The Falcon Heavy rocket is seen in its hangar in Florida before rollout to the launch pad. [credit: SpaceX ] SpaceX's Falcon Heavy rocket will attempt its most technically demanding mission yet on Monday night, with a rideshare flight organized by the US Air Force. Company founder Elon Musk has characterized the mission as "Our most difficult launch ever." During this Space Test Program-2 flight, the world's most powerful operational rocket will attempt to deliver 24 different payloads into three different orbits, resulting in multiple re-lights of the Merlin 1D engine powering the rocket's second stage. It is a critical mission for SpaceX and its Falcon Heavy rocket for a few reasons.