PDS_VERSION_ID = PDS3 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 80 OBJECT = TEXT PUBLICATION_DATE = 1980-10-31 NOTE = "Timeline for Voyager 1 Saturn Radio Science Events. This is Table A-3 in the Voyager 1 Saturn Encounter Radio Science Operations Plan (JPL Document 618-825; see also OP1S_TXT.LBL in the DOCUMENT directory of this archival volume." END_OBJECT = TEXT END 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°. 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°. Direct signal continues drift to high frequencies in SSI display, MB passband. 06:44:12 35. End ring-scattering observations. Scattering angle 12°. 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.