Engineering model controllers are being tested at NASA. (NASA/MSFC)
The engine controller unit on the RS-25 – formerly known as the space shuttle main engine – helped propel all of the space shuttle missions to space. It allows communication between the vehicle and the engine, relaying commands to the engine and transmitting data back to the vehicle. The 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.

The engine controller unit needed a "refresh" to provide the capability necessary for four RS-25 engines to power the core stage of NASA's new rocket, the Space Launch System (SLS), to deep space. An engineering model RS-25 controller is being tweaked and tested at NASA Marshall. At one of the center's test facilities, engineers are simulating the RS-25 in flight, using real engine actuators, sensors, connectors, and harnesses.

A second engineering model controller and RS-25 engine also recently were installed on a test stand at NASA's Stennis Space Center. Pending final preparation and activation work, the engine test series is anticipated to begin this year.