Four months after an explosion tore through its signature Falcon 9 rocket during fueling, destroying the rocket and its multimillion-dollar cargo in just 93 milliseconds, SpaceX says it has isolated what went wrong and is ready to fly again. If the Federal Aviation Administration issues the company a license, likely following the completion of a full-scale engine test scheduled for Jan. 3, the company will launch 10 communications satellites for Iridium on Jan. 8, including an attempt to land the reusable first stage of the rocket on a sea-going robotic platform.