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D-SAT OBDH & COM

OBDH & COM

On-Board data protocol based on Cubesat Space Protocol, a small network-layer delivery protocol designed for Cubesats. The protocol is based on a 32-bit header containing both network and transport layer information. The layering of CSP corresponds to the same layers as the TCP/IP model.

 

D-Sat main addresses are: 1 (D-SAT Unit 1 OBC) and 4 (D-SAT Unit2 OBC).

 

The communication system is composed of a turnstile omnidirectional antenna circularly polarized and a UHF transceiver module able to transmit up to 1 Watt.

 

The UHF communication subsystem has three main functions:

  • to transmit a beacon signal (a Morse signal FM modulated) as tracking signal;

  • to transmit and receive Telemetry and Tele-command;

  • to transmit and receive experiment data.

 

The link frequency value is 437.505 MHz.

 

The transceiver uses a FSK modulation over FM signal at a baud rate of 4800 bps.

The data are coded with a Reed-Solomon (255,223) coding and randomized according to CCSDS standard.​

 

D-ORBIT GROUND station

  • Yagi-Uda Antenna

    • Gain = 15.5 dBi

    • 19 elements

  • Azimuth and Elevation Rotators

    • Transmitted Power = 20 W

  • Kenwood TS-2000 amateur radio transceiver

  • PCs with Software Defined Radio and software for satellite prediction

  • Terminal Node Controller: MSK  modem and CSP router

 

practical information

Practical info

SIGNAL's CHARACteristics

BEACON

​

  • FM Signal @ 437.505 MHz

  • CW tone @800 Hz

  • WPM 20 PARIS alphabet

  • Period 90 sec

 

DATA

​

  • FM Signal @ 437.505 MHz

  • FSK @4800 bps.

  • Reed-Solomon (223,255)

  • CCSDS Randomization

  • Protocol: CSP

​

Possible Data Frame are:

  • D-SAT Real Time Telemetry (CSP port 18);

  • D-SAT Reentry Telemetry (CSP port 21/22);

  • SatAlert MAMES message (CSP port 29).

WHAT DO YOU NEED TO RECEIVE d-sat 

D-Orbit suggests using a directive antenna with a minimum antenna gain of 12 dBi and linear polarization.

The antenna shall be steerable in order to track the satellite during the visibility windows; it’s necessary an Azimuth and Elevation Rotator controlled by a computer.

 

In order to receive and decode D-SAT signal, it’s enough to connect the antenna to an FM transceiver and the transceiver’s AF output port to a computer soundcard. It’s important to remind that the transceiver shall feature a remotely controllable frequency for Doppler Shif compensation and the FM demodulator shall have a minimum bandwidth of 10 kHz.

The Audio Frequency (AF) signal from the transceiver can be processed by a software provided by D-Orbit or recorded at 48000 sample per second for future post-processing.

 

An alternative solution for D-SAT signal reception may foresee the use of a Software Defined Radio (e.g. AirSpy Mini) that connects directly the computer with the antenna.

 

D-Orbit will provide a software based on GNU radio for D-SAT signal decoding able to handle different sources like as: pre-recorded audio files stored on the computer at 48ksps, soundcard input, Airspy Mini SDR and RTL-SDR. The software runs on Ubuntu 14.04 and includes the following main features:

 

  • D-SAT Beacon Morse Decoding

  • D-SAT data decoding

  • MAMES message parsing and printing

  • D-SAT data upload to dedicated database

 

Please note that D-Orbit shall not be considered responsible for any malfunctioning or damages due to activities presented on this page.

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