Saturn INT-20
Encyclopedia
The Saturn INT-20 was a proposed intermediate payload follow-on from the Apollo
Saturn V
launch vehicle. An interstage would be fitted on top of the S-IC
stage to support the S-IVB
stage, so it could be considered either a retrofitted Saturn IB
with a more powerful first stage, or a stubby, cut-down Saturn V without the S-II
second stage.
Three variants were studied, one with three F-1
engines in the first stage, one with four, and one with five.
Using the original five-engine S-IC would require three engines would be shut down 88 seconds after launch, with the remainder of the first-stage flight flown on only two engines. This meant that a considerable amount of the firing time would be carrying three engines of "dead weight". As a consequence the extra payload over a four-engine variant would only have been about one thousand pounds, and the extra cost and complexity of the fifth engine was unjustified.
A four-engine variant would launch with four engines firing and shut down two engines 146 seconds after launch. The remaining two engines would burn until first-stage shutdown 212 seconds after launch. This variant could put approximately 132,000 pounds into a 100 nautical mile
(185 km or 115 statute mile) orbit, versus around 250,000 pounds for the three-stage Saturn V.
The three-engine variant would burn all three engines up to first-stage shutdown at 146 seconds after launch. This variant could put approximately 78,000 pounds of payload into a 100 nautical mile (185 km) orbit, around twice the useful payload of the Saturn IB.
Both three- and four-engine variants would therefore have provided useful payload capacities intermediate between the Saturn IB and Saturn V, and re-using Saturn V components would reduce costs and simplify ground operations compared to building an entirely new launcher in that payload range.
Project Apollo
The Apollo program was the spaceflight effort carried out by the United States' National Aeronautics and Space Administration , that landed the first humans on Earth's Moon. Conceived during the Presidency of Dwight D. Eisenhower, Apollo began in earnest after President John F...
Saturn V
Saturn V
The Saturn V was an American human-rated expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. A multistage liquid-fueled launch vehicle, NASA launched 13 Saturn Vs from the Kennedy Space Center, Florida with no loss of crew or payload...
launch vehicle. An interstage would be fitted on top of the S-IC
S-IC
The S-IC was the first stage of the Saturn V rocket. The S-IC first stage was built by The Boeing Company. Like the first stages of most rockets, most of its mass of over two thousand metric tonnes at launch was propellant, in this case RP-1 rocket fuel and liquid oxygen oxidizer...
stage to support the S-IVB
S-IVB
The S-IVB was built by the Douglas Aircraft Company and served as the third stage on the Saturn V and second stage on the Saturn IB. It had one J-2 engine...
stage, so it could be considered either a retrofitted Saturn IB
Saturn IB
The Saturn IB was an American launch vehicle commissioned by the National Aeronautics and Space Administration for use in the Apollo program...
with a more powerful first stage, or a stubby, cut-down Saturn V without the S-II
S-II
The S-II was the second stage of the Saturn V rocket. It was built by North American Aviation. Using liquid hydrogen and liquid oxygen it had five J-2 engines in a cross pattern...
second stage.
Three variants were studied, one with three F-1
F-1 (rocket engine)
The F-1 is a rocket engine developed by Rocketdyne and used in the Saturn V. 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 is still the most powerful single-chamber liquid-fueled rocket engine ever...
engines in the first stage, one with four, and one with five.
Performance
Without the S-II stage, which made up a large fraction of the mass of the Saturn V, a version of the INT-20 using an unmodified five-engine version of the S-IC booster would be greatly overpowered and accelerate substantially faster than the Saturn V. This would create excessive aerodynamic stress in the low atmosphere. Several solutions to this problem were considered.Using the original five-engine S-IC would require three engines would be shut down 88 seconds after launch, with the remainder of the first-stage flight flown on only two engines. This meant that a considerable amount of the firing time would be carrying three engines of "dead weight". As a consequence the extra payload over a four-engine variant would only have been about one thousand pounds, and the extra cost and complexity of the fifth engine was unjustified.
A four-engine variant would launch with four engines firing and shut down two engines 146 seconds after launch. The remaining two engines would burn until first-stage shutdown 212 seconds after launch. This variant could put approximately 132,000 pounds into a 100 nautical mile
Nautical mile
The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...
(185 km or 115 statute mile) orbit, versus around 250,000 pounds for the three-stage Saturn V.
The three-engine variant would burn all three engines up to first-stage shutdown at 146 seconds after launch. This variant could put approximately 78,000 pounds of payload into a 100 nautical mile (185 km) orbit, around twice the useful payload of the Saturn IB.
Both three- and four-engine variants would therefore have provided useful payload capacities intermediate between the Saturn IB and Saturn V, and re-using Saturn V components would reduce costs and simplify ground operations compared to building an entirely new launcher in that payload range.