Failure Modes of the F-1 Rocket Engine System by Paul S. Ray, Ph.D., PE, CSP, C. Eng. (U.K.) Tuscaloosa, Alabama   Page:  1 | 2 | 3 F-1 is the most powerful rocket engine ever developed by the National Aeronautics and Space Administration (NASA), having successfully overcome the gravitational pull of the Earth for the Saturn V launch vehicle. This study was directed to identify the failure modes of the F-1 engine so that design of future similar engines can be improved by incorporating mitigating provisions [Ref. 3, 6]. Introduction The Rocketdyne F-1 is the engine that hurtled the Saturn V launch vehicle from the Earth to the moon, for the first time in human history, on July 16, 1969. The force that lifted the rocket, overcoming the gravitational force during the first stage of the flight, was provided by a cluster of five Rocketdyne F-1 rocket engines, each developing over 1.5 million pounds of thrust [Ref. 5]. Since 1972, NASA’s focus has been on the Space Shuttle, and Saturn V activity was terminated. However, interest in the rocket system has been revived to meet the National Launch System (NLS) program’s goal of returning to the moon and the exploration of space, including Mars. The new program Space Launch Initiative (SLI) is directed to drastically reduce the payload cost per flight. To accomplish this, it is essential to have the ability to lift huge payloads into low Earth orbit. The logic in favor of adopting the Saturn system, a proven technology, to meet the SLI challenge is very strong, as the F-1 engine was the largest and most powerful liquid-oxygen rocket engine ever built and its performance was exceptional. F-1 Rocket Engine Features The F-1 engine is a single-start, 1,530,000-pound, fixed-thrust, calibrated, bipropellant engine, which uses liquid oxygen as the oxidizer and RP-1 as the fuel. The engine’s features include a bell-shaped thrust chamber with a 10:1 expansion ratio, and a detachable, conical nozzle extension which increases the thrust chamber expansion ratio to 16:1. Liquid oxygen and RP-1 fuel are supplied to the thrust chamber by a single turbo pump powered by a gas generator which uses the same propellant combination. RP-1 fuel is used as the working fluid to generate thrust, and is also used as the turbo pump lubricant. An instrumentation system monitors engine performance and operation. External thermal insulation provides an allowable engine environment during operation [Ref. 5]. Engine Operation Engine operation includes starting, main stage and cut-off. The starting and cut-off phases are periods of transition in which a sequence of activities occurs. These are described below. Engine Start-up: Engine start is part of the terminal countdown sequence. When this point is reached, the ignition sequencer control starts the engine. The checkout valve moves to the engine return position. An electrical signal fires the igniters (four on each engine). A solenoid of a four-way control valve starts and directs ground support equipment hydraulic pressure to flow through a sequence valve to an open gas generator ball valve. Propellants under tank pressure flow into a gas generator combustor, and propellants are ignited by the flame of the igniters. Combustion gas passes through a turbo pump, heat exchanger, exhaust manifold and nozzle extension. Fuel-rich turbine combustion gas is ignited by the flame from the igniters. Combustion gas accelerates the turbo pump, causing the pump discharge pressure to increase. As fuel pressure increases to approximately 375 psig, it ruptures the hypergolic cartridge. The hypergolic fluid and fuel are forced into the thrust chamber where they mix with the liquid oxygen (LOX) to cause ignition.   "Face-to-face interviews were conducted from July 1 to July 26, 2002, to collect data from the memory of the engineers who were associated with the Saturn projects." Transition to Main Stage: Ignition causes the combustion zone pressure to increase. As pressure reaches 20 psig, the ignition monitor valve directs fluid pressure to the main fuel valves. Fluid pressure opens the main fuel valves, and fuel enters the thrust chamber. As pressure increases, the transition to main stage is accomplished. Engine Cut-off: The four-way control valve stop solenoid is energized, which routes closing pressure to the gas generator ball valve, main LOX valves (two each) and main fuel valves (two each). All these valves close, and the thrust chamber pressure decay causes the thrust-okay pressure switch to drop out (three each). The ignition fuel valve and ignition monitoring valve close [Ref. 5]. The basic F-1 engine schematics [Ref. 1] are illustrated in Figure 1.   Figure 1 — Basic F-1 Engine Schematics (Adapted from Biggs, 1992, Ref. 1) . F-1 Rocket Engine Propellants System The propellant system includes hardware for fuel fill and drain operations, tank pressurization prior to and during flight, and delivery of propellants to the engines. The propellant system is divided into two subsystems, the fuel subsystem and the LOX subsystem. During flight, the source of fuel tank pressurization is helium from storage bottles mounted inside the LOX tank. RP-1 delivery is accomplished through two 12-inch ducts that connect the fuel tank to the F-1 engine. As the oxidizer in the bipropellant propulsion system, LOX is contained and delivered through a separate tank and delivery system. The 345,000-gallon tank is filled through two 6-inch fill and drain lines. The pressurization gas used is helium. The pressure derived from the LOX tank height establishes the initial LOX flow rate. A gradual power buildup ensues at a rate determined by the engine propellant inlet conditions. Built-up fuel pressure is applied to rupture the inlet and outlet burst diaphragms of the hypergolic igniter and pushes the igniter fluid into the thrust chamber combustion zone, where it spontaneously ignites upon contact with the already free-flowing LOX. In the final phase of the start sequence, the fuel pump discharge pressure exceeds the ground-supplied hydraulic pressure. This causes the ground supply to be terminated, and engine fuel is substituted for hydraulic fluid for the remainder of the mission. The entire start, from control valve activation to full power level, takes about five seconds [Ref. 1].  NEXT PAGE »