The OMS function is performed by RL-10 engines. OMS LOX is stored in independent spherical containers. OMS LH2 is in a separate container within the main hydrogen tank. An asymmetric aft skirt panel provides directional control during entry. Control is required to overcome flight dispersions so that the stage can return to the vicinity of the launch site. During entry the stage is rotated slowly on its axis. If lift is required, rotation is stopped and the aft skirt is located away from the desired direction. A 0. 25 lift to drag ratio can be developed. During entry as the stage reaches approximately 25 000 m and Mach 2, it is rotated and a ballute is deployed. The ballute stabilizes and slows the stage. In the subsonic region three parachutes are deployed. At approximately 150 m altitude, two SSME's are ignited for final deceleration. The engines, which can be throttled, settle the stage to a soft landing on its landing legs. The booster is a sea landing ballistic entry stage. The most forward component is an interstage forward skirt. The space forward of the LOX tank houses the upper stage engines. The LOX and RP-1 tanks share a common bulkhead. The aft shell structure is primarily an aerodynamic fairing. The thrust structure distributes thrust loads into the external shell and provides the load path from the external shell to the hold-down posts. The hold-down posts support the stage on the ground and are the terminus for the heat shield radial beam structure. The base heat shield consists of two skins separated by 12 cm high stiffeners. Each inner skin is an assembly of two sheets rolled together. The inner of these has expanded ducts for water flow. Formed spray holes are drilled in the skin. When needed during boost and entry, water is sprayed onto the exterior skin. The steam is vented overboard through a metering orifice. The ballistic single stage to orbit vehicle, shown in Figure 12-6, is a dual fuel fully recoverable launch vehicle with a 230 000 kg payload. At liftoff its 48 engines provide a thrust to weight ratio of 1. 3. Twenty-four engines utilize LOX/RP-1 propellants; the other 24 are LOX/LH2 engines. The engines supply thrust vector control by differential throttling. Both engines represent a new engine development. The engines do not have protective doors, instead a steam system provides active engine cooling during entry.
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