Video Shows NASA's RS-25 Engine Spewing Clouds of Steam in Test Fire

The engine is 109 percent more efficient than its original design.

Just in time for Halloween, NASA livestreamed a “BOO-tiful” (NASA’s words) test of the RS-25 engine at the Stennis Space Center in Mississippi on Wednesday afternoon. Watched by an international audience from Korea to Belgium, the 500-second test was made appropriately spooky by the massive clouds of steam produced. It would have blasted away any monster a child could imagine.

The RS-25 engine, also known as the Space Shuttle Main Engine, powered all 135 Space Shuttle flights over the course of three decades. NASA has 16 of them, with plans to build more.

Operators set up the RS-25 on an A-1 stand for hot fire testing


In an effort to understand how the engines and their specific components perform in various scenarios, NASA puts the RS-25 through hot fire tests. During the test, engineers run the engines through various thrust levels that will be required during a flight. The information gleaned during the hot firing enables NASA to test 3D-printed parts, which may help reduce production costs.

After compiling data from the many tests performed since 2015, the 14-foot tall engine now boasts the coveted status as one of the most efficient rocket engines in the world. At its current thrust — or power level — it’s 109 percent more efficient than its original design, with plans to hit 111 percent announced Wednesday.

Testing Protocol

It takes about four hours to prepare for the 500 seconds of billowing steam, reports Tommy Carroll, the RS-25 thrust vector control project manager at Stennis Space Center.

“The RS-25 uses liquid hydrogen for fuel. We mix that with liquid oxygen. Hydrogen, oxygen, H2O,” Carroll explained on Wednesday’s livestream. “When we’re running the RS-25 engine, we’re making steam, we’re making water. That’s it!”

The white clouds released from the RS-25 are simply steam made from good old hydrogen and oxygen.


After the test, the team blasts the engine with heated nitrogen for a few hours to remove any lingering water.

Where Will These Engines Go Next?

The RS-25 engine — or rather, four of them — will play a key role in NASA’s Space Launch System, SLS.

The launch system carries not only two boosters in addition to the four engines, but also the hopes of humankind to travel to deep space. The whole setup will reach speeds of 17,500 miles per hour, 73 times faster than an Indy 500 race car. Before tackling ambitious targets like Mars, NASA plans to combine the Orion spacecraft with SLS for Exploration Mission-1, to venture beyond the moon on an uncrewed voyage.

Originally, EM-1 was scheduled to launch in November 2018, but in an unfortunate but unsurprising delay, NASA acknowledged a more realistic launch date would come in 2019.

For now, NASA treated us all to a display of the engine that will one day take humankind to new frontiers in deep space.

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