The ARC-2 communications (COMM) system is responsible for communications between the satellite and mission control. COMM provides two radio frequency (RF) links for data to be downlinked and commands to be uplinked. COMM is also in charge of checking the health of the Command Data Handling System (CDH).
ARC’s primary RF link will be UHF transmitting in 2-FSK (Frequency Shift Keying). The primary function of the UHF link will be to provide a ten second beacon containing ARC system health information or scientific instrument data. COMM will receive ground station commands through the UHF channel, decode them and then pass them on to the relevant subsystem.
ARC’s second RF link will be in the higher frequency S-band in order to facilitate high data downlink of scientific data and pictures. This link will also transmit using 2-FSK modulation in order to facilitate easy decode of both S-band and UHF RF channels.
In addition to RF capability the COMM system will also act as a health montir for ARC’s CDH. If CDH suffers a failure, COMM will have the ability to reset CDH into a known state. This will provide redundancy and robustness to the ARC system.
Design and Operation
The radios selected for the communications system are Texas Instruments (TI) CCxxxx controlled with the communications board microprocessor, TI MSP430F6779a (MSP). The MSP functions as the backbone of the communications system. It provides communication peripherals, computational capability, and runs three critical tasks in software.
The communications software flow is shown below, starting with a system power on. Upon power up a 45 minute timer will trigger antenna deployment for the ARC system. After antenna deployment the communications system will sit in its default state “receive mode”, waiting for ground commands and running a 10 second UHF health beacon. Upon the communications system receiving a command it will demodulate the command and then pass them off to the specified system.