JPL DESCANSO - Deep Space Communications and Navigation Center of Excellence

Measuring the Aging of GPS Satellites on Orbit by Astronomical Photometry

Presented by:
Dr. Henry Fliegel, The Aerospace Corporation
Dr. Frederick Vrba, US Naval Observatory


The US Naval Observatory has measured the colors and brightnesses of a representative sample of GPS satellites, and has correlated these optical properties with the age of the satellites on orbit. The colors of all satellites are much redder than they would be if the optical properties remained as measured in the factory, and so, show the effect of degradation in space. The hypothesis that most of this degradation is due to self-contamination by effluent from the SV bodies is examined and rejected, being incompatible with the relative brightnesses in the yellow, red, and near infrared.

The Speaker

Dr. Henry Fliegel received his MA degree in physics from Ohio State University in 1959, and his PhD in astronomy from the University of Pennsylvania in 1963. He served in the Time Service Department of the US Naval Observatory from 1963-1965, and was a Member of the Technical Staff at JPL from 1969 to the end of 1981, working on problems of spacecraft navigation and of time transfer. Since 1982 he has been Project Engineer for the Global Positioning System at The Aerospace Corporation, specializing in the logic of ground control software and satellite force modeling.

Dr. Frederick Vrba received his BA in astronomy and physics from the University of Iowa in 1971 and his PhD in astronomy from the University of Arizona in 1976. Since 1976 he has served as Staff Astronomer at the US Naval Observatory -- Flagstaff Station in Flagstaff, Arizona, where he is Director of the Infrared Astronomy Division. His special fields of interest are optical and infrared studies of gamma ray bursts, infrared studies of nebular-embedded stars of extraordinary high or low mass, and the near-infrared astrometry of stars of low mass.