The Space Station Power System Solar Array Battery Power Management & Distribution

1. The Space Station Power SystemSolar ArrayBatteryPower Management & Distribution Dave McKissock NASA Glenn Research Center May 24, 2006 david.b.mckissock@nasa.gov

2. Compare ISS & Your HomeScratch off items not applicable to both locations • Bath tub • Exercise Machine • Kitchen Table & Chairs • Weekly cleaning • Cable TV • Thermal Control • Hot Water Heater • Smoke Alarm • Electrical Power • Trash removal • Clean Gutters • Replenish O2 • Waste water removal • Swim Suit • Lawn Maintenance • Food Preparation

5. ISS Batteries 38 cells wired in series make one Battery Orbital Replacement Unit (Battery ORU)

6. ISS Batteries Battery Charge Discharge Unit (BCDU) One Battery = 2 Battery ORUs Battery ORU Battery ORU

7. Space Station Power SystemOne Channel

8. What’s Next in Space Power? • Crew Exploration Vehicle • Lunar Lander • Lunar Rover • Lunar Base (?) • Mars Base (?)

9. Poll Question #1 Do you support the new plan for space exploration that returns the space shuttle to flight, completes assembly of the space station, builds a replacement for the shuttle, returns to the Moon and then on to Mars and beyond?

10. 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

11. Solar cells make electricity from sunlight Electricity

12. Electricity is described in two ways: • Voltage (Volts, V) • Current (Amperes, A) V A { Power = Voltage * Current }

13. A • 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

14. A - - - - - - - - - + + + + + + + + + end to end Series or side by side Parallel? end to end Series or side by side Parallel? V (currents add) (voltages add)

15. 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?

16. Poll Question #2 • Need 12V at ½ Amp • Each cell generates ½ V at ¼ Amp • What do I need?

17. Discussion of Poll AnswerD: 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

18. Two popular ways to store electrical energy… BatteryFuel Cell

19. 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)

20. In a fuel cell stack, “stuff” is fed to metal plates, reacts and gives/takes charges • separate charges to build up voltage O H Remember H20 ?

21. A - + - - - - - - - - - - - + + + + + + + + + + + Parallel Currents add Series  Voltages add V Energy Storage

22. Batteries on Space Station • Desire 114 Volts • Willing to take whatever current you get • Each Nickel-Hydrogen cell (NiH2) produces 1.5V, rated at 81 Amp-Hours • What series / parallel arrangement do you recommend?

23. Poll Question #3 • Need 114V at whatever Amps • Each cell generates 1½ V at 81 Amp-Hr • What will I need?

24. 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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