NASA’s New Mega-Rocket SLS Hot Fire Test


The hotfire test of the core stage, conducted on January 16 at NASA’s Stennis Space Center in Mississippi.

The hotfire test of the core stage, conducted on January 16 at NASA’s Stennis Space Center in Mississippi.
Image: NASA Television

The second hotfire test of NASA’s Space Launch System (SLS) rocket is scheduled for Thursday. You can watch a livestream of the action right here.

The window for today’s test opens at 3:00 p.m. ET and ends sharply two hours later. NASA’s coverage will begin around 30 minutes prior to ignition. The space agency will provide more precise times and updates throughout the day, which you can track through NASA’s Twitter and Artemis blog.

This will be the second hotfire test of the SLS core stage, the first having been (partially) completed on January 16, 2021. The core stage won’t go anywhere, but the test should generate an impressive plume of smoke around NASA’s Stennis Space Center near Bay St. Louis, Mississippi.

The hotfire test, in which all four RS-25 engines will ignite, should last around 8 minutes—or at least we hope. The previous hotfire test ended prematurely after just 67 seconds. A computer shut down the whole thing when a key parameter having to do with the hydraulics required for gimbaling, or pivoting, went out of whack. Hence the need for a second test, which will be the ninth, and hopefully last, of the Green Run testing regime.

And it’s so far, so good for today’s test, according to NASA. A “go” for the hotfire test was granted during a team meeting held this morning, and preparations are now underway to load more than 700,000 gallons of supercooled liquid oxygen and liquid hydrogen into the 212-foot-tall (65-meter) rocket stage, which is anchored to the B-2 test stand.

Infographic explaining the Green Run test series.

Infographic explaining the Green Run test series.
Graphic: NASA

For today’s test, NASA will seek to emulate the demands of a real launch to the greatest extent possible, and then some. A countdown will commence at T-10 minutes once the “go” for the hotfire test is issued. The ensuing launch sequence will closely approximate the protocols and conditions of an actual SLS launch. Ignition of all four engines should happen around 6 seconds prior to T-0.

“Recording data on how the stage performs at T-0 and as the engines ramp up to 109 percent power is one critical test operation,” according to NASA. “Another is when the engines are throttled down to 95 percent, just as they are throttled down in flight at Max-Q, or maximum dynamic pressure when aerodynamic forces put the greatest stress on the rocket.”

The RS-25 engines will gimbal during the test to simulate its steering abilities, and they’ll be pushed harder than what’s needed for an actual launch. Known as a “frequency response test,” this is being done to ensure that the “thrust vector control system’s response is demonstrated under a variety of flight-like conditions,” says NASA.

Assuming all goes well today, the next time NASA lights up this thing it’ll be the real deal—the Artemis 1 mission, in which an uncrewed SLS rocket will go for a ride into space. That could happen later this year. This rocket, with its 1.6 million pounds of thrust, is a big deal for NASA, as it’s the vehicle that will deliver astronauts to the Moon, and possibly Mars.


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