The Historic Rocket Engine Test Facility (RETF)
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History & Significance

The Rocket Engine Test Facility (RETF) was located at the NASA Glenn Research Center in Cleveland , Ohio . When it opened in 1957, it was a one-of-a-kind facility for testing high-energy rocket engines and components. From its first test on August 15, 1957 until its official shutdown on July 1, 1995 , the RETF remained an experimental facility whose mission was to test out new designs and concepts. They analyzed their successes and failures and designed new and better models in an ongoing process of evaluation and improvement.

Rocket Testing Prior to RETF

Rocket-engine testing dates back to 1926, when Robert Goddard, a professor at Clark University in Massachusetts , launched the world's first liquid-fueled rocket. During the same time, the German scientist Hermann Oberth was developing theoretical work that led to the development of Germany 's Wernher von Braun's V-2 rocket during World War II. The V-2's success during World War II brought about governmental support for rocket research and testing in the United States that was lacking prior to this time. The 1943 dedication of the Aircraft Engine Research Laboratory (AERL) in Cleveland made the lab one of three national aeronautical research laboratories run by the National Advisory Committee for Aeronautics (NACA).

Although NACA directors at the time thought rockets were inappropriate for NACA research because of their military uses, many AERL personnel did not agree-the engineering staff and directors at AERL found rockets to be exciting and of tremendous interest. Due to the lack of knowledge in the field of high-energy liquid propellants, the rocket group at AERL was encouraged to focus on this topic.

Initial rocket research at the AERL worked with risky, volatile fuels such as hydrazine with oxidizers like hydrogen peroxide, chlorine trifluoride, liquid oxygen, nitrogen tetroxide and liquid fluorine. By 1948, an important theoretical study by Paul Ordin and Riley Miller, engineers at Lewis Laboratory (the new name for AERL), concluded that liquid hydrogen was a promising rocket fuel because of its high specific impulse. A classified NACA-sponsored conference in 1948 allowed Lewis engineers to discuss their theoretical performance and experimental data with the Air Force and Navy. In 1949, the Navy gave Lewis Laboratory their first officially sanctioned rocket research.

Believing that liquid hydrogen was going to be an ideal rocket fuel, the Lewis researchers began to focus on it and pushed for a new testing facility. In 1952, the Lewis rocket group proposed an $8.5 million facility (approximately $57 million in 2004 dollars) to test large liquid-propellant rockets. The plan was eventually scaled back to $2.5 million (approximately $17 million in 2004 dollars) and constructed between 1955 and 1957. This new Rocket Engine Test Facility (RETF) conducted its first test on August 15, 1957 .

Rocket Testing at RETF

1950s

The first test conducted was a 20,000-pound thrust rocket engine that ran for several seconds using traditional kerosene-based rocket propellant with liquid oxygen. The test operated properly and the results were gratifying, but the engineers were eager to see how the facility would handle more exotic fuels. On November 14, 1957 they got their wish and tested a rocket engine with hydrogen gas and liquid oxygen.

The late 1950s saw Pratt & Whitney's RL10 liquid-hydrogen engine encounter serious combustion instability problems caused by its injector. Pratt & Whitney were particularly interested in Lewis's work on liquid-hydrogen engines and its unique design for a concentric tube injector that was specifically designed to handle liquid hydrogen and oxygen. Pratt & Whitney made regular visits to Lewis during this time to learn about this new injector.

Pratt & Whitney eventually adopted the concentric injector but had some problems when the hot gases within the combustion chamber warped the faceplate of the injectors. RETF engineers responded by developing a porous material called Rigi-Mesh and fashioning a new injector that resembled a large, shallow mesh colander. The holes in the mesh let gaseous hydrogen through, which cooled the faceplate and diminished the warping. This injector was successfully used in the RL10 engine, the Rocketdyne's J-2, and it is used today in the main engine of the Space Shuttle.

1960s

With President Kennedy's 1961 decision to land an astronaut on the Moon before the end of the decade, researchers at NASA Lewis Research Center (renamed on October 1, 1958 from the NACA Lewis Laboratory) found themselves in the middle of a national emergency where they continued to be key players in the investigations and solutions for rocket engine problems.

The first problem arose in June 1962 when a Rocketdyne F-1 engine exploded a half second after ignition at the Marshall Space Flight Center. The explosion was blamed on combustion instability and placed the entire Apollo program in jeopardy. Lewis research engineers had researched the problem of combustion instability in the 1950s and soon determined that the F-1's injector was seriously flawed. By May 1963, they had developed and tested a concentric-tube injector for the F-1 that was adopted by Rocketdyne.

The RETF proved to be an excellent facility to develop and test injectors to combat combustion instability. The coordination between research scientists and RETF engineers allowed numerous theoretical questions to be answered through direct experimentation. The RETF was able to develop and test all different types of injectors, including sliding injectors, eight-element injectors, zoned injectors, and concentrated pattern injectors. Each injector was unique and gave research engineers the opportunity to see the effect of different variables on injector designs.

1970s

In 1972, President Nixon announced that America would focus on the development of a Shuttle rather than expendable launch vehicles, and NASA was given a new direction. When liquid-hydrogen fuel was chosen for use in the Shuttle's main engine, RETF proved invaluable as a test facility known for low costs and flexibility.

One problem that RETF was given to solve was low-cycle thermal fatigue. Low-cycle thermal fatigue is the structural weaknesses of metals that are caused when the metals are exposed to hot gases during combustion. To test this problem, RETF scientist Richard Quentmeyer came up with the clever lower-cost idea of a "plug nozzle." The plug nozzle simulated the interior of the combustion chamber and could be lined with various coatings to determine how quickly they would crack. The engine was fired, shut off, and fired again in a cyclic fashion to replicate multiple uses. The results showed that most lining materials would harden and become brittle and snap, the phenomenon that Quentmeyer soon called "thermal ratcheting."

RETF also experimented with different thermal barriers to protect the combustion chambers against the high temperatures of hydrogen gas. This led to the experimentation of high aspect ratio cooling channels in rocket engine liners. The use of more than 400 cooling passages, each about ten-thousandths of an inch thick, caused the temperatures within the chamber to be lowered from 1,000° Fahrenheit to between 400° and 600°. High aspect ratio cooling channels are used in all combustion-chamber designs for modern rockets today.

1980s

Up until the 1980s, RETF was able to test rockets at sea level or atmospheric pressure, but they were unable to test rockets in very low pressures that would reproduce the conditions of the upper atmosphere and the vacuum of space. With the addition of Test Stand B in 1984, RETF was able to complete these types of tests. Test Stand B could simulate the vacuum of space and was soon testing engines and high-area-ratio rocket nozzles for a vehicle that could be launched from the Space Shuttle's cargo bay.

Since the beginning of rocketry, the question of how to cool a rocket engine has always been a concern. Between 1986 and 1990, RETF experimented with five different combustion chambers with identical coolant passages to determine if liquid oxygen (LOX) was a feasible cooling agent. Up until this point, NASA researchers were reluctant to use LOX to cool the engine because they feared that if engine cracks were to form, the engine would be flooded with oxygen and might explode. After four years of testing, it was determined that LOX was a workable cooling agent and that leaking LOX into the engine did not affect the integrity of the combustion chamber. This technology has yet to be incorporated into American rocket engines at this time.

1990s

RETF worked with TRW ( Thompson-Ramo-Wooldridge Corporation) on a project to develop a 40,000-pound-thrust rocket engine in 1992. TRW had developed a relatively trouble-free injector that had been tested with LOX/Propane and LOX/RP-1 fuels but never with LOX/Liquid Hydrogen. TRW selected RETF to complete these liquid hydrogen tests. The first of three test phases focused on the stability and efficiency of the engine and investigated the durability of the engines ablative materials. The second and third test phases built upon the findings of the first phase and were completed successfully.

Closure

As early as 1977, a proposed expansion of Cleveland Hopkins International Airport threatened the future of RETF. Throughout the 1980s, negotiations between the City of Cleveland and Brook Park failed to reach an agreement that would allow the airport to expand and RETF to continue its mission. A decision was finally made in 1995 to proceed with the extension of one of the runways, but the extension would cross over the RETF site. NASA canceled its plans to improve RETF and announced the permanent closure of the RETF. RETF was officially shut down on July 1, 1995 .

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