The other day I watched Return of the Jedi again with my son. And as we watched I was reminded of something about that movie -- and the rest of the Star Wars "episodes" -- that used to bug me and still does a little bit. I know there's a whole cottage industry out there that delights in producing criticism of George Lucas and the mistakes he made with the Star Wars movies (and, believe me, I agree with at least a few of those criticisms), but I don't think I have ever run across a critique that draws attention to this one problem that I have, and it's a very basic problem of engineering.
It's this: The Death Star is built wrong.
Mind you, I'm not an engineer myself, and I'm nothing more than a very basic amateur astronomer, but I don't think a station of that size could actually be constructed. At least not the way that construction is portrayed in the Star Wars movies. And the problem is a simple one of gravity.
The force of gravity causes large clumps of matter to collapse in upon themselves. The larger the object is (i.e., with more mass), the greater the gravitational pull to itself is, but even the smallest of objects possess some modicum of gravitational attraction. And they always try to pull themselves together. Leave a whole bunch of loose objects floating around inside an abandoned space craft and they will eventually clump together because gravity is relentless.
This is how planets and moons and asteroids are formed. With small bodies, the gravitational attractions are weaker, and you end up with weird, misshapen piles of rock.
A pile of space rock.
But as the bodies get larger the gravitational forces compress the material even more, and you end up with more spherical shapes that are denser and more like a planet or a moon. This is a process called accretion.
Now, back to the Death Star. It's round, and the characters in the original movie, Star Wars, mistake it for a small moon because it is really big. At the official website of the Star Wars universe, this Death Star is described as being 160 km in diameter. The second Death Star that was under construction in Return of the Jedi is much larger at approximately 900 km in diameter. The problem with this is that, at these sizes, the gravitational forces of all the materials used to build the station would begin to accrete into a dense mass of unusable rubble.
Not dense, and not rubble. At least, not quite yet.
For comparison, here's a picture of an actual asteroid called 433 Eros:
Eros is about 34 km across, so the gravitational forces are not quite strong enough to make it round. It looks like an oddly shaped pile of rock. In fact, it is an oddly shaped pile of rock.
Now, here's another asteroid called 4 Vesta:
Vesta is about 530 km in diameter, which is between the size of the original Death Star and the second one under construction in Return of the Jedi. See its shape? It's almost a ball, which means that its gravitational forces are compressing it together like a couple of cosmic hands crumpling a piece of paper into a lumpy ball.
Now, here's the biggest of the asteroids in our solar system, and it's called Ceres:
It's very much spherical. And do you know how big it is? It's almost 1,000 km across, which is just a little bit bigger than the second Death Star. At that size, the Empire's contractors would need to really start thinking about how to keep the entire structure from collapsing in on itself before they even got into the business of installing life support systems, power plants, or space ship bays, much less fully functional planet-destroying weapons.
So, the Death Star is built wrong, wrong, wrong. Does it make much of a difference in the grander scheme? No, it doesn't. There have been much worse movies with even more egregious mistakes that the directors have tried to pass off as serious efforts. And, despite Lucas's tinkering with the "Special Edition" versions of the movies, the original three Star Wars flicks are still quality cinematic products that make for a great adventure, and I'm not done enjoying them. Not by a long shot. But the depictions of the Death Star still bug me today, just a little bit. And I truly wonder if I'm the first person to give voice to this basic flaw.
Flawed, like the characters within.
P.S.: The process of planet formation called accretion also explains why the planet Naboo is wrong.
A rocky planet with a liquid water core?
Even more wrong.