Busy Summer of SLS Engine Testing on the Stennis A1 Test Stand

Testing of the new brain for the RS-25 engines that will help power the colossal Space Launch System (SLS) rocket uphill from launch pad 39B in the coming years has been on a roll at NASA’s Stennis Space Center all summer, and they just finished up testing of the fourth RS-25 engine controller (the brain) needed for the inaugural flight in 2019 – two weeks after the third test of another RS-25 engine flight controller.

Just like the space shuttle, two tall solid rocket boosters will provide most of the thrust during launch and ascent to reach space, but the main engines are just as critical, and Aerojet Rocketdyne currently has 16 in inventory; 14 are veterans of numerous shuttle missions and 2 are brand new, plus there are 2 development test engines as well.

But differences between the SLS and space shuttle require that the RS-25s now undergo several modifications to adapt to the new environment they will encounter with SLS, to meet the giant 320-foot-tall rocket’s enormous thrust requirements.

Locked down on the A1 test stand at Stennis, the RS-25s have been undergoing hot fire tests now since early 2015, providing engineers with critical data on the engine’s new state-of-the-art controller unit, or the “brain” of the engine, which allows communication between the vehicle and the engine itself, relaying commands to the engine and transmitting data back to the vehicle.

Testing of actual flight controllers began at Stennis in March.

The new controller also provides closed-loop management of the engine by regulating the thrust and fuel mixture ratio while monitoring the engine’s health and status, thanks to updated hardware and software configured to operate with the new SLS avionics architecture.

Higher inlet pressure conditions, thanks to the engines upgrades, are also evaluated.

For shuttle flights the engines pushed 491,000 pounds of thrust during launch—each—and shuttle required three to fly, but for SLS the power level must increase to 512,000 pounds of thrust per engine (more than 12 million horsepower). The SLS will require four to help launch the massive rocket and its payloads with a 70-metric-ton (77-ton) lift capacity that the initial SLS configuration promises (later variants will be even bigger and more powerful).

The engines currently in stock are already assigned their spots to fly the first four SLS missions, but unlike their former lives as reusable engines, these will be their final launches. The SLS is being made as an expendable launcher designed from heritage hardware and ideas; the RS-25 is now one-time use.

NASA awarded Aerojet Rocketdyne a $1.16 billion, nine-year contract to restart production of an expendable version of the RS-25 for SLS in late 2015.

Once the engines are finished testing individually, they will be integrated with an SLS first stage and mounted atop another test stand, to test fire the engines for a full-duration launch. Engineers need to make the engines THINK the rocket is really flying a launch ascent profile, in order to verify everything will operate as expected on launch day.

That test is expected to occur in 2018.

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