Power ICD

The purpose of this document is to describe the interfaces between the Power subsystem and other satellite subsystems. These include all mechanical, electrical, data and thermal interfaces of the Power subsystem to other satellite subsystems. The electrical and data interfaces of the power subsystem are summarized in figure 1 below.

Figure: ICD block diagram

Change Log

Power ICD Change Log

Power Subsystem Electrical & Data Interfaces

Electric Power Interface

POW provides electrical power to ADCS, 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.

Data Interfaces

The power subsystem exchanges data with ADCS, CDH, and THE subsystems. POW interfaces CDH for data exchange via CAN Bus. Although CAN Bus also connects to PLD, POW is not expected to communicate with PLD. POW only communicates with COMS during survival mode to switch to a higher power mode whenever the command is received from ground station.

Electrical and Data Interface Summary

8x Power Distribution Lines with return paths

Switch ID. Power Line Current Limit Voltage

1 ADCS_POW_POS 0.42 Amps 6.4V

2 COMS_POW_POS 0.85 Amps 6.4V

3 PLD_POW_POS 0.25 Amps 6.4V

4 CDH_POW_POS 0.3 Amps 6.4V

5 DPL1_POW_POS 1.8 Amps 6.4V

6 DPL2_POW_POS 1.8 Amps 6.4V

7 HTR1_POW_POS 0.45 Amps 6.4V

8* HTR2_POW_POS 1 Amp 3.3V

* Switch #8 is always on

7x DET Switches used to interface solar strings to distributed power bus
CAN Bus Connection (POW-CDH communication)
SPI Connection (POW-ADCS communications)

The following sections will explore the specific electrical interfaces between POW and other subsystems in more detail.

POW-ADCS Electrical and Data Interface

Electrical Interface

Figure 2 shows that electric power is provided to ADCS from POW through a load distribution. The switch is controlled internally by the EPS controller and connects the ADCS_POWER_POS terminal to the Main Power bus (MPB) when closed. The Selected switch is the Texas Instruments TPS259620 (Refer to the interfacing components section of this ICD for this and other component datasheets).

Figure 2: POW-ADCS Electrical and data

POW-ADCS Electrical Interface Specifications

MPB Voltage: 4.0 V to 7.3 V (Pending Change to actual range)
Current Limit: 0.42 A (EPS controller software)

ADCS Load Switch Specifications

Voltage rating: -0.3 V to 21.0 V
Latching current limit: TBD
ON Resistance: 89 mohms
Turn on delay: < 315 microseconds
Turn off delay: < 15 microseconds

POW-ADCS Data Interface

The data (communication) interface between POW and ADCS occurs through a 4-wire SPI connection. on the POW side, the SPI lines connect directly to the power module controller (Texas Instruments MSP430FR2476PT).

MSP430FR2476 SPI Specifications

Operating voltage: 3.0 V
SPI type: 4-wire (MOSI, MISO, SCLK, CS)
SPI Clock frequency: up to 8 MHz
SOMI data setup time: 40 ns (master mode)
SIMO data valid time: 20 ns (master mode)
SIMO data setup time: 12 ns (slave mode)
SOMI data valid time: 42 ns (slave mode)

POW-(PLD/CDH/COMS) Electrical and Data Interface

Electrical Interface

Figure 3 shows that electric power is provided to COMS, CDH and PLD from POW through distinct load distribution switches. The switches are controlled internally by the EPS controller and connects the respective subsystem POWER_POS terminal to the Main Power bus (MPB) when closed. The Selected switch is the Texas Instruments TPS259620.

Figure 3: POW-(COMS/CDH/PLD) Electrical and data interface

POW-(COMS/CDH/PLD) Electrical Interface Specifications

MPB Voltage: 4.0 V to 7.3 V (pending change to actual range)
Current Limits: 0.25 (PLD), 0.3 (CDH), 0.85 A (COMS) (EPS controller software)

COMS/CDH/PLD Load Switch Specifications

Voltage rating: -0.3 V to 21.0 V
Latching current limit: 0 to 2.0 A
ON Resistance: 89 mohms
Turn on delay: < 315 microseconds
Turn off delay: < 15 microseconds

Data Interface

The data (communication) interface between POW and CDH/COMS/PLD occurs through a 2 wire CAN Bus connection to the EPS controller.

POW-STR Electrical and Data Interface

Figure 3 shows that electric power is provided to STR for solar panel and antenna deployment through two load distribution switches. The switches are controlled internally by the EPS controller and connects the respective deployables POWER-POS terminals to the Main Power bus (MPB) when closed. The Selected switch is the Texas Instruments TPS259620.

Figure 4: POW-STR Electrical Interface

POW-STR Electrical Interface Specifications

MPB Voltage: TBD
Current Limits: TBD (STR requires 0 A for operations)

STR Load Switch Specifications

Voltage rating: -0.3 V to 21.0 V
Latching current limit: 2.0 A
ON Resistance: 89 mohms
Turn on delay: < 315 microseconds
Turn off delay: < 15 microseconds

POW-THE Electrical and Data Interface

Figure 6 shows that two power lines are provided to THE from POW througha DC/DC buck converter. The buck converter is enabled (or disabled) by the EPS controller and connects the DATEC heaters to a regulated 3.3 V bus when enabled. meanwhile the MINCO heaters are directly powered from the MPB, through a thermostat operated by the THE subsystem.

~~The Selected switch is the Texas Instruments TPS259620. The other power line is provided direct from the distributed bus into THE, where is connectes to HTR2_POW_POS through a thermostat.~~

Figure 5: POW-THE Electrical and data interface

POW-THE Electrical Interface Specifications

Regulated bus Voltage: 3.3 V (DATEC heater)
MPB voltage: TBD (MINCO heater)

Data Interface

The data interface between POW and THE provides 7 Analog to Digital conversion channels for temperature readings from thermistors placed in the following locations

Solar array deployables (4x thermistors)
Battery pack (2x Thermistors)
Power MCU (1x Thermistor)

Power Subsystem Mechanical Interface

Mechanical Components interfacing with the power subsystem include:

2 PWB assemblies: located in power module shell (EPS board - UMS-0110-A and EPS controller board (UMS-0110-B)
6x LiFePO4 Cells : located in power module shell (UMS-0038)
21x Solar Cells : located on deployable structure
Battery saddle : located in power module shell
Solar Array Board : located on deployable structure
4x 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

POW Wiring boards Mechanical Properties

UMS-0110-A / UMS-0110-B

Approximate Mass: TBD
Length: 90 mm
Width: 90 mm
Thickness: 1.6 mm
Maximum Component height: 5.97 mm (CTX 33-2P-R Inductor)

UMS-0061: Solar String Boards

TBD

Solar Cell Mechanical Properties

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, mounted with secondary locking features (TBD)

LiFePO4 Cell Mechanical Properties

Cell Mass: 42 g
Cell Length - 65.2 mm
Cell Height - 18.15 mm

Power Module Layout

The power module uses two half-shells and has two cuts made to accommodate the cables from the interface board of the power module up to the ADCS module and one of the torque rods to slightly extend into the module respectively. The mechanical drawings for the power module assembly, PCU board and battery saddle can be seen here .

Power Subsystem Thermal Interface

Power Module PWB Power Consumption

Board ID Peak Power Consumption/Dissipation

UMS-0110-A 0.35 W/orbit (TBC)

UMS-0110-B 1 W/orbit (TBC)

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
MSP430FR2476 processor operating & survival temperature range: -40 to 105 C
TCAN 4550 CAN operating & survival temperature range: -40 to 125 C

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: -20-40 C
Battery heater(s) regulate temperature

Interface Component Datasheets

Mechanical Interface

Include if known:

Mass
Volume/Dimensions
Shock and vibration tolerances
Needed fixtures
Out-gassing characteristics

Electrical Interface

Include if known:

Voltage Ranges
Power Consumption
Pinouts
Grounding Diagrams

Thermal Interface

Include if known:

Emissivity
Heat Capacity
Thermal Conductivity
Storage temperature range
Operational temperature range
Survival temperature range

Data Interface

Include if known:

Command Structure
Telemetry Structure
Error Codes
Data Encoding
User Interface Description

References

Mechanical Structure ICD

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