PRESENT AND FUTURE FREQUENCY AND TIMING CAPABILITIES OF THE DEEP SPACE NETWORK

Abstract
The world-wide Deep Space Network (DSN), with facilities in the United States, Spain, and Australia, uses atomic frequency standards to generate stable frequency and timing signals to meet the telemetry and tracking requirements for space exploration missions. Outer planet navigation requires doppler accuracy of 30 micrometers per second, range accuracy of two meters, angle accuracy of a few nanoradians (using Very Long Baseline Interferometry (VLBI) techniques), and high reliability. These needs impose stability requirements on frequency standards of parts in 10¹⁴ over several hours and 10¹² at one second. In addition, a low drift rate is necessary so as to minimize the number of measurements needed to maintain clock synchronization to 100 nanoseconds and frequency syntonization to 3 x 10^-13 between the three complexes. The Jet Propulsion Laboratory (JPL), which operates the DSN for the National Aeronautics and Space Administration (NASA), uses ensembles of active hydrogen masers, cesium beam frequency standards, and high resolution clocks to achieve the required performance reliably. Time synchronization between complexes is currently achieved by the use of VLBI techniques, traveling clocks, and Loran-C. Use of the Global Positioning Satellites (GPS) is under active investigation as a less costly and more accurate alternative. This article covers the above requirements, equipment, techniques, and more stringent requirements of the 1990 time frame.