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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 865 records · Page 48

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NASA NTRS1988

Determination of the Venus flyby orbits of the Soviet Vega probes using VLBI techniques

In December 1984, the Soviet Union launched two identical Vega spacecraft with the dual objective of exploring Venus and continuing to rendezvous with the comet Halley. The two Vega spacecraft encountered Venus in mid-June 1985 and successfully deployed entry probes and wind-measuring balloons into the Venus atmosphere. An objective of the Venus Balloon experiment was to measure the Venus winds using differential VLBI from the balloon and the flyby bus. NASA's Deep Space 64 meter subnet was part of a world wide network organized to collect data from the Vega probes and balloons. A critical element of this experiment was an accurate determination of the Venus relative flyby orbits of the Vega spacecraft during the 46 hour balloon lifetime. Venus flyby solutions were independently determined by the Soviets using two-way range and Doppler from Soviet stations and by JPL using one-way Doppler and VLBI data collected from the DSN. The Vega flyby solutions determined by the Soviets using a sparse two-way tracking strategy with JPL solutions using the DSN VLBI data to complement the Soviet data and with solutions using only one-way data collected by the DSN were compared.

Ellis, J.↗

NASA NTRS1987

Conceptual design of an optic based engine control system

Use of optics in the aircraft engine control systems would provide immunity to electromagnetic effects (such as lightning, radar, and nuclear pulses) for flight and propulsion control systems located throughout the aircraft and in need of communication and would result in weight reduction. This paper discusses a conceptual design of an optic engine control system that is being developed by the Fiber Optic Control System Integration (FOCSI) program. The features inherent in each of the optic-based components of the optic system, which includes the on-engine full authority digital electonic control, optic sensors, optic-based actuators, and an optic data bus for communication with the aircraft flight control system are described in detail. The diagrams of the FOCSI control system and its components are included.

Davies, W. J.↗

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

Automated load management for spacecraft power systems

An account is given of the results of a study undertaken by NASA's Marshall Space Flight Center to design and implement the load management techniques for autonomous spacecraft power systems, such as the Autonomously Managed Power System Test Facility. Attention is given to four load-management criteria, which encompass power bus balancing on multichannel power systems, energy balancing in such systems, power quality matching of loads to buses, and contingency load shedding/adding. Full implementation of these criteria calls for the addition of a second power channel.

Lollar, Louis F.↗

NASA NTRS1987

Modeling and stability analysis for the upper atmosphere research satellite auxiliary array switch component

A feedback control system, called an auxiliary array switch, was designed to connect or disconnect auxiliary solar panel segments from a spacecraft electrical bus to meet fluctuating demand for power. A simulation of the control system was used to carry out a number of design and analysis tasks that could not economically be performed with a breadboard of the hardware. These tasks included: (1) the diagnosis of a stability problem, (2) identification of parameters to which the performance of the control system was particularly sensitive, (3) verification that the response of the control system to anticipated fluctuations in the electrical load of the spacecraft was satisfactory, and (4) specification of limitations on the frequency and amplitude of the load fluctuations.

Wolfgang, R.↗

NASA NTRS1988

Thermal contact conductance of pressurized surfaces

Thermal vacuum testing has demonstrated the feasibility of the concept of pressurizing contact surfaces for the transfer of waste heat on the Space Station. Data show a thin inflatable bladder design to provide a greater contact conductance than an expandable bellows approach, with substantially less interface volume to transfer the same amount of heat. Extended vacuum testing of the Radiator-to-Thermal Bus assembly indicated a continual increase of conductance as the interface was maintained at 150 psi for a 100-hour period.

Voss, Fred E.↗

NASA NTRS1988

Performance modeling and measurement of real-time multiprocessors with time-shared buses

A closed queueing network model is constructed to address workload effects on computer performance for a highly reliable unibus multiprocessor used in real-time control. The queueing model consists of multiserver nodes and a nonpreemptive priority queue. Use of this model requires partitioning the workload into task classes. The time average steady-state solution of the queueing model directly produces useful results that are necessary in performance evaluation. The model is experimentally justified with the Fault-Tolerant Multiprocessor (FTMP) located at the NASA AIRLAB. Extensive experiments are performed on FTMP with a synthetic workload generator (SWG) to directly measure performance parameters, such as processor idle time, system bus contention, and task processing times. These measurements determine values for parameters in the queueing model. Experimental and analytic results are then compared.

Woodbury, Michael H.↗

NASA NTRS1988

On multigrid methods for the Navier-Stokes Computer

The overall architecture of the multipurpose parallel-processing Navier-Stokes Computer (NSC) being developed by Princeton and NASA Langley (Nosenchuck et al., 1986) is described and illustrated with extensive diagrams, and the NSC implementation of an elementary multigrid algorithm for simulating isotropic turbulence (based on solution of the incompressible time-dependent Navier-Stokes equations with constant viscosity) is characterized in detail. The present NSC design concept calls for 64 nodes, each with the performance of a class VI supercomputer, linked together by a fiber-optic hypercube network and joined to a front-end computer by a global bus. In this configuration, the NSC would have a storage capacity of over 32 Gword and a peak speed of over 40 Gflops. The multigrid Navier-Stokes code discussed would give sustained operation rates of about 25 Gflops.

Nosenchuck, D. M.↗

NASA NTRS1988

The ijk forms of factorization methods. II - Parallel systems

The paper considers the 'ijk forms' of LU and Cholesky factorization on certain parallel computers. This extends an earlier analysis for vector computers. Attention is restricted to local memory systems with processors that may or may not have vector capability. Special attention is given to bus architectures but qualitative analyses are given for other interconnection systems.

Ortega, J. M.↗

NASA NTRS1988

Fault tolerant system performance modeling

With the proliferation of complex digital systems on aircraft, the need to accurately predict system performance early in the system design cycle becomes imperative. In the past, system designers have relied on ad hoc methods for evaluating performance issues. This has produced systems that have not always worked as originally intended. To alleviate these design deficiencies, formal methods, with supporting tools, must be adhered to during the system design process. The use of performance modeling tools is becoming widely accepted as a way to address timing considerations of system design. An additional incentive for the use of these tools is that they allow the system architect to analyze system component interactions (i.e., bus contention, contention of functions for a processing site, and system repair activity on application performance). This inherent flexibility can result in an explicit specification of the system architecture. This paper addresses a method that supports performance modeling of fault tolerant systems using a discrete event simulation tool. An additional focus is on lessons learned from analyzing these classes of problems. The methodology and supporting work provide system architects with the capability to specify candidate architectures and accurately predict their performance in the early stages of design, where changes to system design is most cost effective. The work has been supported under NASA contract NAS1-18099. Integrated Airframe Propulsion Control System Architecture (IAPSA II). This contract addresses methodology, analysis, and detailed design of integrated control system architectures suitable for high-performance aircraft of the 1990's.

Discrete event simulation↗

NASA NTRS1989

Pulse-Population Modulation For Induction Machines

Low-frequency synthesizer developed to provide low-frequency waveform by synthesis from high-frequency power system. Waveform assembled by allowing conduction of discrete half cycles of high-frequency carrier. Frequency of synthesized wave controlled by pulse pattern. By controlling relationship between slip and stator frequencies, one operates induction motor either as motor or generator. Such bidirectional energy transducer used as starter/generator for engine, or as servo-mechanism for control of acceleration and deceleration. Other advantages include operation under controlled voltage-to-frequency ratios to maintain high-efficiency and high power factor, and no reflection of low-frequency noise into 20-kHz distribution bus.

Hansen, Irving G.↗

NASA NTRS1989

Balanced-Load Real-Time Multiprocessor System

Modularity and parallelism provide tolerance to faults and high throughput capacity. System, called MAX, is network of interconnected computers. MAX cluster consists of group of modules - each semiautonomous computer. Modules connected to each other and to other clusters by global bus and circuit-switched communication mesh.

Rasmussen, Robert D.↗

NASA NTRS1989

Adaptive Telemetry Multiplexer

Telemetry-data-acquisition unit adjusted remotely to produce changes in sampling rate, sampling channels, measurement scale, and output-bias level. Functional configuration adapted to changing conditions or new requirements by distant operator over telemetry link. Reconfiguration done in real time, without removing equipment from service. Bus-interface unit accepts reprogramming commands and translates them for low-rate adaptive multiplexer. Reprogrammable equipment reduces need for spare parts, since not necessary to stock variety of hardware with fixed characteristics. Adaptive multiplexer performs well in tests, amplitude errors less than 0.5 percent, distortion less than 0.25 percent, and crosstalk and common-mode rejection indiscernible.

Sinderson, R. L.↗

NASA NTRS1989

Electrodes For Alkali-Metal Thermoelectric Converters

Combination of thin, porous electrode and overlying collector grid reduces internal resistance of alkali-metal thermoelectric converter cell. Low resistance of new electrode and grid boosts power density nearly to 1 W/cm2 of electrode area at typical operating temperatures of 1,000 to 1,300 K. Conductive grid encircles electrode film on alumina tube. Bus wire runs along tube to collect electrical current from grid. Such converters used to transform solar, nuclear, and waste heat into electric power.

Williams, Roger M.↗

NASA NTRS1987

Open control/display system for a telerobotics work station

A working Advanced Space Cockpit was developed that integrated advanced control and display devices into a state-of-the-art multimicroprocessor hardware configuration, using window graphics and running under an object-oriented, multitasking real-time operating system environment. This Open Control/Display System supports the idea that the operator should be able to interactively monitor, select, control, and display information about many payloads aboard the Space Station using sets of I/O devices with a single, software-reconfigurable workstation. This is done while maintaining system consistency, yet the system is completely open to accept new additions and advances in hardware and software. The Advanced Space Cockpit, linked to Grumman's Hybrid Computing Facility and Large Amplitude Space Simulator (LASS), was used to test the Open Control/Display System via full-scale simulation of the following tasks: telerobotic truss assembly, RCS and thermal bus servicing, CMG changeout, RMS constrained motion and space constructible radiator assembly, HPA coordinated control, and OMV docking and tumbling satellite retrieval. The proposed man-machine interface standard discussed has evolved through many iterations of the tasks, and is based on feedback from NASA and Air Force personnel who performed those tasks in the LASS.

Keslowitz, Saul↗

NASA NTRS1988

Preliminary design study of hydrogen and ammonia resistojets for prime and auxiliary thrusters

Designs of high performance resistojets for primary and auxiliary propulsion are described.Thruster power for the primary propulsion application was in the 2 to 3 kW range while auxiliary propulsion power per thruster was 0.15 to 0.25 kW. Propellants considered were hydrogen and ammonia. The report described design techniques used to forecast the temperature and energy flux distributions using mathematical modeling by personal microcomputer. BASIC language is used throughout to give the designer rapid interaction and control. Both designs integrate compact first stage coils with concentric tubular heaters. The hybrid heater design allows better thruster power matching with the spacecraft power bus. Projected specific impulse levels were 760 to 830 s for hydrogen and 380 to 410 s for ammonia.

Page, Russell J.↗

NASA NTRS1988

Technological hurdles to the application of intercalated graphite fibers

Before intercalated graphite fibers can be developed as an effective power material, there are several technological hurdles which must be overcome. These include the environmental stability, homogeneity and bulk properties, connection procedures, and costs. Strides were made within the last several years in stability and homogeneity of intercalated graphite fibers. Bulk properties and connection procedures are areas of active research now. Costs are still prohibitive for all but the most demanding applications. None of these problems, however, appear to be unsolvable, and their solution may result in wide spread GOC application. The development of a relatively simple technology application, such as EMI shielding, would stimulate the solution of scale-up problems. Once this technology is developed, then more demanding applications, such as power bus bars, may be possible.

Gaier, James R.↗

NASA NTRS1988

A flight test design for studying airborne applications of air to ground duplex data link communications

The Automatic En Route Air Traffic Control (AERA) and the Advanced Automated System (AAS) of the NAS plan, call for utilization of data links for such items as computer generated flight clearances, enroute minimum safe altitude warnings, sector probes, out of conformance check, automated flight services, and flow management of advisories. A major technical challenge remaining is the integration, flight testing, and validation of data link equipment and procedures in the aircraft cockpit. The flight test organizational chart, was designed to have the airplane side of data link experiments implemented in the NASA Langley Research Center (LaRC) experimental Boeing 737 airplane. This design would enable investigations into implementation of data link equipment and pilot interface, operations, and procedures. The illustrated ground system consists of a work station with links to a national weather database and a data link transceiver system. The data link transceiver system could be a Mode-S transponder, ACARS, AVSAT, or another type of radio system such as the military type HF data link. The airborne system was designed so that a data link transceiver, workstation, and touch panel could be interfaced with an input output processor to the aircraft system bus and thus have communications access to other digital airplane systems.

Scanlon, Charles H.↗