Hybrid rocket nozzles
Nozzles in hybrid rocket engines present a unique challenge compared to other rocket engine nozzles. Compared to liquid bipropellant rocket engines, hybrid nozzles cannot be easily regeneratively cooled, and thus made from metal. Compared to solid fuel rocket nozzles, these nozzles usually see a significantly more oxidizer-rich environment. The latter is especially true when designing hybrid rocket nozzles for liquid injection thrust vector control, which involves injecting oxidizer into the nozzle to steer the rocket.
A hot fire of the LITVC nozzle system on BURPG's Mk IIb engine