Roger Easton Pioneered Satellite Telemetry And Timing

Roger L. Easton has been recognized by the National Inventors Hall of Fame for pioneering achievements in spacecraft tracking and timing and navigation technology (TIMATION) that led to the development of critical enabling technologies of the NAVSTAR-Global Positioning System (GPS).

At the award ceremony hosted by Under Secretary of Commerce for Intellectual Property and Director of the United States Patent and Trademark Office, David Kappos, Wednesday at the Department of Commerce in Washington, D.C., Roger Easton received the NIHF Medal of Honor for TIMATION, U.S. Patent 3,789,409, the critical system enabling modern GPS.

“Roger’s career contributions and his keen ability to develop new, bigger ‘problem sets’ from his experiences are what impressed me most,” said long time colleague and current Director of NRL’s Naval Center for Space Technology, Pete Wilhelm. “His leap in vision led to the United States’ first satellite tracking network and patent of synchronized timing of spacecraft which became the fundamental basis for GPS.”

Easton began his career in 1943 at NRL as a research physicist, and was part of the team that developed the United States' first satellites.

Easton (left) Supervises Assembly Of Vanguard Satellite Photo Courtesy NRL

When the Soviet Union launched Sputnik into orbit, the United States could not track non-radiating satellites or determine if other launches occurred. Easton solved this problem by extending a system he helped design called MINITRACK, which only needed to transmit a signal of a few milliwatts due to the very high sensitivity of the MINITRACK interferometer antenna design, to actively follow unknown satellites orbiting Earth. Under his leadership, with sponsorship through the Department of Defense Advanced Research Projects Agency, now referred to as DARPA, the Naval Space Surveillance System (NAVSPASUR) became the world's first system to detect and track all types of Earth-orbiting objects, thus contributing to America's national security and sense of well-being during the Cold War.

“As the number of objects in orbit grew it became apparent to Roger that adding a ‘second fence’ parallel to the main fence, with an offset of about 90 miles, a ‘one pass’ solution could be provided to determine the object’s orbit. Roger further improved the accuracy and utility of the data by adding ranging tones to the transmitted signal at the second fence. This however required that the receiving and transmitting sites, which were a number of miles apart, had to be set precisely on the same time base,” added Wilhelm. “Maintaining the accuracy required turned out to be difficult to accomplish and led Roger to the vision that the way to do this was put very good clocks, probably atomic clocks, in satellites,” he said.

MINITRACK Station Photo Courtesy NRL

Easton conceived the idea of using satellite-carried precise atomic clocks for passive ranging. Starting in 1964, he conducted research, carried out space-based experiments, and published his findings that accurate, reliable and instantaneous satellite navigation could be achieved with passive ranging, circular orbits and a constellation of space-borne high-precision clocks synchronized to a master clock, the primary features of modern GPS.

His work exploiting space-based systems for geodesy, navigation, and timing laid the foundations for his visionary leap to the concept he dubbed TIMATION, short for time-navigation. Sponsored by the Naval Air Systems Command, Easton tested his concepts at NRL through the development and launch of four experimental satellites: TIMATION I and II (in 1967 and 1969) and Navigation Technology Satellites (NTS) 1 and 2 (in 1974 and 1977).

NTS-2, the first satellite to fly in the GPS 12-hour orbit and transmit GPS signals, flew the first cesium atomic frequency standard in space. Using time measurements from NTS-2, he experimentally verified Einstein's theory of relativity. A relativistic offset correction that he applied is still in use by every satellite in the GPS constellation. While initially designed for use by the military, GPS has been adapted for civilian use from commercial airline navigation to portable hand-held and wrist-worn devices.

GPS today is a constellation of Earth-orbiting satellites providing precise navigation and timing data to military and civilian end-users around the globe. Easton, as a scientist and engineer at NRL, developed his concept for a time-based navigational system with passive ranging, circular orbits, and space-borne high precision clocks synchronized to a master clock. The U.S. Patent Office received his submittal, "Navigation System Using Satellites and Passive Ranging Techniques," and on January 29, 1974 it was assigned U.S. Patent 3,789,409.

TIMATION Satellite Photo Courtesy NRL

In 2005 Easton was awarded the National Medal of Technology by President George W. Bush for his invention of the MINITRACK satellite tracking system used to determine the orbits of early Vanguard satellites; his development of the Naval Space Surveillance System which remains in use today cataloging all known man-made space objects orbiting Earth; the invention of a Navigation System Using Satellites and Passive Ranging Techniques and his subsequent development of Time Navigation and Navigation Technology Satellites that formed the technological basis for modern GPS.

The National Inventors Hall of Fame honors the women and men responsible for the great technological advances that make human, social and economic progress possible. Each year, the Selection Committee of the National Inventors Hall of Fame Foundation selects inventors for induction from those nominated by peers and the public for contribution to the nation’s welfare and progress of science and useful arts. The Selection Committee includes representatives from leading national scientific and technical organizations. Prior to this year’s induction ceremony, 405 inventors have been inducted to the National Inventors Hall of Fame since its formation in 1973.

FMI: www.invent.org