A FREQUENCY TRANSFER AND CLEANUP SYSTEM FOR ULTRA-HIGH STABILITY AT BOTH LONG AND SHORT TIMES FOR THE CASSINI KA-BAND EXPERIMENT

摘要

NEW RADIO SCIENCE EXPERIMENTS, INCLUDING A GRAVITATIONAL WAVE SEARCH AND SEVERAL ATMOSPHERIC OCCULTATION STUDIES, ARE PLANNED FOR THE CASSINI KA-BAND EXPERIMENT. THESE EXPERIMENTS ARE MADE POSSIBLE BY REDUCED SOLAR-INDUCED PHASE FLUCTUATIONS AT THE HIGH-FREQUENCY (32 GHZ) OF THE RADIO LINK BETWEEN THE EARTH AND THE SPACECRAFT. IN ORDER TO MATCH THE IMPROVED LINK PERFORMANCE, A SIGNIFICANT UPGRADE IS UNDER WAY TO IMPROVE THE FREQUENCY STABILITY CAPABILITIES OF NASA'S DEEP SPACE NETWORK (DSN). SIGNIFICANT IMPROVEMENTS ARE BEING UNDERTAKEN IN MANY AREAS, INCLUDING ANTENNA VIBRATION AND (WET) TROPOSPHERIC CALIBRATION, IN ADDITION TO FREQUENCY GENERATION AND DISTRIBUTION. WE DESCRIBE HERE THE DESIGN AND DEVELOPMENT OF A SYSTEM TO PROVIDE A REFERENCE SIGNAL WITH THE HIGHEST POSSIBLE FREQUENCY STABILITY FOR BOTH LONG-TERM, SHORT-TERM, AND PHASE NOISE, AT AN ANTENNA (DSS 25) THAT IS REMOTE FROM THE FREQUENCY STANDARDS ROOM AT SPC-10 AT THE GOLDSTONE SITE. THE NEW TECHNOLOGIES WERE DEVELOPED IN ORDER TO MEET THE VERY TIGHT REQUIREMENTS. THEY ARE: 1) A STABILIZED FIBER-OPTIC DISTRIBUTION ASSEMBLY (SFODA) THAT INCLUDES ACTIVE COMPENSATION OF THERMAL VARIATIONS TO TRANSFER LONG-TERM STABILITY OVER 16 KM OF ORDINARY FIBER-OPTIC CABLE, AND 2) A COMPENSATED SAPPHIRE OSCILLATOR (CSO) THAT PROVIDES SHORT-TERM PERFORMANCE IN A CRYOCOOLED SAPPHIRE OSCILLATOR WITH ULTRA-HIGH SHORT-TERM STABILITY AND LOW PHASE NOISE.