Aircraft and watercraft are very often symmetrical. They operate within an a liquid that surrounds them, within a directional gravity well, and as a result have consistent and usually-symmetrical forces acting on them. And so, their designs must accommodate this (usually).

Landcraft are more-forgiving because you can be truly at rest - a motorcycle with a sidecar comes to mind - but they still have to make allowances for the forces at play when they’re in motion.

Space demands far fewer conceits. And while spacecraft that also pass through an atmosphere - which includes most every human spaceship for now - must also bow to atmospheric constraints, the world of science fiction spacecraft manufactured for space, in space, allows for far more variance in design (energy-shield-based aerodynamic-compensation notwithstanding).

Sure, a saucer could work everywhere, in every direction. But some shapes are clearly, aggressively extraterrestrial. Perhaps they look so (attractively, engagingly) alien because they’re in a world that we don’t yet inhabit.

Half of that is the reason for asymmetry: you can just do it for alienness’ sake, but the real pull comes from asymmetrical designs where you can intuit why they’re asymmetrical, and understand that it’s right. Not just “because we can,” but “because we needed to.” The honesty lends a sense of believability to the design. In liquid and gravity, yeah, ok, you need symmetry, no designer has to justify why their ship was that way and in turn you can just make up designs and viewers will shrug it off - “yeah I’m not aerospace engineer but that seems plausible.”

In space, you don’t need any particular design one way or the other, which means designs where you buy into the reason feel more real.

From the iconic, infamous Millennium Falcon to unexpected standouts, there’re no laws (of aerodynamics) when you’re in space.

• ALIEN Derelict
• LEGO Blacktron Renegade
• Millennium Falcon