used to derive horizontal winds. The results of the two approaches are compatible, and are largely complementary. Downward velocities are near 1 m/sec at 300 km over the diurnal minimum and the winter polar region, and 1 cm/sec at 100 km over the winter polar region.

Johnson, F. S.↗
NASA NTRS1972

Observations of lunar atmosphere.

A cold cathode ionization gauge was left on the lunar surface by the Apollo 14 astronauts to measure the neutral gas density on the moon. The gauge has detected the presence of a very low concentration of atmospheric particles at night, about 200,000 per cu cm. Gas clouds of locally greater concentrations have been observed at times, and, while the possibility that these are artifacts associated with the Apollo hardware cannot be conclusively ruled out, the clouds appear to be of natural origin. Contaminant gases due to the Apollo operation dominate during the lunar day, but these may dissipate within a few months.

Johnson, F. S.↗
NASA NTRS1972

Lunar atmosphere measurements.

Cold cathode ionization gauges were left on the lunar surface during Apollo missions 14 and 15 to measure the amount of lunar gas. The observed nighttime concentration is very low, about 200,000 per cu cm, which is less than the neon concentration that might be expected from the solar wind. This suggests that the lunar surface is not saturated with solar wind neon, and hence that less neon is being released from the surface than impinges upon it. The low nighttime concentration shows that contaminant gases from the Apollo operations freeze out at night or become adsorbed on the cold lunar surface. Observed daytime concentrations have been two orders of magnitude greater than the nighttime values and appear to be due mainly to contamination in the landing area. The rate at which the contamination is decreasing is characterized by a time constant of a few months. Gas clouds have been seen at times and these appear to have been released from Apollo hardware left on the lunar surface.

Johnson, F. S.↗
NASA NTRS1971

Lunar atmosphere

Lunar atmospheric contributions from solar wind, meteoric volatilization, internal degassing and rocket gases, discussing day and night neon concentrations

Johnson, F. S.↗
NASA NTRS1971

Lunar atmosphere

Solar wind, meteoric volatilization, and internal degassing contributing to lunar rarefied atmosphere, and transient contributions produced by rocket gases during lunar missions

Johnson, F. S.↗
NASA NTRS1969

Origin of planetary atmospheres.

Planetary atmospheres origin, discussing earth formation by planetesimals accumulation and similarity to Mars and Venus, volatiles in outer planets, etc

Johnson, F. S.↗