Power ICD

Introduction

The purpose of this document is to describe the interfaces between the power system and other satellite subsystems. These include all mechanical, electrical, data, and thermal interfaces of the power subsystem to other satellite subsystems. 

Electrical Interfaces 

Electric Power Interface

POW provides electrical power to AODCS, PLD, COMS, CDH, STR and THE subsystems from a distributed power bus, through distribution load switches that are operated by the Power module controller. The distributed bus is formed at the terminal that connects the battery pack directly to the solar string array, hence its voltage is unregulated and fluctuates according to the battery voltage. Electric power on the satellite is generated by an array of solar strings, physically located on Deployable structures. These strings interface electrically to the power subsystem through 7 direct energy transfer (DET) switches. Power will turn on Solar Panel and Antenna Release Circuits after detumbling and the normal operations will continue.

• 1x Main Power Distribution Line with return path. Power to each switch is controlled through the CCLSMs. 

 ID# Power Switch HW Current Limit SW Current Limit Voltage

1 AODCS_POW 0.6 A 0.42 A Vbus [V]*

2 COMS_POW 2 A 1.8 A 12V

3 PLD_POW 2 A 2 A 5V

4 RW_POW 2 A 2 A 5V

5 GNSS_POW 2 A 2 A 3.3V

6 CDH_POW 0.45 A 0.3 A Vbus [V]

7 DPL1_POW 1.8 A 1 A Vbus [V]

8 DPL2_POW 1.8 A 1 A Vbus [V]

9 HTR1_POW 0.8 A 0.45 A Vbus [V]

10 STARTRAC_POW 2.0 A 1.8 A 12V

11 THRUSTER_POW 2.0 A 1.8 A Vbus [V]

* Under normal operations of the spacecraft, Vbus ranges from 6.54~7.2 Volts. 

• 7x DET Switches used to interface solar strings to distributed power bus. These switches are equipped with current sensors that can measure the generated solar current. A summary of the design and tested parameters are listed below. The wiring consists of 7 pairs of wires from the solar panels to the EPS board. 

ID# Diode Ideal Diode Test Current Sensor Current Sensor Test 

1 IDEAL TBT* 0.5 A/V TBT*

2 IDEAL TBT* 0.5 A/V TBT*

3 IDEAL TBT* 0.5 A/V TBT*

4 IDEAL TBT* 0.5 A/V TBT*

5 IDEAL TBT* 0.5 A/V TBT*

6 IDEAL TBT* 0.5 A/V TBT*

7 IDEAL TBT* 0.5 A/V TBT*

*Test results are shown here. 

The Solar panels interface with the power board through harness wires. Each panel contains multiple strings (labeled S1, S2, ... , S6 on each panel). The strings on the panels are put in parallel with blocking diodes in series with each string to ensure current only flows out of the solar cells. The blocking diodes chosen are the NRVB120VLSFT1G Schottky diodes which have forward bias voltages in the range of [0.2 V to 0.3 V]. This will place our solar panel at the power points described in the figure below based on the bus voltage. The solar panel PV plot is shown at 28°C which is higher than the max expected satellite temperature ranges according to the detailed thermal analyses. It is worth noting that the PV curve changes with the temperature of the solar cells and the power generation analyses need to be updated if the thermal analysis values are changed.

• 2x Battery protection circuitry to connect the satellite's battery pack to the power subsystem. This ensures that the batteries are protected against short circuit, over current, over voltage, over charge, and over discharge at the cell level. 

Wire# Battery Pack Section Polarity Wire Gauge 

1 Bottom Negative 12 AWG

2 Bottom Positive 12 AWG

3 Top Negative 12 AWG

4 Top Positive 12 AWG

Data Interfaces

Power-CCLSM

The power subsystem interfaces with the CAN-Controlled Load Switches and Monitors (CCLSM) through the auxiliary CAN bus. Every subsystem that needs electrical power is equipped with one CCLSM as the power input switch. The data interfaces for the CCLSMs are shown in the list below. This shows the data that can be read or manipulated on the CCLSMs by the Power subsystem. 

Data Read/Write Values

Switch R/W ON/OFF

Current R 0~Imax-SW-XX [mA]

Imax-HW-XX R Hardware Current Limit [mA]*

Imax-SW-XX R Software Current Limit [mA]

Voltage R 0~Vbus_max [V]

Fault R True/False (Fault indicator in a subsystem switch) **

Fault_ID R HW_FLT, OC_FLT, LO_VOL, HI_VOL***

Fault_Val R Value that triggered voltage or current faults (Software only) 

Fault_RST W True/False (True resets the fault - Software only) 

Fault_EN R/W True/False (Enables the software faults to turn off the system)

*XX indicates the subsystem that is connected to the CCLSM.

**Fault can indicate a short circuit or overcurrent happening at the output. 

*** HW_FLT=Fault triggered by hardware/ OC_FLT=Software triggered overcurrent fault/ LO_VOL=Software triggered low voltage fault/ HI_VOL=Software triggered high voltage  

Power-CDH

The data interfaces between the Power and CDH subsystems through the main CAN bus are listed below. This shows the data that can be read or manipulated on Power by the CDH subsystem. 

Data Read/Write Value Ranges

Power Mode R/W 1~4 (Critical Hold - Survival - Low Power - Normal)

Distribution Bus Current R 0~4000 [mA] 

Subsystem XX Switch R/W ON/OFF (State of each subsystem) *

Subsystem XX Current R 0~Imax-XX [mA] 

Subsystem XX Voltage R 0~Vbus_max [V] 

Subsystem XX Imax-HW R Hardware Current Limit [mA]

Subsystem XX Imax-SW R Software Current Limit [mA]

Subsystem XX Fault R True/False (Fault indicator in a subsystem switch) *

Subsystem XX Fault_ID R HW_FLT, OC_FLT, LO_VOL, HI_VOL

Subsystem XX Fault_Val R Value that triggered voltage or current faults (Software only) 

Subsystem XX Fault_RST W True/False (True resets the fault - Software only) 

Subsystem XX Fault_EN R/W True/False (Enables the software faults to turn off the system)

Main Bus Voltage R 0~Vbus_max [V] 

Battery Pack Current R 0~Imax-batt [mA] 

Battery Pack Temperature R TLO~THI [°C]

Battery Pack SoC R 0~100 [%]

Solar Panel YY Switch R/W ON/OFF (State of each solar panel) **

Solar Panel YY Current R 0~Imax-sol [mA] 

Solar Panel YY Temperature R TLO~THI [°C]

*XX indicates the subsystem that is connected to the Power subsystem through the CCLSMs.

**YY indicates the solar panel number 

The data interfaces between the Power and CDH subsystems through the auxiliary CAN bus are listed below. This shows the data that can be read or manipulated on CDH's CCLSM by the Power subsystem. 

Data Read/Write Values

CDH Switch R/W ON/OFF

CDH Current R 0~Imax-SW-CDH [mA]

Imax-HW-CDH R Hardware Current Limit [mA]

Imax-SW-CDH R Software Current Limit [mA]

CDH Voltage R 0~Vbus_max [V]

CDH Fault R True/False (Fault indicator in CDH's switch) 

CDH Fault_ID R HW_FLT, OC_FLT, LO_VOL, HI_VOL

CDH Fault_Val R Value that triggered voltage or current faults (Software only) 

CDH Fault_RST W True/False (True resets the fault - Software only) 

CDH Fault_EN R/W True/False (Enables the software faults to turn off the system)

Power-COMS

The data interfaces between the Power and COMS subsystems through the main CAN bus are listed below. This shows the data that can be read or manipulated on Power by the COMS subsystem. 

Data Read/Write Value Ranges

Power Mode R/W 1~4 (Critical Hold - Survival - Low Power - Normal)

Battery Pack SoC R 0~100 [%]

Main Bus Voltage R 0~Vbus_max [V] 

Subsystem XX Switch R/W ON/OFF (State of each subsystem) *

The data interfaces between the Power and COMS subsystems through the auxiliary CAN bus are listed below. This shows the data that can be read or manipulated on COMS's CCLSM by the Power subsystem. 

Data Read/Write Values

COMS Switch R/W ON/OFF

COMS Current R 0~Imax-SW-COMS [mA]

Imax-HW-COMS R Hardware Current Limit [mA]

Imax-SW-COMS R Software Current Limit [mA]

COMS Voltage R 0~Vbus_max [V]

COMS Fault R True/False (Fault indicator in COMS's switch)

COMS Fault_ID R HW_FLT, OC_FLT, LO_VOL, HI_VOL

COMS Fault_Val R Value that triggered voltage or current faults (Software only) 

COMS Fault_RST W True/False (True resets the fault - Software only) 

COMS Fault_EN R/W True/False (Enables the software faults to turn off the system)

Power-PLD

There are no data interfaces between the Power and PLD subsystems through the main CAN bus.

The data interfaces between the Power and PLD subsystems through the auxiliary CAN bus are listed below. This shows the data that can be read or manipulated on PLD's CCLSM by the Power subsystem. 

Data Read/Write Values

PLD Switch R/W ON/OFF

PLD Current R 0~Imax-SW-PLD [mA]

Imax-HW-PLD R Hardware Current Limit [mA]

Imax-SW-PLD R Software Current Limit [mA]

PLD Voltage R 0~Vbus_max [V]

PLD Fault R True/False (Fault indicator in PLD's switch)

PLD Fault_ID R HW_FLT, OC_FLT, LO_VOL, HI_VOL

PLD Fault_Val R Value that triggered voltage or current faults (Software only) 

PLD Fault_RST W True/False (True resets the fault - Software only) 

PLD Fault_EN R/W True/False (Enables the software faults to turn off the system)

Power-AODCS

There are no data interfaces between the Power and AODCS subsystems through the main CAN bus.

The data interfaces between the Power and AODCS subsystems through the auxiliary CAN bus are listed below. This shows the data that can be read or manipulated on AODCS's CCLSM by the Power subsystem. 

Data Read/Write Values

AODCS Switch R/W ON/OFF

AODCS Current R 0~Imax-SW-AODCS [mA]

AODCS GNSS Switch R/W ON/OFF

Imax-HW-AODCS R Hardware Current Limit [mA]

Imax-SW-AODCS R Software Current Limit [mA]

AODCS Voltage R 0~Vbus_max [V]

AODCS Fault R True/False (Fault indicator in AODCS's switch)

AODCS Fault_ID R HW_FLT, OC_FLT, LO_VOL, HI_VOL

AODCS Fault_Val R Value that triggered voltage or current faults (Software only) 

AODCS Fault_RST W True/False (True resets the fault - Software only) 

AODCS Fault_EN R/W True/False (Enables the software faults to turn off the system)

Power-Thermal

There are no data interfaces between the Power and Thermal subsystems through the main CAN bus.

Power collects temperature telemetry data using seven thermistors, mounted on the battery saddle (x2), main solar panel faces (x4), and the power electronic board (x1), through the Analog to Digital Converter (A/D) interface.  

The data interfaces between the Power and Thermal subsystems through the auxiliary CAN bus are listed below. This shows the data that can be read or manipulated on Thermal's CCLSM by the Power subsystem. 

Data Read/Write Values

Thermal Switch R/W ON/OFF

Thermal Current R 0~Imax-SW-Thermal [mA]

Imax-HW-Thermal R Hardware Current Limit [mA]

Imax-SW-Thermal R Software Current Limit [mA]

Thermal Voltage R 0~Vbus_max [V]

Thermal Fault R True/False (Fault indicator in Thermal's switch)

Thermal Fault_ID R HW_FLT, OC_FLT, LO_VOL, HI_VOL

Thermal Fault_Val R Value that triggered voltage or current faults (Software only) 

Thermal Fault_RST W True/False (True resets the fault - Software only) 

Thermal Fault_EN R/W True/False (Enables the software faults to turn off the system)

Thermal Interfaces 

Power Module PWB Power Consumption

       Board ID                             Peak Power Consumption/Dissipation

UMS-0587                              0.35 W/orbit 

Solar Cell Thermal Properties

• Dissipated Power: 1.35 W per orbit 

• Emittance: 0.85 

• Solar Absorptance: 0.88

• Operational temperature range: -40 - 150 C 

• Survival temperature range: -40-150 C 

Power Module MCU Thermal Properties

• Overall operating and survival temperature range: -40 to 85 C (TBC)

• STM32F processor operating & survival temperature range: -40 to 105 C (TBC)

LiFePO4 Cell Thermal Properties

• Operational temperature range: Charging: 0 to 55 C, Discharging: -20 to 60 C

• Survival temperature range: -20 to 60 C

• Storage temperature range: -20 to 40 C

• Battery heater regulates temperature

Power collects temperature telemetry data using six thermistors mounted on the battery saddle (x2) and main solar panel faces (x4)