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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.

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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Communications to 2000 - A forecast of the demand and capacity of U.S. domestic communications satellites

The market demand for the U.S. domestic communications satellites accelerated in the late 70's, exceeding the capacity of the satellites currently in orbit. Satellite carriers have been authorized to build an additional 24 domsats. This paper examines the anticipated market demands, and the capability of the domsats to fulfill these demands. With various practical technical innovations, the domsats appear able to meet the expected market demands until the end of this century.

Fordyce, S. W.↗
NASA NTRS1982

An FDMA system concept for 30/20 GHz high capacity domestic satellite service

The paper summarizes a feasibility study of a multibeam FDMA satellite system operating in the 30/20 GHz band. The system must accommodate a very high volume of traffic within the restrictions of a 5 kW solar cell array and a 2.5 GHz bandwidth. Multibeam satellite operation reduces the DC power demand and allows reuse of the available bandwidth. Interferences among the beams are brought to acceptable levels by appropriate frequency assignments. A transponder design is presented; it is greatly simplified by the application of a regional concept. System analysis shows that MSK modulation is appropriate for a high-capacity system because it conserves the frequency spectrum. Rain attenuation, a serious problem in this frequency band, is combatted with sufficient power margins and with coding. Link budgets, cost analysis, and weight and power calculations are also discussed. A satellite-routed FDMA system compares favorably in performance and cost with a satellite-switched TDMA system.

Berk, G.↗
NASA NTRS1982

Evaluating near-surface soil moisture using Heat Capacity Mapping Mission data

Four dates of Heat Capacity Mapping Mission (HCMM) data were analyzed in order to evaluate HCMM thermal data use in estimating near-surface soil moisture in a complex agricultural landscape. Because of large spatial and temporal ground cover variations, HCMM radiometric temperatures alone did not correlate with soil water content. The radiometric temperatures consisted of radiance contributions from different canopies and their respective soil backgrounds. However, when surface soil temperatures were empirically estimated from HCMM temperatures and percent cover of each pixel, a highly significant correlation was obtained between the estimated soil temperatures and near-surface soil water content.

Heilman, J. L.↗
NASA NTRS1982

The economics of time shared computing: Congestion, user costs and capacity

Time shared systems permit the fixed costs of computing resources to be spread over large numbers of users. However, bottleneck results in the theory of closed queueing networks can be used to show that this economy of scale will be offset by the increased congestion that results as more users are added to the system. If one considers the total costs, including the congestion cost, there is an optimal number of users for a system which equals the saturation value usually used to define system capacity.

Agnew, C. E.↗
NASA NTRS1980

Heat Capacity Mapping Mission (HCMM) Notification Efforts

To encourage wide use of the Heat Capacity Mapping Mission (HCMM) data, especially among the scientific community, special notifications were prepared to inform them about the data's availability, its form, and the procedures for obtaining them. To achieve the widest distribution to the primary audiences of interest, mailings were made to scientists associated with the OSTA Resource Observation Division programs and to scientific and professional societies and journals. Accompanying the notifications to the societies and journals were samples of the HCMM imagery and a description of the image's predominant characteristics. A follow-up survey was completed to determine the effectiveness of the HCMM notifications.

Source record↗
NASA NTRS1981

The heat capacity mapping mission

The first in a series of low cost Atmospheric Explorer Satellites, the Heat Capacity Mapping Mission (HCMM) was designed to evaluate the utility of thermal inertial and other thermal and reflectance data for: (1) discriminating bedrock and unconsolidated regolith types; (2) mapping soil moisture; (3) measuring plant canopy temperatures; (4) examining thermal circulation in large bodies of water; and (5) monitoring urban heat islands. Final reports from the HCMM investigator's program are beginning to define the utility of day/the night thermal data. Under favorable circumstances, some major rock types can be identified, soil moisture in extensive agricultural and alluvial terrains can be detected and at least semiqualitatively assessed; and circulation of currents in large bodies of water can be followed by noting thermal patterns.

Short, N. M.↗
NASA NTRS1983

Capacity and cutoff rate of (M+1)-ary decision rules for noisy M-ary optical PPM channel

The channel capacity C and the cutoff rate R sub o of two (M + 1)-ary decision rules for noisy M slots/symbol optical pulse position modulation (PPM) with ideal photon counting are computed and compared. Also the values of the optimum thresholds needed to minimize the signal requirements are given. With a minor increase in hardware complexity, the symbol by symbol threshold decision rule is shown to be superior to the slot by slot threshold detection and decision rule in two aspects: first, it saves more than 0.5 dB in signal energy for the very noisy cases of more than one noise photon per slot (for low noise cases it also saves signal energy, but a negligibly small amount). Second, it is more robust to variations in the noise level.

Lee, P. J.↗
NASA NTRS1981

Snow hydrology studies using data from the Heat Capacity Mapping Mission

This paper describes a study of the snow hydrology application of thermal infrared (IR) data from the Heat Capacity Mapping Mission (HCMM) satellite. The HCMM data in both imagery and digital tape formats are analyzed for two study areas: the Salt-Verde Watershed in central Arizona and the southern Sierra Nevada in California. The analysis procedures are described, including the development of a unique contour plotting program that makes it possible to overlay HCMM thermal contours directly onto the visible channel imagery. The results indicate that satellite thermal-IR data can provide the hydrologist with additional useful information on snow cover.

Barnes, J. C.↗
NASA NTRS1982

Heat capacities of liquid metals above 1500 K

Heat capacity data are presented for liquid transition metals for temperatures close to the melting point and for 3000, 4000, and 5000 K. The data have been obtained by summarizing the results of levitation, exploding-wire, and drop-calorimetry measurements reported in the literature and by providing analytical estimates where experimental data are not available. The data given here are useful in assigning heat loads and predicting structure survival during extreme temperature excursions caused by nuclear, laser, or particle irradiations.

Margrave, J. L.↗
NASA NTRS1983

Application of Heat Capacity Mapping Mission data to regional geologic analysis for mineral and energy resource evaluation

Heat Capacity Mapping Mission thermal-inertia images of a diversity of terrains and geologic settings were examined in conjunction with topographic, geologic, geophysical, and LANDSAT data. The images were found to have attributes similar to bedrock maps. In the Cascades region, two new features were identified and a method was developed to characterize regional terranes using linear feature data. Two northeast-trending Lineaments were discovered in the Overthrust Belt of Montana and Idaho. The longer of the two extends from the Idaho-Oregon border, through the Idaho batholith and across the Lewis thrust. It coincides, along segments, with mapped faults and an aeromagnetic pattern change. A major lineament crossing the Colorado Plateau and the Southern Rocky Mountians was detected on several thermal-inertial images and evidence was found for the existence of a geologic discontinuity. Vegetation-covered areas in Richfield and the Silver City quadrangle (Arizona and New Mexico) displayed thermal-inertia differences within heavily vegetation areas although no apreciable correlation was found between vegetation cover and thermal inertia. Resistant ridges and knolls have high thermal inertias and thermal-inertia contrasts occurred at lithologic and fault contacts. In the heavy vegetated Pinaleno Mountains, Arizona, a Lithologic unit obscured on LANDSAT MSS data due to the vegetation cover, exhibited a thermal-inertia contrast with its surroundings.

Watson, K.↗
NASA NTRS1983

High capacity heat pipe performance demonstration

A high capacity heat pipe which will operate in one-g and in zero-g is investigated. An artery configuration which is self-priming in one-g was emphasized. Two artery modifications were evolved as candidates to achieve one-g priming and will provide the very high performance: the four artery and the eight artery configurations. These were each evaluated analytically for performance and priming capability. The eight artery configuration was found to be inadequate from a performance standpoint. The four artery showed promise of working. A five-inch long priming element test article was fabricated using the four artery design. Plexiglas viewing windows were made on each end of the heat pipe to permit viewing of the priming activity. The five-inch primary element would not successfully prime in one-g. Difficulties on priming in one-g raised questions about zero-g priming. Therefore a small test element heat pipe for verifying that the proposed configuration will self-prime in zero-g was fabricated and delivered.

Source record↗
NASA NTRS1981

The development of a high-capacity instrument module heat transport system, appendixes

Data sheets provide temperature requirements for 82 individual instruments that are under development or planned for grouping on a space platform or pallet. The scientific objectives of these instrument packages are related to solar physics, space plasma physics, astronomy, high energy astrophysics, resources observations, environmental observations, materials processing, and life sciences. System specifications are given for a high capacity instrument module heat transport system to be used with future payloads.

Source record↗
NASA NTRS1983

Very high-resolution heat-capacity measurements near the lambda point of helium

New measurements of the heat capacity of a sample of helium 3-mm high are reported, which extend to within 5 x 10 to the -8th deg of the lambda transition at the vapor pressure. From an analysis of the results allowing for the effect of gravity, the values -0.0127 + or - 0.0026 (2 sigma) for the exponent alpha (= alpha-prime) and 1,058 + or - 0.004 for the leading singularity ratio A/A-prime are obtained. These values are in closer agreement with the theoretical predictions than those reported previously.

Lipa, J. A.↗
NASA NTRS1983

Simulation of a cockpit display concept for increased airport capacity

A research effort has been undertaken to determine the feasibility of employing a forward-looking cockpit display to provide information that would enable aircraft to utilize reduced separation, and hence increased runway capacity, through the application of multiple-glide-path approach techniques. The current study was an initial exploration into this concept in which traffic information was added to a HUD format to allow the pilot to monitor the traffic situation and to self space on a lead aircraft during a simulated single glide-path approach. The results of this study indicate that this display concept can provide sufficient information to the pilot for traffic monitoring and self separation. Additionally, the pilots noted that an increase in situational awareness, relative to conventional instrument flight, was provided by the traffic information on the display.

Abbott, T. S.↗
NASA NTRS1983

Assessment of wetland productive capacity from a remote-sensing-based model - A NASA/NMFS joint research project

NASA and the U.S. National Marine Fisheries Service have undertaken the development of Landsat Thematic Mapper (TM) technology for the evaluation of the usefulness of wetlands to estuarine fish and shellfish production. Toward this end, a remote sensing-based Productive Capacity model has been developed which characterizes the biological and hydrographic features of a Gulf Coast Marsh to predict detrital export. Regression analyses of TM simulator data for wetland plant production estimation are noted to more accurately estimate the percent of total vegetative cover than biomass, indicating that a nonlinear relationship may be involved.

Butera, M. K.↗
NASA NTRS1988

System capacity and economic modeling computer tool for satellite mobile communications systems

A unique computer modeling tool that combines an engineering tool with a financial analysis program is described. The resulting combination yields a flexible economic model that can predict the cost effectiveness of various mobile systems. Cost modeling is necessary in order to ascertain if a given system with a finite satellite resource is capable of supporting itself financially and to determine what services can be supported. Personal computer techniques using Lotus 123 are used for the model in order to provide as universal an application as possible such that the model can be used and modified to fit many situations and conditions. The output of the engineering portion of the model consists of a channel capacity analysis and link calculations for several qualities of service using up to 16 types of earth terminal configurations. The outputs of the financial model are a revenue analysis, an income statement, and a cost model validation section.

Wiedeman, Robert A.↗
NASA NTRS1987

A high-capacity aeronautical mobile satellite system

This paper describes a conceptual system design for a satellite-based aeronautical safety communications system capable of serving both general aviation aircraft and commercial aviation aircraft in the contiguous U.S. in the mid-1990s. The space segment is described, including satellite locations and coverage, spacecraft configuration, eclipse capability and stationkeeping, transponder design, and mass and power. The spacecraft mass and power budgets are given. The air mobile terminals, ground segment, and frequency plan and channelization are discussed, and the data rate, modulation/demodulation/coding, and channel spacing are considered. The message format, frequency control, system capacity, and system sensitivity are discussed.

Sue, M. K.↗
NASA NTRS1988

Capacity and cutoff rate calculations for a concatenated coding system

A model is developed for a concatenated coding system, and from it the overall channel cutoff rate and capacity is found using random coding arguments. The effects of interleaving between the inner and outer codes and of the availability of side information to the outer decoder are considered. The performance of several specific concatenated coding systems is calculated and used for comparison with the random coding results. From the analysis, a number of general conclusions regarding the design of concatenated coding systems are presented. All the results are derived assuming a block inner code.

Herro, Mark A.↗