The control system for the X-33 linear aerospike engine

The linear aerospike engine is being developed for single-stage-to-orbit (SSTO) applications. The primary advantages of a linear aerospike engine over a conventional bell nozzle engine include altitude compensation, which provides enhanced performance, and lower vehicle weight resulting from the integration of the engine into the vehicle structure. A feature of this integration is the ability to provide thrust vector control (TVC) by differential throttling of the engine combustion elements, rather than the more conventional approach of gimballing the entire engine. An analysis of the X-33 flight trajectories has shown that it is necessary to provide ±15% roll, pitch and yaw TVC authority with an optional capability of ±30% pitch at select times during the mission. The TVC performance requirements for the X-33 engine became a major driver in the design of the engine control system. The thrust level of the X-33 engine as well as the amount of TVC are managed by a control system which consists of electronics, instrumentation, propellant valves, electromechanical actuators, spark igniters, and harnesses