The purpose of this document is to describe the mechanical, electrical, data, and thermal interfaces between the CDH subsystem and other satellite subsystems.
CDH receives power from a distributed power bus at unregulated battery voltage (Vbat = 6.4 +/- 0.4 V) through distribution load switches that are operated by the Power module controller.
Power ON/OFF is controlled by a CAN-Controlled Load Switches and Monitors (CCLSM) through the auxiliary CAN bus, which is commanded and controlled by the Power subsystem
Power ON/OFF is controlled by a CAN-Controlled Load Switches and Monitors (CCLSM) through the auxiliary CAN bus, which is commanded and controlled by the Power subsystem
1 shared CAN Bus connection for PWR, PLD, and GNSS
Data rate: 500 kbps
Protocol: CAN 2.0
For PLD subsystem, CDH only receives processed PLD data
1 shared SPI connection for AODCS and Reaction Wheels
1 separate RS-485 connection for COMMS (half duplex RS-485)
1 separate RS-485 connection for Star Tracker (full duplex RS-485)
1 analog connection for thermistor
Flight Software runs on the CDH's main processing unit (Microsemi's SmartFusion2 SoC)
Default flight software application image is stored in the 256 KB eNVM on the Microsemi M2S010TQ144I system on chip
In-Application Programming (IAP) allows Ground Station to upload a new application with updated Flight Software on the SmartFusion 2 Cortex-M3
Fig. 1: CDH Power and Data Interfaces
The CDH subsystem is made of the CDH Circuit Card Assembly (CCA). All parts of the CDH are soldered onto the CCA and the CCA has no detachable parts.
Position: CDH/AODCS Module
Mass: 41.89 grams
Dimensions (L x W x H): 90mm x 90mm x 1.6mm
Mounting Holes:
four corner holes 2.5 mm diameter each for M2 metric screws
81 mm center-to-center distance
Maximum Component Height: +5.60 mm from board's top and -5.60 mm from board's bottom surface
Outgassing: All hardware components are compliant and will be conformally coated
CDH CAD Drawing: To be made
1 thermistor to measure CDH processor temperature
Operational temperature range: -40°C to 85°C.
Survival temperature range: -40°C to 85°C.
Thermal subsystem, which includes thermistors located throughout the satellite, uses indirect connections to the CDH through other subsystems.
The PLD subsystem provides thermistor information to the CDH over CAN
The PWR subsystem provides thermistor information to the CDH over CAN. Information from the thermistors located on the solar arrays is provided to the CDH by PWR through CAN
The AODCS subsystem provides thermistor information to the CDH over SPI
The COMMS subsystem provides thermistor information to the CDH over RS-485