NASA plans to begin testing RS-25 engines for its new Space Launch System (SLS) in the fall of 2014, and the agency's Stennis Space Center in Mississippi has a very big - literally - item to complete on the preparation checklist.

Fabrication recently began at Stennis on a new 7,755-pound thrust frame adapter for the A-1 Test Stand to enable testing of the engines that will provide core-stage power for NASA's SLS. The stand component is scheduled to be completed and installed by November 2013.

"We initially thought we would have to go offsite to have the equipment built," said Gary Benton, RS-25 test project manager at Stennis. "However, the Stennis design team figured out a way to build it here with resulting cost and schedule savings. It's a big project and a critical one to ensure we obtain accurate data during engine testing."

Each rocket engine type requires a thrust frame adapter unique to its specifications. On the test stand, the adapter is attached to the thrust measurement system. A rocket engine then is attached to the adapter, which must hold the engine in place and absorb the thrust produced during a test, while allowing accurate measurement of the engine performance.

The J-2X equipment installed on the A-1 Test Stand now cannot be used to test RS-25 engines since it does not match the engine specifications and thrust requirements. For instance, the J-2X engine is capable of producing 294,000 pounds of thrust. The RS-25 engine will produce approximately 530,000 pounds of thrust.

NASA and the Lockheed Martin Test Operations Contract Group team worked together in designing the new adapter to make sure such requirements were met. They also communicated closely with the Jacobs Technology welding and machine shop teams to make sure what was being designed actually could be built.

The design had to account for a number of considerations, such as specific stresses on the equipment as an engine is fired and then gimbaled (rotated) during a test; what type and strength of bolts are needed to fully secure the equipment; and what materials can be used to build the adapter.

"This is a very specific process," Benton said. "It is critical that thrust data not be skewed or compromised during a test, so the adapter has to be precisely designed and constructed."

The fabrication process itself involves handling and shaping large segments of certain material, which required welders to receive specialized training. In addition, shop personnel had to create a welding procedure for dealing with the chosen construction material. For instance, the area of material being welded must maintain a heat of 300 degrees in order to ensure welds bond properly. That procedure and other specifications are being incorporated into Stennis standards.

"It's a challenging project," said Kent Morris, RS-25 project manager for Jacobs Technology. "It's similar to the J-2X adapter project, but larger. It will take considerable man hours to perform the welding and machining needed on the material. The material used for the engine mounting block alone is 32 inches in diameter and 20 inches thick."

Physically, the adapter is the largest facility item on the preparation checklist for RS-25 testing, but it is far from the only one, Benton said. Additional modifications will be made to the test stand configuration and equipment once J-2X gimbal testing is complete this summer.

Once testing begins, engineers and test team personnel at Stennis will draw on a wealth of engine testing experience. The RS-25 engines, previously known as the space shuttle main engines were tested at Stennis for more than three decades.