A little more than nine months after the loss of its Dragon spacecraft during a cargo flight to the International Space Station, SpaceX is ready to set matters right. On Wednesday, the company completed a successful static firing of its Falcon 9 rocket engines, and a Thursday readiness review found all systems were go for a launch on Friday afternoon.

The resupply flight will carry 3,136kg of cargo to the station inside the Dragon capsule, including the 1,413kg Bigelow Expandable Activity Module. And while there has been some excitement about the potential for expandable habitats in space, which may lead to much larger living quarters for human activity, much of the anticipation for Friday's launch again revolves around whether SpaceX will make a historic landing on a drone ship at sea. Launch is scheduled for 4:43pm ET (9:43pm BST) on Friday.

During a news conference on Thursday, Hans Koenigsmann, a senior launch official with SpaceX, said the company has learned from previous attempts to gently set the Falcon 9 down at sea. Nevertheless the procedure remains a tricky one, given that SpaceX is trying to land a 70-meter tall rocket stage in the middle of the ocean after it has flown into space at six times the speed of sound. "I certainly hope we're going to nail the landing this time," Koenigsmann admitted.

Although it is easier to land a used rocket on the ground, where there is a larger area and greater stability, perfecting sea-based landings is better for performance. That's because, from a propellant standpoint, it is easier for a rocket to fly back the to ship below the point where it releases its payload into an orbital trajectory, rather than traversing all the way back to a landing site near along the Florida coast.

For Friday's supply mission, the first stage of the Falcon 9 rocket, with its nine Merlin engines, would probably have enough fuel to make it all the way back to make a land-based landing, Koenigsmann said. However the company's next two or three flights, with their more dynamically challenging missions, will require almost all of the rocket's fuel to deliver their payloads into orbit. The first stages will have return by sea. As Friday's flight profile is more benign, he said, it therefore affords "a good opportunity to refine our drone ship landings because in the long run that is something we need to demonstrate over and over again."

So SpaceX will try once again to land on a drone ship, this time Of Course I Still Love You, in the Atlantic Ocean off the Florida coast. As the company seeks, along with Blue Origin, to develop the practice of flying rockets, landing them vertically, and reusing them, having the capability to do so at sea is critical to lowering the costs of launch. Koenigsmann estimated that only about one-third to one-half of SpaceX flights with the Falcon 9 rocket will have enough fuel margin to return to land.

The company is also closely watching Friday's launch because it marks only the third flight of its upgraded Falcon 9 rocket. First flown in December, 2015, the rocket was redesigned so that unnecessary margin on the engines could be used to increase thrust by as much as 20 percent. The airframe and thrust structures were also reinforced to accommodate the additional thrust and increase reliability of the launch system.

The upgraded Falcon 9 rocket also features a new, densified mixture of liquid oxygen and kerosene fuel. With this more dense fuel, SpaceX can put more propellant into the Falcon 9's fuel tank, increasing the rocket's performance by 5 or 6 percent, Koenigsmann said. "It's a substantial improvement worth the effort," he noted. However, working with the more dense fuel is more challenging, because once loaded it warms up quickly, leaving a limited amount of time it can be kept in a vehicle before launch. These fueling issues caused several delays to the last launch of the upgraded Falcon 9 rocket, in March.

"When you put the rocket on the pad for the first time with this propellant you learn things that you're going to have to improve," he said. "I'm pretty sure we have learned the most of it, but I can't promise we have learned all of it. I feel like we have this issue relatively well under control at this time."

As SpaceX flies the upgraded version of its rocket more, it hopes to fall into a more regular cadence of launches. Last month the company's president, Gwynne Shotwell, said SpaceX intended to launch 18 rockets this year. If the space station mission goes off on Friday, that will make just three for the year so far, a rate of less than one per month.

Koenigsmann acknowledged that to meet its customers' demands, SpaceX must pick up the pace. "And we will pick up the pace," he added. The company plans to make one more launch by the end of April, and then another in May shortly thereafter. As the company becomes more comfortable with the upgraded Falcon hardware, he said, SpaceX intends to reach a launch cadence of once every other week by the end of 2016.