The EU H2020 HYPROGEO Project, coordinated by Airbus Defence and Space (Toulouse), called for the design and manufacture of two sets of catalytic injectors for a novel, isochoric hybrid rocket motor. The hybrid motor forms the basis of a propulsion system for future GEO/apogee-kick applications. The motor burns its fuel axially rather than radially and relies on a constant, vortical flow of hot oxygen for ignition and sustained combustion. The hot oxygen is provided by the rapid decomposition of hydrogen peroxide. Two aqueous concentrations were used: 87.5% for an intermediate motor, and 98% for the final breadboard design. Critical to success is the catalyst, referred to as PX1. This comprises a ceramic substrate and an active (catalytic) surface. On contact with hydrogen peroxide, oxygen and steam are liberated exothermically. The efficacy of PX1, used in combination with 98% concentration peroxide, was demonstrated in 2016.