Presentation

Radio Science Systems Group

Space Ops 2002

First Deep Space Operational Experience

with Simultaneous X- and Ka-bands

Coherent Tracking

Sami Asmar

Randy Herrera, John Armstrong

Elias Barbinis, Don Fleischman

Mark Gatti, Gene Goltz, Douglas Johnston

Jet Propulsions Laboratory, California Institute of Technology

Luciano Iess

University of Rome

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

Overview

• International collaboration between NASA and Italian Space Agency (ASI)

• ASI provided a Ka-band Translator (KaT) flown on board Cassini spacecraft as part of a Radio Science instrument. KaT allows for Ka-band uplink and coherent Ka-band downlink

• NASA upgraded a new DSN station – added capability of transmission and reception at X- and Ka-band simultaneously.

• NASA provided X- and S-band links on Cassini

• Cassini Spacecraft and DSS-25 Combination

make the most sophisticated Radio Science

instrument to date.

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

Introduction

• Radio Science investigators examine changes in the phase, amplitude and other characteristic of a radio signal to study the atmosphere, rings, and gravitational fields of he planets and their satellites as well as the sun and conduct experiments based on the theories of relativity

• The search for gravitational waves and improving accuracy of bending parameter (Gamma) drove requirement for higher frequency link (e.g. Ka-band) to minimize as well as fully calibrate the effect of interplanetary plasma.

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

Gravitational Waves

• Propagating, polarized, gravitational fields

• Change distance between separated masses and Shift rates at which separated clocks keep time

• Doppler tracking method: earth and spacecraft as test masses

• Best search at solar oppositions

Deflection of Beam

• In addition to studying the characteristics of the solar corona during solar conjunctions…

• Measure the deflection of a radio beam by gravitational field of the sun (known as gamma parameter) currently constrained to 0.001 of unity, the general relativistic value

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

Spacecraft Development

• Ka-band Translator is a carrier-only transponder

• No telemetry of range modulation

• Receives uplink at Ka-band from Goldstone and transmits a Ka-band signal related to the uplink by a turn-around ratio of 1/15 at the assigned deep space channels

• Capable of generating signal stable to 3 ee-15 Allan deviation at 1000 seconds (pre-launch lab measurement of 1 ee-16)

• Amplification by Ka-TWTA output of 7.2 W via High Gain Antenna

• Two units manufactured – spare back in Italy

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

DSN Development

• Though primary functions to send commands and receive telemetry from space probes, NASA’s Deep Space Network is a world-class instrument for Radio Science research

• One 34-meter Beam Waveguide station (DSS-25) at Goldstone upgraded with a suite of instrumentation for Ka-band uplink and downlink operations

• Affected all existing station subsystems and added new ones

• Surface – deformation affect smaller wavelengths at Ka-band

• Pointing mechanism – develop monopulse tracking

• Handling aberration effect

• Modification to Frequency and Timing System

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

DSN Media Calibration System

• Ka-band sensitive to earth troposphere

• New system developed and installed adjacent to DSS-25 station

• Based on two advanced water vapor radiometers

• Meteorological suite of instruments

• Microwave Profiler

DSN Radio Science Receiver

• New digital receiver developed and installed throughout network

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

DSS-25, 34-m BWG station at Goldstone. Inset is Advanced Water Vapor Radiometer adjacent to the station

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

Discussion

• Early in-flight tests of Cassini Ka-band Translator showed anomalous behavior requiring intense attention

• When powered ON, KaT’s free running downlink frequency was in region outside the channel allocation

• “Bad State” 13 MHz away from nominal

• Persisted daily during test periods under various conditions

• Power cycle brought signal to “good state” for a short time

• Unit was left powered on based on empirical observations by RSSG and independently by ASI and manufacturer (devised a theoretical explanation for the observed behavior)

• A technique of sweeping the uplink signal to KaT also stabilized the device for the long term. Optimum uplink power level and sweep rate were selected

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

Operational Experience

• First deep space operational experience with simultaneous X- and Ka-bands coherent tracking reflect culmination of implementing advanced technologies on Cassini and DSN

• RSSG responsible for operations strategy and acquisition of science data, developed expertise with all new systems, monitored the implementation and testing, and handled the anomalies

• Goal of operations for the test period was to conclude how to operate the “instrument”

• In essence, ground system used to diagnose problem with spacecraft half a billion miles away

• Goal of operations during GWE and SCE experiments was to maximize the quality and quantity of all available data.

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

Radio Science Systems Group

First Deep Space Operational Experience with SimultaneousX- and Ka-bands Coherent Tracking

Conclusion

• Despite anomalies with spacecraft component and steep learning curve with the new ground systems, operations were very successful

• Data quality was excellent and the statistics for data quantity was impressive, considering the various challenges

• Success due to support and commitment as well as the hard work of the entire Deep Space Network organization and the Cassini Program

• Dedicated members of the Radio Science Systems Group were further motivated by the support and advice from the science team, currently processing the data

• Remote operations facilitated quick reaction to problems. Superior ground data system tools for visibility and monitoring health of instrument

• Open communications between various organizations cut short the time to address issues and made the experience very rewarding.