Transcript AE265 Pathfinder EPS

AE256
Satellite Electrical Power Systems
EPS of KUTEsat Pathfinder
Leon S. Searl
April 5, 2006
University of Kansas
KUTEsat Pathfinder EPS
• Pathfinder
• Pico size satellite, 10cm x 10cm x 10cm cube
– < 1kg mass
• Communications
– Dipole Antenna
– Handheld Ham Radio
• Attitude Determination and Control
– Sun sensors and 3 axis Magnetometer (attitude determination)
– 3 axis Electromagnet Torquer coil (attitude coil)
• Payload
– CCD Camera
– Dosimeters
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Pathfinder Diagram
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Pathfinder EPS Requirements
• Do nothing for 20 minutes after Deployment
• No CPU clock allowed
• Go into low power wait mode
• Power CTDH and Communication system
• Allows:
– Transmit Morse code ID every few seconds
– Listen for known signal from ground station to start full powerup
• Full power mode
• Allows CTDH to command power to ADCS, and Payloads
• Deliver 1.5W maximum power
• Emergency Power mode
• Automatic power down of all systems when primary power lost and
secondary power is low
• When primary power available recharge secondary power to minimum for
Power Wait Mode
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Pathfinder EPS Components
• Primary Power
• Dual solar cells on 5 faces of satellite
• Each solar cell delivers 2.05V @ 285mA
• Solar cells wire in series
– 4.1 volts @ 285 mA
– Max Solar Power 4.1V * 0.285 * 1.7 (3 adjacent faces exposed)
= 1.98Watts
• Each cube face wired in parallel
• Secondary Power
• Two Lithium-Ion batteries
– 4.2V to 3.3V, 1800 mAH
• Wired in Parallel
• Primary and Secondary power connected by ORed diodes.
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Pathfinder EPS Components (cont)
• Batter Charger
• Takes Solar power, converts to 4.2V output to battery
– Controls charge current
– On/Off controlled by EPS PIC
• Power Converters
• DC-DC converter takes Solar and Battery and converts to regulated
5V
• 5V is converted to 3.3V regulated output by DC-DC converter
• 5V is converted to 12V regulated output by DC-DC converter
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Pathfinder EPS Components
• Power Buses
• 3.3V and 5V delivered to CTDH continuously
– EPS has signal to CTDH to tell it to be powered down for
Emergency Power Mode
• 3.3V, 12V and 5.5V delivered to Secondary Systems by switch
– Powered off by default
– Only powered on by command from CTDH
• 3.3V, 12V and 5.5V delivered to Secondary Systems by switch
– Powered off by default
– Only powered on by command from CTDH
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Pathfinder EPS Power Bus
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Pathfinder EPS Power Bus Backplane
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Pathfinder EPS Power Bus Backplane
• 50 lines
• 19 Power
• 31 Signal
• Each trace can carry 1.4A
• Each pin can carry 1.5A
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Pathfinder EPS Comonents
• Power Management
• Power is managed by a micro controller (MicroChip PIC)
– Onboard flash and ram
– Holds control program
– Analog to Digital Converters
– Used to measure voltages
– General Purpose IO lines
– Used to control charger, DC-DC converters and switches
• Handles decisions for Emergency Power Mode
• Responds to commands from CTDH (SPI interface)
• Obtains telemetry and delivers it to CTDH (SPI interface)
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Pathfinder EPS Components
• Telemetry
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Measured by PIC and delivered to CTDH via SPI interface
Solar cell voltage combined
Solar cell current (for each panel)
Battery voltage
Battery current
Battery temperature
5V DC-DC output voltage
3.3V DC-DC output voltage
12V DC-DC output voltage
Current into 5V DC-DC
Board temperature
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Pathfinder EPS Components
• Radiation Effects Handling
• Single Event Upset
– PIC has internal WatchDog timer that resets PIC if it stops
running
• Single Event Latchup
– PIC power runs through a self resetting current limiting switch
– When current increases to SEL limit (25mA) the power switch turns
off power to PIC then turns it back on
• No extra shielding added
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Pathfinder EPS Components
• Heat Handling
• Nothing done to distribute waste heat
• Heater added to batteries to keep them warm when temperature drops
below -10C.
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Support Slides
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Radiation
• Any component with transistors is susceptible to:
• Single Event Upset
– Change the binary value from 1 to 0, visa-versa
– Can be handled with Error Correction Codes
– Can be detected with CRC or Parity
– Can often be handled with software
• Single Event Latch-up
– Can cause very high current draw that destroys transistors
– Can be detected with load sensor
– Can be remedied with power cycle of hardware effected
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