The Space Station Power System Solar Array Battery Power Management & Distribution Dave McKissock NASA Glenn Research Center October 27, 2005

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

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

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

Space Station Power System One Channel

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

Poll Question #1

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

Solar cells make electricity from sunlight Electricity

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

end to end Series or side by side Parallel? A V (voltages add) (currents add) end to end Series or side by side Parallel?

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?

Poll Question #2

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

Two popular ways to store electrical energy… Battery Fuel Cell

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)

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 ?

Energy Storage Series  Voltages add V Parallel Currents add A

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?

Poll Question #3

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

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

Upcoming NSTA Web Seminars: Doing Good Science November 2, 2005 Force and Motion: Stop Faking It! November 17, 2005 Watershed Dynamics December 8, :30 PM Eastern Time