The show never got technical...
Yup, for people, like Timo, who are not familiar with the show, Space Ghost would be depicted leaving the Phantom Cruiser (by way of the canopy simply lifting) and then flying to whatever destination Superman style...because he needs to get there faster than the Cruiser can carry him!
Keep in mind he does this seemingly in "deep space" without any visible means of propulsive or life support gear.
Obviously, Space Ghost exists in a quantum reality where the physical laws of nature function VERY different from ours!
But the Phantom Cruiser is STILL a very sweet ride!