Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “bus”

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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

A survey of the state-of-the-art and focused research in range systems, task 1

This final report presents the latest research activity in voice compression. We have designed a non-real time simulation system that is implemented around the IBM-PC where the IBM-PC is used as a speech work station for data acquisition and analysis of voice samples. A real-time implementation is also proposed. This real-time Voice Compression Board (VCB) is built around the Texas Instruments TMS-3220. The voice compression algorithm investigated here was described in an earlier report titled, Low Cost Voice Compression for Mobile Digital Radios, by the author. We will assume the reader is familiar with the voice compression algorithm discussed in this report. The VCB compresses speech waveforms at data rates ranging from 4.8 K bps to 16 K bps. This board interfaces to the IBM-PC 8-bit bus, and plugs into a single expansion slot on the mother board.

Omura, J. K.↗
NASA NTRS1986

Investigation of local area networks for an obiting space station

An investigation and test of various equipment was conducted to determine its state of repair and suitability for use in a test-bed computer network (to be used to simulate a space station configuration of computers for control and monitoring). A research study was also made of various network types, including the IEEE network standards: (1) Carrier Sense Multiple Access with Collision Detection. (2) Token Passing Bus (3) Token Passing Ring, and (4) the draft ANSI standard for a High Speed Local Network, CSMA with Collision Avoidance. No firm conclusions are possible at this time as to which would be most suitable. An evaluation of the user interface of a space station database program, FREDSS (Formatted Retrieval and Entry of Data for Space Station, preliminary version), was also conducted and recommendations were made for possible improvements.

Deacetis, L. A.↗
NASA NTRS1986

Electrical power system for the U.S. space station

The Space Station Electrical Power System presents many interesting challenges. It will be much larger than previous space power systems, and it must be designed for on-orbit maintenance and replacement, along with having a growth capability. The power generation, energy storage, and power management and distribution (PMAD) subsystems comprise the primary elements of the overall system. Each was analyzed by NASA Lewis Research Center and its two contractors -- Rocketdyne and TRW -- in the definition studies of the program to determine the optimum approach to minimize initial costs and life cycle costs. For the PMAD subsystem, a ring bus architecture operating at 440 V, 20 kHz, single phase, was selected. Photovoltaic and solar dynamic power generation subsystems were both studied. Major tradeoffs were made for each subsystem and for the overall system, and a hybrid system (both photovoltaic and solar dynamic) was selected.

Nored, D. L.↗
NASA NTRS1985

An overview of the Space Station Technology/Advanced Development Program

The Advanced Technology Plan of the Fiscal Year (FY) 1986 is designed to focus on the most promising technology options applicable to the Space Station (SS), selected from the list of tasks identified by the FY 1984 Technology Program as the most critical technologies to be developed for the initial SS Initial Operating Capability. Most of the current activities are in the stages of manufacture and life tests of specific SS subsystems. Special attention is given to major technologies, which include power systems (PSs) (with emphasis on a Solar Dynamic PS concept); the thermal control system (with the focus on the 'thermal bus' concept); the environmental control and life support system; and the data management system; all are illustrated schematically. Other tasks, including dynamics, communications, extravehicular activities, mechanics, propulsion, and fluid, as well as the tasks of cost, maintainability, automation and robotics, and productivity are discussed.

Carlisle, R. F.↗
NASA NTRS1985

Parallel, iterative solution of sparse linear systems - Models and architectures

Solving large, sparse, linear systems of equations is a fundamental problem in large scale scientific and engineering computation. A model of a general class of asynchronous, iterative solution methods for linear systems is developed. In the model, the system is solved by creating several cooperating tasks that each compute a portion of the solution vector. A data transfer model predicting both the probability that data must be transferred between two tasks and the amount of data to be transferred is presented. This model is used to derive an execution time model for predicting parallel execution time and an optimal number of tasks given the dimension and sparsity of the coefficient matrix and the costs of computation, synchronization, and communication. The suitability of different parallel architectures for solving randomly sparse linear systems is discussed. Based on the complexity of task scheduling, one parallel architecture, based on a broadcast bus, is presented and analyzed.

Reed, D. A.↗
NASA NTRS1985

Space power systems - 'Spacecraft 2000'

The program 'Spacecraft 2000' has the objective to identify critical, high-payoff, potential spacecraft technologies, taking into account the formulation, advocation, and the management of the requisite technology development programs. This program represents a joint NASA-industry program. The technology areas addressed by 'Spacecraft 2000' are related to spacecraft power/energy storage, thermal control/thermal management, power management and distribution, autonomous operation-control, on-board system integration, spacecraft environmental interactions, secondary propulsion, communications technologies, a total system response approach, and system-subsystem technology verification. The expected benefits of a development of advanced technologies include decreased spacecraft bus system weights, decreased mission costs, increased reliability/lifetimes, and increased operational flexibility.

Faymon, K. A.↗
NASA NTRS1986

A second-generation mobile satellite system

A design for a low-user-cost, 9000 channel capacity second generation mobile satellite system (Msat-2) for continental U.S., Alaska and Canada using two geostationary satellites at 90 and 130 deg west longitude, is presented. The increased capacity over the first generation system is obtained by use of a 20 m deployable antenna with an offset-fed antenna configuration, a high-power satellite bus, and by relaxing the north-south stationkeeping requirement to + or - 2 deg and the eclipse capability to 50 percent. Efficient frequency utilization is achieved for uplink and downlink spectra by a 7-frequency reuse scheme with 285 5-kHz channels per subband, and subband reuse of up to four times. Problems of interbeam interference and multipath fading contributed to the choice of a nonoverlapping feed for the Msat-2, and a proper modulation scheme using Gaussian baseband filtered minimum-shift-keying with differential detection.

Sue, M. K.↗
NASA NTRS1986

Development of a prototype automated on-orbit contact heat exchanger

An automated contact heat exchanger is being developed for use aboard the manned Space Station, serving as an interface heat exchanger between the pressurized module internal thermal buses and the central external thermal bus. The concept makes use of an array of flattened, thin-walled, flexible tubes that expand or contract to make or break the thermal connection as the internal pressure changes. Because of its simplicity, it permits on-orbit assembly by the remote manipulator system, thus eliminating the need for expensive EVA to make connections. A design methodology based on stress and thermal analyses has been developed and used to perform trade-offs between performance and cost, and to optimize design parameters. Simple verification tests have been performed to confirm the stress analysis model. Two conceptual variants of the contact heat exchanger are described, each designed for a 25 kW total heat load and a minimum uniform heat flux of 2.15 W/sq cm.

Lee, C. Y.↗
NASA NTRS1986

The Venus radar mapper spacecraft design

This paper discusses the driving mission requirements on the VRM spacecraft, the resulting design, and the spacecraft performance capabilities. The spacecraft design is driven by fine pointing requirements for radar mapping resolution, by extremes of thermal environment in the Venus orbit, and by high instrument power requirements. The spacecraft design emphasized use of as much existing hardware and software as possible to meet the cost constraints. Existing design was used where hardware was not already available. The VRM spacecraft utilizes the spare Voyager High Gain Antenna (HGA) and equipment bus, the Galileo computers and power conditioning equipment, and Mariner Medium Gain Antenna (MGA). Further cost savings were possible by using the HGA for both radar mapping at S-band frequency and high rate data playback at X-band frequency. The use of the Star 48 B solid rocket motor for VOI reduced propulsion system cost and complexity. The design tradeoffs that led to the VRM spacecraft configuration and the performance capabilities of the spacecraft are summarized for each subsystem.

Gamber, T.↗
NASA NTRS1987

Controller for a High-Power, Brushless dc Motor

Driving and braking torques controllable. Control circuit operates 7-kW, 45-lb-ft (61-N-m), three-phase, brushless dc motor in both motor and generator modes. In motor modes, energy from power source is pulse-width modulated to motor through modified "H-bridge" circuit, in generator mode, energy from motor is pulse-width modulated into bank of load resistors to provide variable braking torques. Circuit provides high-resolution torque control in both directions over wide range of speeds and torques. Tested successfully at bus voltages up to 200 Vdc and currents up to 45 A.

Fleming, David J.↗
NASA NTRS1986

Advanced thermal energy management: A thermal test bed and heat pipe simulation

Work initiated on a common-module thermal test simulation was continued, and a second project on heat pipe simulation was begun. The test bed, constructed from surplus Skylab equipment, was modeled and solved for various thermal load and flow conditions. Low thermal load caused the radiator fluid, Coolanol 25, to thicken due to its temperature avoided by using a regenerator-heat-exchanger. Other possible solutions modeled include a radiator heater and shunting heat from the central thermal bus to the radiator. Also, module air temperature can become excessive with high avionics load. A second preoject concerning advanced heat pipe concepts was initiated. A program was written which calculates fluid physical properties, liquid and vapor pressure in the evaporator and condenser, fluid flow rates, and thermal flux. The program is directed to evaluating newer heat pipe wicks and geometries, especially water in an artery surrounded by six vapor channels. Effects of temperature, groove and slot dimensions, and wick properties are reported.

Barile, Ronald G.↗
NASA NTRS1987

Microgravity fluid management in two-phase thermal systems

Initial studies have indicated that in comparison to an all liquid single phase system, a two-phase liquid/vapor thermal control system requires significantly lower pumping power, demonstrates more isothermal control characteristics, and allows greater operational flexibility in heat load placement. As a function of JSC's Work Package responsibility for thermal management of space station equipment external to the pressurized modules, prototype development programs were initiated on the Two-Phase Thermal Bus System (TBS) and the Space Erectable Radiator System (SERS). JSC currently has several programs underway to enhance the understanding of two-phase fluid flow characteristics. The objective of one of these programs (sponsored by the Microgravity Science and Applications Division at NASA-Headquarters) is to design, fabricate, and fly a two-phase flow regime mapping experiment in the Shuttle vehicle mid-deck. Another program, sponsored by OAST, involves the testing of a two-phase thermal transport loop aboard the KC-135 reduced gravity aircraft to identify system implications of pressure drop variation as a function of the flow quality and flow regime present in a representative thermal system.

Parish, Richard C.↗
NASA NTRS1987

Concurrent communication among multi-transceiver stations over shared media

In order to increase a local-area network's throughput beyond a single bus data rate without using dedicated switching nodes, multiple buses and multitransceiver stations are required. The design space of single-hop interconnections is explored among such stations. Interconnections are presented whose throughput can grow quadratically with the number of transmitters and receivers per station. These are referred to as selective broadcast interconnections (SBIs). The performance of various SBIs are studied. A spread-spectrum channel can accommodate several current successful transmission, and a single-transceiver node can thus utilize only a small fraction of the channel capacity. In order to allocate the appropriate fraction of capacity to a busy node, it is proposed to equip it with several transmitters and receivers, thereby turning it into a supernode. Several architectures and operation policies for supernodes are suggested and compared. It is shown that a supernode can significantly outperform a collection of independent conventional nodes with the same total numbers of transmitters and receivers. Packet-radio networks with half-duplex nodes, as well as networks with full-duplex nodes, are considered.

Birk, Yitzhak↗
NASA NTRS1987

Control considerations for high frequency, resonant, power processing equipment used in large systems

Addressed is a class of resonant power processing equipment designed to be used in an integrated high frequency (20 KHz domain), utility power system for large, multi-user spacecraft and other aerospace vehicles. It describes a hardware approach, which has been the basis for parametric and physical data used to justify the selection of high frequency ac as the PMAD baseline for the space station. This paper is part of a larger effort undertaken by NASA and General Dynamics to be sure that all potential space station contractors and other aerospace power system designers understand and can comfortably use this technology, which is now widely used in the commercial sector. In this paper, we will examine control requirements, stability, and operational modes; and their hardware impacts from an integrated system point of view. The current space station PMAD system will provide the overall requirements model to develop an understanding of the performance of this type of system with regard to: (1) regulation; (2) power bus stability and voltage control; (3) source impedance; (4) transient response; (5) power factor effects, and (6) limits and overloads.

Mildice, J. W.↗
NASA NTRS1987

Development of an emulation-simulation thermal control model for space station application

An improved capability for comparing various techniques for thermal management in the Space Station was developed. Current planning for the orbiting space station calls for a dual keel configuration. The thermal control system (TCS) for the space is composed of a central TCS and internal thermal control systems for the modules, as well as service facilities and attached payloads. The internal TCS may be attacted to the central TCS through a thermal bus. The central TCS is composed of a main transport system which collects waste thermal energy from each of the modules and transports it through coolant lines to the main rejection system. The waste heat loads in the modules arise from electrical and electronic equipment as well as metabolic loads in the manned modules. Several candidate technologies are being considered for acquiring the waste heat loads, for transporting the thermal energy between the acquisition and rejection systems, and for rejecting the waste heat to space. The analysis techniques described were developed for use in evaluating reliability, weights, costs, volumes, and power requirements for configurations using different candidates and different mission parameters.

Hartley, James G.↗
NASA NTRS1987

Effect of long-term exposure to Low Earth Orbit (LEO) space environment

Data obtained from components and materials from the Solar Maximum Mission satellite are presented and compared to data for similar materials obtained from the Advanced Composite Materials Exposure to Space Experiment (ACOMEX) flown on Shuttle mission STS-41G. In addition to evaluation of surface erosion and mass loss that may be of importance to very long-term missions, comparisons of solar absorptance and thermal emittance measurements for both long and short term exposures were made. Although the ratio of absorptance over emittance can be altered by proper choice of materials to ensure a proper operating environment for the spacecraft, once the thermal design is established, it is important that the material properties not change in order to maintain the operating environment for many payload and bus items such as electronics, batteries, fuel, etc. However, data presented show significant changes after short exposure in low Earth environment. Moreover, the measured changes are shown to differ according to the manner of exposure, i.e., normal or oblique, which also affects the resultant eroded surface morphology. These results identify constraints to be considered in development of flight experiments or laboratory testing.

Zimcik, D. G.↗
NASA NTRS1987

Spacecraft 2000: The challenge of the future

Considerable opportunity exists to improve the systems, subsystems, components, etc., included in the space station bus, the non-payload portion of the spacecraft. The steps followed to date, the challenges being faced by industry, and the progress toward establishing a new NASA initiative which will identify the technologies required to build spacecraft of the 21st century and which will implement the technology development/validation programs necessary are described.

Brandhorst, Henry W., Jr.↗
NASA NTRS1987

Network protocols for real-time applications

The Fiber Distributed Data Interface (FDDI) and the SAE AE-9B High Speed Ring Bus (HSRB) are emerging standards for high-performance token ring local area networks. FDDI was designed to be a general-purpose high-performance network. HSRB was designed specifically for military real-time applications. A workshop was conducted at NASA Ames Research Center in January, 1987 to compare and contrast these protocols with respect to their ability to support real-time applications. This report summarizes workshop presentations and includes an independent comparison of the two protocols. A conclusion reached at the workshop was that current protocols for the upper layers of the Open Systems Interconnection (OSI) network model are inadequate for real-time applications.

Johnson, Marjory J.↗