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 Interface
Include if known:
Voltage Ranges
Power Consumption
Pinouts
Grounding Diagrams
Data Interface
Include if known:
Command Structure
Telemetry Structure
Error Codes
Data Encoding
User Interface Description
Mechanical Interface
Include if known:
Mass
Volume/Dimensions
Shock and vibration tolerances.
Needed fixtures.
Out-gassing characteristics
Thermal Interface
Include if known:
Emissivity
Heat Capacity
Thermal Conductivity
Storage temperature range
Operational temperature range
Survival temperature range
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.
Solar panel's PV curve with the expected power points labeled for the entire range of the bus voltage values. (T = 28°C)
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
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
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)
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)
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)
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)
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)
The structural shell and components ensure that all of the power components are securely attached to the body of the satellite and no parts are detachable. It also ensures that the battery and control electronics are safely enclosed inside the shell internal to the structure of the satellite.
Mechanical Components interfacing with the power subsystem include:
PWB assemblies: located in power module shell (EPS board - UMS-0587)
6x LiFePO4 Cells: located in power module shell (UMS-0038)
42x Solar Cells: located on deployable structure
Battery saddle: located in power module shell
Solar Array Board: located on deployable structure
3x Physical Inhibit Switches: located in power module shell
1x Remove Before Flight (RBF) pin: located in power module shell
Power Module Shell: located on satellite structure
M3 or M4 fasteners with hex drive: Used for assembly throughout the shell
UMS-0587
Approximate Mass: TBD
Length: 90 mm
Width: 90 mm
Thickness: 1.6 mm
Maximum Component height: TBD
UMS-0061: Solar String Boards
TBD
Cell mass: 1.35g - 2.27g
Cell area = 27 sq. cm (per cell)
Cell dimensions: 6.91 cm x 3.97 cm
Cell thickness: 80 -225 micrometers
Interface mechanism to deploy solar arrays when needed using burn wire deployment design. The burn resistor heats up when power is applied to it by the power subsystem when commanded by CDH. Finally, the heat from the resistor burns the wire that's holding down the solar panels as described in the Burnwire Hold and Release Mechanism.
Mounted with secondary locking features (Solder and Silver epoxy)
Cell Mass: 42 g
Cell Length: 65.2 mm
Cell Height: 18.15 mm
The power module uses two half-shells and has four cutouts made to accommodate the cables from the interface board of the power module up to the Thruster module. These cutouts exist on the top and bottom side of the shell and allow the shell to easily depressurize when required. The mechanical drawings for the power module assembly, PCU board and battery saddle can be seen [HERE].
The power module is designed to provide protection against radiation in orbit allowing the electronics to be operational for the period of its operation. According to the SPENVIS total radiation dose analysis linked [HERE], the radiation dose expected is around 10 kRad. See Parts list for further information on the radiation and vibration tolerances for Power components.
Single Point Ground for the Satellite
The Structure module is electrically grounded in a single point highlighted in the power shell. The electrical ground comes from the Power board and gets bolted to the structure using a piece of grounding wire as highlighted in the picture below.
Board ID Peak Power Consumption/Dissipation
UMS-0587 0.35 W/orbit
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
Overall operating and survival temperature range: -40 to 85 C (TBC)
STM32F processor operating & survival temperature range: -40 to 105 C (TBC)
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)