Design and Implementation of On-board Electrical Power ... - OUFTI-1

There are two envisaged solutions:1. The switch could be one single transistor with very high reliability, in other word, aflight model. This philosophy was adopted for the shunt regulator, as the problem wasvery similar. In this case the system is composed of one FET, one decoupling capacitor,one pull-down resistor and the thermo cutter. Both command lines are connected tothe gate of the transistor. The schematics of this circuit is shown of the left of figure5.42.2. The switch could be composed of four transistors in quad-mount (two parallel branchesof two transistors in series). In this way, there is redundancy against a risk of malfunction,and the risk of a short circuit is kept very low. The disadvantage is of coursethe required surface on the PCB. This solution will be useful if we can’t find a spacecertified FET. The system would be composed of four FETs and the thermo cutterplus two capacitors and two resistors for the decoupling. Each branch is controlled byone control signal. Controlling two FET in series with the same voltage will not causeproblems for this application (each transistor withstand the bus voltage and there isno critical requirements about the rise time). This is the circuit shown on the right offigure 5.42.Figure 5.42: Propositions for the antennas deployment system.5.6.3 LocationThe deployment system (switch and decoupling) will be located on the EPS PCB. Doing so,it is close to the power source. The required surface is not a concern since there are fewcomponents. The thermo cutter is located near the antennas.5.6.4 ComponentsNo flight model for a low V g s FET has been found (investigations have been done at ThalesAlenia Space to find such a component, without results).85