Update 12/15 10:46 AM ET: SpaceX’s first flight with a pre-flown booster for NASA was a success. After launch, SpaceX successfully touched down its used Falcon 9 rocket at the company’s ground-based Landing Zone 1 at Cape Canaveral. This marks the 14th landing SpaceX has pulled off this year, and the second time this particular vehicle has landed following take off. This is also their 17th launch of 2017.

Original story: Today, SpaceX will once again send cargo to the International Space Station for NASA, but this time, the company is employing mostly used hardware for the job. A Falcon 9 rocket that the company previously launched to the ISS in June will loft a used Dragon cargo capsule, filled with supplies and science experiments for the station crew. It’s the first time SpaceX will fly a used rocket for one of its NASA resupply missions.

SpaceX finally started re-flying its used rockets earlier this year, after years of landing the vehicles post-launch. But so far, only a few of the company’s commercial customers have taken the plunge and put their satellites on previously flown Falcon 9 rockets. Now, NASA has signaled that it’s willing to fly on SpaceX’s used vehicles, too — a big endorsement for the company’s reusable rocket technology. Moving forward, NASA says it will make the decision to fly used rockets for resupply missions on a case-by-case basis.

The first time SpaceX will fly a used rocket for one of its NASA resupply missions

This launch is also a big milestone for SpaceX because of where the mission is taking off from: the company’s launch pad at Cape Canaveral Air Force Station in Florida, SLC-40. The site has been out of commission since last September, after one of SpaceX’s rockets exploded on the pad during a fueling procedure. Since then, the company has worked to rebuild the damaged site and even give it a few upgrades. SpaceX started the bulk of the repairs in February and has spent around $50 million to fix the site up, according to John Muratore, SpaceX’s director at SLC-40. Today’s mission will mark the first time SpaceX has flown from the site since the accident.

And now that the pad is back in action, it paves the way for SpaceX to launch the company’s next big rocket, the Falcon Heavy — a larger version of its Falcon 9 that includes three rocket cores. When SLC-40 went offline last year, SpaceX had to rely on its other pad at the Cape, a site called LC-39A at NASA’s Kennedy Space Center, to launch all of its Florida missions. SpaceX ultimately wants to launch the Falcon Heavy from 39A, too, but the pad needed some modifications first in order to accommodate the larger rocket. SpaceX couldn’t fully focus on the upgrades to 39A while repairs were still being done at SLC-40.

Moving forward, the company plans to launch its Falcon 9 missions from SLC-40 and its Falcon Heavy flights from 39A. Earlier this year, SpaceX CEO Elon Musk said that the first flight of the Falcon Heavy would happen in November, but the demonstration flight has been pushed back to sometime in January now. Meanwhile, SpaceX has just a couple more flights to round out the year, including today’s cargo resupply flight.

This morning’s launch will carry nearly 4,800 pounds of cargo to the ISS

This morning’s launch will carry nearly 4,800 pounds of cargo to the ISS. Included on board is a sensor designed to monitor how much space debris is surrounding the station, as well as another sensor that’s supposed to measure how much sunlight reaches the Earth. And as per usual, SpaceX plans to land this Falcon 9 after take off at the company’s ground-based landing site, Landing Zone 1. If successful, it’ll mark the second time this rocket has landed after a flight and the 14th landing for SpaceX this year.

Today’s mission has suffered from a few delays, though. SpaceX was aiming to launch on December 12th, but wound up pushing back until today. The company said it needed more time to investigate particles it had found in part of the rocket’s fuel system. If SpaceX doesn’t end up launching today, then it’ll have to wait until later in December. But so far, weather is looking good for launch, with a 90 percent chance of favorable conditions.

Take off is scheduled for 10:36AM ET, and SpaceX has an instantaneous launch window for this flight, meaning the rocket has to go up at that time or else the mission will be delayed. NASA’s coverage of the flight begins at 10AM ET, while SpaceX’s coverage begins about 20 minutes before launch. Check back later to watch the mission live.