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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

In Situ Multi-Species (O2, N2, Fuel, Other) Fiber Optic Sensor for Fuel Tank Ullage

A rugged and compact fiber optic sensor system for in situ real-time measurement of nitrogen (N2), oxygen (O2), hydrocarbon (HC) fuel vapors, and other gases has been developed over the past several years at Glenn Research Center. The intrinsically-safe, solid-state fiber optic sensor system provides a 1% precision measurement (by volume) of multiple gases in a 5-sec time window. The sensor has no consumable parts to wear out and requires less than 25 W of electrical power to operate. The sensor head is rugged and compact and is ideal for use in harsh environments such as inside an aircraft fuel tank, or as a feedback sensor in the vent-box of an on-board inert gas generation system (OBIGGS). Multiple sensor heads can be monitored with a single optical detection unit for a cost-effective multi-point sensor system. The present sensor technology is unique in its ability to measure N2 concentration directly, and in its ability to differentiate different types of HC fuels. The present sensor system provides value-added aircraft safety information by simultaneously and directly measuring the nitrogen-oxygen-fuel triplet, which provides the following advantages: (1) information regarding the extent of inerting by N2, (2) information regarding the chemical equivalence ratio, (3) information regarding the composition of the aircraft fuel, and (4) by providing a self-consistent calibration by utilizing a singular sensor for all species. Using the extra information made available by this sensor permits the ignitability of a fuel-oxidizer mixture to be more accurately characterized, which may permit a reduction in the amount of inerting required on a real-time basis, and yet still maintain a fire-safe fuel tank. This translates to an increase in fuel tank fire-safety through a better understanding of the physics of fuel ignition, and at the same time, a reduction in compressed bleed air usage and concomitant aircraft operational costs over the long-run. The present fiber optic sensor can also be used as a false-alarm-free engine/hidden/cargo space fire detector (by measuring increased CO2 and CO, and decreased O2), a multi-point in situ measurement and certification system for halogenated-compound fire protection systems, and for the testing and certification of other aircraft safety sensor systems. The technology (LEW-17826-1) developed in the present sensor system is patent pending.

Nguyen, Quang-Viet↗
NASA NTRS1993

Fiber-Optic Discriminator Stabilizes Microwave Oscillator

New fiber-optic delay line discriminator enables stabilization of oscillators directly at microwave output frequency, eliminating need for frequency multiplication. Discriminator is wide-band device, capable of stabilizing outputs of frequency-agile microwave sources over multigigahertz tuning ranges. Use of advanced fiber-optic delay line with wider bandwidth and low noise predicted to yield corresponding improvements in phase-noise performance.

Logan, Ronald T., Jr.↗
NASA NTRS1991

Fiber optic frequency transfer link

A reference frequency distribution system is disclosed for transmitting a reference frequency from a reference unit to a remote unit while keeping the reference frequency at the reference unit and the remote unit in phase. A fiber optic cable connects the reference unit to the remote unit. A frequency source at the reference unit produces a reference frequency having an adjustable phase. A fiber optic transmitter at the reference unit modulates a light beam with the reference frequency and transmits the light beam into the fiber optic cable. A 50/50 reflector at the remote unit reflects a first portion of the light beam from the reference unit back into the fiber optic cable to the reference unit. A first fiber optic receiver disposed at the remote unit receives a second portion of the light beam and demodulates the reference frequency to be used at the remote unit. A second fiber optic receiver disposed at the reference unit receives the first portion of the light beam and demodulates a reference frequency component. A phase conjugator is connected to the frequency source for comparing the phase of the reference frequency component to the phase of the reference frequency modulating the light beam being transmitted from the reference unit to maintain a conjugate (anti-symmetric) relationship between the reference frequency component and the reference frequency modulating the light beam where virtually no phase difference exists between the phase of the reference frequency component and the phase of the reference frequency modulating the light beam.

Primas, Lori E.↗
NASA NTRS2008

Real-time In-Flight Strain and Deflection Monitoring with Fiber Optic Sensors

This viewgraph presentation reviews Dryden's efforts to develop in-flight monitoring based on Fiber Optics. One of the motivating factors for this development was the breakup of the Helios aircraft. On Ikhana the use of fiber optics for wing shape sensing is being developed. They are being used to flight validate fiber optic sensor measurements and real-time wing shape sensing predictions on NASA's Ikhana vehicle; validate fiber optic mathematical models and design tools; Assess technical viability and, if applicable, develop methodology and approach to incorporate wing shape measurements within the vehicle flight control system, and develop and flight validate advanced approaches to perform active wing shape control.

Richards, Lance↗
NASA NTRS1988

In situ composite cure monitoring using infrared transmitting optical fibers

The development of infrared-transmitting optical fibers as sensors for monitoring the cure of advanced composite materials is reported. Fourier transform infrared spectra are presented which were remotely sensed during the cure of a high performance polyimide resin and a graphite/polyimide matrix prepreg using an 0.1 mm O.D. x 3 m chalcogenide optical fiber. A discussion of the fiber and sensor element, absorption mechanism and potential applications is presented.

Young, Philip R.↗
NASA NTRS1992

RF modulated fiber optic sensing systems and their applications

A fiber optic sensing system with an intensity sensor and a Radio Frequency (RF) modulated source was shown to have sensitivity and resolution much higher than a comparable system employing low modulating frequencies or DC mode of operation. Also the RF modulation with an appropriate configuration of the sensing system provides compensation for the unwanted intensity losses. The basic principles and applications of a fiber optic sensing system employing an RF modulated source are described. In addition the paper discusses various configurations of the system itself, its components, and modulation and detection schemes. Experimental data are also presented.

Adamovsky, Grigory↗
NASA NTRS1993

RF modulated fiber optic sensing systems and their applications

A fiber optic sensing system with an intensity sensor and a Radio Frequency (RF) modulated source was shown to have sensitivity and resolution much higher than a comparable system employing low modulating frequencies or DC mode of operation. Also the RF modulation with an appropriate configuration of the sensing system provides compensation for the unwanted intensity losses. The basic principles and applications of a fiber optic sensing system employing an RF modulated source are described. In addition the paper discusses various configurations of the system itself, its components, and modulation and detection schemes. Experimental data are also presented.

Adamovsky, G.↗
NASA NTRS1992

LDEF fiber optic exposure experiment No. S-0109

Ten fiber optic cable samples of different types were exposed in low-earth orbit for over 5.5 years on the Long-Duration Exposure Facility (LDEF). Four of the samples were mounted externally, and the remaining six were internal, under approximately 0.5 g cm(exp -2) of aluminum. The experiment was recovered in Jan. 1990, and laboratory evaluation of the effects of the exposure has continued since. An increase in fiber loss, presumed to be from radiation darkening, aging effects on polymer materials used in cabling, unique contamination effects on connector terminations, and micrometeoroid impacts were observed. In addition, the sample loss was measured for each sample as a function of temperature before and after the flight. All cable samples were functional, and the best exhibited no measurable change in performance, indicating that conventional fiber optic cables can perform satisfactorily in spacecraft. Experimental results obtained to date are presented and discussed.

A R Johnston↗
NASA NTRSDate not supplied

Finite Element Based Model of Fiber-optic Strain Sensor Mounted on a Semi-monocoque Structure

Fiber-optic strain sensing (FOSS) provides an opportunity for additional awareness and can enable other mitigations such as flutter suppression or gust load alleviation but requires an accurate computational model as part of a design process that integrates structures and controls. A modeling approach for fiber-optic strain sensors has been developed using a shell element formulation in a detailed finite element model. The new FOSS modeling approach is designed to better scale to more complex realistic structures and fiber layouts than previous approaches. The modeling method was applied to the X-56A vehicle and results were compared to experimental static ground-test data. Additionally, the experimental sensor noise of these fiber optic sensors was assessed for the correlations in time and correlations along the fiber. The noise does show significant correlations both in time and along the fibers. These correlations of the noise should also be considered in modeling and assessing algorithms that will use FOSS.

Jeffrey Ouellette↗
NASA NTRSDate not supplied

Finite Element Based Model of Fiber-optic Strain Sensor Mounted on a Semi-monocoque Structure

Fiber-optic strain sensing (FOSS) provides an opportunity for additional awareness and can enable other mitigations such as flutter suppression or gust load alleviation but requires an accurate computational model as part of a design process that integrates structures and controls. A modeling approach for fiber-optic strain sensors has been developed using a shell element formulation in a detailed finite element model. The new FOSS modeling approach is designed to better scale to more complex realistic structures and fiber layouts than previous approaches. The modeling method was applied to the X-56A vehicle and results were compared to experimental static ground-test data. Additionally, the experimental sensor noise of these fiber optic sensors was assessed for the correlations in time and correlations along the fiber. The noise does show significant correlations both in time and along the fibers. These correlations of the noise should also be considered in modeling and assessing algorithms that will use FOSS.

Jeffrey Ouellette↗
NASA NTRS1986

On the application of optical-fiber image scramblers to astronomical spectroscopy

Single, step-index optical fibers, when properly employed, can function as optically efficient image scramblers. Their use as optical feeds for astronomical slit spectrographs can reduce zonal error levels in those instruments by orders of magnitude. As a consequence, the application of optical-fiber couplers to new and existing spectrographs may greatly increase the wavelength metric quality of conventional astronomical spectroscopy. The optical efficiencies of fiber couplers of a few tens of meters in length can be comparable to those of typical coude mirror trains in the visible portions of the spectrum. Elements of the design of fiber couplers are illustrated by discussion of a currently operational instrument.

Heacox, W. D.↗
NASA NTRS1984

High-temperature fiber optic pressure sensor

Attention is given to a program to develop fiber optic methods to measure diaphragm deflection. The end application is intended for pressure transducers capable of operating to 540 C. In this paper are reported the results of a laboratory study to characterize the performance of the fiber-optic microbend sensor. The data presented include sensitivity and spring constant. The advantages and limitations of the microbend sensor for static pressure measurement applications are described. A proposed design is presented for a 540 C pressure transducer using the fiber optic microbend sensor.

Berthold, J. W.↗
NASA NTRS1983

Distributed processing and fiber optic communications in air data measurements

The application of distributed processing, fiber optics, and hardware redundancy to collecting airstream data in Princeton's digitally controlled Variable-Response Research Aircraft (VRA) is described. Microprocessor controlled instrumentation packages in each wingtip of the aircraft collect angle of attack and sideslip data in digital form; after scaling, filtering, and calibrating the data, they send it to the aircraft's microprocessor Digital Flight Control System (micro-DFCS) via digital fiber optic data links. Each wingtip's package is independent of the other; therefore, the system has dual hardware redundancy. The fiber optic link design is presented as well as a description of the calibration and communications software.

Farry, K. A.↗
NASA NTRS2010

Space Flight Applications of Optical Fiber; 30 Years of Space Flight Success

For over thirty years NASA has had success with space flight missions that utilize optical fiber component technology. One of the early environmental characterization experiments that included optical fiber was launched as the Long Duration Exposure Facility in 1978. Since then, multiple missions have launched with optical fiber components that functioned as expected, without failure throughout the mission life. The use of optical fiber in NASA space flight communications links and exploration and science instrumentation is reviewed.

Ott, Melanie N.↗
NASA NTRS2018

System to Perform Radio Frequency Interferometry Using Optical Fiber Sensing Signal Processing Techniques

Aspects of the present disclosure involve a system and method for performing radio frequency interferometry using optical fiber sensing. Optical fiber sensing is performed as a reference signal is defined and compared, in the optical domain, to incoming signals to obtain interference fringe patterns that can be used to decode phase shift offsets with respect to the designated reference signal. The phase shift offsets can be determined by first optically modulating the reference and incoming signals using a laser source as the carrier. In the optical domain, the reference and incoming signals are combined using an optical coupler and then converted back to the electrical domain for processing.

Ott, Melanie N.↗
NASA NTRS1985

Fiber optics common transceiver module

The long term objectives are to develop a space qualified fiber optics transceiver for information networks applications on the Space Station, to advance the technology to increase the system data handling capability, to reduce the overall device size, and to improve efficiency and sensitivity. The characteristics of hybrid fiber optic transceivers and monolithic fiber optic transceivers are reviewed.

Hendricks, Herbert D.↗
NASA NTRS1983

Application of optical fibers to wide-band differential interferometry

A broadband differential optical interferometer that uses an optical-fiber waveguide to transmit coherent light to a surface under inspection is discussed. Input laser light is coupled into two single-mode optical fibers in a stationary input optics enclosure. The fibers transmit the light to a small, remote detection head where it is used in a wide-band differential interferometer to detect continuous and pulsed surface-particle displacements. The effective separation between the input optics and the detection head allows simple surface scanning and probe alignment. Detection of simulated acoustic emission pulses by a prototype test unit is reported.

Garg, A. O.↗