Simulating Gravity Through Rotation

If you’ve ever watched the 2015 movie The Martian, you may have noticed that the spacecraft featured in that film, the Hermes, features a section with arms that extend quite far from the rest of the ship, with each of these arms ending in a room. When the astronauts aboard jump into one of these rooms, they seem to experience gravity like any human would on Earth. How is this so?

Two words: centripetal force.

The idea of simulated gravity through rotation may seem incredibly complicated, but in reality, it’s very similar to something as mundane and common as you getting pushed against your seat when in an accelerating car. However, because it’s unrealistic to constantly accelerate the room toward the ship in a linear direction, the acceleration is generated by the constant rotation of the rooms, as seen on the Hermes.

The formula for centripetal acceleration is F = mv^2/r, with m being mass, v being tangential velocity, and r being radius. The centripetal force in this case is going outward toward the rooms, and because the rooms are further away from the ship and are spinning at the same rate as the center of the mechanism, the tangential velocity of anything in that room is greater, resulting in a stronger centripetal force and stronger simulated gravity.

What will also play a hand in determining the nature of the gravity is the angular speed, acceleration, and torque of the mechanism, – all three can be related to the formula for centripetal force in that they will ultimately determine the “v” of mv^2/r. Torque is F(force) times d(distance), and the greater the torque, the greater the angular acceleration. Likewise, the greater the angular acceleration, the greater the angular speed. Finally, we can deduce from the formula of v = w(angular velocity) times r that a greater angular speed results in greater tangential speed, which itself results in greater centripetal force.

We have a solid understanding of how simulated gravity through rotation works, but can we actually apply this to real-world space travel? Obviously, The Martian is science fiction, and here’s where the fiction part of that comes in.

For now, the answer to my previous question is a solid NO.

The primary constraints to blame are those of cost and size. It would be incredibly difficult to create a system of that scale that could reasonably be carried through space, and even if it were possible, the endeavor would be far too expensive to actually undergo. However, it’s safe to assume that most of the technology either exists or will exist in the not-too-distant future, it’s just a matter of putting it all together. In addition to the technical challenges, the constant rotation of the spacecraft would result in blood flowing away from your brain and a general disparity in what your head and feet would feel, resulting in a rather unwelcome sense of dizziness – in order to remedy this, the spinning spacecraft itself would need to be larger than a football field, and while at least a PROTOTYPE of something the size of the Hermes could MAYBE be built soon, something that large is downright impossible and will be for decades.

I think I’ll stick to my microgravity for now.


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