Engineering topics

Torr, Marsha R.

Publications and source records attributed to Torr, Marsha R..

At least 19 records

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 NTRS1994

The ATLAS-1 mission

Atmospheric Laboratory for Applications and Science (ATLAS)-1 was launched on March 24, 1992, carrying an international payload of 14 investigations, and conducted a successful series of experiments and observations over the subsequent 9 days. The objectives included: measuring the solar irradiance at high precision; remote sensing of the composition of the stratosphere, mesosphere, and thermosphere using techniques for wavelengths from 300 A to 5 mm; and inducing auroras by means of 1.2 amp electron beams. A subset of these instruments will subsequently be flown in a series of shuttle missions at roughly 1-year intervals over an 11-year solar cycle. The frequent recalibration opportunities afforded by such a program allows the transfer of calibrations to longer duration orbiting observatories. The ATLAS-1 mission occurred at the same time as the Upper Atmosphere Research Satellite (UARS), TIROS-N, and ERB satellites were in operation, and correlative measurements were conducted with these. In all, the mission was most successful in achieving its objectives and a unique and important database was acquired, with many scientific firsts accomplished. This paper provides the mission overview for the series of papers that follow.

Torr, Marsha R.↗

NASA NTRS1994

ATLAS-1 and middle atmosphere global change

To understand the extent and trends of middle atmosphere change, it is necessary to establish the baseline of atmospheric behavior and its response to changes in solar irradiance over at least a solar cycle. An element in NASA's global change program is the ATLAS shuttle series. The international payload includes several instruments intended to make precise, absolute measurements of solar irradiance, each being calibrated before and after each shuttle flight. These instruments, in addition to obtaining an 11-year database, will also intercalibrate solar instruments on the Earth Radiation Budget (ERB) and Upper Atmosphere Research (UARS) satellites. Other instruments will measure the atmospheric composition and temperature, also intercalibrating instruments on Television and Infrared Observation Satellite (TIROS)-N and UARS. Some have flown on shuttle missions dating back to 1983 and it is hoped that the ATLAS series will provide a capability until the turn of the century. This paper reviews the early results of the ATLAS-1 mission, which flew between March 24 and April 2, 1992.

Torr, Marsha R.↗

NASA NTRS1993

The scientific objectives of the Atlas-1 Shuttle mission

Six remote sensing atmospheric instruments aboard the 9-day Atlas-1 Space Shuttle mission covered an unprecedented spectrum of regions in the 15-300 km altitude range, yielding a unique data base for the temperature, pressure, and compositions found therein. In addition, experiments were conducted in space plasma physics, which included aurora-induction for photometric imaging camera observations. Measurements were also made of the precipitation of energetic neutrals from the ring current.

Torr, Marsha R.↗

NASA NTRS1993

Thermospheric airglow emissions - A comparison of measurements from Atlas-1 and theory

A comprehensive thermospheric model is presently used to derive conditions appropriate to the time of the Atlas-1 Space Shuttle mission, comparing the slant-path intensities thus computed as a function of altitude, latitude, and local time with a dozen major emissions measured in the course of a specific observing sequence. The agreement thus obtained is found to be reasonably good, implying that the major thermospheric airglow-controlling processes are essentially understood.

Torr, Douglas G.↗

NASA NTRS1993

The first negative bands of N2(+) in the dayglow from the Atlas-1 Shuttle mission

While the integrated column intensities in the 0-0 band emission at 3914 A, as measured from the Atlas-1 mission, are found to be in good agreement with model values, Spacelab 1 intensities appear to have been significantly affected by vehicle-induced effects. The ion environment, in particular, appears to have been highly perturbed. The absence of the large pressurized double-Spacelab module, and the revised Space Shuttle Orbiter processing procedures, appeared to have yielded a much improved remote sensing environment.

Torr, Marsha R.↗

NASA NTRS1993

Retrieval of thermospheric atomic oxygen, nitrogen and temperature from the 732 NM emission measured by the ISO on ATLAS 1

The Imaging Spectrometric Observatory (ISO) was a part of the ATLAS 1 Mission flown on the shuttle Atlantis from March 24 to April 2, 1992. During limb scanning operations, the ISO measured the O+(2P) ion emission at 732 nm. We have used a numerical inversion technique to retrieve thermospheric atomic oxygen, molecular nitrogen and temperature profiles. These preliminary results indicate a lower thermospheric temperature cooler than that predicted by MSIS for the solar conditions during the mission. Although the densities agree at low altitudes, the reduced scale height produces O and N2 densities 25 percent lower than the MSIS at 300 km.

Fennelly, Judy A.↗

NASA NTRS1993

N(2P) in the dayglow - Measurement and theory

During the ATLAS-1 mission, the first dayglow altitude profiles were obtained of the N(2P) emission at 3466 A. These observations were made in the sunlit thermosphere using the Imaging Spectrometric Observatory. As all previous work on this emission has been done under auroral conditions, this study represents the first examination of the photochemical sources and sinks of N(2P) in the normal daytime thermospheric, with comparison with measurements. We find that the observations are explained by a model in which the major source is photodissociation of N2, and quenching by O is the principal low-altitude loss process, with radiative decay to N(2D) dominating above 200 km. As the dominant loss processes are likely to result in the production of N(2D), N(2P) could be a moderate source of N(2D) and may be a factor to be taken into consideration in modeling NO.

Torr, Marsha R.↗

NASA NTRS1993

Filters for the International Solar Terrestrial Physics (ISTP) mission far ultraviolet imager

The far ultraviolet (FUV) imager for the International Solar Terrestrial Physics (ISTP) mission is designed to image four features of the aurora: O I lines at 130.4 nm and 135.6 nm and the N2 Lyman-Birge-Hopfield (LBH) bands between 140 nm - 160 nm (LBH long) and 160 nm - 180 nm (LBH long). In this paper we report the design and fabrication of narrow-band and broadband filters for the ISTP FUV imager. Narrow-band filters designed and fabricated for the O I lines have a bandwidth of less than 5 nm and a peak transmittance of 23.9 percent and 38.3 percent at 130.4 nm and 135.6 nm, respectively. Broadband filters designed and fabricated for LBH bands have the transmittance close to 60 percent. Blocking of out-of-band wavelengths for all filters is better than 5x10(exp -3) percent with the transmittance at 121.6 nm of less than 10(exp -6) percent.

Zukic, Muamer↗

NASA NTRS1993

Radiation Damage Effects in Far Ultraviolet Filters and Substrates

New advances in VUV thin film filter technology have been made using filter designs with multilayers of materials such as Al2O3, BaF2, CaF2, HfO2, LaF3, MgF2, and SiO2. Our immediate application for these filters will be in an imaging system to be flown on a satellite where a 2 X 9 R(sub E) orbit will expose the instrument to approximately 275 krads of radiation. In view of the fact that no previous studies have been made on potential radiation damage of these materials in the thin film format, we report on such an assessment here. Transmittances and reflectances of BaF2, CaF2, HfO2, LaF3, MgF2, and SiO2 thin films on MgF2 substrates, Al2O3 thin films on fused silica substrates, uncoated fused silica and MgF2, and four multilayer filters made from these materials were measured from 120 nm to 180 nm before and after irradiation by 250 krads from a Co-60 gamma radiation source. No radiation-induced losses in transmittance or reflectance occurred in this wavelength range. Additional postradiation measurements from 160 nm to 300 nm indicated a 3 - 5% radiation-induced absorption near 260 nm in some of the samples with MgF2 substrates. From these measurements it is concluded that far ultraviolet filters made from the materials tested should experience less that 5% change from exposure to up to 250 krads of high energy radiation in space applications.

Keffer, Charles E.↗

NASA NTRS1992

The N2(+) first negative system in the dayglow from Spacelab 1

Data obtained by the Spacelab 1 Imaging Spectrometric Observatory represent the first simultaneous multiband spectral measurements of the N2(+) first negative system in the dayglow, and thus the first opportunity to make a detailed comparison of the vibrational and rotational distributions over bands out to nu-prime = 4, free of potential complications. The spectral images show that the bands of the N2(+) first negative system exhibit very unusual vibrational distributions (which correspond to surprisingly high apparent temperatures) and that the intensities are significantly higher than predicted. On the basis of observations of the intensity variation with the solar zenith angle and viewing elevation, it is suggested that there exists a significant induced N2(+) component near the shuttle, which fluoresces when the shuttle is sunlit.

Torr, Marsha R.↗

NASA NTRS1992

Compact Visible And Infrared Spectrometer

New compact spectrometers operate over broad wavelength ranges with moderate spectral resolution. Prototype measures spectral intensity simultaneously at all wavelengths from 3,700 to 11,700 Angstrom, with resolution of 12 Angstrom. Spectrum imaged onto strips on photocathode, then coupled via fiber-optic taper onto charge-coupled-device imager. Suitable for observation of weak phenomena as nocturnal airglow, and for observation of bright auroras and dayglow.

Torr, Marsha R.↗

NASA NTRS1992

The ATLAS-1 Shuttle mission

The Atmospheric Laboratory for Applications and Science (ATLAS-1) encompasses instruments which will be useful in determining long-term solar variability as well as in forging links to the measurements obtained by other spacecraft for the perturbed middle and upper atmosphere. The simultaneous measurements that will be conducted by ATLAS-1 of stratospheric concentrations of ozone, chlorine monoxide and water vapor, at relatively high latitudes during the northern spring, will be especially timely.

Torr, Marsha R.↗

NASA NTRS1992

The ultraviolet imager (UVI) for ISTP

We report the design of an imager with 0.6-millirad angular resolution over an 8-deg field of view sampled with 39,500 pixels, yielding global auroral coherent imaging from above 6 R(E). High performance filters provide spectrally pure measurements of four key FUV features, with 10 exp -4 out-of-band rejection. Together with the solar blind intensified CCD detector, a net rejection of 10 exp -9 of all out-of-band emissions is achieved. The optical design comprises a three-mirror f/3 system which yields a noise equivalent sensitivity of 10 Rayleighs for a 37-sec frame rate. The instantaneous dynamic range is 1000 which can be windowed over a range of 10 exp 4.

Torr, D. G.↗

NASA NTRS1992

Far ultraviolet filters for the ISTP UV imager

The far ultraviolet (FUV) imager for the International Solar-Terrestrial Physics (ISTP) mission is designed to image four features of the aurora: O I lines at 130.4 nm and 135.6 nm and the N2 Lyman-Birge-Hopfield (LBH) bands between 140 nm-160 nm (LBH long) and 160 nm-180 nm (LBH long). We report the design and fabrication of narrow-band and broadband filters for the ISTP FUV imager. Narrow-band filters designed and fabricated for the O I lines have a bandwidth of less than 5 nm and a peak transmittance of 22.3 and 29.6 percent at 130.4 nm and 135.6 nm, respectively. Broadband filters designed and fabricated for LBH bands have the transmittance greater than 40 percent for LBH short and close to 60 percent for LBH long. Blocking of out-of-band wavelengths for all filters is better than 0.001 percent with the transmittance at 121.6 nm of less than 10 exp -6 percent.

Zukic, Muamer↗

NASA NTRS1992

Extreme ultraviolet filters for 58.4 and 83.4 nm

We report the design of an EUV filter for He I at 58.4 nm and the design and fabrication of an EUV filter for O II at 83.4 nm. Both filters are designed as combinations of three narrow-band reflection filters. The net transmittance through both EUV filters is close to 10 percent with bandwidths less than 10 nm, and blocking better than 0.005 percent for out-of-band wavelengths. A theoretical calculation of the 83.4 nm filter predicts higher values for the peak transmittance than the measured spectral performance of the fabricated filter. Since aluminum is one of the film materials used for the fabrication of EUV filters, the aluminum film oxidation can be modeled in order to explain the discrepancy between the theory and experiment. Since the filters operate at angles of incidence up to 50 deg, the optical components of a system can serve as both the filtering and imaging elements.

Zukic, Muamer↗

NASA NTRS1991

High throughput narrowband 83.4 nm self-filtering camera

Photometric imaging of ionospheric/magnetospheric O II emission at 83.4 nm is a primary objective for mapping the distribution of O(+) ions. However, instrumental sensitivity has been a major barrier to realizing this goal. We report an instrumental design employing a low focal ratio three-mirror camera where the reflecting surfaces act as both narrowband reflection filters at 83.4 nm and as a high quality imaging system. The design includes coatings with reflectances that are relatively insensitive to the angle of incidence of light. The peak reflectance per mirror is more than 60 percent at 83.4 nm with the average reflectance for out-of-band wavelengths of less than 5 percent. The net reflective transmission for the three mirrors is greater than 20 percent with 6.8 nm bandwidth and 0.01 percent maximum transmittance for out-of-band wavelengths. The transmittance at 30.4 nm is 0.03 percent at 58.4 nm 0.05 percent, and at 121.6 nm 0.004 percent. When used with an open microchannel plate detector, contamination by H Ly-alpha is essentially eliminated. With this spectral purity and effective elimination of major contributors to background contamination noise, a signal-to-noise ratio (excluding detector noise) of 10 is achievable for a 0.01 R signal in 8.8 seconds for the full 6 deg field-of-view.

Zukic, Muamer↗