University of Kansas

EPS of KUTEsat Pathfinder

Leon S. SearlApril 5, 2006

AE256Satellite Electrical Power Systems

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

University of Kansas

Pathfinder Diagram

University of Kansas

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

University of Kansas

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.

University of Kansas

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

University of Kansas

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

University of Kansas

Pathfinder EPS Power Bus

University of Kansas

Pathfinder EPS Power Bus Backplane

University of Kansas

Pathfinder EPS Power Bus Backplane• 50 lines

• 19 Power

• 31 Signal

• Each trace can carry 1.4A

• Each pin can carry 1.5A

University of Kansas

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)

University of Kansas

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

University of Kansas

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

University of Kansas

Pathfinder EPS Components

• Heat Handling• Nothing done to distribute waste heat

• Heater added to batteries to keep them warm when temperature drops below -10C.

University of Kansas

Support Slides

University of Kansas

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