The plan form of the lifting body is scaled from the Lockheed 1 1/2 stage shuttle phase B study since this shape has a large amount of aerodynamic stability and entry data available. The volumetric requirements of the various systems are given in table VI-B-2-4. From this table it is seen that 60% of the volume is LOX. The GLOW of the 15 engine vehicle is 3,150.3 MT (6,930,682 pounds) of which 2,350 MT (5,170,064 pounds) is LOX. The LOX tank volume requires 2,053.3 cubic meters (72,511 cubic feet). The air frame volume, therefore, is 3,422.1 cubic meters (120,852 cubic feet). This is a 25 percent increase in volume over the phase B shuttle studies of the lifting body. Since the dimensions scale is the cube root of the volume, the scale factor is 1.074. A three view drawing is shown in figure VI-B-2-5. IV. MODIFIED ORBITER The shuttle orbiter carried as a payload on the SSTO heavy lift launch vehicle does not require a main propulsion system. The orbiter, therefore, can be modified to reduce its weight and improve its aerodynamic characteristics. The main propulsion system and thrust structure can be removed. A tail section is added behind the payload bay to reduce base drag. The aft Reaction Control System and Orbit Maneuvering System systems are moved from the side into the tail section, and to provide an off the pad abort capability, one SSME with an expansion ratio of 9 mounted in the back of the tail section. This engine will provide 500,000 pounds of thrust which will lift the orbiter and its payload off the pad with an acceleration of 2g. Since the pad abort SSME requires LOX hydrogen as a propellant, the orbit maneuvering system is changed to use L0X/LH2 as a propellent and two RL10 engines are mounted, one each above and below the abort engine for on-orbit maneuvering. The propellant tanks are mounted in the tail section and are used to fuel either the on-orbit maneuver or the abort engine. The AFT RCS tanks are also mounted in the tail section. The weights for the combined orbit maneuvering and abort system are shown in table VI-B-2-6. An analysis of the inert weight and center of gravity location of the modified shuttle is shown in table VI-B-2-7. Platform and side elevation of the modified orbiter showing the location of the orbit maneuvering system, pad abort engine, and propellant tank is shown in figure VI-B-2-6. The modified orbiter weight summary is shown in table VI-B-2-8.
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