On Thursday, SpaceX is set to launch yet another satellite into orbit from the Florida coast — but this mission will be far from routine for the company. The Falcon 9 rocket that SpaceX is using for the launch has already flown before. Around the same time last year, it sent cargo to the International Space Station for NASA, and then came back to Earth to land upright on a floating drone ship at sea. This is the first time that SpaceX will attempt to reuse one of its rockets.

It’s a feat that SpaceX has been working toward for more than five years now, and it could be a watershed moment for the aerospace industry. Up until now, practically all rockets that can achieve orbit are either destroyed or go unrecovered after each mission. That means an entirely new rocket — which costs tens to hundreds of millions of dollars to make — has to be built for each launch. But SpaceX’s plan has been to recover its rockets after launch rather than throw them away, so that the vehicles can be used again. That way, the company can save on manufacturing a completely new vehicle, and potentially lower the cost of each mission.

A watershed moment for the aerospace industry

In truth, only part of the Falcon 9 is being reused on this upcoming mission. After each launch, SpaceX tries to save just the first stage of its vehicles. That’s the 14-story-tall main body of the Falcon 9 that contains the primary engines and most of the fuel. About 10 minutes or so after each launch, the first stage separates from the top portion of the rocket and makes a controlled dive back to Earth. The leftover fuel is used to reignite the engines on the rocket in a series of burns, to help the vehicle reenter the Earth’s atmosphere and then slow down for landing. This technique is known as supersonic retro propulsion.

It’s “an approach that requires minimal modification,” Bobby Braun, dean of the College of Engineering at the University of Colorado at Boulder, tells The Verge. “You don’t need to add wings, you don’t need to add a parachute. You’re using the same systems you would use for launch. So in terms of the investment required, I would think it would be the most straightforward and the lowest investment.”

SpaceX has tried landing most of the rockets it has launched over the last two years, either by having them touch down at a ground-based landing site or by landing them on one of two autonomous drone ships in the ocean. Out of 13 attempts, eight of the rockets have stuck the touchdown. SpaceX has been testing the recovered stages to see if they are capable of spaceflight again and to figure out how much repairs and refurbishment are needed to make them fly again.

The second Falcon 9 that SpaceX ever recovered has been picked to be the first one to fly again

Now, the second Falcon 9 that SpaceX recovered has been picked to be the first one to fly again. It’s the same rocket that was used for CRS-8, the company’s eighth cargo resupply mission to the ISS for NASA. Launched on April 8th, 2016, the rocket lofted nearly 7,000 pounds of supplies to the crew of the space station, including a new inflatable habitat, and then landed on one of SpaceX’s drone ships in the Atlantic Ocean. SpaceX decided to reuse this booster first, partly because it wanted to hold onto the first Falcon 9 the company landed in December 2015. That one was deemed special by CEO Elon Musk and is currently on display at SpaceX’s headquarters in Hawthorne, California.

The customer flying on this first “flight-proven” rocket is SES, a satellite operator based out of Luxembourg. And the cargo is the SES-10 satellite, which is meant to provide communications services to Latin America. SES-10 will eventually sit in a super high orbit 22,000 miles above the Earth’s surface, known as geostationary orbit. On this path, the satellite follows the Earth’s rotation, allowing it to continuously hover over the same patch of the planet at all times.

SES has been very vocal about its desire to be the first company to launch on a landed rocket, and announced in August that it would be the one to fly on this inaugural mission. “Having been the first commercial satellite operator to launch with SpaceX back in 2013, we are excited to once again be the first customer to launch on SpaceX's first ever mission using a flight-proven rocket,” Martin Halliwell, CTO of SES, said in a statement. “We believe reusable rockets will open up a new era of spaceflight, and make access to space more efficient in terms of cost and manifest management.”

Not only is this Falcon 9 rocket launching for a second time, but it’s landing again, too. The first stage will attempt another drone ship landing in the Atlantic Ocean after takeoff, meaning this particular vehicle could see even more flight time in the future. It’s still unclear just how many times a single first stage of a Falcon 9 can be used again. In the past, Musk has boasted that parts of the Falcon 9 could be reused up to 100 times, but he expects 10 to 20 reuses out of a single vehicle.

The more frequently SpaceX can reuse its Falcon 9s, the greater the economic benefit to the company

The more frequently SpaceX can reuse its Falcon 9s, the greater the economic benefit to the company. The rocket’s engines and tanks are the most expensive part of the vehicle to make, whereas refueling and refurbishing the vehicle could cost as little as a few million dollars. It’s not known just how much launching a used rocket saves the company, but SpaceX President Gwynne Shotwell estimated that customers could see a price reduction of about 30 percent for launches that use landed rockets. (In October, however, she told Space News that SpaceX is only offering 10 percent discounts for the time being.) That means the Falcon 9, which starts at a little more than $60 million, could eventually go for $40 million if it’s a reused vehicle. And lowering the cost of access to space could make spaceflight a more affordable investment for companies in the long term.

“We could open the space frontier,” says Braun, who added that reusing the entire rocket would mean even greater cost savings. “Then you’re talking about a different set of economics for space transportation, and that’s really the key to access to space and what’s been holding us back for decades.”

SpaceX performed a successful static fire test of the Falcon 9 engines on Monday, and right now, takeoff of SES-10 is scheduled for 6PM ET on Thursday from Kennedy Space Center at Cape Canaveral, Florida. There’s a two-and-a-half-hour launch window, so the Falcon 9 can conceivably take off anytime until 8:30PM ET. So far there’s a 70 percent chance that weather conditions will be favorable, according Patrick Air Force Base. Check back here about 20 minutes before the launch window opens on Thursday to watch the launch live.