At the Ad Astra science fiction convention I attended recently in Toronto, a number of panels touched on the question of realistic spaceships in fiction.

Star Wars X-wing fighters? Not realistic, especially in space. With no air for wing surfaces to act on, there’s no reason to have wing-like structures, and no sensible way the ships would swoop and soar, darting in and around larger ships and into canyon-like spaces on death stars.

The mothership from Close Encounters of the Third Kind is gorgeous, and impressive as hell, but I can’t imagine any practical reason to make a ship with so many strange levels, and bizarre things sticking out of it.

Star Trek’s beloved Enterprise? Well the idea that a burst of plasma from a matter-antimatter reaction could push a ship forward is OK, but there’s never any indication of how it slows down again. It creates a “warp field” to allow it to surpass the speed of light and then pops out of warp drive at some unspecified speed that doesn’t seem to be related to anything. Then it goes into orbit around a planet. Real spaceships have to use just as much thrust to slow down as they use to speed up, or possibly harness the drag from a planetary atmosphere for braking (a process that involves a lot of orbits and a lot of excess heat to deal with).

Creators of space-based games like Warhammer 40000 use their imagination to design warships with bat-like wings, spidery legs, huge tail fins, tentacles etc., all to look alien and cool. Except all those frills add huge quantities of extra mass, surplus surface area (the easier to be hit by intentional fire or debris), all amounting to vast areas of waste space.

The Discovery from 2001: A Space Odyssey was realistic, and some of the ways spacecraft behaved in the recent TV series The Expanse weren’t too bad. Overall, though, an awful lot of fiction just plain ignores the realities of space travel, especially the time it would take to get places, the huge amounts of fuel required, and physical properties like inertia and momentum. Things that aren’t moving don’t want to move, and things that are moving don’t want to stop. To make them do either requires a lot of force. To expect to travel through space with the convenience and comfort of the family car, in a sleek package that looks like a futuristic jet fighter, just isn’t, well…realistic.

Of course, the plausibility of a spacecraft design has as much to do with its intended purpose as with its technology.

Gigantic spaceships, many kilometers long (Star Wars, Independence Day, the game Eve online) with vast chambers full of complex plumbing might make for exciting chase scenes and dramatic battle sequences, but large size usually means excessive mass (what on Earth we’d call weight) and the greater the mass, the more force required to get it moving, stop it from moving, or change its course. So high mass is generally not a desirable thing in a spaceship. In a space battle such a behemoth would be virtually impossible to get out of the way of an incoming missile or other weapon. And what do they need so much room for anyway? On the other hand, a colony ship intended to travel to another star could require centuries for the trip, so it would have to be enormous—you’d need to carry enough people to ensure a genetically diverse population for the colony, and maybe even an entire Earth ecosystem to transplant in the new world. Another justification for high mass (though not necessarily large size) would be if the ship required something like a big shield of water around it to protect the occupants from cosmic radiation. (FYI, here’s an amazing graphic showing size comparisons of nearly every fictional spaceship out there. Wow!)

Spaceships that are never intended to enter an atmosphere have no need for a sexy streamlined shape—they can be as ungainly as you want, as long as the structure can handle the strain of acceleration and deceleration. But a shuttle craft to and from a planet’s surface would benefit from an aerodynamic design, able to get some lift on the glide down, and with less wind resistance to contend with on the way back up.

One of the ways TV and movie spaceships most often fail in the realism department is that they don’t include enough space for the fuel the ship would use. They’ll show a craft about the size of a small bus to carry a dozen people to and from orbit (like in the movie Elysium). The American space shuttles were the size of passenger jetliners for a crew of seven, and required a mammoth liquid-fuel rocket and two solid-fuel boosters just to get them into orbit. Sure, we hope there will be significant gains in efficiency in the coming century or two, but as long as spacecraft use reaction drives (shooting something out the back to push them forward) they’ll require a significant amount of mass to eject. And gravity isn’t going away anytime soon.

What’s your biggest complaint about spaceships in fiction—the faux-pas that blow all their credibility out of the water?

There are some ideas being explored that could make “unrealistic” spacecraft into viable concepts. We’ll have some fun looking at them in my next post.