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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.

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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

An analysis of approach navigation accuracy and guidance requirements for the grand tour mission to the outer planets

The navigation and guidance process for the Jupiter, Saturn and Uranus planetary encounter phases of the 1977 Grand Tour interior mission was simulated. Reference approach navigation accuracies were defined and the relative information content of the various observation types were evaluated. Reference encounter guidance requirements were defined, sensitivities to assumed simulation model parameters were determined and the adequacy of the linear estimation theory was assessed. A linear sequential estimator was used to provide an estimate of the augmented state vector, consisting of the six state variables of position and velocity plus the three components of a planet position bias. The guidance process was simulated using a nonspherical model of the execution errors. Computation algorithms which simulate the navigation and guidance process were derived from theory and implemented into two research-oriented computer programs, written in FORTRAN.

Jones, D. W.↗
NASA NTRS1971

The effects of random accelerations on estimation accuracy with applications to the Mariner 1969 relativity experiment

A simple point of view is presented for establishing the relationship between a general modeling error and estimation accuracy. Tentative models are given for the random, nongravitational forces thought likely to affect the Mariner 6 and 7 spacecraft. The navigation data from these spacecraft were used to determine the relativity parameter Gamma. The effect that random accelerations have on the classical least squares filter, which assumes the accelerations do not exist, is calculated, and it is demonstrated that their presence seriously affects the estimates, particularly when an extended data arc is employed. Finally, some preliminary exploration using sequential-type filters, which attempt to model and thus ameliorate the effects of these same accelerations, is reported.

Curkendall, D. W.↗
NASA NTRS1972

The effects of tracking station coordinate uncertainties on GEOS-2 orbital accuracy

Laser and minitrack observational data from GEOS-2 collected during the period April 23, 1971 to May 1971, have been used for the purpose of assessing the influence of tracking station location on the accuracy of orbit determination. These data were processed using a unified set of coordinates for the tracking station locations. Concurrently, these data were processed using nonunified station locations referred to a variety of geodetic datums. The resultant orbits based on the two different sets of station locations were compared and relative differences in the position of the satellite were determined. Differences between the two groups of orbits fitted over four-day data spans ranged from 250 meters to 500 meters for orbits derived from laser data only. For orbits observed from Minitrack data alone the relative differences in GEOS-2 spacecraft position ranged from 50 meters to 190 meters. Utilizing the laser data alone in each arc, definitive orbits were computed using the unified and nonunified station location coordinates. The differences in the satellite position in the overlap region when using the unified laser station coordinates ranged from 25 meters to 150 meters, whereas when using the nonunified laser station coordinates the differences in position ranges from 180 to 650 meters.

Glazer, J.↗
NASA NTRS1972

Numerical check on the accuracy of spherical-wave expansions.

A simple and sensitive test for evaluating the numerical accuracy of a spherical-wave expansion is presented. The basic idea is to compare two different expansions of the same electromagnetic field, computed with respect to different coordinate origins. The use of the technique is illustrated by an example based on the experimental pattern of a horn antenna.

Ludwig, A. C.↗
NASA NTRS1972

The elusive tradeoff - Speed vs accuracy in visual discrimination tasks.

Explicit payoffs were used to control pressures for speed and accuracy in experiments seeking tradeoffs for difficult visual discrimination tasks. The experiments involved stimuli on a cathode ray tube display controlled by a PDP-1 computer, with the subjects performing increasingly complex discrimination tasks and their earnings increasing with their performance. Models for discrimination under time pressure are proposed on the basis of the results.

Swensson, R. G.↗
NASA NTRS1974

An analysis of the accuracy of a parameter optimization

The numerical operations involved in a currently used optimization technique are discussed and analyzed with special attention to the numerical accuracy. Alternative methods for deriving linear system transfer functions, finding the relationships between the transfer function coefficients and the design parameters, and solving a matrix equation are presented for more accurate and cost effective solutions.

Baram, Y.↗