618-828 VOYAGER 2 SATURN ENCOUNTER RADIO SCIENCE OPERATIONS PLAN Prepared by: VOYAGER RADIO SCIENCE SUPPORT TEAM REVISION 0 APRIL 23, 1981 TABLE OF CONTENTS 1.0 INTRODUCTION 2.0 RADIO SCIENCE OBSERVATION DESCRIPTION 2.1 Overview of the Saturn Encounter 2.2 Celestial Mechanics Experiments (XSCEL and X3MASS) 2.3 Saturn Atmosphere/Ionosphere Occultation (XPOCC) 2.4 Ring-Scattering Experiment (XRSCAT) 2.5 Major Events Summary and Expected Signal Profiles 3.0 RADIO SCIENCE GDS CONFIGURATION 3.1 Introduction 3.2 The Deep Space Station 3.2.1 Antenna Mechanical Subsystem 3.2.2 Antenna Microwave Subsystem 3.2.3 Transmitter Subsystem 3.2.4 Receiver-Exciter Subsystem 3.2.5 Tracking Subsystem 3.2.6 Radio Science Subsystem 3.2.7 Monitor and Control Subsystem 3.3 The Ground Communications. Facility 3.3.1 GCF High-Speed Data Subsystem 3.3.2 GCF Wide-Band Subsystem 3.3.3 GCF Data Records Subsystem 3.4 The Network Operations Control 3.4.1 NOCC Radio Science Subsystem 3.4.2 NOCC Monitor Subsystem 3.4.3 NOCC Support Subsystem 3.4.4 NOCC Display Subsystem 3.4.5 NOCC Tracking Subsystem 3.5 Network Radio Science Subsystem 3.6 Mission Support Area 3.7 Radio Science Support Team Data Records System 3.8 Open-Loop Recording System Pre-Pass Calibration 3.8.1 Purpose of the Calibration 3.8.2 X-Band RCP/LCP Test Signal Generation 3.9 Ground Data System Configuration Requirements 3.10 GDS Experience During the First Saturn Encounter 4.0 RADIO SCIENCE ENCOUNTER TIMELINES 4.1 Extended Encounter Timeline (DOYs 228-248) 4.2 Occultation Timeline (DOYs 237-238) 4.3 Time-Ordered Listing of Selected Timeline Events i 4/23/81 5.0 TRACKING STRATEGY AND RADIO SCIENCE SUBSYSTEM OPERATIONS 5.1 Saturn Occultation Uplink and Downlink Strategies 5.1.1 Uplink Tuning Strategy 5.1.2 Pre-Occultation Downlink Tuning 5.1.3 Post-Occultation Downlink Acquisition Tuning 5.1.4 Downlink Tracking Predict Sets 5.2 Antenna Pointing Strategy 5.3 Use of the SSI for Receiver Acquisition 5.4 Radio Science Subsystem Operations 5.4.1 Medium-Band Receiver Configuration 5.4.2 Wide-Band Receiver Configuration 5.4.3 Open-Loop Tuning Predicts 6.0 REAL-TIME OPERATIONS 6.1 Functional Responsibilities 6.1.1 RSST 6.1.2 MCT 6.1.3 DSN 6.1.4 OCT 6.1.5 Radio Science Representative to DSS-43 6.2 Operations Procedures 6.2.1 Voice Net Communications 6.2.2 Graphics Displays and Hardcopy Data Collection 6.2.3 Briefing Strategy 6.2.4 Pre-Pass Countdown Procedures 6.2.5 Checklist Strategy 6.2.6 Post-Pass Tape Logging Procedure 6.2.7 Radio Science Control Functions 6.3 Operations Schedule 6.3.1 Pre-Encounter Ten-Day Period 6.3.2 Near Encounter 6.3.3 Post-Encounter Ten-Day Period 6.4 Contingency Planning 6.4.1 Loss of Prime 64-Meter Station 6.4.2 Loss of Uplink Transmitter or Failure to Acquire Uplink 6.4.3 USO Failure 6.4.4 ODA Halt or Failure 6.4.5 Spacecraft Sequence Error (CCS Load Abort) 6.4.6 Loss of One or More Channels in the Open-Loop System 6.4.7 Saturation of One or More Channels in the Open-Loop System 6.4.8 Major OD Error Resulting in Event Time Shifts 6.4.9 Non-Performance of Pre-Pass Calibration at Prime 64-Meter Station 6.4.10 Loss of Real-Time NRS Data Visibility at JPL 6.4.11 Loss of Open-Loop Signal Due to ODA Predict Set Errors 6.4.12 Unavailability of Key Personnel 6.4.13 Failure of RSS Display Hardware in MSA 6.4.14 Voice Line Outage Between JPL and Station(s) ii 4/23/81 6.5 RSST Support of Maneuver Anomaly Recovery Plan 7.0 DATA HANDLING AND DELIVERY 7.1 RSST Data Records System 7.1.1 Data Sources 7.1.2 Data Processing and Library Facilities 7.1.3 Data Destinations 7.2 Data Collection, Processing, Validation, and Delivery Procedures 7.2.1 Closed-Loop Tracking Data 7.2.2 Medium-Band Open-Loop Data 7.2.3 Wide-Band Open-Loop Data 7.2.4 Spacecraft Trajectory Data 7.2.5 Spacecraft Engineering Data 7.2.6 Maneuver Design and Reconstruction Data 7.2.7 Hardcopy Data 7.3 Quick-Look Data Handling and Delivery Strategy 7.3.1 Closed-Loop Tracking Data 7.3.2 Medium-Band Open-Loop Data 7.3.3 Spacecraft Trajectory Data 7.3.4 Spacecraft Engineering Data 7.3.5 Hardcopy Data 7.4 Final Data Handling and Delivery Strategy 7.4.1 Closed-Loop Tracking Data 7.4.2 Medium-Band Open-Loop Data 7.4.3 Wide-Band Open-Loop Data 7.4.4 Spacecraft Trajectory Data 7.4.5 Spacecraft Engineering Data 7.4.6 Maneuver Reconstruction Data 7.4.7 Hardcopy Data 8.0 APPENDICES 8.1 Major Event Summary and Expected Signal Dynamics (Table A-1 and Figure A-1) 8.2 Useful Data and Formulae (Tables A-2 and A-3 and Figures A-2 and A-3) 8.3 Phone Numbers (Table A-4) 8.4 Pre-Pass Countdown Log (Table A-5) 8.5 Station Configuration Checklists (Tables A-6, A-7, and A-8) 8.6 NOCC Display/Graphics Requests (Tables A-9a through A-9z) 8.7 Abbreviations and Acronyms (Table A-10) iii 4/23/81 LIST OF TABLES 3-1 Antenna Mechanical and Pointing Subsystem Configuration Requirements 3-2 Antenna Microwave Subsystem Configuration Requirements 3-3 Transmitter Subsystem Configuration Requirements 3-4 Receiver-Exciter Subsystem Configuration Requirements 3-5 Tracking Subsystem Configuration Requirements 3-6 Radio Science Subsystem Configuration Requirements 3-7 Monitor and Control Subsystem Configuration Requirements 4-1 Time-Ordered Listing of Selected Timeline Events 5-1 Uplink Predict Set IDs 5-2 Uplink Predict Update Schedule 5-3 Occultation Entrance Receiver Ramps (Typical Values) 5-4 Occultation Exit Receiver Ramps (Typical Values) 5-5 Downlink Tracking Predict Sets 5-6 Status Display for SLCP/SRCP SSI Ports During Receiver Acquisition 5-7 Status Display for XLCP/XRCP SSI Ports During Receiver Acquisition 5-8 Wide-Band Receiver Synthesizer Frequencies 5-9 Saturn Encounter ODA Predict Sets 6-1 Near-Encounter Radio Science Display Requirements 6-2 Daily RSST Briefing Agenda 6-3 Radio Science Control Functions During Critical-Event Periods 6-4 Maneuver Anomaly Recovery Plan Open-Loop System Configuration 7-1 Data Products Delivery Strategy and Schedule A-1 Major Event Summary for Saturn and Rings A-2 Formulae for Reconstruction of the Antenna Frequency from the Extracted Signal Frequency in the Open-Loop Receiver Filters A-3 Received Maximum Power Levels and Spacecraft Frequencies for the 64-Meter Subnet During the Voyager 2 Near Encounter A-4 Phone Numbers of Key Radio Science Personnel A-5 Voyager Radio Science PrePass Countdown Log A-6 Station Configuration Checklist for DSS-42 A-7 Station Configuration Checklist for DSS-43 A-8 Station Configuration Checklist for DSS-44 A-9 NOCC Display/Graphics Requests (Tables A-9a to A-9z) A-10 Abbreviations and Acronyms iv 4/23/81 LIST OF FIGURES 2-1 Voyager 2 Saturn Encounter Radio Science Observation Timeline 2-2 Saturn Near-Encounter Phase - Voyager 2 2-3 Earth View of Voyager 2 Saturn Occultation 2-4 Ring Scattering Geometry 3-1 Voyager Radio Science System: Detailed Planning Block Diagram for Voyager 2 Saturn Encounter 4-1 Voyager Radio Science Extended Encounter Timeline 4-2 Voyager Radio Science Occultation Timeline 5-1 Uplink Ramp Errors During the Post-Occultation Period (Nominal Arrival Time) 5-2 Uplink Ramp Errors During the Post-Occultation Period (+3 sigma Time-of-Arrival Error) 5-3 Uplink Ramp Errors During the Post-Occultation Period (-3 sigma Time-of-Arrival Error) 5-4 Doppler Profile for the Occultation Period 5-5 Closed-Loop Receiver Ramp Errors During the Occultation Period 5-6 Open-Loop Receiver Ramps During the Occultation Period 5-7 ODA Predict Set Ramp Errors During the Occultation Period (Nominal Arrival Time) 5-8 ODA Predict Set Ramp Errors During the Occultation Period (+3 sigma Time-of-Arrival Error) 5-9 ODA Predict Set Ramp Errors During the Occultation Period (-3 sigma Time-of-Arrival Error) 5-10 Wide-Band System Residuals During the Occultation Period 6-1 Near-Encounter Radio Science Voice Net Configuration 6-2 Maneuver Anomaly Recovery Plan Timeline 7-1 RSST Data Records System Block Diagram A-1 Saturn and Ring Signal Dynamics A-2 Occultation Data Assembly ADC Input Power Level Versus Input SNR Calibration Curve A-3 DSS-43 Elevation Angles Versus Time on Day 238 v 4/23/81 1.0 INTRODUCTION This document has been prepared by the Voyager Radio Science Support Team (RSST) with the assistance of the Radio Science Working Group (RSWG) for the purpose of coordinating all ground activities required to conduct the Voyager 2 Saturn encounter radio science experiments. In addition to specifications of the radio science operations activities and ground instrumentation configurations, this plan includes descriptions of the radio science observations and relevant design considerations. The controlling document for the conduct of all Project operations (including radio science operations) is the Integrated Sequence of Events (ISOE). This plan supplements the ISOE; in fact, several checklists and logs from this plan are referenced in the ISOE. Should any conflict arise between activities specified herein and those in the ISOE, the ISOE-specified events shall take precedence. Three major radio science experiments will be conducted during the Voyager 2 Saturn encounter. These three observations are listed below along with the primary characteristics and data types associated with each. Section 2.0 of this document provides expanded descriptions of the observations and the Appendix contains amplitude and frequency profiles predicted for the occultation events. A detailed listing of the scientifically significant events is also contained in the Appendix. MAJOR VOYAGER 2 RADIO SCIENCE OBSERVATIONS Celestial Mechanics (XSCEL) - Maps gravity field of planet, (Entire 64-meter network, rings, and satellites. Also Saturn encounter +10 days) obtains gravitational redshift and USO frequency stability data. Spacecraft sequence is routine. Utilizes closed-loop doppler and range tracking. Saturn Occultation (XPOCC) - Investigates atmosphere and iono- (DSS-43, 8/26/81 UTC) sphere of Saturn. Involves spacecraft maneuvers and downlink carrier power switches. Utilizes both open-loop (medium-band) and closed-loop data. Ring Scattering (XRSCAT) - Measures microwave scattering (DSS-43, 8/26/81 UTC) properties of rings at oblique angles. Spacecraft maneuvers to track desired region of rings. Utilizes only open-loop (medium- band) data. 1 4/23/81 Section 3.0 describes the Ground Data System elements supporting the acquisition of radio science data and contains a functional block diagram of the instrumentation required to complete the observations. The material in this section focuses on the DSN portion of the Radio Science GDS while Section 7 deals with the data records aspects of the GDS. The equipment at the 64- meter stations has been specially configured for the Saturn encounters; key features of the GDS configuration are described. Section 4.0 contains two timelines illustrating the time relationships of primary supporting events in the operational periods of interest. One timeline covers the plus-and-minus tenday period. The other timeline covers the plus- and-minus one-day period and expands on the events of the first timeline. Associated Project milestones are also shown on the timeline where they are directly or indirectly related to the operations supporting the radio science observations. Section 5.0 discusses the operational strategies planned for utilizing the Tracking and Radio Science Subsystems of the DSN. Uplink and downlink tuning strategies are presented for closedloop and openloop data acquisition. Section 6.0 presents plans for coordinating real-time operations. Functional responsibilities of each major operational element are given and operational interfaces are described. Communications interfaces between operational positions are defined. One subsection characterizes the role of the Radio Science Representative dispatched to DSS-43 in support of the Saturn occultation and ring-scattering experiments. The RSST's support of the Project's maneuver anomaly recovery plan is also discussed. Section 7.0 describes the RSST Data Records System elements supporting the handling and delivery of data products in the post-acquisition period. A block diagram of this portion of the Radio Science GDS is provided along with an explanation of the path each radio science data type follows through the collection processing, validation, and delivery phases. Delivery strategies and schedules are presented for quicklook and final data products. Section 8.0 is an Appendix of supporting data, tables, forms, and formulae. Multiple references are made to the Appendix by the preceding sections of the document. The Appendix also contains useful handbook-type material to allow verification of computations and parameters specified previously. 2 4/23/81 2.0 RADIO SCIENCE OBSERVATION DESCRIPTION 2.1 Overview of the Saturn Encounter Radio science observations with Voyager 2 span the entire encounter period from 81 days before Saturn closest approach until 31 days after closest approach. The approximate times of these observations are shown in Figure 2-1. The period of highest radio science (and other science) activity is the Near- Encounter Phase which is comprised of the two days centered on the Saturn flyby. The Saturn radio occultation, the radio ring scattering experiment, characterization of Saturn's plasma environment, and the most intensive celestial mechanics measurements occur during these two days. Figure 2-2 shows the relative timing of all of the Near-Encounter Phase science observations (including the radio science events). Some radio science observations are, however, conducted before and after the Near-Encounter Phase. The celestial mechanics measurements continue 24 hours per day for 10 days before and after the closest approach to Saturn; for the rest of the encounter period, these observations are made only once per day. 2.2 Celestial Mechanics Experiments (XSCEL and X3MASS) The celestial mechanics experiments are conducted by integrating into the spacecraft sequence a series of TWNC-on* and TWNC-off* commands so as to guarantee a desirable balance of oneway and two-way (or three-way) tracking data throughout the encounter period. It should be noted that in Figure 2-1, XSCEL represents only the one-way (TWNC-on) tracking periods; two-way ranging or three-way tracking is scheduled for all non-XSCEL (TWNC-off) periods within 10 days of closest approach. The oneway data will be used to measure the redshift caused by placing the USO (Ultra-Stable Oscillator) in the Saturn gravitational field, to determine the effect of Saturn's radiation environment upon the USO, and to build a USO frequency stability data base required for analysis of the radio occultation data. The two-way ranging and three-way tracking data will be used to investigate the gravity fields of Saturn, its satellites, and its rings by examining their effect on the spacecraft's trajectory; the Tethys mass determination (X3MASS), in particular, is expected to yield a * TWNC is an acronym for Two-way Non Coherent, which refers to a switch in the spacecraft's Radio Frequency Subsystem. When TWNC is on, the downlink carrier frequency is referenced to the USO without regard to the uplink carrier. When TWNC is off, the downlink carrier is coherent with the uplink (if one is present) but is referenced to the USO if no uplink is present. 3 4/23/81 significantly improved value. In addition, all of the dual-frequency tracking data will be used to characterize the Saturn system plasma environment. The period of two-way data acquisition for X3MASS commences a round-trip light-time after the transmission of a real-time command to turn TWNC off command. The TWNC off was not included in the sequence due to concern that spacecraft receiver's best-lock frequency (BLF) may not be known well enough to guarantee clean downlink telemetry so shortly after occultation exit. (The reasons for the BLF uncertainty are discussed in section 5.1.1.) Since the TWNC-off command will only get into the spacecraft if the BLF is within the expected range of values, it is certain that the ensuing downlink will be either pure two-way or pure one-way and that the telemetry will be usable. The ground events associated with the celestial mechanics experiments consist of standard closed-loop tracking procedures with special range parameters and doppler sample rates specified in the Project ISOEs. 2.3 Saturn Atmosphere/Ionosphere Occultation (XPOCC) The Saturn radio occultation begins approximately 36 degrees minutes after the closest approach to Saturn and lasts for about 95 minutes. As shown in Figure 2-3, the spacecraft enters occultation at 36 degrees N latitude and exits occultation at 31 S latitude (planetographic latitudes). The spacecraft will perform limb-tracking maneuvers for the first five minutes and the last seven minutes of the occultation period. The limb-tracking maneuvers are designed to keep the HGA pointed at the virtual image of the Earth as that image moves around the limb of Saturn. (The virtual image of the Earth is that point where, at a given time, the radio raypath can be refracted around Saturn and back to the Earth). Since this is a diametric occultation, the virtual image remains at the entrance latitude throughout the entrance maneuver and at the exit latitude throughout the exit maneuver. The objectives of the Saturn occultation experiment can be summarized as follows: - Measure atmospheric temperature and pressure as a function of height and help determine the hydrogen-to-helium ratio; - Investigate the micro-wave absorbing properties of the atmosphere and determine the ammonia abundance; - Determine the vertical structure and characteristics of Saturn's ionosphere; - Measure the oblateness of Saturn; 4 4/23/81 - Investigate turbulence and waves in the neutral atmosphere; - Investigate ionospheric irregularities; and - Interpret the measured dynamics for indications of large-scale motion and energy flow in the atmosphere and ionosphere. The spacecraft will be sequenced to optimize the downlink for atmospheric measurements at occultation entrance and exit. The S-band downlink power will be maximized by turning off the ranging channel and telemetry drivers and by setting the TWTA (traveling wave tube amplifier) to its high-power mode. The X-band downlink SNR will be improved by turning off the ranging channel and telemetry drivers; however, the TWTA must remain in the low-power mode because thermal constraints allow only one TWTA to be in the high-power mode at any given time. TWNC will be on to guarantee that both S and X downlink frequencies will be referenced to an on-board oscillator (the USO) throughout the occultation. The limb-tracking maneuver will be performed in two parts during the time periods shown in Figure 2-3. Part I consists of one gyro-drift turn segment and Part 11 consists of two segments. After completion of the exit ionosphere measurements, a mini-ASCAL maneuver has been sequenced which uses gyrodrift turns to move the HGA boresight in a +- 0.4 degree cross-hair pattern about the Earth-direction. This maneuver will be used to aid in the reconstruction of the space-craft's attitude during the Saturn occultation and ring-scattering measurements. After the completion of the mini-ASCAL, the downlink is reconfigured for telemetry and for celestial mechanics tracking and ranging. The ground events for the Saturn occultation occur primarily at DSS-43. DSS-44 will provide S-band closed-loop occultation backup coverage and DSS-42 will perform dual-frequency closedloop tracking of Voyager I to obtain independent measurements of the solar plasma for calibration of the occultation data. DSS- 43 will track Voyager 2 with CONSCAN off and with a fixed subreflector focus position so as to minimize station-induced signal level variations in the data. The occultation downlink will be recorded on the four-channel medium- band open-loop system at DSS-43. Ionosphere data will be obtained from the closed-loop system. 2.4 Ring-Scattering Experiment (XRSCAT) The ring-scattering experiment is conducted during a period of 25 minutes in duration immediately before the atmospheric occultation exit measurements. Figure 2-3 shows the relative timing of these events and Figure 2-4 shows the geometry of the ring-scattering observation. As seen in Figure 2-4 the Earth and Voyager 2 are north and south of the ring plane, respectively, and the spacecraft is moving away from Saturn and "down" from the ring plane. Meanwhile, the spacecraft is being maneuvered so 5 4/23/81 as to track the center of the C ring with the HGA boresight. The ring- scattering measurements will be made in the transmission mode. The interaction of the X-band beam (3-dB contour) with the C ring is shown in Figure 2-4 at the first and last moments of the XRSCAT observation. The ring-tracking* maneuver is aimed at the C ring since the A ring was measured by Voyager I and the B ring is too opaque to scatter enough signal power back to Earth to perform a viable experiment. The objectives of the ring-scattering experiment can be summarized as follows: - Determine ring particle size and size distribution in the decimeter to meter size range; and - Determine the vertical structure of the rings (i.e. distinguish between monolayer and cloud-like ring structures). The spacecraft will be sequenced to perform the ringtracking maneuver in the following downlink configuration: X-band high power, S-band low power, ranging channels off, telemetry drivers off, and TWNC on. The ring-tracking maneuver consists of three gyro-drift turn segments designed to trace out an approximation of the raypath shown in Figure 2-4. All of the ground events for the ring-scattering experiment occur at DSS-43. The station configuration will be nearly identical to that described for the atmosphere/ ionosphere occultation. The use of the four-channel medium-band system for the entire occultation period is driven by the ring-scattering experiment: Since polarization information is a primary data source, both RCP and LCP channels for Sand X-band downlink will be recorded; the medium bandwidth system is required because large frequency dispersions are expected during the ringscattering experiment. 2.5 Major Events Summary and Expected Signal Profiles The Appendix contains Table A-1 which outlines the major radio science events during the Saturn occultation and ringscattering observation periods,, The times listed in that table are approximate-the ISOE will be the controlling document for these time periods., The Appendix also includes Figure A-1 which shows the expected signal profiles for these observation periods. The figure includes predicted S and X signal level changes and X-band frequency variations for the duration of the radio science events. The descriptions and predictions of signal conditions and dynamics are based on Voyager I results and model calculations so only the general character of the phenomenon induced signal events can be stated with confidence. 6 4/23/81 3.0 RADIO SCIENCE GDS CONFIGURATION 3.1 Introduction The Radio Science Ground Data System is comprised of six major components: - The Deep Space Stations; - The Ground Communication Facility (GCF); - The Network Operations Control Center (NOCC); - The Network Radio Science Subsystem (CTA-21); - The Voyager Mission Support Area (MCT); and - The RSST Data Records System. These components and their interrelationship are depicted in the block diagram of the Radio Science Ground Data System included in Figure 3-1. This section focuses on the Deep Space Station instrumentation configuration and calibration requirements. The other components of the GDS are mentioned briefly in this section, but are discussed in more detail elsewhere in this document. Most notably, the RSST Data Records System is described in Section 7. 3.2 The Deep Space Stations The DSS is the Radio Science System instrument. System performance directly determines the degree of success of the experiment and system calibration determines the degree of uncertainty in the results of the experiment. The following paragraphs describe those functions performed by the individual subsystems depicted in Figure 3-1. Specific configuration and calibration requirements are addressed in a separate sub-section after the functional descriptions of the subsystems. 3.2.1 The Antenna Mechanical Subsystem The DSS-43 64-meter Antenna Mechanical Subsystem functions as a large-aperture collector which, by double reflection, focuses incoming radio frequency (S- and X-band RCP/LCP) energy into the Sand X-band feedhorns (part of the Antenna Microwave Subsystem). The large collecting surface of the antenna focuses the incoming rf energy onto the hyperboloid subreflector which is adjustable in both axial and tilt positions to permit optimizing the focusing of energy into the feedhorns. 7 4/23/81 NOTE THE SUBREFLECTOR IS LOCKED INTO A FIXED POSITION FOR SOME RADIO SCIENCE EVENTS. THE ISOE WILL SPECIFY THE POSITIONS TO BE USED. The subreflector then reflects the received energy to the dichroic plate, a device which reflects S-band energy to the S-band feedhorn and transmits X- band energy to the X-band feedhorn. Transmitted S-band rf energy emanating from the feedhorn is focused by the same reflectors into a narrow, cylindrical beam. Since the beam is very narrow, it must be pointed with high accuracy and precision. This is accomplished by a series of drive motors and gear trains which rotate those portions of the structure which support the reflectors., position sensors, and related electronics. Electronic servo-amplifiers are used to amplify and condition the axes-angle or position error signals which are received and are provided to the drive motor controls. Pointing angles are computed from an ephemeris provided by the Project, and the antenna is pointed to these angles. Once the receiver has acquired a signal to provide feedback, a radio source can be tracked by scanning around it (CONSCAN) and computing pointing angles from signal-level information supplied by the receiver. NOTE DURING PERIODS WHEN EXCESSIVE SIGNAL-LEVEL DYNAMICS OR LOW RECEIVED SIGNAL LEVELS ARE EXPECTED, I.E., OCCULTATIONS AND SOME OTHER RADIO SCIENCE EXPERIMENTS, CONSCAN CANNOT BE USED AND ANGLE POINTING IS ACCOMPLISHED BY USING THE LAST CONSCAN-CALCULATED OFFSETS TO THE COMPUTED ANGLE PREDICT SET. SEE SECTION 5.2 FOR DETAILS. 3.2.2 The Antenna Microwave Subsystem The Antenna Microwave Subsystem accepts the received S- and X-band RCP/LCP signals at the feedhorn from the Antenna Mechanical Subsystem. The received signals are transmitted through the polarizer plates to the orthomode transducer. The polarizer plates are adjusted so that RCP signals are directed to X-band TWM 2 and S-band TWM 1 and so that LCP signals are directed to X- band TWM I and S-band TWM 2. After amplification by the traveling wave masers, the signals are routed to the Receiver-Exciter Subsystem via the microwave switching assembly. 8 4/23/81 The S-band uplink signal is transmitted via the diplexer assembly through the feedhorn to the antenna where it is focused and beamed to the spacecraft. The noise diode assemblies under control of the Precision Power Monitor inject known amounts of noise power into the received signal path so that accurate real-time system temperature measurements may be made. 3.2.3 The Transmitter Subsystem The Transmitter Subsystem accepts the S-band frequency exciter signal from the Receiver-Exciter Subsystem and amplifies it to a transmitted output level of 18 kW. The amplified signal is then routed via the diplexer to the antenna and then focused and beamed to the spacecraft. 3.2.4 The Receiver-Exciter Subsystem The Receiver-Exciter Subsystem receives, amplifies, and down-converts the frequencies of spacecraftradiated S- and X-band RCP/LCP signals. The closed- loop receivers provide doppler and ranging signals to the Tracking Subsystem. Dedicated openloop receivers provide baseband signals to the Radio Science Subsystem and fixed-tuned wide bandwidth open-loop receivers provide backup systems to the narrow-band and medium-band openloop receivers. The exciter generates the S-band drive signal provided to the Tranmitter Subsystem for the spacecraft uplink signal. The Spectral Signal Indicator (SSI) provides local displays of received signal spectra and routes spectral data to the Radio Science Subsystem. These displays are used to validate Radio Science System data at the DSS, NOCC, and Mission Support Areas. The Precision Power Monitor (PPM) measures system temperatures by injecting known amounts of noise power into the signal path and comparing the total power within a given bandwidth before and during periods of noise injection. System temperature measurements are made for each of the four masers by utilizing the closed-loop receivers as monitoring devices. This use of the receivers imposes a configuration restraint on them when they are used to monitor all four masers. That is, the BLK IV receivers must monitor X-band RCP/LCP masers and the BLK III receivers are used to monitor S-band RCP/LCP masers. 3.2.5 The Tracking Subsystem The Tracking Subsystem receives the ranging spectra and doppler signals from the Receiver-Exciter Subsystem. it generates a range code that is routed to the exciter and modu 9 4/23/81 lates the S-band uplink carrier. The demodulated range spectrum is compared to a model of the transmitted range code and the round-trip signal delay to the spacecraft is computed, formatted, and transmitted to the GCF Data Records System which produces an IDR tape upon which the data are delivered to the Project. Similarly, the doppler phase is counted, formatted, and delivered to the Project. In addition, the Tracking Subsystem computes data residuals and noise estimates, receives and stores tuning predicts, and provides partial status information to the Monitor and Control Subsystem, including receiver agc levels and lock status. 3.2.6 The Radio Science Subsystem The DSS Radio Science Subsystem (DRS) digitizes, bandwidth reduces, and records (1) very narrow, (2) narrow, and (3) medium bandwidth radio science data, and digitizes and records wide bandwidth radio science data. It receives radio science frequency predicts from NOCC, accepts configuration and control data from the Monitor and Control Subsystem, and transmits S- and X-band RCP/LCP signals from the SSI to NOCC and the Project Mission Support Area via the GCF wide-band data lines. It controls the narrow-band open-loop receiver LO by sending frequency control information to the Receiver-Exciter Subsystem. it records system temperature information received from the PPM. 3.2.7 Monitor and Control Subsystem The Monitor and Control Subsystem provides control messages to the centrally controlled DSS subsystems, including the Radio Science and Tracking Subsystems. It provides partial status information for these same subsystems. It generates the angle drive tape needed by the Antenna Pointing Subsystem and, in addition, controls the SSI and PPM in the Receiver-Exciter Subsystem. It receives the system temperature information from the PPM and displays it on the Data System Terminal (DST). It relays the system temperature information to the NOCC Monitor Subsystem for display in NOCC and the Project Mission Support Area. 3.3 The Ground Communications Facility The Ground Communications Facility (GCF) provides the communication networks needed to support the communication requirements of the Radio Science System. These facilities exist at the DSS and JPL and are briefly described in the following paragraphs. 3.3.1 GCF High-Speed Data Subsystem The High-Speed Data Subsystem transmits radio science open-loop tuning predictions from the NOCC to the DSS and CTA-21 and 10 4/23/81 sends Radio Science System performance validation data from the DSS to the NOCC. 3.3.2 GCF Wideband Subsystem In real time, the Wideband Subsystem transmits SSI data from the DSS to the NOCC. In non-real time, this subsystem sends radio science data from the DSS to the NOCC. 3.3.3 GCF Data Records Subsystem The GCF Data Records Subsystem formats and provides radio science data on computer-compatible tapes to the Flight Project. 3.4 Network Operations Control Center (NOCC) 3.4.1 NOCC Radio Science Subsystem The NOCC Radio Science Subsystem (NRS) generates open- and closed-loop Radio Science DTV graphics displays and DRS status and configuration displays. In addition, the NRS provides the planetary atmosphere refracted trajectory input (see paragraph 3.4.3) to the NOCC Support Subsystem. 3.4.2 NOCC Monitor Subsystem The NOCC Monitor Subsystem displays system temperature information. 3.4.3 NOCC Support Subsystem The NOCC Support Subsystem generates DSS frequency and tracking predicts using a polynominal coefficient tape (PCT) produced by the POEAS software. In addition, predicts can be generated using manual inputs. 3.4.4 NOCC Display Subsystem The NOCC Display Subsystem provides radio science displays generated by the NOCC Radio Science Subsystem to the Network Operations Control Area and the Project Radio Science Areas, and provides control data to the NOCC Radio Science Subsystem. 3.5 Network Radio Science Subsystem The Network Radio Science Subsystem is located in CTA-21. It performs bandwidth reductions of wide bandwidth radio science data recorded at the DSS. It receives digital wide bandwidth and medium bandwidth radio science data from the DSS Radio Science Subsystem and provides medium and wide bandwidth radio science data on computer-compatible tapes to the Voyager RSST. 11 4/23/81 3.6 Mission Support Area The Mission Support Area contains the real-time control center for the Radio Science System. DTV displays and hardcopy capability are provided to the Project's real-time operations personnel to aid in operations control. (See Section 6 for a more complete description of this area.) 3.7 Radio Science Support Team Data Records System This is the Project's data records handling system for the Voyager Radio Science System. It consists of the personnel, software, and procedures required to log in, reformat, validate archive, and deliver to the Radio Science Team all data products of the Voyager Radio Science System. The RSST Data Records System is described in detail in Section 7. 3.8 Open-Loop Recording System Pre-Pass Calibration The recorded open-loop receiver signals are the prime data type for the Saturn occultation and the ringscattering experiment. For this reason, it is extremely important that the openloop system be properly configured prior to the recording pass, and that a calibration tape be made. These data do not calibrate the DSS, but rather serve as a calibration of the results of the experiment. The following paragraphs describe these calibrations. 3.8.1 Purpose of the Calibration The open-loop recording calibration tapes are made to accomplish the following: (1) To establish the output of the open-loop receivers at a level that will not saturate the input to the ODA or DRA A/D converters; and ' (2) To provide data that will establish baseline values for the phase, frequency, and amplitude stability of the open-loop system. To achieve goal No. 1, the calibration recording is made using a test signal generated by the exciter/ translator that is set to the maximum predicted signal level for the upcoming pass. Then the output level of the receivers is adjusted to the level determined by the equation: S = L * [(SNR + 1)/(2*SNR + 2K*sqrt(2*SNR) + K^2)]^(1/2) (1) Where: S = receiver output level (volts rms) SNR = expected received SNR 12 4/23/81 k = number of sigma (saturation margin) L = A/D converter saturation level The value chosen for k for all of the Voyager Radio Science events is 5. Equation (1) governs the determination of receiver output power except in the case of the wideband backup system. Due to the wide recorded bandwidth and the resulting low SNR, the receiver output signal is almost all noise and is thus directly proportional to system temperature. Hence, the output signal power changes approximately TBD dB when the antenna is moved from zenith (where the calibration recording 'is made) to 45 degrees of elevation (where the data recording period is centered). Therefore, TBD dB is subtracted from the level as determined by equation (1) for the wideband backup systems. In order to achieve goal No. 2 for medium-band recording, it is necessary to step the test signal across the bandpass of the receiver filter. This is done in ten 5-kHz (at S-band) steps. Stepping the signal in frequency in this manner allows the necessary phase, frequency, and amplitude calibrations to be made. 3.8.2 X-Band RCP/LCP Test Signal Generation So that an X-band RCP/LCP test signal may be generated, a cap is provided (for placement over the Xband feedhorn) from which a linearly polarized signal is injected into the horn. This cap is oriented such that the linearly polarized signal is transmitted equally by the orthomode coupler to its RCP and LCP output ports, thus providing equal RCP/LCP calibration signals. A consequence of using a cap over the feedhorn to generate a test signal is that the X-band system temperature has been increased approximately 10 dB. It has, in effect, been terminated into an ambient load. To counter the 10- dB increase in receiver output power due to the presence of the cap, it is necessary to insert 10-dB pads into the signal path at appropriate points. These must be removed after the calibration recording is made. 3.9 Ground Data System Configuration Requirements This section consists of a set of tables (3-1 through 3-7) that specify subsystem configuration requirements for the Voyager Saturn encounter radio science experiments. 3.10 GDS Experience During the First Saturn Encounter TBD - Awaiting the release of the Radio Science Data Anomaly Working Group's final report. 13 4/23/81 TABLE 3-1 ANTENNA MECHANICAL AND POINTING SUBSYSTEM CONFIGURATION REQUIREMENTS RADIO SCIENCE CELESTIAL OBSERVATION MECHANICS SATURN RING ENTIRE NETWORK OCCULTATION SCATTERING SUBSYSTEM +-10 DAYS* DSS-43 DSS-43 ASSEMBLY 8/26/81 8/26/81 Subreflector Auto mode per Fixed subreflector Fixed subreflector Autofocusing standard setting optimized setting optimized Control operating for 450 elevation for 450 elevation Assembly procedures angle angle Angle CONSCAN on per CONSCAN off-- Use Use last offset as Tracking normal operating last offset as determined by procedures determined by CONSCAN CONSCAN *See final ISOE for exact times and duration. 4/23/81 TABLE 3-2 ANTENNA MICROWAVE SUBSYSTEM CONFIGURATION REQIREMENTS RADIO SCIENCE CELESTIAL OBSERVATION MECHANICS SATURN RING ENTIRE NETWORK OCCULTATION SCATTERING SUBSYSTEM +-10 DAYS* DSS-43 DSS-43 ASSEMBLY 8/26/81 8/26/81 Polarizer RCP switched to RCP to low-noise RCP to low-noise Control low-noise masers masers masers TWM S-band: S-band: S-band: Assignments TWM #1 = SRCP TWM #1 = SRCP TWM #1 = SRCP TWM #2 = SLCP TWM #2 = SLCP X-band: X-band: X-band: TWM #2 = XRCP TWM #2 = XRCP TWM #2 = XRCP TWM #1 = XLCP TWM #1 = XLCP *See final ISOE for exact times and duration. 4/23/81 TABLE 3-3 TRANSMITTER SUBSYSTEM CONFIGURATION RADIO SCIENCE CELESTIAL OBSERVATION MECHANICS SATURN RING ENTIRE NETWORK OCCULTATION SCATTER SUBSYSTEM +-10 DAYS DSS-43 DSS-43 ASSEMBLY 8/26/81 8/26/81 20 kW Nominal Output Power = 18 kW Transmitter See ISOE for exact transmission times. HI Power EMERGENCY USE ONLY Transmitter 4/23/81 TABLE 3-4a RECEIVER-EXCITER SUBSYSTEM CONFIGURATION REQUIREIMENTS RADIO SCIENCE CELESTIAL OBSERVATION MECHANICS SATURN RING ENTIRE NETWORK OCCULTATION SCATTERING SUBSYSTEM +-10 DAYS* DSS-43 DSS-43 ASSEMBLY 8/26/81 8/26/81 Closed-Loop Standard Voyager Closed-loop** Not required Receivers closed-loop data doppler data acquisition and required. BLK III, calibrations S-band 2 BLO = 12Hz required BLK IV, X-band 2 BLO = 30 Hz; AGC BW = MED Precision Power Two channel S- Four channel S- and Four channel S- and Monitor (PPM) and X-band RCP- X-band RCP/LCP sys- X-band RCP/LCP sys- only system tem temperature tem temperature temperature measurements measurements measurements required required required *See final ISOE for exact event times and duration. **See Section 5.0 for detailed signal acquisition strategy. 4/23/81 TABLE 3-4b RECEIVER-EXCITER SUBSYSTEM CONFIGURATION REQUIREMENTS RADIO SCIENCE CELESTIAL OBSERVATION MECHANICS SATURN RING ENTIRE NETWORK OCCULTATION SCATTERING SUBSYSTEM +-10 DAYS DSS-43 DSS-43 ASSEMBLY 8/26/81 8/26/81 Open-Loop Not applicable MMR medium-band MMR medium-band S- Receivers S-band RCP band- band RCP bandwidth = Prime System width = 50 kHz; 50 kHz; S-band LCP S-band LCP band- bandwidth = 50 kHz width = 50 kHz X-band RCP band- X-band RCP bandwidth width = 150 kHz; = 150 kHz; X-band LCP X-band LCP band- bandwidth = 150 kHz width = 150 kHz Filter select = 8 Filter select = 8 S- and X-band RCP/ S- and X-band RCP/ LCP RCVR power out- LCP RCVR power output put = +13 dBm with = +13 dBm with cali- calibration signal bration signal levels levels = TBS dBm = TBS dBm X-band, X-band, TBS dBm TBS dBm S-band S-band 4/23/81 TABLE 3-4c RECEIVER-EXCITER SUBSYSTEM CONFIGURATION REQUIREMENTS RADIO SCIENCE CELESTIAL OBSERVATION MECHANICS SATURN RING ENTIRE NETWORK OCCULTATION SCATTERING SUBSYSTEM +-10 DAYS DSS-43 DSS-43 ASSEMBLY 8/26/81 8/26/81 Open-Loop Not applicable MMR Wideband RCVR: Receivers Channel 1 = S-band RCP, Second LO = TBS mHz Backup System Channel 2 = S-band LCP, Second LO = TBS mHz Channel 3 = X-band RCP, Second LO = TBS mHz Channel 4 = X-band LCP, Second LO = TBS mHz RCVR First LO SYN FREQ = See Section 5.0 Received Signal Levels: S-band = TBS X-band = TBS RCVR Output Power = +13 dBm Spectral Not applicable For open-loop recording events, the Signal SSI will be configured as detailed Indicator in the final ISOE. (SSI) 4/23/81 TABLE 3-5 RADIO SCIENCE SUBSYSTEM CONFIGURATION REQUIREMENTS RADIO SCIENCE CELESTIAL OBSERVATION MECHANICS SATURN RING ENTIRE NETWORK OCCULTATION SCATTERING SUBSYSTEM +-10 DAYS DSS-43 DSS-43 ASSEMBLY 8/26/81 8/26/81 Occultation Not required Medium-band recording required; Data Assembly Pass dependent parameters are: (ODA) MBS 300K, SCN 32, PRD TBS Digital Not Required DRA #1 records medium-band data, Recording IPS = 30 Assembly (DRA) DRA #2 records wide-band back-up data, IPS = 120 4/23/81 TABLE 3-6 TRACKING SUBSYSTEM CONFIGURATION REQUIREMENTS RADIO SCIENCE CELESTIAL OBSERVATION MECHANICS SATURN RING ENTIRE NETWORK OCCULTATION SCATTERING SUBSYSTEM +-10 DAYS* DSS-43 DSS-43 ASSEMBLY 8/26/81 8/26/81 Metric Data Voyager 2 SOP for High rate doppler High rate doppler Assembly (MDA) acquiring ranging data required,* data required,* and and doppler data-- S-band = CHN 1 S-band = CHN 1 Planetary various sample X-band = CHN 3 X-band = CHN 3 Ranging rates and ranging Assembly (PRA) parameters required as per ISOE *See final ISOE for exact event times and duration. 4/23/81 TABLE 3-7 MONITOR AND CONTROL SYSTEM CONFIGURATION REQUIREMENTS RADIO SCIENCE CELESTIAL OBSERVATION MECHANICS SATURN RING ENTIRE NETWORK OCCULTATION SCATTERING SUBSYSTEM +-10 DAYS* DSS-43 DSS-43 ASSEMBLY 8/26/81 8/26/81 Digital Infor- Standard Operations AGC TOL = 2 AGC TOL = 2 mation Subsystem Procedures (SOP) Collect AGC Collect AGC (DIS) Data on line Data on line printer printer Data System SOP SOP SOP Terminal (DST) *See final ISOE for exact event times and duration. 4/23/81 4.0 RADIO SCIENCE ENCOUNTER TIMELINES The radio science encounter timelines and time-ordered listings provide a rapid and concise means of determining radio science activities on a daily basis. 4.1 Extended Encounter Timeline (DOYs 228-248) The Extended Encounter Timeline (Figure 4-1) covers a 20-day period centered on the closest approach to Saturn on DOY 238. Items included are: 64-meter station tracking coverage, relevant Voyager 2 Spacecraft events, science events, special ground coordination events, meetings and briefings, and spacecraft sequence development milestones. Note that on the science events line, the periods labeled XSCEL are one-way (or two-way noncoherent) tracking periods; the CELMECH periods are two-way coherent or three-way tracking periods. 4.2 Occultation Timeline (DOYs 237-238) The Occultation Timeline (Figure 4-2) is a greatly expanded version of the central two days of the encounter. It contains more detailed events and additional item lines to cover Voyager 1 events for the plasma calibration observation, as well as DSS-42 and DSS-44 tracking events. 4.3 Time-Ordered Listing of Selected Timeline Events The Time-Ordered Listing (Table 4-1) is a useful adjunct to the timelines. It contains exact times for selected timeline events such as meetings and briefings. Generally, only non-ISOE events appear in this listing. 14 4/23/81 TABLE 4-1 TIME-ORDERED LISTING OF SELECTED TIMELINE EVENTS TIME (UTC) EVENT 225/22:00:00 ORT-B3 Operations Strategy Briefing (FOOsponsored) 229/00:00:00 DSS-43 Rep Briefing 231/00:00:00 DSS-43 Rep Briefing 232/00:00:00 DSS-43 Rep Briefing/Pre-Pass Briefing (ORT-B3) 232/03:20:00 RSST on-line MSA (ORT-B3) 232/04:50:00 Start Radio Science Critical-Events Period (ORT-B3) 232/08:00:00 End Radio Science Critical-Events Period (ORT-B3) 232/09:05:00 RSST off-line (ORT-B3) 232/10:05:00 DSS-43 Post-Pass Briefing (ORT-B3) 232/22:00:00 NE Operations Strategy Briefing (FOOsponsored) 233/00:00:00 DSS-43 Rep Briefing 233/08:00:00 DSS-43 Station Personnel Operations Briefing 232/18:00:00 Final POEAS O-L Predicts Run Delivery 234/18:00:00 Final O-L Tuning Predict Generation Completed 235/00:00:00 Verify Final O-L Tuning Predicts 235/18:00:00 Transmit O-L Tuning Predicts to DSS-43 237/00:00:00 DSS-43 Rep Briefing 237/04:00:00 Quick-Look OD Update Delivery 237/22:00:00 DSS-43 Pre-Pass Briefing 237/21:00:00 Probe Ephemeris Tape Delivery (Uplink Predicts) 4/23/81 TABLE 4-1 (Continued) TIME (UTC) EVENT 237/21:30:00 POEAS Run Delivery (Uplink Predicts) 237/23:00:00 Uplink Predicts Generation Complete 238/03:00:00 RSST On-Line in MSA 238/04:30:00 Begin Radio Science Critical-Events Period 238/07:40:00 End Radio Science Critical-Events Period 239/00:00:00 DSS-43 Rep Briefing 240/00:00:00 DSS-43 Rep Briefing 4/23/81 5.0 TRACKING AND RADIO SCIENCE SUBSYSTEM OPERATIONS 5.1 Saturn Occultation Uplink and Downlink Strategies 5.1.1 Uplink Tuning Strategy The pre- and post-occultation uplink strategies will be different from standard cruise support in four respects: 1) Large doppler effects necessitate the use of so many uplink ramps that two different predict sets will be loaded into the MDA during the DSS-43 occultation pass; (2) Large doppler uncertainties force a late update of the post-occultation uplink tuning predicts; (3) A modified BLF determination will be performed after occultation exit; and (4) An adaptive tracking technique will be employed after the BLF has been determined. All of these features of the uplink strategy stem from the inability of Voyager 2's damaged receiver to track the uplink frequency. Since the required number of uplink ramps for the DSS-43 occultation pass cannot be accommodated by the MDA in one predict set, the DSS-43 uplink predicts will be separated into two distinct sets. The first set will cover the pre-occultation period (segment I of the pass) and the second set will cover the post-occultation period (segment 2 of the pass). In addition, the transfer from DSS-14 to DSS-43 prior to the occultation must be delayed from the normal transfer time in order to keep the number of ramps in the pre- occultation set within the MDA's limit of 28. The second predict set will be loaded into the MDA during the time when the DSS-43 transmitter is turned off for the occultation. Due to the large RTLT, the interruption in tracking data resulting from the predict-loading process will occur before the start of the radio occultation measurements. Refer to Table 5-1 for a list of the uplink tuning predicts to be used during the pre- and post-occultation passes. 15 4/23/001 TABLE 5-1 UPLINK PREDICT SET IDs DSS PRIME BACKUP COVERAGE 14 XP80 --- Pass #TBD (Entire Pass) 43 XP80 --- Pass #1471 (Segment 1) 43 TBD XP95 Pass #1471 (Segment 2) 63 XP90 XP95 Pass #1471 (Entire Pass) Two-way tracking resumes about forty minutes after occultation exit for the Tethys mass determination. However, given the narrowness of the spacecraft receiver's tracking-loop bandwidth combined with uncertainties in BLF due to doppler effects, thermal transients in the receiver electronics bay, and possible radiation effects, it will be difficult to establish a two-way lock. Thus, it is desirable to eliminate, as much as possible, the errors due to trajectory uncertainties. To this end, the Voyager Navigation Team will update the trajectory using all navigation data available sixteen hours before the closest approach to Saturn. Based on this update, a post-occultation uplink predict set with a 2-sigma uncertainty of 10 Hz or less (S-band) will be transmitted to DSS-43 in near-real time. In the event that the predicts cannot be updated per this scheme, a backup set of uplink predicts based on an earlier orbit determination will already be at the station for post- occultation use (see Table 5-1). The S-band residuals resulting from a comparison between these uplink ramps and the expected BLF are shown in Figure 5-1. The effect of early and late arrival time errors (3-sigma) upon these residuals is shown in Figures 5-2 and 5-3. Time and/or frequency offsets may be manually applied to the backup set to offset the orbit error if necessary. An integrated Navigation Team-NOCC schedule for these update activities is given in Table 5-2. TABLE 5-2 UPLINK PREDICTS UPDATE SCHEDULE TIME (UTC) EVENT 237/14:30:00 Tracking IDR delivery to Voyager Navigation 237/21:00:00 Probe Ephemeris Tape delivery to DSN 16 4/23/81 TABLE 5-2 (Continued) TIME (UTC) EVENT 237/21:30:00 POEAS tape (atmosphere off) tape delivery to DSN 237/23:00:00 Uplink predicts generation completed 238/00:00:00 Transfer uplink from DSS-14 to DSS-43 238/02:15:00 DSS43 transmitter off 238/02:20:00 Uplink predicts transmitted to DSS-43 238/03:45:00 Uplink predicts loaded into MDA and ramping initialized 238/04:35:00 DSS-43 transmitter on 238/05:26:30 Enter occultation 238/07:01:46 Exit occultation 238/09:35:00 Transfer uplink from DSS-43 to DSS-63 The post-occultation DSS-63 pass will require only one set of uplink ramps for the MDA; however, that set will be updated when the second set of DSS-43 predicts are updated per Table 5-2. The updated DSS-63 predicts will be transmitted before AOS. A modified BLF determination sequence consisting of 30-minute ramps will be used after exiting occultation. Special ramp rates will be supplied by Voyager Telecom analysts and the ISOE shall be followed for specific times. Upon determination of the BLF, adaptive tracking will be accomplished by applying frequency offsets to normal uplink ramps. These offsets will be updated as necessary and provided by Voyager Telecom analysts. 5.1.2 Pre-Occultation Downlink Tuning DSS-43. During the entry of atmospheric occultation, the received signal power (agc) will drop steadily to below receiver threshold and the received frequency will be changing as fast as 10 Hz/second at S-band. To maintain receiver lock as long as possible, it will be necessary to ramp the closed- loop receivers along the predicted frequency profile. It should be possible to maintain receiver lock for up to 10 minutes after the start of 17 4/23/81 atmospheric occultation. If the closed-loop receivers should drop lock while there is still a strong enough signal in the SSI, then the frequency determined by the SSI should be used to relock the receivers. The receiver ramping for the occultation entrance will end just after the set-up maneuver for XRSCAT begins since there can no longer be a a signal for the closed-loop receivers to lock up on. The receiver tuning will be within +100 Hz (S band). The static phase error in the receivers should be zeroed out prior to the first receiver ramp. Preliminary ramps are specified in Table 5-3. These ramps will be updated after the final OD solution and sent to the stations by TWX. Figure 5-4 shows the expected one-way (USO) doppler profile, and the deviation of the S-band receiver ramps from the predicted doppler is depicted in Figure 5-5. TABLE 5-3 OCCULTATION ENTRANCE RECEIVER RAMPS (TYPICAL VALUES) RECEIVER RATE RECEIVER RATE UTC BLOCK III BLOCK IV S-BAND X-BAND 05:10:00 +0.099225 +0.41091 05:27:14 -0.098425 -0.40760 05:38:26 -0.074465 -0.30916 05:40:00 0.0 0.0 DSS-44. The strategy for receiver tuning at DSS-44 is similar to that at DSS- 44 except that the receivers will drop lock earlier and there will be no SSI to assist in relocking the receivers. The receivers should be manually ramped to follow the profile in Table 5-3 for Block III S-band. 5.1.3 Post-Occultation Downlink Acquisition Tuning DSS-43. Just prior to the beginning of part 2 of the limbtracking maneuver, the closed-loop receivers will again be ramped in order to acquire closed-loop lock as soon as possible. As in the occultation entrance, the ramps provided will keep the closed-loop receivers within 100 Hz (S-band) of the predicted signal. The SSI should be used to aid in locking up the closedloop receivers. If lock has not been achieved by 4 minutes prior to atmospheric occultation exit, then the receivers should be 18 4/23/81 swept through the predicted downlink frequency Dl +-800 Hz (S-band) at 100 Hz/s (S-band), where D1 is the average between the time the sweeping is started and the time of atmospheric occultation exit. Thus, the sweep should cross the downlink frequency once every 16 seconds. During the sweeping, automatic triggering at zero-beat detection (ATZ) should be on so that when lock is achieved,, ramping will continue. Table 5-4 lists the preliminary occultation exit receiver ramps. Figure 5-5 shows the deviation between these S-band receiver ramps and the predicted doppler profile. TABLE 5 -4 OCCULTATION EXIT RECEIVER RAMPS (TYPICAL VALUES) RECEIVER RATE RECEIVER RATE UTC BLOCK III BLOCK IV S-BAND X-BAND 06:50:00 -0.10591 -0.43857 07:08:00 +0.05901 +0.24435 07:10:00 0.0 0.0 DSS-44 will not be able to achieve lock as early as DSS-43 and will probably not be able to do so until after occultation exit. The receiver operator should begin to sweep D1 +-100 Hz (S-band) one minute prior to occultation exit. 5.1.4 Downlink Tracking Predict Sets The downlink tracking predict sets for the DSS-43 occultation pass are given in Table 5-5. The two "normal" predict sets, XA90 and XU90, should be used for calculation of expected frequencies during downlink signal acquisition throughout the pass. However, the XS90 predict set should reside in the MDA from AOS until occultation entrance since this set models the uplink ramps and will allow an accurate correlation between doppler residuals and trajectory errors. From occultation exit until LOS, the "normal" predict sets will be used for doppler residuals because of the difficulties in predicting the uplink ramps to be used during this period. Fortunately, a straightforward relationship between trajectory errors and doppler residuals after the occultation is not essential to operations. Prior to the occultation, the doppler residuals will be factored into decisions regarding the potential applications of manual timing offsets to the open-loop tuning predicts. ' 19 4/23/81 TABLE 5-5 DOWNLINK TRACKING PREDICT SETS, SET ID CONTENTS USE XA90 Normal COH Predicts All COH downlink signal acquisitions and residual calculations during post- occultation COH period. XU90 Normal NCOH Predicts All NCOH downlink signal acquisitions and residual calculations during all NCOH periods. XS90 Special COH Predicts Residual calculations (uplink ramps modeled during pre-occultation in from XP90) periods. 5.2 Antenna Pointing Strategy Compared with the Voyager 1 Saturn occultation low elevation angle strategy, the antenna pointing at DSS-43 for the Voyager 2 encounter will be straight- forward. The elevation angles will be 52.36 0 at atmospheric occultation entrance and 39.070 at atmospheric occultation exit. The pointing drift during this period (at such high elevation angles) will not be large enough to require the manual insertion of pointing offsets. Therefore, once CONSCAN is turned off, the antenna pointing will be performed with the last automatically calculated offsets until CONSCAN control is resumed. 5.3 Use of the SSI for Receiver Acquisition The SSI should be used whenever possible to aid in downlink acquisition. Procedures for this use are outlined in the Voyager Network Operations Plan (618-700, Revision D), Appendix F (pp. F14-F19). At DSS-43, the receiver frequencies (both Block III and Block IV) can be computed, directly by the SSI for display at the DST. To accomplish this, the following steps should be followed: (1) Enter the RVCO frequencies for receiver three and four using the OCIs: (It is not necessary to reenter these values.) CFG RCV3 VCO = 26.XXXXXX MHz CFG RCV4 VCO = 26.XXXXXX MHz 20 4/23/81 (2) Enter the most current MMR POCA frequency: CFG SRCP POCA = 41.XXXXXX MHz This value should be re-entered for every frequency update. (3) Place the SSI cursor over the signal. (4) Call up an S- or X-band MMR channel at the SSI-detailed station's display by using the OCI: D STS. This display is depicted in Tables 5-6 and 5-7. TABLE 5-6 STATUS DISPLAY FOR SLCP/SRCP PORTS DURING REC91VER ACQUISITION FLT = MB S-Band = 2295.XXXXXX Mhz MMR POCA = 41.XXXXXX MHz RCVl VCO = 23.XXXXXX MHz RCV2 VCO = 23.XXXXXX MHz RCV3 VCO = 26.XXXXXX MHz POCA = 46.XXXXXX MHz RCV4 VCO = 26.XXXXXX MHz POCA = 46.XXXXXX MHz TABLE 5-7 STATUS DISPLAY FOR XLCP/XRCP SSI PORTS DURING RECEIVER ACQUISITION FLT = MB X-Band = 8415.XXXXXX MHz MMR POCA = 41.XXXXXX MHz 21 4/23/81 RCV3 VCO = 26.XXXXXX MHz POCA = 41.XXXXXX MHz RCV4 VCO = 26.XXXXXX MHz POCA = 41.XXXXXX MHz 5.4 Radio Science Subsystem Operations 5.4.1 Medium-Band Receiver Configuration Radio science operations during the Voyager. 2 Saturn encounter on August 26 will primarily consist of open-loop receiver recording during three contiguous periods: Saturn occultation entry, the ringscattering experiment, and Saturn occultation exit. These three events will occur over DSS-43 and will be recorded from 04:25:00 to 08:00:00 using the fourchannel medium-band radio science subsystem. The two S-band signals, RCP and LCP, will pass through separate 50-kHz receiver filters and the two Xband signals, RCP and LCP, will pass through separate 150-kHz receiver filters. These filtered signals will be sampled at 300,000 samples per second with a quantization of 8 bits per sample. 5.4.2 Wide-Band Receiver Configuration In addition to the medium-band recordings scheduled for encounter, DSS-43 will record the downlink signals during the previously mentioned time span using the backup wide bandwidth receivers and DRA recording capabilities. The DSS-43 wide-band system consists of two 600-kHz S-band filters and two 1.7 MHz X-band filters stacked on top of one another into an 8- MHz bandwidth which is recorded by a DRA. Nominal first LO synthesizer frequency settings for the wide-band receiver are specified in Table 5-8. Figure 5-10 illustrates the signal drift through the S-band wide-band filters at DSS-43. TABLE 5-8 WIDE-BAND RECEIVER FIRST LO SYNTHESIZER FREQUENCIES MODE FREQUENCY NCOH 41589000.00 COH 41558000.00 22 4/23/81 In the event of a USO failure, the COH frequency should be used in the wide- band OLR. 5.4.3 Open-Loop Tuning Predicts For the Saturn occultation and ring-scattering experiments, three radio science tuning predict sets, one prime and two contingency sets, will be generated. These predict sets are described in Table 5-9 and the receiver ramps for the prime set are shown in Figure 5-6. The frequency tolerance of the predict sets will be 1.5 kHz for XPOCC (including errors due to ramp linearity and time uncertainties) and 1.0 kHz for XRSCAT (ramp linearity only). The tuning will be biased by +2.5 kHz for the duration of the predict sets except for the XRSCAT observation period when no bias will be inserted. (The bias will simplify analysis of the XPOCC data.) TABLE 5-9 SATURN OCCULTATION PREDICT SETS SET ID CONTENTS USE RX01 Mode switches, Prime USO reference RX02 One-way only, DSS TXR failures or USO reference missed uplink RX03 One-way only, USO failure, two or three- AUX OSC reference way entry, one-way exit with AUX OSC reference As indicated in Table 5-9, the RX03 predict set may be used as a two-way, three-way, or one-way (in the event of a USO failure) predict set because the uplink doppler is ramped out for Voyager 2 in order to acquire the damaged spacecraft receiver. It may be necessary to enter a manual frequency offset into the ODA to center the downlink signal in the receiver filters in the event that this predict set is used since auxiliary oscillator frequency used to generate RX03 may not turn out to be correct. Comparisons of the predicted open-loop receiver frequency ramps with the nominal signal frequency profiles are shown in Figure 5-7. The effect of +-3 sigma arrival time errors upon the residuals is shown in Figures 5-8 and 5-9. 23 4/23/81 6.0 REAL-TIME OPERATIONS Real-time operations for the Voyager 2 Saturn encounter will span a 20-day period centered on the Saturn flyby and Earth occultation on DOY 238. The ten days preceeding the closest approach to Saturn will be occupied by final preparations for the encounter. Major preparations for radio science operations will include final verification of the ground data system and operational readiness via ORTB3, generation and delivery of final tuning predicts to DSS-43, daily status briefings between the Radio Science Representative to DSS-43 and the Radio Science Support Team via the Radio Science Coordination Net, and operative briefings for DSS-43 personnel by the Representative. The NearEncounter Phase radio science operations on DOY 238 will consist of a complex series of real-time activities aimed at maximizing the science data return. Elements of the Radio Science Support Team (RSST), Mission Control Team (MCT), Deep Space Network (DSN) operations staff, and Operations Coordination Team (OCT) will be deeply involved in radio science real-time operations. The ten days following Saturn encounter will emphasize delivery, quick-look processing, and analysis of the data for preliminary scientific results. In addition, throughout this plus-and-minus ten-day period, celestial mechanics observations will be made via continuous one-way, two-way, and three-way doppler tracking. The following sections detail responsibilities., procedures, operation schedules, and anomaly contingency plans for radio science real-time operations. 6.1 Functional Responsibilities The functional responsibilities of the major supporting elements for the radio science investigations at Titan and Saturn are specified in this section. Normal Project support for the experiment, as defined by interface agreements contained in the Voyager Space Flight Operations Plan (document 618-505) will not be described herein. 6.1.1 Radio Science Support Team The radio science operations desk in the Voyager Mission Support Area (MSA) will be staffed by three members of the RSST during the scheduled radio science operations periods. A fourth member of the RSST will provide additional operations support from a remote location. The responsibilities of these RSST members are defined as follows: Operations Coordinator. The Operations Coordinator is responsible for verification of the proper conduct of real-time operations for the radio science investigation, as specified in the Voyager Project ISOE. Thus, he handles all communications with the Project's mission controller (ACE) via the voice net. All requests by the RSST for actions to be taken by the MCT or 24 4/23/81 DSN are communicated through the ACE by the Operations Coordinator, with the exception of the radio science control functions (see Section 6.2.7). Additionally, he coordinate's communications and interactions between the Science Advisor, Operations Engineer, and Operations Advisor. In general, the Operations Coordinator oversees all radio science business in the MSA. Operations Engineer. The Operations Engineer is responsible for verification of proper operation of the Occultation Data Assembly (ODA), Spectral Signal Indicator (SSI), Precision Power Monitor (PPM), Metric Data Assembly (MDA), Planetary Ranging Assembly (PRA), and other DSS subsystems supporting radio science observations. This is accomplished via monitoring of the realtime DTV displays at the radio science desk in the MSA. The Operations Engineer communicates via the voice net with the NOPE (Network Operations Project Engineer), NOA (Network Operations Analyst), and BUSS (Voyager Spacecraft Monitor Controller) to coordinate DTV operations. He advises the Operations Coordinator on the status of the Radio Science Ground Data System. Additionally, he communicates directly with the Radio Science Representative as required by the Science Advisor, and assists in prepass checklist verification and post-pass briefings with the Representative. Science Advisor. The Science Advisor is responsible for monitoring the progress of the experiment and for providing operational recommendations to the Operations Coordinator based upon scientific considerations. He is the principle contact for the Radio Science Representative via the Radio Science Coordination Net, and during the radio science critical-events period, he will direct the use of the radio science control functions via this Net. The Science Advisor may request assistance from the Operations Coordinator and Operations Engineer when making control function decisions. Operations Advisor. The Operations Advisor staffs the third floor radio science operations room and is responsible for assisting the RSST MSA personnel in monitoring experiment progress. He communicates with the Operations Coordinator via the MISD Net. The Operations Advisor is available to work on operational problems which are too time-consuming for the MSA personnel to work on and he may delegate work to the Radio Science Team investigators or other support personnel as required. Additionally, he operates the VTR which will be recording the SSI display and makes hardcopies of the real-time DTV displays when appropriate 6.1.2 Mission Control Team Support to the RSST The MCT will provide communications support via the ACE-to-OPCH-to-DSS voice net link for all operational requests from the RSST with the exception of the control functions used when a 25 4/23/81 radio science critical events period is in effect. Aside from these functions (see Section 6.2.7) which are controlled via the Radio Science Coordination Net, all communications and support by the MCT will follow normal operational procedures. 6.1.3 Deep Space Network Support to the RSST A Network Operations Analyst (NOA) will be required to generate tuning predicts for both the ODA and backup DRAs. In addition, a Network Operations Project Engineer (NOPE) will be required to assist in the real-time operations of the NOCC. The NOPE and NOA will plan, integrate, and operate the real-time NOCC displays. They will also assist the Radio Science Operations Engineer in the analysis of the displayed data and advise the RSST of the real-time display system's operational status. 6.1.4 Operations Coordination Team Support to the RSST The Operations Coordination Team (OCT) will be responsible for supporting SOE redline activities if the real-time TWNC-off commanding strategy planned to support the post-occultation celestial mechanics observations cannot be successfully implemented. Redlines for the TWNC-off activity will be prepared in advance and approved and distributed at the request of the Radio Science Operations Coordinator. Redline support may also be required for other unexpected events affecting the radio science experiments. In addition, the OCT will prepare preliminary encounter and ORT ISOEs for the RSST and DSN two weeks in advance of the normal delivery dates. These will be used for review and training purposes. 6.1.5 Radio Science Representative to DSS-43 The Radio Science Representative to DSS-43 will represent the Voyager Radio Science Support Team at the DSS. He will brief the station staff on the radio science experiment's objectives and operational requirements for the Saturn encounter. He will also act as the real-time operations interface between the DSS Shift Supervisor and the Radio Science Support Team (specifically, the Science Advisor) during the radio science criticalevents periods in order to expedite the control functions specified in Section 6.2.7. Prior to the high- activity period, the Radio Science Representative will participate in the daily briefings and information exchange between the DSS and the Radio Science Support Team. 6.2 Operations Procedures 6.2.1 Voice Net Communications The Ground Communications Facility voice nets provide both the means of controlling worldwide spacecraft tracking operations 26 4/23/81 and for relaying information required to verify proper operation of the various DSS and spacecraft subsystems. Figure 6-1 illustrates the operational net structure as it will be used for the NearEncounter Phase operations. Descriptions of these nets follow; MICON-1: Project's operational net for communications between MSA personnel and the ACE. MICON-2: MCT's internal net for communication between spacecraft subsystem analysts, the Cognizant Systems Engineer, and the BUSS. MISD-3: Mission Director's net reserved for internal RSST communications during the encounter period. TRK ANAL2: Standard Project operational net to NOCC for communication with the NOPE and the NOA. INTER-1: Standard Project operational net to NOCC for communication between the ACE and the OPS Chief. DSS-1: Standard NOCC-to-DSS control net. RADSCI: The Radio Science Coordination Net has a special function and is described in detail below. Due to the dynamic nature of the Saturn radio occultation and ring-scattering experiments, it is important that communications be established which can provide for the rapid and precise control of extremely complicated equipment at locations remote from JPL. As a means of relieving the strain on the standard operations nets during the encounter observations, an additional net is used which provides for a direct voice link between the RSST and DSS-43. This net is designated the Radio Science Coordination Net. The danger exists that confusion can arise if conflicting inputs are given to the tracking system over more than one net. Thus, RSST control authority via the Radio Science Coordination Net is carefully regulated. Six specific radio science control functions have been identified (see Section 6.2.7) which are critical for successful radio science operations. Control of these items may be exercised directly by the RSST only during specified radio science critical-events periods which are identified in the timeline and time-ordered listings (Section 4 of this plan) and in the Project ISOE. Under these conditions, requests from the RSST's Science Advisor are relayed by the Radio Science Representative directly to DSS-43 Shift Supervisor. Outside of the critical-events periods, all control function requests will go through the standard Radio Science Operations Cordinator-to-ACE-to-OPCH-to-DSS communications link. 27 4/23/81 TABLE 6-1 NEAR ENCOUNTER DTV DISPLAY REQUIREMENTS DISPLAY SYSTEM/DTV CHANNEL COMMENTS HS and WB AGC plots TTS/Channel D-3 M-824 and M-827 displays Radio Science page 15 TTS/Channel D-4, 5, or 9 Will negotiate channel in real time Real-time station monitor for stations RTDS/Channel 15 thru 25 Will negotiate channels in real time 42 and 43 DSS-43 SSI-display NRS/NOCC-9 DSS-43 NRS/DRS displays F706, F707 NRS/NOCC-2 F708. S/C 32 monitor, DSS-43, 44; F402 Monitor/NOCC-2 for DSS-43 S/C 31 monitor DSS-42; F207 Monitor NOCC channels to be allocated in real time Doppler status for DSS-42,43,44; F207 Tracking NOCC channels to be allocated in real time TRK analysis summary DSS-42, 43, 44; Tracking NOCC channels to be allocated in real F204 time S/X - band AGC plots Monitor/NOCC-6 S-band doppler frequency Monitor/NOCC-7 S-band doppler residual Monitor/NOCC-7 4/23/81 6.2.2 Graphics Displays and Hardcopy Data Collection The DTV displays available to the RSST in the MSA and on the third floor provide the principle data source for monitoring operation of the radio science experiment. Due to the complexity of events and the large body of data available, proper organization and coordination of the DTV data displays is essential. It will be the responsibility of the Radio Science Operations Engineer to interact with the MCT and the NOPE/NOA to assure the proper selection and display of data on the DTVs. The desired displays are summarized in Table 6-1. There are four primary display systems: The Project's TTS and the NOCC's Monitor, Tracking, and NRS Systems. Each type of display is indicated along with the desired DTV channel location. The NOCC graphics requirements are specified in detail in Tables A- 9a through A-9z. All hardcopies of DTV displays made by the RSST will be collected and organized by the Operations Coordinator at the end of the radio science, operations period. Copies will be produced and delivered to the Science Advisor, and the originals will be archived at JPL. 6.2.3 Briefing Strategy During the period of time that the Radio Science Representative is at the Australia tracking complex, a series of daily briefings will be conducted. The purpose of these briefings is to keep the Station Representative informed of Project status, operations plan and ISOE updates, and any miscellaneous issues, problems, or concerns which may arise. Similarly, the Representative will use the briefings to inform the RSST of any station problems, unresolved issues concerning operations or procedures, and encounter preparation status. Refer to Section 4 for the briefing schedule. Table 6-2 contains the briefing agenda. TABLE 6-2 DAILY RSST BRIEFING AGENDA A. Station Inputs 1. General station status and weather report 2. Radio Science System status 28 4/23/81 3. Shift-briefing status 4. Concerns at station 5. Information required by station B. JPL Inputs 1. General Voyager status 2. Updates to Radio Science Operations Plan 3. ISOE updates 4. Confirmation of predict set transmission 5. Date and time of next briefing 6.2.4 Pre-Pass Countdown Procedures The pre-pass countdown log for DSS-43 will be used to record the results of special DSS Radio Science System calibration tests as well as the logging of information critical for post-event data decalibration and interpretation. It is the responsibility of the Radio Science Representative to assure that calibration procedures are conducted properly and that the logs are filled out. This data will be delivered by the Representative to the RSST upon return to JPL. The countdown log is in the Appendix (Table A-5), and the open-loop calibrations are described in Section 3.8. 6.2.5 Checklist Strategy In order to verify correct station configuration without overburdening the ISOE and voice nets, a set of checklists for station subsystem configurations are used (refer to Section 3.2 for descriptions of the DSS Subsystems). Each checklist is identified by station number. The checklists cover all applicable subsystems, specifying all required test procedures and instrument configuration settings. The status referred to in the checklists refers to station configuration at AOS. Any further changes will be explicitly called out in the ISOE. It will be the responsibility of the Radio Science Representative, in conjunction with the station's operations personnel, to verify compliance with each checklist at DSS-43. 29 4/23/81 Verification will then be relayed to the Station Shift Supervisor who will pass the information to the RSST via the standard operational network (DSS-to- OPCH-to-ACE-to-RSST). At DSS-42 and DSS44, the Shift Supervisor will confirm that the station is configured per checklist and will relay that information via the standard operational network. Checklists will be completed in sufficient time to provide verification at the times specified in the ISOE. Refer to Tables A-6, A-7, and A-8 in the Appendix for the checklists for DSS- 42, DSS-43, and DSS-44. 6.2.6 Post-Pass Tape Logging Procedure Due to the high value of the radio occultation data, the large number of tapes generated, and the distance between JPL and DSS-439 it is essential to establish appropriate logging procedures for all stationgenerated radio science tapes. There are three categories of tapes to be logged: (1) the ODA POCA tape, (2) the medium-band DRA tapes, and (3) the wideband backup DRA tapes. As soon as it is possible after the end of open-loop recording, the Radio Science Representative will report tape ID numbers and start and stop times to the RSST via the Radio Science Coordination Net. Upon completion of the postoccultation calibrations and tape duplications, a complete written report will be prepared. This report will be sent to JPL via teletype, and will contain tape ID numbers, recording times, and tape drive ID numbers. In addition to the tapes described above, the report will include medium and wide-band calibration tapes, and duplicate tape ID numbers. 6.2.7 Radio Science Control Functions The six control functions itemized in Table 6-3 will be exercised via the Radio Science Coordination Net to the Radio Science Representative during the critical-event periods only. (During other operational periods, the RSST will request needed changes via the Project operational net.) Specifically, the Science Advisor will be responsible for making the requests to the Representative. However, the Science Advisor may transfer control to another RSST-member on-line in the Mission Support Area if the need arises to do so. An initial set of parameters for these control functions will be provided to the station both in the Project ISOE and during RSST/Representative briefings. However, due to experimental uncertainties or system failures, the need for realtime changes may arise unpredictably. 30 4/23/81 TABLE 6-3 RADIO SCIENCE CONTROL FUNCTIONS DURING CRITICAL-EVENT PERIODS 1. Selection of ODA predict sets 2. Selection of ODA time offsets 3. Selection of ODA frequency offsets 4. Selection of SSI display channels 5. Selection of ODA run/idle modes 6. Selection of PPM noise diode and integration time 6.3 Operations Schedule Real-time operations for the encounter radio science observations will be separated into three periods: The pre-encounter period covering the ten days before the Saturn occultation, the near-encounter occultation events on DOY 238, and the ten-day post-encounter period (as delineated in Section 6.0). Refer to the Expanded Encounter Timeline, the Occultation Timeline, and the Time-Ordered Listing in Section 4 for the complete schedule of events for radio science operations. 6.3.1 Pre-Encounter Ten-Day Period The science objectives for this period are fully discussed in Section 2.2. Required operations support for the celestial mechanics observations will be nominal; they are relatively routine. Activity during the pre-encounter ten-day period will focus upon final Ground Data System preparations for the Saturn radio occultation and ring-scattering experiments. Principle activities will include ORT-B3 and daily briefings between the RSST at JPL and the DSS-43 Radio Science Representative. The status briefings will commence on DOY 229, with the only exception to the daily schedule occurring during preparation for ORT-B3. These briefings will be conducted from the radio science desk in the MSA, utilizing the Radio Science Coordination Net. The Operations Coordinator, Operations Engineer, and Science Advisor will be in attendance. Refer to Table 6-2 for the briefing agenda. 31 4/23/81 ORT-B3 will occur on DOY 232. This test will be the final confirmation of GDS readiness. The RSST will staff the MSA with the full complement of operations personnel in the same way that the Near-Encounter Operations will be conducted. Manning for the test will commence when the RSST goes online at 03:20 UTC on DOY 232. They will remain on-line until 09:05 UTC. The critical event period will extend from 232/04:50 until 232/08:00. Refer to the ORT-B3 Operations Plan for more details. 6.3.2 Near-Encounter Operations Period Near-Encounter operations will begin with the DSS-43 prepass briefing at 22:30 UTC on DOY 238. In addition to the briefing agenda items listed in Table 6.2, the pre-pass calibration and checklist status will be discussed. The full RSST Operations Team should staff the MSA for this briefing. The RSST will return to the MSA and be on-line starting at 238/03:00. During the initial time period ' voice lines will be checked out, DTV displays brought up, checklists verified, and any other preparatory business will be concluded. The Voyager NOPE and NOA will be required for NOCC coordination at this time. The formal start of radio science occultation activities will be at 04:00 UTC. At this time, the Project ISOE will be the controlling operations document. The critical-event period will extend from 04:30 UTC until 07:40 UTC, during which time the Saturn occultation and ringscattering observations will be made. Occultation activities will conclude at 08:20 UTC. At this time, tape logging will be done via the Radio Science Coordination Net. However, the full RSST staff will not be required after 08:00 UTC. An Operations Coordinator will remain on-line through the BLF determination and real-time commanded TWNC-off period to monitor celestial mechanics activities. At 10:00 UTC, the postpass briefing will be conducted with the Radio Science Representative. Once again, the full RSST operational team will be online in the MSA. This briefing will focus on wrapping up any open items concerning station calibration, configuration, operations, and wide-band open-loop playbacks. This briefing will conclude the Near-Encounter radio science real- time activities at Saturn. 6.3.3 Post-Encounter Ten-Day Period As with the pre-encounter period, the post-encounter ten-day period will involve minimal real-time operations activity. Daily briefings with the Representative will continue until he leaves DSS-43 to return to JPL. The RSST may require some postencounter calibrations if problems arise during the encounter. Otherwise, post-encounter operations will be comprised primarily of data delivery (hardcopy and tapes) and preliminary processing of that data. Section 7 discusses data handling and delivery procedures and schedules. 32 4/23/81 6.4 Contingency Planning In the course of real-time operations during the encounter, the potential exists for a variety of equipment failures or problems. While it is impossible to list all potential problems, major failure modes which are considered most likely to affect the radio science effort are covered here. Each contingency plan contains a discussion of the major steps required for recovery of the desired fall-back position if the problem is unsolvable in real time. 6.4.1 Loss of the Prime 64-Meter Station In this case, the RSST would transfer the 34-meter station covering Voyager I for the plasma calibration to Voyager 2. The RSST would then establish closed- loop tracking modes equivalent to those specified in the ISOE for the 64-meter station. The RSST would not switch the 26-meter backup to Voyager I but would choose to give up the plasma calibration and keep the backup on Voyager 2. This scenario would cause the Radio Science Team to lose all of the open-loop data. However, much can be done with the closed-loop data as long as the closed-loop system can be kept in lock. 6.4.2 Loss of Uplink Transmitter or Failure to Acquire Uplink The RSST would request a switch to contingency predicts for the all-one-way mode, after which new transmitter-on times would be negotiated. 6.4.3 USO Failure A failure in the USO would result in the loss of a very stable signal whose frequency is known quite precisely. The RSST would request a switch to the predict sets for the auxiliary oscillator. Since the auxiliary oscillator's frequency is not precisely known, the RSST would then request frequency offsets in the predict sets in order to center the signal in the MMR openloop filter bandpass. 6.4.4 ODA Halt or Failure The station's personnel would perform on-site diagnostics and corrective actions at their discretion. The backup system (DRA) should not be disturbed during the diagnostic work or corrective action. The RSST would be available for advice and real-time analysis, through the Radio Science Representative, via the coordination net. 6.4.5 Spacecraft Sequence Error (CCS Load Abort) The Radio Science Team would use transmitter on/off events 33 4/23/81 to control tracking mode change requirements in lieu of sequenced TWNC on/off events. Also, the RSST would request switching to backup predict sets in order to keep the signal in the center of the open-loop filter in the MMR. 6.4.6 Loss of One or More Channels in the Open-Loop System The RSST would request a change in the microwave, polarizer, or receiver configurations as required to maintain data collection in accordance with the following priorities: (1) XRCP, (2) SRCP, (3) XLCP, and (4) SLCP. In the event of the failure of the spacecraft's primary X-band TWTA prior to or during the radio science observations, the DSS-43 receiver's XRCP and XLCP ports will be reversed. This is because the spacecraft backup TWTA transmits in the LCP mode. When possible, configuration changes should be made without disturbing the backup system. 6.4.7 Saturation of One or More Channels in the Open-Loop System The RSST would request that the station increase the attenuation in the rf path in 6 dB steps on a channel-by-channel basis. The effect of each 6-dB increase in attenuation would be assessed before additional increments are added. 6.4.8 Major OD Error Resulting in Event Time Shifts The RSST would request time offsets in the ODA to correct the problem. Frequency offsets would be requested, if necessary, to compensate for non- linear effects. 6.4.9 Non-Performance of Pre-Pass Calibration at Prime 64-Meter Station The RSST would request that the station perform a post-pass calibration. If, due to an adverse weather situation, a postpass calibration is not possible, the RSST would request that the station freeze its configuration until the calibration procedure can be performed. 6.4.10 Loss of Real-Time NRS Data Visibility at JPL The RSST would inform the Representative as to the outage and request that he increase the level of verbal reporting. Also, if the problem is in an RTM, the RSST would instruct the NOCC to hold the last DTV displays in order to make hardcopies before the system is reinitialized (either warm or cold load). 34 4/23/81 6.4.11 Loss of open-Loop Signal Due to ODA Predict Set Errors The RSST would estimate how long the outage will exist. The RST would then the ascertain if valid points exist in the contingency sets on the ODA disk to solve the anomaly. The RSST would request a switch to a contingency set if the duration of the outage is unacceptable. ODA frequency offsets will be used as a last resort. 6.4.12 Unavailability of Key Personnel A vacancy in the real-time operations assignment will be filled by the Radio Science Experiment Representative, RSST Software Engineer, and RSST Test Operations Engineer in that order. 6.4.13 Failure of RSS Display Hardware in MSA The RSST would request emergency maintenance and would utilize the alternate work station on the third floor if necessary, relying on verbal reports from the Operations Advisor via the MISD net. The Operations Coordinator would ascertain the desirability of assigning one of the real-time operations personnel to the third floor. At the minimum, two real-time operations people will be required in the Mission Support Area for voice net communications. 6.4.14 Voice Line Outage Between JPL and Station(s) The RSST would inform the ACE of the outage and use the Project's operational net, ACE-to-OPCH, if operable. The Radio Science Representative will act at his own discretion until lines are back in operation. 6.5 RSST Support of the Maneuver Anomaly Recovery Plan During the encounter period, a Radio Science Operations Coordinator will be on-call in the event of an off-Earth-line maneuver anomaly, as identified in the Project duty roster. If an anomaly occurs, the Operations Coordinator will be notified by the ACE via telephone, beeper, or ESP, and should be on-line at the radio science desk in the MSA within one hour of notification. In addition, the ACE will notify the on-duty Science Operations Coordinator, who will man the VTR in the RSST's third floor operations room for recording the SSI display. The Operations Coordinator will advise the ACE on the operation of the ODA/SSI via the standard operations net. He will also assist the Telecom Engineer in determining the time of peak signal level. Specific functional responsibilities and interactions with the Project and DSN are detailed in the Voyager 35 4/23/81 Network Operations Plan (618-828) and the Spacecraft Contingency Plan (618- 538) and will not be further detailed here. The openloop system will be configured in the narrow-band mode, with the SSI configured for X-band. Specific settings are contained in Table 6-4. Figure 6-2 contains the recovery plan timeline. TABLE 6-4 MANEUVER ANOMALY RECOVERY PLAN OPEN-LOOP SYSTEM CONFIGURATION ODA CONFIGURATION Mode: Narrow Band OLR Filters: 500 Hz S-band/500 Hz X-band Sample Rate: 1 kHz SSI CONFIGURATION Port: ODAN SSI Channel: X-RCP (Channel 9) SSI Bandwidth: 5 kHz Center Frequency: 2.5 kHz Transform Size: 1024 Number of Averages: 32 36 4/23/81 7.0 DATA HANDLING AND DELIVERY As the final link in the Radio Science Ground Data System, this section will describe the RSST Data Records System, the data collection, processing, validation and delivery procedures, and the quick-look and final data strategies required to support the radio science investigation. The description of the RSST Data Records System will include the sources of the data, the processing and library facilities, and the final destinations of the various data products. The second section will discuss the procedures which each of the RSST data types must follow from collection to delivery. The third and fourth sections will detail the strategies for quick-look and final data production. Note that this section does not describe the handling and delivery of the celestial mechanics data products. The radio science investigator who analyzes the celestial mechanics data will obtain the required products by arrangement with the Voyager Navigation Team rather than through the RSST Data Records System. 7.1 RSST Data Records System The RSST Data Records System includes the software and procedures required to convert the data collected in support of radio science observations to data products which are usable by the investigators. Figure 7-1 is a block diagram of this system. The figure is arranged such that the data sources are to the left, the final data destinations are to the right, and the required processing and library facilities are in between. The following subsections describe those elements of the RSST Data Records System. 7.1.1 Data Sources The radio science data sources shown in Figure 7-1 are DSS43, the NOCC, the Voyager Navigation Team (NAV Team), the Voyager Spacecraft Team (SCT), and the Voyager Science Data Team (SDT). The data types generated by each of these entities are shown on the figure and are described in detail in Section 7.2 below. 7.1.2 Data Processing and Library Facilities The facilities required to transport and process the various radio science data types are scattered throughout the JPL organization. These facilities include the DSN Network Data Center (NDC) in Building 230 through which all DSN data must be released to the Project, the IBM 360 library in Building 230, the Information Processing Center (IPC) 1100/81 computer and library which are located off-Lab, the DSN's CTA-21 facility in Building 125, and the Radio Occultation Data Analysis (RODAN) Facility's Prime computer and library in Building 230, The role of each of these processing and library facilities in the collection, processing, 37 4/23/81 validation, and delivery of each of the radio science data types is described in Section 7.2. 7.1.3 Data Destinations After completion of all data preparation processes, the data products must be archived at JPL and shipped to the Voyager Radio Science Team (RST) investigators who are located at Stan-ford University, SRI International, and JPL. The details of the delivery procedures for each of the radio science data types is described in Section 7.2. 7.2 Data Collection, Processing, Validation, and Delivery Procedures The following subsections describe the flow of each radio science data type through the RSST Data Records System. This flow of data products from collection, through processing and validation, to delivery is shown in a left- to-right sense in Figure 7-1 7.2.1 Closed-Loop Tracking Data (Procedures for the tracking IDRs and ATDFs are TBS.) 7.2.2 Medium-Band Open-Loop Data (Procedures for the MBODRs. MBIDRs, and POCA taps are TBS.) 7.2.3 Wide-Band Open-Loop Data (Procedures for the WBODRs and WBIDRs are TBS.) 7.2.4 Spacecraft Trajectory Data (Procedures for the CRS tapes are TBS.) 7.2.5 Spacecraft Engineering Data (Procedures for the RSSEDRs are TBS.) 7.2.6 Maneuver Design and Reconstruction Data (Procedures for the POEAS runs, maneuver design specification tapes, and maneuver reconstruction tapes are TBS.) 7.2.7 Hardcopy Data (Procedures for the delivery and disposition of hardcopy data from DSS-43 are TBS.) 38 4/23/81 7.3 Quick-Look Handling and Delivery Strategy The RSST must deliver a number of quick-look data products to the radio science investigators within a very short period of time following the occultation and ring-scattering events. This data set will include closed-loop tracking data covering the occultation ingress and egress measurements, mediumband and POCA data covering a several-minutes long period to be determined and requested in near-real time, supporting spacecraft engineering data, hardcopy data from DSS-43, and a spacecraft trajectory reconstructed from post-encounter data. These data will be used by the investigators to prepare quicklook results for the Project-sponsored press conferences and the "30-day" report. the following paragraphs discuss the scientific significance and processing strategy for each of the quick-look data types. The strategies and delivery schedules are summarized in Table 7-1. 7.3.1 Closed-Loop Tracking Data (See Table 7-1 under "Quick-Look TRK IDR"--details TBS.) 7.3.2 Medium-Band Open-Loop Data (See Table 7-1 under "Wide-band playback MBIDR, POCA"--details are TBS.) 7.3.3 Spacecraft Trajectory Data (See Table 7-1 under "CRS Tape"--details are TBS.) 7.3.4 Spacecraft Engineering Data (See Table 7-1 under "DIS dump of agc/PPM . . ."--details are TBS.) 7.4 Final Data Handling and Delivery Strategy The final data set differs from the quick-look data set in four ways: (1) The final data set will include tracking data (in the form of ATDFs) from the DSS-42, 43, and 44 occultation passes whereas the quick-look data set contained only brief spans of tracking data; (2) The quick-look data set essentially omitted the openloop data products whereas the final data set will include medium-band data ready for use by the investigators. Wide-band backup data will be prepared for analysis only if necessary. POCA data containing system noise temperatures and open-loop receiver tuning information will also be included in the final data set; 39 4/23/81 (3) There will be a final trajectory tape generated by the Navigation Team about three months after the encounter; and (4) There will be a maneuver reconstruction tape generated by the Spacecraft Team about one month after the encounter. Detailed discussions regarding the preparation of each data type in the final data set are included in the following paragraphs. The final data strategies and delivery schedules are summarized in Table 7-1. 7.4.1 Closed-Loop Tracking Data (See Table 7-1 under "Final TRK IDRs . . ."--details are TBS.) 7.4.2 Medium-Band Open-Loop Data (See Table 7-1 under "MBODRs"--details are TBS.) 7.4.3 Wide-Band Open-Loop Data (See Table 7-1 under "Backup wide-band . . ."--details are TBS.) 7.4.4 Spacecraft Trajectory Data (See Table 7-1 under "CRS Tape"--details are TBS.) 7.4.5 Spacecraft Engineering Data (See Table 7-1 under "RSSEDR"--details are TBS.) 7.4.6 Maneuver Reconstruction Data (Details are TBS.) 7.4.7 Hardcopy Data (See Table 7-1 under "DIS dump of agc/PPM . . ."details are TBS.). 40 4/23/81 TABLE 7-1 DATA PRODUCTS STRATEGY AND DELIVERY SCHEDULE EVENT DATA TYPE DELIVERY STRATEGY DELIVERY SCHEDULE Saturn Ingress Quick-Look TRK IDR Tape delivery from NDC to 360 library Data period: 238/04:00 - for delivery to IPC. Tape ID will be 238/06:00. Initial delivery communicated to RSST via NOPE over TRK to IPC by 06:30 UTC (23:30 ANAL 2 NET. (Special runner to IPC PDT) return of ATDF (result- will be required for timely delivery) ant data product) within 30 after tape processing has been comple- minutes after completion of ted at IPC, RSST will request a special processing at IPC. delivery from IPC to Building 230, Room 105C RODAN Facility for quick-look analysis of ATDF. Saturn Egress Quick-Look TRK IDR Same as above. Data period: 238/06:50 - 238/07:45. Initial delivery to IPC by 08:15 UTC (01:15 PDT) return of ATDF (result- ant data product) within 30 minutes after completion of processing at IPC. Saturn Final TRK IDRs for Tape delivery from NDC to 360 library All IDRs to be delivered Occultation both Voyager 1 and for delivery to IPC. Tape IDs will be within 12 hours following and Ring 2 passes. communicated to RSST Data Records the completion of the radio Scattering Coordinator x7846 or x4991 via the science events at 238/08:20. NOPE. RSST will coordinate the return Tapes should be at IPC by of data tapes from IPC after processing 14:20 PDT on August 27. has been completed on an individual basis. Wide-band playback Tape delivery from NDC to RSST RODAN Start MBIDR wide-band play- MBIDR, POCA Facility, Building 230, Room 105C. back at 238/08:30 UTC. MBIDR playback has priority over POCA Delivery to RSST will be data playback. within one hour following the completion of each playback data set. TABLE 7-1 (Continued) EVENT DATA TYPE DELIVERY STRATEGY DELIVERY SCHEDULE CRS Tape Delivery from NAV to RSST via tape CRS data periods and interface at IPC. release schedule is TBD. RSSEDR Delivery from SDT to RSST via tape Delivery will be accom- interface at IPC. plished as soon as possible following the merger of the SASDRS files but no later than one week following the occultation events. MBODRS (9 tapes) Following the radio science occulta- Delivery of expedited data tion events, the Station Representative should be within two weeks will relay the MBODR ID numbers to the following the occultation. RSST via the Radio Science Coordination A desirable goal is to have Net. The station will copy the MBODRs the data at JPL in one week. and expedite shipment of the MBODR copies Original data will be re- to NDC JPL, attention: N. Fanelli. For quested within one week final delivery to the RSST RODAN Facility following the completion of Building 230, Room 105C. The RSST will data validation. log in the MBODRs and arrange for re- duction to IDRs with CTA-21 delivery to CTA-21 will be via Interface Agreement NOCT-30. Original MBODRs will be requested from the station by the RSST after the MBIDRs have been validated. DIS dump of AGC/ Deliver with expedited MBODR copies. Same as MBODR copies. PPM data terminet printout and SNT stripchart Backup wide-band Following the radio science occultation Expedited delivery upon DRA ODRs (20 tapes) events, the Station Representative will request of specific tape(s) relay the wide-band ODR ID numbers to by the RSST. It is desir- the RSST via the Radio Science Coordina- able to have shipment arrive tion Net. Upon request from RSST of a at JPL within one week fol- specific time period, the station will lowing request. TABLE 7-1 (Continued) DELIVERY STRATEGY copy the appropriate DRA ODR, shipping the requested tapes to NDC, JPL attention: N. Fanelli for delivery to the RSST RODAN Facility, Building 230, Room 105C. Originals will be requested following validation of copy(s). TABLE A-1 MAJOR EVENT SUMMARY FOR SATURN AND RINGS, (Note: All times are approximate-- the ISOE is the controlling document.) TIME (ERT) EVENT 04:01 1. Fix subreflector focus for 450 elevation. 04:11 2. Begin roll turn to clear VRDYN obscuration. X-band signal begins gradual 1 dB decrease. 04:17 3. Turn CONSCAN off. 04:18 4. End roll turn. 04:25 5. Start MB and WB recording. Begin collection of open-loop S/X data for calibration purposes. 04:35 6. Begin FSMAN3 roll turn. X-band signal gradually decreases 2 dB, then gradually increases 1 dB. 04:52 7. End roll turn. 04:54 8. S/C executes boresight correction turn. X-band signal increases to pre-roll level. 04:59 9. Configure downlink for occultation. TWTA power modes changed to S-HI/X-LO. S/X telemetry drivers and ranging channels off. (Net signal increases of 10.3 dB S-band 13.1 dB X-band.) 05:03 10. TWNC On. S/C switches to stable on-board frequency reference (USO) for occultation measurement. Ground station goes to non-coherent two-way tracking. 05:10 11. Begin ionospheric occultation. Measurement of topside ionosphere primarily affects S/X doppler; signal levels stable. 05:24 12. Ionospheric occultation (entrance). Complex signal structure expected. Large 4/23/81 TABLE A-1 (Continued) signal level fluctuations and possibly large frequency excursions observed. 05:27 13. Nominal start of atmospheric occultation. Rapid decrease in S/X signal levels during first few minutes with probable large excursions in doppler pseudo-residuals. Signal dynamics can be monitored with SSI for at least several minutes. Part I of limb-tracking maneuver begins. 05:31 14. Probable loss of S/X signal. 05:32 15. End of limb-tracking maneuver (Part I). Latest possible loss of X-band signal. 05:39 16. Latest possible loss of S-band signal. 06:27 17. Begin ring-scatter experiment. S/C maneuvers to track rings while behind planet. Only signals scattered by rings will reach Earth, may be too weak to observe on SSI. 06:52 18. End of ring-tracking maneuver. Perform yaw turn to position S/C for start of limb-tracking maneuver, Part II. Earliest possible reappearance of S-band signal on SSI. 06:54 19. Begin limb-tracking maneuver (Part II). Earliest possible reappearance of X-band signal on SSI. 06:57 20. Probable reappearance of S/X signals. Rapid signal strength increase. 07:01 21. Exit atmospheric occultation. End limb-tracking maneuver (Part II). S/X signals return to pre-occultation levels. 07:04 22. Exit ionospheric occultation. Possible large fluctuation in signal strength and frequency. 07:07 23. S/C executes roll turn to align UVS slit. Negligible change in signal strength expected. 4/23/81 TABLE A-1 (Continued) 07:08 24. End roll turn. 07:10 25. S/C boresight correction turn. Negligible change in signal strength expected. 07:26 26. S/C executes mini-ASCAL turns. X-band signal varies 5.6 dB or more; S-band signal varies 0.3 dB or more. 07:33 27. End mini-ASCAL turns. 07:34 28. Reconfigure downlink for telemetry and ranging. TWTA power modes changed to X-HI/S-LO. S/X telemetry drivers and ranging channels on. (Net signal decreases of 10.3 dB S-band and 13.1 dB X-band.) 07:39 29. Possible change from one-way to two-way tracking. (Depends upon successful real- time commanding of a TWNC-off command.) Beginning of Tethys mass determination. 07:41 30. Resume normal subreflector refocusing. 07:42 31. Turn CONSCAN on. 08:00 32. End MB and WB recording. 4/23/81 TABLE A-2 FORMULAE FOR RECONSTRUCTION OF THE ANTENNA FREQUENCY FROM THE EXTRACTED SIGNAL FREQUENCY IN THE OPEN-LOOP RECEIVER FILTERS Narrow-Band/Medium Band MMR Open-Loop Receivers (DSS-43) fs = 48 x fpo + 300 x 10^+6 + folrs fx = 11/3 x (48 x fpo + 300 x 10^+6 ) + folrx Where: fs = Antenna frequency at S-band in Hertz fx = Antenna frequency at X-band in Hertz fpo = Programmed oscillator frequency in Hertz folrs = Extracted signal frequency in the S-band open-loop filter in Hertz folrx = Extracted signal frequency in the X-band open-loop filter in Hertz Note: fpo = Approximately 41 x 10^+6 Hertz at DSS-43 fx/fs = 11/3 for all tracking modes 4/23/81 TABLE A-3 RECEIVED MAXIMUM POWER LEVELS AND SPACECRAFT FREQUENCIES FOR THE 64-METER SUBNET DURING THE VOYAGER 2 NEAR ENCOUNTER Received maximum power levels for: Saturn occultation entrance (DSS-43) S-band Low Power = TBD dBm Ring-Scattering Observation X-band High Power = TBD dBm (DSS-43) Saturn Occultation Exit (DSS-43) Voyager 2 USO frequency (before Doppler): 2296.481098 MHz* Voyager 2 auxiliary oscillator frequency (before Doppler): 2295.000280 MHz** * This USO frequency has not been adjusted for the effect of radiation at Saturn--these effects are expected to be very small (approximately 1 Hz). ** This auxiliary oscillator frequency is the average of the two auxiliary oscillators on-board Voyager 2. Frequency offsets would be used in real time for a particular auxiliary oscillator, if selected. 4/23/81 TABLE A-4 PHONE NUMBERS OF KEY RADIO SCIENCE PERSONNEL AND OPERATIONS STATIONS KEY RADIO SCIENCE PERSONNEL NAME WORK PHONE HOME PHONE BEEPER B. Buckles 4015 (805) 724-1356 --- P. Doms 7934/7576 (213) 797-1362 817 N. Fanelli 5541 --- --- D. Finnerty 7988/7576 (213) 797-2162 178 D. Holmes 2841 (714) 626-1773 682 B. Koppany 7988/7576 (213) 876-3944 --- R. Kursinski 7353 --- --- D. Sweetnam 6197/7576 (213) 790-6154 107 G. Tyler (415) 497-3535 (415) 327-7648 --- (Stanford) OPERATIONS STATIONS STATION WORK PHONE Voyager ACE 7882 Data Chief 7711 NATTRK 7810/7911 Ops Chief 5858 Ops Con 5994 Radio Science/MCT 7835 Radio Science/RSST 7985/7359 Support Chief 7955 Telecom/MCT 7871 NOPE 5868 4/23/81 TABLE A-5 VOYAGER RADIO SCIENCE PRE-PASS COUNTDOWN LOG 1. Radio Science Representative: DOY HHMMSS: 2. Zenith System Temperatures: SPD: XR01: MOD3: XR02: 3. Maser Configuration: MASER POLARIZATION SPD MOD3 XR01 XR02 4/23/81 TABLE A-5 (Continued) 4. DTS AGC Calibration Curves (Paste calibration curves here.) 4/34/81 TABLE A-5 (Continued) 5. MEDIUM-BAND OLR/ODA/DRA CONFIGURATION CONFIGURATION CALIBRATION SIGNAL SPECTRA FRE- BAND FILTER RCVR QUENCY POLAR- MASER ATTEN- WIDTH SERIAL OUTPUT SIGNAL SNR LINEARITY BASEBAND COMPOSITION CHANNEL BAND IZATION UATOR (KHZ) NUMBER LEVEL LEVEL FREQUENCY 1 2 3 4 A/D Drive Signal: Input Frequency (S-band): Sample Rate: Recorder Speed: 4/23/81 TABLE A-5 (Continued) 6. WIDE-BAND OLR/DRA CONFIGURATION CONFIGURATION CALIBRATION SPECTRA FREQUENCY RECEIVER RCVR 2ND LO BAND RECEIVER OUTPUT SIGNAL BASEBAND CHANNEL FREQUENCY POLARIZATION MASER ATTENUATOR BANDWIDTH LEVEL LEVEL FREQUENCY COMPOSITION 1 2 3 4 First LO Frequency: Combined Signal A/D Drive: Recorder Speed: Sample Rate: 4/23/81 TABLE A-5 (Continued) 7. PPM Configuration RECEIVER BAND POLARIZATION 1 2 3 4 Mode: 8. Sim Synthesizer Frequency: 9. Calibration Pads Removed: 10. Weather 4/23/81 TABLE A-6 STATION CONFIGURATION CHECKLIST FOR DSS-42 1. Verify that Level 1 Prepass Readiness Tests per procedure 853-103; 5A-01 have been performed for the following systems: TEST COMPLETED a. Tracking System b. Command System c. Monitor and Control System 2. Closed-Loop System Checks a. Receivers S-band: 2BLO = 12 Hz AGC = Narrow X-band: 2BLO = 12 Hz AGC = Narrow b. DIS AGC TOL = 2 c . MDA Doppler sample rate = 1 per second 4/23/81 TABLE A-7 STATION CONFIGURATION CHECKLIST FOR DSS-43 1. Verify that Level I Prepass Readiness Tests per procedure 853-103; 5A-01 have been performed for the following systems: TEST COMPLETED a. Tracking System b. Command System c. Monitor and Control System 2. Closed-Loop System Checks a. Receivers - S-band: SRCP = RCVR 2 SLCP = RCVR 1 2BLO = 12 Hz AGC = Narrow, unless otherwise specified in the ISOE X-band: XRCP = RCVR 4 XLCP = RCVR 3 2BLO = 30 Hz AGC = Narrow, unless otherwise specified in the ISOE b. DIS - AGC TOL = 2 AGC information to line printer c. MDA - Predict Sets - TBD CH1/CH3 enabled, separate predicts required for each channel. Doppler sample rate: 1 per 10 seconds, unless otherwise specified in the ISOE. d. PPM - Four channel configuration monitor S-band RCP/LCP and X-band RCP/LCP system noise temperatures. Auto mode. 4/23/81 TABLE A-7 (Continued) 3. Open-Loop System Checks a. Prime Receiver (Medium-Band) Filter Select = 8 Bandwidth: S-band = 50 kHz X-band = 150 kHz Calibration Signal Levels: S-band RCP/LCP = TBD X-band RCP/LCP = TBD Receiver Calibration Output Power Levels: S-band RCP/LCP = TBD X-band RCP/LCP = TBD b. Back-up Receivers Calibration Signal-Levels: S-band RCP/LCP = TBD X-band RCP/LCP = TBD Receiver Calibration Output Power Levels: TBD S- and X-band First LO Synthesizer Frequency: TBD Channel 1 Second LO Frequency TBD Channel 2 Second LO Frequency TBD Channel 3 Second LO Frequency TBD Channel 4 Second LO Frequency TBD c. ODA - Configure for medium-band recording, pass-dependent parameters are: MSB 300K SCN 32 PRD TBD d. DRA - DRA #1 medium-band recorder, IPS = 30 DRA #2 wide-band recorder, IPS = 120 e. SSI - As per ISOE. 4/23/81 TABLE A-7 (Continued) 4. Microwave Subsystem SPD = SRCP MOD-3 = SLCP XR02 = XRCP XR01 = XLCP 4/23/81 TABLE A-8 STATION CONFIGURATION CHECKLIST FOR DSS-44 1. Verify that Level 1 Prepass Readiness Tests per procedure 853-103; 5A-01 have been performed for the following systems: TEST COMPLETED a. Tracking System b. Command System c. Monitor and Control System 2. Closed-Loop System Checks a. Receivers S-band: 2BLO = 12 Hz AGC = Wide, unless otherwise specified in the ISOE b. DIS AGC TOL = 2 c. MDA Doppler sample rate = 1 per 10 seconds, unless otherwise specified in the ISOE. 4/23/81 TABLES A-9a THROUGH A-9z NOCC DISPLAY/GRAPHICS REQUESTS (One request form per required display.) - TBD - 4/23/81 TABLE A-10 ABBREVIATIONS AND ACRONYMS A/D Analog-to-digital converter ACE Voyager Mission Controller agc Automatic gain control signal level AOS Acquisition of signal at a DSS ASCAL Antenna-Sun-sensor calibration (spacecraft) ATDF Archival Tracking Data File tape ATZ Automatic triggering zero-beat detection AUX OSC One of two auxiliary oscillators in the spacecraft BLF Best-lock frequency (spacecraft receiver) BLK III Closed-loop receiver (design phase III) BLK IV Closed-loop receiver (design phase IV) BUSS Voyager Spacecraft Monitor Controller COH Coherent downlink CONSCAN Computation of antenna pointing angles from signal- level information CRS Celestial Reference System orbit determination tape CTA-21 DSS mock-up at JPL D/A Digital-to-analog converter Dl Predicted one-way downlink frequency DIS Digital Information Subsystem DOY Day of year (UTC) DRA Digital Recording Assembly DRS DSS Radio Science Subsystem DSN Deep Space Network DSS Deep Space Station DST Data System Terminal DTV Video data monitoring display device ESP Extra-Sensory Perception (an RSST prerequisite) GCF Ground Communications Facility GDS Ground Data System HGA High-gain antenna (spacecraft) IDR Intermediate data records tape IPC Information Processing Center (JPL computer facility) ISOE Integrated Sequence of Events LCP Left-handed circularly polarized LO Local oscillator LOS Loss of signal at a DSS MB Medium-band MBIDR Medium-band open-loop data records tape (computer-compatible) 4/23/81 TABLE A-10 (Continued) MBODR Medium-band open-loop data records tape (not computer-compatible) MCT Voyager Mission Control Team MDA Metric Data Assembly MISD Mission Director's Voice Net MMR Multimission receiver (open-loop) MSA Project mission support area NB Narrow-band NCOH Non-coherent downlink NOA Network Operations Analyst NOCC Network Operations Control Center NOPE Network Operations Project Engineer NRS NOCC Radio Science Subsystem OCI Operator control input (into the DST) OCT Voyager Operations Coordination Team OD Orbit determination by the Project's Navigation Team ODA Occultation Data Assembly ODR Original data records tape OLR Open-Loop Receiver OPCH DSN Operations Chief ORT Operational Readiness Test PCT Polynomial coefficient tape POCA Programmable Oscillator Control Assembly POEAS Software used to generate tuning predicts during atmospheric occultation PPM Precision Power Monitor PRA Planetary Ranging Assembly RCP Right-handed circularly polarized rf Radio frequency RODAN Radio Occultation Data Analysis Computer Facility RSS Radio Science System RSST Radio Science Support Team RST Radio Science Team (investigators) RSWG Radio Science Working Group RTLT Round-trip light-time between Earth and the spacecraft RTM Real-Time Monitor (supplies data to NOCC graphics/ display systems) SNR Signal-to-noise ratio SOP Standard Operations Procedures SSI Spectral Signal Indicator TTS Test and Telemetry System TWM Traveling wave maser TWNC Two-way non-coherent switch (spacecraft) 4/23/81 TABLE A-10 (Continued) TWTA Traveling wave tube amplifier (spacecraft) TWX Teletype message TXR DSS transmitter USO Ultra-stable oscillator (spacecraft) VTR Video tape recorder WB Wide-band WBIDR Wide-band openloop data records tape (computer compatible) WBODR Wide-band open-loop data records tape (noncomputer compatible) X3MASS Radio science Tethys mass determination experiment XPOCC Radio science Saturn occultation experiment XRSCAT Radio science ring-scattering experiment XSCEL Radio science celestial mechanics experiment 4/23/81