MAE 4262: ROCKETS AND MISSION ANALYSIS

1. MAE 4262: ROCKETS AND MISSION ANALYSIS Rocket Cycle Analysis November 27, 2012 Mechanical and Aerospace Engineering Department Florida Institute of Technology D. R. Kirk

2. CONTENTS • Overview • Propellant Feed Systems / Cycle Examples • Gas Feed System • Turbopump Systems • Gas Generator • Preburner • Topping / Expander Cycle • Example: Step by Step Operation Process for Liquid Rocket • Supplemental Rocket Flow Diagrams • Summary of Key Points

3. OVERVIEW • GOAL: Understand and describe propellant feed system / rocket cycle • NOTE: Usually denser of two propellants is placed forward • Shifts center of mass forward – increases stability • For STS, LOX is forward since it is denser than LH2

4. OVERVIEW • For liquid rockets: • How do we feed propellants into combustion chamber? • How do we select a pressurization cycle? • For liquid and solid rockets: • How do we ensure structural integrity and cool hot components? How can we represent this complex system in a simplified way?

5. SSME FLOW DIAGRAM

6. GAS PRESSURIZATION • Advantages • Simplicity • Reliability • Disadvantages • Low chamber pressures • Weight of both gas and propellant tanks • Examples • SSOMS, SSRCS

7. GAS GENERATOR (OPEN) • Advantages • Simple start-up, even in space • Straightforward development process • Disadvantages • Overboard dump of exhaust reduces effective Isp • Examples • V-2 (H2O2), Atlas, Delta, Saturn V, Titan, F-1 engine RS-68 Delta IV F-1

8. STAGED-COMBUSTION / PREBURNER (CLOSED) • Advantages • Ability to operate at very high chamber pressure, high Isp • Flexibility of cycle design • Disadvantages • Complex design, cost, pump pressures • Start-up issues • Examples • SSME, RD-170, RD-180 RD-180 SSME

9. EXPANDER / TOPPING CYCLE (CLOSED) • Advantages • Relatively high Isp • simple relative to preburner • Disadvantages • Complex start-up dependent on stored heat in system • Limit on Pc, due to turbine drive gas limit • Examples • RL-10, Centaur

10. CLASSIFICATION OF LIQUID FEED SYSTEMS

11. EXAMPLE: LIQUID ROCKET OVERVIEW • FUEL: RED • OXIDIZER: GREEN • COMBUSTION GASES: YELLOW

12. PROPELLANT STORAGE Gas pressurization Turbopumps and Valves • Fuel and oxidizer tanks with gas pressure systems • Fuel and oxidizer stored in separate tanks • Valve releases propellants into cycle • Cryogenic propellants have to be carefully insulated • Cryogenics re-circulated through umbilical to external cooler

13. OPEN VALVES • Before operation valves are opened and propellant fills propellant feed lines • Propellants flow past compressors in turbopump up to a second set of valves • Compressors not pumping • Downstream valves prevent propellant from oozing into combustion chamber • This can cause problems, want fuel and oxidizer to flow into combustion chamber under high pressure and at high quantity

14. STARTER MOTOR Starter Motor • Ready to start rocket engine • Small solid rocket engine, called a starter motor, ignited by an electrical charge • This motor burns pushing turbine, which turns gearbox and starts compressor • Exhaust from the starter motor will be discussed later • Process can also be initiated by decomposition of monopropellant

15. PRESSURIZED PROPELLANT FEED LINES Solenoid Valve • Compressor are pumping • Fuel pressure rises rapidly to the operating pressure • When this happens a solenoid detects pressure rise and opens downstream valves allowing fuel to flow into combustion chamber

16. COMBUSTION CHAMBER • High-pressure propellant flows into combustion chamber • Fuel circulates around nozzle and combustion chamber for cooling • Usually oxidizer flows into combustion chamber ahead of fuel for smoother start • Ignition source in combustion chamber (electrical sparks, hot wire, small detonator, small flame) • Hypergolic propellants will spontaneously combust when mixed

17. SUSTAINING TURBOPUMP Small combustion chamber • Starter motor dies out very quickly • Tap off some propellant to small combustion chamber to drive turbopump • Flow regulators are critical • Too much propellant, push to turbopump too hard causing catastrophic failure • Not enough propellant, turbopump moves too slowly and thrust is too low • If adjustable throttle control of thrust accomplished by adjusting flow • Small combustion chamber that drives turbine is run with a fuel rich mixture

18. OIL PRESSURE Oil Supply • Turbopump and gearbox operate at extremely high speeds • Oil is needed for them to function • Oil is forced through system under pressure using exhaust from motor that sustains turbopump

19. OIL COOLANT Heat Exchanger • Oil used to lubricate the turbopump and gear box must also be cooled • Common to cool oil by running it through a heat exchanger with fuel • Fuel that goes through heat exchanger re-used • But if connected back to main feed line, there would be no flow through heat exchanger • Must be fed back into system at a low pressure area upstream of compressor • Cooled oil then goes back into turbopump cooling gearbox and bearings

20. FUEL TANK PRESSURE Fuel Tank Pressurization and Heat Exchanger • Two ways to provide pressurizing gas to a propellant tank • Provide inert gas from separate tank • Tap off excess gas from turbopump drive system (fuel rich) • This gas is too hot and needs to be cooled, to cool this gas use a heat exchanger • Some unused fuel is drawn from main fuel line to cool gas • Fuel sent back to fuel line upstream of the compressor in order to get a flow

21. OXIDIZER TANK PRESSURE Oxidizer Pressurization Heat Exchanger • Oxidizer tank pressurized in manner similar to fuel tank • Cannot use exhaust gasses (fuel rich) • Some oxidizer drawn from main oxidizer line and heated by exhaust gasses from engine used to drive turbopump • This vaporizes oxidizer inside a pressure line which is used to pressurize oxidizer tank

22. ATTITUDE CONTROL • Remaining exhaust gasses from motor driving turbopump: • Dumped overboard • Roll attitude control Attitude Control Thruster

23. SUMMARY • Overview was one of many possible approaches • Simpler engines possible (smaller thrusters) where turbopump not required • In these cases either a small electrical pump or pressure from tanks themselves provide enough propellant flow to provide design thrust.

24. SHUTDOWN • Running until fuel or oxidizer depletion • Known as 'hard' shutdown • As compressors ingest gas instead of liquid, resistance from pumps to turbine is reduced, and can quickly reach a point when turbine side goes too fast • Burns up bearings or turbine blades can break off • Turbopump fails and locks up. Without a smooth flow of fuel to combustion chamber, combustion may be disrupted and 'cough'. Both of these conditions are destructive to engine and induce violent shaking of vehicle • Controlled shutdown is more desirable • Fuel and oxidizer left unused, inefficient • Easier on vehicle and contents, reuse engine • To perform controlled shut down cut off propellant to motor driving turbopump • Turbopump slows down and reduces pressure on propellant feed lines • When this pressure gets below a minimum threshold solenoid controlling pressure valves downstream of compressors closes combustion chamber inlet valves • The shut off pressure is same pressure at startup that solenoids had to detect before opening the valves

25. EXAMPLE: RD-170

26. EXAMPLES: RD-170

27. EXAMPLE: H-1 (SATURN C-1 BOOSTER)

28. EXAMPLE: SHUTTLE OMS

29. EXAMPLE: ARIANE 5

30. EXAMPLE: VIKING

31. EXAMPLE: ARIANE HM7B

32. EXAMPLE: SSME

33. EXAMPLE: ARIANE VULCAN

34. EXAMPLE: TURBOPUMP (HPFTP)

35. EXAMPLE: TURBOPUMP (RS-27 DELTA)

36. SUMMARY OF KEY POINTS • Rocket systems are complex, multi-purpose systems • Choice of system, strongly related to: • Combustion chamber pressure • Size of engine • Thrust requirement • Primary Propellant Feed System Types: • Cold Flow / Pressurized Gas • Turbopump • Gas Generator • Preburner • Expander / Topping • Understand Advantages / Disadvantages of each • References • http://www.pratt-whitney.com/how.htm • http://woodmansee.com/science/rocket/r-liquid/index-liquid.html