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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Geophysical parameters of the earth-moon system

Doppler tracking data from Lunar Orbiter 4 have been combined with laser ranging data from lunar retroreflectors to yield a number of geophysical and geodetic parameters for the earth and moon. This joint solution gives values of (1) the lunar principal polar moment C/M R squared = 0.3905 plus or minus 0.0023, (2) GM(E) = 398600.461 plus or minus 0.026 cu km/sq s, and (3) an earth/moon mass ratio at 81.300587 plus or minus 0.000049. Also determined are the harmonics of a complete lunar gravity field through degree and order 5, the obliquity of the lunar pole, selenocentric coordinates of the lunar retroreflectors, geocentric coordinates of the McDonald Observatory, and the lunar secular acceleration. The lunar potential Love number is weakly determined at 0.022 plus or minus 0.013, and a suprisingly large dissipation of rotational energy is inferred, though either solid body tidal dissipation or liquid core mantle interactions could be causes.

Ferrari, A. J.↗
NASA NTRS1982

Rangefinder Corrects for Air Density and Moisture

Proposed distance-measuring instrument compensates for variations in both dry atmospheric density and water-vapor content. Instrument would be expected to be more accurate than previous laser-ranging instruments. New rangefinder sends three signal trains to target: Two trains are at optical frequencies, and one is at a microwave frequency. All three signals are phase-locked.

Abshire, J. B.↗
NASA NTRS1980

Crustal dynamics project observing plan for highly mobile systems 1981 - 1986

Measurement of crustal motion in the western United States and other tectonically active regions makes use of fixed, movable and highly mobile satellite laser ranging and very long baseline interferometry systems. Measurement of the rotational dynamics of the Earth as well as regional deformation and plate motion are discussed.

Frey, H.↗
NASA NTRS1981

A global tectonic activity map with orbital photographic supplement

A three part map showing equatorial and polar regions was compiled showing tectonic and volcanic activity of the past one million years, including the present. Features shown include actively spreading ridges, spreading rates, major active faults, subduction zones, well defined plates, and volcanic areas active within the past one million years. Activity within this period was inferred from seismicity (instrumental and historic), physiography, and published literature. The tectonic activity map was used for planning global geodetic programs of satellite laser ranging and very long base line interferometry and for geologic education.

Lowman, P. D., Jr.↗
NASA NTRS1981

Time and frequency stability for the Crustal Dynamics Project

Very long base interferometry (VLBI) and laser ranging to artificial satellites and the Moon were used to determined vector baselines between stations with precisions of about one part in 10 to the 8th power. Deformations and strain accumulations in active earthquake regions were determined by making frequent measurements of baselines between many stations in active areas near plate boundaries.

Coates, R. J.↗
NASA NTRS1981

Prospects for TLRS baseline accuracies in the western USA

One of the main goals of the LAGEOS satellite mission is the detection of regional geotectonic movements. A parametric study with the intention to obtain the optimal baseline precision from dynamic solutions of laser ranging to LAGEOS is presented. The varied parameters are: length of reduced arc, number of tracking stations, data noise and rate, biases, refraction errors, system efficiency, gravity model errors in the value of GM. The baseline precisions are 1-10 cm depending upon the set of parameters adopted. General principles obtained are also presented.

Christodoulidis, D.↗
NASA NTRS1981

NASA selects scientific investigations for Earth dynamics studies

Forty two domestic investigators affiliated with U.S. universities, governmental agencies, or private concerns and 14 investigators from France, West Germany, the Netherlands, Switzerland, Spain, Sweden, Australia, New Zealand, Venezuela, and Canada were selected to use precise geodetic data obtained by laser ranging and very long base interferometry in a study of the Earth's tectonic plate movement, crustal deformation, and rotational dynamics. The studies to be made and the principal investigators for each are listed.

Source record↗
NASA NTRS1980

Distance corrections for single- and dual-color lasers by ray tracing

The physical arc length difference between the red and blue beam of a dual-color laser generates an error term in determining Delta-n as well as n (the refractive index) and D (the line length). Numerical ray trace examples and theoretical approximations show that the resulting relative error Delta-D/D increases as D-squared. Error reduction by a factor of nearly 10 is possible by using the pressure, temperature, and humidity of both endpoints to calculate n. The present study results from a desire to improve the precision of monitoring the local and regional position of the Lunar Laser Ranging Observatory atop Haleakala, Maui, Hawaii; the monitoring of the earth's crustal deformation and strain is a primary concern of the study.

Berg, E.↗
NASA NTRS1980

Global gravity field to degree and order 30 from Geos 3 satellite altimetry and other data

A model of the geopotential field in spherical harmonics to degree and order 30 is obtained from Geos 3 satellite to sea surface altimetry data, terrestrial gravity measurements and satellite perturbation analysis. A general perturbation solution is employed for the calculation of the orbits of 10 satellites based on satellite laser ranging data, and 1 deg x 1 deg surface gravity data are used to compute 550 km x 550 km block anomalies by means of autocovariance analysis. Altimeter-determined sea-surface heights, which are taken as the geoid, are averaged for each 1 deg x 1 deg ocean surface area and treated by autocovariance analysis to obtain 550 x 550 km block undulations. Observation and normal equations are formed from the altimeter and surface gravity data, which together cover 1635 out of 1654 possible surface elements, and are combined with the available satellite-derived normal equations to obtain a solution for the spherical harmonics coefficients. In addition, a value of 6,378,138.23 + or - 1.3 m is obtained for the earth's semimajor axis.

Gaposchkin, E. M.↗
NASA NTRS1981

Tidal variations of earth rotation

The periodic variations of the earths' rotation resulting from the tidal deformation of the earth by the sun and moon were rederived including terms with amplitudes of 0.002 millisec and greater. The series applies to the mantle, crust, and oceans which rotate together for characteristic tidal periods; the scaling parameter is the ratio of the fraction of the Love number producing tidal variations in the moment of inertia of the coupled mantle and oceans (k) to the dimensionless polar moment of inertia of the coupled moments (C). The lunar laser ranging data shows that k/C at monthly and fortnightly frequencies equals 0.99 + or - 0.15 and 0.99 + or - 0.20 as compared to the theoretical value of 0.94 + or - 0.04.

Yoder, C. F.↗
NASA NTRS1980

Orbit accuracy assessment for Seasat

Laser range measurements are used to determine the orbit of Seasat during the period from July 28, 1978, to Aug. 14, 1978, and the influence of the gravity field, atmospheric drag, and solar radiation pressure on the orbit accuracy is investigated. It is noted that for the orbits of three-day duration, little distinction can be made between the influence of different atmospheric models. It is found that the special Seasat gravity field PGS-S3 is most consistent with the data for three-day orbits, but an unmodeled systematic effect in radiation pressure is noted. For orbits of 18-day duration, little distinction can be made between the results derived from the PGS gravity fields. It is also found that the geomagnetic field is an influential factor in the atmospheric modeling during this time period. Seasat altimeter measurements are used to determine the accuracy of the altimeter measurement time tag and to evaluate the orbital accuracy.

Schutz, B. E.↗
NASA NTRS1981

Numerical model of the moon's rotation

The differential equations for the Euler angles that define the moon's orientation with respect to an inertial coordinate frame have been integrated numerically. This numerical model of the moon's rotation, when used in conjunction with current lunar-orbit and earth-rotation models, fits lunar laser ranging observations over a five-year period within 28 cm (rms). The present model is also compared with the numerical model of Williams (1975) and Eckhardt's (1981) semianalytical model.

Cappalo, R. J.↗
NASA NTRS1981

Short period tidal variations of earth rotation

It is explained that the tidal deformation of the earth's polar moment of inertia by the moon and sun cause periodic variations in rotation. The short period oscillations give rise to a meter-sized, diurnal signature in the lunar laser ranging data obtained at McDonald Observatory. A solution is given for the scale parameter k/C at fortnightly and monthly tidal frequencies. The results are compared with those obtained by other investigators and with a theoretical estimate which includes the effect of oceans and a decoupled fluid core.

Yoder, C. F.↗
NASA NTRS1981

Tidal dissipation in the moon

Euler's equations of motion, modified to include elasticity and solid friction, were used to study the rotation of the moon. Two heuristic models for the anelasticity were considered: Q independent of frequency and Q inversely proportional to the frequency and Q inversely proportional to the frequency of the strain oscillation. Parameters in each model were estimated by weighted least squares from 9 years of lunar laser range observations. The root mean square of the postfit range residuals was 19 cm in each case. For a strain period of 1 month, the estimates of Q obtained with the two models were similar and surprisingly low: 23 + or - 6. The range of uncertaintly, + or - 6, represents our estimate of the true standard deviation of the estimate of Q, as affected by systematic errors; it is 3 times larger than the formal, statistical, standard error.

Cappallo, R. J.↗
NASA NTRS1982

Cube-Corner Retroreflector Modeling

Collection of computer programs analyzes arrays of optical cube corners used in laser ranging. Programs compute impulse-response and interference effects of reflected pulses from optical cube corners and calculates interference-effects histogram and far-field diffraction patterns.

Kirk, J. G.↗
NASA NTRS1982

A study of autonomous rendezvous and docking systems

An overview of activities in the automatic rendezvous and docking area is presented. A representative mission scenario is covered. A statement of the problem is made and the requirements for the extraction of relative attitude and position data are delineated. A systems block diagram is included and the integral functions which go to make up an autonomous docking system is described. A system was simulated, and the digital simulation is described along with some representative results of a system based a laser ranging device as the sensor. A television camera as the ranging sensor was also considered, one video based automatic docking scheme is discussed along with some representative results.

Michael, J. D.↗
NASA NTRS1981

A proposal to conduct a Caribbean plate project involving the application of space technology to the study of Caribbean geology

The Caribbean plate project is designed to improve current understanding of geological resources and geological hazards within the Caribbean region. Models of mineral occurrence and genesis (including energy resources) on a regional scale, which contribute to nonrenewable resource investigations. Models of lithospheric stress and strain on a regional scale, which contribute to forecasting geological hazards such as earthquakes and major volcanic eruptions are developed. Geological information is synthesize, and research tools provided by space technology the study of the Earth's crust are used. The project was organized in a thematic fashion, to focus on specific geological aspects of the Caribbean plate which are considered to be key factors in developing the types of models described. The project adopts a synoptic perspective in seeking to characterize the three dimensional structure, composition, state of stress, and evolution of the entire Caribbean plate. Geological information derived from analysis of space acquired data is combined with information provided by conventional methods to obtain insight into the structure, composition, and evolution of the Earth's crust. In addition, very long baseline interferometry and laser ranging techniques, which are also based upon the use of space technology, obtain information concerning crustal motion that, in turn, provides insight into the distribution and localization of crustal stress.

Wadge, G.↗