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The Space Station Power System Solar Array Battery Power Management & Distribution Dave McKissock NASA Glenn Research Center October 27, 2005 david.b.mckissock@nasa.gov
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Compare ISS & Your Home Scratch off items not applicable to both locations Electrical Power Trash removal Clean Gutters Replenish O 2 Waste water removal Swim Suit Lawn Maintenance Food Preparation Bath tub Exercise Machine Kitchen Table & Chairs Weekly cleaning Cable TV Thermal Control Hot Water Heater Smoke Alarm
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ISS Batteries 38 cells wired in series make one Battery Orbital Replacement Unit (Battery ORU)
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ISS Batteries Battery ORU Battery Charge Discharge Unit (BCDU) One Battery = 2 Battery ORUs
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Space Station Power System One Channel
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What’s Next in Space Power? –Crew Exploration Vehicle –Lunar Lander –Lunar Rover –Lunar Base (?) –Mars Base (?)
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Poll Question #1
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July 2004 Gallup Survey Results With funding for NASA’s program expected not to exceed 1% of the federal budget, 42% of adults surveyed say they support the proposed Exploration program
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Solar cells make electricity from sunlight Electricity
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Electricity is described in two ways: – Voltage (Volts, V) – Current (Amperes, A) { Power = Voltage * Current } V A
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Connect solar cells together… – Series (end to end): to build up voltage – Parallel (side by side): to build up current – This makes a solar array A
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end to end Series or side by side Parallel? A - + - + - + - + - + V - + - + - + - + (voltages add) (currents add) end to end Series or side by side Parallel?
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Example: Airplane model propeller motor – Electric motor wants 12 volts and ½ amperes – Each solar cell can provide: ½ volt and ¼ amperes – How do you connect the solar cells?
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Poll Question #2
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Discussion of Poll Answer D: Both A & C 24 cells (end-to-end) –Add ½ volt plus ½ volt 24 times = 12V (or ½ x 24 = 12) 2 cells (side by side) –Add ¼ amp plus ¼ amp = ½ amp Individual cell performance varies as environment changes
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Two popular ways to store electrical energy… Battery Fuel Cell
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In battery cell, chemicals react at 2 electrodes and separate charges – stores charges, builds up voltage – if connected to a light bulb, charges flow (current)
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In a fuel cell stack, “stuff” is fed to metal plates, reacts and gives/takes charges – separate charges to build up voltage H O Remember H 2 0 ?
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Energy Storage - + - + - + - + - + - + - + - + - + - + - + - + Series Voltages add V Parallel Currents add A
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Batteries on Space Station Desire 114 Volts Willing to take whatever current you get Each Nickel-Hydrogen cell (NiH 2 ) produces 1.5V, rated at 81 Amp-Hours What series / parallel arrangement do you recommend?
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Poll Question #3
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Discussion of Poll Results Correct Answer is “A”, 76 cells in series at 1.5 volts per cell yields 76 x 1.5 = 114 V No spare cells for voltage redundancy –Batteries designed to last 6.5 years and provide needed voltage Nuclear power not an option in low earth orbit
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Orbits Low Earth Orbit h = 160 nautical miles T = 90 minutes V = 25,300 ft/s Geosynchronous Orbit h = 19,324 nmiles T = 23 h 56 m 4 s V = 10,087 ft/sec
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Upcoming NSTA Web Seminars: Doing Good Science November 2, 2005 Force and Motion: Stop Faking It! November 17, 2005 Watershed Dynamics December 8, 2005 6:30 PM Eastern Time
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