introduction to space systems and spacecraft design space systems design power systems design -i
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Introduction to Space Systems and Spacecraft DesignSpace Systems Design
Power Systems Design -I
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Power System Design Considerations
Power Systems Design -I
Power System Requirements
Power Sources
Power Storage
Power Distribution
Power Control
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Primary Secondary
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Primary – non rechargeable batteries
Secondary – rechargeable batteries
Electrical Power Battery Storage
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Operating regimes of spacecraft power sources
Power Systems Design -I
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Energy Storage
Not Rechargeable
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Not Rechargeable
Not Rechargeable
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Power Systems Design -I Not Rechargeable
Not Good
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Power Systems Design -I Rechargeable
Old Technology
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Power Systems Design -I Rechargeable
Old Technology
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Power Systems Design -I Rechargeable
Old Technology
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Power Systems Design -I Rechargeable
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Power Systems Design -I Rechargeable
New Technology
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Power Systems Design -I Batteries
Most common form of electrical storage for spacecraft
Battery terms:Ampere-hour capacity = total capacity of a battery (e.g. 40 A for
1 hr = 40 A-hrDepth of discharge (DOD) = percentage of battery capacity used in
discharge (75% DOD means 25% capacity remaining. DOD usually limited for long cycle life)Watt-hour capacity = stored energy of battery, equal to
A-hr capacity times average discharge voltage.Charge rate = rate at which battery can accept
charge (measured in A)Average discharge voltage = number of cells in series times
cell discharge voltage (1.25 v for
most commonly used cells)
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Considerations for power calculations
We have a battery that has a power capacity of:
1000mA (1000mAHrs)@ 1.2vIt can supply 1000mA for 1 hour or 500mA for 2 hours or 250mA for 4 hours @ a voltage of 1.2 v.Power rating of 1000mA x 1.2 v = 1.2 watt hours
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Battery selection:
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Considerations for power calculations
Two batteries in series.
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Considerations for power calculations
Two batteries in parallel.
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Power Systems Design -I Rechargeable
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Operating regimes of spacecraft power sources
Power Systems Design -I
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Power Systems Design -I
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Power Systems Design -I
New Technology
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Sun spectral irradiance
Solar cell response
Peak sun irradiance
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Dual Junction Cell
Added by second junction
Efficiency
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Use of the Sun’s Spectrum
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Power Systems Design -I Triple Junction Cell
Added by second junction
Added by third junction
Efficiency
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Reduce Efficiency
Good Efficiency
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Max Cell Voltage when open circuit
Max Cell Current when short circuit
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Peak Power
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Add cell voltages to get string voltage
String of cells
Parallel strings to cover panel
Solar Cell Strings
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Power Systems Design -I
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ShadowingKills all power
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• Use of NiCd batteries required reconditioning
• Reconditioning not required for Li Ion batteries.
Reconditioning battery system
Close sw to crowbar battery
Close sw to crowbar second battery
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How much Battery Charge Left?
Charging causes heating
Discharging causes heating
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Some Solar Notes
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Sun
Approx Cosine
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Eclipse
Parallel Sun Rays
Sun
Earth
Satellite Orbit
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Gravity Gradient Stabilized
Sun
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Passive Magnetic Stabilized
N
S
SNSN
S N
S NS
N
S
N
S
N
S
N
S
N
S
N
S
N
SN
SN
SN
Sun
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Inertially StabilizedPower Systems Design -I
Sun
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Power Systems Design -I
Power Systems Design -I or EPS
Solar Panels - source
Charge Control
Batteries
Voltage
Bus
Voltage
DC/DC
Voltage
DC/DC
Subsystem
Subsystem
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Radios
• Fixed voltage busses (5v, -5v, 7v, 3.3v, 12v, etc.)
• Quieter – generates less noise on voltage bus
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• DC/DC Converter/Regulators
• Regulate 2 Li Ion batteries - ~7.2v 5v
• “Buck Up” 1 Li Ion battery - ~3.6v 5v
Requires less circuitry, more efficient to regulate down
Requires more circuitry, less efficient to “buck up” voltage.
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Could be caused by arcing due to spacecraft charging
Failure in subsystem that causes a short
Feedback on voltage bus from some components
Multiple return paths for current to battery – don’t use grounded frame
Power cycling required to reset components that have latch up due to radiation
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What type of solar panel system does it take to generate 47.5 watts peak and 27.8 watts average?
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Questions?