Rubidium Standard Marks 20 Years in GPS Orbit

Both military troops and private citizens rely on the navigation precision of the Global Positioning System (GPS), and that in turn depends on the time-keeping accuracy and frequency stability of the system’s satellites and its frequency reference oscillators. In support of the GPS system, the supplier of its rubidium (Ru) atomic frequency standard (RAFS), Excelitas Technologies, recently celebrated 20 years of continuous, reliable, failure-free on-orbit operation of the RAFS aboard one of the U.S. Air Force’s GPS satellites. The rubidium frequency reference was placed in orbit as part of the U.S. Air Force’s first GPS IIR satellite on July 23, 1997 and remotely activated on August 13 of the same year.

The RAFS technology is a critical time- and frequency-keeping component of the navigation payloads designed by Harris Corp. for GPS IIR, GPS IIR-M, and next-generation GPS III satellite systems produced by Lockheed Martin. A total of 12 GPS IIR and 7 GPS IIR-M satellites are currently in orbit with the RAFS technology from Excelitas, laying claim to more than 250 total years of reliable operation. The 19 satellites represent more than 60% of the current GPS satellite constellation. The first GPS III satellite with an Excelitas RAF aboard is expected to launch in 2018.