The Space Station Power SystemSolar Array

BatteryPower Management & Distribution

Dave McKissockNASA Glenn Research Center

May 24, 2006david.b.mckissock@nasa.gov

Compare ISS & Your HomeScratch off items not applicable to both

locations

•Electrical Power•Trash removal•Clean Gutters•Replenish O2

•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 Batteries38 cells wired in series make one Battery Orbital Replacement Unit (Battery ORU)

ISS Batteries

Battery ORU Battery ORU

Battery Charge Discharge Unit (BCDU)

One Battery = 2 Battery ORUs

Space Station Power SystemOne Channel

What’s Next in Space Power?

– Crew Exploration Vehicle– Lunar Lander– Lunar Rover– Lunar Base (?)– Mars Base (?)

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?

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 }

VA

• 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 endSeries or

side by side Parallel?

A

- + - + - + - +- +

V

- +

- +- +- +

(voltages add) (currents add)

end to endSeries 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

• Need 12V at ½ Amp• Each cell generates ½ V at ¼ Amp

What do I need?

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

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 H20 ?

Energy Storage

- +- +- +- +- +- +- +- +- +- +- +- +

Series Voltages addV

ParallelCurrents add

A

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?

Poll Question #3

• Need 114V at whatever Amps• Each cell generates 1½ V at 81 Amp-Hr

What will I need?

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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