SLS Structural Test Stands Construction Begins This Month, RS-25 Engine Testing Preps Continue

This month, a year-long construction project to build the structural test stands for NASA’s Space Launch System’s gigantic core stage will begin at the agency’s Marshall Space Flight Center in Huntsville, Ala. The stands, one of which will be built on the foundation of the stand where the Saturn-V F-1 engine was tested, will be used to test the largest cryogenic fuel tanks ever used on a rocket to ensure that the huge structures can withstand the incredible stresses the skyscraper-size vehicle will experience during launch.

“These stands are necessary to accommodate the sheer size of the core stage components, and the extreme loads we are putting on them — some up to 9 million pounds,” said Tim Gautney, element discipline lead engineer for SLS core stage testing. “We will use hydraulic cylinders to push, pull, twist and bend these pieces to make sure they can withstand the loads and environments they may experience on the launch pad and upon ascent. The tests also will verify the models already in place that predict the amount of loads the core stage can endure.”

Construction of the stands is being contracted by NASA through the U.S. Army Corps of Engineers, which has awarded a $45 million contract to Brasfield & Gorrie, one of the nation’s largest construction firms. The stands were designed by a joint venture team of the architecture and engineering firms Goodwyn Mills and Cawood, of Montgomery, Ala., and Merrick & Company of Greenwood Village, Colo.

“These test stands will play a vital role in strengthening America’s space exploration capabilities,” Brasfield & Gorrie Vice President and Division Manager Alan Anthony said Tuesday. “We are proud to continue our strong working relationship with the U.S. Army Corps of Engineers and our work at Redstone Arsenal while supporting NASA’s Space Launch System.”

The mammoth 27-foot-diameter SLS core stage, the largest of its kind ever built, will tower more than 200 feet high and will store cryogenic liquid hydrogen and liquid oxygen that will feed the vehicle’s four Aerojet Rocketdyne-designed RS-25 engines—the same engines used to power the space shuttle with 100 percent success over 135 missions. The core stage will also house critical hardware such as the vehicle’s avionics and flight computer and is made up of the engine section, liquid hydrogen tank, intertank, liquid oxygen tank, and forward skirt—all of which will be shipped by barge from NASA’s Michoud Assembly Facility in New Orleans to Marshall for testing.

Some 2,150 tons of steel will be required to build the largest of the two structures, Test Stand 4693, which is designed as a twin-tower configuration for structural testing of the 185-foot-tall liquid hydrogen tank. When ready next year, the tank will be placed in the stand vertically and be loaded with liquid nitrogen for stress testing.

The second structure, Test Stand 4697, will tower 85 feet above the ground and will require over 690 tons of steel to build. It will be used to test the liquid oxygen tank and forward skirt in Marshall’s West Test Area.

“Within the foundation of this stand, we have 1.75 miles of embedded anchor rods — that gives you an idea of the type of stability we need to test these parts with such high-level force,” said Byron Williams, project manager for the liquid oxygen tank and forward skirt test stand.

Preparing to test the engines that will send humans deeper into space than ever before

Work at Stennis Space Center continues to ready the historic A-1 test stand for SLS RS-25 engine testing this summer, and on May 1 engineers completed a cold-shock test of the new structural piping system needed for the RS-25 engine—a major milestone which now sets the stage for engine installation in the coming weeks and hot-fire engine testing this summer.

The piping system installed at the A-1 Test Stand is not your bathroom plumbing; these pipes need to flex without fail as they expand and contract due to the extreme temperature changes caused by the propellant flows (temperature changes during a hot-fire test can be as much as 500 degrees). The piping system needs to handle both liquid oxygen (which flows at almost -300 degrees Fahrenheit) and liquid hydrogen (which is colder than -400 degrees Fahrenheit). The RS-25 engines, which are upgraded from their former space shuttle days for more power, will burn a mixture of the two to generate an incredible 512,000 pounds vacuum thrust each.

To ensure the piping system design allows the necessary movement, engineers at Stennis flowed liquid nitrogen through it at -320 degrees Fahrenheit and monitored the effects.

“A test like this may sound benign since no flammable propellant is used, but it is very significant to make sure we have the proper piping design and setup for engine testing,” said Jeff Henderson, the A-1 Test Stand director.

Engineers also performed checks of the liquid oxygen tank and vent system and conducted a calibration run of the new thrust measurement system (TMS)—important because engineers need the TMS to obtain accurate measurements of engine thrust during tests. Additional TMS components will be installed at the A-1 Test Stand soon, and various sequence and equipment checks will be performed in preparation for the hot-fire tests this summer. NASA has not announced a specific date for delivery of the engine that will be used in the first round of tests, but engine No. 0525 will be delivered to Stennis and installed at the Test Stand very soon, and NASA is still on schedule for engine testing beginning in July.

Of particular importance is the performance of the RS-25’s new engine controller, which regulates valves that control the flow of propellant to the engine and determines the amount of thrust generated during a hot-fire.

“In flight, propellant flow and engine thrust determine the speed and trajectory of a spacecraft, allowing it to follow the proper flight and orbit path,” according to NASA. “The controller also regulates the engine startup sequence, including valve positioning and timing. Likewise, the controller determines the engine shutdown sequence, ensuring it will occur properly in both normal and emergency conditions.”

Preliminary tests will be run on the engine to collect data on the performance of its new controller to ensure its engine startup and shutdown sequences occur as expected.

To put the power of the Aerojet Rocketdyne-built RS-25 engines into perspective, consider this:

The fuel turbine on the RS-25’s high-pressure fuel turbopump is so powerful that if it were spinning an electrical generator instead of a pump, it could power 11 locomotives; 1,315 Toyota Prius cars; 1,231,519 iPads; lighting for 430 Major League baseball stadiums; or 9,844 miles of residential street lights—all the street lights in Chicago, Los Angeles, or New York City.

Pressure within the RS-25 is equivalent to the pressure a submarine experiences three miles beneath the ocean.

The four RS-25 engines on the SLS launch vehicle gobble propellant at the rate of 1,500 gallons per second. That’s enough to drain an average family-sized swimming pool in 60 seconds.

“This is a very exciting time at NASA,” said Gary Benton, RS-25 rocket engine test project manager. “We are moving closer and closer to making unprecedented space exploration missions a reality. By mid-summer, we will be testing the engines that will carry humans deeper into space than ever before.”

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