Update December 5th, 12:45PM ET: SpaceX’s Falcon 9 rocket successfully took off from Cape Canaveral, Florida and deployed the company’s Dragon cargo capsule into orbit. Following the launch, the Falcon 9 also landed on SpaceX’s drone ship in the Atlantic. The Dragon cargo capsule is slated to meet up with the ISS on Sunday, December 8th.

Original Story: This afternoon, SpaceX is set to launch its Dragon cargo capsule, filled with nearly 5,700 pounds of cargo and supplies for the crew of the International Space Station. It’s SpaceX’s last resupply mission to the station for 2019. Following the flight, SpaceX will attempt one of its signature rocket landings, targeting a drone ship floating in the Atlantic Ocean.

It’s atypical for SpaceX to do an ocean landing after a flight to the ISS. Normally, the company tries to land its Falcon 9 rocket on a concrete landing pad on solid ground. That’s because there’s usually enough propellant left over to pull off such a ground landing. Getting to low Earth orbit — where the space station lives — is a fairly short trip. That means there’s usually enough leftover propellant for SpaceX to turn around and head back to land, a process that eats up more propellant than landing in the ocean.

It’s atypical for SpaceX to do an ocean landing after a flight to the ISS

However, SpaceX is trying something new for this mission. After the Falcon 9 drops off the Dragon capsule in orbit, the top portion of the rocket will stay in space longer than usual, performing a lengthy six-hour coast. It’s a “thermal demonstration” that SpaceX is performing for some of its other customers, according to Jessica Jensen, director of Dragon mission management at SpaceX. “I can’t give too much more detail about it,” she said during a press conference before the launch, adding that the maneuver was for “longer demonstration missions that we’re going to have to fly in the future.”

Because of this, SpaceX needs to burn extra propellant on the way up, which means the Falcon 9 won’t have as much leftover propellant to travel back to the landing site. An ocean landing will have to do.

If the launch goes as planned today, SpaceX’s Dragon capsule is set to meet up with the International Space Station on Sunday, December 8th. It will bring numerous science experiments to the ISS, including one that will study how flames spread when in small spaces. Dragon is also carrying the first Mexican-developed small satellite to be deployed from the space station, created by students in Mexico to demonstrate ways for satellites to communicate with one another in orbit. Dragon will stay at the ISS for about a month before returning back to Earth, filled with 3,800 pounds of cargo and scientific samples. “When it returns, it’ll be bringing back samples that represent about 54 investigations,” Bryan Dansberry, the assistant program scientist with the International Space Station program science office, said during the press conference.

Today’s launch will jump-start a busy traffic month for the ISS. After SpaceX makes it to the station, a Russian cargo ship will also launch to the ISS on December 6th. Then, on December 19th, Boeing will launch its new passenger spacecraft, the CST-100 Starliner, to the ISS for the very first time. No astronauts will be on board, but the spacecraft will run through all the things it’s supposed to do during future flights: it will attempt to dock with the station, stay attached for four to five days, and then make the perilous journey back to Earth (hopefully in one piece). If all goes well, it should pave the way for Boeing’s next big flight with the Starliner sometime next year, which will transport its first passengers to the ISS.

this launch will jump-start a busy traffic month for the ISS

SpaceX also has a busy couple of months ahead. The company is set to launch a communications satellite in mid-December, followed by another launch of its Starlink satellites potentially by the end of the month. SpaceX is also on tap to perform a test flight with its own passenger spacecraft, the Crew Dragon, to demonstrate the capabilities of the vehicle’s emergency escape system. That flight could happen this month or in early January.

But first, today’s launch needs to get underway. SpaceX is using a brand-new Falcon 9 for this job, although the Dragon capsule has flown the space station twice before. The Falcon 9’s landing attempt will take place about eight minutes after takeoff.

Liftoff is scheduled for 12:29PM ET from SpaceX’s launch site at Cape Canaveral Air Force Station in Florida. Originally, SpaceX was supposed to launch on Wednesday, December 4th, but the company postponed the flight due to high winds above the launch site as well as choppy conditions at the drone ship in the Atlantic where the rocket is supposed to land. For today, the weather is looking better, with an 80 percent chance that conditions will be favorable, though there is some concern about high clouds will build over the area.

Both NASA and SpaceX will provide live coverage. NASA’s begins at 12PM ET, and SpaceX’s will begin about 15 minutes before takeoff. Check back then to see if the Falcon 9 can fly this second time around.

Update December 4th, 12:05PM ET: This post was updated after SpaceX delayed its first launch attempt.

Correction, December 4th, 11:45AM ET: A previous version of this article misstated that the Dragon would carry the first Mexican-developed small satellite. It’s the first one to be deployed from the space station, and the article has been corrected.