Not as hard as you’d think. Clever move, Rebels.
Spoilers for Rogue One below. If you don’t want to know anything about the movie before seeing it, turn back now. It’s cool though.
No matter what you think of Rogue One as a Star Wars film, the movie has moments of inarguable badassery. Speaking as a sci-fientist™, the best moment was when the crew of the hammerhead corvette “Lightmaker” uses basic physics to push a massive, dead-in-the-space Star Destroyer into another Star Destroyer. It’s a brilliant tactic: use what little resources you have to make highly effective strikes. But just how hard would pushing a Star Destroyer be, and could the little-corvette-that-could pull it off?
In space, no one can hear you scream. There is also zero air resistance, but that isn’t as catchy. Because traveling through empty space is nearly drag-free, it’s relatively easy to figure out how hard you’d have to push a large mass to move it. Nerdy numbers abound on the internet, but the mass of an Imperial Star Destroyer is somewhere in the ballpark of a billion kilograms. Thanks to Newton and his laws of motion, we know that the force required to move an object is equal to the object’s mass multiplied by how the object is accelerating, or F=m*a. In the scene from Rogue One, when the hammerhead turns on the jets, the Star Destroyer starts accelerating very slowly–let’s say, two meters per second per second, a fraction of what free fall on Earth would do. (The numbers have wiggle room here, but I believe we’re within an order of magnitude ¯\_(ツ)_/¯.)
Multiply the mass and acceleration together and we get a force: two billion Newtons. This is what the Lightmaker would have to push with if it wanted to start accelerating the dead Star Destroyer. But could the corvette produce this kind of thrust? We Earthlings, at least, are getting close. When the SpaceX Falcon Heavy finally lifts off, it will be blasting off of Earth’s face with 22 million Newtons, just 90 times less than what it would take to push a star destroyer around.
So could a Rebel ship with engines strong enough to push it past lightspeed produce the oomph that throws Imperial command ships around? It’s certainly plausible. During the scene in question, the corvette isn’t even pushing the entire Star Destroyer; it appears to be simply pushing the tip of the ship into the other Destroyer. And, unlike what supertanker tugboats have to deal with in similar situations here on Earth, the corvette could accelerate the Destroyer to any velocity and it would continue on towards a collision. In space, you continue in a straight line at a constant velocity unless acted upon by an outside force (still not catchy…).
So be thankful that if a Star Destroyer suddenly drops out of hyperspace, only 100 of Elon Musk’s best rockets would be needed to push that scum into the sun.
Images: Disney, Lucasfilm
Why Chewbacca’s bowcaster is stronger than any blaster: