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Feasibility of Robotic Investigations of Extra-Solar Planets Brice Cassenti Mechanical Engineering University of Connecticut Feasibility of Robotic Investigations of Extra-Solar Planets • Extra-Solar Planets • Solar System Robotic Exploration – Some History – Some Results • Interstellar Missions – Requirements – The Propulsion Question – Feasibility Extra-Solar Planets - Current Status Extra-Solar Planets • First ordinary extra-solar planet discovered in 1995 • Currently almost 350 have been confirmed • Nearest – Epsilon Eridani b 10.5 light years – 1.2 to 1.8 times Jupiter’s mass • Most Earthlike – Gliese 581 at 20.5 light years – Gliese 581 e is at least 1.94 times Earth’s mass – Gliese 581 d is inside the “habitable” zone Gliese 581 Credit ESO at http://www.space.com/scienceastronomy/090423-am-earth-mass-planets.html Epsilon Eridani http://www.solstation.com/stars/eps-erid.htm Solar System Robotic Exploration – A History Solar System Observations • 1800 – Sketches • 1900-1960 – Telescopic Photography • 1960-2010 – – – – Robotic fly-by probes Robotic orbiters/landers Manned lunar landings Earth orbital telescopes Mars Exploration 1800s Proctor - 1867 Schiaparelli - 1888 Mars Exploration 1900 - 1960 Yerkes - 1909 Mars Exploration 1960-2010 Mariner 4 NASA Mariner 7 NASA Hubble NASA Mercury Exploration Antoniadi 1929 Schiaparelli 1889 Mercury Messenger NASA - 2004 Mariner 10 NASA - 1974 More and More and More … Jupiter Pioneer 10 - NASA Pluto Hubble- NASA Conclusion? Robotic Exploration Works Io Galileo- NASA Distant vs. In-Situ Observations of Extra-Solar Planets • Near Term Distant Observations • Long Term Distant Observations • In-Situ Observations Near Term Distant Observations of Extra-Solar Planets • Celestial Mechanics – motion • Photometric observations – surface reflectivity – atmosphere properties • Spectral observations – chemistry Long Term Distant Observations of Extra-Solar Planets • Objective – Solar System Hubble Telescope Resolution – Mirror is 2.4 meters (~94 inches) • Use Mars as example – 6780 km nearest typically 0.52 AU – At 10 light years requires 1000 times diameter • 2.4 km (~1.4 miles) – At least another 100 times for crater counts • i.e., 240 km (~140 miles) For In-Situ Observations We Need Interstellar Missions Astronomical Distances Earth to Moon 4x105 km Earth to Neptune 4x109 km Earth to Alpha Centauri C 4x1013 km Design Criteria • Crew trip time 40 years – Manned crew uses on board ship time – Unmanned crew uses Earth elapsed time • Payload mass – 500 tons for unmanned (Hubble is ~ 12 tons) – 5000 tons outbound for manned – 2500 tons inbound for manned Performance Estimates • Use Special Relativity • Attach origin to spacecraft Interstellar Rockets • Low Speed Total speed change mass exp – Initial Final mass Exhaust velocity – Initial mass Mass of propellent final mass – Exhaust velocity Specific impulse Acceleration of • Relativistic Speed gravity – Replace velocities with rapidities • Conclusion – Speed change and specific impulse are key Rocket Specific Impulse Today • Chemical – Solid: 350 seconds – Liquid: 450 seconds • Nuclear – NERVA Program: 900 seconds • Ion – Typical: 2000 seconds Interstellar Precursor Missions Distance AU Kuiper Belt Objects 100 Solar Focus 550 Oort Cloud 5,000 a Centauri 270,000 Mission *Mass Ratio 40 Year Fly-By Specific Impulse - sec 200,000 600,000 1,000,000 1.01 1.00 1.00 1.03 1.01 1.01 1.34 1.10 1.06 7151803 192.67 23.49 *Mass Ratio 40 Year Round Trip Distance Specific Impulse - sec Mission AU 200,000 600,000 1,000,000 Kuiper Belt Objects 100 1.05 1.02 1.01 Solar Focus 550 1.29 1.09 1.05 Oort Cloud 5,000 10.36 2.18 1.60 a Centauri 270,000 6.84E+54 1.90E+18 92696819562 *Note: Mass ratio is initial mass / final mass 2,000,000 1.00 1.00 1.03 4.85 2,000,000 1.00 1.03 1.26 304462 The Question is Propulsion Saturn F-1 Engine Thrust: 1.5 million pounds Specific Impulse: 350 seconds Sutton, Courtesy of Rocketdyne The Nuclear Option Nuclear Fission Rockets • Nuclear thermal rockets (NTR) – Bimodal – LOX Augmented NTR (LANTR) • Gas core rockets (GCR) – Vortex – Nuclear light bulb (NLB) • Nuclear pulse propulsion – Orion Fission Reaction Nuclear Thermal Rocket Vortex Contained Gas Core Nuclear Rocket Nuclear Light Bulb Orion Performance of Nuclear Fission Rockets minitial MR e m final v I sp g 0 minitial m final m propellant Rocket Chemcal NTR GCR Orion Specific Impulse - s 450 910 1,900 10,000 Note: For a constant Isp energy efficient rocket v 1.6 I sp g 0 Nuclear Fusion Propulsion • Nuclear Reactions • Propulsion Concepts • Solar System Missions Nuclear Reactions • Uranium Fission N1 N2 238 1 1 n U X X n 0 92 k1 k2 0 • DT Reaction 2 3 4 1 H H He n 1 1 2 0 • Lithium Fission 1 6 4 3 n Li He H 0 3 2 1 Propulsion Concepts • Critical Mass Systems • Antiproton Triggered Systems – Hybrid Fission-Fusion Pellets – MICF Hybrid Pellets • External Compression Systems Medusa http://en.wikipedia.org/wiki/File:MedusaNuclearPropulsionOperatingSequenceDrawing.png Medusa Specific Impulse: 500,000-1,000,000 http://en.wikipedia.org/wiki/File:MedusaNuclearPropulsionOperatingSequenceDrawing.png Matter-Antimatter Annihilation Positron-Electron Annihilation e e p p m 0 n n n p m (n 1) n 0 Antiproton-Uranium Nucleus Annihilation p 92 U 238 2 X kn + p p n Pellet Ignition Tritium Fuel Considerations • Tritium is naturally radioactive – Beta decay – Half-life ~12 years • Tritium requires cryogenic storage • Lithium-6 is not radioactive • Lithium-6 does not require cryogenic storage Fusion Reactions • The DT reaction 2 3 4 1 H H He n 1 1 2 0 • And Lithium fission reaction 1 6 4 3 n Li He H 0 3 2 1 • Are equivalent to 1H 2 6 4 3 Li 2 He 2 He 4 Pellet Construction Typical Pellet Geometry • • • • • Core radius Fuel Radius Tungsten Shell Thickness Antiproton Beam Radius Uranium Hemisphere Radius 0.05 mm 1.00 cm 0.10 mm 0.10 mm 0.30 mm Typical Pellet Performance • • • • Antiproton Pulse Maximum Field Pellet Mass Specific Impulse 2x1013 for 30 ns 24 MG 3.5 g – 600,000 s for 100% fusion – 200,000 s for 10% fusion – 3,000 s for contained fusion Solar System Transit Times One-Way Isp: 200,000 sec MR: 1.5 Accel: 0.07g0 Time (days) 8 6 6 13 14 25 44 86 133 175 Limited By Mercury Acceleration Venus Acceleration Mars Acceleration Ceres Acceleration Vesta Specific Impulse Jupiter Specific Impulse Saturn Specific Impulse Uranus Specific Impulse Neptune Specific Impulse Pluto Specific Impulse To Daedalus Study British Interplanetary Society From Nicolson “The Road to the Stars” Daedalus http://www.grc.nasa.gov/WWW/PAO/images/warp/warp44.gif Exotic Propulsion Alternatives Sanger Electron-Positron Annihilation Rocket By G. Matloff Proton-Antiproton Reaction p p m n n 0 Proton-Antiproton Reaction p p m n n 0 Proton-Antiproton Reaction p p m n n 0 m m m m Proton-Antiproton Reaction p p m n n 0 m m e e m e e m m m Proton-Antiproton Reaction p p m n n 0 m m e e m + e e m m m Proton-Antiproton Reaction p p m n n 0 m m e e m + e e m m m Pion Rocket By R. Forward a Centauri C Fly-By • 40 years to arrive Propulsion • 4 light years distance System Pellet Fusion • 0.1c final speed ICF MCF Antimatter Photon Isp sec 500,000 1,000,000 2,000,000 10,000,000 31,557,600 Mass Ratio 550.882 23.471 4.845 1.371 1.105 Pion Rockets Minimum Energy Manned Missions be = 0.95, h = 0.6 Constant Exhaust Velocity Mssion Sun ↔ a Centauri Sun ↔ Reticuli 1 ↔ 2 Reticuli Distance Crew Observer l.y. Time - yr. Time - yr. 4.1 37.5 0.083 40 40 40 41 86 40 Mass Ratio 3.54 8010 1.49 AntimatterFinal Mass Ratio 1.00 3150 0.19 Optimum Exhaust Velocity Mssion Sun ↔ a Centauri Sun ↔ Reticuli Distance Crew Observer l.y. Time - yr. Time - yr. 4.1 37.5 40 40 41 86 Mass Ratio 4.9 5 AntimatterFinal Mass Ratio 0.0052 1.5 Even More Exotic Propulsion • Wormholes • Warp Drives • Interstellar Ramjet Conclusions • Interstellar robotic missions are hard but not impossible. • A 2.4 km telescope in the solar system can significantly add to our knowledge and will be much less expensive. • But what about a 240 km telescope? – We can send robots after picking out target extra-solar planets with a 2.4 km telescopes. Questions?