Ceramic Matrix Composite materials (CMC) have been developped by SEP Solid Propulsion an Composite Materials Division in Le Haillan since the seventies for solid propulsion applications. In the race to create a new generation of small high performance bipropellant engines, SEP has opted for Ceramic Matrix Composite (CMC) such as SEPCARBINOX (R) or CERASEP (R), as combustion chamber and nozzle material. The main advantage of these composites is enabling increase of maximum combustion temperature to 1600°C without requiring anti-oxydation coatings, and with improved resistance to thermal cycles. SEP's Defense and Space group started preliminary work on choosing the composite materials best adapted to liquid bipropellant engines in 1983. Based on some 30 5N thrust combustion chambers, about 20 different materials were evaluated during firing tests. Next, using different combustion chambers sizes, SEP implemented a program designed to demonstrate the endurance of this material, and initiated a study on producing larger size parts including large area ratio nozzles. This program comprised the production and testing of combustion chambers rated at 200N and 6000N, associated with injectors derived from other applications. Finaly, in order to simulate the operating conditions experienced by certain motors on HERMES spaceplane, tests of the 200N motor were also carried out with an external thermal protection system. As of end 1987, designers had set the thrust level required for the HERMES attitude control system at between 10 and 30N. SEP therefore decided to focus further work on 20N-thrust engines, a choice which took into consideration the potential applications of this thrust level for satellite attitude control systems. Starting in mid-1988 and continuing until fall 1990, this program is designed to validate before going into final qualification all technologies required for the two planned applications: • - the HERMES spaceplane, which has several thrusters integrated in the nose, • - satellites, where the motor is free to radiate heat into space. Manufacturing procedures for the composite parts apply to the production of both thrust chambers and nozzles common to both applications. HERMES specific parts are also in production; these basically involve exhaust elements connected to a highly-scarfed nozzle, which enables the integration of the motor and its insulation in the spaceplane nose. Injection studies comprise the design, production and testing of injectors of two different types: • - a high performance version, for satellite thrusters, with a specific impulse goal of 300 s. • - another, designed for HERMES, which will limit wall temperature when the motor is insulated, with a specific impulse of about 287 s. The SEP 20N thrusters are presented with specific topics for HERMES attitude control application.