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Lee, T. J.

Publications and source records attributed to Lee, T. J..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Production and Potential Detection of Functionalized Hexamethylene-Tetramine Compounds in Space

Laboratory studies have shown that exposure of mixed ices of astrophysical interest to ionizing radiation such as ultraviolet (UV) photons or energetic particles (electrons, protons) leads to the production of large numbers of new, more complex compounds. A significant portion of these new species appear to belong to a family of molecules that consist of hexamethylenetetramine (HMT; C6N4H12) and HMT to which different chemical side groups have been substituted for a peripheral H atom. This work presents the identification of HMT-methanol (HMT-CH2OH), one of these HMT variants, in organic residues produced from the UV irradiation of astrophysically relevant ice mixtures at < 20 K. We also present the infrared (IR) spectra of HMT, HMTCH2OH, and a number of other HMT variants computed using density functional theory (DFT) computations. These spectra can be compared with each other and show similarities that can be used to search for this family of compounds in space.

UV Irradiation↗
NASA NTRS2015

Overview of a New NASA Activity Focused on Planetary Defense

The National Aeronautics and Space Administration (NASA) has initiated a new Planetary Defense research activity, led by the NASA Ames Research Center. The objective of the effort is to provide tools for reliably assessing the impact damage that Potentially Hazardous Asteroids (PHAs) could inflict on the Earth. This research will support decisions regarding appropriate mitigation action in the event that an impact threat is discovered. The activity includes four interrelated tasks: PHA characterization, physics-based simulations of atmospheric entry/breakup, simulations of surface damage due to airbursts, land impacts, or tsunamis, and an integrated assessment of the overall risks posed by potential PHA strikes. This paper outlines the objectives, research approaches, products, and interrelations of the activity’s four tasks, and presents an overview of their current progress and preliminary results. Companion papers in this conference provide additional details of the work in the four task areas.

Arnold, J. O.↗
NASA NTRS2015

Overview of a New NASA Activity Focused on Planetary Defense

The National Aeronautics and Space Administration (NASA) has initiated a new Planetary Defense research activity, led by the NASA Ames Research Center. The objective of the effort is to provide tools for reliably assessing the impact damage that Potentially Hazardous Asteroids (PHAs) could inflict on the Earth. This research will support decisions regarding appropriate mitigation action in the event that an impact threat is discovered. The activity includes four interrelated tasks: PHA characterization, physics-based simulations of atmospheric entry breakup, simulations of surface damage due to airbursts, land impacts, or tsunamis, and an integrated assessment of the overall risks posed by potential PHA strikes. This paper outlines the objectives, research approaches, products, and interrelations of the activity's four tasks, and presents an overview of their current progress and preliminary results. Companion papers in this conference provide additional details of the work in the four task areas.

Arnold, J. O.↗
NASA NTRS1995

Inferring the thermal-infrared hemispheric emission from a sparsely-vegetated surface by directional measurements

The thermal-infrared (longwave) emission from a vegetated terrain is generally anisotropic, i.e., the emission temperature varies with the view direction. If a directional measurement of temperature is considered to be equal to the effective temperature of the hemispheric emission, then the estimate of the latter can be significantly in error. The view-direction (zenith angle theta(sub eq) at which the emission equivalence does hold is determined in our modeling study. In a two-temperature field-of-view (soil and plants), theta(sub eq) falls in a narrow range depending on plant density and canopy architecture. Theta(sub eq) does not depend on soil and (uniform) plant temperatures nor on their ratio, even though the pattern of emission vs. the view direction depends crucially on this ratio. For a sparse canopy represented as thin, vertical cylindrical stalks (or vertical blades uniformly distributed in azimuth) with horizontal facets, theta(sub eq) ranges from 48 to 53 deg depending on the optical density of the vertical elements alone. When plant elements are modeled as small spheres, theta(sub eq) lies between 53 to 57 deg (for the same values of the canopy optical density). Only for horizontal leaves (a truly planophile canopy) is the temperature measured from any direction equal to the temperature of the hemispheric emission. When the emission temperature changes with optical depth within the canopy at a specified rate, theta(sub eq) depends to some extent on that rate. For practically any sparsely vegetated surface, a directional measurement at the zenith angle of 50 deg offers an appropriate evaluation of the hemispheric emission, since the error in the estimate will, at most, only slightly exceed 1% (around 4 W/sq m). Estimates of the hemispheric emission through a nadir measurement, on the other hand, can be in error in some cases by about 10%, i.e., on the order of 40 W/sq m.

Otterman, J.↗
NASA NTRS1992

Some thoughts on the management of large, complex international space ventures

Management issues relevant to the development and deployment of large international space ventures are discussed with particular attention given to previous experience. Management approaches utilized in the past are labeled as either simple or complex, and signs of efficient management are examined. Simple approaches include those in which experiments and subsystems are developed for integration into spacecraft, and the Apollo-Soyuz Test Project is given as an example of a simple multinational approach. Complex approaches include those for ESA's Spacelab Project and the Space Station Freedom in which functional interfaces cross agency and political boundaries. It is concluded that individual elements of space programs should be managed by individual participating agencies, and overall configuration control is coordinated by level with a program director acting to manage overall objectives and project interfaces.

Lee, T. J.↗
NASA NTRS1991

Nonlinear influence of mesoscale land use on weather and climate

It is shown that the influence of mesoscale landscape spatial variability on the atmosphere must be parameterized or explicitly modeled in larger-scale atmospheric model simulations including general circulation models. The mesoscale fluxes of heat that result from this variability are shown to be of the same order of magnitude but with a different vertical structure than found for the turbulent fluxes. These conclusions are based on experiments in which no phase changes of water were permitted. To parameterize surface thermal inhomogeneities, the influence of landscape must be evaluated using spectral analysis or an equivalent procedure. To include the nonlinear contribution of each scale, numerical model simulations for the range of observed surface and overlying atmospheric conditions must be performed.

Pielke, R. A.↗
NASA NTRS1988

Space transportation systems for the future

A summary of the potential requirements, proposed configurations, inherent development problems, and technologies to be considered for future space transportation systems is presented. Such systems will include the improved Space Shuttle, new and derivative cargo launch vehicles, new propulsion systems, orbital transfer and maneuvering vehicles, and a second-generation Space Shuttle. It is concluded that more efficient and capable systems can be developed by placing strong emphasis on high reliability, safety, and improved ground and flight operations. These improvements can result from the introduction of advanced technologies and vehicles designed for operations and maintainability with the flexibility to adapt to mission needs.

Lee, T. J.↗
NASA NTRS1983

An infrared study of the eclipsing dwarf nova U Geminorum

One series of data comprising the present J, H, K broadband IR photometry of the cataclysmic binary system U Geminorum over the course of two orbital cycles was obtained several days before an outburst, while a second was gathered when the system had almost completely returned to quiescence from that outburst. In quiescence, the M4-M5.5 red dwarf star supplies most of the IR luminosity of the system, while the light curves at this time are tidally induced ellipsoidal variations of the red dwarf which exhibit an amplitude such that the red dwarf must fill, or nearly fill, its Roche lobe. This shows directly that Roche lobe overflow is important in cataclysmic variable stars. The range of the disk IR colors after outbursts suggest that cool and optically thick gas, together with optically thin gas, supply most of the IR light of the disk.

Berriman, G.↗
NASA NTRS1982

New members of the infrared cluster in the Orion Molecular Cloud

Near-infrared high-resolution scans (3.5 arcsec) of the core of the Orion Molecular Cloud (no. 1) have revealed 26 sources. Eleven of these are identified with faint visible stars. The remainder are thought to be highly reddened stars embedded in the molecular cloud and include at least two of the previously known infrared cluster members. Comparison of the distribution of infrared and visible stars on the plane of the sky and in an infrared color-magnitude diagram shows that the obscured infrared sources form a separate cluster of stars. The newly discovered sources appear to fall into two categories: (1) optically identified stars probably on the front surface of the cloud and associated with the Trapezium cluster; and (2) unidentified infrared stars probably associated with the molecular cloud and the embedded infrared cluster. It is plausible that the newly discovered infrared sources in the OMC-1 region are stars less massive than the previously known members and younger than visible stars of similar mass in Orion Association.

Lonsdale, C. J.↗
NASA NTRS1981

The largest H II regions in M101

Coordinated millimeter, infrared, and ultraviolet observations of the five brightest H II regions in M101 are presented. A CO complex has been found to be associated with NGC 5461 which is much more massive than any Milky Way counterpart. A narrow line width has been observed which suggests that the molecular complex may consist of numerous fragments with a volume filling fraction approximately 0.01. NGC 5461 also shows a 10 micron and 20 micron excess which is similar to that of galactic H II regions. The ultraviolet observations show that the 2200 A dust feature is greatly attenuated in all of the H II regions but least of all in NGC 5461. The near-infrared flux densities and B-gamma line strengths are consistent with the hypothesis that a significant fraction of the infrared emission is free-free.

Blitz, L.↗
NASA NTRS1980

Io - Ground-based observations of hot spots

Observations of Io in eclipse demonstrate conclusively that Io emits substantial amounts of radiation at 4.8 and 3.8 micrometers and a measurable amount at 2.2 micrometers. Color temperatures derived from the observations fit blackbody emission at 560 K. The required source area to yield the observed 4.8-micrometer flux is approximately 5 x 10 to the -5th of the disk of Io and is most likely comprised of small hot spots in the vicinity of the volcanoes.

Sinton, W. M.↗
NASA NTRS1979

The cost benefits of the Spacelab system to scientific investigations and space applications

Cost advantages of the Spacelab system to scientific experiments in space and space operations are presented. The payload integration concepts developed for Spacelab are examined, and it is shown that Spacelab and Shuttle integration, communications and data processing, launch support requirements and flight operations will provide a considerable savings in the costs of space research relative to previous space systems. Spacelab modular design, incorporating features such as standard payload interfaces, optional mission dependent equipment and standard services, such as the Experiment Computer Operating System, is shown to offer the user a wider range of services than previous programs, also at significantly lower costs. It is concluded that the Spacelab system will greatly reduce the costs and broaden the opportunities for scientific investigation in space.

Jean, O. C.↗
NASA NTRS1976

Spacelab operations planning

The paper reviews NASA planning in the fields of ground, launch and flight operations and experiment integration to effectively operate Spacelab. Payload mission planning is discussed taking consideration of orbital analysis and the mission of a multiuser payload which may be either single or multidiscipline. Payload analytical integration - as active process of analyses to ensure that the experiment payload is compatible to the mission objectives and profile ground and flight operations and that the resource demands upon Spacelab can be satisfied - is considered. Software integration is touched upon and the major integration levels in ground operational processing of Spacelab and its experimental payloads are examined. Flight operations, encompassing the operation of the Space Transportation System and the payload, are discussed as are the initial Spacelab missions. Charts and diagrams are presented illustrating the various planning areas.

Lee, T. J.↗
NASA NTRS1975

Spacelab - A key element in the Space Shuttle Space Transportation System

Spacelab will be a key element in the Space Transportation System (STS) to be initiated with the advent of the first operational flight of Space Shuttle in 1980. Spacelab is an international, cooperative venture between the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA), which is structured to provide the scientific community an earthlike laboratory in space by 1980. The responsibilities of both ESA and NASA are divided into design and development to be accomplished by ESA and the experiment integration and operation with the Space Shuttle by NASA. While the Spacelab is a key element in the STS, it is highly dependent on other elements in the system for its resources and payload support capabilities. This paper presents the relationship of the Spacelab to other elements and the operational planning that NASA is undertaking to make the Spacelab a flexible and efficient laboratory in space.

Lee, T. J.↗
NASA NTRS1973

The design and utilization of a spacelab for sortie missions

Consideration of the feasibility of a 'sortie' type mission in which a manned laboratory is carried into near-earth orbit for a 7- to 30-day mission and is then returned to earth for reconfiguration and subsequent reflight. The fundamental difference in approach between the proposed Spacelab and concepts previously considered for space stations is that the spacelab will remain attached to the Shuttle Orbiter during its entire mission in space. An important trend in the design approach is the introduction of structural modularity of the Spacelab. Another factor which has been a significant design consideration is the need to properly balance the Shuttle and Spacelab configuration over a wide range of aerodynamic regimes and landing conditions. Also considered are the requirements which may be placed on the laboratory by potential users in fields of science and space applications.

Lord, D. R.↗