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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

A 2 THz Heterodyne Array Receiver for SOFIA: Summary of Research

We proposed to perform a comprehensive design study of a 16-element heterodyne array receiver for SOFIA. The array was designed to utilize hot-electron bolometers in an efficient, low-cost waveguide mount to achieve low noise performance between approximately 1500 and 2400 GHz. Due to the prevailing physical conditions in the interstellar medium, this frequency range is one of the richest in the Far-Infra Red (FIR) portion of the spectrum. An array designed for this wavelength range will make excellent use of the telescope and the available atmospheric transmission, and will provide a new perspective on stellar, chemical, and galactic evolution in the present as well as past epochs. A few of the most important molecular and atomic species which the instrument will sample are CII, OI, CO, OH, NII, and CH. The system used the most sensitive detectors available in an efficient optical system. The local oscillator was a compact CO2 pumped far-infrared laser currently under development for SOFIA. The backend spectrometer was an array acousto-optic spectrometer (aAOS). The spectrometer utilizes proven hardware and technologies to provide broadband performance (> 1 GHz per AOS channel) and high spectral resolution (1 MHz) with the maximum sensitivity and minimum complexity and cost. The proposed instrument would be the fastest and most sensitive heterodyne receiver ever to operate in the 1.5 - 2.4 THz band. One of the key technologies developed for the proposed instrument is the laser micromachining of waveguide structures. These structures provide both the optical link between the instrument and the telescope (via an array of efficient feedhorns) and the impedance transformation between the detectors and free space. With the assistance of funds provided from this grant, we were able to fabricate and test the world's first laser micromachined feedhorns. The quality of the waveguide structure is far better than that obtainable using any other fabrication technique. The beam parameters are an excellent match to what is expected from theory. The success of this experiment demonstrates the viability of using laser micromachined components in the development of high performance, large format array receivers. We have continued our development efforts and will propose to build a 2nd generation instrument based on the same design concepts.

Walker, Christopher K.↗
NASA NTRS1999

Time-Frequency Analysis of the Dispersion of Lamb Modes

Accurate knowledge of the velocity dispersion of Lamb modes is important for ultrasonic nondestructive evaluation methods used in detecting and locating flaws in thin plates and in determining their elastic stiffness coefficients. Lamb mode dispersion is also important in the acoustic emission technique for accurately triangulating the location of emissions in thin plates. In this research, the ability to characterize Lamb mode dispersion through a time-frequency analysis (the pseudo-Wigner-Ville distribution) was demonstrated. A major advantage of time-frequency methods is the ability to analyze acoustic signals containing multiple propagation modes, which overlap and superimpose in the time domain signal. By combining time-frequency analysis with a broadband acoustic excitation source, the dispersion of multiple Lamb modes over a wide frequency range can be determined from as little as a single measurement. In addition, the technique provides a direct measurement of the group velocity dispersion. The technique was first demonstrated in the analysis of a simulated waveform in an aluminum plate in which the Lamb mode dispersion was well known. Portions of the dispersion curves of the AO, A I , So, and S2 Lamb modes were obtained from this one waveform. The technique was also applied for the analysis of experimental waveforms from a unidirectional graphite/epoxy composite plate. Measurements were made both along and perpendicular to the fiber direction. In this case, the signals contained only the lowest order symmetric and antisymmetric modes. A least squares fit of the results from several source to detector distances was used. Theoretical dispersion curves were calculated and are shown to be in good agreement with experimental results.

Prosser, W. H.↗
NASA NTRS1998

A Study of Pulse Shape Evolution and X-Ray Reprocessing in Her X-1

This study focused on the pulse shape evolution and spectral properties of the X-ray binary Her X-1 with regard to the well known 35-day cycle of Her X-1. A follow-up set of RXTE observations has been conducted in RXTE AO-2 phase and the two observation sets are being analyzed together. We presented results of early analysis of pulse shape evolution in "Proceedings of the Fourth Compton Symposium". More advanced analysis was presented at the HEAD meeting in November, 1997 in Estes Park, Colorado. A related study of the 35-day cycle using RXTE/ASM data, which laid out the overall picture within which the more detailed PCA observations could be placed has also been conducted. The results of this study have been published. A pair of papers on the detailed pulse evolution and the spectral/color evolution are currently being prepared for publication. Some of the significant results of this study have been a confirmation of the detailed pulse profile changes at the end of the Main High state in HerX-1 first observed by GINGA, observations of the pulse evolution in several Short High states which agree with the pulse evolution pattern predicted using a disk occultation model, observation of a systematic lengthening of the eclipse egress during the Main High state of the 35-day phase and observation of a new type of extended eclipse ingress during which pulsations cease to observed during the Short High state.

Cushman, Paula P.↗
NASA NTRS1998

Coronal Temperature and Emission Measure Distributions for he Active G Supergiant Beta Dra and other ASCA Projects

This NASA grant supported my ASCA observing and data analysis programs during AOs 1-4. This research involved four Guest Observer projects. Analysis of data from all four programs has been completed. This grant included the following ASCA GO programs: AO1 - "Coronal Temperature and Emission Measure Distributions for the Active G Supergiant Beta Dra" AO2 - "Contemporaneous ASCA, EUVE, IUE, and VLA/AT Observations of Atmospheric Structure of the RS CVn Binary HR1099". AO3 - "Coronal Temperature and Emission Measure Distributions for the hybrid-chromosphere star alpha TrA". AO4-"Activity on the edge of convection: The atmosphere of Canopus (alpha Car, FO Ib-II)".

Brown, Alexander↗
NASA NTRS2000

Operational Methodology for the International Space Station (ISS) High Rate Communications Outage Recorder (HCOR)

The HCOR will be used onboard the ISS to record digital data during Ku-band Loss of Signal (LOS) periods. This recorded data will be played back to the ground during Ku-band Acquisition of Signal (AOS) periods. The Data Management (DM) Team at the Payload Operations and Integration Center is the primary operator of this complex recorder. The record and playback capabilities - along with the memory management functions - are presented in this paper. To illustrate how the DM Team plans to manage the record, playback and memory management tasks of operating the HCOR, an operational scenario for a ninety-minute orbit is presented.

Mixson, C. David↗
NASA NTRS1996

A 2 THz Heterodyne Array Receiver for SOFIA

We proposed to perform a comprehensive design study of a 16-element heterodyne array receiver for SOFIA. The array was designed to utilize hot-electron bolometers in an efficient, low-cost waveguide mount to achieve low noise performance between approx. 1500 and 2400 GHz. Due to the prevailing physical conditions in the interstellar medium, this frequency range is one of the richest in the FIR portion of the spectrum. An array designed for this wavelength range will make excellent use of the telescope and the available atmospheric transmission, and will provide a new perspective on stellar, chemical, and galaxy evolution in the present as well as past epochs. A few of the most important molecular and atomic species which the instrument will sample are CII, OI, CO, OH, NII, and CH. The system used the most sensitive detectors available in an efficient optical system. The local oscillator was a compact CO2 pumped far-infrared laser currently under development for SOFIA. The backend spectrometer was an array acousto-optic spectrometer (aAOS). The spectrometer utilizes proven hardware and technologies to provide broadband performance (greater than or equal to 1 GHz per AOS channel) and high spectral resolution (1 MHz) with the maximum sensitivity and minimum complexity and cost. The proposed instrument would be the fastest and most sensitive heterodyne receiver ever to operate in the 1.5 - 2.4 THz band. One of the key technologies developed for the proposed instrument is the laser micromachining of waveguide structures. These structures provide both the optical link between the instrument and the telescope (via an array of efficient feedhorns) and the impedance transformation between the detectors and free space. With the assistance of funds provided from this grant, we were able to fabricate and test the world's first laser micromachined feedhorns. The quality of the waveguide structure is far better than that obtainable using any other fabrication technique. The beam parameters are an excellent match to what is expected from theory. The success of this experiment demonstrates the viability of using laser micromachined components in the development of high performance, large format array receivers. Unfortunately, our instrument proposal was not selected as a first generation SOFIA instrument. However, we have continued our development efforts and will propose to build a 2nd generation instrument based on the same design concepts.

Walker, Christopher K.↗
NASA NTRS1999

Aft Body Closure: Predicted Strut Effects at M=2.4

This paper reports the predicted M = 2.4 strut-interference effects on a closed aftbody with empennage for the TCA baseline model. The strut mounting technique was needed in order to assess the impact of aft-end shaping, i.e. open for a sting or closed to better represent a flight vehicle. However,this technique can potentially lead to unanticipated effects that are measured on the aft body. Therefore, a set of computations were performed in order to examine the closed aft body with and without strut present, at both zero and non-zero angles of sideslip (AOS). The work was divided into a computational task performed by Javier A. Garriz, using an inviscid (Euler) solver, and a monitoring/reporting task done by John E. Lamar. All this work was performed during FY98 at the NASA Langley Research Center.

Lamar, John E.↗
NASA NTRS2000

Coordinated ASCA Observations of Coronal Structure and Flares on the RS CVn Binary Sigma CrB

This NASA grant supported my ASCA observing and data analysis during AO 5. This research involved a multiwavelength observation of the short period (1.14 day) active binary sigma(sup 2) CrB using the ASCA and RXTE satellites and the NRAO VLA radio array. ASCA observed sigma(sup 2) CrB for 81 ksec on 1997 March 11-13. A large flare outburst, with a flare enhancement over of quiescence of a factor of 6, was seen starting on March 12.23. This flare was also observed by RXTE and the VLA. Two-temperature spectral fitting indicates the presence of a nonvarying cooler component at 8 mk and a hotter component that increased from a quiescent temperature of 22 mk to 50 mk at the peak of the flare. Continuous emission measure distributions derived from the spectra are consistent with the two-temperature fits and also indicate the presence of very hot (100 MK) plasma during the rise phase of the flare. The detailed analysis of all the spectral and radio data for sigma(sup 2) CrB is published in Osten et al. (2000).

Brown, Alexander↗
NASA NTRS1991

Demographics of Investigators Involved in OSSA-Funded Research

The birth of the U.S. civil space program and the subsequent, dramatic growth in the ranks of the space science research population occurred in the 1950s and 1960s'. The large, post- Sputnik/ Apollo buildup in space program manpower is now approximately one career-lifetime in the past. It is therefore natural to anticipate that a large fraction of the space program engineers, scientists, and managers who pioneered the early exploration of space are approaching retirement. Such a "retirement wave" bodes both a loss of manpower and, more fundamentally, a loss of experience from the civil-space manpower base. Such losses could play a critical role constraining in NASA's ability to expand or maintain its technical capabilities. If this indeed applies to the NASA space science research population, then the potential for problems is exacerbated by the anticipated growth in flight rates, data volume, and data-set diversity which will accompany the planned expansion in the OSSA science effort during the 1990s and 2000s. The purpose of this study was to describe the OSSA PI/Co-I population and to determine the degree to which the OSSA space science investigator population faces a retirement wave, and to estimate the future population of PIs in the 1990-2010 era. To conduct such a study, we investigated the present demographics of the PI and Co-1 population contained in the NASA/OSSA Announcement of Opportunity (AO) mailing list. PIs represent the "leadership" class of the OSSA scientific researcher population, and Co-Is represent one important, oncoming component of the "replacement" generation. Using the PI population data, we then make projection estimates of the future PI population from 1991 through 2010, under various NASA growth/PI demand scenarios.

Stern, S. Alan↗
NASA NTRS2001

The Variability of the Horizontal Circulation in the Troposphere and Stratosphere: A Comparison

The variability of the horizontal circulation in the stratosphere and troposphere of the Northern Hemisphere (NH) is compared by using various approaches. Spatial degrees of freedom (dof) on different time scales were derived. Modes of variability were computed in geopotential height fields at the tropospheric and stratospheric pressure levels by applying multivariate statistical approaches. Features of the spatial and temporal variability of the winterly zonal wind were studied with the help of recurrence and persistence analyses. The geopotential height and zonally-averaged zonal wind at the 50-, 500- and 1000-hPa level are used to investigate the behavior of the horizontal circulation in the lower stratosphere, mid-troposphere and at the near surface level, respectively. It is illustrated that the features of the variability of the horizontal circulation are very similar in the mid-troposphere and at the near surface level. Due to the filtering of tropospheric disturbances by the stratospheric and upper tropospheric zonal mean flow, the variability of the stratospheric circulation exhibits less spatial complexity than the circulation at tropospheric pressure levels. There exist enormous differences in the number of degrees of freedom (or free variability modes) between both atmospheric layers. Results of the analyses clearly show that the concept of a zonally symmetric AO with a simple structure in the troposphere similar to the one in the stratosphere is not valid. It is concluded that the spatially filtered climate change signal can be detected earlier in the stratosphere than in the mid-troposphere or at the near surface level.

Perlwitz, Judith↗
NASA NTRS2001

Brown Dwarfs: Discovery and Detailed Studies

We obtained the optical and IR spectra of Gliese 229B and identified Cs, I, and CO features - as expected in theoretical models. Our optical IR spectrum showed that most of the refractory metals have condensed out of the atmosphere and the presence of Cs, I and CO shows evidence for disequilibrium chemistry. We reported orbital evidence for Gliese 229B. The HST measured optical magnitudes provide additional evidence for the absence of dust in the atmosphere of this cool object. The luminosity of brown dwarfs depend on their masses and ages and in order to interpret the results of the survey we have carried out an extensive Monte Carlo analysis. Our conclusion is that warm brown dwarfs are rare, as companions in the orbital period range beyond approximately 30 - 50 AU. The Palomer survey poses no constraint for brown dwarfs in planetary orbits similar to those of the outer planets. We have just started a program of imaging nearby stars with the newly commissioned AO system at Palomar and Keck and have already found a brown dwarf candidate.

Kulkarni, Shrinivas R.↗
NASA NTRS2002

XTE Observations of Intermediate Polars: RXTE TOO Observations of Supernovae

Two intermediate polar cataclysmic variables, PQ Gem and AO Psc, were observed jointly with the Rossi X-ray Timing Explorer (RXTE) and ground-based photometry. The analysis of intermediate polars (IPs) is complex because these objects exhibit light curves that behave differently as a function of energy and that behave differently when phased on the orbital or on the spin periods. The presence of two periods in one system is essentially equivalent to analyzing two different X-ray sources. A preliminary analysis of the PQ Gem data was carried out and presented at the Annapolis Workshop on Magnetic Cataclysmic Variables. The final analysis of the data were held up by problems with the background estimation. The RXTE PCA team has released a new version of the background estimator. The PQ Gem must be reanalyzed using the new background. We have also installed a spectral model that calculates the expected emission from an accretion column. That model is undergoing final testing before we apply it to the data.

Schlegel, E.↗
NASA NTRS2002

Research on Hazardous States of Awareness and Physiological Factors in Aerospace Operations

The technical memorandum describes research conducted to examine the etiologies and nature of hazardous states of awareness and the psychophysiological factors involved in their onset in aerospace operations. A considerable amount of research has been conducted at NASA that examines psychological and human factors issues that may play a role in aviation safety. The technical memorandum describes some of the research that was conducted between 1998 and 2001, both in-house and as cooperative agreements, which addressed some of these issues. The research was sponsored as part of the physiological factors subelement of the Aviation Operation Systems (AOS) program and Physiological / Psychological Stressors and Factors project. Dr. Lance Prinzel is the Level III subelement lead and can be contacted at l.j.prinzel@larc.nasa.gov.

Prinzel, Lawrence J., III↗
NASA NTRS2002

The Unusual Wolf-Rayet Star EZ CMa

The XMM-Newton observations were obtained on 29 - 30 October 2001 during the AO-1 Guest Observer program. Our X-ray analysis focused on data from the European Photon Imaging Camera (EPIC). The VLA observations were obtained during a 3.5 hour interval on 1999 Oct. 19 with the array in hybrid BnA configuration. Radio continuum data were acquired at five different frequencies 1.42 GHz (21 cm), 4.86 GHz (6 cm), 8.44 GHz (3.6 cm), 14.94 GHz (2 cm), and 22.46 GHz (1.3 cm). These radio data are unique since they provide an excellent snapshot picture of the dependence of the radio flux on frequency obtained over a short time interval and are thus immune to the variability effects which can distort results obtained from non-contemporaneous observations at different frequencies.

Skinner, Stephen L.↗
NASA NTRS2003

Team-Centered Perspective for Adaptive Automation Design

Automation represents a very active area of human factors research. The journal, Human Factors, published a special issue on automation in 1985. Since then, hundreds of scientific studies have been published examining the nature of automation and its interaction with human performance. However, despite a dramatic increase in research investigating human factors issues in aviation automation, there remain areas that need further exploration. This NASA Technical Memorandum describes a new area of automation design and research, called adaptive automation. It discusses the concepts and outlines the human factors issues associated with the new method of adaptive function allocation. The primary focus is on human-centered design, and specifically on ensuring that adaptive automation is from a team-centered perspective. The document shows that adaptive automation has many human factors issues common to traditional automation design. Much like the introduction of other new technologies and paradigm shifts, adaptive automation presents an opportunity to remediate current problems but poses new ones for human-automation interaction in aerospace operations. The review here is intended to communicate the philosophical perspective and direction of adaptive automation research conducted under the Aerospace Operations Systems (AOS), Physiological and Psychological Stressors and Factors (PPSF) project.

Prinzel, Lawrence J., III↗
NASA NTRS2003

Brown Dwarfs: Discovery and Detailed Studies

The grant supported my research and that of my student (Ben Lane) and post-doctoral fellow (Zapatero Osorio). We were productive as can be seen from the list of publications below. In particular, we note three firsts. Using the exquisite angular resolution provided by the AO system at Keck we were able to directly determine the masses of two objects and show that one was a brown dwarf -- the first direct determination of the mass of a brown dwarf. Next, Mr. Lane reported the first direct demonstration of pulsations of a Cepheid star (this report received attention in the popular press). Finally, Dr. Zapatero Osorio continued her work on the search for young brown dwarfs and planets in young clusters with considerable success -- namely the detection of objects with mass below 10 M_J (these can be plausibly argued to be freely floating planets). Mr. Lane graduated and is now a Pappalardo Fellow at MIT and Dr. Zapatero Osorio obtained a position back in her home country.

Kulkarni, Shrinivas R.↗
NASA NTRS2003

Observations of the Mars Polar Vortex

The winter season, westerly circumpolar flow of the Martian atmosphere, and of the terrestrial stratosphere, is concentrated into a jet whose latitude falls between 60 and 80 degrees. This jet is known as the polar vortex. The terrestrial polar vortex has been understood to be the dynamical controlling mechanism for ozone depletion in the polar stratosphere for more than a decade. More recently, the earth's stratospheric annular modes, which are essentially a weakening/strengthening oscillation of the polar vortex jet, have been shown to be coupled to and possibly even a driving mechanism for, the tropospheric Arctic Oscillation (AO) / North Atlantic Oscillation (NAO) phenomenon.

T H McConnochie↗
NASA NTRS2003

Durability of ITO-MgF2 Films for Space-Inflatable Polymer Structures

This paper presents results from ITO-MgF2 film durability evaluations that included tape peel, fold, thermal cycle, and AO exposure testing. Polymer coupon preparation is described as well as ITO-MgF2 film deposition equipment, procedures and film characterization. Durability testing methods are also described. The pre- and post-test condition of the films is assessed visually, microscopically, and electrically. Results show that at ~500 ITO - 9 vol% MgF2 film is suitable to protect polymer surfaces, such as those used in space-inflatable structures of the PowerSphere microsatellite concept, during a 1-year Earth orbiting mission. Future plans for ground-based and orbital testing of this film are also discussed.

Kerslake, Thomas W.↗