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lecture_24 - 16.512 Rocket Propulsion Prof Manuel...

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16.512, Rocket Propulsion Prof. Manuel Martinez-Sanchez Lecture 24: Pressurization and Pump Cycles Thrust Chamber Pressurization 1. Introduction The most technically demanding part of a modern high pressure liquid propellant rocket is the chamber pressurization system. Consider for example the cluster of four RD-170 engines powering the Energia first stage. Their shared oxygen pump must deliver 1792 Kg/sec (1.63 m 3 ) of LOX at 614 atm pressure to the combustors, for a power of 176,000 HP. The whole engine weighs 9500 Kg . Similarly, the SSME LH pump (see Fig. 3 in lecture 25) delivers 73 Kg/sec of LH (1.06 m 3 /sec) at 470 atm pressure, for a power of 76,000 HP. The SSME mass is 2870 Kg, of which the LH turbopump is 344 Kg . And these flow rates are both dwarfed by those of the old F1 Saturn engine, which swallowed a small river (3.5 m 3 / sec) of LOX , albeit at a more modest pressure. Because of the importance of this system, we will devote this lecture to engine pressurization cycles and components. 2. Gas Pressurization Systems The simplest way to achieve the required thrust chamber pressure is to provide a small, high pressure gas reservoir, which, at firing time, pressurizes the propellant tanks. The tanks must then be thick enough to support the thrust chamber pressure, plus the injector drop. In addition, the gas reservoirs are also relatively heavy. Thus, the performance of a gas-pressurized rocket lags that of a pump-pressurized rocket (where the tanks can be much lighter), as shown in Fig. 1 (from Ref. 40). We notice here that the relative size of the gains due to a turbo pump system become overpowering for high V rockets, but may not be worth the extra complexity for small V 16.512, Rocket Propulsion Lecture 24 Prof. Manuel Martinez-Sanchez Page 1 of 5
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Fig. 1. Payload ratio for typical gas pressurization and pump pressurization
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