Think about negotiating an intricate maze, and you begin to appreciate the challenge of designing and fabricating test stand piping for NASA's RS-25 rocket engine.

NASA is meeting that challenge at its Stennis Space Center near Bay St. Louis, Miss., where liquid oxygen (LOX), liquid hydrogen and related piping is being produced for RS-25 engine testing on the A-1 test stand. Testing of the core-stage engine for NASA's new Space Launch System (SLS) is scheduled to begin next spring. The SLS is being developed to carry humans deeper into space than ever before.

"This is a big undertaking," said Robert Ek, systems engineer for the RS-25 test project at Stennis. "These are massive lines, weighing hundreds of pounds, and they have to be threaded through a great deal of other stand equipment and structure needed for testing. It's a real challenge."

NASA engineers now are conducting gimbal, or pivot, testing on a J-2X engine on the A-1 stand, but that hot fire series is scheduled to end in early September. Stand equipment then must be modified to meet RS-25 rocket engine drawing and specification requirements. A new thrust frame adapter already has been fabricated for installation on the stand this fall. Fabrication of the new piping system is under way.

Design of the piping was an involved process that required collecting a lot of information about the RS-25 engine and its performance specifications. Even though RS-25 engines were used as space shuttle main engines, some modifications will be made before testing begins.

"Even with the RS-25 engine's flawless performance on all 135 space shuttle missions, a different rocket like SLS has new environmental and thrust conditions and therefore different test considerations," said Mike Kynard, SLS Liquid Engines program manager. "Anytime we make changes to an engine, or to environmental conditions in which it will run, we'll need to put it through a full set of tests. What we typically do in the rocket engine industry is run things twice as long as we plan to use them in flight to ensure the robustness of the design. We run it at different conditions to make sure we've covered the full range of the design."

Engineers had to take into account new engine performance factors to determine such things as the flow rate of cryogenic fuels needed in the lines and the pressures under which they must operate. In terms of simple geometry, they also had to make sure piping connections were located properly and identify how and where to install supports to hold the piping in place.

"Negotiating a maze is a good analogy," Ek said. "There was a lot of ingenuity and working together to make sure good decisions were made. The design engineering team, supported by both operations and systems engineering, did a great job in finding answers along the way."

The RS-25 testing project was accelerated by a few months, shortening the time for preparation work on the A-1 test stand. The piping now being fabricated by Jacobs Technology crews at Stennis is expected to be completed and installed on the stand by the end of the year.

Once in place, the lines will be sealed and tests performed to make sure there are no leaks in the system and that they perform properly at the extremely low temperatures required to flow LOX and liquid hydrogen propellants. The first installation of an RS-25 engine will be in early April 2014, with a series of LOX chill tests and eight hot fire tests to follow.

Once tested and certified, the engines will be used for both SLS test flights and operational missions, a fact that Ek and others at Stennis find gratifying. "I used to work on space shuttle main engines during the Space Shuttle Program," Ek said. "That program has ended, but the engines live on to fly again. It's very exciting to help make that happen."