Jason DavisAug 13, 2015

SLS Engine Roars through Flight Test in Mississippi

The white cloud of steam and rocket exhaust shot quickly down the flame bucket, expanding and hissing as it mingled with the pale, blue Mississippi sky. From a vantage point less than a half-mile away, the sound arrived almost instantaneously: A thundering roar that pitched up and down, up and down.

RS-25 engine test
RS-25 engine test Image: Jason Davis / The Planetary Society

The cloud came from the mouth of test stand A-1 at Stennis Space Center, where NASA has been testing rocket engines since the dawn of the space age. The engines that powered the Saturn V, the biggest rocket ever built, were once tested here, and the engine type currently bolted into the stand—the RS-25—will propel another big rocket, the Space Launch System. SLS, NASA’s heavy lift vehicle for carrying humans and cargo to lunar orbit and beyond, will evolve over the years to out-muster even the Saturn V in power.

The engine was slated to run for 535 seconds—the amount of time it takes to lift the SLS upper stage to a spot where it can push onward to orbit. The first payload will be the Orion crew capsule—sans crew—bound for a lunar orbit shakedown cruise. The flight is scheduled to happen no later than November 2018. 

The RS-25 nozzle was barely visible within the mammoth, concrete and metal test structure and as the source of the nine-minute fireworks display. The engine runs on liquid hydrogen and liquid oxygen, and its by-product is largely water vapor. This superheated exhaust funnels through a deluge of water used for cooling and sound suppression, creating the roiling steam cloud. 

Several hundred NASA employees, media representatives and social media invitees were on hand for the test. Watching an actual rocket launch is so fast and breathtaking, you can hardly look away; here, the nine-minute event allowed enough time for photographers to readjust cameras and capture alternate angles.

This was the sixth and penultimate firing of RS-25 development engine 0525, which is not intended for flight. The first trial occurred in January, and after a long rain delay this spring, NASA is poised to finish the entire test series before the close of fiscal year 2015 as scheduled (the agency says the final test is tentatively scheduled for August 27). That’s a bright spot for SLS, Orion and the ground systems office—all of which have been hard-pressed from a scheduling standpoint

Flying in sets of three, the RS-25 powered the space shuttle to orbit for 30 years. For SLS, that number increases to four-at-a-time; eight leftover shuttle engines are already picked out for the first two SLS flights. That will deplete NASA’s stock by about half. SLS core stages are jettisoned into the ocean, whereas space shuttles brought their engines back to Kennedy Space Center for reuse. Aerojet Rocketdyne, the engine manufacturer, is already working on a cheaper, expendable version dubbed the RS-25E. 

The engine's four turbopumps fell silent, stopping the flow of compressed fuel and oxygen. The engine gently flamed out with a final burp, and the test was over. A cheer went up from the spectators as the steam cloud began dissipating. Photographers packed up their gear, the crowd broke into excited chatter and the Mississippi bayou was quiet once more.

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