A commercial off the shelf (COTS) packet communications subsystem for the Montana EaRth-Orbiting Pico-Explorer (MEROPE) CubeSat

The MEROPE communications subsystem consists almost entirely of commercial off the shelf components. Simple and robust, it is centered around a Paccomm Picopacket terminal node controller (TNC) operating continuously in "transparent" mode, whereby all serial data from the processor are immediately packetized and transmitted through a Yaesu VX-1R dual-band radio. The entire subsystem weighs less than 140 grams and occupies a total volume (including antennas and interconnects) of 180 cm³ - less than 1/5 of the total spacecraft weight and volume budgets - with a hardware cost of less than $400. MEROPE communications uses the AX.25 packet radio protocol at 1200 baud. Uplink is at a frequency of 145.835 MHz with 20 kHz of available bandwidth. Downlink is at 437.445 MHz with a 30 kHz bandwidth. Communications flow is controlled by the Motorola HC12 flight processor, which is linked through a 9600 baud RS232 serial connection to the TNC. The entire communications link (ground-MEROPE-ground) is seamless, initialized by a single encrypted uplink command. The MEROPE antenna is a center-fed dipole tuned to the 2m uplink, which is nearly harmonic with the 70 cm downlink.