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At least 1,135 records · Page 63

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NASA NTRS1988

Optically controlled phased-array technology for space communication systems

Using MMICs in phased-array applications above 20 GHz requires complex RF and control signal distribution systems. Conventional waveguide, coaxial cable, and microstrip methods are undesirable due to their high weight, high loss, limited mechanical flexibility and large volume. An attractive alternative to these transmission media, for RF and control signal distribution in MMIC phased-array antennas, is optical fiber. Presented are potential system architectures and their associated characteristics. The status of high frequency opto-electronic components needed to realize the potential system architectures is also discussed. It is concluded that an optical fiber network will reduce weight and complexity, and increase reliability and performance, but may require higher power.

Kunath, Richard R.↗

NASA NTRS1993

Optical flameout detector

A device has been developed which monitors the presence of a flame within a combustion chamber. The optical flameout detection system responds to gross changes in combustor light intensity, which is monitored in two spectral bands. A photomultiplier tube makes optical measurements in the ultraviolet portion of the spectrum, and a silicon photodiode covers the visible region. The detectors, located outside the combustion chamber, receive the light energy radiated from the combustion process through fiber optic probes designed to operate in a high pressure environment. The optical fibers are aimed diagonally through the center of the injector at the combustion chamber wall downstream of the injector. The probes observe events occurring within a narrow conical-shaped field of view so that the system can quickly detect longitudinal movement of the flame front away from the injector. If a change in intensity of the flame is detected, the fuel supply to the combustion chamber is shut off, limiting the amount of unburned fuel in the combustion chamber which could reignite.

Borg, Stephen E.↗

NASA NTRS1998

Optical Flameout Detector

A device has been developed which monitors the presence of a flame within a combustion chamber. The optical flameout detection system responds to gross changes in combustor light intensity which is monitored in two spectral bands. A photomultiplier tube makes optical measurements in the ultraviolet portion of the spectrum and a silicon photodiode covers the visible region. The detectors, located outside the combustion chamber, receive the light energy radiated from the combustion process through fiber optic probes designed to operate in a high pressure environment. The optical fibers are aimed diagonally through the center of the injector at the combustion chamber wall downstream of the injector. The probe observes events occurring within a narrow conical-shaped field of view so that the system can quickly detect longitudinal movement of the flame front away from the injector. If a change in intensity of the flame is detected, the fuel supply to the combustion chamber is shut off limiting the amount of unburned fuel in the combustion chamber which could reignite.

Borg, Stephen E.↗

NASA NTRS2006

Digital Front End for Wide-Band VLBI Science Receiver

An upgrade to the very-long-baseline-interferometry (VLBI) science receiver (VSR) a radio receiver used in NASA's Deep Space Network (DSN) is currently being implemented. The current VSR samples standard DSN intermediate- frequency (IF) signals at 256 MHz and after digital down-conversion records data from up to four 16-MHz baseband channels. Currently, IF signals are limited to the 265-to-375-MHz range, and recording rates are limited to less than 80 Mbps. The new digital front end, denoted the Wideband VSR, provides improvements to enable the receiver to process wider bandwidth signals and accommodate more data channels for recording. The Wideband VSR utilizes state-of-the-art commercial analog-to-digital converter and field-programmable gate array (FPGA) integrated circuits, and fiber-optic connections in a custom architecture. It accepts IF signals from 100 to 600 MHz, sampling the signal at 1.28 GHz. The sample data are sent to a digital processing module, using a fiber-optic link for isolation. The digital processing module includes boards designed around an Advanced Telecom Computing Architecture (ATCA) industry-standard backplane. Digital signal processing implemented in FPGAs down-convert the data signals in up to 16 baseband channels with programmable bandwidths from 1 kHz to 16 MHz. Baseband samples are transmitted to a computer via multiple Ethernet connections allowing recording to disk at rates of up to 1 Gbps.

Jongeling, Andre↗

NASA NTRS1985

Bevalac calibration of the SOFIE range and hodoscope detectors

The scintillating optical fiber isotope experiment (SOFIE) is a Cerenkov-dE/dx-Range experiment which was developed initially for balloon flight to study the isotopic composition of cosmic rays in the iron region. The electronic range and hodoscope detectors use scintillating optical fibers to image the tracks of stopping charged particles and to determine their trajectory. The particle range is determined and used together with a Cerenkov measurement to determine the mass of the stopping particle. Preliminary results of a Bevalac calibration performed in August, 1984 with a prototype of the balloon flight instrument, to study the measurement precision in range and trajectory which could be attained with this detector are described.

Binns, W. R.↗

NASA NTRS1988

Beam Director For Optical Pyrometer

Optical-fiber pyrometer under development observes fields of view as much as 31 degree off axis. Prismlike end fitting bends viewing angle so pyrometer can "look" at object off axis. Angled face directs thermal radiation from object into optical-fiber cable along axis.

Wyett, Lynn M.↗

NASA NTRS1993

High-speed data duplication/data distribution: An adjunct to the mass storage equation

The term 'mass storage' invokes the image of large on-site disk and tape farms which contain huge quantities of low- to medium-access data. Although the cost of such bulk storage is recognized, the cost of the bulk distribution of this data rarely is given much attention. Mass data distribution becomes an even more acute problem if the bulk data is part of a national or international system. If the bulk data distribution is to travel from one large data center to another large data center then fiber-optic cables or the use of satellite channels is feasible. However, if the distribution must be disseminated from a central site to a number of much smaller, and, perhaps varying sites, then cost prohibits the use of fiber-optic cable or satellite communication. Given these cost constraints much of the bulk distribution of data will continue to be disseminated via inexpensive magnetic tape using the various next day postal service options. For non-transmitted bulk data, our working hypotheses are that the desired duplication efficiency of the total bulk data should be established before selecting any particular data duplication system; and, that the data duplication algorithm should be determined before any bulk data duplication method is selected.

Howard, Kevin↗

NASA NTRS1998

Rayleigh Scattering Diagnostic for Measurement of Temperature and Velocity in Harsh Environments

A molecular Rayleigh scattering system for temperature and velocity measurements in unseeded flows is described. The system is capable of making measurements in the harsh environments commonly found in aerospace test facilities, which may have high acoustic sound levels, varying temperatures, and high vibration levels. Light from an argon-ion laser is transmitted via an optical fiber to a remote location where two flow experiments were located. One was a subsonic free air jet; the second was a low-speed heated airjet. Rayleigh scattered light from the probe volume was transmitted through another optical fiber from the remote location to a controlled environment where a Fabry-Perot interferometer and cooled CCD camera were used to analyze the Rayleigh scattered light. Good agreement between the measured velocity and the velocity calculated from isentropic flow relations was demonstrated (less than 5 m/sec). The temperature measurements, however, exhibited systematic errors on the order of 10-15%.

Seasholtz, Richard G.↗

NASA NTRS2000

MACS, An Instrument and a Methodology for Simultaneous and Global Measurements of the Coronal Electron Temperature and the Solar Wind Velocity on the Solar Corona

In Cram's theory for the formation of the K-coronal spectrum he observed the existence of temperature sensitive anti-nodes, which were separated by temperature insensitive nodes, at certain wave-lengths in the K-coronal spectrum. Cram also showed these properties were remarkably independent of altitude above the solar limb. In this thesis Cram's theory has been extended to incorporate the role of the solar wind in the formation of the K-corona, and we have identified both temperature and wind sensitive intensity ratios. The instrument, MACS, for Multi Aperture Coronal Spectrometer, a fiber optic based spectrograph, was designed for global and simultaneous measurements of the thermal electron temperature and the solar wind velocity in the solar corona. The first ever experiment of this nature was conducted in conjunction with the total solar eclipse of 11 August 1999 in Elazig, Turkey. Here twenty fiber optic tips were positioned in the focal plane of the telescope to observe simultaneously at many different latitudes and two different radial distances in the solar corona. The other ends were vertically stacked and placed at the primary focus of the spectrograph. By isolating the K-coronal spectrum from each fiber the temperature and the wind sensitive intensity ratios were calculated.

Reginald, Nelson L.↗

NASA NTRS1978

Window flaw detection by backscatter lighting

Portable fiber-optic probe detects tiny flaws in transparent materials. Probe transmits light through surface to illuminate interior of material by backscattering off its edges. Light-sensitive contact paper records scratch pattern. Technique can be used for rapid visual checks. Flexible fiber optics are safely used in explosive or flammable areas; they present no hazard of breakage or contamination in controlled environments.

Crockett, L. K.↗

NASA NTRS1990

The hemisphere-cylinder at an angle of attack

The investigation of the flow over a cylinder with a hemispherical nose at an angle of attack is presented. Experiments were conducted in a 6 ft x 6 ft low-turbulence tunnel. The focus of this research is the separated region as well as the evaluation and testing of a new diagnostic tool, a fiber-optic laser-Doppler probe. A two-fold contribution is offered. On one hand, pressure distributions are provided along a fine grid over the body. On the other hand, a feasibility study is presented on the use of a fiber-optic LDV probe which can obtain data from inside the model.

Telionis, D. P.↗

NASA NTRS2010

Polarization Dependent Coupling of Whispering Gallery Modes in Microspheres

Two sets of resonances in glass microspheres attached to a standard communication-grade single-mode optical fiber have been observed. It has been found that the strength of the resonances depends strongly on the polarization of the coupled light. Furthermore, the position of the resonances in the wavelength domain depends on the polarization of light in the optical fiber with maximum magnitudes shifted by approximately 45 .

Adamovsky, G.↗

NASA NTRS2000

MACS, An Instrument, and a Methodology for Simulations and Global Measurements of the Coronal Electron Temperature and the Solar Wind Velocity on the Solar Corona

The determination of the radial and latitudinal temperature and wind profiles of the solar corona is of great importance in understanding the coronal heating mechanism and the dynamics of coronal expansion. Cram presented the theory for the formation of the K-coronal spectrum and identified two important observations. He observed the existence of temperature sensitive anti-nodes at certain wavelengths in the theoretical K-coronal spectra. The anti-nodes are separated by temperature-insensitive nodes. Remarkably, Cram showed that the wavelengths of the nodes and anti-nodes are almost independent of altitude above the solar limb. Because of these features, Cram suggested that the intensity ratios at two anti-nodes could be used as a diagnostic of the electron temperature in the K-corona. Based on this temperature diagnostic technique prescribed by Cram a slit-based spectroscopic study was performed by Ichimoto et al. on the solar corona in conjunction with the total solar eclipse of 3 Nov 1994 in Putre, Chile to determine the temperature profile of the solar corona. In this thesis Cram's theory has been extended to incorporate the role of the solar wind in the formation of the K-corona, and we have identified both temperature and wind sensitive intensity ratios. The instrument, MACS, for Multi Aperture Coronal Spectrometer, a fiber optic based spectrograph, was designed for global and simultaneous measurement of the thermal electron temperature and the solar wind velocity in the solar corona. The first ever experiment of this nature was conducted in conjunction with the total solar eclipse of 11 Aug 1999 in Elazig, Turkey. In this instrument one end of each of twenty fiber optic tips were positioned in the focal plane of the telescope in such a way that we could observe conditions simultaneously at many different latitudes and two different radial distances in the solar corona. The other ends of the fibers were vertically aligned and placed at the primary focus of the collimating lens of the spectrograph to obtain simultaneous and global spectra on the solar corona. By isolating the K-coronal spectrum from the spectrum recorded by each fiber the temperature and the wind sensitive intensity ratios were calculated to obtain simultaneous and global measurements of the thermal electron temperature and the solar wind velocity. We were successful in obtaining reliable estimates of the coronal temperature at many positions in the corona. This is the first time that simultaneous measurements of coronal temperatures have been obtained at so many points. However due to instrumental scattering encountered during observations, reliable estimates of the wind velocity turned out to be impossible to obtain. Although remedial measures were taken prior to observation, this task proved to be difficult owing to the inability to replicate the conditions expected during an eclipse in the laboratory. The full extent of the instrumental scattering was apparent only when we analyzed the observational sequence. Nevertheless the experience obtained from this very first attempt to simultaneously and globally measure both the wind velocity and the temperature on the solar corona have provided valuable information to conduct any future observations successfully.

Reginald, Nelson L.↗

NASA NTRS1996

High Temperature Testing with Sapphire Fiber White-Light Michelson Interferometers

In the design of new aerospace materials, developmental testing is conducted to characterize the behavior of the material under severe environmental conditions of high stress, temperature, and vibration. But to test these materials under extreme conditions requires sensors that can perform in harsh environments. Current sensors can only monitor high temperature test samples using long throw instrumentation, but this is inherently less accurate than a surface mounted sensor, and provides no means for fabrication process monitoring. A promising alternative is the use of sapphire optical fiber sensors. Sapphire is an incredibly rugged material, being extremely hard (9 mhos), chemically inert, and having a melting temperature (over 2000 C). Additionally, there is a extensive background of optical fiber sensors upon which to draw for sapphire sensor configurations.

Barnes, A.↗

NASA NTRS1990

Design of an optically controlled Ka-band GaAs MMIC phased-array antenna

Phased array antennas long were investigated to support the agile, multibeam radiating apertures with rapid reconfigurability needs of radar and communications. With the development of the Monolithic Microwave Integrated Circuit (MMIC), phased array antennas having the stated characteristics are becoming realizable. However, at K-band frequencies (20 to 40 GHz) and higher, the problem of controlling the MMICs using conventional techniques either severely limits the array size or becomes insurmountable due to the close spacing of the radiating elements necessary to achieve the desired antenna performance. Investigations were made that indicate using fiber optics as a transmission line for control information for the MMICs provides a potential solution. By adding an optical interface circuit to pre-existing MMIC designs, it is possible to take advantage of the small size, lightweight, mechanical flexibility and RFI/EMI resistant characteristics of fiber optics to distribute MMIC control signals. The architecture, circuit development, testing and integration of optically controlled K-band MMIC phased array antennas are described.

Kunath, Richard R.↗

NASA NTRS1990

Design of an optically controlled Ka-band GaAs MMIC phased-array antenna

Kunath, Richard R.↗

NASA NTRS1988

Diode-pumped laser research

The Laboratory for Oceans is currently working on the development of compact laser diode array (LD) pumped Nd:YAG lasers for use in space-based altimetry and ranging. Laser diode-array pumping technology promises to increase the electrical to optical efficiency of solid state lasers by an order of magnitude with a lifetime increase of nearly three orders of magnitude relative to today's conventional flashlamp-pumped laser systems. The small size, efficiency, and ruggedness make LD-pumped solid state lasers ideal for space based applications. In an in-house RTOP effort, a novel multiple-pass LD-pumped Nd:YAG laser amplifier was designed and tested to increase the 100 microjoule output pulse energy of the Lightwave laser oscillator. Preliminary results have yielded a round trip amplifier gain of about 15 percent using 7 microjoule LD-pump energy. As a parallel activity, funding was recently obtained to investigate the possible use of custom made fiber optic arrays to obtain an efficient optical coupling mechanism between the emitting laser diode-arrays and the target solid state laser material. Fiber optic coupling arrays would allow for the easy manipulation of the spatial emitting pattern of the diode pump sources to match either an end or side pumping laser configuration.

Ramos-Izquierdo, L.↗

NASA NTRS1989

High resolution color band pyrometer ratioing

The sensing head of a two-color band ratioing pyrometer of a known type using a fiber optic cable to couple radiation to dual detector photodiodes is improved to have high spatial resolution by focusing the radiation received through an objective lens (i.e., by focusing the image of a target area) onto an opaque sheet spaced in front of the input end of the fiber optic cable. A two-mil hole in that sheet then passes radiation to the input end of the cable. The detector has two channels, one for each color band, with an electronic-chopper stabilized current amplifier as the input stage followed by an electronic-chopper stabilized voltage amplifier.

Bickler, Donald B.↗