EPS of KUTEsat Pathfinder

1
AE256Satellite Electrical Power Systems

• EPS of KUTEsat Pathfinder
• Leon S. Searl
• April 5, 2006

2
KUTEsat Pathfinder EPS

• Pathfinder
• Pico size satellite, 10cm x 10cm x 10cm cube
• lt 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

3
Pathfinder Diagram
4
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

5
Pathfinder EPS Components

• Primary Power
• Dual solar cells on 5 faces of satellite
• Each solar cell delivers 2.05V _at_ 285mA
• Solar cells wire in series
• 4.1 volts _at_ 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.

6
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

7
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

8
Pathfinder EPS Power Bus
9
Pathfinder EPS Power Bus Backplane
10
Pathfinder EPS Power Bus Backplane

• 50 lines
• 19 Power
• 31 Signal
• Each trace can carry 1.4A
• Each pin can carry 1.5A

11
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)

12
Pathfinder EPS Components

• Telemetry
• 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

13
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

14
Pathfinder EPS Components

• Heat Handling
• Nothing done to distribute waste heat
• Heater added to batteries to keep them warm when
  temperature drops below -10C.

15
Support Slides
16
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