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At least 199 records · Page 11

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NASA NTRS1991

An ultrasonic technique to measure the depth of burn wounds in humans

Whenever ultrasound encounters discontinuity in its medium of propagation, some energy is reflected from the interface. Such reflections or echoes occur when incident energy encounters the front skin, viable/necrotic, and dermis/fat skin tissue interfaces. It was shown that the most probable cause of the viable/necrotic interface is the uncoiling of collagen in the necrotic tissue, which can cause a reflection at the viable/necrotic interface of approximately 10 percent of the wave amplitude, and is approximately the same as that from the other two interfaces noted. The instrument, still in the prototype stage, was designed to detect the various reflections from within the skin layer. It is shown that, by studying the timing between the various echoes, one can use ultrasound as an aid in diagnosing the depth of burned skin tissue in humans. The instrument is a 60-MHz A-scan unit, modified to more easily identify the echoes occurring within the short time interval during which the reflections are received from the skin layers. A high frequency unit was selected so that various transducers could be utilized to optimize the system. Signal conditioning circuits were modified and added to provide an adequate display of the principle reflections expected. The unit was successful in studying burned tissue in pigs and was recently used to study burn wounds in humans. Measurement techniques and preliminary results are presented.

Yost, William T.↗

NASA NTRS1989

A digital pitch and roll monitor

A digital pitch and roll monitor was developed that will provide an easy measurement of angle in two axes simultaneously to an accuracy of approximately 0.005 degree. This system provides advantages over any other commercially available angle-measuring device in that an inexperienced operator can obtain quick reliable measurements. The system utilizes three mutually perpendicular accelerometers, mounted on an inclinometer base, and the intelligent signal conditioning equipment needed to convert the output of these sensors to pitch and roll. The two-axis inclinometer consists of three mutually perpendicular accelerometers mounted on an inclinometer base, three digital multimeters to provide power to the accelerometers and digitize their output, a computer to calculate the angles, and a printer to provide hardcopy output.

Finley, Tom↗

NASA NTRS1992

LDEF experiment M0003 meteoroid and debris survey

A survey of the meteoroid and space debris impacts on LDEF experiment M0003 was performed. The purpose was to document impact phenomenology and to obtain impact crater data for comparison to current debris and micrometeoroid models. The survey consists of photomicrographs of significant impacts in a variety of material types, accurate measurements of impact crater coordinates and dimensions for selected experiment surfaces and data basing of the crater data for reduction, manipulation, and comparison models. Large area surfaces which were studied include the experiment power and data system sunshields, environment exposure control canister sunshields, and the M0003 signal conditioning unit covers. Crater diameters down to 25 microns were measured and catalogued. Both leading and trailing edge surfaces were studied and compared. The results shows the different response of materials to hypervelocity impacts. Comparison of the data to curves derived from the Kessler debris model and the Cour-Palais micrometeoroid model indicates a marked tendency for overprediction of small impacts and underprediction of large impacts with there being better agreement for the medium sized impacts. Representative impact data is presented.

Meshishnek, M. J.↗

NASA NTRS1992

Operation and design considerations for unsteady data acquisition with PC-based systems in high Reynolds number hypersonic flowfields

Operation and design considerations for personal-computer-based data acquisition are analyzed, and a system is created that is portable, inexpensive, and capable of high-frequency response. This system performed well when given an extensive analysis of the characteristics of the radio-frequency noise in the test environment. The system architecture is well-suited for support of high-frequency data acquisition from both pressure transducers and high-frequency-response thermocouple gauges. As configured, the system provides a data resolution of approximately 0.09 psia and 0.56 F. Considering the constraints placed upon this design, this data resolution is acceptable. The $5000 budget did require use of an existing PC and rental of signal-conditioning equipment.

Flanagan, M. J., Jr.↗

NASA NTRS1992

Model attitude measurements at NASA Langley Research Center

This paper describes the predominant instrumentation used to make precision model attitude measurements in wind tunnel testing at NASA Langley Research Center (LaRC). It covers all aspects of precision model attitude measurements: the type of sensors, testing and calibration, packaging preparation, signal conditioning, and user instructions. The paper concludes with descriptions of alternate methods to make precision model attitude measurements and future directions in this field.

Finley, Tom D.↗

NASA NTRS1991

In situ backscatter measurements over Pacific Ocean using two coherent focused CO2 lidars

Preliminary results of CS lidar measurements over the Pacific Ocean using two CO2 Doppler lidars operating at 9.1 and 10.6 microns are presented. SNR calculations during real-time and postprocessing were performed using a multistep signal search and signal power estimation algorithm optimized for weak signal conditions. Typical aerosol structure observed in the troposphere was found to consist of a boundary layer, a cloud-pumped layer, and a clean background layer; backscatter from cloud-free air was found to vary over three to four orders of magnitude or more.

Rothermel, Jeffry↗

NASA NTRS1993

Piezoelectric devices for vibration suppression: Modeling and application to a truss structure

For a space structure assembled from truss members, an effective way to control the structure may be to replace the regular truss elements by active members. The active members play the role of load carrying elements as well as actuators. A piezo strut, made of a stack of piezoceramics, may be an ideal active member to be integrated into a truss space structure. An electrically driven piezo strut generates a pair of forces, and is considered as a two-point actuator in contrast to a one-point actuator such as a thruster or a shaker. To achieve good structural vibration control, sensing signals compatible to the control actuators are desirable. A strain gage or a piezo film with proper signal conditioning to measure member strain or strain rate, respectively, are ideal control sensors for use with a piezo actuator. The Phase 0 CSI Evolutionary Model (CEM) at NASA Langley Research Center used cold air thrusters as actuators to control both rigid body motions and flexible body vibrations. For the Phase 1 and 2 CEM, it is proposed to use piezo struts to control the flexible modes and thrusters to control the rigid body modes. A tenbay truss structure with active piezo struts is built to study the modeling, controller designs, and experimental issues. In this paper, the tenbay structure with piezo active members is modelled using an energy method approach. Decentralized and centralized control schemes are designed and implemented, and preliminary analytical and experimental results are presented.

Won, Chin C.↗

NASA NTRS1992

Application of high-precision two-way ranging to Galileo Earth-1 encounter navigation

The application of precision two-way ranging to orbit determination with relatively short data arcs is investigated for the Galileo spacecraft's approach to its first Earth encounter (December 8, 1990). Analysis of previous S-band (2.3-GHz) ranging data acquired from Galileo indicated that under good signal conditions submeter precision and 10-m ranging accuracy were achieved. It is shown that ranging data of sufficient accuracy, when acquired from multiple stations, can sense the geocentric angular position of a distant spacecraft. A range data filtering technique, in which explicit modeling of range measurement bias parameters for each station pass is utilized, is shown to largely remove the systematic ground system calibration errors and transmission media effects from the Galileo range measurements, which would otherwise corrupt the angle-finding capabilities of the data. The accuracy of the Galileo orbit solutions obtained with S-band Doppler and precision ranging were found to be consistent with simple theoretical calculations, which predicted that angular accuracies of 0.26-0.34 microrad were achievable. In addition, the navigation accuracy achieved with precision ranging was marginally better than that obtained using delta-differenced one-way range (delta DOR), the principal data type that was previously used to obtain spacecraft angular position measurements operationally.

Pollmeier, V. M.↗

NASA NTRS1991

An integrated autonomous rendezvous and docking system architecture using Centaur modern avionics

The avionics system for the Centaur upper stage is in the process of being modernized with the current state-of-the-art in strapdown inertial guidance equipment. This equipment includes an integrated flight control processor with a ring laser gyro based inertial guidance system. This inertial navigation unit (INU) uses two MIL-STD-1750A processors and communicates over the MIL-STD-1553B data bus. Commands are translated into load activation through a Remote Control Unit (RCU) which incorporates the use of solid state relays. Also, a programmable data acquisition system replaces separate multiplexer and signal conditioning units. This modern avionics suite is currently being enhanced through independent research and development programs to provide autonomous rendezvous and docking capability using advanced cruise missile image processing technology and integrated GPS navigational aids. A system concept was developed to combine these technologies in order to achieve a fully autonomous rendezvous, docking, and autoland capability. The current system architecture and the evolution of this architecture using advanced modular avionics concepts being pursued for the National Launch System are discussed.

Nelson, Kurt↗

NASA NTRS1992

Measurement of the Relative and Absolute Microgravity Environment of Space Platforms, Recent Flight Results, and Determination of the Spatial Microgravity Field

Microgravity material processing in space, such as crystal growth, requires specific and accurate knowledge of the very low frequency, very low level microgravity. This means knowledge of absolute microgravity levels. Most acceleration measurement systems for space platforms only measure 'microvibrations,' the measurement of the absolute microgravity level being severely corrupted by bias errors, temperature hysteresis, nonlinearity by-products, and bias changes due to launch vibrations. An advanced system was developed incorporating a fixed 3-axis acceleration measurement system with improved signal conditioning and Invertible Accelerometers for absolute measurements. The higher sensitivity channels have lower frequency low pass filtering to meet crystal growers demands for recording of low level/low frequency disturbances. Also included is a pre-flight bias adjustment feature.

Bijvoet, J. A.↗

NASA NTRS1993

Long Duration Exposure Facility (LDEF) experiment M0003 meteoroid and debris survey

A survey of the meteoroid and space debris impacts on LDEF experiment M0003 was performed. The purpose of this survey was to document significant impact phenomenology and to obtain impact crater data for comparison to current space debris and micrometeoroid models. The survey consists of the following: photomicrographs of significant impacts in a variety of material types; accurate measurements of impact crater coordinates and dimensions for selected experiment surfaces; and databasing of the crater data for reduction, manipulation, and comparison to models. Large area surfaces that were studied include the experiment power and data system (EPDS) sunshields, environment exposure control canister (EECC) sunshields, and the M0003 signal conditioning unit (SCU) covers. Crater diameters down to 25 microns were measured and cataloged. Both leading (D8) and trailing (D4) edge surfaces were studied and compared. The EPDS sunshields are aluminum panels painted with Chemglaze A-276 white thermal control paint, the EECC sunshields are chromic acid-anodized aluminum, and the SCU covers are aluminum painted with S13GLO white thermal control paint. Typical materials that have documented impacts are metals, glasses and ceramics, composites, polymers, electronic materials, and paints. The results of this survey demonstrate the different response of materials to hypervelocity impacts. Comparison of the survey data to curves derived from the Kessler debris model and the Cour-Palais micrometeoroid model indicates that these models overpredict small impacts (less than 100 micron) and may underpredict large impacts (greater than 1000 micron) while having fair to good agreement for the intermediate impacts. Comparison of the impact distributions among the various surfaces indicates significant variations, which may be a function of material response effects, or in some cases surface roughness. Representative photographs and summary graphs of the impact data are presented.

Meshishnek, M. J.↗

NASA NTRS1993

The middeck 0-gravity dynamics experiment

The Middeck 0-Gravity Dynamics Experiment (MODE), flown onboard the Shuttle STS-48 Mission, consists of three major elements: the Experiment Support Module, a dynamics test bed providing computer experiment control, analog signal conditioning, power conditioning, an operator interface consisting of a keypad and display, experiment electrical and thermal control, and archival data storage: the Fluid Test Article assembly, used to investigate the dynamics of fluid-structure interaction in 0-gravity; and the Structural Test Article for investigating the open-loop dynamics of structures in 0-gravity. Deployable, erectable, and rotary modules were assembled to form three one- and two-dimensional structures, in which variations in bracing wire and rotary joint preload could be introduced. Change in linear modal parameters as well as the change in nonlinear nature of the response is examined. Trends in modal parameters are presented as a function of force amplitude, joint preload, and ambient gravity. An experimental study of the lateral slosh behavior of contained fluids is also presented. A comparison of the measured earth and space results identifies and highlights the effects of gravity on the linear and nonlinear slosh behavior of these fluids.

Crawley, Edward F.↗

NASA NTRS1994

Cryogenic on-orbit liquid depot storage acquisition and transfer (COLD-SAT) experiment subsystem instrumentation and wire harness design report

Subcritical cryogens such as liquid hydrogen (LH2) and liquid oxygen (LO2) are required for space based transportation propellant, reactant, and life support systems. Future long-duration space missions will require on-orbit systems capable of long-term cryogen storage and efficient fluid transfer capabilities. COLD-SAT, which stands for cryogenic orbiting liquid depot-storage acquisition and transfer, is a free-flying liquid hydrogen management flight experiment. Experiments to determine optimum methods of fluid storage and transfer will be performed on the COLD-SAT mission. The success of the mission is directly related to the type and accuracy of measurements made. The instrumentation and measurement techniques used are therefore critical to the success of the mission. This paper presents the results of the COLD-SAT experiment subsystem instrumentation and wire harness design effort. Candidate transducers capable of fulfilling the COLD-SAT experiment measurement requirements are identified. Signal conditioning techniques, data acquisition requirements, and measurement uncertainty analysis are presented. Electrical harnessing materials and wiring techniques for the instrumentation designed to minimize heat conduction to the cryogenic tanks and provide optimum measurement accuracy are listed.

Edwards, Lawrence G.↗

NASA NTRS1994

Fiber optic (flight quality) sensors for advanced aircraft propulsion

Development of flight prototype, fiber-optic sensing system components for measuring nine sensed parameters (three temperatures, two speeds, three positions, and one flame) on an F404-400 aircraft engine is described. Details of each sensor's design, functionality, and environmental testing, and the electro-optics architecture for sensor signal conditioning are presented. Eight different optical sensing techniques were utilized. Design, assembly, and environmental testing of an engine-mounted, electro-optics chassis unit (EOU), providing MIL-C-1553 data output, are related. Interconnection cables and connectors between the EOU and the sensors are identified. Results of sensor/cable/circuitry integrated testing, and installation and ground testing of the sensor system on an engine in October 1993 and April 1994 are given, including comparisons with the engine control system's electrical sensors. Lessons learned about the design, fabrication, testing, and integration of the sensor system components are included.

Poppel, Gary L.↗

NASA NTRS1994

High temperature strain gage technology for gas turbine engines

This report summarizes the results of a six month study that addressed specific issues to transfer the Pd-13Cr static strain sensor to a gas turbine engine environment. The application issues that were addressed include: (1) evaluation of a miniature, variable potentiometer for use as the ballast resistor, in conjunction with a conventional strain gage signal conditioning unit; (2) evaluation of a metal sheathed, platinum conductor leadwire assembly for use with the three-wire sensor; and (3) subjecting the sensor to dynamic strain cyclic testing to determine fatigue characteristics. Results indicate a useful static strain gage system at all temperature levels up to 1350 F. The fatigue characteristics also appear to be very promising, indicating a potential use in dynamic strain measurement applications. The procedure, set-up, and data for all tests are presented in this report. This report also discusses the specific strain gage installation technique for the Pd-13Cr gage because of its potential impact on the quality of the output data.

Fichtel, Edward J.↗

NASA NTRS1993

Pump and Flow Control Subassembly of Thermal Control Subsystem for Photovoltaic Power Module

The pump and flow control subassembly (PFCS) is an orbital replacement unit (ORU) on the Space Station Freedom photovoltaic power module (PVM). The PFCS pumps liquid ammonia at a constant rate of approximately 1170 kg/hr while providing temperature control by flow regulation between the radiator and the bypass loop. Also, housed within the ORU is an accumulator to compensate for fluid volumetric changes as well as the electronics and firmware for monitoring and control of the photovoltaic thermal control system (PVTCS). Major electronic functions include signal conditioning, data interfacing and motor control. This paper will provide a description of each major component within the PFCS along with performance test data. In addition, this paper will discuss the flow control algorithm and describe how the nickel hydrogen batteries and associated power electronics will be thermally controlled through regulation of coolant flow to the radiator.

Motil, Brian↗

NASA NTRS1995

Evaluation Of Vibration-Monitoring Gear-Diagnostic System

Report describes experimental evaluation of commercial electronic system designed to monitor vibration signal from accelerometer on gear-box to detect vibrations indicative of damage to gears. System includes signal-conditioning subsystem and personal computer in which analog-to-digital converter installed. Results show system fairly effective in detecting surface fatigue pits on spur-gear teeth.

Townsend, Dennis P.↗

NASA NTRS1995

Artifacts Of Spectral Analysis Of Instrument Readings

Report presents experimental and theoretical study of some of artifacts introduced by processing outputs of two nominally identical low-frequency-reading instruments; high-sensitivity servo-accelerometers mounted together and operating, in conjunction with signal-conditioning circuits, as seismometers. Processing involved analog-to-digital conversion with anti-aliasing filtering, followed by digital processing including frequency weighting and computation of different measures of power spectral density (PSD).

Wise, James H.↗