Space Shuttle Engine Testing: T Plus 30 Years and Counting

Thirty years ago there was no Internet, laptop computers or CDs; Gerald Ford was president; “The Mary Tyler Moore Show” was on TV; and “Jaws” was at the movies.

But in South Mississippi, NASA engineers were testing a new reusable rocket engine, built to power the world’s first reusable spacecraft – America’s Space Shuttle.

This year marks the 30th anniversary of testing the Space Shuttle Main Engines (SSMEs) at NASA’s Stennis Space Center (SSC), which will culminate with an engine test Aug. 11.

Since the first test on May 19, 1975, the NASA/contractor team at SSC has conducted more than 2,200 tests on SSMEs, including the ones that helped propel Space Shuttle Discovery on STS-114, NASA’s Return to Flight mission.

A total of 10 tests were conducted in the first two months to help establish fuel preburner, oxygen preburner and main combustion chamber ignition. Three years later, test teams at SSC were firing the Main Propulsion Test Article: the three-engine cluster that helps propel the Space Shuttle into orbit. On Jan. 21, 2004, SSC celebrated 1 million seconds of successful SSME engine firings, both in testing and flight operations. This milestone is a testament to the employees and to the engine itself, which has never experienced a major anomaly.

“The unmatched reliability and durability of the SSME serves as an enormous credit to the NASA/contractor teams that have manufactured and tested the engine for three decades,” said Ronnie Rigney, SSME Project Manager at SSC. “They’ve done an extraordinary job.”

There have been 114 missions since the first Space Shuttle took flight from Kennedy Space Center (KSC) on April 12, 1981, all powered by SSMEs tested at SSC.

The engines are tested on the A-1 and A-2 Test Stands which were built in the 1960s to test the first and second stages of the Apollo Saturn V rocket that safely transported Americans to the Moon. The stands were converted from the Apollo/Saturn V configuration to accommodate SSMEs.

“The SSME is a unique engine, and 30 years of testing the engine at Stennis is highly unique, also,” said Dave Geiger, Pratt & Whitney Rocketdyne’s site manager at SSC. “We have learned a lot about how to not only improve the engine, but also the test facilities and capabilities.”

During testing at SSC, the engines are mounted vertically on the 185-foot-tall stands for test- firing. Instruments are added, and then the engines are hot-fire tested, usually for about 520 seconds (about 8 1/2 minutes), the amount of time it takes to lift the Space Shuttle into space.

Each SSME is 14 feet long, weighs about 7,000 pounds and is 7 1/2 feet in diameter at the end of the nozzle. The engine operates at greater temperature extremes than any other mechanical system in use today. It is fueled by liquid hydrogen – at -423 degrees Fahrenheit, the second-coldest liquid on Earth.

When it is combusted with liquid oxygen, the temperature in the Main Combustion Chamber of the SSME is 6,000 degrees Fahrenheit, hotter than the boiling point of iron. The three SSMEs on a Space Shuttle produce the equivalent of more than 37 million horsepower; if they pumped water instead of fuel, they could drain an average-sized swimming pool in 25 seconds.

Pratt & Whitney Rocketdyne, in Canoga Park, Calif., manufactures the SSME and its high- pressure turbo pumps. Marshall Space Flight Center in Huntsville, Ala., manages the Space Shuttle Main Engine Project for the Space Shuttle Program.

The engines are assembled at KSC in Florida and shipped to SSC for testing. After passing flight acceptance tests, they are weighed and subjected to a formal acceptance review, then shipped back to KSC for installation on a Space Shuttle Orbiter. The result is a safe, strong, reliable engine, thoroughly tested at SSC for the last 30 years.

“What’s amazing is that 30 years of knowledge has been passed on without a gap in important information,” said Miguel Rodriguez, Propulsion Test Director. “Most processes suffer through a knowledge gap over this many years. Because this program has been continuously maintained, others have had the opportunity to learn from people like Pat Mooney or Al Lenz of the SSME test world, carrying on the 30 years of knowledge developed over the entire period. Indeed, a very unique situation.”

After a Shuttle mission, the engines receive post-flight inspections and maintenance at KSC, and then may be shipped back to SSC for a pre-flight acceptance test prior to use on another mission.

The Space Shuttle’s Return to Flight begins the journey to finish construction of the International Space Station, return to the Moon and go on to explore Mars and the solar system. Discoveries from these explorations will continue to advance scientific knowledge as well as lead to the development of new, everyday technologies.