PROPULSION SYSTEM COMPRISING A HYDROGEN-BURNING GAS TURBINE ENGINE

A propulsion system 100 comprises a propulsive hydrogen-burning gas turbine engine 190A, a first tank 106 storing liquid hydrogen with an ullage 105 and a first fuel line 108 including a fuel pump 112 and a vaporiser 116, the first fuel line providing gaseous hydrogen to the engine during operation of the system. A second tank 132 storing gaseous hydrogen is coupled by a second fuel line 134 to the first fuel line at a position thereon between the vaporiser and the engine, providing for engine start-up (when the vaporiser is inoperative) and power-boosting during operation of the system. A duct 156 connects gaseous hydrogen within the second tank to the ullage in the first tank in order maintain pressure in the first tank as liquid hydrogen within it is depleted, preventing cavitation of liquid hydrogen within the fuel pump.