A pressuriser device as autogenous a propellant reservoir

A pressurizing autogenous device (50) of a main propellant reservoir (10, 30) comprises a pressurizing conduit (13, 33) connected to the main reservoir (10, 30) for injecting propellant into said reservoir main, a pressurizing valve (13a, 33a) disposed on the pressurizing conduit (13, 33) and a heater (17, 37) for heating the propellant upstream of the pressurizing valve (13a, 33a). The pressurizing device (50) comprises a buffer tank (15, 35) connected to the pressurizing conduit (13, 33) upstream of the pressurizing valve (13a, 33a).