Spareribs, which correspond to.

RCS PROPELLANT MANIFOLD VALVES RCS FUEL RCS OXIDIZER TANK VERNIER THRUSTERS (2 PER AFT POD) PRIMARY THRUSTERS RCS (12 PER AFT POD) PRESSURIZATION COMPONENTS Figures 4-2 — Reaction control system. 4-31 4. ORBITER SYSTEMS Propulsion A ORBITER MANEUVERING SYSTEM........... 4-5 REACTION CONTROL SYSTEM (RCS) POD ELEVON ACTUATORS (4) SIDEWALL PAYLOAD.