SpaceX postponed the launch of its fifth resupply mission to the International Space Station on Tuesday morning due to a problem with the second stage of its Falcon 9 rocket. The next window for a launch is on Friday. The flight will mark the first time the commercial rocket company will try to bring a rocket back for a soft landing, an important step toward cheaper, quick-turnaround space flights. SpaceX will try to land the booster rocket on a drone platform in the Atlantic after it sends the Dragon capsule toward the space station with 5,200 pounds of cargo.