The SS Thrusters are a part of the Spaceship, which is required to win a Space Race victory.
The massive Thrusters are, much like the Engine, designed to function in a myriad of ways. Designed in stages like the Engines, the Thrusters channel the exhaust used to propel the Space Ship through all of its phases of travel. In the initial phase, the external booster rockets channel their fuel through the Thrusters array until they run out of fuel, at which point they are jettisoned. After that, the powerful electromagnets built into the Thrusters help accelerate the charged particles of the ion drive to near the speed of light, providing a great deal of thrust for the Space Ship.
Finally, in the last stages of travel, the Thrusters are responsible for maneuvering the Space Ship into the planet's gravity well and providing a counter thrust to slow the vessel to a manageable velocity to settle into a geo-synchronous orbit. In order to fulfill all of these functions, the Thrusters array had to be capable of the ultra-sensitive duty of accelerating high energy ions as well as be able to handle the hundreds of thousands of pounds of thrust produced by the solid fuel boosters.
The engineers who designed the Thrusters were able to fulfill both of these functions as well as making them articulated to allow for maneuverability that is remarkable considering the mass and projected velocities of the craft.