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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Modeling the effects of high-G stress on pilots in a tracking task

Air-to-air tracking experiments were conducted at the Aerospace Medical Research Laboratories using both fixed and moving base dynamic environment simulators. The obtained data, which includes longitudinal error of a simulated air-to-air tracking task as well as other auxiliary variables, was analyzed using an ensemble averaging method. In conjunction with these experiments, the optimal control model is applied to model a human operator under high-G stress.

Korn, J.↗
NASA NTRS1977

Parameter estimation in a human operator describing function model for a two-dimensional tracking task

A previously described parameter estimation program was applied to a number of control tasks, each involving a human operator model consisting of more than one describing function. One of these experiments is treated in more detail. It consisted of a two dimensional tracking task with identical controlled elements. The tracking errors were presented on one display as two vertically moving horizontal lines. Each loop had its own manipulator. The two forcing functions were mutually independent and consisted each of 9 sine waves. A human operator model was chosen consisting of 4 describing functions, thus taking into account possible linear cross couplings. From the Fourier coefficients of the relevant signals the model parameters were estimated after alignment, averaging over a number of runs and decoupling. The results show that for the elements in the main loops the crossover model applies. A weak linear cross coupling existed with the same dynamics as the elements in the main loops but with a negative sign.

Vanlunteren, A.↗
NASA NTRS1977

Multi-attribute subjective evaluations of manual tracking tasks vs. objective performance of the human operator

A computational method to deal with the multidimensional nature of tracking and/or monitoring tasks is developed. Operator centered variables, including the operator's perception of the task, are considered. Matrix ratings are defined based on multidimensional scaling techniques and multivariate analysis. The method consists of two distinct steps: (1) to determine the mathematical space of subjective judgements of a certain individual (or group of evaluators) for a given set of tasks and experimental conditionings; and (2) to relate this space with respect to both the task variables and the objective performance criteria used. Results for a variety of second-order trackings with smoothed noise-driven inputs indicate that: (1) many of the internally perceived task variables form a nonorthogonal set; and (2) the structure of the subjective space varies among groups of individuals according to the degree of familiarity they have with such tasks.

Siapkaras, A.↗
NASA NTRS1979

Solar tracking control system Sun Chaser

The solar tracking control system (Sun Chaser) is believed to be an improved method of tracking the Sun in all types of weather conditions. The Sun Chaser will follow the Sun from east to west in clear or cloudy weather, and reset itself to the east position after sundown in readiness for the next sunrise. A description of the Sun Chaser hardware and its operation together with results is presented.

Scott, D. R.↗
NASA NTRS1979

Design, fabrication, and delivery of a charge injection device as a stellar tracking device

Six 128 x 128 CID imagers fabricated on bulk silicon and with thin polysilicon upper-level electrodes were tested in a star tracking mode. Noise and spectral response were measured as a function of temperature over the range of +25 C to -40 C. Noise at 0 C and below was less than 40 rms carriers/pixel for all devices at an effective noise bandwidth of 150 Hz. Quantum yield for all devices averaged 40% from 0.4 to 1.0 microns with no measurable temperature dependence. Extrapolating from these performance parameters to those of a large (400 x 400) array and accounting for design and processing improvements, indicates that the larger array would show a further improvement in noise performance -- on the order of 25 carriers. A preliminary evaluation of the projected performance of the 400 x 400 array and a representative set of star sensor requirements indicates that the CID has excellent potential as a stellar tracking device.

Burke, H. K.↗
NASA NTRS1978

Radio tracking of a fin whale /Balaenoptera physalus/

Tracking of a fin whale tagged with an implantable beacon transmitter (IBT) is described. The IBT, which was fired from a modified 12-gauge shotgun, weighs 517 g and is 70 cm long, including a 46-cm antenna. Data on whale movement and breathing are presented. Contact was lost after 27.8 hours of intermittent tracking, presumably as a result of battery leakage. Potential range and duration of IBT transmission are considered, and the significance of transmitter location and orientation in the whale blubber is considered.

Ray, G. C.↗
NASA NTRS1978

Microcrater and solar-flare track maturation of the lunar regolith

The microcrater, pancake and cosmic ray track record in the 100-200 microns feldspar fraction of a variety of surface soils and Apollo and Luna 16-24 cores have been studied. In Luna 24, a study of the glassy agglutinates plus breccias in 9 levels revealed this core was deposited as discrete layers, most of which are immature. Luna 16 and 20 cores were found respectively mature and immature. Glassy agglutinates and impact microcraters, absent to rare in immature soils such as 12033 and 14141, are present in similar abundances on crystals from submature to mature soils. In submature and mature soils, pancakes are present on 60 to 100 percent of crystals and craters on 50 to 70 percent. Microcrater, track and solar wind gas data suggest feldspar crystals in the size range considered reach an equilibrium maturity grade faster than bulk soils. This is interpreted as due to the limited lifetime of these crystals in the lunar regolith.

Poupeau, G.↗
NASA NTRS1978

Particle track densities in the Luna 24 core

We report track density measurements in soil grains at six locations in the Luna 24 core. Irradiation levels are generally high precluding information on the depositional history, but indicating that the soils were exposed at the lunar surface at sometime in the past. Maturity levels determined from track density parameters disagree with those determined from ferromagnetic resonance and agglutinate contents. This discrepancy is not understood, but it could possibly indicate an ancient epoch of increased solar-flare activity.

Blanford, G. E.↗
NASA NTRS1978

Nuclear particle tracks and the regolith at the Luna 24 site

Track investigations of feldspars and pyroxenes in Luna 24 soils indicate that most of the grains resided within millimeters of the lunar surface. The two deepest samples appear to be less mature than the upper ones. Lack of correlation between tracks, agglutinates, and I sub S/FeO is puzzling and unique.

Crozaz, G.↗
NASA NTRS1979

Detecting a gravitational-radiation background using spacecraft Doppler tracking

The sensitivity of NASA's Deep Space Network spacecraft tracking system to an isotropic cosmological background of gravitational radiation is analyzed. It is found that by using the autocovariance function of the Doppler record in the so-called 'three-way' tracking mode to dig into the noise it is possible to put significant limits on this background with current and future planned deep-space missions.

Hellings, R. W.↗
NASA NTRS1979

Tracking and data relay satellite system - NASA's new spacecraft data acquisition system

This paper describes NASA's new spacecraft acquisition system provided by the Tracking and Data Relay Satellite System (TDRSS). Four satellites in geostationary orbit and a ground terminal will provide complete tracking, telemetry, and command service for all of NASA's orbital satellites below a 12,000 km altitude. Western Union will lease the system, operate the ground terminal and provide operational satellite control. NASA's network control center will be the focal point for scheduling user services and controlling the interface between TDRSS and the NASA communications network, project control centers, and data processing. TDRSS single access user spacecraft data systems will be designed for time shared data relay support, and reimbursement policy and rate structure for non-NASA users are being developed.

Schneider, W. C.↗
NASA NTRS1980

Improved code-tracking loop

Delay-locked loop tracks pseudonoise codes without introducing dc timing errors, because it is not sensitive to gain imbalance between signal processing arms. "Early" and "late" reference codes pass in combined form through both arms, and each arm acts on both codes. Circuit accomodates 1 dB weaker input signals with tracking ability equal to that of tau-dither loops.

Laflame, D. T.↗
NASA NTRS1980

The OMNIUM-G HTC-25 tracking concentrator

A point focusing, two axis tracking, high concentration ratio parabolic reflector is described. Field experience coupled with engineering improvements are shown to have manifested a design that is economic in the areas of manufacturing, packaging, delivering, installing, and commissioning the system into operation. The initial problems specifically with the OMNIUM-G model HTC-25 tracking concentrator are addressed.

Zelinger, S.↗
NASA NTRS1979

Earth feature identification and tracking technology development

The paper discusses needs for smart sensing in terrestrial and atmospheric remote sensing as related to current technology and a scheduled Shuttle experiment. An approach is outlined involving Shuttle-borne experiments to develop earth feature identification and tracking technology including a Feature Identification and Location Experiment (FILE) scheduled for flight on the NASA Shuttle with an objective of classifying earth features into categories of bare land, water, vegetation, and clouds, snow, and ice. The plan for evolution of the FILE-related technology leads to capabilities for pointing instruments to predetermined sites, reacquiring earth features or landmarks, and tracking features such as coastlines and rivers. Technology concepts relative to an overall system transfer function is discussed, and the development status outlined.

Wilson, R. G.↗
NASA NTRS1981

Satellite-tracking and Earth dynamics research programs

The major focus for operations during this period was the preliminary MERIT Campaign and its intensive tracking of LAGEOS for polar motion and Earth rotation studies. The data acquired from LAGEOS were used for other geophysical investigations, including studies of crustal dynamics, and Earth and ocean tides, and for the general development of precision orbit determination. The network performed regular tracking of several other retroreflector satellites including GEOS-1, GEOS-3, BE-C, and Starlette for refined determinations of station coordinates and Earth's gravity field and for studies of solid Earth dynamics.

Source record↗
NASA NTRS1981

The effects of receiver tracking phase error on the performance of the concatenated Reed-Solomon/Viterbi channel coding system

Analytical and experimental results are presented of the effects of receiver tracking phase error, caused by weak signal conditions on either the uplink or the downlink or both, on the performance of the concatenated Reed-Solomon (RS) Viterbi channel coding system. The test results were obtained under an emulated S band uplink and X band downlink, two way space communication channel in the telecommunication development laboratory of JPL with data rates ranging from 4 kHz to 20 kHz. It is shown that, with ideal interleaving, the concatenated RS/Viterbi coding system is capable of yielding large coding gains at very low bit error probabilities over the Viterbi decoded convolutional only coding system. Results on the effects of receiver tracking phase errors on the performance of the concatenated coding system with antenna array combining are included.

Liu, K. Y.↗
NASA NTRS1981

PN lock indicator for dithered PN code tracking loop

In a delay-lock one-delta (+or - 1/2 chip) dithered PN code tracking loop, an indication of lock in the PN code tracking loop is provided by delaying the dithered local PN code by a half chip to produce a +0, -1 dithered PN code that is then multiplied with the received PN-spread IF signal to produce a signal proportional to the correlation of this dithered code offset from the received code. The correlation signal is bandpass filtered, amplified with AGC control, and square-law detected to obtain a dc signal proportional to the degree of correlation. The dc signal is multiplied by the dithering control signal to effectivity substract noise voltage from the lock correlation signal which is then compared with a PN lock status signal.

Carson, L. M.↗
NASA NTRS1980

Determination of the geopotential from satellite-to-satellite tracking data

Ground-based observation of the deviation of artificial satellite trajectories from a reference path is the classical means for determining the parameters of the global geopotential. However, for the short wavelengths (less than 10 deg), tracking coverage from ground stations of sufficient density is impossible to obtain. But one or more satellites can observe another satellite and obtain the needed global data coverage. Results are presented of error analyses of possible satellite-to-satellite tracking missions to determine the geopotential at a resolution of 1 x 1 deg. To achieve an accuracy of a few milligals at this resolution requires a satellite altitude at or near 150 km and measurements of intersatellite speed to 10 to the -6th m/s.

Douglas, B. C.↗