Since 1997, SRI International has been under contract to support the USAF GPS Joint Program Office by regularly monitoring the L-band transmissions of all newly launched and currently operational GPS satellites. The objective is to verify that all deployed satellites are consistently and reliably performing according to specification. SRI measures signal power, code delay, frequency content, and bandwidth to verify the proper operation of the satellite constellation. Archived data enables the comparison of multiple data sets.

SRI is currently upgrading the RF and data-acquisition systems at a 47 m (150 ft) diameter parabolic antenna that has been used to collect these measurements and is also testing an automated 3 m (10 ft) antenna and coherent receiver. Due to its faster slew rate and automated control, the new system will speed monitoring operations and reduce manpower requirements.

SRI’s GPS Calibration and Monitoring System is designed to collect essential state-of-health information on the GPS constellation for the next decade.