In an exclusive interview with "Mad Money" host Jim Cramer, Boeing CEO Dennis Muilenburg told CNBC that Boeing will beat Elon Musk's SpaceX to Mars. Musk took to Twitter to clap back at Muilenburg, saying "Do it." Boeing, Muilenburg tells CNBC, is in the final assembly stages of developing a rocket called the Space Launch System, with the help of NASA. He estimates that the Space Launch System will be ready for a test flight by 2019 and that it will bring humans to Mars for the first time, ahead of Elon Musk and SpaceX.

Dennis Muilenburg, CEO of Boeing (l) and Elon Musk, CEO of SpaceX. Getty Images