US Patent 7509796 Pintle-controlled propulsion system with external dynamic seal

A propulsion system with a pintle for variable thrust is constructed such that the pintle contains a shaft at its fore end which passes through an opening in the thrust chamber wall and extends into a boss on the outside surface of the thrust chamber. A dynamic seal that maintains the pressurization of the thrust chamber while allowing movement of the pintle is positioned inside the boss, between the pintle shaft and the boss, and actuation of the pintle is achieved by a rack affixed to the fore end of the pintle and a gear that engages the rack. The dynamic seal, rack and gear are thus external to the thrust chamber, providing the thrust chamber with a compact external envelope, a greater thermal standoff, or both.