Satellite Communications


Spacecraft Communications

The Helium-100 transceiver will operate in full-duplex, allowing communications to be receiving and transmitting simultaneously. Land Line telephones are an example of full duplex communications. Benefits from using a full duplex system are stations (or nodes) do not have to wait until others complete their transmission, since there is only one transmitter for each twisted pair. Time is not wasted, since no frames need to be retransmitted, as there are no collisions and full data capacity is available in both directions because the send and receive functions are separated.
The spacecraft will transmit and receive on antennas designed by the communications systems team. The transmitting antenna on the 145 MHz amateur radio band and the 437 Mhz band will transmit telemetry and payload data. The antennas will be designed using a common measuring tape because the material naturally wants to keep a straight profile when deployed by the spacecraft.

Ground Station

The SKC ground station consists of two Yagi antennas mounted on a rotating mast. The antennas can be rotated in the horizontal axis and the in the vertical axis. One antenna receives in the 420-450 MHz frequency range, and the second antenna transmits in the 144-148 MHZ frequency range. A Kenwood TS-2000 transceiver is used in conjunction with a computer system running custom software to transmit encoded and encrypted commands to the spacecraft. A second computer runs software that tracks the satellite, display a real time map and directs the antennas to point at the spacecraft when it is within range of the ground station. A third computer runs GNURadio and is connected to a Ettus N200 Universal Software Radio Peripheral (USRP). This station receives and demodulates radio signals from the spacecraft. It then transmits those bits to a fourth computer. The fourth computer runs a custom LabVIEW program which decodes telemetry and pictures saving them to a secure location. The system is semi-automated and remotely accessible via a secure connection.