'Star Trek' fusion impulse engine in the works | Crave - CNET: "The fusion fuel we're focusing on is deuterium [a stable isotope of hydrogen] and Li6 [a stable isotope of the metal lithium] in a crystal structure," Txchnologist quotes team member and aerospace engineering Ph.D. candidate Ross Cortez saying. "That's basically dilithium crystals we're using." Let's pause and savor that for a moment. Dilithium crystals. Awesome.