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NASA and Aerojet Rocketdyne test SLS core engine

The orange glow of excited hydrogen atoms can be clearly seen at the opening of the nozzle on the RS-25 at the conclusion of the test. Photo credit: Curt Godwin

The orange glow of excited hydrogen atoms can be clearly seen at the opening of the nozzle on the RS-25 at the conclusion of the test. Click to enlarge. Photo credit: Curt Godwin

NASA and Aerojet Rocketdyne recently tested an RS-25 engine at NASA’s Stennis Space Center in coastal Mississippi in an effort to learn more about how the engine may react to the conditions it may encounter on an actual SLS launch.

Engine 0528, a development engine, was active for 420 seconds and was throttled between 80 to 111 percent of original rated power level. Though it may seem unusual to classify levels over 100 percent, it makes more sense to do so than re-write a multitude of pre-existing documentation as refinements come along. With the original design being the 100 percent benchmark, all follow-up enhancements have been measured against that metric.

Initially, SLS is slated to have its four core RS-25 engines operate at up to 109 percent rated thrust, though future mission plans call for it to be boosted to 111 percent. This most recent test ran the engine at that higher level for nearly five seconds. When the engines were used on the Space Shuttle, they would operate at nominal levels of 104.5 percent of rated thrust, though they could peak at 109 percent in an abort scenario.

As with many tests of this type, NASA provided live coverage via their NASA TV outlet. It must be noted, though, that watching the test via broadcast pales in comparison to witnessing the raw power coming from the test stand in-person. Experiencing the test from 1,200 feet (366 meters) away, one can feel every thump and pop from the engine as it is put through its test regime.

With this most recent test, engine 0528 has accumulated 1,263 seconds (slightly more than 21 minutes) of test firings.

Though the initial SLS missions will be powered by repurposed Space Shuttle Main Engines (SSMEs), which were designed to be reusable, Aerojet Rocketdyne hopes to develop a less expensive version for the single-use SLS core stage.

“For the nation to explore Mars, it is imperative to make each element as affordable as possible, which is why Aerojet Rocketdyne is targeting more than a 30 percent cost reduction in the RS-25 engine from the version that flew on the Space Shuttle,” according to Jim Paulsen, vice president for NASA programs at Aerojet Rocketdyne, in a release issued by the company. “We are using the lessons learned from our test firings to further enhance our operational efficiency and reduce costs.”

To that end, Aerojet Rocketdyne is investigating the use of advanced manufacturing techniques and materials into the newer iteration of the RS-25. According to the company, they have identified 45 engine components that are candidates to be made via additive manufacturing (3-D printing). Even such a seemingly small number of components as that has the potential to reduce manufacturing timelines by 25 percent.

While the latest static fire was successful in running tests on a single engine, NASA’s Stennis Space Center is currently in the latter stages of its $100 million refurbishment of the B-2 test stand, and supporting infrastructure, which will be used to test the entire core stage – comprising four RS-25 engines – for a full-duration test fire, known as a “green run”. Slated to occur in late 2017, or early 2018, the test will mimic a nominal flight profile and will run for 483 seconds.

It will be the most powerful test since the final Saturn V first stage (S-IC) test firing in 1970.

The RS-25's exhaust is simply super-heated water vapor: steam. Photo credit: Curt Godwin

The RS-25’s exhaust is simply super-heated water vapor: steam. Photo credit: Curt Godwin

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