RL-10 engine characteristics. The RL-10 engine was developed under the management of the Marshall Space Flight Center (MSFC) to power the Saturn I upper stage (S-IV stage). The six RL-10 engines, which used liquid hydrogen and liquid oxygen as propellants, were arranged in a circle on the aft end of the S-IV stage.

This drawing clearly shows the comparative sizes of the rocket engines used to launch the Saturn vehicles. The RL-10 and the H-1 engines were used to launch the Saturn I rockets. The J-2 engine was used on the second stage of Saturn IB and the second and third stages of Saturn V. The F-1 engine was used on the first stage of the Saturn V.

The Saturn I S-IV stage (second stage) for the SA-7 mission being prepared for shipment to Cape Canaveral, Florida. The S-IV stage had six RL-10 engines, which used liquid hydrogen and liquid oxygen as its propellants, arranged in a circle. Each RL-10 engine produced a thrust of 15,000 pounds for a total combined thrust of 90,000 pounds. The SA-7 mission was launched on September 18, 1964 from Cape Canaveral, Florida, and its S-IV stage made the second orbital flight.

The launch of the SA-5 on January 29, 1964 was the fifth Saturn I launch vehicle. The SA-5 marked a number of firsts in the Marshall Space Flight Center-managed Saturn development program, including the first flight of Saturn I Block II vehicle with eight aerodynamic fins at the bottom of the S-I stage (first stage) for enhanced stability in flight. This also was the first flight of a live S-IV (second or upper) stage with the cluster of six liquid hydrogen-fueled RL-10 engines. the first successful second stage separation, and the first use of the Launch Complex 37.

The Saturn I S-IV stage (second stage) assembly for the SA-9 mission underwent the weight and balance test in the hangar building at Cape Canaveral. The S-IV stage had six RL-10 engines which used liquid hydrogen and liquid oxygen as its propellants arranged in a circle. Each RL-10 engine produced a thrust of 15,000 pounds, a total combined thrust of 90,000 pounds. The SA-9 mission was the first Saturn with operational payload Pegasus I, meteoroid detection satellite, and launched on February 16, 1965.

This image illustrates the basic differences between the three Saturn launch vehicles developed by the Marshall Space Flight Center. The Saturn I, consisted of two stages, the S-I (eight H-1 engines) and the S-IV (six RL-10 engines). The Saturn IB (center) also consisted of two stages, the S-IB (eight H-1 engines) and the S-IVB (one J-2 engine). The Saturn V consisted of three stages, the S-IC (five F-1 engines), the S-II (five J-2 engines), and the S-IVB (one J-2 engine).

A completed Saturn I launch vehicle in the Fabrication and Assembly Engineering Division at the Marshall Space Flight Center. The Saturn I launch vehicle is composed of an S-I first stage or booster (rear), powered by eight H-1 engines having a thrust of 1,500,000 pounds, followed by a dummy S-IV second stage with six RL-10 engine, with a total thrust of 90,000 pounds.

This cutaway of the Saturn I S-IV stage (second stage) illustrates the booster's components. Powered by six RL-10 engines, the S-IV stage was capable of producing 90,000 pounds of thrust. Development of the Saturn S-IV stage by the Marshall Space Flight Center (MSFC) contributed many technological breakthroughs vital to the success of the Apollo lunar program, including the use of liquid hydrogen as a propellant.

An engineer at the National Aeronautics and Space Administration (NASA) Lewis Research Center examines a drawing showing the assembly and details of a 20,000-pound thrust regeneratively cooled rocket engine. The engine was being designed for testing in Lewis’ new Rocket Engine Test Facility, which began operating in the fall of 1957. The facility was the largest high-energy test facility in the country that was capable of handling liquid hydrogen and other liquid chemical fuels. The facility’s use of subscale engines up to 20,000 pounds of thrust permitted a cost-effective method of testing engines under various conditions. The Rocket Engine Test Facility was critical to the development of the technology that led to the use of hydrogen as a rocket fuel and the development of lightweight, regeneratively-cooled, hydrogen-fueled rocket engines. Regeneratively-cooled engines use the cryogenic liquid hydrogen as both the propellant and the coolant to prevent the engine from burning up. The fuel was fed through rows of narrow tubes that surrounded the combustion chamber and nozzle before being ignited inside the combustion chamber. The tubes are visible in the liner sitting on the desk. At the time, Pratt and Whitney was designing a 20,000-pound thrust liquid-hydrogen rocket engine, the RL-10. Two RL-10s would be used to power the Centaur second-stage rocket in the 1960s. The successful development of the Centaur rocket and the upper stages of the Saturn V were largely credited to the work carried out Lewis.

A cutaway illustration of Saturn 1 launch vehicle mission. The Saturn I, first of the Saturn launch vehicles' family, is a two-stage vehicle with a low-earth-orbit payload capability of approximately 25,000 pounds. The research and development program was plarned in two phases or blocks; one for first stage development (Block I) and the second for first and second stage development (Block II). The S-I (first) stage consisted of a cluster of nine propellant tanks and eight H-1 engines built by Rocketdyne, yeilding a total thrust of 1,500,000 pounds. The second stage of Saturn I, identified as S-IV, was designed as a single cylinder with a common bulkhead separating the liquid oxygen from the liquid hydrogen. Propulsion was provided by six RL-10 engines built by Pratt Whitney, capable of producing a combined thrust of 90,000 pounds. Of the 10 Saturn I's planned, the first eight were designed and built at the Marshall Space Flight Center. The remaining two were built by the Chrysler Corporation.

A cutaway illustration of Saturn I launch vehicle characteristics: The Saturn I, first of the Saturn launch vehicles' family, is a two-stage vehicle with a low-earth-orbit payload capability of approximately 25,000 pounds. The research and development program was plarned in two phases or blocks; one for first stage development (Block I) and the second for first and second stage development (Block II). The S-I (first) stage consisted of a cluster of nine propellant tanks and eight H-1 engines built by Rocketdyne, yeilding a total thrust of 1,500,000 pounds. The second stage identified as S-IV, was designed as a single cylinder with a common bulkhead separating the liquid oxygen from the liquid hydrogen. Propulsion was provided by six RL-10 engines built by Pratt Whitney, capable of producing a combined thrust of 90,000 pounds. Of the 10 Saturn I's planned, the first eight were designed and built at the Marshall Space Flight Center. The remaining two were built by the Chrysler Corporation.

Developed at MSFC under the direction of Dr. Wernher von Braun, the SA-5 incorporated a Saturn I, Block II engine. Launched on January 29, 1964, SA-5 was the first two stage (Block II) Saturn with orbital capability and performed the first test of Instrument Unit and successful stage separation. Block II vehicles had two live stages, and were basically in the two-stage configuration of the Saturn I vehicle. There were marked changes between the Block I and II versions. The Block II S-I stage had eight fins added for greater aerodynamic stability in the lower atmosphere. All Block II H-1 engines had a thrust of 188,000 pounds each for a combined thrust over 1,500,000 pounds. The Block II second stage (S-IV) had six RL-10 hydrogen-oxygen engines, each producing a thrust of 15,000 pounds for a total combined thrust of 90,000 pounds. A motion picture camera capsule loated on stage I was successful recovered.

Test engineers monitor an engine firing from the control room of the Rocket Engine Test Facility at the National Advisory Committee for Aeronautics (NACA) Lewis Flight Propulsion Laboratory. The Rocket Engine Test Facility, built in the early 1950s, had a rocket stand designed to evaluate high-energy propellants and rocket engine designs. The facility was used to study numerous different types of rocket engines including the Pratt and Whitney RL-10 engine for the Centaur rocket and Rocketdyne’s F-1 and J-2 engines for the Saturn rockets. The Rocket Engine Test Facility was built in a ravine at the far end of the laboratory because of its use of the dangerous propellants such as liquid hydrogen and liquid fluorine. The control room was located in a building 1,600 feet north of the test stand to protect the engineers running the tests. The main control and instrument consoles were centrally located in the control room and surrounded by boards controlling and monitoring the major valves, pumps, motors, and actuators. A camera system at the test stand allowed the operators to view the tests, but the researchers were reliant on data recording equipment, sensors, and other devices to provide test data. The facility’s control room was upgraded several times over the years. Programmable logic controllers replaced the electro-mechanical control devices. The new controllers were programed to operate the valves and actuators controlling the fuel, oxidant, and ignition sequence according to a predetermined time schedule.