What better way to show the reach of the Empire, and the grave danger it poses than with the image of a literal death machine looming large on the horizon? In the first official poster for the next Star Wars film, Rogue One: A Star Wars Story, we get a glimpse of the original Death Star. And it is large. In fact, it’s too large. At least according to this perspective, it should be destroyed long before the Rebels get to it.
Only recently in our history have we had technology sophisticated enough to track and place the heavenly bodies that wander in the skies above us. But even thousands of years ago we had the mathematical knowhow to calculate how far away our own moon (which is a moon, and not a space station) is from us. All it took was the angular size of the moon in the night sky and some clever estimations during lunar eclipses. Today, we know that the moon is 2,159 miles (3,475 kilometers) in diameter and 238,900 miles (384,400 kilometers) away.
The Death Star in the poster is disturbingly different. We know that the first Death Star is somewhere between 140 km-160 km in diameter, which, sure, is fine, but would mean it’s way too close for survival in the above image. “The main issue is how far away the thing needs to be for there to be a stable orbit possible,” astrophysicist Katie Mack told me. “If a satellite gets too close to the thing it’s orbiting, tidal effects can rip it apart.”
“If the [Death Star] is only 150 km in size, I think that’s basically impossibly close.”
Dr. Mack quickly calculated that the battle station in the poster, if the above size, would be less than 100 kilometers from the planet’s surface. That puts it well within the so-called Roche limit, or the distance at which an orbiting body will be ripped apart by its partner’s gravitational forces. If our moon was shoved to an orbit less than 10,000 km around us, for example, it would disintegrate. In a few million years, Mack pointed out, the same thing will happen to the Martian moon Phobos.
So if that is the Death Star in the Rogue One poster as seen from the planet’s surface—not some photoshopped metaphor for the Empire’s influence—it would be quickly ripped apart by the planet’s gravitational forces (if the planet is roughly Earth-sized) and go on to form a series of rings. Rings littered with storm troopers and half-finished TIE fighter hangar bays.
The Imperial Corps of Engineers isn’t exactly known for thinking of all the ways it can lose a battle station.
Images: Lucasfilm; Disney