SEARCH · Engineering Papers
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Technique employs computer-controlled light-emitting diode (LED), precision machined mask, and analog-to-digital coverter (ADC). Computer turns on LED which floods masked face of tube. Intensity pattern, generated as tube is electromagnetically swept, is fed to ADC which controls tube calibration.
Carbon fiber sampling instruments were developed: passive collectors made of sticky bridal veil mesh, and active instruments using a light emitting diode (LED) source. These instruments measured the number or number rate of carbon fibers released from carbon/graphite composite material when the material was burned in a 10.7 m (35 ft) dia JP-4 pool fire for approximately 20 minutes. The instruments were placed in an array suspended from a 305 m by 305 m (1000 ft by 1000 ft) Jacob's Ladder net held vertically aloft by balloons and oriented crosswind approximately 140 meters downwind of the pool fire. Three tests were conducted during which released carbon fiber data were acquired. These data were reduced and analyzed to obtain the characteristics of the released fibers including their spatial and size distributions and estimates of the number and total mass of fibers released. The results of the data analyses showed that 2.5 to 3.5 x 10 to the 8th power single carbon fibers were released during the 20 minute burn of 30 to 50 kg mass of initial, unburned carbon fiber material. The mass released as single carbon fibers was estimated to be between 0.1 and 0.2% of the initial, unburned fiber mass.
The minority carrier diffusion length Ln in the base or substrate region is an important parameter which governs a solar cell's performance. The present investigation is concerned with the development of a multiwavelength analyzer (MWA) technique for the nondestructive spatial testing of polycrystalline solar cells. The MWA method is based on the utilization of the short-circuit current generated by two or more light-emitting diodes (LEDs) operating at different wavelengths and modulated 180 deg out-of-phase. For a determination of Ln by the MWA technique, it is necessary to know the value of the absorption coefficient.
Power-supply voltages quickly monitored by circuit equipped with light-emitting-diode (LED) display. Operator looking at display quickly spots whether power output voltage is above, below, or within acceptable limits. Tricolor LED displays high, low, and intermediate output voltages.
A sensing system is presented which includes a pulse-modulated light-emitting diode (LED) and an all-fibre-optic loop generating a reference signal in the time domain. The basic principle of operation and parameters are introduced, and some properties of such a system are experimentally examined using a microbend sensor.
Al(0.3)Ga(0.7)As/Al(0.05)Ga(0.95)As double-heterostructure light-emitting diodes (LEDs) were successfully grown for the first time by liquid phase epitaxy on a GaAs-coated Si substrate that was prepared by a sequential process of migration-enhanced epitaxy and molecular beam epitaxy. The edge-emitting LEDs had diode ideality factors of 1.54 at a forward-biased voltage higher than 0.9 V and external quantum efficiencies of 0.0033 W/A per facet. This efficiency is 50 times higher than the previously reported value, and is on the same order as that of AlGaAs homojunction LEDs fabricated on the GaAs substrates by liquid phase epitaxy.
Programmable Display Pushbutton (PDP) is pushbutton device available from Micro Switch having programmable 16X35 matrix of light-emitting diodes on pushbutton surface. Any desired legends display on PDP's, producing user-friendly applications reducing need for dedicated manual controls. Interacts with operator, calls for correct response before transmitting next message. Both simple manual control and sophisticated programmable link between operator and host system. Programmable Display Pushbutton Legend Editor (PDPE) computer program used to create light-emitting-diode (LED) displays for pushbuttons. Written in FORTRAN.
Control circuit operates two independent stepping motors, one at a time. Provides following operating features: After selected motor stepped to chosen position, power turned off to reduce dissipation; Includes two up/down counters that remember at which one of eight steps each motor set. For selected motor, step indicated by illumination of one of eight light-emitting diodes (LED's) in ring; Selected motor advanced one step at time or repeatedly at rate controlled; Motor current - 30 mA at 90 degree positions, 60 mA at 45 degree positions - indicated by high or low intensity of LED that serves as motor-current monitor; Power-on reset feature provides trouble-free starts; To maintain synchronism between control circuit and motors, stepping of counters inhibited when motor power turned off.
Optoelectronic terminal for digital communication both transmits and receives over single optical fiber. Uses same semiconductor device - light-emitting diode (LED) - as both transmitting and receiving transducer. Dual-purpose LED's reduce cost.
Recent developments in spatial light modulators have led to devices which are capable of continuous phase modulation, even if only over a limited range. One of these devices, the deformable mirror device is used, to compare the relative merits of binary and partially-continuous phase filters in a specific problem of pattern recognition by optical correlation. Each filter was physically limited to only about a radiation of modulation. Researchers have predicted that for low input noise levels, continuous phase-only filters should have a higher absolute correlator peak output than the corresponding binary filters, as well as having a larger SNR. When continuous and binary filters were implemented on the DMD and they exhibited the same performance; an ad hoc filter optimization procedure was developed for use in the laboratory. The optimized continuous filter gave higher correlation peaks than did an independently optimized binary filter. Background behavior in the correlation plane was similar for the two filters, and thus the SNR showed the same improvement for the continuous filter. A phasor diagram analysis and computer simulation have explained part of the optimization procedure's success.
A description of the Large Gap Magnetic Suspension System (LGMSS) ground-based experiment is presented. The LGMSS provides five degrees of freedom control of a cylindrical suspended element which is levitated above a floor-mounted array of air core electromagnets. The uncontrolled degree of freedom is rotation about the long axis of the cylinder (roll). Levitation and control forces are produced on a permanent magnet core which is embedded in the cylinder. The cylinder also contains light emitting diodes (LEDs), assorted electrons, and a power supply. The LEDs provide active targets for an optical position measurement system which is being developed in-house at the Langley Research Center. The optical position measurement system will provide six degrees of freedom position information for the LGMSS control system.
An algorithm is presented that incorporates real time data from two infrared cameras and computes the attitude parameters of the Spacecraft COntrol Lab Experiment (SCOLE), a lab apparatus representing an offset feed antenna attached to the Space Shuttle by a flexible mast. The algorithm uses camera position data of three miniature light emitting diodes (LEDs), mounted on the SCOLE platform, permitting arbitrary camera placement and an on-line attitude extraction. The continuous nature of the algorithm allows identification of the placement of the two cameras with respect to some initial position of the three reference LEDs, followed by on-line six degrees of freedom attitude tracking, regardless of the attitude time history. A description is provided of the algorithm in the camera identification mode as well as the mode of target tracking. Experimental data from a reduced size SCOLE-like lab model, reflecting the performance of the camera identification and the tracking processes, are presented. Computer code for camera placement identification and SCOLE attitude tracking is listed.
A demonstration of the ability of an existing optical fiber cable to survive the harsh environment of a rocket engine was performed at the NASA Lewis Research Center. The intent of this demonstration was to prove the feasibility of applying fiber optic technology to rocket engine instrumentation systems. Extreme thermal transient tests were achieved by wrapping a high temperature optical fiber, which was cablized for mechanical robustness, around the combustion chamber outside wall of a 1500 lb Hydrogen-Oxygen rocket engine. Additionally, the fiber was wrapped around coolant inlet pipes which were subject to near liquid hydrogen temperatures. Light from an LED was sent through the multimode fiber, and output power was monitored as a function of time while the engine was fired. The fiber showed no mechanical damage after 419 firings during which it was subject to transients from 30 K to 350 K, and total exposure time to near liquid hydrogen temperatures in excess of 990 seconds. These extreme temperatures did cause attenuation greater than 3 dB, but the signal was fully recovered at room temperature. This experiment demonstrates that commercially available optical fiber cables can survive the environment seen by a typical rocket engine instrumentation system, and disclose a temperature-dependent attenuation observed during exposure to near liquid hydrogen temperatures.
Electronic circuit provides bar-graph display of difference between carrier frequency of pulsed laser transmitter and frequency of another laser serving as local oscillator in receiver. Display device linear array of light-emitting diodes (LED's), each representing 1-MHz portion of beat-frequency range from 20 to 40 MHz. Middle LED and neighbors green; LED's representing edges of passband yellow; LED's of frequencies outside passband red. Operator determines approximate relative frequency of transmitter at a glance by observing color and position of illuminated LED.
Betavoltaic power supplies based on gallium phosphide can supply long term low-level power with high reliability. Results are presented for GaP devices powered by Ni-63 and tritiarated phosphors. Leakage currents as low as 1.2 x 10(exp -17) A/cm(exp 2) have been measured and the temperature dependence of the reverse saturation current is found to have ideal behavior. A small demonstration system has been assembled that generates and stores enough electricity to light up an LED.
While considerable attention has been given to visual-vestibular interaction (VVI) during angular motion of the head as might occur during an aircraft spin, much less attention has been given to VVI during linear motion of the head. Such interaction might occur, for example, while viewing a stationary or moving display during vertical take-off and landing operations Research into linear VVI, particularly during prolonged periods of linear acceleration, has been hampered by the unavailability of a programmable translator capable of large excursions We collaborated with Otis Elevator Co. and used their research tower and elevator, whose motion could be digitally programmed, to vertically translate human subjects over a distance of 92.3 meters with a peak linear acceleration of 2 meters/sec(exp 2) During pulsatile or sinusoidal translation, the subjects viewed moving stripes (optokinetic stimulus) or a fixed point source (light emitting diode, led, display), respectively and it was generally found that. The direction of linear acceleration relative to the cardinal head axes and the direction of the slow component of optokinetic nystagmus (OKN) determined the extent of VVI during concomitant stripe motion and linear acceleration. Acceleration along the z head axis (A(sub z)) produced the largest VVI, particularly when the slow component of OKN was in the same direction as eye movements produced by the linear acceleration and Eye movements produced by linear acceleration are suppressed by viewing a fixed target at frequencies below 10 Hz But, above this frequency the suppression produced by VVI is removed. Finally, as demonstrated in non-human primates, vergence of the eyes appears to modulate the vertical eye movement response to linear acceleration in humans.
The Free-Flying Magnetometer (FFM) is an autonomous "sensorcraft" developed at the Jet Propulsion Laboratory (JPL) for the Enstrophy sounding rocket mission. This mission was a collaborative project between the University of New Hampshire, Cornell University and JPL. The science goal of the mission was the study of current filamentation phenomena in the northern auroral region through multipoint measurements of magnetic field. The technical objective of the mission was the proof of concept of the JPL FFM design and the demonstration of an in-situ multipoint measurement technique employing many free-flying spacecraft. Four FFMs were successfully deployed from a sounding rocket launched from Poker Flats, Alaska on February 11, 1999. These hockey-puck-sized (80 mm diameter, 38 mm. height, 250 gram mass) free flyers each carry a miniature 3-axis flux-gate magnetometer that output +/- 2 V signals corresponding to a +/- 60,000 nT measurement range for each axis. The FFM uses a synchronized four-channel Sigma(Delta) Analog-to-Digital Converter (ADC) having a dynamic range of +/- 2.5V and converting at a rate of 279 samples/second/channel. Three channels are used to digitize the magnetometer signals to 17-bit (1.144 nT/bit) resolution. The fourth ADC channel is multiplexed for system monitoring of four temperature sensors and two battery voltages. The FFM also contains two sun sensors, a laser diode which emits a fan-shaped beam, a miniature S-band transmitter for direct communication to the ground station antennas, an ultra-stable Temperature Compensated Crystal Oscillator (TCXO) clock, an integrated data subsystem implemented in a Field-Programmable Gate Array (FPGA), a 4 Mbit Static Random Access Memory (SRAM) for data storage and Lithium Thionyl Chloride batteries for power. Communicating commands to the FFM prior to deployment is achieved with an infrared (IR) link. The FFM IR receiver responds to 9-bit pulse coded signals that are generated by an IR Light Emitting Diode (LED) in the payload for turning FFM power on or off and placing the FFM in a test mode or flight mode. The IR links are also used to synchronize (zero) the clocks onboard all the FFMs through a reset pulse originating from the payload GPS receiver that is issued when the FFMs are in flight mode. The FPGA based data subsystem manages continuous data collection from the four ADC channels and sun sensors, formatting and storing the data to SRAM, and controlling downlink transmission. The transmitter is powered only after a 2547 frame SRAM buffer has been filled (approx. 5 minutes of data). The data is Viterbi encoded and sent to the S-band transmitter via a First-In-First-Out (FIFO) buffer who's output is clocked at 100 bits/second. After the 26-second transmission, the transmitter is turned off to reduce noise coupling to the sensitive magnetometer. The data subsystem control consists of a master state machine that performs data flow management and is interfaced through a prioritized interrupt scheme to state machines that service the ADC, sun sensors and transmitter FIFO. Continuous data collection prevents the missing of data during transmission and provides implicit time tagging of the data acquired by the ADC because of synchronization with the TCXO clock.
Biomedical Optical Company of America's (BOCA) suntiger lenses, similar in principle to natural filters in the eyes of hawks and eagles, bar 99 percent of potentially harmful wavelengths, while allowing visually useful colors of light (red, orange, green) to pass through. They also improve visual acuity, night vision and haze or fog visibility. The lenses evolved from work done by James B. Stephens and Dr. Charles G. Miller of the Jet Propulsion Laboratory. They developed a formula and produced a commercial welding curtain that absorbs, filters, and scatters light. This research led to protective glasses now used by dentists, workers in hazardous environments, CRT operators and skiers.