Although the Cislunar Explorers make use of autonomous, optical navigation for position determination, they still need to report their position back to us here on Earth! These are not fully autonomous spacecraft; they only perform maneuvers as directed by our ground station here at Cornell. In order for the spacecraft to receive these commands, and for us to hear back from them on their progress, we need a radio for communication!
The ground station back home is added on to Cornell University’s existing radio station, run by its amateur radio club. We use the “70 cm” (~437 MHz) amateur radio band and PSK modulation at low data rates (150 to 250 bps). These are commonly used modes in Ham radio communications and known as PSK125 and PSK250 respectively. The radio board includes a AX5043 transceiver chip, originally developed for IoT and SIGFOX applications but that has all the functionalities required. In order to close the link with sufficient margin we are including a 7W external Power Amplifier and implementing FEC algorithms. Thus, we will be able to overcome the immense path loss at Moon distance and beyond (maximum distance from the Earth is estimated at more that 1 Million km).