Engineering topics

Donivan, F. F., Jr.

Publications and source records attributed to Donivan, F. F., Jr..

4 records

NASA NTRS1986

Precise interferometric tracking of the DSCS II geosynchronous orbiter

A demonstration of the precise tracking of a geosynchronous orbiter by radio metric techniques based on very-long-baseline interferometry (VLBI) has been jointly conducted by the Jet Propulsion Laboratory and Japan's Radio Research Laboratory. Simultaneous observations of a U.S. Air Force communications satellite from tracking stations in California, Australia, and Japan have determined the satellite's position with an accuracy of a few meters. Accuracy claims are based on formal statistics, which include the effects of errors in non-estimated parameters and which are supported by a chi-squared of less than one, and on the consistency of orbit solutions from disjoint data sets. A study made to assess the impact of shorter baselines and reduced data noise concludes that with a properly designed system, similar accuracy could be obtained for either a satellite viewed from stations located within the continental U.S. or for a satellite viewed from stations within Japanese territory.

Border, J. S.↗

NASA NTRS1984

Geosynchronous orbiter tracking by VLBI - Demonstration design

A demonstration has been designed to determine the three dimensional position of a satellite in geosynchronous earth orbit, with 5 meter accuracy, using tracking techniques based on very-long-base-line interferometry (VLBI). Two experiments are analyzed: the first uses tracking stations in California, Australia, and Guam, and the second uses stations in California, Australia, and Japan. Satellite VLBI observables are defined and measurement errors are predicted. Both experiments employ alternate observations between the satellite and extra-galactic radio sources to determine the satellite plane-of-sky position. Positional accuracy resulting from various combinations of data acquired over the satellite's orbital period is discussed. A strategy is devised for resolving integer cycle phase ambiguities, inherent in VLBI, without relying on an externally provided reference trajectory.

Border, J. S.↗

NASA NTRS1984

Geosynchronous orbiter tracking by VLBI - Demonstration results

Results are presented on two experiments which were designed to demonstrate the feasibility of tracking geosynchronous satellites to an accuracy of 5 meters using Very-Long-Baseline Interferometry (VLBI). A communications relay satellite located over the mid-Pacific was observed using baselines between California, Australia and Guam Island. Differential VLBI observations between the satellite and angularly nearby extragalactic radio sources were used to measure the position of the satellite in the plane of the sky. Post-fit residuals to the adjusted trajectory were obtained which correspond to less than 10 meters in one dimension of the satellite position.

Donivan, F. F., Jr.↗

NASA NTRS1974

Radio observations of two clusters of galaxies

Maps including the Coma and Hercules clusters of galaxies were made at 195, 318, and 611 MHz, and were compared with optical counts of galaxies in the clusters. An extended region of radio emission approximately 20 minutes in diameter was observed at the center of the Coma cluster. A distributed source region was also observed which appears to include the Hercules cluster, although the possibility that it is just an irregularity in the galactic foreground radiation cannot be completely ruled out.

Donivan, F. F., Jr.↗