Update July 25th, 6:15PM ET: SpaceX’s Falcon 9 successfully took off from Cape Canaveral Florida at 6:01PM ET on Thursday, July 25th, putting the Dragon cargo capsule into orbit. The majority of the rocket also touched down on one of SpaceX’s concrete landing pads at the Cape after launch. Now, the Dragon cargo capsule is scheduled to meet up with the space station on Saturday, July 27th.

Original story: This afternoon, SpaceX is slated to launch its latest cargo mission from Florida for NASA, sending about 5,000 pounds of supplies to the crew on the International Space Station. For this mission, the company is employing a Dragon cargo capsule that’s already been to space twice before. If successful, it’ll be the first time the same Dragon has gone on a third trip to space.

Packed inside the Dragon’s main storage compartment are some interesting goodies and science experiments for the crew to work with over the next few months. These include a printer designed to create 3D organ-like tissues in space, as well as an experiment to culture cells taken from patients with multiple sclerosis and Parkinson’s disease.

The launch will also be carrying a key piece of hardware for the station itself. Tucked within the Dragon’s trunk — the unpressurized cylindrical structure that rides on the back of the capsule during flight — is a new dock for the ISS. Known as the International Docking Adaptor, this will eventually be attached to a port on the exterior of the ISS. The installation will create a new parking spot for two future commercial spacecraft, both currently in development by SpaceX and Boeing.

This docking adapter is actually the third of its kind

This docking adapter, made by Boeing, is actually the third of its kind. The first International Docking Adaptor was destroyed in 2015, when the SpaceX Falcon 9 rocket carrying it to the station disintegrated after takeoff. A second docking adaptor was launched in 2016 on another Falcon 9 and then installed to a port during a spacewalk. That adaptor saw some action for the first time this March when SpaceX’s new Crew Dragon capsule automatically docked with the port during an uncrewed test flight. Once this new dock is installed, SpaceX and Boeing will have two parking options at the ISS, providing more flexibility for future missions.

“We’re really looking forward to getting this on there,” Bill Spetch, NASA’s deputy manager of the International Space Station Transportation Office, said during a press conference. “It’s an important piece of hardware for the future of ISS, as it sets the stage for how we are going to operate with Commercial Crew vehicles and our partners in the future.”

Today’s flight is one of the final cargo missions SpaceX will do under its first resupply contract with NASA. Through this agreement, SpaceX is tasked with launching 20 cargo missions to the space station, and this upcoming flight is the company’s 18th resupply launch. Both the 19th and 20th resupply missions will also fly Dragons on their third trips to space, according to SpaceX.

SpaceX’s vision of reusing hardware is on full display for this mission

SpaceX will continue launching supplies to the ISS once the 20th mission is complete. NASA awarded SpaceX a second contract, tasking the company with launching even more supply missions through 2024. For those flights, SpaceX plans to switch over to a new version of the Dragon cargo capsule, one that’s very similar to SpaceX’s Crew Dragon that will soon carry NASA astronauts to the station. Just like the Crew Dragon, the cargo version will be able to automatically dock with the ISS. SpaceX’s current cargo capsules have to be grabbed by the station’s robotic arm and then placed onto the ISS. Soon, all Dragons will be able to get to the station on their own.

That future is still a few years off. In the meantime, SpaceX’s vision of reusing hardware is on full display for this mission. Not only has the Dragon cargo capsule already flown twice (once in 2015 and once in 2017), but most of the Falcon 9 rocket on this flight also flew to space and back for another cargo mission in May. For this launch, the rocket will attempt to touch down on one of SpaceX’s concrete landing pads at Cape Canaveral, Florida after takeoff. SpaceX boasts a nearly perfect record for ground landings — except for one rocket ditched into the ocean on accident.

Today’s flight is slated for liftoff at 6:01PM ET from SpaceX’s launchpad at Cape Canaveral Air Force Station. The company has an instantaneous launch window, so the rocket has to take off on time or the mission must be delayed. It’s looking likely that this flight may not happen today — or even this week. There’s only a 30 percent chance that weather will cooperate this afternoon, the same odds as yesterday when SpaceX tried to launch this mission the first time. If SpaceX has to postpone today, the earliest this flight can get off the ground is in August, because of other spacecraft scheduled to arrive and depart the ISS in the coming weeks.

For now, the launch is on, and both NASA and SpaceX plan to provide live coverage. NASA’s live stream will begin at 5:45PM ET on the agency’s dedicated TV channel, and SpaceX’s live stream will begin around the same time.