Mission Design for the CubeSat OUFTI-1

CHAPTER 10.COMMUNICATION SYSTEMstream at 1200 bds, giving about 950 bds real data throughput.Concerning the antennas, we need four different quarter-wave deployable antennas:two about 17 cm long for the downlink and two about 50 cm long forthe uplink. They have to be folded during launch and deployed once in orbit.To this end, they will be wrapped around contact points and maintained inthis configuration using the deployment mechanism. As mentioned in chapter7.3, they are omnidirectional and don’t require any specific orientation of thesatellite respect to the earth.More information about the communication hardware and the D-STAR protocolcan be found in [RD5].10.2 Link budgetA link budget is the accounting of all of the gains and losses from the transmitter,through the space, to the receiver in a telecommunication system: its goal is toverify if the ratio of received energy-per-bit to noise-density E bN 0and the signalto-noiseratio S are higher than some limit values depending on the modulationNtype.As the available power is not too much, the link budget assumes a capitalrole: we need in fact to verify that the power is enough to guarantee a goodcommunication level.Starting from the available power for communication P 0 , through the systemefficiency η we have the power available at the transmitting antenna:P T = ηP 0 (10.1)Then we better pass to decibel-watt instead of watt, where:P T [dBW ] = 10log 10 (P T [W ]) (10.2)In this way, we deal with algebraic sum instead that with multiplicationsand divisions. Hereafter, if not differently specified, all the values will be indecibel-watt or decibel.The first step is to identify the Effective Isotropic Radiated Power (EIRP)which represents the power that effectively leaves the antenna:EIRP = P T + L T + G T (10.3)where L T and G T are respectively losses and gains in the transmitting antenna.Once the electromagnetic waves have left the transmitting antenna, they needGalli Stefania 99 University of Liège