The Communications Subsystem ensures that payload, telemetry and telecommand data are successfully exchanged between the AcubeSAT and the ground station through the following:
- Link Budget Analysis
- Antenna Design
- Digital Signal Processing
- Radio Frequency (RF) Front-End Design
- Ground Station Setup
The AcubeSAT makes use of radio amateur frequencies and consists of two radios, one operating on 2.4-2.45 GHz (S band) for downlinking the payload data and a half-duplex radio on 435-438 MHz (Ultra High Frequency (UHF) band) for housekeeping telemetry (TM) transmission and telecommands (TC) reception.
S band Radio
Since the scientific payload data comprises mainly of images, a high data rate of at least 250 kbps is necessary in order to acquire the data in its entirety, while maintaining the mimimum power consumption possible. Microchip’s AT86RF233 transceiver was incorporated in our design and the radio has the general characteristics:
- Modulation: OQPSK
- Bandwidth: 2.3 MHz
- Bit Rate: 250 kbps
- FEC: LDPC
- Framing: CCSDS 132.0-B-2
- Tx Power: 1.5 W
For the 2.4-2.45 GHz band we have designed and are currently testing a circular polarization, multi-layered patch antenna.
The UHF radio is based on ON Semiconductor’s AX5043 transceiver module, which offers an excellent sensitivity of less than -120 dB with Viterbi (convolutional) decoding and supports Automatic Frequency Check (AFC) for Doppler shift compensation.
- Modulation: GMSK
- Bandwidth: 20 kHz
- Bit Rate: 20 kbps
- FEC: Convolutional
- Framing: CCSDS 132.0-B-2 (TM), CCSDS 232.0-B3 (TC)
- Tx Power: 1 W
In order to reliably control the satellite in all cases of orientation, a two-monopole, circular polarization antenna mounted on UPSat’s deployment mechanism is being designed.
The ground station, currently under development, will be based on Aristotle University of Thessaloniki and be a part of the SatNOGS global network of satellite ground stations.