The world’s largest solid rocket booster roared to life today, shaking the serene countryside of Promontory, Utah, for a full two minutes. The booster filled the area with smoke and flame; viewers could actually see the fiery plumes "dance" and move around as they mixed with the surrounding soil. Below the test stand, a layer of sand protecting underlying concrete structures melted into glass from the heat. Bystanders were treated to a real-life example of how light travels faster than sound: the flames and vibrations were readily observable before the sound from the booster was heard.

The development of NASA’s Space Launch System is the largest engineering feat since the Apollo era. Data collected from today’s test will ensure the program is capable of launching humans to Mars and beyond. Today’s test, dubbed Qualification Motor–1 (QM–1), is a test of the SLS five-segmented solid rocket motor, meant to evaluate how the booster operates in high temperatures. The booster hardware is heated to 90°F before the propellant is ignited. The test is being run because the propellant in the booster burns faster at hotter temperatures, and that burn rate is a key component of the performance before and during launch. To prepare the booster for the test, the roll-away test stand cover was heated over the course of several days, until sensors within the booster signaled that the hardware reached the targeted 90 degrees.

Before the historic first flight of SLS, the different components must be thoroughly tested. The launcher’s initial thrust capacity is expected to exceed 8 million pounds, with three-quarters of that provided by two solid rocket boosters. That’s 3.5 million pounds of thrust per booster — roughly the equivalent of the acceleration of 1,000 NASCAR stock cars.

"These two qualification tests are integral steps in getting the booster certified to fly on the first two planned flights of the SLS in 2018, and a key step on the journey to Mars," SLS Boosters Office Manager Alex Priskos told The Verge.

(NASA/Orbital ATK)

Rockets are fueled with two different types of propellant — liquid and solid. Liquid engines are controlled by nozzles and plumbing, while solids cannot be stopped once ignited. Beginning with the dawn of the shuttle era in 1981, twin strap-on solid rocket boosters have been used to achieve the necessary thrust to escape Earth’s gravity and keep the vehicle’s weight in check. The boosters operate in tandem with the vehicle’s main engines, providing the thrust necessary to escape Earth’s gravity. When it launches, SLS will employ two identical solid rocket boosters, just like the ones flown on the space shuttle, each one measuring 177 feet tall and 12 feet in diameter — larger than the Statue of Liberty is from feet to torch.

On the surface, the SLS SRBs look fairly similar to the ones used during the shuttle program, and for good reason. Each SLS booster is composed of five segments, one more than in the older shuttle SRBs. And many of these boosters are being reused.The five-segment booster is capped off with a forward skirt, nose cap, and frustum at the top, and an aft skirt at the bottom, housing all of the avionics. When vertical, the aft skirt is what supports the entire weight of the motor.

(NASA/Orbital ATK)

During the shuttle era, the SRBs were designed to be reused: approximately two minutes after ignition, after burnout, the SRBs would be automatically jettisoned and recovered from the Atlantic Ocean. Next they would be examined, refurbished, and flown again. The SLS SRBs won’t be reused in this way, due to monetary constraints, coupled with an abundance of booster segments and very few planned flights.

Altogether, the boosters for QM–1, QM–2, and the currently planned exploration missions will use hardware from 23 total shuttle flights. Aside from the first and last shuttle mission, others of note are the first mission to begin assembling the International Space Station and the return to flight following the Columbia disaster.

NASA and Orbital ATK have worked together to carry out three full-scale development tests leading up to this initial qualification test of the SLS booster. Once the two planned qualification tests are completed, the SLS boosters will be ready to proceed towards the maiden flight of SLS.

"When talking about our journey to Mars, we often get hung up on the destination and forget it really is a journey," says Charlie Precourt, vice president and general manager of Orbital ATK’s Space Launch System. The first flight test of SLS is planned for 2018 and will launch an uncrewed Orion capsule beyond low-Earth orbit before eventually carrying human to Mars, and beyond.

Correction: This article initially mischaracterized the difference between solid and liquid rocket systems. We regret the error.