F-1 (rocket engine)
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History
The Rocketdyne-developed F-1 engine is the most powerful single-nozzle liquid fueled rocket engine ever developed. Five F-1s powered the S-IC first stage of the Saturn V "moon rocket." The F-1 was originally developed by Rocketdyne to meet a 1955 US Air Force requirement for a new very large rocket engine. The eventual result of that requirement was two different engines—the E-1 and the much larger F-1. The E-1, although successfully tested in static firing, was quickly seen as a technological dead-end and was abandoned for the larger and more powerful F-1. The USAF eventually halted research and development of the F-1 due to a perceived lack of requirement for such a large engine. However the recently created NASA realized the capability afforded by an engine with so much power and contracted Rocketdyne to complete the development of the F-1. The first static firing of a full stage developmental F-1 was performed in March 1959. (Earlier test firings of F-1 components had been performed as early as 1957.)
Early F-1 tests revealed serious combustion instability problems which would sometimes cause catastrophic failure. Progress on this problem was initially slow, as the problem onset was intermittent and unpredictable. Eventually engineers developed a technique of detonating small explosive charges (which they called "bombs") inside the combustion chamber while the engine was firing. This artificially created combustion instability on demand. The designers could then quickly experiment with different fuel injector designs to obtain the one most resistant to instability. These problems were addressed from 1959 through 1961. Eventually the engine's combustion was so stable it would self damp artificially-induced instability within about 1/10th of a second.
The F-1 burned two short tons (1.8 t) of liquid oxygen (LOX) and one ton (0.9 t) of RP-1 (kerosene) each second generating over 1.5 million pounds-force (6.7 meganewtons) of thrust. During their two and one-half minutes of operation, the 5 F-1s propelled the Saturn-V vehicle to a height of 52 km (32 miles) and a speed of 8,700 km/h (5,400 mi/h). The propellant flow rate of the five F-1s in the Saturn V could fill a 30,000 gallon (114,000 liter) backyard swimming pool in ten seconds. Each F-1 engine has more thrust than all three space shuttle main engines combined.
There were proposals to use eight F-1 engines on the first stage of the Nova rocket.
Original F-1 specifications
Thrust (sea level): 1,500,000 lbf (6.7 MN)
Burn time: 150 s
Specific impulse: 260 s (2.55 kN·s/kg)
Engine weight dry: 18,416 lb (8,353 kg)
Engine weight burnout: 20,096 lb (9,115 kg)
Height: 18.5 ft (5.6 m)
Diameter: 12.2 ft (3.7 m)
Ratio: 16 to 1
Propellants: LOX & RP-1
Mixture ratio: 2.27
Contractor: NAA/Rocketdyne
Vehicle application: Saturn V / S-IC 1st stage - 5-engines
F-1 improvments during Apollo
F-1 thrust and efficiency were improved between Apollo 8 (SA-503) and Apollo 17 (SA-512). This was necessary for Saturn V payload capacity to meet the inceasing demands of the later Apollo missions. There were small performance variations between engines on a given mission, and variations in average thrust between missions. For Apollo 15, F-1 performance was:
Thrust (average, per engine, sea level liftoff): 1,553,200 lbf (6.909 MN)
Specific impulse: 264.72 s
Burn time: 159 s
Mixture ratio: 2.2674
S-IC total sea level liftoff thrust: 7,766,000 lbf (34.55 MN)
Measuring and making comparisons of rocket engine thrust is more complicated than first appears. Based on actual measurement the liftoff thrust of Apollo 15 was 7.823 million lbf (34.8 MN), which equates to an average F-1 thrust of 1.565 million lbf (6.962 MN), which is significantly more than the specified value. For more information, see S-IC thrust comparisons
F-1 developments
There was an uprating redevelopment of the F-1 undertaken by Rocketdyne during the 1960s which resulted in a new engine specification known as the F-1A. While outwardly appearing to be very similar to the F-1, the F-1A was actually lighter and yet significantly more powerful (9.1 MN compared to F-1's 6.7 MN) and would have been used on future Saturn V vehicles in the post-Apollo era. However, the Saturn V production line was closed prior to the end of Project Apollo and no F-1A engine ever flew on a launch vehicle.
The F-1 engine remained the most powerful liquid fuel rocket engine at 6.7 MN of thrust at sea level until overshadowed by RD-170 rocket engine from the Soviet Union. The RD-170 is actually a cluster of four separate combustion chambers and nozzles driven by a single turbopump. It visually appears to be and is considered by some a cluster of four engines, not a single engine. Viewed as a single engine it is the most powerful liquid fueled rocket engine ever developed. The F-1 still holds the crown of largest single-chamber, single-nozzle liquid fuel engine ever flown. However among solid-fuel engines, more powerful engines exist such as the Space Shuttle Solid Rocket Boosters, which each boast a thrust of 14.7 MN.
References
- Apollo 15 Press Kit
- Saturn V Launch Vehicle, Flight Evaluation Report, AS-510, MSFC-MPR-SAT-FE-71-2, October 28, 1971