LIFE IN A STAR DESTROYER: IF GRAVITY IN MOVIES WAS REAL

What if we imagined building a gigantic spaceship similar to the famous star cruisers from the Star Wars movie?

Science fiction movies set in space represent for decades now a substantial part of cinematography literature. Heroic battles with futuristic weapons, far-off worlds and enormous space ships of different shapes inspire our imagination by ferring us to a still unknown and charming Universe. Sometimes movies and tv series on “science fiction” topics seem so convincing that we believe that life in space could really take place as well as it is represented. It would be exciting to go inside a small spacecraft and sit comfortably at the command post and with the seat belts fastened fly away from Earth driving the spaceship among the stars like a go-kart. But, is it really that simple?

The answer is a clear no. The greatest virtue of science fiction consists in going beyond everyday life; it adds a surreal part often based on our previous knowledge in order to create something new within the vent of our creativity. The sure thing is that often science fiction reveals the arrival of new technologies thanks to that pinch of intuition which is the basis of progress, but it needs to be fed and shaped by the critical thinking of the scientific method.

Although it shouldn’t be forgotten that science fiction is pure fiction designed to entertain and delight, it can be interesting to think about the absurd consequences of turning some events of our favorite movies into reality. And with the full spirit of a nerd, I want to dedicate this reflection to one of the most famous franchises of the last 40 years, that is Star Wars.

It was a cold February evening before the lock down; my colleague/roommate who recently returned from a mission in Antarctica and I were sipping a beer waiting for our stew with julienne vegetables to reach the desired cooking. In the background, resting on the cabinet next to the entrance, one of my latest purchases stood out proudly: a model under construction of Star Destroyer, one of the cruisers of the imperial army in the Star Wars series with a typical triangular shape. With its not entirely indifferent dimensions (over 110 cm) it continuously attracted our eyes. Needless to say that between a chat and another, the topic of the discussion soon resulted in the spaceship and (maybe due to an excessive amount of alcohol) in the possibility of actually building such an object to travel in interstellar space.

Let’s skip the useless technical details of WHERE and HOW to build a colossal spaceship on Earth (considering that, according to the descriptions found on the net, a Star Destroyer should reach a length of over 1500 m, that is about five cruise ships in a row), not to mention the amount of energy needed to make it escape from the attraction of our planet. Let’s focus on the real possibility of living inside a cruiser of such dimensions; let’s imagine for a moment that we are commanders of the Star Destroyer, in the ship’s cockpit, busy giving orders to the crew.

Probably, the first problem we should consider would be to be able to walk or even more simply to understand how to stay up. Indeed we can’t forget the effect of that energy that “moves the Sun and the other stars”; not Love, as Dante quoted in the final verse of the Divine Comedy, but gravity, the last of the four fundamental interactions of nature that rules the Universe on a large scale.

We are used to perceiving the gravity of our planet through the acceleration that makes us “fall down”. Whenever we throw an object, jump or simply climb a flight of stairs, we feel this return effect that inevitably leads us to touch the ground. Since our life, also and above all from a biological point of view, is based exactly on the structure of Earth gravity, it can seem natural to think that even aboard a spaceship things are not so different. Unfortunately it is not so: force of gravity is strongly linked to the size and shape of the object that exerts it on us.

First of all it’s necessary to make an essential distinction: one thing is speaking of gravitational force, but it’s different to speak of gravitational field and potential. Although the concepts are often confused, field and potential refer to the effect caused in the surrounding Universe by the presence of a single object, for example the Earth. Instead force is the mutual interaction that occurs between two objects, for example Earth and ourselves; as such it depends on both quantities involved. In simple terms, the gravitational force between Earth and Moon is billions of times higher than the force between Earth and human beings, although the gravitational field generated by the Earth always has the same expression.

Let’s analyze the second key point: gravity on the surface of our planet. The gravitational interaction is defined as central, that is the increasing force we feel as we get closer to the center of our source (in this case the Earth). Besides, the strength of this interaction, with the same distance, is still the same in any direction. Since the planet has pretty much a spheroidal shape (although there are people who still say the opposite, cit.), a human being feels the same force of gravity at every point on the surface. That’s why having a walk in a flat area in Milan or taking it in London, in terms of exertion for our legs, has the same result.

The shape of a Star Destroyer is anything but spherical; calculating the gravitational field and the force that would act on a poor soldier of the Imperial troops is very tricky; especially considering the complex structure of the spacecraft. Thanks to some simplifications and the help of a small numerical simulation, I was able to determine in general what would happen if we were inside or near the spacecraft.

Needless to say that considering the total weight of the cruiser, that is immeasurable to our eyes but insignificant if compared to the mass of the Earth, the whole gravitational field is about one millionth of that generated by our planet. Basically none of us would feel anything, but would happily float through the corridors of the ship. However, as we move forward in our insane mental journey, we try to ask ourselves what would happen if the triangular space had an average gravity of the same magnitude as that on the surface of our planet, about ten meters per second squared.

For the interested reader, here are some more details; the two graphs below show the structure of the acceleration of gravity felt at a height of one meter from the floor. In the first, the acting acceleration along the direction of the axis of the triangle (the length of the ship) is represented. The black areas show a push towards the bottom of the ship while the yellow areas indicate a push towards the tip of the triangle. The red color instead indicates the areas where the gravity is lower. In the second graph I showed the acceleration that we would feel to the right (yellow) or to the left (black) within the various areas of the cruiser.


Gravity acceleration in the Star Destroyer model along the vertical (to the left) and horizontal (to the right) directions perceived at one meter from the floor.

So summing up, staying on the bottom or the tip of the ship would throw us towards its center; similarly, managing a turret on the edges would be quite difficult because it would be pushed towards the inside of the spaceship. Next to the edges there are even areas where, at a distance of a few meters, gravity doubles or halves; imagine that, by stretching one arm, its end is pulled with a double force than the rest of the body. So, it is a whole other thing than the fluid movements shown in movies.

If this psychedelic lucubration has taught us anything (besides the warning to never leave a pc in the hands of a physicist), we could say that no matter how fascinating and majestic it is, the shape of the Star Destroyer would certainly not be the most suitable for a future spaceship destined to interstellar travel. Now sorry, but I have to go back to my calculations to figure out if it would be wise to cook a plate of spaghetti in the center of the Death Star.

Over and out

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