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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Switching skeletons: hydrostatic support in molting crabs

Skeletal support systems are essential for support, movement, muscular antagonism, and locomotion. Crustaceans shed their rigid exoskeleton at each molt yet are still capable of forceful movement. We hypothesize that the soft water-inflated body of newly molted crabs may rely on a hydrostatic skeleton, similar to that of worms and polyps. We measured internal hydrostatic pressure and the force exerted during claw adduction and observed a strong correlation between force and hydrostatic pressure, consistent with hydrostatic skeletal support. This alternation between the two basic skeletal types may be widespread among arthropods.

Non-NASA Center↗
NASA NTRS1989

Monolithic transistor gate energy recovery system

Energy is recovered from an insulated gate semiconductor switch, such as a MOSFET, that is otherwise lost in the gate capacitance by producing a notch in the gate control voltage for an interval B following an interval A after initial application of a gate control voltage pulse for turning the switch on, and a notch for an interval C following termination of the gate control voltage pulse followed by interval D during which the switch is turned on again, where each interval is a period .DELTA.T given by ##EQU1## L.sub.s is the inductance (discrete and/or parasitic) in series with the gate electrode of the insulated gate semiconductor switch, and C.sub.in is the capacitance of that switch between its gate and source electrodes. The interval .DELTA.T may be provided directly by timing in a pulse forming circuit for the gate control voltage applied, or adaptively by sensing the gate voltage v.sub.g and comparing it with fixed progressively higher voltages v.sub.1, v.sub.2 and v.sub.3, where v.sub.2 is intermediate v.sub.1 and v.sub.3 which correspond to the lower and upper levels of v.sub.g as the switch is turned off and on.

Rippel, Wally E.↗
NASA NTRS1988

Overview of NASA research in fiber optics for aircraft controls

The challenge of those involved in aircraft control system hardware development is to accommodate an ever-increasing complexity in aircraft control, while limiting the size and weight of the components and improving system reliability. A technology that displays promise towards this end is fiber optics. The primary advantages of employing optical fibers, passive optical sensors and optically controlled actuators are weight/volume reduction, immunity from electromagnetic effects, high bandwidth capabilities and freedom from short circuits/sparking contacts. Since 1975, NASA Lewis has been performing in-house, contract and grant research in fiber optic sensors, high temperature electro-optic switches and fly-by-light control system architecture. Passive optical sensor development is an essential yet challenging area of work and has therefore received much attention during this period. A major effort to develop fly-by-light control system technology, known as the Fiber Optic Control System Integration (FOCSI) program, was initiated in 1985 as a cooperative effort between NASA and DOD. Phase 1 of FOCSI, completed in 1986, was aimed at the design of a fiber optic integrated propulsion/flight control system. Phase 2 will provide subcomponent and system development and system testing. In addition to a summary of the benefits of fiber optics, the FOCSI program, sensor advances, and future directions in the NASA Lewis program are discussed.

Seng, Gary T.↗
NASA NTRS1996

Exact-Output Tracking Theory for Systems with Parameter Jumps

In this paper we consider the exact output tracking problem for systems with parameter jumps. Necessary and sufficient conditions are derived for the elimination of switching-introduced output transient. Previous works have studied this problem by developing a regulator that maintains exact tracking through parameter jumps (switches). Such techniques are, however, only applicable to minimum-phase systems. In contrast, our approach is applicable to nonminimum-phase systems and obtains bounded but possibly non-causal solutions. If the reference trajectories are generated by an exo-system, then we develop an exact-tracking controller in a feedback form. As in standard regulator theory, we obtain a linear map from the states of the exo-system to the desired system state which is defined via a matrix differential equation. The constant solution of this differential equation provides asymptotic tracking, and coincides with the feedback law used in standard regulator theory. The obtained results are applied to a simple flexible manipulator with jumps in the pay-load mass.

Devasia, Santosh↗
NASA NTRS1997

Exact-Output Tracking Theory for Systems with Parameter Jumps

We consider the exact output tracking problem for systems with parameter jumps. Necessary and sufficient conditions are derived for the elimination of switching-introduced output transient. Previous works have studied this problem by developing a regulator that maintains exact tracking through parameter jumps (switches). Such techniques are, however, only applicable to minimum-phase systems. In contrast, our approach is applicable to non-minimum-phase systems and it obtains bounded but possibly non-causal solutions. If the reference trajectories are generated by an exosystem, then we develop an exact-tracking controller in a feed-back form. As in standard regulator theory, we obtain a linear map from the states of the exosystem to the desired system state which is defined via a matrix differential equation. The constant solution of this differential equation provides asymptotic tracking, and coincides with the feedback law used in standard regulator theory. The obtained results are applied to a simple flexible manipulator with jumps in the pay-load mass.

Devasia, Santosh↗
NASA NTRS1995

Micromechanical Switches on GaAs for Microwave Applications

In this presentation, we describe the fabrication of micro-electro-mechanical system (MEMS) devices, in particular, of low-frequency multi-element electrical switches using SiO2 cantilevers. The switches discussed are related to micromechanical membrane structures used to perform switching of optical signals on silicon substrates. These switches use a thin metal membrane which is actuated by an electrostatic potential, causing the switch to make or break contact. The advantages include: superior isolation, high power handling capabilities, high radiation hardening, very low power operations, and the ability to integrate onto GaAs monolithic microwave integrated circuit (MMIC) chips.

Randall, John N.↗
NASA NTRS2003

Twinning, Epitaxy and Domain Switching in Ferroelastic Inclusion Compounds

Our research is in the area of solid-state organic chemistry, which lies at the interface between physical organic chemistry and materials science. We use crystalline solids as models to probe fundamental issues about physical processes, molecular interactions and chemical reactions that are important for fabrication, stabilization and application of technological materials. Much of our most recent work has focused on the phenomena of ferroelastic and ferroelectric domain switching, in which application of an external force or electric field to a crystal causes the molecules inside the crystal to reorient, in tandem, to a new orientational state. To better understand and control the domain switching process, we have designed and synthesized over twenty closely related, ferroelastic organic crystals. Our approach has been to use crystalline inclusion compounds, in which one molecule (the guest) is trapped within the crystalline framework of a second molecule (the host). By keeping the host constant and varying the proportions and kinds of guests, it has been possible to tailor these materials so that domain switching is rapid and reversible (which is desirable for high technology applications). Inclusion compounds therefore serve as powerful systems for understanding the specific molecular mechanisms that control domain switching.

Hollingsworth, Mark D.↗
NASA NTRS1994

Development of a Solid State Power Switch for the Cassini Spacecraft

The Cassini spacecraft uses a new hybrid device to replace the load switching relays used on previous missions. These hybrid devices provide additional functions such as circuit breaking, controlled voltage turn-on and current limiting features. The current limiting function makes an uninterruptible power system possible. This hybrid, the Solid State Power Switch (SSPS), performs the function of connecting the 192 Cassini loads to the spacecraft power bus in response to commands from the Command and Data subsystem.

Cassini↗
NASA NTRS2017

Lighting Automation - Flying an Earthlike Habitat

Currently, spacecraft lighting systems are not demonstrating innovations in automation due to perceived costs in designing circuitry for the communication and automation of lights. The majority of spacecraft lighting systems employ lamps or zone specific manual switches and dimmers. This type of 'hardwired' solution does not easily convert to automation. With advances in solid state lighting, the potential to enhance a spacecraft habitat is lost if the communication and automation problem is not tackled. If we are to build long duration environments, which provide earth-like habitats, minimize crew time, and optimize spacecraft power reserves, innovation in lighting automation is a must. This project researched the use of the DMX512 communication protocol originally developed for high channel count lighting systems. DMX512 is an internationally governed, industry-accepted, lighting communication protocol with wide industry support. The lighting industry markets a wealth of hardware and software that utilizes DMX512, and there may be incentive to space certify the system. Our goal in this research is to enable the development of automated spacecraft habitats for long duration missions. To transform how spacecraft lighting environments are automated, our project conducted a variety of tests to determine a potential scope of capability. We investigated utilization and application of an industry accepted lighting control protocol, DMX512 by showcasing how the lighting system could help conserve power, assist with lighting countermeasures, and utilize spatial body tracking. We hope evaluation and the demonstrations we built will inspire other NASA engineers, architects and researchers to consider employing DMX512 "smart lighting" capabilities into their system architecture. By using DMX512 we will prove the 'wheel' does not need to be reinvented in terms of smart lighting and future spacecraft can use a standard lighting protocol to produce an effective, optimized and potentially earthlike habitat.

Clark, Tori A.↗
NASA NTRS2017

Lighting Automation Flying an Earthlike Habitat

Currently, spacecraft lighting systems are not demonstrating innovations in automation due to perceived costs in designing circuitry for the communication and automation of lights. The majority of spacecraft lighting systems employ lamps or zone specific manual switches and dimmers. This type of 'hardwired' solution does not easily convert to automation. With advances in solid state lighting, the potential to enhance a spacecraft habitat is lost if the communication and automation problem is not tackled. If we are to build long duration environments, which provide earth-like habitats, minimize crew time, and optimize spacecraft power reserves, innovation in lighting automation is a must. This project researched the use of the DMX512 communication protocol originally developed for high channel count lighting systems. DMX512 is an internationally governed, industry-accepted, lighting communication protocol with wide industry support. The lighting industry markets a wealth of hardware and software that utilizes DMX512, and there may be incentive to space certify the system. Our goal in this research is to enable the development of automated spacecraft habitats for long duration missions. To transform how spacecraft lighting environments are automated, our project conducted a variety of tests to determine a potential scope of capability. We investigated utilization and application of an industry accepted lighting control protocol, DMX512 by showcasing how the lighting system could help conserve power, assist with lighting countermeasures, and utilize spatial body tracking. We hope evaluation and the demonstrations we built will inspire other NASA engineers, architects and researchers to consider employing DMX512 "smart lighting" capabilities into their system architecture. By using DMX512 we will prove the 'wheel' does not need to be reinvented in terms of smart lighting and future spacecraft can use a standard lighting protocol to produce an effective, optimized and potentially earthlike habitat.

Clark, Toni A.↗
NASA NTRS1992

Dealing with the time-varying parameter problem of robot manipulators performing path tracking tasks

Many robotic applications involve time-varying payloads during the operation of the robot. It is therefore of interest to consider control schemes that deal with time-varying parameters. Using the properties of the element by element (or Hadarmad) product of matrices, we obtain the robot dynamics in parameter-isolated form, from which a new control scheme is developed. The controller proposed yields zero asymptotic tracking errors when applied to robotic systems with time-varying parameters by using a switching type control law. The results obtained are global in the initial state of the robot, and can be applied to rapidly varying systems.

Song, Y. D.↗
NASA NTRS1978

Critical fault patterns determination in fault-tolerant computer systems

The method proposed tries to enumerate all the critical fault-patterns (successive occurrences of failures) without analyzing every single possible fault. The conditions for the system to be operating in a given mode can be expressed in terms of the static states. Thus, one can find all the system states that correspond to a given critical mode of operation. The next step consists in analyzing the fault-detection mechanisms, the diagnosis algorithm and the process of switch control. From them, one can find all the possible system configurations that can result from a failure occurrence. Thus, one can list all the characteristics, with respect to detection, diagnosis, and switch control, that failures must have to constitute critical fault-patterns. Such an enumeration of the critical fault-patterns can be directly used to evaluate the overall system tolerance to failures. Present research is focused on how to efficiently make use of these system-level characteristics to enumerate all the failures that verify these characteristics.

Mccluskey, E. J.↗
NASA NTRS2023

Channel Measurements for Switching Strategies in Hybrid RF/Optical Communications

Free space optical (FSO) communication links increase data rate, reduce size and power, and increase security. These criteria are particularly important in space communication. Increasing mission complexity and crowding of lower frequency bands is driving the need for optical communications. This makes FSO communication technology extremely attractive, and there is significant ongoing work towards the development of FSO transceivers, ground stations, and relays. Notable projects include the Laser Communications Relay Demonstrator (LCRD), Integrated LCRD Low-Earth Orbit User Modem and Amplifier Terminal (ILLUMA-T), and CubeSat Laser Infrared Crosslink (CLICK) CubeSats. These technologies will eventually operate in unison with existing Radio Frequency (RF) systems, but there is little experimental investigation of such hybrid networks. This paper presents some experimental underpinnings of switching strategies for hybrid RF/FSO systems in various attenuation conditions. A 170 m optical path was constructed in an enclosed test chamber where atmospheric conditions can be tightly controlled. The performance of a 1550 nm infrared FSO link was evaluated in this chamber under varying conditions of turbulence and jitter. The system will eventually be used to investigate switching criteria between the FSO and RF channels. Optimizing the use of RF/FSO communication links will allow data rate, size, power, and security improvements. Therefore, this research will help to mature the network architecture and improve the performance of communication networks to be used for LEO, GEO, Lagrange, Lunar missions and beyond.

Space Networks↗
NASA NTRS2014

Time Triggered Ethernet System Testing Means and Method

Methods and apparatus are provided for evaluating the performance of a Time Triggered Ethernet (TTE) system employing Time Triggered (TT) communication. A real TTE system under test (SUT) having real input elements communicating using TT messages with output elements via one or more first TTE switches during a first time interval schedule established for the SUT. A simulation system is also provided having input simulators that communicate using TT messages via one or more second TTE switches with the same output elements during a second time interval schedule established for the simulation system. The first and second time interval schedules are off-set slightly so that messages from the input simulators, when present, arrive at the output elements prior to messages from the analogous real inputs, thereby having priority over messages from the real inputs and causing the system to operate based on the simulated inputs when present.

Smithgall, William Todd↗
NASA NTRS1998

Integrated Power and Attitude Control System (IPACS)

Recent advances in materials, circuit integration and power switching have given the concept of dynamic energy and momentum storage important weight size, and operational advantages over the conventional momentum wheel-battery configuration. Simultaneous momentum and energy storage for a three axes stabilized spacecraft can be accomplished with a topology of at least four wheels where energy (a scalar) is stored or retrieved in such a manner as to keep the momentum vector invariant. This study, instead, considers the case of two counter-rotating wheels in one axis to more effectively portray the principles involved. General scalable system design equations are derived which demonstrate the role of momentum storage when combined with energy storage.

Michaelis, Theodore D.↗
NASA NTRS1973

Visual examination apparatus

An automated visual examination apparatus for measuring visual sensitivity and mapping blind spot location is described. The apparatus includes a projection system for displaying to a patient a series of visual stimuli, a response switch enabling him to indicate his reaction to the stimuli, and a recording system responsive to both the visual stimuli per se and the patient's response. The recording system provides a correlated permanent record of both stimuli and response from which a substantive and readily apparent visual evaluation can be made.

Haines, R. F.↗
NASA NTRS1976

Visual examination apparatus

An automated visual examination apparatus for measuring visual sensitivity and mapping blind spot location including a projection system for displaying to a patient a series of visual stimuli. A response switch enables him to indicate his reaction to the stimuli, and a recording system responsive to both the visual stimuli per se and the patient's response. The recording system thereby provides a correlated permanent record of both stimuli and response from which a substantive and readily apparent visual evaluation can be made.

Haines, R. F.↗
NASA NTRS1983

Design considerations for high-power VHF radar transceivers (keynote paper)

A review and analysis of conference papers addressing the design of high power VHF radar tranceivers is presented. Specific design topics include: (1) distributed versus single transmitters; (2) coded pulses and decoder design; (3) large transmitter design considerations; and (4) T/R switch design. The topics in the discussion on future directions include the following: (1) enhanced receiver performance; (2) transmitter systems for unattended operation; (3) limitations of the current T/R switch designs; (4) data processing (is eight bits enough); and (5) new frequencies (200 MHz and/or 400 MHz).

Brosnahan, J. W.↗