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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 217 records · Page 12

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NASA NTRS1991

A new active virtual pivot six-degree-of-freedom hand controller for aerospace applications

During 1989 a new six-degree-of-freedom (6-DOF) active hand controller concept was designed and constructed based on the concept of a virtual pivot. This concept, labeled VPHC, was first demonstrated in a 1985 study and a patent was issued in 1990. Operator control input occurs via a force/torque sensor rigidly mounted to the handgrip. Sensed force/torque signals are used by microprocessors to generate motor drive control for each of six independently controlled motors mounted on the three-legged mechanism. The control microprocessor uses input biasing and rate-feedback motor controllers to generate the sensed feel of virtual springs and deadbands found in more conventional designs. An important advantage of this design is that the location of the virtual pivots, reflective forces and torques, breakout force levels, sensed spring rates, and operating modes, can be changed simply by changing the software. This approach yields an autonomous VPHC that can easily adapt itself to an individual operator (by software extension). A proof-of-concept version has been demonstrated, and further improvements are currently being studied and implemented.

Marshall, William C.↗

NASA NTRS1990

High power density dc-to-dc converters for aerospace applications

Three dc-to-dc converter topologies aimed at high-power high-frequency applications are introduced. Major system parasitics, namely, the leakage inductance of the transformer and the device output capacitance are efficiently utilized. Of the three circuits, the single-phase and three-phase versions of the dual active bridge topology demonstrate minimal stresses, better utilization of the transformer, bidirectional, and buck-boost modes of operation. All circuits operate at a constant switching frequency, thus simplifying design of the reactive elements. The power transfer characteristics and soft-switching regions on the Vout-Iout plane are identified. Two coaxial transformers with different cross-sections were built for a rating of 50 kVA. Based on the single-phase dual active bridge topology, a 50 kW, 50 kHz converter operating at an input voltage of 200 Vdc and an output voltage of 1600 Vdc was fabricated. Characteristics of current-fed output make the dual active bridge topologies amenable to paralleling and hence extension to megawatt power levels. Projections to a 1 MW system operating from a 500 Vdc input, at an output voltage of 10 kVdc and a switching frequency of 50 kHz, using MOS-controlled thyristors, coaxially wound transformers operating at three times the present current density with cooling, and multilayer ceramic capacitors, suggests an overall power density of 0.075 to 0.08 kg/kW and an overall efficiency of 96 percent.

Divan, Deepakraj M.↗

NASA NTRS1991

Electrodeposited Zinc-Nickel as an Alternative to Cadmium Plating for Aerospace Application

Corrosion evaluation studies were conducted on 4130 alloy steel samples coated with electrodeposited zinc-nickel and samples coated with electrodeposited cadmium. The zinc nickel was deposited by the selection electrochemical metallizing process. These coated samples were exposed to a 5-percent salt fog environment at 35 plus or minus 2 C for a period ranging from 96 to 240 hours. An evaluation of the effect of dichromate coatings on the performance of each plating was conducted. The protection afforded by platings with a dichromate seal was compared to platings without the seal. During the later stages of testing, deposit adhesion and the potential for hydrogen entrapment were also evaluated.

Mcmillan, V. C.↗

NASA NTRS1991

Small capacity, low cost (Ni-H2) design concept for commercial, military, and higher-volume aerospace applications

Nickel-Hydrogen (Ni-H2) batteries have become the technology of choice for both commercial and defense-related satellites in geosynchronous orbits. Their use for low-earth- orbit (LEO) applications is not as advanced, but seems just as inevitable because of their inherent advantages over nickel-cadmium batteries. These include superior energy density, longer cycle life, and better tolerance to over-charge and reversal. Ni-H2 cells have the added advantage in both construction and operation of not presenting the environmental possibility of cadmium pollution. Unfortunately, but necessarily, the design of these cells has been driven to high cost by the sophistication of the satellites and their uses. Now, using most of the same concepts but less costly materials and techniques, a low-cost, small cell design has been developed. Combined with the concept of the common pressure vessel, this new design promises to be ideal for the "small-sat" and commercial markets which, increasingly, are calling for large numbers of less-expensive satellites.

James R Wheeler↗

NASA NTRS1990

Aerospace applications of high temperature superconductivity

A review is presented of all the applications that are part of the NASA program to develop space technology capitalizing on the potential benefit of high temperature superconducting materials. The applications in three major areas are being pursued: sensors and cryogenic systems, space communications, and propulsion and power systems. This review places emphasis on space communications applications and the propulsion and power applications. It is concluded that the power and propulsion applications will eventually be limited by structural considerations rather than by the availability of suitable superconductors. A cursory examination of structural limitations implied by the virial theorem suggested that there is an upper limit to the size of high field magnetic systems that are feasible in space.

Connolly, D. J.↗

NASA NTRS1990

A review of properties and potential aerospace applications of electrically conducting polymers

An overview of current research in conducting polymers is presented. Emphasis is placed on development of materials useful for aeronautic and space applications. Research on organic conducting polymers began in the early 1970s with the discovery of polyacetylene. Since then, many polymers which share structural characteristics with polyacetylene have been prepared which conduct electricity, especially when they are doped with suitable agents. Problems with environmental instability, difficult processing, poor mechanical properties and high cost have slowed the development of conducting polymers. However, practical use of these materials is imminent, based on recent refinements in understanding how polymers conduct, more systematic approaches to the development of new materials, and significant improvements in both the processing and properties.

Meador, Mary Ann B.↗

NASA NTRS1990

A fiber-optic current sensor for aerospace applications

A robust, accurate, broadband, alternating current sensor using fiber optics is being developed for space applications at power frequencies as high as 20 kHz. It can also be used in low and high voltage 60-Hz terrestrial power systems and in 400-Hz aircraft systems. It is intrinsically electromagnetic interference (EMI) immune and has the added benefit of excellent isolation. The sensor uses the Faraday effect in optical fiber and standard polarimetric measurements to sense electrical current. The primary component of the sensor is a specially treated coil of single-mode optical fiber, through which the current carrying conductor passes. Improved precision is accomplished by temperature compensation by means of signals from a novel fiber-optic temperature sensor embedded in the sensing head. The technology used in the sensor is examined and the results of precision tests conducted at various temperatures within the wide operating range are given. The results of early EMI tests are also given.

Patterson, Richard L.↗

NASA NTRS1990

A fiber-optic current sensor for aerospace applications

A robust, accurate, broadband, alternating current sensor using fiber optics is being developed for space applications at power frequencies as high as 20 kHz. It can also be used in low- and high-voltage 60-Hz terrestrial power systems and in 400-Hz aircraft systems. It is intrinsically EMI (electromagnetic interference) immune and has the added benefit of excellent isolation. The sensor uses the Faraday effect in optical fiber and standard polarimetric measurements to sense electrical current. The primary component of the sensor is a specially treated coil of single-mode optical fiber, through which the current carrying conductor passes. Improved precision is accomplished by temperature compensation by means of signals from a fiber-optic temperature sensor embedded in the sensing head. The authors report on the technology contained in the sensor and also relate the results of precision tests conducted at various temperatures within the wide operating range. The results of early EMI tests are shown.

Patterson, Richard L.↗

NASA NTRS1991

Electrically conducting polymers for aerospace applications

Current research on electrically conducting polymers from 1974 to the present is reviewed focusing on the development of materials for aeronautic and space applications. Problems discussed include extended pi-systems, pyrolytic polymers, charge-transfer systems, conductive matrix resins for composite materials, and prospects for the use of conducting polymers in space photovoltaics.

Meador, Mary Ann B.↗

NASA NTRS1990

Optical techniques for determination of normal shock position in supersonic flows for aerospace applications

Techniques for the quantitative determination of shock position in supersonic flows using direct and indirect methods is presented. A description of an experimental setup is also presented, different configurations of shock position sensing systems are explained, and some experimental results are given. All of the methods discussed are analyzed to determine the ease of technology transfer from the laboratory to in-flight operation.

Adamovsky, Grigory↗

NASA NTRS1992

Progress in the development of lightweight nickel electrode for aerospace applications

The NASA Lewis Research Center is currently developing nickel electrodes for nickel-hydrogen (Ni-H2) cells and batteries. These electrodes are lighter in weight and have higher specific energy than the heavy sintered state of the art nickel electrodes. In the present approach, lightweight materials or plaques are used as conductive supports for the nickel hydroxide active material. These plaques (fiber, felt, and nickel plated plastic) are fabricated into nickel electrodes by electrochemically impregnating them with active material. Initial performance tests include capacity measurements at five discharge levels, C/2, 1.0C, 1.37C, 2.0C, and 2.74C. The electrodes that pass the initial tests are life cycle tested at 40 and 80 percent depths of discharge (DOD). Different formulations of nickel fiber materials obtained from several manufacturers are currently being tested as possible candidates for nickel electrodes. Over 7,000 cycles of life cycle testing have been accumulated at 40 percent DOD, using the lightweight fiber electrode in a boiler plate Ni-H2 cell with stable voltage.

Britton, Doris L.↗

NASA NTRS1991

Li/BCX, SVO, and CSC cells: Power sources for aerospace applications

The operating characteristics and designs are given for some electrochemical cells. All of the electrochemistries have lithium compounds. Descriptions are given for each cell including open circuit voltage, room temperature discharge currents, operating temperature range, weight, safety fuse, energy density, and discharge currents.

Clark, William D. K.↗

NASA NTRS1992

Temperature and heat flux measurements: Challenges for high temperature aerospace application

The measurement of high temperatures and the influence of heat transfer data is not strictly a problem of either the high temperatures involved or the level of the heating rates to be measured at those high temperatures. It is a problem of duration during which measurements are made and the nature of the materials in which the measurements are made. Thermal measurement techniques for each application must respect and work with the unique features of that application. Six challenges in the development of measurement technology are discussed: (1) to capture the character and localized peak values within highly nonuniform heating regions; (2) to manage large volumes of thermal instrumentation in order to efficiently derive critical information; (3) to accommodate thermal sensors into practical flight structures; (4) to broaden the capabilities of thermal survey techniques to replace discrete gages in flight and on the ground; (5) to provide supporting instrumentation conduits which connect the measurement points to the thermally controlled data acquisition system; and (6) to develop a class of 'vehicle tending' thermal sensors to assure the integrity of flight vehicles in an efficient manner.

Neumann, Richard D.↗

NASA NTRS1992

Cerebellar neurocontroller project, for aerospace applications, in a civilian neurocomputing initiative in the 'decade of the brain'

A key question is how to utilize civilian government agencies along with an industrial consortium to successfully complement the so far primarily defense-oriented neural network research. Civilian artificial neural system projects, such as artificial cerebellar neurocontrollers aimed at duplicating nature's existing neural network solutions for adaptive sensorimotor coordination, are proposed by such a synthesis. The cerebellum provides an intelligent interface between higher possibly symbolic levels of human intelligence and repetitious demands of real world conventional controllers. The generation of such intelligent interfaces could be crucial to the economic feasibility of the human settlement of space and an improvement in telerobotics techniques to permit the cost-effective exploitation of nonterrestrial materials and planetary exploration and monitoring. The authors propose a scientific framework within which such interagency activities could effectively cooperate.

Pellionisz, Andras J.↗

NASA NTRS1993

Engineering science research issues in high power density transmission dynamics for aerospace applications

This paper discusses analytical and experimental approaches that will be needed to understand dynamic, vibro-acoustic and design characteristics of high power density rotorcraft transmissions. Complexities associated with mathematical modeling of such systems will be discussed. An overview of research work planned during the next several years will be presented, with emphasis on engineering science issues such as gear contact mechanics, multi-mesh drive dynamics, parameter uncertainties, vibration transmission through bearings, and vibro-acoustic characteristics of geared rotor systems and housing-mount structures. A few examples of work in progress are cited.

Singh, Rajendra↗

NASA NTRS1993

The development of hydrogen sensor technology for aerospace applications

The motivation and present status of each of the major components of the NASA Lewis Research Center hydrogen sensor program. The testing facility used to test the sensors and the proposed expansion of this facility are discussed. The Schottky diode prototype sensors, the use of SiC as a semiconductor for a hydrogen sensor, and the present characterization of PdCr are addressed. Future directions for the program are examined. It is concluded that results thus far are encouraging and that further development work is necessary.

Hunter, Gary W.↗

NASA NTRS1993

Cognitive engineering in aerospace application: Pilot interaction with cockpit automation

Because of recent incidents involving glass-cockpit aircraft, there is growing concern with cockpit automation and its potential effects on pilot performance. However, little is known about the nature and causes of problems that arise in pilot-automation interaction. The results of two studies that provide converging, complementary data on pilots' difficulties with understanding and operating one of the core systems of cockpit automation, the Flight Management System (FMS) is reported. A survey asking pilots to describe specific incidents with the FMS and observations of pilots undergoing transition training to a glass cockpit aircraft served as vehicles to gather a corpus on the nature and variety of FMS-related problems. The results of both studies indicate that pilots become proficient in standard FMS operations through ground training and subsequent line experience. But even with considerable line experience, they still have difficulties tracking FMS status and behavior in certain flight contexts, and they show gaps in their understanding of the functional structure of the system. The results suggest that design-related factors such as opaque interfaces contribute to these difficulties which can affect pilots' situation awareness. The results of this research are relevant for both the design of cockpit automation and the development of training curricula specifically tailored to the needs of glass cockpits.

Sarter, Nadine R.↗

NASA NTRS1993

Actively controlled shaft seals for aerospace applications

An electronically controlled mechanical seal for use as the purge gas seal in a liquid oxygen turbo pump has been fabricated and tested under transient operating conditions. The thickness of the lubricating film is controlled by adjusting the coning of the carbon face. This is accomplished by applying a voltage to a piezoelectric actuator to which the carbon face is bonded. The seal has been operated with a closed-loop control system that utilizes either the leakage rate or the seal face temperature as the feedback. Both speed and pressure transients have been imposed on the seal. The transient tests have demonstrated that the seal is capable of maintaining low leakage rates while limiting the face temperatures.

Salant, Richard F.↗