Rocketdyne F-1

The F-1 is a rocket engine developed by Rocketdyne. The engine uses a gas-generator cycle developed in the United States in the late 1950s and was used in the Saturn V rocket in the 1960s and early 1970s. Five F-1 engines were used in the S-IC first stage of each Saturn V, which served as the main launch vehicle of the Apollo program. The F-1 remains the most powerful single combustion chamber liquid-propellant rocket engine ever developed.

Rocketdyne developed the F-1 and the E-1 to meet a 1955 U.S. Air Force requirement for a very large rocket engine. The E-1, although successfully tested in static firing, was quickly seen as a technological dead-end, and was abandoned for the larger, more powerful F-1. The Air Force eventually halted development of the F-1 because of a lack of requirement for such a large engine. However, the recently created National Aeronautics and Space Administration (NASA) appreciated the usefulness of an engine with so much power and contracted Rocketdyne to complete its development. Test firings of F-1 components had been performed as early as 1957. The first static firing of a full-stage developmental F-1 was performed in March 1959. The first F-1 was delivered to NASA MSFC in October 1963. In December 1964, the F-1 completed flight rating tests. Testing continued at least through 1965.

Early development tests revealed serious combustion instability problems which sometimes caused catastrophic failure. Initially, progress on this problem was slow, as it was intermittent and unpredictable. Oscillations of 4 kHz with harmonics to 24 kHz were observed. Eventually, engineers developed a diagnostic technique of detonating small explosive charges (which they called "bombs") outside the combustion chamber, through a tangential tube (RDX, C-4 or black powder were used) while the engine was firing. This allowed them to determine exactly how the running chamber responded to variations in pressure, and to determine how to nullify these oscillations. The designers could then quickly experiment with different co-axial fuel-injector designs to obtain the one most resistant to instability. These problems were addressed from 1959 through 1961. Eventually, engine combustion was so stable, it would self-damp artificially induced instability within one-tenth of a second.

The F-1 engine is the most powerful single-chamber liquid-fueled rocket engine ever flown. The M-1 rocket engine was designed to have more thrust, but it was only tested at the component level. The later developed RD-170 is much more stable, technologically more advanced, more efficient and produces more thrust, but features four combustion chambers fed by a single pump. The F-1 burned RP-1 (rocket grade kerosene) as the fuel and used liquid oxygen (LOX) as the oxidizer. A turbopump was used to inject fuel and oxygen into the combustion chamber.

One notable challenge in the construction of the F-1 was regenerative cooling of the thrust chamber. Chemical engineer Dennis "Dan" Brevik was faced with the task of ensuring the preliminary combustion chamber tube bundle and manifold design produced by Al Bokstellar would run cool. In essence, Brevik's job was to "make sure it doesn’t melt." Through Brevik's calculations of the hydrodynamic and thermodynamic characteristics of the F-1, he and his team were able to fix an issue known as ‘starvation’. This is when an imbalance of static pressure leads to 'hot spots' in the manifolds. The material used for the F-1 thrust chamber tube bundle, reinforcing bands and manifold was Inconel-X750, a refractory nickel based alloy capable of withstanding high temperatures.

The heart of the engine was the thrust chamber, which mixed and burned the fuel and oxidizer to produce thrust. A domed chamber at the top of the engine served as a manifold supplying liquid oxygen to the injectors, and also served as a mount for the gimbal bearing which transmitted the thrust to the body of the rocket. Below this dome were the injectors, which directed fuel and oxidizer into the thrust chamber in a way designed to promote mixing and combustion. Fuel was supplied to the injectors from a separate manifold; some of the fuel first traveled in 178 tubes down the length of the thrust chamber — which formed approximately the upper half of the exhaust nozzle — and back in order to cool the nozzle.

A gas generator was used to drive a turbine which drove separate fuel and oxygen pumps, each feeding the thrust chamber assembly. The turbine was driven at 5,500 RPM, producing 55,000 brake horsepower (41 MW). The fuel pump delivered 15,471 US gallons (58,560 litres) of RP-1 per minute while the oxidizer pump delivered 24,811 US gal (93,920 L) of liquid oxygen per minute. Environmentally, the turbopump was required to withstand temperatures ranging from input gas at 1,500 °F (820 °C) to liquid oxygen at −300 °F (−184 °C). Structurally, fuel was used to lubricate and cool the turbine bearings.

Below the thrust chamber was the nozzle extension, roughly half the length of the engine. This extension increased the expansion ratio of the engine from 10:1 to 16:1. The exhaust from the turbine was fed into the nozzle extension by a large, tapered manifold; this relatively cool gas formed a film which protected the nozzle extension from the hot (5,800 °F (3,200 °C)) exhaust gas.