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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Applications of PTTI to new techniques for determining crustal movements, polar motion, and the rotation of the earth

New extra-terrestrial techniques are discussed for geodesy and geodynamics include laser range measurements to the moon or to artificial satellites, Doppler measurements with the Transit satellite system, and both independent-clock and linked-antenna microwave interferometry. The ways in which PTTI measurements are used in these techniques will be reviewed, and the accuracies expected during the latter half of the 1970's will be discussed. At least 3 of the techniques appear capable of giving accuracies of 5 cm or better in each coordinate for many points on the earth's surface, and comparable accuracies for the earth's rotation and polar motion. For fixed stations or for sites a few hundred km apart, baseline lengths accurate to 1 cm may be achieved. Ways in which the complementary aspects of the different techniques can be exploited will be discussed, as well as how they tie in with improved ground techniques for determining crustal movements. Some recent results from the extra-terrestrial methods will be mentioned.

Bender, P. L.↗
NASA NTRS1974

Dynamic techniques for studies of secular variations in position from ranging to satellites

Evaluation of numerous laser range data obtained in orbit determination experiments and by analysis of orbit perturbations due to solid-earth and ocean tides. Results obtained from both a single-laser tracking system and two-laser systems are discussed. With the introduction of radar altimeters, satellite-to-satellite tracking techniques, and more accurate laser data in greater quantities, significant improvements in the gravity field, GM, and station coordinates can be projected such that 10-cm precision relative positioning should be a realizable objective from a single four-pass orbital arc. The use of simultaneous range measurements to a satellite from two stations several hundred km apart is being used to measure the motion between points 900 km apart on opposite sides of the San Andreas fault. Computer simulation of this experiment shows that it will permit determination of the change in baseline (plate motion) to better than 0.5 cm/yr over a seven-year period.

Smith, D. E.↗
NASA NTRS1975

Optical and infrared transfer function of the GEOS 3 retroreflector array

The transfer function of the retroreflector array carried by the Geos 3 satellite was computed at three wavelength: 5300, 6943, and 10600 A. The range correction is given for extrapolating laser range measurements to the center of gravity of the satellite. The reflectivity of the array was computed for estimating laser-echo signal strengths.

Arnold, D. A.↗
NASA NTRS1975

The effects of random path fluctuations on the accuracy of laser ranging systems

The precision of satellite ranging systems, limited in part by atmospheric refraction and scattering, is examined. The effects of atmospheric turbulence on the accuracy of single color and multicolor ranging systems is discussed. The statistical characteristics of the random path length fluctuations induced by turbulence are examined. Correlation and structure functions are derived using several proposed models for the variations of the optical path length. For single color systems it is shown that the random path length fluctuations can limit the accuracy of a range measurement to a few centimeters. Two color systems can partially correct for the random path fluctuations so that in most cases their accuracy is limited to a few millimeters. However, at low elevation angles and over long horizontal paths two color systems can also have errors approaching a few centimeters.

Gardner, C. S.↗
NASA NTRS1975

ATS-5 trilateration support

The development of an L-band trilateration network capable of locating the ATS-5 satellite, determining the satellite's orbital elements, and predicting the satellite position was investigated. An automatic tone-code ranging transponder was used to compare ranging measurements and communications reliability for the VHF and L-band. The L-band transponder network, analytical techniques, and the determination of the Kepler orbit parameters are described along with the calibration procedures, operation procedures, and verification of trilateration position.

Brisken, A. F.↗
NASA NTRS1976

GEOS-C C-band transponder prelaunch calibration and test data

The delay characteristics and spacecraft telemetry housekeeping data for the GEOS-C C-Band transponders are presented. The data are presented in graphical form to provide a convenient method for computing radar range measurement corrections as a function of signal strength at the transponder and spacecraft environment. The data are also presented in tabular form along with the mathematical models used to derive the curves. Also included are a list of the operating characteristics of each transponder and a description of the calibration test equipment set-up.

Selser, A. R.↗
NASA NTRS1976

Report on the lunar ranging at McDonald Observatory, 1 February - 31 May 1976

The four spring lunations produced 105 acquisitions, including the 2000th range measurement made at McDonald Observatory. Statistics were normal for the spring months. Laser and electronics problems are noted. The Loran-C station delay was corrected. Preliminary doubles data is shown. New magnetic tape data formats are presented. R and D efforts include a new laser modification design.

Palm, C. S.↗
NASA NTRS1976

Navigation between the planets

Recent advances in spacecraft tracking, chronometry, ephemerides, and orbit and trajectory determinations are reviewed. Improvements in timekeeping are reviewed, as well as precision distance and range measurements; orbit determinations, trajectory-correction maneuvers, flight path optimization, and information provided by rotation of the tracking station with the earth's surface. Doppler and tropospheric wave propagation effects are dealt with. Nongravitational perturbations (solar radiation pressure, release of gases from the spacecraft, stochastic unmodeled accelerations and sequential estimation to cope with them), the effect of the target planet's gravitational field upon close approach, and navigation problems in the outer reaches of the solar system (TV data telemetered back for inertial navigation) are covered. By-products of the research include: refined data on the mass of planets, on planetary mass distributions, planet configurations, on physical properties of the atmospheres and ionospheres of planets, and opportunities for refined tests of gravitation and relativity theories and models.

Melbourne, W. G.↗
NASA NTRS1976

Location of ATS-5 by L-band trilateration

Near real-time ATS-5 satellite positions and short term position predictions were derived from an experimental L-band trilateration network. Satellite position accuracies of approximately 0.0002 degrees in latitude and longitude and 20 meters in earth center distance were demonstrated. Individual slant range measurements from the master ground station to the satellite were precise to within 12 meters; from the satellite to each of two automatic remote transponders, 23 meters. The trilateration network comprised a master ground station near Schenectady, New York and remote unmanned transponders in Buenos Aires, Argentina and near Wahiawa, Hawaii.

Brisken, A. F.↗
NASA NTRS1977

Viking S-band Doppler RMS phase fluctuations used to calibrate the mean 1976 equatorial corona

Viking S-band Doppler RMS phase fluctuations (noise) and comparisons of Viking Doppler noise to Viking differenced S-X range measurements are used to construct a mean equatorial electron density model for 1976. Using Pioneer Doppler noise results (at high heliographic latitudes, also from 1976), an equivalent nonequatorial electron density model is approximated.

Berman, A. L.↗
NASA NTRS1976

Precision orbit computations for Starlette

The Starlette satellite, launched in February 1975 by the French Centre National d'Etudes Spatiales, was designed to minimize the effects of nongravitational forces and to obtain the highest possible accuracy for laser range measurements. Analyses of the first four months of global laser tracking data confirmed the stability of the orbit and the precision to which the satellite's position is established.

Marsh, J. G.↗
NASA NTRS1976

The Lageos satellite

The fundamental concept of Lageos is a long-lived, dense, electrically and mechanically inert spherical satellite with its surface speckled with retroreflecting cube corners, designed such that range measurements between duly equipped laser ground stations and the satellite are possible with an ultimate accuracy of 2 cm when data from a single satellite pass are appropriately averaged. The Lageos concept requires that the satellite be placed in an orbit for which an ephemeris can be determined ultimately to 5 cm rms uncertainty for a 24-hour arc. These required satellite characteristics should allow the several geodynamic motions experienced by ground stations to be determined typically with 2 cm accuracy.

Johnson, C. W.↗
NASA NTRS1977

Report on the lunar ranging at McDonald Observatory

Range measurements to an accuracy of 5 cm were achieved following improvements in the laser oscillator configuration and the photomultiplier system. Modifications to the laser include a redesigned pockel cell mount to eliminate stressing of the cell crystal; an improved electrically triggered spark gap for sharpening the electrical pulse; the use of a brewster plate in the cavity to eliminate pre-pulsing; improved alignment for the oscillator system; and increased cavity lifetime through thin film polarizer technology. Laser calibration data are presented along with the lunar laser operations log for June to October 1977.

Silverberg, E. C.↗
NASA NTRS1978

Coal thickness gauge using RRAS techniques, part 1

A noncontacting sensor having a measurement range of 0 to 6 in or more, and with an accuracy of 0.5 in or better is needed to control the machinery used in modern coal mining so that the thickness of the coal layer remaining over the rock is maintained within selected bounds. The feasibility of using the radiofrequency resonance absorption (RRAS) techniques of electron magnetic resonance (EMR) and nuclear magnetic resonance (NMR) as the basis of a coal thickness gauge is discussed. The EMR technique was found, by analysis and experiments, to be well suited for this application.

Rollwitz, W. L.↗
NASA NTRS1978

Optical and infrared transfer function of the Lageos retroreflector array

The transfer function of the retroreflector array carried by the LAGEOS satellite (1976 39A) was computed at three wavelengths: 5230, 6943, and 106000 A. The range correction is given for extrapolating laser range measurements to the center of gravity of the satellite. The reflectivity of the array was calculated for estimating laser-echo signal strengths.

Arnold, D. A.↗
NASA NTRS1977

Multilaterating the GEOS-3 satellite

It is demonstrated by means of rigorous simulations with an operational software system that multilateration of the GEOS-3 satellite is possible. This operation, i.e., the processing of simultaneous range measurements from the satellite to a real world constellation of stations using strictly geometric reduction of the observables, will result in the determination of the interstation coordinates to accuracies approaching those of the data measurements obtained at the stations. The satellite-to-satellite link between the GEOS-3 and ATS-6 can be used to further enhance the station covariance matrix.

Escobal, P. R.↗
NASA NTRS1978

Precision orbit computations for Starlette

The Starlette satellite, launched in February 1975 was designed to minimize the effects of nongravitational forces and to obtain the highest possible accuracy for laser range measurements. Analyses of the first four months of laser tracking data from nine stations have confirmed the stability of the orbit and the precision to which the satellite's position can be established. Initial orbit computations using the GSFC GEM - 7 gravity model produced rms fits of about 8 to 10 meters for arc lengths of 5 days. After tailoring a gravity model specifically to Starlette, the rms fits for the 5 day arcs were reduced significantly to the 1 to 2 meter level. An rms fit of 4.3 meters was obtained for a 90 day arc. Five day arcs overlapped by 2.5 days showed rms satellite position differences generally less than 2 meters. Prediction errors at the end of two months were less than 30 milliseconds.

Marsh, J. G.↗