Engineering topics

Richards, P.

Publications and source records attributed to Richards, P..

10 records

NASA NTRS2001

Determination of Ionospheric Conductivities from UVI Intensity Ratios

Germany et al. examined the viability of using LBH emission ratios to infer auroral conductances, using modeled line brightnesses representative of the (then) planned UVI bandpasses. Here we extend that work by using actual UVI bandpass information instead of single modeled lines. Conductances are calculated using combined two stream and Field Line Interhemispheric Plasma (FLIP) model calculations to specify the ionosphere. The dependence of modeled conductances to UVI bandpass intensities is examined as a function of incident average energy, total energy flux, and changes in solar and magnetic activity levels. Potential parameterizations of conductance with UVI intensity ratios will be examined, as will error estimates of the conductance determinations.

Spann, James F., Jr.↗

NASA NTRS1995

Thermospheric nitric oxide from the ATLAS 1 and Spacelab 1 missions

Spectral and spatial images obtained with the Imaging Spectrometric Observatory on the ATLAS 1 and Spacelab 1 missions are used to study the ultraviolet emissions of nitric oxide in the thermosphere. By synthetically fitting the measured NO gamma bands, intensities are derived as a function of altitude and latitude. We find that the NO concentrations inferred from the ATLAS 1 measurements are higher than predicted by our thermospheric airglow model and tend to lie to the high side of a number of earlier measurements. By comparison with synthetic spectral fits, the shape of the NO gamma bands is used to derive temperature as a function of altitude. Using the simultaneous spectral and spatial imaging capability of the instrument, we present the first simultaneously acquired altitude images of NO gamma band temperature and intensity in the thermosphere. The lower thermospheric temperature images show structure as a function of altitude. The spatial imaging technique appears to be a viable means of obtaining temperatures in the middle and lower thermosphere, provided that good information is also obtained at the higher altitudes, as the contribution of the overlying, hotter NO is nonnegligible. By fitting both self-absorbed and nonabsorbed bands of the NO gamma system, we show that the self absorption effects are observable up to 200 km, although small above 150 km. The spectral resolution of the instrument (1.6 A) allows separation of the N(+)(S-5) doublet, and we show the contribution of this feature to the combination of the NO gamma (1, 0) band and the N(+)(S-5) doublet as a function of altitude (less than 10% below 200 km). Spectral images including the NO delta bands support previous findings that the fluorescence efficiency is much higher than that determined from laboratory measurements. The Spacelab 1 data indicate the presence of a significant population of hot NO in the vehicle environment of that early shuttle mission.

Torr, Marsha R.↗

NASA NTRS1994

N2 Lyman-Birge-Hopfield dayglow from ATLAS 1

Spectral measurements of the far ultraviolet dayglow were made from the ATLAS 1 shuttle mission using an intensified charge coupled device (CCD) imaging spectrometer array. The instrument imaged relatively large (177 A) segments of the spectrum simultaneously and had the capability to image altitude in the second dimension of the two-dimensional focal plane detector when the entrance slit of the instrument was oriented perpendicular to the limb of the Earth. The far ultraviolet (FUV) channel of the instrument used a CsTe photocathode rather than the more conventionally used and more solar blind CsI photocathode material. As a result, the spectra were also measured with good sensitivity at FUV wavelengths longer than 1500 A. In this paper, data are selected of specific interest to a study of the N2 Lyman-Birge-Hopfield system using two shuttle attitudes: In the first the field of view was held at a fixed tangent ray height of approximately 140 km while scanning in wavelength, providing repeated FUV spectra over a range of latitudes and allowing comparison with our thermospheric airglow model. In the second observing sequence the line of sight of the instrument was scanned down through the atmosphere but covered about 75% of the full wavelength range. This sequence allows comparison of height dependence,including O2 absorption effects, with the thermospheric model. In all cases, relatively good agreement is obtained with the model (run strictly in a predictive mode) in comparisions in which the line of sight must be intergrated along a path that spans a considerable range of conditions (height, local time, latitude, solar zenith angle). In the case of the data sets examined in this study the vibrational population distributions show mixed results. In one case the distribution agrees well with a theoretical model based on direct electron impact excitation without a significant cascade contribution. A second case indicated a lower population in nu' = 3 and a higher population in nu' = 6 than would be expected from direct impact excitation alone. This supports previous indications that conditions resulting in the cascade mechanism may not always be operative.

Torr, Marsha R.↗

NASA NTRS1993

Measurements of the anisotropy of the cosmic background radiation at 0.5 deg scale near the star Mu Pegasi

Results are presented from the third flight of the MAX experiment, an attitude-controlled balloon-borne millimeter-wave telescope with a 0.5 deg beam, a 1 deg chop, and a three-channel bolometric photometer. Several hours of high-quality data were obtained during a flight on 1991 June 5, including long integrations to search for CBR anisotropy, two separate measurements of dust in the Galactic plane, a brief scan of the Coma Cluster to search for the Sunyaev-Zel'dovich (SZ) effect, and a number of important systematic tests. Data from one of the long CBR integrations, carried out in a region of sky near the star Mu Pegasi, are presented. The primary structure in the data is shown to be emission from Galactic dust via its spectrum and correlation with the IRAS 100/micron map. Several approaches are used to fit this dust component and remove it from the data. An upper limit to CBR anisotropy of deltaT/T less than 2.5 x 10 exp -5 is obtained for a Gaussian autocorrelation function with coherence angle omega(c) = 25'. This limit is significantly higher than the measurement sensitivity of deltaT/T about 1 x 10 exp -5 due to the presence of residual structure in the data after removal of the dust component.

Meinhold, P.↗

NASA NTRS1991

Report of the direct infrared sensors panel

The direct infrared sensors panel considered a wide range of options for technologies relevant to the science goals of the Astrotech 21 mission set. Among the technologies assessed are: large format arrays; photon counting detectors; higher temperature 1 to 10 micro-m arrays; impurity band conduction (IBC) or blocked impurity band (BIB) detectors; readout electronics; and adapting the Space Infrared Telescope Facility and Hubble Space Telescope. Detailed development plans were presented for each of these technology areas.

Mccreight, Craig↗

NASA NTRS1990

The flow of plasma in the solar terrestrial environment

The overall goal of our NASA Theory Program was to study the coupling, time delays, and feedback mechanisms between the various regions of the solar-terrestrial system in a self-consistent, quantitative manner. To accomplish this goal, it will eventually be necessary to have time-dependent macroscopic models of the different regions of the solar-terrestrial system and we are continually working toward this goal. However, with the funding from this NASA program, we concentrated on the near-earth plasma environment, including the ionosphere, the plasmasphere, and the polar wind. In this area, we developed unique global models that allowed us to study the coupling between the different regions. These results are highlighted in the next section. Another important aspect of our NASA Theory Program concerned the effect that localized 'structure' had on the macroscopic flow in the ionosphere, plasmasphere, thermosphere, and polar wind. The localized structure can be created by structured magnetospheric inputs (i.e., structured plasma convection, particle precipitation or Birkland current patterns) or time variations in these input due to storms and substorms. Also, some of the plasma flows that we predicted with our macroscopic models could be unstable, and another one of our goals was to examine the stability of our predicted flows. Because time-dependent, three-dimensional numerical models of the solar-terrestrial environment generally require extensive computer resources, they are usually based on relatively simple mathematical formulations (i.e., simple MHD or hydrodynamic formulations). Therefore, another goal of our NASA Theory Program was to study the conditions under which various mathematical formulations can be applied to specific solar-terrestrial regions. This could involve a detailed comparison of kinetic, semi-kinetic, and hydrodynamic predictions for a given polar wind scenario or it could involve the comparison of a small-scale particle-in-cell (PIC) simulation of a plasma expansion event with a similar macroscopic expansion event. The different mathematical formulations have different strengths and weaknesses and a careful comparison of model predictions for similar geophysical situations provides insight into when the various models can be used with confidence.

Schunk, Robert W.↗

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 NTRS1984

SAGA: A project to automate the management of software production systems

The project to automate the management of software production systems is described. The SAGA system is a software environment that is designed to support most of the software development activities that occur in a software lifecycle. The system can be configured to support specific software development applications using given programming languages, tools, and methodologies. Meta-tools are provided to ease configuration. Several major components of the SAGA system are completed to prototype form. The construction methods are described.

Campbell, R. H.↗

NASA NTRS1980

A computer simulation of the midlatitude plasmasphere and ionosphere

A computer model has been developed to simulate species density, temperature, and plasma flow in the ionosphere and plasmasphere. A new approach, the flux preserving method involving a Newton iteration, is used to solve a system of governing equations comprising four second-order partial differentials. Tests are performed to demonstrate that the simulation converges to a stable steady state solution, then steady state ion fluxes are analyzed. Finally, simulations of the collapse of the sunset ionosphere are presented. Comparisons with satellite and radar data show good agreement in a number of cases.

Young, E. R.↗

NASA NTRS1980

Quenching of O+/2D/ by electrons in the thermosphere

Satellite measurements of relevant ionospheric parameters were used to determine the rate coefficient for quenching of O+(2D) by electrons as a function of temperature. The results agree with the theoretically determined rate coefficient to within statistical uncertainties. The study provides confirmation of the absolute magnitude of the rate coefficient given by theoretical calculation at these temperatures, but it also indicates a somewhat steeper dependence on electron temperature than that predicted by theory.

Torr, M. R.↗