SEARCH · Engineering Papers

Results for “TERMINAL”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53

All sources NASA NTRS DOE OSTI

NASA NTRS1990

Standard-M mobile satellite terminal employing electronic beam squint tracking

In recent years, extensive experience has been built up at the University of Bristol in the use of the Electronic Beam Squint (EBS) tracking technique, applied to large earth station facilities. The current interest in land mobile satellite terminals, using small tracking antennas, has prompted the investigation of the applicability of the EBS technique to this environment. The development of an L-band mechanically steered vehicle antenna is presented. A description of the antenna is followed by a detailed investigation of the tracking environment and its implications on the error detection capability of the system. Finally, the overall hardware configuration is described along with plans for future work.

Hawkins, G. J.↗

NASA NTRS1992

A 1-W, 30-ghz, CPW Amplifier for ACTS Small Terminal Uplink

The progress is described of the development of a 1 W, 30 GHz, coplanar waveguide (CPW) amplifier for the Advanced Communication Technology Satellite (ACTS)Small Terminal Uplink. The amplifier is based on Texas Instruments' monolithic microwave integrated circuit (MMIC) amplifiers; a three stage, low power amplifier, and a single stage, high power amplifier. The amplifiers have a power output of 190 mW and 0.710 W, gain of 23 and 4.2 dB, and efficiencies of 30.2 and 24 percent for the three stage and one stage amplifiers, respectively. The chips are to be combined via a CPW power divider/combiner circuit to yield the desired 1 W of output power.

Taub, Susan R.↗

NASA NTRS1992

Ka-band dual frequency array feed for a low cost ACTS ground terminal

Because of low cost and ease of fabrication, microstrip arrays are attractive as feeds for reflector antenna systems. The development of a 4 x 4 microstrip array which will be used as a feed for a low cost Advanced Communications Technology Satellite (ACTS) ground terminal is described. The array feed consisting of four 2 x 2 subarrays is fed with coplanar waveguide power dividing networks. The patch radiator is designed to excite two orthogonal, linearly polarized waves at Ka-band frequencies (around 20 and 30 GHz). Test results for the developed array are presented.

Lee, Richard Q.↗

NASA NTRS1992

A 1-W, 30-GHz, CPW amplifier for ACTS small terminal uplink

The progress to date of the development of a 1-W, 30-GHz, coplanar waveguide (CPW) amplifier for the Advanced Communication Technology Satellite (ACTS) Small Terminal Uplink is described. The amplifier is based on Texas Instruments' monolithic microwave integrated circuit (MMIC) amplifiers; a three-stage, low-power amplifier and a single stage, high-power amplifier. The amplifiers have a power output of 190 mW and 0.710 W, gain of 23 and 4.2 dB, and efficiencies of 30.2 and 24 percent for the three-stage and one-stage amplifiers, respectively. The chips are to be combined via a CPW power divider/combiner circuit to yield the desired 1 W of output power.

Taub, Susan R.↗

NASA NTRS1992

Ground terminal expert (GTEX). Part 2: Expert system diagnostics for a 30/20 Gigahertz satellite transponder

A research effort was undertaken to investigate how expert system technology could be applied to a satellite communications system. The focus of the expert system is the satellite earth station. A proof of concept expert system called the Ground Terminal Expert (GTEX) was developed at the University of Akron in collaboration with the NASA Lewis Research Center. With the increasing demand for satellite earth stations, maintenance is becoming a vital issue. Vendors of such systems will be looking for cost effective means of maintaining such systems. The objective of GTEX is to aid in diagnosis of faults occurring with the digital earth station. GTEX was developed on a personal computer using the Automated Reasoning Tool for Information Management (ART-IM) developed by the Inference Corporation. Developed for the Phase 2 digital earth station, GTEX is a part of the Systems Integration Test and Evaluation (SITE) facility located at the NASA Lewis Research Center.

Durkin, John↗

NASA NTRS1992

Ka-Band Dual Frequency Array Feed for a Low Cost ACTS Ground Terminal

Because of low cost and ease of fabrication, microstrip arrays are attractive as feeds for reflector antenna systems. This paper describes the development of a 4x4 microstrip array which will be used as a feed for a low cost ACTS ground terminal. The array feed consisting of four 2x2 subarrays is fed with coplanar waveguide power dividing networks. The patch radiator is designed to excite two orthogonal, linearly polarized waves at Ka-band frequencies (around 20 and 30 GHz). Test results for the developed array are presented.

Lee, Richard Q.↗

NASA NTRS1990

Immunoreactive prohormone atrial natriuretic peptides 1-30 and 31-67 - Existence of a single circulating amino-terminal peptide

Sep-Pak C18 extraction of human plasma and radioimmunoassay using antibodies which recognize atrial natriuretic peptide (99-128) and the prohormone sequences 1-30 and 31-67 resulted in mean values from 20 normal subjects of 26.2 (+/- 9.2), 362 (+/- 173) and 368 (+/- 160) pg/ml, respectively. A high correlation coefficient between values obtained using antibodies recognizing prohormone sequences 1-30 and 31-67 was observed (R = 0.84). Extracted plasma immunoreactivity of 1-30 and 31-67 both eluted at 46 percent acetonitrile. In contrast, chromatographic elution of synthetic peptides 1-30 and 31-67 was observed at 48 and 39 percent acetonitrile, respectively. Data suggest that the radioimmunoassay of plasma using antibodies recognizing prohormone sequences 1-30 and 31-67 may represent the measurement of a unique larger amino-terminal peptide fragment containing antigenic sites recognized by both antisera.

Chen, Yu-Ming↗

NASA NTRS1991

Sufficient conditions for a local minimum of the Bolza problem with multiple terminal point constraints

Sufficient conditions for a weak relative minimum are derived for a form of the Bolza problem of variational calculus. The derivation ties together first-order and second-order conditions in a unified consistent manner, addresses controllability considerations in some detail, and clarifies some small inconsistencies in earlier work. The resulting second-order conditions of optimality involve the integration of fewer backward-sweep matrix elements than the standard conditions in the literature for problems with an unspecified final time. As a result, the backward-sweep matrices have the same general structure and dimensionality whether the final time is specified or free, with the terminal values of two of three sweep matrices being more complicated in the latter case.

Wood, Lincoln J.↗

NASA NTRS1991

Modeled performance of monolithic, 3-terminal InP/Ga(0.47)In(0.53)As concentrator solar cells as a function of temperature and concentration ratio

Using measured device parameters from a monolithic three-terminal In/GaInAs (0.75 eV) tandem concentrator solar cell, a numerical model is constructed that calculates efficiency as a function of temperature and concentration ratio. The device measurements indicate that the series resistance in the InP top cell severely limits the maximum efficiency at high concentration ratios. Results from the model in which a single-junction InP concentrator solar cell that has a lower resistance by a factor of six was substituted for the top cell show that peak 20 C air-mass-zero (AM0) efficiencies should approach 30 percent at concentration ratios greater than 100. At 80 C, this tandem cell should exceed 24 percent AM0 efficiency.

Osterwald, C. R.↗

NASA NTRS1993

Styrene-Terminated Polysulfone Oligomers As Matrix Materials

Report summarizes preliminary experimental study and evaluation of styrene-terminated polysulfone oligomers as matrix materials in graphite-fiber/matrix composites. Composites evaluated in terms of methods of fabrication and of mechanical properties.

Bowles, Kenneth J.↗

NASA NTRS1993

Dynamic Termination On Radiating Coaxial Cable

Radiation pattern dithered to reduce adverse effect of nulls. In improved system for radio communication between base station and portable units within building, tunnel, ship, or other large structure, radiating or "leaky" coaxial cable serves as base-station antenna, and radiation pattern of cable dithered by dithering impedance of termination at end of cable remote from base station.

Lombardi, Robert↗

NASA NTRS1992

Space Communication Artificial Intelligence for Link Evaluation Terminal (SCAILET)

A software application to assist end-users of the high burst rate (HBR) link evaluation terminal (LET) for satellite communications is being developed. The HBR LET system developed at NASA Lewis Research Center is an element of the Advanced Communications Technology Satellite (ACTS) Project. The HBR LET is divided into seven major subsystems, each with its own expert. Programming scripts, test procedures defined by design engineers, set up the HBR LET system. These programming scripts are cryptic, hard to maintain and require a steep learning curve. These scripts were developed by the system engineers who will not be available for the end-users of the system. To increase end-user productivity a friendly interface needs to be added to the system. One possible solution is to provide the user with adequate documentation to perform the needed tasks. With the complexity of this system the vast amount of documentation needed would be overwhelming and the information would be hard to retrieve. With limited resources, maintenance is another reason for not using this form of documentation. An advanced form of interaction is being explored using current computer techniques. This application, which incorporates a combination of multimedia and artificial intelligence (AI) techniques to provided end-users with an intelligent interface to the HBR LET system, is comprised of an intelligent assistant, intelligent tutoring, and hypermedia documentation. The intelligent assistant and tutoring systems address the critical programming needs of the end-user.

Shahidi, Anoosh K.↗

NASA NTRS1991

A PARC system for terminal docking

A Panoramic viewing system for Automated Rendezvous and Capture (PARC) has been proposed as a visual information feedback system for terminal docking/berthing. The system relies on a unique Panoramic Annular Lens (PAL) which captures an image of its surroundings in real time. This paper describes the evolution of the PAL along with technical details of its imaging capabilities. Several examples are given of radial metrology, where PAL imaging systems are used to perform visual inspections and measurements. Digital image acquisition and processing techniques, used to interpret various features appearing in the images and to transform images for improved human viewing, are also included. These discussions are followed by a potential application for PARC involving berthing of active and passive mechanical assemblies associated with Space Station Freedom.

Gilbert, John A.↗

NASA NTRS1992

Two neural network algorithms for designing optimal terminal controllers with open final time

Multilayer neural networks, trained by the backpropagation through time algorithm (BPTT), have been used successfully as state-feedback controllers for nonlinear terminal control problems. Current BPTT techniques, however, are not able to deal systematically with open final-time situations such as minimum-time problems. Two approaches which extend BPTT to open final-time problems are presented. In the first, a neural network learns a mapping from initial-state to time-to-go. In the second, the optimal number of steps for each trial run is found using a line-search. Both methods are derived using Lagrange multiplier techniques. This theoretical framework is used to demonstrate that the derived algorithms are direct extensions of forward/backward sweep methods used in N-stage optimal control. The two algorithms are tested on a Zermelo problem and the resulting trajectories compare favorably to optimal control results.

Plumer, Edward S.↗

NASA NTRS1993

Airborne derivation of microburst alerts from ground-based Terminal Doppler Weather Radar information: A flight evaluation

An element of the NASA/FAA windshear program is the integration of ground-based microburst information on the flight deck, to support airborne windshear alerting and microburst avoidance. NASA conducted a windshear flight test program in the summer of 1991 during which airborne processing of Terminal Doppler Weather Radar (TDWR) data was used to derive microburst alerts. Microburst information was extracted from TDWR, transmitted to a NASA Boeing 737 in flight via data link, and processed to estimate the windshear hazard level (F-factor) that would be experienced by the aircraft in each microburst. The microburst location and F-factor were used to derive a situation display and alerts. The situation display was successfully used to maneuver the aircraft for microburst penetrations, during which atmospheric 'truth' measurements were made. A total of 19 penetrations were made of TDWR-reported microburst locations, resulting in 18 airborne microburst alerts from the TDWR data and two microburst alerts from the airborne reactive windshear detection system. The primary factors affecting alerting performance were spatial offset of the flight path from the region of strongest shear, differences in TDWR measurement altitude and airplane penetration altitude, and variations in microburst outflow profiles. Predicted and measured F-factors agreed well in penetrations near microburst cores. Although improvements in airborne and ground processing of the TDWR measurements would be required to support an airborne executive-level alerting protocol, the practicality of airborne utilization of TDWR data link data has been demonstrated.

Hinton, David A.↗

NASA NTRS1992

On the termination of the closed field line region of the magnetotail

Experimental models and global computer simulations are used to study the field structure and location of the site where the closed plasma sheet terminates. The site - also called the 'distant neutral line' - is described with references to several solar-wind parameters that can change its characteristic properties. A laboratory experiment is then conducted in which a flowing magnetized plasma beam interacts with a dipole field. High-latitude nightside reconnection is supported by the simulation results comparing the effects of northward and southward interplanetary fields. The results support the models by Dungey (1961, 1963) that predict high-latitude nightside reconnection and an open magnetosphere. A significant finding is that a magnetic neutral line at the closed-field line region is not a necessary component of the region.

Birn, J.↗

NASA NTRS1992

Flight test evaluation of precision-code differential GPS for terminal approach and landing

A flight test evaluation conducted at the NASA Ames Research Center of precision-code differential GPS for terminal approach and landing is described. Differential corrections to satellite range and range-rate measurements are computed in a stationary ground reference system, uplinked to the test aircraft, and employed to correct corresponding airborne satellite data. Differentially corrected range and range-rate data, combined with inertial data, are then utilized with satellite position and velocity to compute aircraft position and velocity employing an eight-state extended Kalman filter.

Mcnally, B. D.↗

NASA NTRS1992

Gimballess multi-access transceiver lasercom terminal development

A breadboard sync satellite terminal has been developed incorporating a unique concept of a gimballess multi-access transceiver, which is capable of simultaneously communicating with six independent, asynchronous LEO satellites. The developmental hardware illustrates that low power, weight, and volume is achievable compared to multiple independent gimballed transceivers, while also putting a lesser burden of power, size, and weight on the LEO satellite tranceivers that communicate with the multiple-access transceiver.

Clarke, E. S.↗