The First stage of the PSLV attitude control is provided by a Secondary Injection Thrust Vector Control system (SITVC) for yaw and pitch. For SITVC, Strontium Perchlorate is used as a secondary fluid that is injected from the side into the Hypersonic Flow (ring with 24 injection ports) in the nozzle, causing a lateral thrust element that is precisely steered for attitude control. The SITVC fluid is stored in two cylindrical aluminum tanks strapped to the core stage. The tanks are pressurized with Nitrogen. Additional, fixed in line on the SITVC tanks, follows a liquid fuel tanks (fuel combination MMH / MON) of the Roll Control System (RCS) with small thrusters. In two PSOMs for roll control augmentation a further SITVC is installed that injected the nozzle.
The PSLV-CA uses not PSOMs, instead two additional units of unknown function*. These units are fixed opposite the two combined SITVC / RCS tanks.
probably stabilizers


RCS tank with thruster

SITVC tanks

SITVC tank pipe


SITVC/RCS mounting



 One PSOM with SITVC

PSLV-CA: RCS ignition

 PSLV-XL: RCS ignition

 PS-1 nozzle: Injection ports