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Torr, D. G.

Publications and source records attributed to Torr, D. G..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

OH A 2Sigma - X 2Pi (0,0) band rotational line emission rate factors

This paper presents the results of the emission-rate factor (g factor) calculations for the (0,0) band of the OH (A 2Sigma - X 2Pi) system, for the temperatures 200.0, 240.0, 296.0, 300.0, and 500.0 K, as well as for the individual g factors for each rotational line of the band. The derived g factor at 240 K for the entire band is 0.00055 + or - 0.00011 photon/sec. The g factor for the entire band was found to decrease with increasing temperature, but the difference in the change was less than 10 percent for the temperature range studied. The data on the individual rotational line g factors are valuable for future work on determining OH concentration profiles in the atmosphere, through the observation of the UV fluorescence in the OH (A 2Sigma - X 2Pi) (0,0) band using high-resolution spectrometers of a low-scattered-light design.

Fennelly, J. A.↗
NASA NTRS1989

The behavior of the electron density and temperatue at Millstone Hill during the equinox transition study September 1984

The ionospheric electron density and temperature variations is simulated during the equinox transition study in September 1984 and the results are compared with measurements made at Millstone Hill. The agreement between the modeled and measured electron density and temperature for the quiet day (18 September) is very good but there are large differences on the day of the storm (19 September). On the storm day, the measured electron density decreases by a factor of 1.7 over the previous day, while the model density actually increases slightly. The model failure is attributed to an inadequate increase in the ratio of atomic oxygen to molecular neutral densities in the MSIS neutral atmosphere model, for this particular storm. A factor of 3 to 5 increase in the molecular to atomic oxygen density ratio at 300 km is needed to explain the observed decrease in electron density. The effect of vibrationally excited N sub 2 on the electron density were studied and found to be small.

Richards, P. G.↗
NASA NTRS1989

Temporal features of the outflow of heavy ionospheric ions in response to a high altitude plasma cavity

Using a hydrodynamic model for the plasma, it is demonstrated that the auroral plasma cavity is capable of drawing an appreciably large flux of oxygen ions, which are normally gravitationally bound. This escape mechanism of O(+) does not involve any additional heating or acceleration of the plasma in the ionosphere. The temporal evolution of the outflow shows that it starts near the cavity and penetrates into the ionosphere with a flux front moving down with the ion-acoustic speed. A steady outflow is reached in a few hours for a cavity at a height of one R(e) if the cavity is maintained. This time reduces to less than 1 hour for cavity heights less than 3000 km. During the transient state the outflux can appreciably exceed that in the steady state. In view of the horizontal convection, the transient outflow is of special significance. As the cavity descends, the ionospheric flux of O(+) increases; for the lower edge of the cavity in the altitude range 3000-10,000 km, the steady flux is found to be in the range 10 to the 7th to 10 to the 9th. An analysis for the steady state shows that outflow is controlled by the density scale height in the cavity.

Singh, Nagendra↗
NASA NTRS1988

A compact imaging spectrometer for studies of space vehicle induced environment emissions

On the basis of spectral measurements made from the Space Shuttle and on models of the possible Space Station external environment, it appears likely that, even at the planned altitudes of Space Station, photon emissions will be induced. These emissions will occur to some degree throughout the UV-visible-IR spectrum. The emissions arise from a combination of processes including gas phase collisions between relatively energetic ambient and surface emitted or re-emitted atoms or molecules, where the surface raises some species to excited energy states. At present it is not possible to model these processes or the anticipated intensity levels with accuracy, as a number of fundamental parameters needed for such calculations are still poorly known or unknown. However, it is possible that certain spectral line and band features will exceed the desired goal that contaminant emissions not exceed the natural zodiacal background. However, in the near infrared and infrared, it appears that this level will be exceeded to a significant degree. Therefore it will be necessary to monitor emission levels in the vicinity of Space Station, both in order to establish the levels and to better model the environment. In this note, we briefly describe a small spectrometer that is suitable for monitoring the spectrum from 1200A to less than or approximately 12,000A. This instrument uses focal plane array detectors to image this full spectral range simultaneously. The spectral resolution is 4 to 12A, depending on the portion of the wavelength range.

Torr, Marsha R.↗
NASA NTRS1988

The induced environment around Space Station

The potential impact of the International Space Station on its immediate environment is discussed, summarizing the results of recent investigations by NASA working groups. Consideration is given to the neutral-gas environment, induced photon emission, particulate contamination, the ionized environment, the Induced-environment Monitoring Package proposed for inclusion in the Space Station equipment, and recommendations for further research. Diagrams, drawings, graphs, and tables of numerical data are provided.

Torr, Marsha R.↗
NASA NTRS1988

Space station contamination study: Assessment of contaminant spectral brightness

The assessment of spectral brightness resulting from the ambient-contaminant interaction requires a knowledge of the details of cross sections and excitation mechanisms. The approach adopted was to utilize the spectral brightness measurements made on Spacelab 1 and on the S3-4 spacecraft to identify source mechanisms, key cross sections and hence, the abundance of contaminant species. These inferred abundances were then used to update the composition comprising the total column concentrations predicted by the Science and Engineering Associates' configuration contamination model for the Space Station and to scale the irradiances to four altitudes: 300, 350, 400, and 463 km. The concentration irradiances are compared with zodiacal natural background levels. The results demonstrate that emissive contamination is significantly more severe than anticipated. It is shown that spectral emissions can become competitive with the zodiacal background up to altitudes as high as 400 km for the vacuum ultraviolet and visible emissions.

Torr, D. G.↗
NASA NTRS1988

Calculation of space station infrared irradiance from atmosphere-induced emissions

The excitation mechanisms and radiance estimates over the 1 to 10 micron region for CO2(v), H2O(v), CO(v), OH(v), NO2(2B-2A) and N2(B3 pi - A3 sigma) are discussed. The infrared irradiance of the Space Station at an altitude of 460 km was estimated. The surface material was presumed to be non-carbonaceous and inert. The determined number densities of the various gases relevant to the Space Station from both ambient and outgassing sources are presented. A model for the production of and emission from the infrared active molecules was constructed that considers two classes of production processes: (1) gas phase excitation of molecules in the near Station environment by collision with ambient flux; and (2) surface processes that lead to molecular excitation. A composite spectrum of all major emitting species shows that the observed irradiance is non-uniform over the 1 to 8 micron region. The comparison of predicted irradiance with the zodiacal background indicates that the Space Station infrared background from atmosphere-induced emissions may be a problem of consequence.

Fraser, M. E.↗
NASA NTRS1988

Ratios of photoelectron to EUV ionization rates for aeronomic studies

This paper presents calculations performed on the photoelectron impact to EUV photoionization rate ratios for atmospheric O, O2, and N2, and also for the production of N(+) by photodissociative ionization of N2. It was found that the ratios vary greatly with altitude. At high altitudes in the absence of photoelectron transport, the O(+) and N2(+) ionization rate ratios are about 0.35, but they increase with increasing optical depth; in the vicinity of the ionization peak, the photoelectron rate can exceed the EUV ionization rate for O(+) and N2(+). At high altitudes, the O2(+) ionization rate ratio is about half that of O(+); this ratio increases with increasing optical depth to reach a peak of about 0.4. There are also seasonal variations in the ratios at high altitudes depending on the magnitude of the conjugate photoelectron flux.

Richards, P. G.↗
NASA NTRS1988

Optical environment of the Spacelab 1 mission

The passing of large orbital vehicles through the space environment often generates such emissions as glows on or near the vehicle surface and halos surrounding the vehicle. These induced emissions may affect observations made with the optical instrumentation carried by the vehicles. The glows' causative mechanisms appear to be a complex function of altitude, time in orbit, materials, insolation, and vehicular size and orientation. Attention is presently given to contamination environment data obtained for the instrument suite carried by the Spacelab 1 Space Shuttle mission.

Torr, Marsha R.↗
NASA NTRS1988

Imaging spectrometer for high resolution measurements of stratospheric trace constituents in the ultraviolet

A high-resolution spectrometer has been developed for studies of minor constituents in the middle atmosphere at ultraviolet wavelengths. In particular, the instrument is intended for observations of upper stratospheric UV bands. The spectrometer has a slit width of 0.08 A obtained by means of an echelle grating and a cross-disperser grating. The image plane detector is an intensified CCD consisting of a high gain proximity focused image intensifier that is fiber optically coupled to a two-dimensional CCD array. An instantaneous bandwidth of 9.2 A is resolved across 488 pixels at 0.018 A/pixel, permitting simultaneous acquisition of multiple lines of selected OH bands and the neighboring background. The spectrometer and the approach have been successfully demonstrated as a technique for measuring the concentration of OH on two high-altitude balloon flights. This paper reports the instrument design and its achieved performance.

Torr, Marsha R.↗
NASA NTRS1988

Hydrodynamic models of the plasmasphere

A brief history of the application of hydrodynamic models to the understanding of the plasmaspheric density distribution is presented. Then results from recent modeling are discussed in more detail and areas of agreement between theory and measurement are established. Finally, some calculations are presented which indicate important discrepancies between theory and measurement.

Richards, P. G.↗
NASA NTRS1988

Review of microscopic plasma processes of occurring during refilling of the plasmasphere

Refilling of the plasmashere after geomagnetic storms involves both macroscopic and microscopic plasma processes. The latter types of processes facilitate the refilling by trapping the plasma in the flux tube and by thermalizing the interhemispheric flow. A review of studies on microscopic processes is presented. The primary focus in this review is on the processes when the density is low and the plasma is collisionless. The discussion includes electrostatic shock formation, pitch angle scatterring extended ion heating and localized ion heating in the equatorial region.

Singh, N.↗
NASA NTRS1988

A modified Lorentz theory as a test theory of special relativity

Attention has been given recently to a modified Lorentz theory (MLT) that is based on the generalized Galilean transformation. Some explicit formulas within the framework of MLT, dealing with the one-way velocity of light, slow-clock transport, and the Doppler effect are derived. A number of typical experiments are analyzed on this basis. Results indicate that the empirical equivalence between MLT and special relativity is still maintained to second order terms. The results of previous works that predict that the MLT might be distinguished from special relativity at the third order by Doppler centrifuge tests capable of a fractional frequency detection threshold of 10 to the -15th are confirmed.

Chang, T.↗
NASA NTRS1988

Dual properties of spacetime under an alternative Lorentz transformation

A coordinate time, t(A), with absolute synchronization is defined as an alternative fourth spatial coordinate for model universes with flat space-time, and the theoretical implications of t(A) are explored in detail. Particular attention is given to a t(A)-based reformulation of the Lorentz transformation, the generalized Galilean transformation, which is found to offer significant advantages in understanding special-relativistic phenomena such as length contraction, time dilation, and the interaction of objects with the physical vacuum. With respect to astrophysical observations of superluminal motion, it is shown that the problem of causality violation can be avoided; the theory also predicts that weak anisotropic effects may be detectable in the earth reference frame.

Chang, T.↗
NASA NTRS1987

Measurements of OH(X2pi) in the stratosphere by high resolution UV spectroscopy

This paper reports the first results obtained using high spectral resolution imaging ultraviolet spectroscopy to observe multiple rotational lines of OH A2 Sigma-X2pi (0-0) band. A 9.2 A spectral segment from 3075.8 A to 3085.0 A is imaged at 0.08 A FWHM spectral resolution, allowing the simultaneous acquisition of six of the brightest OH resonance fluorescence emission lines. The high spectral resolution and low scattered light design of the instrument allows these lines to be detected above the Rayleigh scattered sunlight background. The technique permits remote sensing of stratospheric OH from a high altitude instrument. The instrument was flown to an altitude of 40 km on Aug. 25, 1983, and again on June 12, 1986, on scientific balloons from Palestine, TX. The OH profiles inverted from the limb scans made during these flights are reported here. These profiles represent the first measurements of the temporal variation of OH over an extended height range. The results demonstrate that the technique can be used to monitor OH from orbit.

Torr, D. G.↗
NASA NTRS1987

Interpretation of the N2 LBH glow observed on the S3-4 spacecraft

Emissions in the vacuum ultraviolet Lyman-Birge-Hopfield (LBH) bands of N2 were observed at night from the S3-4 spacecraft and from the Space Shuttle. No atmospheric source of this emission was identified. Conway et al. have reported that the intensity of the S3-4 LBH emission varied as the cube power of the N2 or N2O concentration. A vehicle-atmosphere interaction was suggested as the source but it was found that the needed excitation cross section would have to be unacceptably large. Recent models of the gas concentration build-up around large space vehicles predict concentrations that may be consistent with the observe LBH intensity variation with altitude. The emission in the model is generated primarily by secondary collisional excitation by ambient N2 and/or O of desorbed metastable molecular constituents. A Chapman-like production function in the induced gaseous environment results in the observed cube power of the N2 concentration altitude variation. A cross section of approximately 2.5 x 10(-18) sq cm is required for excitation of desorbed metastable N2(A) to the N2 (a 1 Pi g) state to account for the observed intensities.

Torr, D. G.↗
NASA NTRS1987

The natural background at Shuttle altitudes

In order to make astronomical observations from the Shuttle, the observer needs good information on the intensities and spectral characteristics of various sources. This paper presents a model spectrum for the natural airglow background. The spectrum is modeled over a wavelength range extending from the extreme ultraviolet to the near-infrared. This model is based on the present knowledge of the upper atmosphere. The effect of different viewing configurations is illustrated, together with day-to-night variations. The results synthesized here assume an ideal vehicle in the sense that no contaminant emissions are induced by the Shuttle and payload. These spectra therefore represent a baseline which can be used to locate unanticipated or nonambient features.

Torr, Marsha R.↗