VOYAGER 1 SATURN ENCOUNTER RADIO SCIENCE OPERATIONS PLAN 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 X5MASS) 2.3 Atmosphere/Ionosphere Occultations 2.4 Ring Observations 2.5 Major Events Summary and Expected Signal Profiles 3.0 Radio Science GDS Configuration 3.1 Introduction 3.2 The Deep Space Stations 3.3 The Ground Communications Facility 3.4 Network Operations Control Center 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 3.9 Ground Data System Configuration Requirements 4.0 Radio Science Encounter Timelines 4.1 Extended Timeline DOY 308 to 328 4.2 Near Encounter Timeline DOY 317 and 318 5.0 Tracking and Radio Science System Operations 5.1 Titan Occultation Uplink and Downlink Strategies 5.2 Low Elevation Antenna Pointing 5.3 Saturn Uplink and Downlink Acquisition Strategies 5.4 Use of the SSI for Receiver Acquisition 5.5 Radio Science Operations 6.0 Real-Time Operations 6.1 Functional Responsibilities 6.2 Operations 6.3 Operations Schedule - 1 - 6.4 Contingency Planning 7.0 Data Handling and Delivery 7.1 Data Products List and Delivery Schedule 7.2 Near-Real-Time Data Processing 7.3 Post Encounter Medium-Band Data Conversion -2- 1.0 INTRODUCTION The purpose of this Plan is to coordinate all ground support activities contributing to the success of the Radio Science Experiment at the Voyager I Saturn encounter. It is intended to provide descriptive material relative to the observations, as well as to directly specify detailed supporting events necessary to assure operational success. The controlling document for the conduct of Project operations is the Integrated Sequence of Events (ISOE). This document supplements the ISOE and elements of this document are referenced in the ISOE (checklists, etc.). Should any conflict arise between activities specified herein and those in the ISOE, the ISOE-specified events shall take precedence. The Voyager 1 Saturn encounter plans five major Radio Science observations. These five 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 (Section 8.0) contains amplitude and frequency profiles predicted for the occultation events. A detailed listing of the scientifically relevant events and periods is also contained in the Appendix. MAJOR VOYAGER 1 RADIO SCIENCE OBSERVATIONS Celestial Mechanics (XSCEL) - Maps gravity field of planet, rings, (Entire 64-meter network, and satellites. Spacecraft sequence +/-10 days) is routine. Utilizes closed-loop doppler and range tracking. Titan Occultation (XTOCC) - Investigates atmosphere and iono- (DSS-63, 11/12/80 UTC) sphere of Titan. Involves spacecraft maneuver and downlink carrier power switches. Utilizes both open-loop (medium band) and closed-loop data. Saturn Occultation (XPOCC) - Investigates atmosphere and iono- DSS-43 set and DSS-63 sphere of Saturn. Involves space rise, 11/13/80 UTC) craft maneuver and downlink carrier power switches. Utilizes both open loop (narrow band at DSS-43, medium band at DSS-63) and closed-loop data. Ring Occultation (XROCC) - Investigates microwave transmission (DSS-63, 11/13/80 UTC) and scattering properties of the ring particles. Begins immediately following the exit from atmospheric occultation at Saturn, Uses both open-loop (medium band) and closed loop data. -1.1- Ring Scattering (XRSCAT) - Investigates microwave scattering (DSS-63, 11/13/80 UTC) properties of rings at oblique angles. Spacecraft maneuvers to track desired region of rings. Utilizes only open-loop (medium band) data. Section 3.0 describes Ground Data System elements supporting the acquisition of Experiment data and contains a functional block diagram of instrumentation required to complete the observations. The equipment at the 64-meter stations has been specially configured for the Saturn encounters and 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 10-day period. The second covers the plus-and-minus 2-day period and expands on the events of the first timeline. Associated Project milestones are also shown on the timeline where directly or indirectly related to the operations supporting the Experiment. Section 5.0 discusses the operational strategies planned for utilizing the Tracking and Radio Science Systems of the DSN. Uplink and downlink tuning strategies are presented for closed-loop and open-loop data acquisition. Special antenna-pointing procedures are described that aid in the optimization of downlink amplitude measurements at low-elevation angles. 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 depicted in Figures. A special discussion characterizes the role of the Radio Science Representatives dispatched to the overseas stations in support of the Experiment.. Section 7.0 briefly describes the considerations and planning for handling and delivery of data products in the post-acquisition period. The material in this section addresses only the events and interfaces for data delivery that are external to the Project. The ultimate delivery of the products to investigators of the Radio Science Team is controlled by internal Project procedures developed by the Radio Science Support Team. Such procedures are not duplicated herein. 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. -1.2- 2.0 Radio Science Observation Description 2.1 Overview of the Saturn Encounter Radio Science observations with Voyager I span the entire encounter period from 82 days before Saturn closest approach until 35 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 Titan, Saturn, and ring radio occultations, 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). Several significant 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. Also, two solar conjunction experiments were carried out for several weeks in August, September, and October at the beginning of the encounter period. The data taken during those experiments will be used to investigate the spatial and temporal variations of the solar corona and to determine the gravitational time delay induced by the passage of the raypath near the Sun. 2.2 Celestial Mechanics Experiments (XSCEL and X5MASS) 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 one-way 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 one-way 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 field of Saturn, its satellites, and its rings by examining their effect on the spacecraft's trajectory; the Rhea and Titan mass determinations, in particular, are expected to yield significantly improved values. In addition, all of the dual-frequency tracking data will be used to characterize the Saturn system plasma environment. * 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. -2.1- 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 Atmosphere/Ionosphere Occultations 2.3.1 Titan Radio Occultation (XTOCC) The Titan radio occultation occurs about 18 hours before Saturn encounter at a spacecraft-to-limb range of approximately 10,000 - 20,000 km as shown in Figure 2-3. The occultation, as seen from Earth, will be diametric so as to allow the deepest possible atmospheric penetration of the raypath to Earth. The expected duration of the occultation is approximately 12 minutes. The objectives of the Titan occultation experiment can be summarized as follows: - Measure atmospheric temperature and pressure as a function of height and contribute to the determination of atmospheric constituents; - Investigate the microwave absorbing properties of the atmosphere; - Determine ionospheric profiles and plasma densities at the entrance and exit locations on Titan; and - Measure the radius of the solid surface and help determine the mean density of Titan. The spacecraft will be sequenced to optimize the downlink configuration and to perform the entrance and exit measurements at selected HGA-Earth offset angles. The S-band downlink power will be maximized by turning off the ranging channel and telemetry drivers and by setting the TWTA 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 Titan occultation ingress measurements will be made with the spacecraft's HGA boresight offset 0.11' from Earth in the direction shown in Figure 2-3. This offset is obtained by performing a gyro-drift turn prior to ionosphere entrance; the amount of offset was selected to optimize dual- frequency ionosphere and upper atmosphere measurements. After completion of the entrance measurements, the spacecraft will be drift-turned to offset the HGA boresight 2.36' from Earth in preparation for the exit measurement (as shown in Figure 2-3). This offset angle will provide for a continuous S-band measurement for a thick atmosphere (from the surface of Titan to the ionosphere) with a brief dual-frequency measurement possible at one depth only (approximately the 1-bar level). After ionospheric occultation exit, the boresight will be realigned with Earth by a third gyro-drift turn. Finally, a "mini-ASCAL" maneuver has been sequenced which uses gyro-drift turns to move the HGA boresight in a +/-0.4' cross-hair pattern about the Earth direction. This -2.2- maneuver will be used to aid in the reconstruction of the spacecraft's attitude during the Titan occultation measurements. After the completion of the mini-ASCAL, the downlink is reconfigured for telemetry and celestial mechanics tracking and ranging. The ground events for the Titan occultation occur primarily at DSS-63. However, DSS-62 will provide S-band, closed-loop occultation backup coverage and DSS-61 will perform dual-frequency, closed-loop tracking of Voyager 2 (which is near Voyager 1 in the sky) in order to obtain independent measurements of the solar plasma for calibration of the occultation data. DSS- 63 will be tracking Voyager 1 during the Titan occultation with CONSCAN off and a fixed subreflector focus position so as to remove station-induced signal variations from the data. The occultation downlink will be recorded on the medium-band, open-loop system in the two-channel configuration. Ionospheric data will also be obtained from the closed-loop system. 2.3.2 Saturn Radio Occultation (XPOCC) The Saturn radio occultation begins approximately 100 minutes after Saturn closest approach and lasts for about 90 minutes. As shown in Figure 2-4, the spacecraft enters occultation in the high southern latitudes and exits occultation near Saturn's equator. The spacecraft will perform a limb-tracking maneuver for the duration of the occultation, with the exception of a 35- minute period when the spacecraft is held still for the benefit of the UVS Sun occultation exit measurement. The limb-tracking maneuver is 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.) As can be seen in Figure 2-4, the virtual image travels from the entrance point, around the south polar region, then north to the equator during the occultation; thus, atmospheric occultation data will be obtained in all of these regions. 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 microwave-absorbing properties of the atmosphere, and determine the ammonia abundance; - Determine the structure and characteristics of Saturn's ionosphere; - Measure the oblateness of Saturn; - 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. -2.3- The spacecraft will be sequenced to optimize the downlink for atmospheric measurements at occultation entrance and to optimize for ring measurements at occultation exit. The switch to ring optimization is done during atmospheric occultation so as to avoid changing downlink configuration during a possibly nonexistent "gap" between upper atmosphere and inner rings. The atmospheric downlink configuration is the same as that used for the Titan occultation. The ring configuration is the same, but with the X-band TWTA in the high-power mode and the S-band TWTA in the low-power mode. The limbtracking maneuver will be performed in two parts during the time periods shown in Figure 2-4. Part I is a series of eight gyro-drift turn segments and Part II consists of two segments. The ground events for the Saturn occultation occur primarily at DSS-43 for the entrance measurements and at DSS-63 for the exit measurements. Due to general mission planning considerations and science trade-offs which were made during the trajectory-selection process, DSS-43 sets about one minute before occultation exit and DSS-63 rises about halfway through the occultation. This geometry necessitated the development of special low-elevation tracking procedures designed to maintain accurate antenna pointing during periods of extreme signal dynamics. DSS-44 and DSS-62 will provide S-band, closed-loop occultation backup coverage, and DSS-42 and DSS-61 will perform dual- frequency, closed-loop tracking of Voyager 2 to obtain independent measurements of the solar plasma for calibration of the occultation data. DSS- 43 and DSS-63 will track Voyager I with CONSCAN off and a fixed subreflector focus position so as to remove station-induced signal variations from the data. The occultation downlink will be recorded on the narrow-band, open-loop system at DSS-43 and on the four-channel, medium-band, open-loop system at DSS-63. Ionospheric data will also be obtained from the closed-loop system. 2.4 Ring Observations 2.4.1 Radio Ring Occultation (XROCC) The ring occultation occurs immediately after the Saturn occultation exit. The rings may extend into the planet's atmosphere; therefore, the trajectory was targeted to exit the atmospheric occultation as close as possible to the equator so as to provide a ring-plane occultation at a very low altitude (see Figure 24). The ring occultation thus lasts from the atmosphere of Saturn until exit from "F" ring occultation. The "F" ring is the outermost visible ring; its approximate location is shown in Figure 2-4. The duration of the ring occultation measurements is approximately 27 minutes. The objectives of the ring occultation experiment can be summarized as follows: - Map the optical depth of the rings at two radio wavelengths versus radial distance with high (<100 km) radial resolution; - Determine the predominant particle size; and - Determine the number of particles per unit area (,and thus the mass of the rings). -2.4- The spacecraft HGA will remain pointed at Earth for the duration of the ring occultation and the downlink configuration will be the same as that used during the Saturn occultation exit: X-band high power, S-band low power, ranging channels off, telemetry drivers off, and TWNC on. As during the Titan and Saturn exit occultations, the primary ground events will occur over DSS-63 while DSS-62 provides S-band, closed-loop backup coverage and DSS-61 tracks Voyager 2 for the purpose of solar plasma calibration. Once again, open-loop recording will be performed at DSS-63; however, the ring occultation drives a different open-loop configuration. Since polarization information is a primary data source, both RCP and LCP channels for S- and X-band downlink will be recorded. Also, these signals will be recorded on the medium bandwidth system because large frequency dispersions are expected during the ring occultation. As in the other observations, CONSCAN will remain off and the subreflector focus will be maintained in a fixed position so as to remove station-induced signal variations from the data. It is not expected that closed-loop lock-up will be possible during all of the ring occultation. 2.4.2 Radio Ring-Scattering Experiment (XRSCAT) The ring-scattering experiment is conducted during a period of approximately 100 minutes in duration immediately after the completion of the ring occultation measurements. The observation period is roughly centered on the time of ring-plane crossing. Figure 2-4 shows the relative timing of these events and Figure 2-5 shows the geometry of the ring-scattering observation from two different perspectives. As seen in the lower part of Figure 2-5, the spacecraft is moving away from Saturn and "up" through the ring plane. Meanwhile, the spacecraft is being maneuvered so as to track the center of the "A" ring with the HGA boresight (.see the upper portion of Figure 2-5). Prior to the ring-plane crossing, the ring scattering will be in the transmission mode; after the crossing, the scattering will be in the reflection mode. The ring-tracking maneuver is aimed at the "A" ring since this is the ring which is most likely 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 dispersion 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 a ring-tracking maneuver while retaining the downlink configuration used for the ring occultation measurements. The ring-tracking maneuver consists of five gyro-drift turn segments designed to trace out an approximation of the raypath shown in the upper portion of Figure 2-5. Another gyro-drift turn is used to rotate to the starting attitude of the ring-tracking maneuver immediately after the time of ring occultation exit. After the completion of the ringtracking maneuver (when the HGA is 12' off-Earth), commanded pitch and yaw turns return the spacecraft to Earth-line orientation. Shortly thereafter, a mini-ASCAL (,as described in the Titan occultation section) is executed to -2.5- obtain data required for reconstruction of the spacecraft's attitude throughout the Saturn occultation and ring observations. After the mini-ASCAL, the downlink is reconfigured for telemetry and celestial mechanics tracking and ranging. All of the ground events for the ring-scattering experiment occur at DSS-63. The station configuration will be identical to that described for the ring occultation, since polarization data are once again required over a large frequency range. 2.5 Major Events Summary and Expected Signal Profiles The Appendix contains tables outlining the major Radio Science events during the Titan and Saturn observation periods. The times listed in those tables are approximate--the ISOE will be the controlling document for these time periods. The Appendix also includes Figures which show the expected signal profiles for these observation periods. The Figures include 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 model calculations (since there have been no previous observations of the type undertaken here), so only the general character of the phenomenon- induced signal events can be stated with confidence. -2.6- 3.0 Radio Science GDS Configuration 3.1 Introduction Figure 3.1 is a block-diagram representation of the Voyager Radio Science System Ground Data System. The Deep Space Network Deep Space Stations are the heart of this system. In particular, DSS-63 and DSS-43 are the prime supporting stations for the Radio Science experiments at Voyager I Saturn encounter. DSS-63 supports the Titan occultation, the Saturn occultation egress, ring occultation, and ring-scattering experiments with four-channel, medium-band, open-loop receiver recording. DSS-43 supports the Saturn occultation ingress with two-channel, narrowband, open-loop receiver recording. Both stations provide wide-bandwidth, open-loop receiver recording capability as a backup to the prime narrowband and medium-band open-loop systems. In addition to the open-loop recording capability, the DSSs are supporting the experiment with closed-loop doppler and ranging data acquisition. The Precision Power Monitor measures system temperatures and transmits these data to NOCC where these data are recorded on a Monitor IDR tape that is delivered to the Voyager Radio Science Team. The Spectral Signal Indicator monitors the open-loop recording system at several points providing spectral information for the monitored signal at the DSS, NOCC, and at the Voyager Mission Support Area. The following paragraphs describe the DSS subsystems that support the Radio Science System in more detail. In addition, each of the other facilities (GCF, NOCC, Voyager MSA) and their functions are described. The narrative, in general, will describe the flow of data from receipt at the antenna through the system as indicated on the Radio Science System block diagram, Figure 3.1. 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 paragraph after the functional descriptions of the subsystems. 3.2.1 The Antenna Mechanical Subsystem The DSS-43 and DSS-63 64-meter Antenna Mechanical Subsystems function as large aperture collectors which, by double reflection, focus incoming radio frequency (S- and X-band RCP/LCP) energy into the S- and X-band feedhorns (part of the Antenna Microwave Subsystem). -3.1- 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. NOTE THE SUBREFLECTOR IS LOCKED INTO A FIXED POSITION FOR MANY RADIO SCIENCE EVENTS. SEE ISOE FOR SPECIFIC EVENTS WHICH WILL SPECIFY POSITIONS TO BE USED. The subreflector then reflects the received energy to the dichroic plate, a device that 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 MANUALLY INSERTING OFFSETS TO THE COMPUTED ANGLE PREDICT SET. SEE SECTION 5.2 FOR MORE DETAILS AND SPECIFIC OFFSETS. 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 I and so that LCP signals are directed to X- band TWM 1 and S-band TWM 2. After amplification by the masers, the signals are routed to the receiver-exciter subsystem via the microwave switching assembly. 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. -3.2- The noise diode assemblies under control of the PPM 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 20 KW. The 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 frequency down converts spacecraft-radiated S- and X-band RCP/LCP signals. The closed-loop receivers provide doppler and ranging signals to the Tracking Subsystem. Dedicated open-loop receivers provide baseband signals to the Radio Science Subsystem and fixed-tuned wide bandwidth open-loop receivers provide backup systems to the narrowband and medium-band open-loop receivers. The exciter generates the S-band drive signal provided to the Transmitter Subsystem that provides the spacecraft uplink signal. The Spectral Signal Indicator provides local displays of received signal spectrum 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 spectrum and doppler signals from the Receiver-Exciter Subsystem. It generates a range code that is routed to the exciter and modulates 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 Subsystem which produces an IN 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 predicts, and provides partial status information to the Monitor and Control Subsystem, including receiver agc levels and lock status. -3.3- 3.2.6 The Radio Science Subsystem The Radio Science Subsystem digitizes, bandwidth reduces, and records (1) very narrow; (2) narrow; and (35 medium bandwidth Radio Science data, and digitizes and records wide bandwidth Radio Science data. It receives Radio Science frequency predicts from NOCC, configuration and control data from the Monitor and Control Subsystem, and S- and X-band RCP/LCP signals from the Receiver- Exciter Subsystem. It transmits spectral information from the SSI to NOCC and the Project Mission Support Area via the GCF wideband data lines. It controls the narrow-band, open-loop receiver LO by sending frequency control information to the Receiver-Exciter Subsystem. 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 provides the communication networks required 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 predictions from the NOCC to the DSS and CTA 21 and Radio Science System performance validation data from the DSS to NOCC. 3.3.2 GCF Wideband Subsystem In real time, the Wideband Subsystem transmits SSI 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 the computer-compatible tape to the Flight Project. 3.4 Network Operations Control Center 3.4.1 NOCC Radio Science Subsystem The NOCC Radio Science Subsystem generates open- and closed-loop Radio Science DTV graphics displays and DRS status and configuration displays. -3.4- In addition, the NRS provides the planetary atmosphere refracted trajectory input (PCT) to the NOCC Support Subsystem. 3.4.2 NOCC Monitor Subsystem The NOCC Monitor Subsystem displays system temperature information and provides the monitor IDR tape upon which system temperature information is delivered to the Project. 3.4.3 NOCC Support Subsystem The NOCC Support Subsystem generates DSS frequency and tracking predicts using a polynomial coefficient tape produced by the POEAS software as input. In addition, predicts can be generated using manual inputs. 3.4.4 NOCC Display Subsystem The NOCC Display Subsystem provides the NOCC Radio Science Subsystem generated Radio Science displays to the Network Operations Control Area and to Project Radio Science areas, and provides control data to the NOCC Radio Science Subsystem. 3.4.5 NOCC Tracking Subsystem The NOCC Tracking Subsystem generates tracking system status displays and transmits them to the display subsystem to be routed and displayed. 3.5 Network Radio Science Subsystem The Network Radio Science Subsystem is located in CTA 21. It bandwidth reduces 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, generates bandwidth-reduced Radio Science data, and provides medium and wide bandwidth Radio Science data on computer-compatible tape to the Flight Project. 3.6 Mission Support Area The Mission Support Area is the real-time control center for the Radio Science System. DTV displays and hardcopy capability are provided to the Project real- time operations personnel to aid this task. 3.7 Radio Science Support Team Data Records System This is the data records handling system for the Voyager Radio Science System. It consists of the personnel, software, and procedures required to log in, reformat, archive, and deliver to the Radio Science Team all data products by the Voyager Radio Science System. 3.8 Open-Loop Recording System Pre-Pass Calibration The recorded open-loop receiver signals are the prime data type for the Titan and Saturn ring occultations and the ring-scattering experiment. -3.5- For this reason, it is extremely important that the open-loop system be properly set up 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 for the data later recorded and, in fact, serve to establish the basic uncertainty in 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. 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 = ((SNR + 1)/ (2 SNR + 2 k sqrt(2SNR) +k^2))^1/2 (1) Where S = receiver output levels (volts rms) SNR = expected received SNR k = number of sigma margin desired for saturation 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 thus directly proportional to system temperature. Hence, the output signal power changes approximately 3 dB when the antenna is moved from zenith (where the calibration recording is made) to horizon, where data recording begins at DSS- 63 and ends at DSS-43. Therefore, 3 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. The above is not necessary for narrow-band recording. -3.6- 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 that is placed over the X-band 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 in this manner 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 that specify subsystem configuration requirements for Voyager Saturn encounter Radio Science experiments. -3.7- RADIO SCIENCE CELESTIAL TITAN SATURN RING RING OBSERVATION MECHANICS OCCULTATION OCCULTATION OCCULTATION SCATTERING *(ENTIRE NETWORK *DSS-63 11/12/80 *DSS-43 SET *DSS-63 11/13/80 *DSS-63 11/13/80 SUBSYSTEM +/-10 DAYS) DSS-63 RISE ASSEMBLY 11/13/80 Subreflector Auto Mode per Fixed subreflector Fixed subreflector Fixed subreflector Fixed subreflector Autofocusing Standard setting optimized setting optimized setting optimized setting optimized Control operating for 40 deg elevation for 20 deg elevation for 20 deg elevation for 20 deg elevation Assembly procedures angle at DSS-43 and 20 deg angle angle elevation at DSS-63 Angle Tracking CONSCAN On per CONSCAN Off CONSCAN Off CONSCAN Off CONSCAN Off normal operating Use angle offsets Use angle offsets Use angle offsets Use angle offsets procedures as provided by as provided by as provided by as provided by Section 5.0 Section 5.0 Section 5.0 Section 5.0 *See final ISOE for exact event times and duration. Table 3. 9. 1 Antenna Mechanical and Pointing Subsystem Configuration Requirements RADIO SCIENCE CELESTIAL TITAN SATURN RING RING OBSERVATION MECHANICS OCCULTATION OCCULTATION OCCULTATION SCATTERING *(ENTIRE NETWORK *DSS-63 11/12/80 *DSS-43 SET, *DSS-63 11/13/80 *DSS-63 11/13/80 SUBSYSTEM +/-10 DAYS) DSS-63 RISE ASSEMBLY Polarizer RCP Switched to RCP to Low- RCP to Low- RCP to Low- RCP to Low- Control Low-Noise Masers Noise Masers Noise Masers Noise Masers Noise Masers TWM S-Band: S-Band: S-Band: S-Band: S-Band: TWM #1 = SRCP TWM #1 = SRCP TWM #1 = SRCP TWM #1 = SRCP TWM #1 = SRCP Assignments X-Band: X-Band: X-Band: TWM #2 = SLXP TWM #2 = SLCP TWM #2 = XRCP TWM #2 = XRCP TWM #2 = XRCP X-Band: X-Band: TWM #2 = XRCP TWM #2 = XRCP TWM #1 = XLCP TWM #1 = XLCP *See final ISOE for exact times and duration. Table 3.9.2 Antenna Microwave Subsystem Configuration Requirements RADIO SCIENCE CELESTIAL TITAN SATURN RING RING OBSERVATION MECHANICS OCCULTATION OCCULTATION OCCULTATION SCATTERING *(ENTIRE NETWORK *DSS-63 11/12/80 *DSS-43 SET, *DSS-63 11/13/80 *DSS-63 11/13/80 SUBSYSTEM +/-10 DAYS) DSS-63 RISE ASSEMBLY Closed Loop Standard Voyager Closed-Loop Closed-Loop Closed-Loop Closed-Loop Receivers Closed-Loop Data Doppler Data Doppler Data Doppler Data Doppler Data Acquisition and + Required + Required + Required Required Calibrations S-Band 2 BLO = S-Band 2 BLO = RCVR 1 = SCRP RCVR 1 = SRCP Required 10 HZ 10 HZ RCVR 2 = SLCP RCVR 2 = SLCP X-Band 2 BLO = X-Band 2 BLO = RCVR 3 = XRCP RCVR 3 = XRCP 30 HZ WIDE 30 HZ RCVR 4 = XLCP RCVR 4 = XLCP AGC BW = MED AGC BW = MED X-Band 2BLO = X-Band 2BLO = 30 HZ 30 HZ S-Band 2BLO = 12 HZ S-Band 2BLO = 12 Hz PPM Two Channel Two Channel Two Channel Four Channel Four Channel S & X-Band S & X-Band S & X-Band S & X-Band RCP/LCP S & X-Band RCP only system RCP only system RCP only system system temperature RCP/LCP temperature temperature temperature measurements system measurements measurements measurements required temperature required required required measurements required *See final ISOE for exact event times and duration. + See Section 5.0 for detailed signal acquisition strategy. Table 3.9.3 Receiver-Exciter Subsystem Configuration Requirements RADIO SCIENCE CELESTIAL TITAN SATURN RING RING OBSERVATION MECHANICS OCCULTATION OCCULTATION OCCULTATION SCATTERING *(ENTIRE NETWORK *DSS-63 11/12/80 *DSS-43 SET, *DSS-63 11/13/80 *DSS-63 11/13/80 SUBSYSTEM +/-10 DAYS) DSS-63 RISE ASSEMBLY Open-Loop Not Applicable MMR Medium Band OL Narrow Band MMR Medium Band MMR Medium Band Receivers S-Band RCP Band- S-Band Bandwidth S-Band RCP Band- S-Band RCP Band- Prime System width = 50 KHZ = 5 KHZ width = 50 KHZ width = 50 KHZ X-Band RCP Band- X-Band Bandwidth S-Band LCP Band- S-Band LCP Band- width = 150 KHZ = 15 KHZ width = 50 KHZ width = 50 KHZ Filter Select = 8 Filter select = 6 X-Band RCP Band- X-Band RCP Band- S & X-Band RCP S-Band RCVR power width = 150 KHZ width = 150 KHZ RCVR Power Output output = + 15 dbm X-Band LCP Band- X-Band LCP Band- = +13 dbm with X-Band RCVR power width = 150 KHZ width = 150 KHZ calibration Output = + 17 dbm Filter Select = 8 Filter Select =8 signal levels with calibration -134 dbm X-band signal levels = S & X-Band RCP/LCP S & X-Band -144 dbm S-band -132.3 dbm X-band RCVR Power Output RCP/LCP RCVR -149 dbm S-band = +13 dbm with Power Output calibration = +13 dbm with signal levels = calibration -132.3 dbm X-band signal levels = -149 dbm S-band -132 dbm X-band -149 dbm S-band *See final ISOE for exact event times and duration. Table 3.9.3 Continuation of Configuration Requirements for Receiver- Exciter Subsystem RADIO SCIENCE CELESTIAL TITAN SATURN RING RING OBSERVATION MECHANICS OCCULTATION OCCULTATION OCCULTATION SCATTERING *(ENTIRE NETWORK *DSS-63 11/12/80 *DSS-43 SET, *DSS-63 11/13/80 *DSS-63 11/13/80 SUBSYSTEM +/-10 DAYS) DSS-63 RISE ASSEMBLY Open-Loop Not Applicable MMR Wideband OLR Wideband MMR Wideband RCVR Receivers S-Band RCP to S-Band RCP to Backup Systems Channel 1 Channel 1 Chan 1 = S-Band RCP, 2nd LO = 299.572 MHZ 2nd LO FREQ = 2nd LO SYN Chan 2 = S-Band LCP, 2nd LO, = 298.715 MHZ 299.572 MHZ FREQ = Chan 3 = X-Band RCP, 2nd LO = 296.715 MHZ X-Band RCP to See Section 5.0 Chan 4 = X-Band LCP, 2nd LO = 293.572 MHZ Channel 3 RCVR 1st LO SYN FREQ = See Section 5.0 2nd LO FREQ = X-Band RCP to 296.715 MHZ Channel 2 For RCVD Signal Level RCVR 1st LO 1st and 2nd LO S-Band = 149.0 Synthesizer SYN (HP) FREQ = X-Band = 132.3 FREQ = See Section 5.0 See Section 5.0 RCVR Output RCVR Output PWR = TBS PWR = + 4 dbm For Received for RCVD Signal Level Signal Level S-band = -144.4 S-band = -144.4 X-band = -134.2 X-band = -134.2 *See final ISOE for exact event times and duration. Table 3.9.3 Continuation of Configuration Requirements for Receiver-Exciter Subsystem RADIO SCIENCE CELESTIAL TITAN SATURN RING RING OBSERVATION MECHANICS OCCULTATION OCCULTATION OCCULTATION SCATTERING *(ENTIRE NETWORK *DSS-63 11/12/80 *DSS-43 SET, *DSS-63 11/13/80 *DSS-63 11/13/80 SUBSYSTEM +/-10 DAYS) DSS-63 RISE ASSEMBLY SSI As Required FOR OPEN-LOOP RECORDING EVENTS THE SSI WILL BE NOMINALLY CONFIGURED AS FOLLOWS: ANALYSIS BANDWIDTH = 5K NO. OF AVERAGES = 128 TRANSFORM SIZE = 2048 AVERAGING MODE = LINEAR CENTER FREQUENCY = AS REQUIRED NOMINAL OBSERVED SIGNAL WILL BE ODA CONVERTER OUTPUT X OR X, RCP/LCP AS REQUIRED *See final ISOE for exact event times and duration. Table 3.9.3 Continuation of Configuration Requirements for Receiver-Exciter Subsystem RADIO SCIENCE CELESTIAL TITAN SATURN RING RING OBSERVATION MECHANICS OCCULTATION OCCULTATION OCCULTATION SCATTERING *(ENTIRE NETWORK *DSS-63 11/12/80 *DSS-43 SET, *DSS-63 11/13/80 *DSS-63 11/13/80 SUBSYSTEM +/-10 DAYS) DSS-63 RISE ASSEMBLY Occultation Not Required Medium Band Narrow Band Medium Band Recording Data Assembly Recording Recording Required Required Required Pass Dependent Pass Dependent Pass Dependent Parameters Parameters are: Parameters are: MBS 300K MOD 4 6 8 MBS 300K SCN 31 CHN 1 3 3 3 SCN 31 PRD TI01 PRD SA01 PRD SA01 SCN 31 Digital Not Required DRA #1 DRA Records DRA #1 Records Medium Band Recording Records Medium Backup Data Data, IPS = 30 Assembly Band Data IPS = 30 IPS = 30 DRA #2 Records Backup RCVR DRA #2 Data, IPS 120 Records Backup Data IPS = 120 *See final ISOE for exact event times and duration. Table 3.9.4 Radio Science Subsystem Configuration Requirements RADIO SCIENCE CELESTIAL TITAN SATURN RING RING OBSERVATION MECHANICS OCCULTATION OCCULTATION OCCULTATION SCATTERING *(ENTIRE NETWORK *DSS-63 11/12/80 *DSS-43 SET, *DSS-63 11/13/80 *DSS-63 11/13/80 SUBSYSTEM +/-10 DAYS) DSS-63 RISE ASSEMBLY MDA/PRA SOP For High Rate High Rate High Rate High Rate Acquiring Doppler Data Doppler Data Doppler Data Doppler Data Ranging and Required Required Required Required Doppler Data See ISOE See ISOE S-Band = CHN 1 S-Band = CHN 1 Various Sample For Sample For Sample X-Band = CHN 3 X-Band = CHN 3 Rates Required Rate Changes Rate Changes Per ISOE *See final ISOE for exact event times and duration. Table 3.9.5 Tracking Subsystem Configuration Requirements RADIO SCIENCE CELESTIAL TITAN SATURN RING RING OBSERVATION MECHANICS OCCULTATION OCCULTATION OCCULTATION SCATTERING *(ENTIRE NETWORK *DSS-63 11/12/80 *DSS-43 SET, *DSS-63 11/13/80 *DSS-63 11/13/80 SUBSYSTEM +/-10 DAYS) DSS-63 RISE ASSEMBLY DIS DOP AGC TOL = 2 AGC TOL = 2 AGC TOL = 2 AGC TOL 2 Collect AGC Collect AGC Collect AGC Collect AGC Data on Line Data on Line Data on Line Data on Line Printer Printer Printer Printer DST SOP SOP SOP SOP SOP *See final ISOE for exact event times and duration. Table 3.9.6 Monitor and Control Subsystem Configuration Requirements 4.0 Radio Science Encounter Timelines The Voyager 1 Saturn encounter Radio Science activities span a four-month period from August 22 through December 16, 1980. During this time period, observations of unprecedented magnitude and complexity are being undertaken. The focus of this activity is on the 20 days centered around the Titan and Saturn occultations on November 12 and 13, respectively. During this period, nearly continuous celestial mechanics observations will be made, as well as the occultation observations themselves. Specific details of the Radio Science observations are contained in Section 2.0. In order to provide a clear, concise profile of Radio Science activities, two separate timelines have been constructed. The first timeline emphasizes the broad overview, covering from November 3 (DOY 308) through November 23 (DOY 328). General operational events for this entire period are covered without attempting to detail specifics of the high-activity occultation period. The second timeline focuses on the Titan, Saturn, and ring experiments on November 17 and 18, respectively. Specific operational events for the Radio Science links are included. 4.1 Extended Timeline DOY 308 to 328 Tracking Station Coverage - 64-meter station scheduled tracking periods - AOS and LOS times Voyager 1 Spacecraft Events - Radio Science maneuvers - CCS load start points RSS Science Events - Periods of Radio Science observations - RSS links Ground Coordination Events - POEAS runs and ODA predict generation - Predict deliveries - Predict review meetings - Predict transmission times to stations - ISOE transmission times to stations - Operations briefings - Radio Science Working Group meetings - Daily station representative status reports -4.1- Ground Coordination Events (cont.) - Critical RSS operation periods - Data shipment dates Sequence Development - Inputs meetings - ESF/SOE review deadlines - Product H/I meetings 4.2 Near Encounter Timeline DOY 317 and 318 This timeline will include these additional events: Tracking Station Coverage - 26-meter backup pass tracking periods - 34-meter plasma calibration tracking periods - Special station configuration events - Special pre-cal and post-cal periods Voyager Events - Detailed maneuvers - Specific spacecraft configuration changes Science Events - Special science events -4.2- 5.0 Tracking and Radio Science System Operations This section details the operations strategies required to acquire and maintain the uplink and downlink with the Voyager 1 spacecraft during both the Titan and Saturn occultations. 5.1 Titan Occultation Uplink and Downlink Strategies 5.1.1 Pre-Occultation Uplink Tuning - DSS-43 The uplink with the Voyager 1 spacecraft is expected to be maintained until 04:05:00 GMT. This time closely coincides with the nominal time for a transfer from DSS-43 to DSS-63. Therefore, DSS-43 will continue transmitting until this point and simply turn its transmitter off instead of transferring. In order to eliminate the necessity for tuning to an outgoing XA frequency, the tracking synthesizer frequency (TSF) for the pass will be chosen to nearly equal the XA at the 04:05:00 GMT transmitter-off time. It should be noted that some additional tuning time may be required at the transfer from DSS-14 to DSS-43 because of this choice of TSF. 5.1.2 Pre-Occultation Downlink Tuning - DSS-63 As previously discussed in Section 2.0 (see specifically Table 2-1 and Figure 2-6 given in the Appendix), the downlink signal should remain stable in amplitude until the approximate start of the ionospheric occultation (- 07:08:00 GMT). At this time, frequency fluctuations may begin. Starting at approximately 07:11:00 GMT, signal level fluctuations may also be seen, possibly causing the closed-loop receivers to drop lock. Finally, within one minute of the start of atmospheric occultation (~07:12:15 GMT), both S- and X- band receivers should drop lock. In order to maximize the time the receiver can be maintained in lock and to minimize lock-up time, the receivers should be ramped during this time period. Ramps will be provided which keep the receiver frequency within approximately 100 Hz (S-band) of the predicted frequency. A typical sequence of ramps is given in Table 5-1. A comparison of the receiver tuning with the expected downlink frequency is shown in Figure 5-1. The doppler profile for the entire Titan occultation is given in Figure 5-2. Figure 5-3 illustrates the expected one-way doppler frequency rate of change. Prior to beginning these ramps, the station should (carefully) zero out any static phase error in the receiver. If the receiver drops lock during this period, the operator should be prepared to re-lock the receiver as soon as possible. GMT RATE (S) RATE(X) 07:08:00 0.0089 0.0077 07:12:12 -1.6746 -1.4448 07:14: 30 -1.1092 -0.9569 07:16:00 0.0000 0.0000 Table 5-1 DSS-63 Receiver Ramps -5.1- 5.1.3 Post-Occultation Uplink Acquisition - DSS-63 The post-occultation uplink acquisition sweep at DSS-63 has been designed to be as simple as possible, yet ensure that the uplink will be acquired. The acquisition will be timed so that the spacecraft receiver will be acquired during the period following the end of the mini-ASCAL and prior to the two-way non-coherent (TWNC) off command. Thus, no tuning effects should be visible at the station. The sweep will be in a single direction starting below XA and ending at the tracking synthesizer frequency (TSF). This sweep corresponds to a sweep range of XA +/- 150 Hz which compensates for the expected 3 sigma time and frequency errors. The sweep rate will be 2 Hz per second. Since the XA continues to increase during the remainder of the pass, the TSF will not differ greatly from the XAs, thereby minimizing the spacecraft receiver loop phase error. The typical sweep for reacquisition will then be: GMT EVENT 05:26:00 Snap to 44055120. 0 05:27:00 Transmitter on at 18 KW 05:27:30 Start tuning at 2 Hz/sec. to TSF 05:30:00 Stop tuning at TSF=44055420.0 The sweep is illustrated in Figure 5-4. 5.1.4 Post Occultation Downlink Acquisition and Tuning 5.1.4.1 DSS-63 As in the pre-occultation case, an attempt will be made to acquire the downlink with the closed-loop receivers at the earliest possible time. To do this, a combination of receiver ramps and sweeps will be employed. Because of the uncertainty in the signal levels and the high (~30 Hz/ sec., S- band) doppler rates expected near spacecraft exit from occultation, it is not practical to immediately sweep the receivers. Instead, starting four minutes prior to exit occultation (~07:19:00 GMT), the receivers should be ramped to follow the expected frequency profile. During this time, the station should also use the SSI to attempt to determine the frequency of the downlink signal. It should be noted that the open- and closed-loop receivers will follow very similar ramp profiles. It would be helpful, therefore, to apply the frequency offset observed in the SSI (modified to Block IV levels) to the receiver frequency in order to achieve lock. If the downlink has not been acquired by one minute prior to the end of occultation (~07:22:00 GMT), the receivers should be swept through a range of frequencies corresponding to: Biased D1 +/- 750 Hz (S-band) -5.2- The D1 bias will be based on the best estimate of the frequency error apparent prior to entering occultation. The sweep rate will be 100 Hz/sec. (S-band). Thus, the sweep should cross the expected frequency approximately every 15 seconds and at a rate slow enough to acquire a weak signal. Finally, during this sweep, automatic trigger at zero-beat detection (ATZ) should be switched on. Once the signal has been acquired, the receivers should again be ramped to follow the expected frequency profile. The nominal sequence of events for the reacquisition of the downlink is, then: GMT EVENT 07:19:00 Begin ramping receivers along expected frequency profile (see Table 5-2). 07:22:00 If signal has not been acquired, begin sweep of DI +/- 750 Hz (S- band). 07:23:00 Upon acquisition of signal, begin receiver ramps. GMT RATE(S) RATE(X) 07:19:00 -1.8571 -1.6022 07:21:12 -1.2544 -1.6022 07:23:00 -0.0123 -0.0106 07:30:00 0.0000 0.0000 Table 5-2: Post Occultation Tuning Rates 5.1.4.2 DSS-62 As is the case at DSS-63, DSS-62 should attempt to maintain receiver lock as long as possible prior to entering occultation by manually tuning the receivers. In order to quickly acquire the downlink, the station should begin sweeping the receivers through a range corresponding to: Biased D1 +/- 100 Hz (S-band) starting approximately 30 seconds prior to the expected exit occultation (~07:22:30 GMT). Since signal dynamics are expected after exit occultation, the station should be prepared to quickly relock the receivers if they should drop lock. 5.2 Low Elevation Antenna Pointing 5.2.1 DSS-43 Procedures During the Saturn occultation, both DSS-43 and DSS-63 will be required to track at low elevations without benefit of CONSCAN. Additionally, during -5.3- this period an X-band signal amplitude stability of less than 0.5 dB must be maintained in order to allow atmospheric and ring scatter effects on the spacecraft signal to be analyzed. To meet both of these constraints, special low elevation antenna-pointing procedures have been developed. These procedures are described in the subsequent subsections. During every Voyager I track at DSS-43 prior to encounter, angle residuals will be plotted and analyzed in order to provide the data base necessary to determine the angle offsets from the elevation corresponding to the CONSCAN- off time until spacecraft set. For the Saturn occultation pass, the antenna will be pointed using CONSCAN prior to the start of the Radio Science activities. In order to facilitate the entry of offsets after CONSCAN is turned off, hour angle and declination offsets should not be entered manually, but should be determined by the CONSCAN. Azimuth and elevation angle offsets may be manually entered. Commencing at meridian crossing, the angle sample rate will be increased to one sample per 30 seconds in order to compare performance with the data base previously assembled. CONSCAN will be turned off at approximately 02:19:00 GMT. At this time, the accumulated angle offsets will automatically become the initial pointing offsets. An additional small offset may be required at this point depending on where in the CONSCAN cycle the antenna is left. This offset will be determined within five minutes of the end of the CONSCAN drive. Current experience indicates that the angle offsets at this point will provide the required signal amplitude stability until an elevation of approximately 11 deg is reached (~04:08:00 GMT). At that point, a small (< 0.007 deg or -0.2 dB) additional offset may be entered. This offset will be determined by comparing the angle residual drift with data acquired in previous passes. It should be noted that this offset will be provided at DSS-43 in hour angle and declination coordinates. Additionally, it will represent an additional offset value rather than the total offset. By way of summary, the nominal antenna pointing sequence at DSS-43 is: GMT EVENT 317/23:00:00 DSS-43 set (S-band channel ) angle sample rate to I per 30 seconds. 318/01:30:00 Verify that HA/DEC Antenna Pointing Subsystem (APS) offsets have been cleared. 318/02:00:00 Cease subreflector focusing and set for 20 deg elevation. 318/02:19:00 CONSCAN off with accumulated offsets left in. -5.4- GMT EVENT 318/02:23:00 Enter additional HA/DEC offsets (if required) 318/04:08:00 Enter additional HA/DEC offsets 318/04:32:07 DSS-43 end of track 5.2.2 DSS-63 Procedures The DSS-63 low elevation pointing procedure will be significantly different from that of DSS-43 due to the fact that the station will rise during the occultation. Since CONSCAN obviously cannot be used during this period, the a priori knowledge of the specific offsets to be used that day will not be as good as at DSS-43. The accumulated data base of offsets from previous passes will be used to determine the angle offsets to be used during this pass. Experience, thus far, indicates that these offsets are generally consistent from pass to pass. Additionally, a single offset has proven sufficient to maintain the signal to within 0.5 dB of the expected level. Prior to the Saturn occultation pass, the angle offsets (expected to be ~0.011 deg HA, ~0.030 deg DEC, 0 deg AZ/EL) will be provided to DSS-63 for entry into the APS computer. The subreflector focus should be set for 20 deg elevation. Shortly after starting to drive the antenna, some small additional offsets may be required to bring the residuals into line with the expected residuals. There will be no need to apply additional offsets after this time. The typical sequence for DSS-63 low elevation pointing is: GMT EVENT 03:40:00 Set subreflector focus for 20 deg elevation. Ensure correct offsets are entered into APS. 03:45:00 Angle sample rate to 1/30 seconds. 03:45:38 (Rise) Begin offset antenna pointing. 03:47:00 Enter additional offsets (if required). 07:31:04 Refocus subreflector. 07:32:04 Begin CONSCAN. 5.3 Saturn Uplink and Downlink Acquisition Strategies 5.3.1 Pre-Occultation Uplink Tuning - DSS-43 The plan for the pre-occultation uplink tuning at Saturn will be similar to that used prior to the Titan occultation. That is, the TSF at DSS-43 will be nearly equal to the XA at the transmitter-off time. Thus, no tuning will be required prior to entering occultation. It should be noted, however, -5.5- that this placement of TSF will require extra tuning during the transfer from DSS-14. Additionally, the difference between TSF and XA will be quite large [~800 Hz (DCO)] prior to occultation. Thus, in case of a transmitter failure during this period, the uplink should be reacquired not by sweeping around XA, but rather by sweeping through a frequency determined by the relaxation characteristics of the spacecraft receiver tracking loop. A Hewlitt Packard calculator program has been provided to the NOCT for use in calculating the correct sweep frequencies. The nominal XA profile with TSF overlaid is shown in Figure 5-5. 5.3.2 Occultation Downlink Tuning - DSS-43/44 5.3.2.1 DSS-43 As indicated in Section 2.0, the downlink signal is expected to be fairly dynamic (in both frequency and amplitude) as it begins to probe the ionosphere and atmosphere of Saturn. Table A-2 describes these dynamics and indicates that, for much of the time during this period, it may be possible to achieve closed-loop receiver lock. Acquisition of radiometric data (from these receivers) during these times would greatly enhance the Radio Science observations. Also during this time period, the rate of change of the signal frequency is expected to be moderately high (~-6 Hz/second at S-band, and ~-22 Hz/second at X-band) as shown in Figure 5-6. The expected doppler profile is shown in Figure 5-7. Because of the importance of the closed-loop data, it will be necessary to ramp the receivers. This should minimize the out-of-lock time and facilitate the relocking of the receivers. Ramps will be provided which keep the receiver frequency within 100 Hz (S-band) of the expected downlink frequency (see Figure 5-8). During periods when the signal is present, the SSI should be used to assist in relocking the receivers. The typical ramp sequence at DSS-43 is shown in Table 5-3. The ramps are scheduled to start at 02:50:00 GMT and should continue throughout the remainder of the pass. Immediately prior to starting the ramps, the receiver operator should carefully zero out any residual phase error in the receivers. Table 5-3: DSS-43 Receiver Ramps GMT RATE(S) RATE(X) 02:50:00 0.2635 0.2274 03:06:40 0.0315 0.0272 03:15:10 0.1301 0.1122 03:25:49 0.2554 0.2203 03:36:10 0.3764 0.3247 03:48:30 0.4121 0.3556 04:01:30 0.3020 0.2605 04:10:25 0.1464 0.1263 04:18:50 0.0022 0.0019 04:29:05 -0.0682 -0.0588 04:33:00 0.0000 0.0000 -5.6- The downlink will be lost between part one and part two of the limbtracking maneuver (~03:57:00 GMT to 04:21:47 GMT). Intermittent receiver lock may be achieved starting at about 04:21:47 GMT. Therefore, starting at 04:21:00, the receivers should be swept through frequencies corresponding to: D1 +/- 300 Hz (S-band) where D1 is the average one-way doppler frequency over the remainder of the pass. The sweep rate will be 50 Hz/second (S-band). Once receiver lock is achieved, ramping should start again. Note that the frequency range of the sweep will be sufficient to reacquire the downlink whenever lock is dropped between 04:21:00 GMT and the end of the DSS-43 pass. 5.3.2.2 DSS-44 DSS-44 should be able to maintain receiver lock until the ~03:04:00 GMT beginning of ionospheric occultation. It is recommended that the station (manually) ramp the receivers to follow the frequency profile (Figures 5-6 and 5-7) in order to minimize phase error during this period. It is not expected that DSS-44 will be able to relock its receivers following the start of occultation. 5.3.3 Post-Occultation Uplink Acquisition - DSS-63 The post-occultation uplink acquisition sweep will be similar to that performed following for Titan occultation. The sweep will occur during the period following the mini-ASCAL and prior to the two-way non-coherent (TWNC) off command. Thus, tuning effects should not be visible on the downlink. In order to ensure acquisition and to account for expected 3 sigma frequency and trajectory errors, the sweep-range will be approximately XA +/- 200 Hz (DCO). Since the XA will be decreasing throughout the remainder of the DSS-63 pass, the sweep will start at XA + 200 Hz and go (.in the direction of the change of XA) to a TSF chosen to be approximately equal to XA - 200 Hz. This TSF will cause the spacecraft receiver phase error to be minimized during the rest of the pass and will be very nearly equal to the XA at the transfer from DSS-63 to DSS-14. The sweep rate will again be 2 hertz per second. The typical sequence will then be: GMT EVENT 04:12:00 Snap to turn on frequency 44054700.0 Hz 04:13:00 Transmitter on at 18 KW 04:13:30 Start tuning to TSF at 2 Hz/sec. 04:16:50 Stop tuning at 44054300.0 Hz The sweep profile is illustrated in Figure 5-9. -5.7- 5.3.4 Occultation Downlink Tuning - DSS-63/62 5.3.4.1 DSS-63 The signal levels expected at DSS-63 rise are expected to be very weak and hence it may be extremely difficult (if at all possible) to acquire the downlink. Additionally, as shown in Figure 5-10, the doppler rates will be quite high during the period immediately following rise. The expected doppler profile is shown in Figure 5-11 (,Note: Doppler bias will be -1 MHz). A further complication to this situation is the need to configure both Block IV receivers (with POCA control) for X-band and both Block III receivers (manually controlled) for S-band. Therefore, at rise, it is suggested that the station sweep the S-band receiver, as possible, through the predicted doppler. The X-band receiver should be ramped along the expected frequency profile using the provided ramps (Table 5-4 is an example of these ramps). This ramping should facilitate acquisition by keeping the receiver frequency very close to the expected downlink frequency. From Table 2-2, it can be seen that all signals will disappear at the end of the first part of the limb-tracking maneuver (03:56:55) and not reappear until the second part of the maneuver begins at 04:21:47. At that time, the receivers should be swept through frequencies corresponding to: (average for 04:22:00 - 04:38:00) D1 +/- 300 Hz (S-band) at a rate of approximately 50 Hz/second (S-band). X-band receiver ramping should begin as soon as lock is achieved. The S-band receivers should be manually tuned whenever possible. Table 2-2 indicates times when the receivers may drop lock. The previously mentioned sweep frequencies can be used for reacquisition whenever the receivers drop lock during this period (04:21:00 - 04:38:00) eliminating the need for recalculation of frequencies. GMT RATE(S) RATE(X) 03:45:38 0.4099 0.3536 04:02:45 0.2835 0.2446 04:11:25 0.1271 0.1097 04:19:55 -0.0139 -0.0120 04:30:31 -0.0642 -0.0554 04:36:02 0.1302 0.1123 05:08:49 0.1004 0.0866 05:53:16 0.0730 0.0630 06:46:30 0.0504 0.0435 07:55:00 0.0000 0.0000 Table 5-4: DSS-63 Receiver Rates After 04:38:00, the frequency rates will again increase. To reacquire during this period, it is recommended that the SSI be used to provide acquisition frequencies. Again, the X-band receiver ramps should facilitate the reacquisition of the downlink in these cases. -5.8- During the XRSCAT observations, it will be possible to maintain S-band receiver lock on the signals radiated through the spacecraft antenna sidelobes. The receiver phase error should be closely monitored during this period and minimized as necessary. The X-band signal level will drop off quickly during this period with receiver lock not possible until the spacecraft returns to the Earth line. The SSI will not be usable for providing frequencies during this time since the open-loop receivers will be following the expected profile of the scattered signal. 5.3.4.2 DSS-62 It will probably not be possible for DSS-62 to acquire the downlink until the spacecraft emerges from behind Saturn at approximately 04:38:00 GMT. Therefore, starting three minutes prior to exit occultation, the station should begin sweeping its receivers through frequencies corresponding to: Biased D1 +/- 300 Hz (S-band). Upon acquiring the downlink, the receivers should be manually ramped to follow the frequency profile. During the ring occultation period, it will obviously be difficult to maintain receiver lock. Table 2-2 describes the expected signal characteristics during this time. Attempts should be made to acquire the downlink whenever possible. 5.4 Use of the SSI for Receiver Acquisition The SSI should be used whenever possible to aid in the downlink acquisition. Procedures for this use are outlined in-the Voyager Network Operations Plan (618-700, Rev. C), Appendix F (pp. F21-F26). At DSS-63, 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 receivers three and four using the OCIS: CFG RCV3 VCO = 26.XXXXXX MHZ CFG RCV4 VCO = 26.XXXXXX MHZ It is not necessary to re-enter these values. 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 which may be called up using the OCI: D STS. This display is depicted in Figures 5-12 and 5-13. -5.9- FLT = MB SBAND = 2295.XXXXXX MHZ MMR POCA = 41.XXXXXX MHz RCV1 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 Figure 5-12: Status Display for SLCP/SRCP SSI Ports FLT = MB XBAND = 8415.XXXXXX MHz MMR POCA = 41.XXXXXX MHz RCV3 VCO = 26.XXXXXX MHz POCA = 41.XXXXXX MHz RCV4 VCO = 26.XXXXXX MHz POCA = 41.XXXXXX MHz Figure 5-13: Status Display for XLCP/XRCP SSI Ports 5.5 Radio Science Operations 5.5.1 Open-Loop Receiver Configuration Radio Science operations during the Voyager 1 Saturn encounter on November 12 and 13 will primarily consist of open-loop receiver recordings during four critical periods: Titan occultation, Saturn occultation, ring occultation, and the ring-scattering experiment. The Titan occultation will occur over DSS-63 and will be recorded from 06:32:00 to 08:34:38 on two channels of the four- channel, medium-band Radio Science subsystem S- and X-band RCP signals will be recorded using 50 and 150 KHz receiver bandwidths, respectively. The use of the medium-band capability for the Titan recording has become necessary due to the large uncertainty in Titan's radius. DSS-43 will record all but the final four or five minutes of the Saturn occultation on November 13. This recording is scheduled from 02:24:47 to 04:36:54 using the 4.091 and 15 KHz narrow-band receiver, filters for S- and X-band, respectively. DSS-43 will be unable to observe the spacecraft exit Saturn occultation. DSS-63 will rise during the Saturn occultation and will record from 03:40:59 to 07:28:05 using the full four-channel capability of the medium bandwidth subsystem. This period will cover the second half of the Saturn occultation, the entire ring occultation, and the ring-scattering experiment. S-band RCP and LCP signals will be recorded in separate 50 KHz receiver filters and X- band RCP and LCP signals will be recorded in separate 150 KHz receiver filters. -5.10- The medium-band receiver channels at DSS-63 will be sampled at 300 K samples per second with a quantization of 8 bits per sample. The narrow-bandwidth receiver channels at DSS-43 will be sampled at 10 K and 30 K samples per second, respectively, for S- and X-band with 8 bits per sample quantization. The MOD and CHN OCIs for DSS-43 are: MOD 4 6 8 CHN 1 3 5.5.2 Wide-Band Receiver Configuration In addition to the medium- and narrow-band recordings scheduled for encounter, DSS-63 and 43 will also record the downlink signals during the previously mentioned time spans using their backup wide-bandwidth receivers and DRA recording capabilities. The DSS-63 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. The DSS-43 wide-band system consists of a 300 KHz S-band filter on which a 1.3 MHz X-band filter is stacked forming a 2 MHz total bandwidth which is recorded by the DRA. Nominal synthesizer frequency settings for the wideband receivers may be found in Table 5-5. Figures 5-14 through 5-16 illustrate the signal drift through the wide-band filters at DSS 43 and 63. DSS BAND EVENT MODE FREQUENCY 63 S/X TITAN COH 41593880.00 63 S/X TITAN NCOH 41563007.33 63 S/X SATURN NCOH 41563636.03 43 S SATURN COH 49389680.00 43 X SATURN COH 46794449.00 43 S SATURN NCOH 49148192.67 43 X SATURN NCOH 46764262.73 Table 5-5: Wide-Band Receiver Synthesizer Frequencies -5.11- 5.5.3 Radio Science Predictions For the Titan occultation, five Radio Science predicts sets, one prime and four contingency sets, will be available. A description of these predicts may be found in Table 5-6. Since this will be a medium-band recording, the frequency tolerance on the predicts will be 1 KHz. For the Saturn occultation, four Radio Science predicts sets, one prime and three contingency sets, will be generated. These four sets will be generated under the same guidelines as the first four sets generated for the Titan occultation. The frequency tolerance on these sets of predicts will be 50 Hz. Additionally, the predicts for DSS-63 will model the frequency profile expected during the XRSCAT experiment. A description of these predicts may be found in Table 5-7. Specification of the prediction set will be made to the station via the DSN representative. SET CONTENTS USE T101 MODE SWITCHES, USO REF PRIME T102 MODE SWITCHES, AUX OSC REF USO FAILURE T103 ONE WAY ONLY, USO REF DSS TXR FAIL MISSED UPLINK ACQ T104 ONE WAY ONLY AUX DSC REF USO FAILURE, DSS TXR FAILURE T105 TWO WAY ENTER, ONE WAY EXIT EARLY USO FAILURE AUX OSC REF Table 5-6: Titan Occultation Predicts Sets Comparisons of the predicted open-loop receiver frequency ramps with the nominal signal frequency profiles have been made and are shown in Figures 5-17 through 5-19. The center of the bandwidth is denoted by the horizontal line through the center of the plots. Barring atmospheric and ionospheric perturbations, the signal will move through the bandwidths as shown. A study of possible time-of-arrival errors was made with the results given in Figures 5-20 through 5-25. As can be seen, a 3-sigma (27 seconds) error at Titan will cause the signal to move approximately 1200 hertz further from the center than in the nominal case. A 3-sigma error at Saturn arrival would cause the signal to move a maximum of 700 hertz from the center. In both of these cases, the signal would remain in the receiver bandpass even under adverse conditions. -5.12 SET CONTENTS USE SA01 MODE SWITCHES, USO REF PRIME SA02 MODE SWITCHES, AUX OSC REF USO FAILURES SA03 ONE-WAY, USO REF TXR FAIL, MISSED UPLINK ACQ SA04 ONE WAY, AUX OSC REF TXR FAIL, MISSED UPLINK ACQ AND USO FAIL Table 5-7: Saturn Occultation Predict Sets -5.13- 6.0 Real-Time Operations The real-time operations of the Voyager 1 Saturn encounter will encompass a period of +/- ten days centered on encounter with the peak of activity occurring during the two-day Radio Science Titan and Saturn encounter events. A ten-day period preceding the encounter will emphasize final encounter preparations. Examples of these events will include the generation and delivery of final tuning predict sets, final preparations for real-time operations which relate to the last ORT, arrival of the DSS-63 and DSS-43 representatives at the stations, and daily discussions with the representatives over the Radio Science coordination net. The Radio Science Near Encounter Phase Observations on days 317 and 318 will entail real-time activities which will optimize the Radio Science data acquisition using elements of the RSST, OCT, MCT, and DSN. The ten-day period following the encounter will focus on the delivery of the data, and quick-look processing and analysis for preliminary scientific results. The following section provides functional responsibilities of the elements supporting Radio Science real-time operations. Future sections detail specific real-time operational functions, operations schedules, and contingency plans. 6.1 Functional Responsibilities The functional responsibilities of the major supporting elements of the Radio Science investigations at Titan and Saturn are specified in this section. Normal Project support for the experiment, as defined by Interface Agreements in the SFOP, is assumed and will not be described herein. 6.1.1 Mission Support to RSST The MCT will provide communications support via the ACE to OPS Chief to the station from the RSST for all directed requests outside of the six control functions specified in Section 6.2.4 for the Radio Science coordination net. All other communications and support should be as per normal operational procedures. 6.1.2 DSN Support to RSST A NOA will be required for the generation of low elevation angle predicts for the DSS-43 to DSS-63 Saturn passes and the generation of tuning predicts for both the ODA and backup DRAs. The NOPE/NOA will assist in real-time operations of the NOCC by planning and integrating the display strategy with respect to Radio Science requirements and assisting in the real-time analysis of the displayed data. 6.1.3 RSST Functional Responsibilities Three members of the RSST will occupy positions at the Radio Science desk within the MSA during scheduled Radio Science operational periods. The roles of each are as follows: Operations Coordinator - Responsible for all communications to the Project via the ACE interface. All information directing action to -6.1- be taken by the Project or the DSN will be communicated through the ACE by the Operations Coordinator, with the exception of the six specified Radio Science control functions during the critical event periods. In general, the Operations Coordinator is responsible for the conduct of Radio Science business within the MSA. Operations Analyst - The Operations Analyst monitors the real-time displays, verifies the operation of the ODA, PPM, SSI, and other supporting subsystems. The Operations Analyst will advise the Operations Coordinator of the status of the experiment and will require communications with the NOPE, NOA, and NOCC. The Operations Analyst will also communicate with the DSS-63 Radio Science Representative during the DSS-43 to DSS-63 overlap in order to assist the Science Adviser who will be the lead for station representative communications. The Operations Analyst will also assist in the pre-pass checklist and post-pass briefings from the station representatives. Science Adviser - The Science Adviser will be responsible for following the progress of the experiment and making determinations based on science issues as to what the Radio Science control parameters ought to be and when they should be changed. In this capacity, the Science Adviser will be the lead for communicating over the coordination net to the Radio Science Representatives at the stations. The Science Adviser will accept inputs from the Operations Coordinator, Operations Analyst, and the Radio Science Team members via a third to fifth floor MISD net in order to help make control function decisions. 6.1.4 Radio Science Representatives to the DSS The Radio Science Representatives at DSS-43 and DSS-63 will represent the Voyager Radio Science Support Team at the DSS. This includes the responsibility for briefing the station staff on the Radio Science objectives and detailing operational requirements for the Titan and Saturn encounters. He will also act as the real-time operations interface between the DSS shift supervisor and the Radio Science Support Team during the Radio Science critical-event periods, as defined in the ISOE, in order to expedite the six functions specified in 6.2.4. Prior to the high-activity periods, the Radio Science Representatives will participate in the daily briefings and information exchange between the DSS and the Radio Science Support Team. 6.2 Operations 6.2.1 Voice Net Communications Due to the dynamic nature of the Titan occultation, Saturn occultation, ring occultation, and the Saturn ring-scattering experiment, it is necessary that the DSS-43/63 Project Radio Science Representative talk directly to the station operations. This direct control communication will be allowed only for a specific set of control functions pertaining to Radio Science activity. This change in operational procedure was agreed to by the TDA Office and Division 37 management. -6.2- The specific control functions that will be communicated directly to the DSS- 43/63 station operations by the Radio Science Representatives are detailed in Table 6-3 in Section 6.2.4. During Radio Science critical-event periods, Radio Science activities will have priority over routine Project activities. This priority is necessary to minimize confusion and station loading during high-activity Radio Science periods. However, a priority change may be recommended in real time to the FOOM, who will have ultimate authority for priority assignment. During the Radio Science critical-event periods, normal operational net reporting will be held to a minimum in order to avoid conflicting direction to the station. The NOPE will be responsible for monitoring the traffic on the coordination and DSS-l nets to insure direction to the station is given for the specific control functions and that other requests over the operational net are not in conflict. The Radio Science coordination net will be used in a talk/listen configuration by the RSST Science Adviser at JPL and the Radio Science Team Representatives at DSS-43 and 63 to conduct the Radio Science activities. The Radio Science Team Representatives at DSS-43 and 63 will interface with the shift supervisor to directly control the six specific control functions for the Radio Science activity specified in Table 6-3. The Representatives will talk directly to station operations via communications media provided by DSS-43 or 63 station management. If it becomes necessary to make Radio Science real-time changes in areas other than the six specified control functions, standard procedures must be followed--Radio Science Operations Coordinator to ACE, ACE to OPS Chief, OPS Chief to DSS-43 or 63. Figure 6-1 illustrates the integration of the Radio Science coordination net within the operational net structure. Net operation during critical-event periods will be conducted as discussed above. During non-critical periods and for communications other than the six mentioned control functions, net operation will follow normal procedures. The functions of the other supporting nets are as follows: ACE via MICON-1 Project operational net, Operations Coordinator to ACE SYSTEMS via MICON-2 Project prepass and postpass briefings and status reports RSS via MISD-3 Mission Director's net for use by Radio Science during the encounter period. Radio Science Team investigators to RSST in Mission Support Area. NOPE/NOA via TRK ANAL2 Real-time analysis, status, and graphics/display coordination. -6.3- 6.2.2 Graphics Display and Hardcopy Data Collection Procedures Due to the myriad of Radio Science events occurring during the encounter period, it will be necessary to schedule the graphics and data format displays prior to the events. The vehicle for these requests is a form which is presented as Figure 6-2. Display and graphics strategy will be coordinated with the NOPE/NOA three days prior to the beginning of the Near Encounter Radio Science events. The coordination will minimize overloading during high- rate, closed-loop data acquisition periods and optimize the data types and content during the Titan, Saturn occultation, and Saturn ring experiments. After the graphics/displays have been coordinated, the RSST will generate the required graphics/display request forms for the Titan events and provide them to the NAT area at least four hours prior to the start of Radio Science activities on DOY 317. For Saturn, request forms for the graphics/displays will also be provided to the NAT area at least four hours before the start of Radio Science activities on DOY 318. Refer to the Section 4.0 timeline for the above events. Table 6-1 is a list of displays which will be required during the Radio Science events of the Titan/Saturn encounter period. Table 6-1 Near Encounter Radio Science Display Requirements TTS Displays DOY 317, 318 during RSST Support - Radio Science Page 15, D-3 - HS and WB AGC plots on either D-9, 4 or 5 NOCC Displays DOY 317, 318 during RSST Support - NOCC-9 SSI Display DSS-63 - NOCC-10 SSI Display DSS-43 - NOCC-6, 7, 8 Radio Science Graphics (Request forms will be provided to NOA for display configuration.) The following displays are also required, but the channels will be negotiated so as not to interfere with other users. - NRS/DRS at DSS-43 and DSS-63 F707, F708, F709 - Monitor of SC-31; DSS-63/62, DSS-43/44 F402 - Monitor of SC-32; DSS-61, DSS-42 F402 - Track of SC-31; DSS-63/62; DSS-43/44 F204, F207 - Track of SC-32; DSS-61, DSS-42 F204, F207 6.2.3 Briefing and Checklist Strategy During the period of time that the Radio Science Representatives are at the stations, the RSST will conduct daily briefings. The purpose of the briefings will be to keep the Representatives informed of Project status, plan and ISOE updates, problems and concerns which affect the experiment, etc. -6.4- In turn, the Representatives will use the briefing to inform the RSST of any station problems, unresolved issues concerning equipment, operations or procedures, etc. Table 6-2 is an outline form of the agenda for the conduct of the briefings. The briefings with the Representatives at both DSS-63 and DSS- 43 will be conducted over the Radio Science coordination net with JPL. Refer to the timeline in Section 4.0 for the briefing times. Table 6-2 Daily RSST Briefing Agenda A. Station Inputs 1. Station general status and weather report 2. Radio Science System status 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. Confirm predict set numbers 5. Date and time of next briefing Prior to the Radio Science encounter events at both Titan and Saturn, the RSST will verify station calibration and configuration parameters using a checklist via the Radio Science coordination net with the Representatives. Postpass reports will also be conducted in a similar manner in order to insure hardcopy data acquisition, tape IDs, playback status, DRs, etc. The checklists are included in the Appendix. 6.2.4 Radio Science Control Function Strategy The six control functions itemized in Table 6-3 will be exercised via the Radio Science coordination net to the Radio Science Representatives during critical-event periods only. (-During other operational periods, the RSST will request needed changes via the Project operational net,) Specifically, the Science Adviser will be responsible for making the requests to the stations. However, the Science Adviser may transfer control to another RSST member on line in the Mission Support Area during the Saturn DSS-43 to DSS-63 overlap period. The choice of parameters will be a function of the uncertainties in the experiment to include system failures, as well as the need for real-time visibility. As such, it is impossible to determine beforehand when changes -6.5- will be required. An initial set of parameters for these functions will be provided to the stations during the RSST/DSS Representative briefings. 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. Initiating, extending, and restarting ODA run/idle modes 6. Selection of PPM noise diode and integration times 6.3 Operations Schedule Refer to the +/- ten-day timeline and the Near Encounter expanded timeline in Section 4.0 for the complete integrated schedule of events. The normal manpower complement, by function, at the Radio Science desk in the Mission Support Area will be: one Operations Coordinator, one Science Adviser, and one Operations Analyst. The RSST Chief, Experiment Representative, and Software Engineer form the core of alternate manpower. Refer to the Appendix for a list of Radio Science operations personnel. Real-time operations will be separated into three periods: the pre-encounter period which is ten days before the Titan events, the Titan and Saturn events of Near Encounter on days 317 and 318, and the Post Encounter period of ten days following the Saturn events. 6.3.1 Pre-Encounter Ten-Day Period During the pre-encounter period, the RSST will man the Radio Science desk in the Mission Support Area for the daily briefings to the Radio Science Representatives and during ORT-5. The daily briefings between JPL and the Radio Science Representatives will begin on DOY 308. In order to allow a reasonable shift schedule for the Representatives, the briefings from DSS-43 and DSS-63 will be scheduled at separate times during the day. If coordination is required between the Representatives, a special coordination net can be scheduled. The exception to the separate daily briefings is the ORT-5 briefing on DOY 310 in which both Representatives will be on the net for a common briefing. The briefing will be conducted from the Radio Science desk in the Mission Support Area with Operations Coordinator, Science Adviser, and RSST Chief as a minimum complement. ORT-5 will occur during this period of DOYs 310-311. The RSST will man the Mission Support Area with the full complement of operations personnel in the same way the Near Encounter period operations will be conducted. -6.6- Manning for the test will begin with the RSST on line at 22:00 UTC on DOY 310 and will remain on line until 09:00 on DOY 311. The critical-event period for ORT-5 will be from 310/02:24 to 311/07:39. 6.3.2 Near Encounter Operations Period During the Near Encounter Radio Science period, real-time operations will begin with the Titan prepass briefing with the DSS-63 Representative at 03:00 UTC on DOY 317. The full complement of RSST operations personnel will be on line in the Mission Support Area at 04:45 UTC, completing Titan real-time operations at 09:00 UTC with a post-pass briefing. The Radio Science critical- event period for the Titan observation begins at 06:00 UTC and continues through to 08:30 UTC. For the Radio Science Saturn occultation and ring experiments, the RSST will begin real-time operations with the DSS-43 pre-pass briefing at 17:00 UTC on DOY 317. This briefing will not be conducted with the full complement of RSST real-time operations personnel because of manpower scheduling conflicts, but will be conducted by someone designated by the RSST who will not have been on during the previous night's Titan occultation. The full complement of RSST real-time operations personnel will be on line in the Mission Support Area at 00:30 UTC on DOY 318. At 01:00 an update briefing will be held with the DSS-43 Representative. The critical-event period for operations will begin at 02:00 and continue through to 07:15. Due to real-time operations, the pre-pass briefing with DSS-63 will consist of a go/no-go indication, with all verification being accomplished by the Representative. Any problems with station configuration, however, can be communicated through the net at any time and to the NOPE on duty if the RSST is not on line. Post-pass briefings will be conducted following the Saturn ring-scattering experiment for both DSS-43 and DSS-63 beginning at 08:00. Part of the RSST may be required to remain on line beyond the Radio Science events in order to support the maneuver anomaly recovery strategy. 6.3.3 Post-Encounter Ten-Day Period The ten days following the Near Encounter will be light for real-time operations by the RSST. Briefings with the Radio Science Representatives will continue as before until the Representatives leave the stations to return to JPL. The RSST may require some post-encounter calibrations if problems arise during the encounter. Otherwise, post-encounter operations will be primarily concerned with the delivery of data, hardcopy products, and the processing of that data. Section 7.0 will discuss data handling and delivery. 6.4 Contingency Planning The following contingencies reflect the known or plausible problems that could arise which would seriously impair the Radio Science experiment. As such, a complete list would be impossible to generate, but the chance of some situation occurring outside of this list, hopefully, is small. The RSST feels the following set of contingencies is possible given past history and current uncertainties. With each contingency, a discussion of the major steps for recovery or the desired fallback position is presented. -6.7- These steps do not discuss the greater details, for they would depend on the exact circumstances of the problem, but they clearly point the direction toward a solution. 6.4.1 Loss of a Prime 64-Meter Station In this case, the RSST would transfer the 34-meter station covering Voyager 2 for the plasma calibration to Voyager 1. The RSST would then establish equivalent closed-loop tracking modes per the ISOE as for the 64-meter station. The RSST would not switch the 26-meter backup to Voyager 2, but would choose to give up the plasma calibration and keep the backup on Voyager 1. 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 a data type 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 is not precisely known, the RSST would then request frequency offsets in the predict sets in order to center the signal in the MMR open-loop filter bandpass. 6.4.4 ODA Halt or Failure The station would perform on-site diagnostics and corrective action 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 to control tracking mode change requirements in lieu of TWNC on/off sequenced events. Also, the RSST would require switching to backup predict sets in order to maintain the signal in the center of the open-loop filter in the MMR 6.4.6 Loss of One or More Channels in Four-Channel, Open-Loop Configuration 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 -6.8- 3. XLCP* 4. SLCP * XRCP, XLCP will be reversed in priority if the spacecraft experiences an X- band TWTA failure prior to or during the observations. When possible, configuration changes should be made without disturbing the backup system. 6.4.7 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 trim up tuning as a result of non-linear effects. 6.4.8 Major Spacecraft Antenna Pointing Error Following Any of the Near Encounter Maneuvers The RSST will support the Spacecraft Team and the Flight Operations Office in their contingency plan by providing real-time support in the Mission Support Area to include SSI operations support, open-loop signal level reporting, and real-time analysis on the open-loop data. 6.4.9 Loss of One or More Open-Loop Channels in the Two-Channel Configuration The station would perform on-site diagnostics and corrective action at their discretion. The backup DRA system 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. 6.4.10 Obvious 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-per-channel basis. The effect of each would be assessed before additional steps performed. 6.4.11 Unable to Perform Required Pre-Pass Calibrations at Prime 64-Meter Stations The RSST would request that the station perform a post-pass calibration. If, due to an adverse weather situation, a post-pass calibration is not possible, the RSST would request that the station hold their configuration until the calibration procedure can be performed. 6.4.12 Loss of Real-Time NRS Data Visibility at JPL The RSST would inform the station representative as to the outage and to enhance the verbal reporting. Also, if the problem is in the RTM, the RSST would instruct NOCC to hold the last displays in order to make hardcopies before the system is reinitialized. -6.9- 6.4.13 Loss of Open-Loop Signal Due to ODA Predict Set Errors The RSST would estimate how long the outage will exist. The RSST will then ascertain if valid points exist in the contingency sets on the ODA disk to solve the anomaly. The RSST will switch to a contingency set if the duration of the outage is unacceptable. ODA frequency offsets will be used as a last resort. 6.4.14 Unavailability of Key Personnel Due to Sickness or Otherwise A vacancy in the real-time operations assignment will be filled by the RSST Chief, Experiment Representative, and RSST Software Engineer in that order. (Refer to Appendix) 6.4.15 Failure of the 5th Floor Mission Support Area Radio Science Display Hardware The RSST would request emergency maintenance and would utilize the alternate work station on the 3rd floor, if necessary, i.e., verbal reports via MIDS net. The Operations Coordinator would ascertain the desirability of assigning one of the real-time operations personnel to the 3rd floor. At the minimum, two real-time operations people will be required at the 5th floor Mission Support Area for voice net communications. 6.4.16 Voice Line Outage Between JPL and Station(s) The RSST would inform the ACE of the outage and use the Project operational net, ACE to OPS Chief, if operable. The DSN representatives will act at his/their own discretion until lines are back in operation. -6.10- 7.0 Data Handling and Delivery This section presents the delivery and handling of the data products expected as a result of the Radio Science experiment, the support requirements for near-real-time processing, and the support required from CTA-21 for converting the medium-band ODRs to computer compatible tapes. 7.1 Data Products List and Delivery Schedule Table 7-1 is a list of the resultant data products from the Titan and Saturn occultations, Saturn ring occultation, and ring-scattering experiments. The products are tabulated by event with an estimate of the total number of tapes expected. Only the primary products are included in this list and not the final deliveries to the experimenter. The second and third columns contain information on the delivery strategy (if tapes are to be copied, where to be delivered, etc.). The second column includes the delivery schedule which is driven by requirements for Radio Science Team quick-look and post-encounter processing. 7.2 Near-Real-Time Data Processing In order to provide quick-look response for the Radio Science investigators, special tracking IDRs will be delivered to the RSST within one hour following the Titan occultation and Saturn ingress events. The RSST will then request priority on the 1100/81 E machine to strip the tapes into ATDF formats. Delivery of the ATDF to the experimenter must be no later than three hours following the event. The experimenter will use the ATDF and the CRS tapes from DOY 315 in order to produce preliminary atmospheric profiles of Titan and Saturn entrance. The RSST will also process, in near-real time, the playback open-loop IDR from DSS-43 Saturn ingress. Processing this tape will involve stripping to an REDR and plotting the Fourier transform of the data on the 1100/81 E computer. The plots will be part of the Radio Science Team quick-look report following encounter. 7.3 Post Encounter Medium-Band Data Conversion The medium-band, open-loop tapes from DSS-63 are a special case from all other products. The RSST will accept delivery of the medium-band ODRs, log them in, and forward the tapes to CTA-21 for conversion to computer-compatible tapes. The RSST will include with the delivery, a log sheet to maintain continuous records of the data, requests for specific processing periods, priorities for processing, and prenumbered labels for the resultant tapes. An example of the label is illustrated below: TAPE ID# ________ START TIME _______ STOP TIME_______ CHANNEL # ________ -7.1- Completion of the processing at CTA-21 should take approximately three to four weeks following the receipt of the MB ODRs. The expected output quantity is: Titan ~100 data IDRs ~20 calibration IDRs Saturn ~366 data IDRs ~48 calibration IDRs After completing the conversion to computer-compatible tapes, CTA-21 will ship the MB ODRs and labeled MB IDRs to the RSST. -7.2- TABLE 7-1 DATA PRODUCTS-DELIVERY-STRATEGY SCHEDULE EVENT DATA TYPE DELIVERY STRATEGY DELIVERY SCHEDULE Titan DSS-63 Quick-Look TRK IDR Deliver directly to RSST Within one hour following event (317/06:00-317/08:00) 264-365 Titan DSS-63/62/61 Final TRK IDR Deliver directly to RSST Within 12 hours following event Voyager I passes 264-365 Final TRK IDR Deliver directly to RSST Within 12 hours following event Voyager 2 passes 264-365 Titan DSS-63 CRS Tape Deliver from NAV to RSST Deliver by 315/17:00:00 (first late predict) NOCC Monitor IDR Deliver directly to RSST Deliver within 12 hours following 264-365 event MB ODRs (3 tapes) Copy originals at station Expedite shipment to JPL immediately and send copies to NDC JPL, following copy process (Originals attention: N. Fanelli will be requested within two weeks (Shipment of originals will be after validation of copies--approxi- requested after copies have been mately 4 to 6 weeks following event.) converted to computer- compatible tapes and validated.) DIS DUMP of AGC/PPM Ship with tape products Same as tape shipment data. TERMINET Printout. SNT Stripchart Backup DRA tapes Upon request from RSST of a Expedited delivery upon request of specific time period, station RSST. Maintain originals at station will copy the appropriate DRA for a minimum of 8 weeks. tape and send a copy to JPL NDC, attention: N. Fanelli. Originals will be requested after receipt and validation of copy. RSSEDR Delivery from SDT to RSST via As soon as possible following the tape. merger of the SASDRS files. Maneuver Reconstruc- Delivery from SCT to RSST via Within 20 days following event tion Tape tape. EVENT DATA TYPE DELIVERY STRATEGY DELIVERY SCHEDULE Saturn Ingress DSS-43 Quick Look TRK IDR Deliver directly to RSST Within one hour following event. (318/01:30-318/04:00) 264-365. Saturn Ingress Final TRK IDR Deliver directly to RSST Within 12 hours following event. DSS-43/42/44 Voyager I passes 264-365. Final TRK IDR Deliver directly to RSST Within 12 hours following event. Voyager 2 passes 264-365. Saturn Ingress DSS-43 Playback OL IDR Playback time to start at 05:15 Within 1 hour following completion of (data period to be UTC. Deliver directly to RSST, playback. determined in real 264-365. time) NOCC Monitor IDR Deliver directly to RSST Deliver within 12 hours following event. 264-365. NB ODRs (15 tapes) Copy originals at station and Expedite shipment to JPL immediately send copies to NDC JPL, atten- following copy process (originals will tion: N. Fanelli (shipment be requested within two weeks after of originals will be requested validation of copies) after copies have been validated) DIS DUMP of AGC/PPM Ship with tape products Same as tape shipment data. TERMINET Printout. SNT Stripchart Backup DRA Tapes Upon request from RSST of a Expedited delivery upon request of specific time period, station RSST. Maintain originals at station will copy the appropriate DRA for a minimum of 8 weeks. tape and send a copy to JPL NDC Attention: N. Fanelli. Origi- nals will be requested after receipt and validation of copy. Saturn Egress/Ring Final TRK IDR Deliver directly to RSST Within 12 hours following event Occultation/Ring Voyager I passes 264-365 Scattering Final TRK IDR Deliver directly to RSST Within 12 hours following event DSS-63/62/61 Voyager I passes 264-365 Saturn Egress/Ring NOCC Monitor IDR Deliver directly to RSST Within 12 hours following event Occ. and Scat. DSS-63 264-365 EVENT DATA TYPE DELIVERY STRATEGY DELIVERY SCHEDULE Saturn Egress/Ring MB ODRs (5) Copy originals at station and send Expedite shipment to JPL immediately Occ. and Scat. DSS-63 copies to NDC JPL, Attention: N. following copy process (originals will Fanelli (shipment of originals will be requested within 2 weeks after be requested after copies have been validation of copies--approximately converted to computer compatible 4 to 6 weeks following event) tapes and validated) DIS DUMP of AGC/PPM Ship with tape products Same as tape shipment data. TERMINET printout. SNT stripchart Backup DRA Tapes Upon request from RSST of a Expedited delivery upon request of specific time period, station RSST. Maintain originals at station will copy the appropriate DRS for a minimum of 8 weeks. tape and send a copy to JPL NDC, attention: N. Fanelli. Originals will be requested after receipt and validation of copy. CRS Tape Delivery from NAV to RSST Delivery by 317/16:00 (second late predict) RSSEDR Delivery from SDT to RSST via Deliver as soon as possible follow- tape ing the merger of the SASDRS files. XSCEL Events TRKIDRs Deliver copies of TRKIDRs for Deliver within three weeks following XSCEL event periods to RSST, events. (XSCEL event periods 264-365. defined on Project timelines.) 8.0 Appendix This section contains material that is supplementary to the text of the preceding sections of this document. Additionally, it contains material of general usefulness to the Experiment. The contents of this section are listed in order below. Table A-1 Formulae for Reconstruction of the Antenna Frequency from the Extracted Signal Frequency in the Open-Loop Receiver Filters Table A-2 Major Event Summary for the Titan Occultation Table A-3 Major Event Summary for the Saturn Occultation and Ring Observations Figure A-1 Titan Occultation Signal Dynamics Figure A-2 Saturn and Ring Signal Dynamics Table A-4 Received Maximum Power Levels and Spacecraft Frequencies for the 64-Meter Subnet of the Voyager 1 Saturn Encounter Figure A-3 Occultation Data Assembly ADC Input Power Level Versus Input SNR Calibration Curve Figure A-4 Elevation Angle Table A-5 Phone Numbers of Key Radio Science Personnel & Operations Stations Table A-6 Checklist DSS-42 Pass 1184 Table A-7 Checklist DSS-43 Pass 1168 Table A-8 Checklist DSS-44 Pass 1168 Table A-9 Checklist DSS-61 Pass 1183/1184 Table A-10 Checklist DSS-62 Pass 1183/1184 Table A-11 Checklist DSS-63 Pass 1167 Table A-12 Checklist DSS-63 Pass 1168 TABLE A-1 Formulae for Reconstruction of the Antenna Frequency from the Extracted Signal Frequency in the Open-loop Receiver Filters Modified Block III Open-loop Receivers (DSS-43) fs = 48*fpo + 50 x 10^+6 - folrs fx = 11/3 * (48*fpo + 50 x 10^+6) - folrx Narrow-band/Medium-band MMR Open-loop Receivers (DSS-63) fs = 48*fpo + 300 x 10^+6 + folrs fx = 11/3 * (48*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 46 x 10^+6 at DSS-43 and 41 x 10^+6 at DSS-63 (Hertz) fx/fs = 11/3 for all tracking modes TABLE A-2 MAJOR EVENT SUMMARY--TITAN (Note: All times are approximate--the ISOE is the controlling document.) TIME (ERT) EVENT 317/06:32:00 1. Start ground recordings. Open-loop system begins recording. 06:42:21 2. CONSCAN off. 06:44:00 3. Configure S/C for occultation. TWTA power mode changes to optimize S/N. Telemetry and ranging off. 06:49:00 4. TWNC on. Switch to S/C frequency standard. 06:52:00 5. Turn S/C to occultation ingress attitude. Offsets antenna axis 0.11 deg from Earth line to optimize occultation entry data for X-band. 06:53:-- 6. Nominal start of quiet period. Provides baseline frequency and amplitude data. Last chance to verify ground configuration. 07:08:-- 7. Approximate start of ionospheric occultation. Measurement of topside ionosphere near sunset. Primarily affects S/X Doppler, signal levels stable. 07:11:-- 8. Ionospheric occultation (entrance). Probes sunset ionosphere. Structure unknown, may be complex. Ground may observe signal level fluctuations, especially at S-band. O/L conditions may occur for closed-loop system. Can be monitored on SSI. 07:12:15 9. Nominal start of atmospheric occultation. Probes neutral atmosphere at sunset. Actual start time highly uncertain. Rapid decrease in S- and X-band signal levels expected. O/L condition at Xband expected not later than about 20 seconds from start: O/L condition at S-band expected not later than about one minute from start. Signal dynamics can be monitored on SSI. 07:15:10 10. Begin S/C turn to occultation egress attitude. Offset antenna for occultation exit geometry. No signals expected to be observable in this period. TABLE A-2 (cont.) TIME (ERT) EVENT 07:19:30 11. Begin atmospheric occultation exit observations. Probes neutral atmosphere near sunrise. Level of signals transmitted highly uncertain. Deep atmosphere case: S/X signals will peak at nominal time of 07:23. Duration of X-band signal about 20 seconds. Thin atmosphere case: No signals will be observed prior to nominal occultation exit time, then S-band only. Can be monitored on SSI. 07:24:30? 12. Complete atmospheric occultation. Signal levels low due to offset antenna pointing. Approximately -30db X-band, -15db S-band. 07:25:-- 13. Ionospheric occultation (exit). Probes ionosphere near sunrise. Similar to entrance, but possibly only S-band signal observable in real time. Dynamic signals possible. 07:29:-- 14. Nominal completion of topside ionospheric occultation (exit). Similar to entrance conditions. Signals stable in frequency and amplitude after this time. 07:29:00 15. Begin quiet period. Provides baseline data following occultation. 07:58:10 16. Begin turn to Earth line. Removes antenna offsets provided for occultation. S/X signal levels increase to pre-occultation values. 08:07:24 17. Begin mini-ASCAL. Provides calibration data for maneuver reconstruction. X-band signals vary at least 5.6 db. S-band signals vary at least 0.3 db. 08:15:-- 18. Reconfigure S/C for telemetry. TWTA power modes restored to telemetry configuration. Telemetry and ranging on. TWNC off. TABLE A-3 MAJOR EVENT SUMMARY- -SATURN/ RINGS (Note: All times are approximate--the ISOE is the controlling document.) TIME (ERT) EVENT 318/02:07:-- 1. Finalize occultation configuration of DSS-43. 02:24:47 2. Start narrow-band ODA recording. Begin collection of open-loop S/X data for calibration purposes. 02:30:-- 3. S/C executes small maneuver to correct boresight for FP roll. Small X-band signal level increase expected. 02:30:00 4. Configure S/C for atmospheric occultation. TWTA power modes changed to optimize S/N (X-Lo, S-Hi). Telemetry and ranging modulation off. 02:35:25 5. TWNC On Spacecraft is switched to stable on-board reference source for occultation measurement. Ground stations go to non-coherent two-way tracking. 02:50:-- 6. Begin ionospheric occultation. Measurement of topside ionosphere near sunset. Primarily affects S/X Doppler, signal levels stable. 03:04:-- 7. Ionospheric occultation (entrance) Probes sunset ionosphere. Complex signal structure expected. Ground will observe large signal level fluctuations, possible large frequency excursions. O/L conditions may occur for closed-loop system, with S-band more severely impacted than X-band. Effects can be monitored on SSI. 03:06:37 8. Nominal start of atmospheric occultation. Probes neutral atmosphere in S. Arctic region. Rapid decrease in S/X signal levels during first few minutes, probable large excursions in Doppler pseudoresiduals. Signal dynamics can be monitored with SSI for at least several minutes. Part 1 of limbtracking maneuver begins. TABLE A-3 (cont.) TIME (ERT) EVENT 03:10:-- 9. Deep atmospheric occultation. Probes south polar region of atmosphere and ionosphere. Model calculations indicate that signal may be above closed-loop threshold much of time, although this is highly uncertain. Plasma effects in Saturn auroral zone may be important; if so, the S-band signal will be dynamic. Signals probably will be visible on SSI. 03:32:59 10. DSS-63 rise. DSS-63 begins observation of occultation events. 03:56:55 11. End limb-tracking maneuver - Part 1. If detectable prior to this time, all signals will disappear. 04:00:00 12. Change prime station to DSS-63 from DSS-43. 04:01:-- 13. Reconfigure TWTAs for occultation exit and ring events. TWTA power-mode change (S-Lo, X-Hi) to optimize ring experiments. Not observable from ground, free space signal levels at exit will be different from those at entrance. 04:02:00 14. UVS Sun occultation exit. 04:21:47 15. Resume limb-tracking maneuver. Begin Part 2 of limb-tracking maneuver. Signals expected to be visible on SSI. Closed-loop receivers may lock up intermittently at this time. Occultation ray is also passing through Ring A. 04:23:45 16. Occultation ray in Cassini Division. Momentarily stable signals expected, 25 db below free space values. 04:24:15 17. Occultation ray contacts B Ring. Unknown path characteristics. Probable loss of signal if previously detected. 04:32:00 18. Occultation ray contacts C Ring. Unknown path characteristics. S/X signals probably detectable on SSI, may be possible to lock up closed-loop system. Signal levels increasing at both wavelengths. 04:32:07 19. DSS-43 set. TABLE A-3 (cont.) TIME (ERT) EVENT 04:36:03 20. Atmospheric occultation exit. Voyager I reappears from behind Saturn within the eastern ansa of the rings. Signal levels at free space values. End limb-tracking maneuver - Part 2. 04:38:00 21. Ionospheric occultation (exit). Probes sunrise ionosphere. Similar to entrance measurements, dynamic S/X signals expected. O/L conditions may occur in closed-loop receivers. Can be monitored by SSI. 04:44:31 22. Occultation by Ring C. Ray contacts inner edge of Ring C. Possible start of slow decrease in signal level, possible low-level signal scintillations. Monitor on SSI and closed-loop AGC. 04:49:17 23. Observe French gap. Probable momentary return of signal level to near free space value, 27 seconds' duration. Monitor on SSI and closed-loop AGC. 04:49:44 24. Occultation by Ring B. Begin occultation by B Ring. Expected strong scintillations, weak signals. Average signal level expected to continue to decrease well below values seen in Ring C. Monitor on SSI and closed-loop AGC. 04:53:-- 25. Occultation by "outer" Ring B. Approximate beginning of occultation by optically most dense portion of ring. Average signal level expected to be near or below noise level, gaps in ring may allow brief, near instantaneous return of signal levels to near free space value. Monitor on SSI and closed-loop AGC. 04:55:33 26. Enter Cassini Division. Ray passes through Cassini Division, 50 seconds' duration. Expect return of signal levels to near free space values, although signal levels may scintillate if significant material is present within the Division. Expect to achieve closed-loop lock. Monitor on SSI and closed-loop AGC. TABLE A-3 (cont.) TIME (ERT) EVENT 04:56:26 27. Occultation by Ring A. Ray contacts inner edge of Ring A. Expect return to signal conditions observed near outer edge of Ring B. Monitor on SSI and closed-loop AGC. Signal levels should increase and dynamic fluctuations decrease after brief period. 04:58:40 28. Observe Encke gap. Ray passes through Encke gap, 10-second duration. Expect return of signal to level near free space value, significant scintillations may be present. Expect to achieve at least momentary closed-loop lock. Monitor on SSI and closed-loop AGC. 04:58:50 29. Occultation by Outer A Ring. Ray continues through outer portions of Ring A. Expect increasing signal levels and decreasing signal dynamics. Monitor on SSI and closed-loop AGC. 04:59:46 30. Observe Pioneer gap. Ray passes through Pioneer Division, 40-seconds' duration. Expect closed-loop system to lock up, signal levels near free space value. Monitor on SSI and closed-loop AGC. 05:00:08 31. Occultation by F Ring. Ray enters final significant known ring, 6 seconds' duration. Expect momentary signal fluctuations, decreasing effects. Monitor on SSI and closed-loop AGC. 05:00:10 32. Complete occultation by primary rings. Signal levels return to free space values. 05:03:16 33. Begin ring-scattering observations. Illuminate rings from underside with Voyager signals and observe energy scattered toward Earth. Initially observe diffusely transmitted signal at scattering angle of 0.9-6.6 deg. Spacecraft begins ring-scatter maneuver, direct signals will slowly decrease over extended period. Direct signal begins slow drift to higher frequencies in SSI display. Scattered signal probably not visible on SSI. Monitor on SSI. TABLE A-3 (cont.) TIME (ERT) EVENT 05:45.-- 34. Ring-plane crossing. Spacecraft moves to same side of ring plane as Earth. Scattering shifts from diffuse transmission to diffuse reflection. Scattering angle 6.6 deg. Direct signal continues drift to high frequencies in SSI display, MB passband. 06:44:12 35. End ring-scattering observations. Scattering angle 12 deg. 06:45:11 36. S/C returns to Earth pointing. 06:55:23 37. Begin mini-ASCAL Provides calibration data for maneuver reconstruction. X-band signal level varies by 5.6 db or more. S-band signal level varies by 0.3 db or more. 07:03:-- 38. Reconfigure spacecraft for telemetry. Telemetry and ranging modulation on. End of occultation science events. TABLE A-4 RECEIVED MAXIMUM POWER LEVELS AND SPACECRAFT FREQUENCIES FOR THE 64-METER SUBNET OF THE VOYAGER I SATURN ENCOUNTER Received maximum power levels for: Titan entry and exit (DSS-63) \ / S-band High Power = -144.4 dBm Saturn entry (DSS-43) / \ X-band Low Power = -134.2 dBm Received maximum power levels for: Saturn exit (DSS-63) \ / S-band Low Power = -149.0 dBm Ring Occultation (DSS-63) > < X-band High Power = -132.3 dBm Ring-Scattering Observation (DSS-63) / \ Voyager I USO frequency (before Doppler): 2294.998678 MHz Voyager I Auxiliary Oscillator frequency (before Doppler): 2296.484000 MHz *This USO frequency has been adjusted for expected effects of radiation at Saturn. **This auxiliary oscillator frequency is the average of the two auxiliary oscillators on-board Voyager 1. Frequency offsets would be used in real time for a particular auxiliary oscillator, if selected. TABLE A-5 PHONE NUMBERS OF KEY RADIO SCIENCE PERSONNEL & OPERATIONS STATIONS KEY RADIO SCIENCE PERSONNEL Name Work Phone Home Phone Beeper B. Buckles 4015/5555 805-724-1356 --- P. Doms 7934 213-797-1362 817 N. Fanelli 5541 --- --- D. Finnerty 7988 213-797-2162 178 D. Holmes 2841 714-626-1773 682 H. Hotz 6197 213-352-6538 --- D. Johnston 7539 213-799-3387 --- R. Kursinski 5250-313 --- --- D. Sweetnam 6197 213-790-6154 107 G. Tyler (Stanford) 415-497-3535 415-327-7648 --- J. Wackley 7641 --- --- G. Wood 4638/7359 213-790-7613 --- OPERATIONS STATIONS Station 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 TABLE A-6 CHECKLIST DSS 42 PASS 1184 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 & 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 10 SECONDS TABLE A-7 CHECKLIST DSS 43 PASS 1168 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 & CONTROL SYSTEM D. RADIO SCIENCE SYSTEM 2. CLOSED LOOP SYSTEM CHECKS A. RECEIVERS S-BAND 2BLO = 10 HZ AGC = WIDE X-BAND 2BLO = 30 HZ AGC = WIDE B. DIS AGC TOL = 2 AGC INFO TO LINE PRINTER C. MDA DOPPLER SAMPLE RATE = 1 per second D. PPM TWO CHANNEL MODE MONITORING SRCP/XRCP SYSTEM TEMPERATURES TABLE A-7 (cont.) 2. OPEN LOOP SYSTEM CHECKS A. PRIME RECEIVERS FILTER SELECT = 6 S-BAND = 5 KHZ X-BAND = 15 KHZ S-BAND RCVR OUTPUT POWER = +15 dbm X-BAND RCVR OUTPUT POWER = +17 dbm CALIBRATION SIGNAL LEVEL = S-BAND = -144 dbm X-BAND = -134 dbm B. BACKUP RECEIVERS FOR RECEIVED SIGNAL LEVELS OF: S-BAND = -144 dbm X-BAND = -134 dbm OUTPUT SIGNAL LEVEL = +4 dbm 1ST AND 2ND LO FREQUENCY SYNTHESIZERS SET PER SECTION 5.5.2 OF RS OPS PLAN C. ODA CONFIGURE FOR RECORDING PASS DEPENDENT PARAMETERS ARE: MOD 4 6 8 CHN 1 3 3 3 SCN 31 PRD SA01 D. DRA IPS = 30 E. SSI ANALYSIS BANDWIDTH = 5K NO. OF AVERAGES = 128 TRANSFORM SIZE = 1024 AVERAGING MODE = LINEAR CENTER FREQUENCY = AS REQUIRED 3. MICROWAVE SUBSYSTEM S-BAND TWM #1 = SRCP X-BAND TWM #2 = XRCP TABLE A-8 CHECKLIST DSS 44 PASS 1168 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 & CONTROL SYSTEM 2. CLOSED LOOP SYSTEM CHECKS A. RECEIVERS S-BAND 2BLO = 12 HZ AGC = WIDE B. DIS AGC TOL = 2 C. MDA DOPPLER SAMPLE RATE = 10 PER SECOND TABLE A-9 CHECKLIST DSS 61 PASS 1183/1184 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 & 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 10 SECOND TABLE A-10 CHECKLIST DSS 62 PASS 1183/1184 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 & CONTROL SYSTEM 2. CLOSED LOOP SYSTEM CHECKS A. RECEIVERS S-BAND 2BLO = 12 HZ AGC = MED (1183), WIDE (1184) B. DIS AGC TOL = 2 C. MDA DOPPLER SAMPLE RATE = 10 PER SECOND TABLE A-11 CHECKLIST DSS 63 PASS 1167 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 & CONTROL SYSTEM D. RADIO SCIENCE SYSTEM 2. CLOSED LOOP SYSTEM CHECKS A. RECEIVERS S-BAND 2BLO = 10 HZ AGC = MED X-BAND 2BLO = 30 HZ AGC = MED B. DIS AGC TOL = 2 AGC INFO TO LINE PRINTER C. MDA DOPPLER SAMPLE RATE = 1 PER SECOND D. PPM TWO CHANNEL MODE MONITORING SRCP/XRCP SYSTEM TEMPERATURES TABLE A-11 (cont.) 2. OPEN LOOP SYSTEM CHECKS A. PRIME RECEIVER (MEDIUM BAND) FILTER SELECT = 8 ATTENUATORS SET FOR RECEIVER OUTPUT POWER = +13 dbm FOR S AND X-BAND RCP CHANNELS AND RECEIVED SIGNAL POWER EQUAL TO -134 dbm X-BAND -144 dbm S-BAND B. BACKUP RECEIVER OUTPUT SIGNAL LEVEL = +6 dbm FOR RECEIVED SIGNAL LEVELS OF S-BAND = -144 dbm X-BAND = -134 dbm CHANNEL 1 2ND LO FREQUENCY = 299.572 MHZ CHANNEL 3 2ND, LO FREQUENCY = 296.715 MHZ 1ST LO SYNTHESIZER FREQUENCY = PER SECTION 5.5.2 OF OPS PLAN C. ODA CONFIGURE FOR MEDIUM BAND RECORDING PASS DEPENDENT PARAMETERS ARE: MBS 300K SCN 31 PRD TIO1 D. DRA DRA #1 MEDIUM BAND RECORDER IPS = 30 DRA #2 WIDE BAND RECORDER IPS = 120 E. SSI ANALYSIS BANDWIDTH 5K NO. OF AVERAGES = 128 TRANSFORM SIZE = 1024 AVERAGING MODE = LINEAR CENTER FREQUENCY = AS REQUIRED 3. MICROWAVE SUBSYSTEM S-BAND TWM #1 = SRCP X-BAND TWM #2 = XRCP TABLE A-12 CHECKLIST DSS 63 PASS 1168 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 & CONTROL SYSTEM D. RADIO SCIENCE SYSTEM 2. CLOSED LOOP SYSTEM CHECKS A. RECEIVERS S-BAND RCVR 1 = SRCP RCVR 2 = SLCP 2BLO = 12 HZ AGC = WIDE X-BAND RCVR 3 = XRCP RCVR 4 = XLCP 2 BLO = 30 HZ AGC = WIDE B. DIS AGC TOL = 2 AGC INFO TO LINE PRINTER C. MDA DOPPLER SAMPLE RATE = 10 PER SECOND D. PPM FOUR CHANNEL MODE MONITORING S-BAND RCP/LCP AND X-BAND RCP/LCP SYSTEM TEMPERATURES TABLE A-12 (cont.) 2. OPEN LOOP SYSTEM CHECKS A. PRIME RECEIVER (MEDIUM BAND) FILTER SELECT = 8 ATTENUATORS SET FOR RECEIVER OUTPUT POWER = +13 dbm FOR S AND X-BAND RCP CHANNELS AND RECEIVED SIGNAL POWER EQUAL TO -134 dbm X-BAND -144 dbm S-BAND B. BACKUP RECEIVER OUTPUT SIGNAL LEVEL = TBS FOR RECEIVED SIGNAL LEVELS OF S-BAND = -144 dbm X-BAND = -134 dbm CHANNEL 1 2ND LO FREQUENCY 299.572 MHZ CHANNEL 2 2ND LO FREQUENCY 298.715 MHZ CHANNEL 3 2ND LO FREQUENCY 296.715 MHZ CHANNEL 4 2ND LO FREQUENCY 293.572 MHZ 1ST LO SYNTHESIZER FREQUENCY = PER SECTION 5.5.2 OF OPS PLAN C. ODA CONFIGURE FOR MEDIUM BAND RECORDING PASS DEPENDENT PARAMETERS ARE: MBS 300K SCN 31 PRD SA01 D. DRA DRA #1 MEDIUM BAND RECORDER IPS = 30 DRA #2 WIDE BAND RECORDER IPS = 120 E. SSI ANALYSIS BANDWIDTH 5K NO. OF AVERAGES = 128 TRANSFORM SIZE = 1024 AVERAGING MODE = LINEAR CENTER FREQUENCY = AS REQUIRED 3. MICROWAVE SUBSYSTEM S-BAND TWM #1 = SRCP S-BAND TWM #2 SLCP X-BAND TWM #2 = XRCP X-BAND TWM #1 XLCP