Lecture 22-Nuclear Power in Space

Transcription

1 Lecture 22-Nuclear Power in Space G. L. Kulcinski March 8, 2004 Rawlings, SAIC 1

2 There are Many Requirements and Solutions to the Power Needs in Space Near Earth Missions Chemical Unmanned Missions To Solar System Manned Missions To Solar System NEEDS Solar Nuclear Unmanned Missions Out of The Solar System Beamed 2

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4 International Space Station Power Requirements -Full Station Envisioned- Total continuous needs->105 kw e (MIR 30kW e ) Two independent PV supplies (US=79 kw e, Russian=29 kw e ) 120 VDC for US, 28 VDC for Russian system US array-33.1 by 73.2 meters (54% of football field) Mass 3.1 kg/m 2, 7.56 tonnes Power density 100 kg/kw e US system-24 NiH batteries (eclipse, 168 kg, 6.5 y) Plus coolant to keep 0-10 C 4

5 Solar Power is Impractical Beyond Mars 2.0 Solar Energy Flux (Earth = 1.0) Earth Mars Jupiter Saturn Uranus Neptune Pluto Distance from Sun (AU)

6 The Use of Nuclear Power in Space is Absolutely Necessary for High Power and Long Time Operations 10 5 Electric Power Level (kwe) Chemical 1 hour Solar & Chemical Fission Reactors Fission Reactors & Solar Dynamic Radioisotope Generators & Solar Radioisotope Thermoelectric Generators & Solar 1 day 1 month 1 year 10 years 6

7 What is the Advantage of Using Nuclear Energy in Space? 1 kg of nuclear fuel contains 10,000,000 times the energy in 1 kg of chemicals 7

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9 Nuclear Energy Can Be Converted to Electricity in a Variety of Ways Nuclear Heat Source Radioisotopes Nuclear Reactors Static Dynamic Thermoelectrics Thermionics Rankine Brayton Stirling 9

10 There Have Been Many Driving Forces Behind the Development of Nuclear Power in Space 1 Sputnik Apollo Research Competition With USSR Near-Earth Applications SDI SEI Mission To Earth Human Exploration Initiative ??

11 CHRONOLOGY OF SPACE NUCLEAR POWER DEVELOPMENT 1 Sputnik Apollo SDI SEI 0.9 NUCLEAR AIRCRAFT USA SMALL NUCLEAR REACTORS USSR/Russia Nuclear Rockets Radioisotope Thermoelectric Generators SP-100 MMW

12 The U. S. and USSR Took Different Approaches to Nuclear Power Units in Space # of Nuclear Systems US 1 in Orbit 20 in interplanetary space 11 in orbit 6 on the Moon 4 on Mars 3 failed to orbit 1 re-entered 33 in orbit 2 failed to orbit 2 reentered 2 in orbit 2 on the Moon 2 failed to orbit 37 6 USSR RTG's Reactors 12

13 RTG s Produce Power by Radioactive Decay Half life of radioactive species: Law of Radioactive Decay dn/dt =- λn Integrating, N(t) = N o exp (-λt) Where the decay constant λ = ln2/t 1/2 = 0.693/t 1/2 Units of radioactive decay rate: 1 Curie = 3.7 x disintegrations/s (dps) 1 Becqeral = 1 dps 13

14 The Energy Released Depends on the Mass Difference Between Isotopes Maximum energy released in the decay of parent isotope A X z to daughter s Σ A iy Z i E = m c 2 Example: E = (mass A X Σ z -mass A iy Z i ) c2 238 Pu 94 --> 234 U He 2 1 amu=931.5 MeV Mass 238 Pu 94 = amu Mass 234 U 92 = amu Mass 4 He 2 = amu m = amu or E = 5.59 MeV 14

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16 238 Pu-The Radioisotope of Choice for Long Term Space Missions Half life-87.4 years Energy released per decay-5.6 MeV Specific activity-17 Ci/g Specific power density-30 Ci/W Power density-0.56 W/g Energy content for 10y mission-47 kwh/g Useful form-puo 2 (MP = 2,250 C) Production rate in fission reactor: 15 kg/1,000 MW e y Cost of 238 Pu-$300/g 16

17 Thermoelectricity-A Reliable Way to Convert Heat Energy Directly into Electricity T high efficiency = η carnot η mat Material A Material B + η carnot = (T H -T L )/ T H 50% (V th ) A,B - η mat % Typical Efficiencies 5-10% T low 17

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22 The Cassini Space Craft RTG s (3) 22

23 Cassini RTG Performance Characterisitics # of RTG s Mass/RTG Total Total EOL BOL Thermal Power Conversion Efficiency Mass PuO 2 /RTG Mass Pu/RTG Mass of 238 Pu/RTG 3 56 kg (168 kg total) 888 Watts (electric) 628 Watts (electric) 13, 182 Watts 6.7% 10.9 kg (32.7 kg total) 9.71 kg (28.8 kg total) 7.72 kg (23.2 kg total) (21% of all 238 Pu already launched) 23

24 Cassini Fuel Composition at Launch Other Actinides 2% Pu % Pu % Pu-240 2% Oxygen 12% Pu % Pu % 24

25 Cassini Electrical Power Requirements W at Saturn (1.6 billion km from sun) for 11 years RTG s Mass 168 kg Advantages Small size 1.13m x0.43 m dia. No moving parts Easy maneuverability Disadvantages Public fear of nuclear Solar panels Mass 1,337 kg Advantages No nuclear material Disadvantages No rocket available Slow maneuverability Higher risk of failure 25

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29 Cassini RHU Performance Characterisitics # of RHU s Mass/RHU Thermal g (6.28 kg total) 1 Watt Mass PuO 2 /RHU Mass Pu/RHU Mass of 238 Pu/RHU 2.7 g (424 g total) 2.38 g (374 g total) 1.91 g (300 g total) 29

30 (tot.) RTG s Have Had a Remarkable Performance Record # of Launches # of RTG s Power /unit, W e Mission Launch Dates , 25,25, 30 TRANSIT (navigation) , NIBUS (meteorology) APOLLO( Lunar Exp., 11 ht only) PIONEER-10, 11 (interplanetary) VIKING-1,2 (Mars) LES (communication) Voyager-1,2 (Interplanetary) Galileo (Jupiter) ULYSSES (Sun) CASSINI (Saturn) tot. Mission failures TRANSIT (failed to reach orbit) NIMBUS (destroyed during launch) APOLLO-13 (mission aborted)