SEARCH · Search NASA
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.
The development of the Advanced Comunications Technology Satelite (ACTS) Mobile Terminal (AMT) and it's follow-on, the Broadband Aeronautical Terminal(BAT), have provided an excellent testbed for the evaluation K- and Ka-band mobile satellite communications systems.
For the first time, a unipolar terminal-attractor based neural associative memory (TABAM)system with adaptive threshold and perfect convergence is presented. By adaptively setting thethreshold values for the dynamic iteration for the unipolar binary neuron states with terminal-attractors and inner-product approach, we demonstrate via computer simulation the achievement ofperfect convergence and correct retrieval. The simulation is completed with a small number of storedstates (M) and a small number of neurons (N) but a large M/N ratio. An experiment with exclusive-or logic operation using LCTV SLMs is used to show feasibility of the optoelectronic implementationof the models.
Terminal lakes in the Great Basin (GB) of the western US host critical wildlife habitat and food for migrating birds and can be associated with serious human health and economic consequences when they desiccate. Water levels have declined dramatically in the last 100+ years due to diversion of inflows, drought and climate change. Satellite-derived environmental science data records (ESDRs) from the MODerate-resolution Imaging Spectroradiometer (MODIS) (snow cover, evapotranspiration (ET) and land surface temperature (LST)), enable a unique approach to evaluate the effects of aridification on terminal lakes and to study their individual vulnerabilities. Surface and air temperatures in the GB are rising dramatically, with a sharp rise in the rate of increase observed beginning around 2011, while the number of days of snow cover is declining especially in the western mountainous part of the GB as exemplified in Mono Basin, California. Rising temperatures coincide with fewer days of snow cover, a decrease of inflow to the lakes and greater evaporation of water from the lakes. MODIS ESDRs show strong and statistically significant increasing surface temperature (LST) in the GB, a reduction in the number of days of snow cover, and mixed results in ET. ET declined slightly in the more arid parts of the GB due to greater moisture restrictions to evaporation from extended drought, while ET increased in the more-vegetated, wetter, mountainous northeastern parts as temperatures have risen. Severe and costly ecological, human health and economic consequences are expected if the lakes continue to decline as predicted.
Both uncrewed and crewed launch vehicles (LV) require Flight Termination Systems (FTS) for Range Safety to protect the public and ground assets in the event of a LV failure. Flight crew safety in this context is an added consideration for human spaceflight. The FTS is an electroexplosive system that activates destruct charges to rupture propellant tanks and shutdown engines during flight termination. Commercially available FTS units have been developed for uncrewed applications and are now being repurposed to crewed applications. A consequence of using these systems is that they are designed for public and ground crew safety, though inadequate for flight crew safety. Missing are Human Space Flight (HSF) design controls for inadvertent activation during crewed ascent and protection for crew emergency abort.
We present the initial results from testing of the Low-Cost Optical Terminal (LCOT) at NASA-Goddard Space Flight Center (GSFC). LCOT is designed to be a single modular design that can be quickly reconfigured to support different laser communication missions. LCOT is built around a 70 cm commercially available telescope designed with optical and quantum communications in mind. We have installed a state-of-the-art adaptive optics system, novel high-power laser amplifiers, and other innovative subsystems developed by our team to facilitate laser communications. We have conducted tests of our LCOT system against operational space terminals, demonstrating our ability to receive a downlink and transmit an uplink. We show the results of these tests and give analysis of the results.
We present the initial results from testing of the Low-Cost Optical Terminal (LCOT) at NASA-Goddard Space Flight Center (GSFC). LCOT is designed to be a single modular design that can be quickly reconfigured to support different laser communication missions. LCOT is built around a 70 cm commercially available telescope designed with optical and quantum communications in mind. We have installed a state-of-the-art adaptive optics system, novel high-power laser amplifiers, and other innovative subsystems developed by our team to facilitate laser communications. We have conducted tests of our LCOT system against operational space terminals, demonstrating our ability to receive a downlink and transmit an uplink. We show the results of these tests and give an analysis of the results.
Terminals are reflowed in a hot strata and solidified in a cooler strata, without physical contact with each other, any fixturing, or the container. Terminals are passed through the upper portion of a reflow flask containing hot peanut oil, and then through the lower portion containing oil at ambient temperatures.
Experimental SST terminal for satellite L band communications/surveillance ATC system, establishing terminal requirements for NASA and FAA studies
Termination adapter replaces braid ring and ensures permanent attachment and grounding of sheath wires. The inner ferrule of the termination is slipped inside the exposed ends of the sheath wires and the outer ferrule is placed over the wires and crimped in place to secure the wires for grounding.
Assemblies consist of window piece, conductor spacer, insulator, outer seal, and molded portion that integrates all components. Preparation of FCC for molded plug termination requires that terminated ends of conductors in each cable be accurately folded simultaneously into spacer end and groove.
Newly developed Gunn oscillator is three-terminal device which consists of piece of gallium arsenide with source, drain, and gate contacts. Voltage tunable three-terminal device does not require bulky resonant cavity and allows oscillation frequency to be rapidly tuned with simple circuitry.
A study was made of a polynomial filter for computing range rate information from CSM VHF range data. The filter's performance during the terminal phase of the rendezvous is discussed. Two modifications of the filter were also made and tested. A manual terminal rendezvous was simulated and desired accuracies were achieved for vehicles on an intercept trajectory, except for short periods following each braking maneuver when the estimated range rate was initially in error by the magnitude of the burn.
The performance of a path diversity satellite-to-ground millimeter wave link with two ground terminals separated by 4 km is discussed. At this separation distance the duration of fades below 6 dB was decreased by at least a factor of 10 when using path diversity and the cumulative crosscorrelation between the attenuations observed at the two terminals during rain events was approximately 0.45. Narrow beam radiometers directed along the propagation paths were also utilized to relate the path radiometric temperature to the path attenuation. An analysis of downlink propagation data for generating diversity link performance statistics is included.
The design and operation of a quad redundant data terminal and a multiplexer/demultiplexer (MDU) is described. The most unique feature is the design of the quad redundant data terminal. This is one of the few designs where the unit is fail/op, fail/op, fail/safe. Laboratory tests confirm that the unit will operate satisfactorily with the failure of three out of four channels. Although the design utilizes state-of-the-art technology, the waveform error checks, the voting techniques, and the parity bit checks are believed to be used in unique configurations. Correct word selection routines are also novel. The MDU design, while not redundant, utilizes, the latest state-of-the-art advantages of light coupler and interested amplifiers. Much of the technology employed was an evolution of prior NASA contracts related to the Addressable Time Division Data System. A good example of the earlier technology development was the development of a low level analog multiplexer, a high level analog multiplexer, and a digital multiplexer. A list of all drawings is included for reference and all schematic, block and timing diagrams are incorporated.
A concept for automating the control of air traffic in the terminal area in which the primary man-machine interface is the cockpit is described. The ground and airborne inputs required for implementing this concept are discussed. Digital data link requirements of 10,000 bits per second are explained. A particular implementation of this concept including a sequencing and separation algorithm which generates flight paths and implements a natural order landing sequence is presented. Onboard computer/display avionics utilizing a traffic situation display is described. A preliminary simulation of this concept has been developed which includes a simple, efficient sequencing algorithm and a complete aircraft dynamics model. This simulated jet transport was flown through automated terminal-area traffic situations by pilots using relatively sophisticated displays, and pilot performance and observations are discussed.
By terminating the discharge of energy into an insensitive electroexplosive device, firing-energy parameters can be determined. A simple capacitor-discharge system providing exponential pulses terminated at an adjustable width is described. Basic theory and application to testing are discussed.
Investigation of the conditions whereunder context-sensitive grammars generate context-free languages. The obtained results indicate that, if every noncontext-free rewriting rule of a context-sensitive grammar has as left context a string of terminal symbols and the left context is at least as long as the right context, then the language generated is context-free. Likewise, if every noncontext-free rewriting rule of a context-sensitive grammar has strings of terminal symbols as left and right contexts, then the language generated is also context-free.
Development of an arrival air-traffic management system for a single runway. Traffic is segregated throughout most of the near terminal area according to performance characteristics. Nominal approach routes for each class of aircraft are determined by an optimization procedure. In this fashion, the nominal approach routes are dependent upon and, hence, determined by the near terminal area operating capabilities of each class of aircraft. The landing order and spacing of aircraft on the common approach path are determined so that a measure of total system deviation from the nominal landing times is minimized and safety standards are met. Delay maneuvers required to satisfy sequencing needs are then carried out in a manner dependent upon the particular class of aircraft being maneuvered. Finally, results are presented to illustrate the effects of the rate of arrivals upon a one-runway system serving three different classes of aircraft employing several different sequencing strategies and measures of total system deviation.