NASA will eventually use the Space Launch System to send humans to Mars -- it might even carry a crew the very first time it launches. Unfortunately the world's most powerful rocket is a tad behind schedule (it was originally supposed to launch this year) and over budget. However, NASA has released an interesting 360-degree video of a hot-fire test of the main RS-25 engine, one of four shown above. From one vantage point, you're standing in a place you really wouldn't want to be in person -- near the flame trench directly behind the 512,000-pound-thrust rocket.
The liquid-fueled RS-25 is an updated version of the Space Shuttle's main engines (not the side-mounted boosters) that, in total, will pump out about a quarter of the SLS's 8.8 million pounds of thrust. When the rocket is launched, the motors will fire non-stop for about 8.5 minutes, powering the Orion capsule into orbit and well, well beyond. The RS-25 pumps out hot gases at 13 times the speed of sound, and at one camera position near the flame trench, "the extreme force of smoke and water literally covers the camera," NASA says. Watch, and try not to duck.