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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 703 records · Page 39

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NASA NTRS1987

Results of the ACCESS experiment

All basic EVA space construction tasks included in the experiment were accomplished on-orbit successfully, and the construction task time shows good correlation with neutral buoyancy data. However, the flight assembly times were slightly longer than the best times obtained in the water tank. This result was attributed by the EVA astronauts to the new, tighter tolerance truss hardware used on-orbit as opposed to the well-worn training hardware used in the neutral buoyancy and was, thus, not a space related phenomenon. The baseline experiment demonstrated that erectable structure can be assembled effectively by astronauts in EVA. The success of ACCESS confirmed the feasibility of EVA space assembly of erectable trusses and played a role in the decision to baseline the Space Station as a 5 meter erectable structure.

Heard, Walter L., Jr.↗

NASA NTRS1988

An access alternative for mobile satellite networks

Conceptually, this paper discusses strategies of digital satellite communication networks for a very large number of low density traffic stations. These stations can be either aeronautical, land mobile, or maritime. The techniques can be applied to international, domestic, regional, and special purpose satellite networks. The applications can be commercial, scientific, military, emergency, navigational or educational. The key strategy is the use of a non-orthogonal access method, which tolerates overlapping signals. With n being either time or frequency partitions, and with a single overlapping signal allowed, a low cost mobile satellite system can be designed with n squared (n squared + n + 1) number of terminals.

Wu, W. W.↗

NASA NTRS1987

Study of optoelectronic switch for satellite-switched time-division multiple access

The use of optoelectronic switching for satellite switched time division multiple access will improve the isolation and reduce the crosstalk of an IF switch matrix. The results are presented of a study on optoelectronic switching. Tasks include literature search, system requirements study, candidate switching architecture analysis, and switch model optimization. The results show that the power divided and crossbar switching architectures are good candidates for an IF switch matrix.

Su, Shing-Fong↗

NASA NTRS1988

Accessing space: A catalogue of process, equipment and resources for commercial users

This catalogue, produced by NASA's Office of Commercial Programs, provides a broad source of information for the commercial developer interested in the areas of microgravity research and remote sensing. Methods for accessing space for research are reviewed including the shuttle, expendable launch vehicles, suborbital sounding rockets, experimental aircraft, and drop towers and other ground-based facilities. Procedures for using these vehicles and facilities are described along with funding options to pay for their use. Experiment apparatus and carriers for microgravity research are also described. A separate directory of resources and services is also included which contains a listing of transportation products and services, a listing of businesses and industries which provide space-related services and products, and a listing of the NASA and CCDS (Center for the Commercial Development of Space) points of contact.

Source record↗

NASA NTRS1989

Parallel Optical Random Access Memory (PORAM)

It is shown that the need to minimize component count, power and size, and to maximize packing density require a parallel optical random access memory to be designed in a two-level hierarchy: a modular level and an interconnect level. Three module designs are proposed, in the order of research and development requirements. The first uses state-of-the-art components, including individually addressed laser diode arrays, acousto-optic (AO) deflectors and magneto-optic (MO) storage medium, aimed at moderate size, moderate power, and high packing density. The next design level uses an electron-trapping (ET) medium to reduce optical power requirements. The third design uses a beam-steering grating surface emitter (GSE) array to reduce size further and minimize the number of components.

Alphonse, G. A.↗

NASA NTRS1988

A 20/30 GHz personal access satellite system study

JPL is exploring the potential and feasibility of a personal access satellite system which will offer the user freedom and mobility. This paper defines the system concept and applications, presents a strawman design, and identifies the enabling technologies. The system as currently conceived could provide voice and data services to users in the Contiguous United States (CONUS) in the late 1990s to the early 2000s using the 20/30 GHz bands.

Sue, Miles K.↗

NASA NTRS1989

Frequency-hopping codes for multiple-access channels - A geometric approach

Basic notions pertinent to code-division multiple-user communication signals are defined in set-theoretic terms. A general treatment of composition codes by identifying a time-frequency spectrogram with a set of points in a finite plane is provided. It is shown that a finite affine plane is a powerful generator of frequency-hopping codes for multiple-access channels, and that it provides optimum performance codes in a noiseless environment.

Jevtic, Dusan B.↗

NASA NTRS1990

Programmable Direct-Memory-Access Controller

Proposed programmable direct-memory-access controller (DMAC) operates with computer systems of 32000 series, which have 32-bit data buses and use addresses of 24 (or potentially 32) bits. Controller functions with or without help of central processing unit (CPU) and starts itself. Includes such advanced features as ability to compare two blocks of memory for equality and to search block of memory for specific value. Made as single very-large-scale integrated-circuit chip.

Hendry, David F.↗

NASA NTRS1990

Computer-Access-Code Matrices

Authorized users respond to changing challenges with changing passwords. Scheme for controlling access to computers defeats eavesdroppers and "hackers". Based on password system of challenge and password or sign, challenge, and countersign correlated with random alphanumeric codes in matrices of two or more dimensions. Codes stored on floppy disk or plug-in card and changed frequently. For even higher security, matrices of four or more dimensions used, just as cubes compounded into hypercubes in concurrent processing.

Collins, Earl R., Jr.↗

NASA NTRS1989

Satellite-matrix-switched, time-division-multiple-access network simulator

A versatile experimental Ka-band network simulator has been implemented at the NASA Lewis Research Center to demonstrate and evaluate a satellite-matrix-switched, time-division-multiple-access (SMS-TDMA) network and to evaluate future digital ground terminals and radiofrequency (RF) components. The simulator was implemented by using proof-of-concept RF components developed under NASA contracts and digital ground terminal and link simulation hardware developed at Lewis. This simulator provides many unique capabilities such as satellite range delay and variation simulation and rain fade simulation. All network parameters (e.g., signal-to-noise ratio, satellite range variation rate, burst density, and rain fade) are controlled and monitored by a central computer. The simulator is presently configured as a three-ground-terminal SMS-TDMA network.

Ivancic, William D.↗

NASA NTRS1989

Access to Max '91 information via computer networks

Various types of flare information, activity, active region reports, x ray plots and daily Campaign Action notices are now available on SPAN, and INTERNET. Although this system was developed for use by Max '91 participants during campaigns, it is updated daily and maintained at times outside of campaigns. Thus it is available for general use outside of campaigns. The Space Environment Laboratory maintains VAX and Apollo systems, both of which are on INTERNET. The VAX is also on the SPAN network as node SELVAX or 9555. Details of access to files on the VAX are given.

Kiplinger, Alan L.↗

NASA NTRS1989

Satellite range delay simulator for a matrix-switched time division multiple-access network simulator

The Systems Integration, Test, and Evaluation (SITE) facility at NASA Lewis Research Center is presently configured as a satellite-switched time division multiple access (SS-TDMA) network simulator. The purpose of SITE is to demonstrate and evaluate advanced communication satellite technologies, presently embodied by POC components developed under NASA contracts in addition to other hardware, such as ground terminals, designed and built in-house at NASA Lewis. Each ground terminal in a satellite communications system will experience a different aspect of the satellite's motion due mainly to daily tidal effects and station keeping, hence a different duration and rate of variation in the range delay. As a result of this and other effects such as local oscillator instability, each ground terminal must constantly adjust its transmit burst timing so that data bursts from separate ground terminals arrive at the satellite in their assigned time slots, preventing overlap and keeping the system in synchronism. On the receiving end, ground terminals must synchronize their local clocks using reference transmissions received through the satellite link. A feature of the SITE facility is its capability to simulate the varying propagation delays and associated Doppler frequency shifts that the ground terminals in the network have to cope with. Delay is achieved by means of two NASA Lewis designed and built range delay simulator (RDS) systems, each independently controlled locally with front panel switches or remotely by an experiment control and monitor (EC/M) computer.

Nagy, Lawrence A.↗

NASA NTRS1990

Design of a telescoping tube system for access and handling equipment

Spacecraft processing presents unique problems for the design of ground support equipment. A telescoping tube system consists of a number of nested structural tubes that can be extended and retracted (telescoped) while supporting a load. A typical telescoping tube system provides lateral, torsional, and vertical support for an access platform. Several concepts for improved telescoping tubes were developed with emphasis placed on reliability, ease of maintenance, and cost effectiveness. The most promising prototype design utilizes adjustable rollers running on tracks bolted to the tube sections. A wire rope deployment system ensures that all tube sections are controlled during extension and retraction. Track shimming and roller adjustment allow for fabrication of a high precision tube assembly that does not require extensive machining or unusually large shop equipment. The use of rolling contact eliminates the contamination problems encountered with sliding tubes in previous designs. The prototype design is suitable for indoor or outdoor use. A prototype tube assembly was fabricated and tested for strength, stiffness, maintainability, and endurance.

Littlefield, Alan C.↗

NASA NTRS1990

Clean access platform for orbiter

The design of the Clean Access Platform at the Kennedy Space Center, beginning with the design requirements and tracing the effort throughout development and manufacturing is described. Also examined are: (1) A system description; (2) Testing requirements and conclusions; (3) Safety and reliability features; (4) Major problems experienced during the project; and (5) Lessons learned, including features necessary for the effective design of mechanisms used in clean systems.

Morrison, H.↗

NASA NTRS1990

Satellite range delay simulator for a matrix-switched time division multiple-access network simulation system

The Systems Integration, Test, and Evaluation (SITE) facility at NASA Lewis Research Center is presently configured as a satellite-switched time division multiple access (SS-TDMA) network simulator. The purpose of SITE is to demonstrate and evaluate advanced communication satellite technologies, presently embodied by POC components developed under NASA contracts in addition to other hardware, such as ground terminals, designed and built in-house at NASA Lewis. Each ground terminal in a satellite communications system will experience a different aspect of the satellite's motion due mainly to daily tidal effects and station keeping, hence a different duration and rate of variation in the range delay. As a result of this and other effects such as local oscillator instability, each ground terminal must constantly adjust its transmit burst timing so that data bursts from separate ground terminals arrive at the satellite in their assigned time slots, preventing overlap and keeping the system in synchronism. On the receiving end, ground terminals must synchronize their local clocks using reference transmissions received through the satellite link. A feature of the SITE facility is its capability to simulate the varying propagation delays and associated Doppler frequency shifts that the ground terminals in the network have to cope with. Delay is ahcieved by means of two NASA Lewis designed and built range delay simulator (RDS) systems, each independently controlled locally with front panel switches or remotely by an experiment control and monitor (EC/M) computer.

Nagy, Lawrence A.↗

NASA NTRS1990

Satellite-matrix-switched, time-division-multiple-access network simulator

Ivancic, William D.↗

NASA NTRS1989

Ku-band interferences for the Space Station multiple access link

The multiple access (MA) system, an essential part of the United States Space Station, will be used to provide simultaneous communication services, voice and command, telemetry and video, between the Space Station and all the different coorbiting user vehicles. The system is designed to operate in the Ku-band frequencies between 14 GHz and 14.89 GHz. Within this band, there are other users that could pose serious interference potential. The extent of the interference and its impact on the system operations are analyzed using a Monte Carlo simulation. Worst-case analysis indicated that certain links are very susceptible to interference. Mitigation techniques involving both hardware changes and operation constraints are presented. With the modification of some of the design and implementation of some of the mitigation techniques, the interference levels were found to be only a few percent and to occur in a burst manner.

Loh, Y. C.↗

NASA NTRS1991

Self-Testing Static Random-Access Memory

Proposed static random-access memory for computer features improved error-detecting and -correcting capabilities. New self-testing scheme provides for detection and correction of errors at any time during normal operation - even while data being written into memory. Faults in equipment causing errors in output data detected by repeatedly testing every memory cell to determine whether it can still store both "one" and "zero", without destroying data stored in memory.

Chau, Savio↗