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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Analysis of the TDRS multiple access system for possible use as an attitude control system sensor

A member of the constellation of TDR satellites (TDRS) has experienced a failure of its prime earth sensor. Failure of the remaining earth sensor could result in the inability of the satellite to control its attitude and provide user services. Loss of the satellite would be a serious event. The multiple access (MA) antenna array on the TDRS has been proposed for use as a backup sensor for the attitude control system. This paper describes our analysis of the performance of the MA array as an interferometer used for accurate attitude determination. A least squares fit of a plane to the MA phase information appears to represent the TDRS body roll and pitch within about 0.1 deg. This is sufficient for SGL pointing and MA and SSA user services. Analytic improvements that include ionospheric correction may yield sufficient accuracy for KSA user services.

Blevins, Bruce Allyn↗
NASA NTRS1993

A protocol for satellite access via use of spot-beams

In this paper, we develop a new protocol for multiple access to a GEO-satellite that utilizes an electronically-switched spot-beam. The emphasis is on an integrated voice/data protocol which takes advantage of the propagation latency and which offers centralized control with excellent delay and throughput characteristics. The protocol also allows full exploitation of the advantages of a hopping beam satellite, such as smaller earth stations and frequency re-use.

Ramseier, Stefan↗
NASA NTRS1994

Access to space study

This report summarizes the results of a comprehensive NASA in-house study to identify and assess alternate approaches to access to space through the year 2030, and to select and recommend a preferred cause of action. The goals of the study were to identify the best vehicles and transportation architectures to make major reductions in the cost of space transportation (at least 50%), while at the same time increasing safety for flight crews by at least an order of magnitude. In addition, vehicle reliability was to exceed 0.98 percent, and, as important, the robustness, pad time, turnaround time, and other aspects of operability were to be vastly improved. This study examined three major optional architectures: (1) retain and upgrade the Space Shuttle and expendable launch vehicles; (2) develop new expendable vehicles using conventional technologies and transition from current vehicles beginning in 2005; and (3) develop new reusable vehicles using advanced technology, and transition from current vehicles beginning in 2008. The launch-needs, mission model utilized for for the study was based upon today's projection of civil, defense, and commercial mission payload requirements.

Source record↗
NASA NTRS1994

NASA Access Mechanism: Lessons learned document

The six-month beta test of the NASA Access Mechanism (NAM) prototype was completed on June 30, 1993. This report documents the lessons learned from the use of this Graphical User Interface to NASA databases such as the NASA STI Database, outside databases, Internet resources, and peers in the NASA R&D community. Design decisions, such as the use of XWindows software, a client-server distributed architecture, and use of the NASA Science Internet, are explained. Users' reactions to the interface and suggestions for design changes are reported, as are the changes made by the software developers based on new technology for information discovery and retrieval. The lessons learned section also reports reactions from the public, both at demonstrations and in response to articles in the trade press and journals. Recommendations are included for future versions, such as a World Wide Web (WWW) and Mosaic based interface to heterogeneous databases, and NAM-Lite, a version which allows customization to include utilities provided locally at NASA Centers.

Burdick, Lisa↗
NASA NTRS1993

Express Payload Project - A new method for rapid access to Space Station Freedom

The deployment and permanent operation of Space Station Freedom will enable researchers to enter a new era in the 21st century, in which continuous on-orbit experimentation and observation become routine. In support of this objective, the Space Station Freedom Program Office has initiated the Express Payload Project. The fundamental project goal is to reduce the marginal cost associated with small payload development, integration, and operation. This is to be accomplished by developing small payload accommodations hardware and a new streamlined small payload integration process. Standardization of small payload interfaces, certification of small payload containers, and increased payload developer responsibility for mission success are key aspects of the Express Payload Project. As the project progresses, the principles will be applied to both pressurized payloads flown inside the station laboratories and unpressurized payloads attached to the station external structures. The increased access to space afforded by Space Station Freedom and the Express Payload Project has the potential to significantly expand the scope, magnitude, and success of future research in the microgravity environment.

Uhran, Mark L.↗
NASA NTRS1994

NASA's access to space study

A NASA study to identify and assess the major alternatives for a long range direction for space transportation is summarized. The scope of this 'access to space' study was to support all U.S. needs for space transportation for several decades into the future, including civilian, commercial, and defense needs.

Aldrich, Arnold D.↗
NASA NTRS1994

Dynamic file-access characteristics of a production parallel scientific workload

Multiprocessors have permitted astounding increases in computational performance, but many cannot meet the intense I/O requirements of some scientific applications. An important component of any solution to this I/O bottleneck is a parallel file system that can provide high-bandwidth access to tremendous amounts of data in parallel to hundreds or thousands of processors. Most successful systems are based on a solid understanding of the expected workload, but thus far there have been no comprehensive workload characterizations of multiprocessor file systems. This paper presents the results of a three week tracing study in which all file-related activity on a massively parallel computer was recorded. Our instrumentation differs from previous efforts in that it collects information about every I/O request and about the mix of jobs running in a production environment. We also present the results of a trace-driven caching simulation and recommendations for designers of multiprocessor file systems.

Kotz, David↗
NASA NTRS1994

Integrated, nonvolatile, high-speed analog random access memory

This invention provides an integrated, non-volatile, high-speed random access memory. A magnetically switchable ferromagnetic or ferrimagnetic layer is sandwiched between an electrical conductor which provides the ability to magnetize the magnetically switchable layer and a magneto resistive or Hall effect material which allows sensing the magnetic field which emanates from the magnetization of the magnetically switchable layer. By using this integrated three-layer form, the writing process, which is controlled by the conductor, is separated from the storage medium in the magnetic layer and from the readback process which is controlled by the magnetoresistive layer. A circuit for implementing the memory in CMOS or the like is disclosed.

Katti, Romney R.↗
NASA NTRS1995

On-line access to weather satellite imagery and image manipulation software

Advanced Very High Resolution Radiometer and Geostationary Operational Environmental Satellite imagery, received by antennas located at the University of Colorado, are made available to the Internet users through an on-line data access system. Created as a 'test bed' system for the National Aeronautics and Space Administration's future Earth Observing System Data and Information System, this test bed provides an opportunity to test both the technical requirements of an on-line data system and the different ways in which the general user community would employ such a system. Initiated in December 1991, the basic data system experiment four major evolutionary changes in response to user requests and requirements. Features added with these changes were the addition of on-line browse, user subsetting, and dynamic image processing/navigation. Over its lifetime the system has grown to a maximum of over 2500 registered users, and after losing many of these users due to hardware changes, the system is once again growing with its own independent mass storage system.

Emery, W.↗
NASA NTRS1995

Garnet Random-Access Memory

Random-access memory (RAM) devices of proposed type exploit magneto-optical properties of magnetic garnets exhibiting perpendicular anisotropy. Magnetic writing and optical readout used. Provides nonvolatile storage and resists damage by ionizing radiation. Because of basic architecture and pinout requirements, most likely useful as small-capacity memory devices.

Katti, Romney R.↗
NASA NTRS1993

Intelligent computer aided training systems in the real world: Making the technology accessible to the educational mainstream

Intelligent computer aided training systems hold great promise for the application of this technology to mainstream education and training. Yet, this technology, which holds such a vast potential impact for the future of education and training, has had little impact beyond the enclaves of government research labs. This is largely due to the inaccessibility of the technology to those individuals in whose hands it can have the greatest impact, teachers and educators. Simply throwing technology at an educator and expecting them to use it as an effective tool is not the answer. This paper provides a background into the use of technology as a training tool. MindLink, developed by HyperTech Systems, provides trainers with a powerful rule-based tool that can be integrated directly into a Windows application. By embedding expert systems technology it becomes more accessible and easier to master.

Kovarik, Madeline↗
NASA NTRS1995

Analysis of multiple access techniques in multi-satellite and multi-spot mobile satellite systems

In this paper the analysis of mobile satellite systems adopting constellations of multi-spot satellites over non-geostationary orbits is addressed. A link design procedure is outlined, taking into account system spectrum efficiency, probability of bit error and outage probability. A semi-analytic approach to the evaluation of outage probability in the presence of fading and imperfect power control is described, and applied to single channel per carrier (SCPC) and code division multiple access (CDMA) techniques. Some results are shown for the Globalstar, Iridium and Odyssey orbital configurations.

Corazza, Giovanni E.↗
NASA NTRS1995

Use of CDMA access technology in mobile satellite systems

Use of Code Division Multiple Access (CDMA) technology in terrestrial wireless systems is fairly well understood. Similarly, design and operation of Power Control in a CDMA-based system in a terrestrial environment is also well established. Terrestrial multipath characteristics, and optimum design of the CDMA receiver to deal with multipath and fading conditions are reliably established. But the satellite environment is different. When the CDMA technology is adopted to the satellite environment, other design features need to be incorporated (for example; interleaving, open-loop and closed-loop power control design, diversity characteristics) to achieve comparable level of system performance. In fact, the GLOBALSTAR LEO/MSS system has incorporated all these features. Contrary to some published reports, CDMA retains the advantages in the satellite environment that are similar to those achieved in the terrestrial environment. This document gives a description of the CDMA waveform and other design features adopted for mobile satellite applications.

Ramasastry, Jay↗
NASA NTRS1996

TPS Sizing for Access-to-Space Vehicles

A study was carried out to identify, develop, and benchmark simulation techniques needed for optimum thermal protection system (TPS) material selection and sizing for reusable launch vehicles. Fully viscous, chemically reacting, Navier-Stokes flow solutions over the Langley wing-body single stage to orbit (SSTO) configuration were generated and coupled with an in-depth conduction code. Results from the study provide detailed TPS heat shield materials selection and thickness sizing for the wing-body SSTO. These results are the first ever achieved through the use of a complete, trajectory based hypersonic, Navier-Stokes solution database. TPS designs were obtained for both laminar and turbulent entry trajectories using the Access-to-Space baseline materials such as tailorable advanced blanket insulation. The TPS design effects (materials selection and thickness) of coupling material characteristics to the aerothermal environment are illustrated. Finally, a sample validation case using the shuttle flight database is included.

Henline, William↗
NASA NTRS1995

On-Line Access to Weather Satellite Imagery and Image Manipulation Software

Advanced Very High Resolution Radiometer and Geostationary Operational Environmental Satellite Imagery, received by antennas located at the University of Colorado, are made available to the Internet users through an on-line data access system. Created as a 'test bed' data system for the National Aeronautics and Space Administration's future Earth Observing System Data and Information System, this test bed provides an opportunity to test both the technical requirements of an on-line data system and the different ways in which the general user community would employ such a system. Initiated in December 1991, the basic data system experienced four major evolutionary changes in response to user requests and requirements. Features added with these changes were the addition of on-line browse, user subsetting, and dynamic image processing/navigation. Over its lifetime the system has grown to a maximum of over 2500 registered users, and after losing many of these users due to hardware changes, the system is once again growing with its own independent mass storage system.

Emery, William J.↗
NASA NTRS1999

Carrier Estimation Using Classic Spectral Estimation Techniques for the Proposed Demand Assignment Multiple Access Service

In any satellite communication, the Doppler shift associated with the satellite's position and velocity must be calculated in order to determine the carrier frequency. If the satellite state vector is unknown then some estimate must be formed of the Doppler-shifted carrier frequency. One elementary technique is to examine the signal spectrum and base the estimate on the dominant spectral component. If, however, the carrier is spread (as in most satellite communications) this technique may fail unless the chip rate-to-data rate ratio (processing gain) associated with the carrier is small. In this case, there may be enough spectral energy to allow peak detection against a noise background. In this thesis, we present a method to estimate the frequency (without knowledge of the Doppler shift) of a spread-spectrum carrier assuming a small processing gain and binary-phase shift keying (BPSK) modulation. Our method relies on an averaged discrete Fourier transform along with peak detection on spectral match filtered data. We provide theory and simulation results indicating the accuracy of this method. In addition, we will describe an all-digital hardware design based around a Motorola DSP56303 and high-speed A/D which implements this technique in real-time. The hardware design is to be used in NMSU's implementation of NASA's demand assignment, multiple access (DAMA) service.

Scaife, Bradley James↗
NASA NTRS1999

"An On-Line Access System for TRMM Data"

The Tropical Rainfall Measuring Mission (TRMM), jointly sponsored by the National Aeronautics and Space Administration (NASA) of United States and the National Space Development Agency (NASDA) of Japan, provides visible, infrared, and microwave observations of tropical and subtropical rain system. The satellite observations are complemented by ground radar and rain gauge measurements to validate satellite rain estimation techniques. TRMM satellite was launched on November 27, 1997(EST). Data from TRMM are being archived, processed, and disseminated by DAAC at the Goddard Space Flight Center (GSFC) of NASA. The Goddard DAAC has been archiving Tropical Rainfall Measuring Mission (TRMM) data since the launch. The TRMM level 1 and level 2 products first have been released to public on June 15, 1998. Now, most of TRMM products, including some ground validation products are released to public. TRMM data are useful for forecast model research, disaster mitigation, climatological studies, agricultural predictions, and many other applications. An online system or user interface is designed for easy, friendly, and quick display, access, and ordering of the TRMM data. Components, features, and limitations of the system will be discussed and demonstrated. The TRMM standard products and variety of the subsets and ancillary data will be shown, and their availability will be discussed.

Rui, Hualan↗
NASA NTRS1999

Earth Science Data Archive and Access at the NASA/Goddard Space Flight Center Distributed Active Archive Center (DAAC)

The Goddard Distributed Active Archive Center (DAAC), as an integral part of the Earth Observing System Data and Information System (EOSDIS), is the official source of data for several important earth remote sensing missions. These include the Sea-viewing Wide-Field-of-view Sensor (SeaWiFS) launched in August 1997, the Tropical Rainfall Measuring Mission (TRMM) launched in November 1997, and the Moderate Resolution Imaging Spectroradiometer (MODIS) scheduled for launch in mid 1999 as part of the EOS AM-1 instrumentation package. The data generated from these missions supports a host of users in the hydrological, land biosphere and oceanographic research and applications communities. The volume and nature of the data present unique challenges to an Earth science data archive and distribution system such as the DAAC. The DAAC system receives, archives and distributes a large number of standard data products on a daily basis, including data files that have been reprocessed with updated calibration data or improved analytical algorithms. A World Wide Web interface is provided allowing interactive data selection and automatic data subscriptions as distribution options. The DAAC also creates customized and value-added data products, which allow additional user flexibility and reduced data volume. Another significant part of our overall mission is to provide ancillary data support services and archive support for worldwide field campaigns designed to validate the results from the various satellite-derived measurements. In addition to direct data services, accompanying documentation, WWW links to related resources, support for EOSDIS data formats, and informed response to inquiries are routinely provided to users. The current GDAAC WWW search and order system is being restructured to provide users with a simplified, hierarchical access to data. Data Browsers have been developed for several data sets to aid users in ordering data. These Browsers allow users to specify spatial, temporal, and other parameter criteria in searching for and previewing data.

Leptoukh, Gregory↗