Washington D.C. - National Air and Space Museum - Rocketdyne F-1 3D Anaglyph
The F-1 is a gas-generator cycle rocket engine developed by Rocketdyne in the late 1950s and 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 in the Apollo program. The F-1 remains the most powerful single-chamber liquid-fueled rocket engine ever developed.
The F-1 was originally developed by Rocketdyne to meet a 1955 US Air Force requirement for a very large rocket engine. The eventual result of that requirement was two 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, 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 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.
During 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 technique of detonating small explosive charges (which they called "bombs") outside the combustion chamber, through a tangential tube (RDX, C4 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 1/10 of a second.
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 increasing 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 pounds-force (6.909 MN)
- Burn time: 159 s
- Specific impulse: 264.72 seconds (2.5960 km/s)
- Mixture ratio: 2.2674
- S-IC total sea level liftoff thrust: 7,766,000 pounds-force (34.54 MN)
Measuring and making comparisons of rocket engine thrust is more complicated than it first appears. Based on actual measurement the liftoff thrust of Apollo 15 was 7,823,000 lbf (34.80 MN), which equates to an average F-1 thrust of 1,565,000 lbf (6.96 MN) - significantly more than the specified value.