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The Voyager Uranus Travel Guide

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The Voyager Uranus Travel Guide PD 618-150 The Voyager Uranus Travel Guide UMB IEL URANUS ARIEL ~ · .. (NASA- C - 188441) THE VOYAGER URA NU S TRAV EL ~91-7128 GU I DE (JPL) 171 p Unclas 00/13 0015283 August 15, 1985 National Aeronautics and Space Administration ..IPL Jet Propulsion Laboratory California Institute of Technology Pasadena, California JPL D-2580 Voyager 2 approaches the sunlit hemisphere of the tilted gas giant known as Uranus. In this geometrically-accurate view, two hours before closest approach on January 24, 1986 we are able to spot the small orb of Umbriel {at 10 o'clock from the spacecraft), one of the five presently known moons of Uranus. Voyager 2 will also scan the nine narrow rings that are darker than coal dust. VOYAGER URANUS GU Prepared by Voyager Mission Planning Office Staff by: Charles Kohlhase er, Mission Planning Voyager Project Table of Contents Page l. Introduction • • • • • • • • • • • 0 • • • • • • • • • • • • • • • • • • • • • • • $ • l Voyager's Past •••• • • • • • • • • • • • • • • • • • 0 • • • • • • • • • © • 3 Anticipating Uranus • • • • • • • • • • • • • • • • 0 • • • • • • • • • @ • 5 2. Uranus e • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 7 Overview of the Planet • • • • • • • • • • • • • 0 • • • • • • • • • • • 8 The Atmosphere of Uranus • • • • • • • • • • • • • • • • • • 0 • • • • 11 The Magnetosphere of Uranus ...... 12 The Satellites of Uranus • • • • • • • • • • • • • • • • • • Q • • @ • 14 The Rings of Uranus . .. 3. Getting The Job Done . .. .. .. .. 19 Planning • • • • • • • • • • • . • • • • • • • • • • •• • • • • • • • • • • •• • • 19 Sequencing . ... .. .. .. .. .. .. 22 Flight Operations . .. .. .. .. ...... 24 Commanding . .. .. .. O e e G 111 25 Receiving Data . .. .. .. ... • • (II • 26 The Results . .. .. .. .. .. 29 4. Scientific Objectives . .. 31 Imaging Science Subsystem ( ISS) . ... 32 Infrared Interferometer spectrometer and Radiometer (IRIS) . .. .. .. .. .. Ultraviolet Spectrometer (UVS) •••••••••••••••.• 36 Photopolarimeter Subsystem (PPS) ••••••••••••••• 38 Radio Science Subsystem (RSS) •••••••••••••••••• 39 Fields and Particles Experiments • • • • • • • • • • • • 0 ~ • 43 Planetary Radio Astronomy (PRA) . .. .. ~ .. Magnetometer (MAG) . .. .. .. , . 44 Particle Detectors • • • • • • • • • • • • • • • • • • • • • • • • • • $ 0 • 45 i Table of Contents Page Plasma Subsystem (PLS) ••••••••••••••••••••••••• 45 Low-Energy Charged Particle (LECP) and Cosmic Ray Subsystem (CRS) ••••••••••••••••••• 45 Plasma Wave Subsystem (PWS) •••••••••••••••••••• 46 Sensor Engineering Characteristics . 48 The Physics of the Optical Target Body Instruments . .. .. 48 Science Links . .. 52 5. Voyager Spacecraft ••••••••••••••••••••••••••••••• 57 The High Gain Antenna •••••••••••••••••••••••••• 58 Spacecraft Attitude Control •••••••••••••••••••• 60 Spacecraft Maneuvers ••••••••••••••••••••••••••• 61 Scan Platform •••••••••••••••••••••••••••••••••• 63 Spacecraft Power Subsystem ••••••••••••••••••••• 64 Digital Tape Recorder •••••••••••••••••••••••••• 66 The Spacecraft Receiver •••••••••••••••••••••••• 67 The Computer Command Subsystem ••••••••••••••••• 69 The Flight Data Subsystem •••••••••••••••••••••• 70 The Science Instruments •••••••••••••••••••••••• 72 6 • ssion Highlights ••••••••••••••••••••••••••••••• 75 Pre-Encounter Test and Calibration Activities •• 76 Observatory Phase {OB) ••••••••••••••••••••••••• 79 Far Encounter Phase (FE) ••••••••••••••••••••••• 80 Critical Late Activities ••••••••••••••••••••••• 81 Near Encounter Phase (NE) . .. 82 Post Encounter Phase (PE) . .. .. 90 Contingency Sequences . .. .. .. 92 Cruise to Neptune •••••••••••••••••••••••••••••• 94 ii Table of Contents Page 7. What's New • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • @ • 95 Maintaining a Strong Signal •••••••••••••••••••• Discarding Unnecessary Picture Data •••••••••••• 96 More Accuracy for Fewer Bits •••••••••••••••• Taking Good Pictures in Feeble Light Levels 98 Diagnosing the Health of the Actuators ••••••••• 101 Faster Response from the "Old" Robot ••••••••••• 101 Big Changes in the Deep Space Network ••••.••••• 102 The Bottom Line • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • $ • 103 8. Gee-Whiz Facts ••••••••••••••••••••••••••••••••••• 105 Overall Mission •••••••••••••••••••••••••••••••• 105 Voyager Spacecraft • • • • • • • • • • • • • • • • • • • • • • • • • • @ • • l Navigation . • • • • • • • • • • • • • • • • • •• • • • • • • . .. .. 110 Science . .. .. ... .. • • • • • • e • • 111 The Future . .. • • • • . .. .. • • ...... • • • • • • 0 • • 112 9. How Far and How Fast • • • • • • • • • • • • • • • • • • • • • • • • • • 0 • • 113 The Great Escape .. .. .. .. .. 114 Voyager 2 at Uranus •••••••••••••••••••••••••••• 117 Key Events, Distances, and Speeds • • • • • • • • • • • $ @ • 120 10. Jupiter and Saturn Highlights • • • • • • • • • • • • • • • • • • ® • 125 Jupiter ....................................... @ .. 125 Jupiter's Rings • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 0 • 128 Jupiter's Moons • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 0 • 128 Jupiter's Magnetosphere •••••••••••••••••••••••• 132 Saturn .......••.•••...•.••.....•...•....•...... 132 Saturn's Rings • e o • • o • o o e o o e • • • e • • e e • e o e e • e • e e e e 135 Saturn's Moons • • 0 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • ® 137 Saturn's Magnetosphere . .. .. .. .. .. 140 iii Table of Contents Page 11. To Neptune and Beyond . .. .. .. .. 143 Neptune Kingdom••·•·•··•···•••••·•••••··••• 144 Neptune and Triton Encounter Planning •••••••••• 146 Post-Neptune Cruise Science . .. .. .. .. .. .. 148 p 12. ect Functional Areas • • • • • • • • • • • • • • • • • • • • • • e • • 159 13. Acknowledgments • • • • * • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 165 1 Index • • • • • • • • • • • • • • • • • • • • 4 • • • • • • • • • • • • • • • • • • • • • • • 167 iv The most beautiful experience we can have is the mysterious. It is the fundamental emotion that stands at the cradle of true art and true science. E e 1. INTRODUCTION Congratulations! You are now the proud owner of a Voyager Uranus Travel Guide, hereafter simply called the Guide. Its purpose is to explain in simple lan age, including numerous illustrations, the Voyager-2 plans to examine Uranus and its moons, rings, particles, and fields. The Guide will also contain a variety of interesting facts about the Voyager mission, both past and future. Before jumping into the Uranus mission particulars we should briefly review the basic elements of an unmanned space mission. These elements are shown in Figure 1-1. You must, course, have a SPACECRAFT capable of carrying a varie of sensors to the destination in order to conduct the SCI you have in mind. The spacecraft cannot escape from Earth's gravity well without the help of a LAUNCH VEHICLE, an expendable set of rocket stages in the olden days or a reusable Space Transportation System, or Shuttle, with ah energy upper stage in the future. No launch vehicle or spacecraft has an error-free guidance system, and so the process of NAVIGATION is necessary to deliver the spacecraft to a precise location at the destination. As shown in Figure 1-2, the navigation process uses range and doppler measurements from huge tracki antennas to estimate the spacecraft location to an accura 1000-3000 km (620-1860 mi). As the spacecraft nears the destination, it takes pictures of natural satellites ag star background (optical navigation) to improve its pos ion estimate to better than 100 km (62 mi). If the spacecraft flight path is off course, mission controllers send corn that cause the spacecraft to use small thrusters to correct its course. l N GATION / --- ---- AUNCH VEHICLE ----!'I - - - -- ~' F re 1 These are the five basic elements of an unmanned space mission. Earth Base is comprised of a large complex of people, computers, communication lines, and tracking antennas. A manned space mission has a sixth element, the human crew for whom life support systems are required. As you have guessed by now, Voyager needs a lot of rt from EARTH BASE, which consists of a vast complex of e, computers, communication lines, and special equipment. ager can cruise happily along, locked onto the sun and a i star, even using onboard fault protection logic to react to problems, but it still needs to hear from Earth regarding its activity plan. A group of scientists decide upon an observation they like Voyager to make. Flight team personnel from such areas as mission planning, science support, spacecraft engineering, flight operations, and sequence im­ plementation, schedule and design the observation into a master activity timeline. As shown in 2 EARTH Figure 1~2. Navigators from Earth Base use radio tracking data and satellite-star images to estimate Voyager's position and heading. Figure 1-3, several steps are taken before Voyager finally carries out these instructions from Earth. Since Voyager has its own internal clock, desired activities can be loaded into its computers many days before they are to be executed. Each set of activities is termed a command load. Voyager's Past The Voyager mission has had quite a past. As shown in Figure 1-4, two spacefaring robots were launched from Earth in 1977, bound for the giant planets of the outer solar system. These amazing machines are like distant extensions of human sensory organs, having already exposed the once-secret lives 3 Figure 1-3. Many steps are necessary to develop activity sequences
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