One of our biggest problems we face when travelling
in space, is the atrophy our bodies endure while in microgravity. The astronauts on the
international space station have to exercise several times a day to maintain their bone
and muscle strength. But is there an alternative? Can we create Artificial Gravity?
I’m sure you have seen the idea before in movies like 2001: A Space Odyssey where the
entire space station spins to create an artificial gravity. The people inside can now walk comfortably
just like just on earth. It does this by exploiting centrifugal force.
Now it seems that whenever someone mentions centrifugal force, angry mobs will show up
in the comment section. Declaring it isn’t real. Which just isn’t the case. Let’s
see why NASA developed this huge centrifuge to test
the possibility of simulated gravity back in the 1960s. Here we are looking from inertial
frame of reference, that just means we are looking from outside perspective and we can
clearly see that there is no force pulling this guy outwards. It is just his inertia
carrying him forward, and the floor he is walking on provides the centripetal force
to prevent him from flying off. But what happens if our reference frame moves
with the astronaut. This is called a rotating reference frame, or a non-inertial reference
frame. To him, the rest of the world is moving, and he is standing stationary. In this reference
frame centrifugal force is absolutely a real and measurable force, pushing him downwards
just like gravity. The only thing that is fictitious is his perception of what is causing
it. This occurs because in physics and engineering,
we must balance forces. The system has to be in equilibrium. Newton’s third law states
for every action there is an equal and opposite reaction.
So if centripetal force exists in this reference frame there has to be a force pushing him
outwards. That is centrifugal force. And the moment the rotation stops it vanishes again.
So if this works so well, why haven’t we seen a spinning space station yet? Well one
problem is size. To make this practical we need a massive ship, which would be incredibly
expensive to get into orbit. The acceleration your body will experience
is directly proportional to speed and radius of the space station. We can calculate the
gravity Space Station V from 2001: A Space Odyssey would generate with some pretty simple
math. The space station V had a diameter of 300 meters and spun on it’s axis once every
60 seconds. That would put its gravity at about the same
as the moons. For it to have a gravity similar to earths it would need to spin once every
24 seconds. If were to make this a realistic size, let’s
say the same size as the international space station. It would need to spin once every
10 seconds. This would probably be pretty disorientating, just ask Sandra bullock.
Another problem we face on smaller stations like this, is the gradient in acceleration
you would experience. Because the acceleration is directly proportional to the distance to
the rotational center, your head will experience less artificial gravity than your feet. This
would force the blood to your feet, just like when you spin a bucket of water around. This
effect will diminish with a larger stations. So to make a practical space station with
artificial gravity the station would have to be huge, which is simply too expensive.
Besides, the ISS is most valuable to us as a laboratory to test the effects of microgravity.
But what if money was not an issue. What would it take to get a space ship like Elysium,
built for the mega rich as an escape from turmoil on earth, into orbit?
Elysium dwarves Space Station V measuring in at 60 kilometers wide and it is estimated
to weigh about a million metric tons. Space x can currently launch a kilogram into space
for about 2720 dollars, with their falcon 9 rocket. This will be reduced to about 1650
dollars per kilo when they launch their falcon heavy variant at the end of the year. But
it would take over 18 thousand launches to bring the one million metric tonnes to low
earth orbit, that’s 1.65 trillion dollars to just get the materials of Elysium into
space with current technologies. Then we have to worry about the costs of materials and
engineering that would go into building something of this magnitude.
That is far more difficult to calculate, but we can take some clues from the ISS. It is
estimated to have cost about 150 billion in total. It took 36 shuttle flights at a cost
of 1.4 billion each to bring the materials to space. That’s a total of 50.4 billion
dollars. So the launch costs were just 33% of the total cost. A conservative estimate
for the costs of Elysium could be put at 5 trillion dollars. That’s 62.3 Bill Gates,
but there are half a million people on board Elysium, so if the cost was split between
everyone that would be about 10 million each. That isn’t so far-fetched and the price
of space travel is destined to reduce in the future.
We do have materials strong enough to build a structure like this. The forces on Elysium
would be similar to the ISS, other than the additional stress created by centripetal and
centrifugal force. It’s interesting to note that the designers of Elysium took note of
this. The stress in a spinning structure like this would decrease as you move away from
the rotational center. This means it would need a stronger structure the closer you get
to the center. This clearly influenced their design with these tapering spokes. But we
run into some problems when we realize there isn’t enough aluminum in the world to build
this thing. It would take at least 10 years’ worth of the world’s total aluminum production
just to build the structure. This would cause a huge surge in the cost of the material.
An alternative method could be sourcing the materials from space. This could reduce the
launch costs and there is plenty of metallic material available on the moon and on near
earth asteroids. So this technology is definitely possible,
our only barriers are launch costs and material availability. Something on the scale of Space
Station V would be easily achievable, who knows maybe we’ll be travelling to space
as tourists in the near future. Once again thanks for watching, I have a little
bonus for you at the end of this outro, you can skip ahead or wait to watch it. I’d
like to thank my Patreon supporters Bastien, Nick and FG for helping me revise this video.
Your support is really appreciated. Thank you. If you would like to see more content
or support Real Engineering. The links for my Patreon, Instagram, Facebook and Twitter
accounts are below. So I promised to include this in my last video,
but I couldn’t figure out how to include it in this video in a seamless way. The centrifugal
governor was used in the industrial revolution to control the amount of steam entering the
steam piston. Which was essential as the supply and demand can vary with fuel and load.
For example if the engineer puts more coal into the boiler, the pressure will rise and
these masses spin faster, which increases the centrifugal force and pushes them outwards.
This raises this sleeve up which in turn closes the valve to reduce the amount of steam entering
the engine. So the centrifugal governor acts as a sensor to provide direct mechanical feedback
to control the speed of the engine. It is one of my favorite inventions of the industrial
revolution. Thanks for watching till the end everyone. Hope you liked the video and feel
free to ask me any questions on twitter.