Search NASA⌕ Search

SEARCH · Search NASA

Results for “PERSPECTIVE”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Perspectives on NASA flight software development - Apollo, Shuttle, Space Station

Flight data systems' software development is chronicled for the period encompassing NASA's Apollo, Space Shuttle, and (ongoing) Space Station Freedom programs, with attention to the methodologies and 'development tools' employed in each case and their mutual relationships. A dominant concern in all three programs has been the accommodation of software change; it has also been noted that any such long-term program carries the additional challenge of identifying which elements of its software-related 'institutional memory' are most critical, in order to preclude their loss through the retirement, promotion, or transfer of its 'last expert'.

Garman, John R.↗
NASA NTRS1990

Windshear detection - Airborne system perspective

Functional requirements for airborne windshear detection and warning are discussed based on performance criteria of remote sensor devices such as Doppler radar, Doppler laser radar, and infrared radiometric techniques. These types of sensors are considered able to detect hazardous windshear conditions and provide adequate warning time for the flight crew to escape the encounter. Radar simulation and analysis show that windshear from microbursts can be detected. The Doppler systems can provide line-of-sight information from a region extending 2-4 km in front of the aircraft. The temperature drop associated with the formation of windshear can be measured by an airborne infrared radiometer which compares emission from CO2 in the immediate neighborhood of the aircraft to the emissions from CO2 in the air 4-5 km away. It is suggested that an integration of airborne sensor and ground derived data can support microburst avoidance.

Bowles, Roland L.↗
NASA NTRS1990

A unified perspective on robot control - The energy Lyapunov function approach

A unified framework for the stability analysis of robot tracking control is presented. By using an energy-motivated Lyapunov function candidate, the closed-loop stability is shown for a large family of control laws sharing a common structure of proportional and derivative feedback and a model-based feedforward. The feedforward can be zero, partial or complete linearized dynamics, partial or complete nonlinear dynamics, or linearized or nonlinear dynamics with parameter adaptation. As result, the dichotomous approaches to the robot control problem based on the open-loop linearization and nonlinear Lyapunov analysis are both included in this treatment. Furthermore, quantitative estimates of the trade-offs between different schemes in terms of the tracking performance, steady state error, domain of convergence, realtime computation load and required a prior model information are derived.

Wen, John T.↗
NASA NTRS1990

Software safety - A user's practical perspective

Software safety assurance philosophy and practices at the NASA Ames are discussed. It is shown that, to be safe, software must be error-free. Software developments on two digital flight control systems and two ground facility systems are examined, including the overall system and software organization and function, the software-safety issues, and their resolution. The effectiveness of safety assurance methods is discussed, including conventional life-cycle practices, verification and validation testing, software safety analysis, and formal design methods. It is concluded (1) that a practical software safety technology does not yet exist, (2) that it is unlikely that a set of general-purpose analytical techniques can be developed for proving that software is safe, and (3) that successful software safety-assurance practices will have to take into account the detailed design processes employed and show that the software will execute correctly under all possible conditions.

Dunn, William R.↗
NASA NTRS1990

Surface radiation budget - Current perspective

The surface radiation budget of the earth is important in climate research because it gives an understanding of the distribution of solar and IR radiation exchanges at the surface. Data on the distribution and exchange of these surface radiations are needed over the entire earth on a long-term basis. Global satellite data, coupled with highly developed models, now provide estimates of the surface radiation budget which are near the accuracy required for climate research. A description of surface radiation research, its current state, and planned programs are presented.

Darnell, Wayne L.↗
NASA NTRS1990

The Galileo mission earth encounters - An earth remote sensing perspective

After its Venus-Earth-Earth Gravity Assist trajectory, the Galileo spacecraft will arrive at Jupiter in 1995. The gravity-assist portion of the mission, however, will allow the spacecraft, which is equipped with a unique set of remote-sensing instruments, to observe earth from 970 km during its December 1990 approach, and from as little as 304 km in its second and last approach of December, 1992. An evaluation is presented of the role that the Galileo instrument suite can play in these earth encounters in virtue of their outstanding spectral and spatial resolutions.

Ocampo, Adriana↗
NASA NTRS1991

Climatological perspectives, oceanographic and meteorological, on variability in the subtropical convergence zone in the northwestern Atlantic

The large-scale climatological environment of the Frontal Air-Sea Interaction Experiment (FASINEX) is described, with emphasis on the largest scales. Both long-term and annual sea surface temperature (SST) variability is discussed; a climatology of the west-central North Atlantic, derived from various sets of data obtained during the intensive phases of January-March, is presented, and the meteorological and oceanographic context for FASINEX is thus established. Surface marine observations and SST variability are discussed, and the marine meteorology of the FASINEX area is examined in terms of the surface pressure and winds, the sea-air temperature difference, and the cloud cover. Near 28 deg N in February is found to be a favorable time and place to observe large mean temperature gradients and downward Ekman pumping. The large-scale processes that set up the favorable environment for frontal activity are not limited to the winter months.

Hanson, Howard P.↗
NASA NTRS1991

Perspectives on wind shear flight

Wind shears originating from downbursts have been the cause of many aircraft accidents in the past two decades. In turn, this has led to considerable research on wind shear avoidance systems and wind shear recovery systems. This paper reviews recent advances in wind shear recovery systems. It summarizes the work done at Rice University on trajectory optimization and trajectory guidance for two basic flight conditions: takeoff and abort landing. It appears that, in the relatively near future, an advanced wind shear control system can be developed, that is, capable of functioning in different wind models and covering the spectrum of flight conditions having interest in a wind shear encounter.

Miele, A.↗
NASA NTRS1991

An historical perspective of the NERVA nuclear rocket engine technology program

Nuclear rocket research and development was initiated in the United States in 1955 and is still being pursued to a limited extent. The major technology emphasis occurred in the decade of the 1960s and was primarily associated with the Rover/NERVA Program where the technology for a nuclear rocket engine system for space application was developed and demonstrated. The NERVA (Nuclear Engine for Rocket Vehicle Application) technology developed twenty years ago provides a comprehensive and viable propulsion technology base that can be applied and will prove to be valuable for application to the NASA Space Exploration Initiative (SEI). This paper, which is historical in scope, provides an overview of the conduct of the NERVA Engine Program, its organization and management, development philosophy, the engine configuration, and significant accomplishments.

Robbins, W. H.↗
NASA NTRS1991

Historical perspectives - The role of the NASA Lewis Research Center in the national space nuclear power programs

The history of the NASA Lewis Research Center's role in space nuclear power programs is reviewed. Lewis has provided leadership in research, development, and the advancement of space power and propulsion systems. Lewis' pioneering efforts in nuclear reactor technology, shielding, high temperature materials, fluid dynamics, heat transfer, mechanical and direct energy conversion, high-energy propellants, electric propulsion and high performance rocket fuels and nozzles have led to significant technical and management roles in many natural space nuclear power and propulsion programs.

Bloomfield, H. S.↗
NASA NTRS1991

Data compression: The end-to-end information systems perspective for NASA space science missions

The unique characteristics of compressed data have important implications to the design of space science data systems, science applications, and data compression techniques. The sequential nature or data dependence between each of the sample values within a block of compressed data introduces an error multiplication or propagation factor which compounds the effects of communication errors. The data communication characteristics of the onboard data acquisition, storage, and telecommunication channels may influence the size of the compressed blocks and the frequency of included re-initialization points. The organization of the compressed data are continually changing depending on the entropy of the input data. This also results in a variable output rate from the instrument which may require buffering to interface with the spacecraft data system. On the ground, there exist key tradeoff issues associated with the distribution and management of the science data products when data compression techniques are applied in order to alleviate the constraints imposed by ground communication bandwidth and data storage capacity.

Tai, Wallace↗
NASA NTRS1991

High-Energy Astrophysics. American and Soviet Perspectives

The proceedings of the American-Soviet high energy astrophysics workshop, which was held at the Institute for Space Research in Moscow and the Abastumani Laboratory and Observatory in the republic of Georgia from June 18 to July 1, 1989, is presented. Topics discussed at the workshop include the inflationary universe; the large scale structure of the universe, the diffuse x-ray background; gravitational lenses, quasars, and active galactic nuclei (AGNs); infrared galaxies (results from IRAS); Supernova 1987A; millisecond radio pulsars; quasi-periodic oscillations in the x-ray flux of low mass X-ray binaries; and gamma ray bursts.

Lewin, Walter H. G.↗
NASA NTRS1991

Functional characteristics of the calcium modulated proteins seen from an evolutionary perspective

We have constructed dendrograms relating 173 EF-hand proteins of known amino acid sequence. We aligned all of these proteins by their EF-hand domains, omitting interdomain regions. Initial dendrograms were computed by minimum mutation distance methods. Using these as starting points, we determined the best dendrogram by the method of maximum parsimony, scored by minimum mutation distance. We identified 14 distinct subfamilies as well as 6 unique proteins that are perhaps the sole representatives of other subfamilies. This information is given in tabular form. Within subfamilies one can easily align interdomain regions. The resulting dendrograms are very similar to those computed using domains only. Dendrograms constructed using pairs of domains show general congruence. However, there are enough exceptions to caution against an overly simple scheme in which one pair of gene duplications leads from one domain precurser to a four domain prototype from which all other forms evolved. The ability to bind calcium was lost and acquired several times during evolution. The distribution of introns does not conform to the dendrogram based on amino acid sequences. The rates of evolution appear to be much slower within subfamilies, especially within calmodulin, than those prior to the definition of subfamily.

Kretsinger, R. H.↗
NASA NTRS1991

A historical perspective on space station

The historical development of space stations is presented through a series of various spacecraft configurations including: (1) Salut 6; (2) Skylab; (3) the Space Operations Center (SOC); (4) the Manned Science and Applications Space Platform; (5) Space Station Freedom; and (4) the Mir Space Station.

Hook, W. Ray↗
NASA NTRS1991

Perspectives on high temperature superconducting electronics

The major challenges in making high temperature superconducting (HTSC) electronics viable are predominantly materials problems. Unlike their predecessors, the metal oxide-based superconductors are integratable with other advanced technologies such as opto-electronics and micro-electronics. The materials problems to be addressed relate to the epitaxial growth of high quality films, highly oriented films on non-lattice matched substrates, heterostructures with atomically sharp interfaces of junctions and other novel devices, and the processing of these films with negligible deterioration of the superconducting properties. These issues are illustrated with results based on films prepared in-situ by a pulsed laser deposition process. Films with zero-transition temperatures of 90 K and critical current densities of 5 x 10(exp 6) A/sq cm at 77 K have been prepared by this technique. Ultra-thin films, less than 100 A show T(sub c) is greater than 80 K, supporting the idea of two-dimensional transport in these materials. By the use of appropriate buffer layers, films with T(sub c) of 87 K and J(sub c) of 6 x 10(exp 4) A/sq cm were fabricated on silicon substrates. Submicron structures with J(sub c) is greater than 2 x 10(exp 7) at 10 K were fabricated. Results on nonlinear switching elements, IR detectors, and microwave studies will be briefly summarized.

Venkatesan, T.↗
NASA NTRS1991

Investigator Perspectives

A detailed presentation is given in the form of viewgraphs on principal investigator requirements ranging from simple to complex payloads. It is stated that the program was very important to the US science community, and that there was already concern that its funding was under stress, impacting the number of missions flown, down from around 44 to 25 or so. It is also stated that the program needs more help at NASA HQ.

Mendillo, Michael↗
NASA NTRS1992

Some comments on turbulence modeling from an industrial perspective

In propulsion industry, computational techniques (namely computational fluid dynamics) are gradually becoming engineering design and analysis tools, especially in the case of high performance aircraft engines, high speed air breathing propulsion, rocket propulsion, and advanced nuclear propulsion and electric propulsion. The key issues in acceptance of CFD are turn around time, cost, and accuracy. The turn around time of analysis has to fit program schedules. Cost is still the bottom line, the value of CFD to the program should at least balance its cost. CFD can be used if it can be divided into two major parts: numerics and physical models.

Sindir, Munir M.↗