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This double stage flow control valve is used to control the propellant supply to the thruster. Additionally each thruster is equipped with an internal redundant catalyst bed heater and with thermal insulation to guarantee optimum start up.
All materials used in the valve and thrust chamber assembly have been selected for compatibility with hydrazine propellant. The flow of propellant to the decomposition chamber is controlled by the Flow Control Valve (FCV), which consists of two independent consecutive monostable, normally closed valve stages.
When the valve is activated, propellant is supplied through a fuel supply pipe, mounted inside the heat barrier, to the injection plate. The flow rate is adjusted by a constriction in this pipe to ensure that the delivered thrust is within the specified limits. The lower end of the pipe is welded to the injection plate, which provides the correct number and inclination of injection holes to ensure an adequate distribution of the propellant across the catalyst bed.
When the propellant comes in contact with the catalyst, the decomposition reaction is initiated. At low and preheated temperatures the decomposition of the hydrazine is solely due to the contact with catalyst.
At higher temperatures (typically above 600°C) a thermal equilibrium is reached across the complete catalyst bed and the hydrazine is solely decomposed due to temperature (thermal decomposition). Subsequent to the decomposition of the hydrazine the reaction gases are expanded through a conical nozzle with an area ratio of 60, thereby generating the desired thrust.