Download The Space Station Power System

The Space Station Power System
Solar Array
Battery
Power Management & Distribution
Dave McKissock
NASA Glenn Research Center
May 24, 2006
david.b.mckissock@nasa.gov
Compare ISS & Your Home
Scratch 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
38 cells wired in
series make one
Battery Orbital
Replacement Unit
(Battery ORU)
ISS Batteries
ISS Batteries
Battery Charge Discharge Unit (BCDU)
One Battery = 2 Battery ORUs
Battery ORU
Battery ORU
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
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)
V
A
{ Power = Voltage * Current }
• 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
A
end to end
Series
or
side by side
Parallel?
end to end
Series
or
side by side
Parallel?
-
+
-
+
-
+
-
V
(voltages add)
+
-
+
-
+
+
+
+
(currents add)
• 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 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
O
H
Remember H20 ?
Energy Storage
- +- +- +- +
- +- +- +- +
- +- +- +- +
V
Series  Voltages add
A
Parallel
Currents add
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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