Who doesn't love the idea of floating freely in the zero gravity environment of outer
space. It looks like a ton of fun, and people will happily pay
Jeff Bezos and Richard Branson millions of dollars just to experience zerog for only a
few minutes at a time. But if our goal is to live in outer
space for the long haul, then the lack of gravity is going to be
the biggest obstacle that we face. So in order to achieve a sustainable human
presence in space on the Moon or even on Mars, we need to solve
the biggest logistical challenge of all artificial gravity. This is the space race.
Of course, whenever we say something like zerog, what we actually mean is
micro gravity, because gravity is everywhere all the time. It's the force that
holds the structure of the Solar System and the galaxy together. Everything that has
mass creates a gravitational effect, but it takes a very large concentration of mass
like a planet, to actually have a discernible effect with enough force that would
make you stick to the ground. This is an oversimplification, but I know
you don't come to this channel for a detailed physics lesson. So we have
to also remember that the effect of gravity tapers off very quickly from the source.
Gravitational waves continue on infinitely into the universe. But just like heat,
gravity is only felt intensely when very close to the source. That's the easiest
way to think about this. I'm not going to bother you with trying to
explain the inverse square law today. Just imagine that you are sitting very close
to a fireplace and you hold your hand out towards the flame. If you
move that hand either backwards or forwards by a distance of just one foot,
that could make the difference between warm, hot, or burning. The gradient
of the heat is very extreme at this distance. But if you move back
and are now six feet away from the fire, and you hold your hand
out again, you'll still feel the heat, but much less of it.
And if you move your hand forwards or backwards by one foot, option of
heat will be more or less the same. In all positions. At this
distance, the gradient of heat is much softer. This is all important.
Just stick with me and we'll get to the cool sci fi stuff very surely.
The gravitational flame of the Earth is its core, which is a giant
ball of solid metal that's surrounded by a thick outer layer of swirling liquid metal,
an incredible amount of concentrated mass that creates a gravity well right in the
middle of the planet, and that force radiates out to the surface of the
Earth and even into space. Because the surface of the Earth is over six
thousand kilometers away from the center of the gravity well, we do not experience
an extreme gradient in the force of gravity out here. The effect tapers off
at a very shallow rate, So it doesn't matter if you are in an
underground bunker or the top floor of the tallest building, your experience of gravity
will be more or less the same, no perceivable difference. In fact,
if you were to climb a ladder straight up into the sky all the way
to a height of four hundred kilometers, which is the altitude of the International
Space Station, you would still be experiencing ninety percent of the gravity that you
left behind on the surface, and if you let go of that ladder,
you would fall all the way back down. You might be confused at this
point, why do people in spaceships float at the same altitude that people on
ladders fall down. Well, that's because an orbital spaceship or space station is
in a constant state of free fall. This is what happens to the people
in those Blue Origin capsules. They're not weightless because they are in space.
They've just been launched straight up at a very high speed by a rocket engine.
But then that engine cuts off and releases the capsule to coast up for
a little while before it starts to fall back down again. While in freefall,
the crew will float. Same thing happens in those airplanes that NASA has
been using to train astronauts for decades. The difference between a Blue Origin capsule
and a real spaceship like a crew Dragon, is that the dragon has reached
orbital velocity, where it is moving so fast parallel to the Earth's surface that
it is literally falling around the Earth. Here's the easiest way to think about
this. If you throw a baseball, it will eventually curve downwards and hit
the ground because gravity pulled it down. The faster you throw the baseball,
the further it goes before its path eventually meets the ground. We can't stop
gravity, but we know that the Earth's surface also curves down as it moves
away from us. So imagine if you could throw a baseball so fast that
the downward curve of the ball match the curve of the Earth's surface. At
this point, the ball would still be falling towards the ground, but the
ground would be falling away from the ball at the same rate, so the
ball would stay in the air. Of course, we know that even if
you could throw a ball that fast, the resistance from the atmosphere would slow
it back down again, and it would still eventually hit the ground. But
in space, once you reach that orbital velocity, there's pretty much nothing to
slow you back down again, so you can continue to fall around the Earth,
moving in a circular pattern of free fall, but never getting any closer
to the surface. So all of that to say that gravity is extremely complicated,
yet at the same time essential to our survival. The human body evolved
under the force of Earth gravity. Our entire muscular and skeletal structure is designed
to resist the force of gravity. All of our internal organs are meant to
function in step with gravity. Food goes in the top, waste comes out
the bottom. Our entire circulatory system is meant to keep our blood moving up
and down in spite of the force of gravity. That means when you take
gravity out of the equation, the entire body becomes a confused mess. It
freaks out. Nothing is functioning the way it is supposed to, And if
you stay in that state of anti gravity for a prolonged period of time,
then your body is going to have a very difficult struggle bringing you back to
the natural equilibrium when you finally return to the Earth's surface. Coming back from
weightlessness is like a full body hangover, except this one lasts for months,
and if you stay weightless for too long, you may never get back to
the way you were before. We're talking permanent damage. So with all of
that in mind, we know that if humanity is ever to become a true
space faring civilization and explore the outer reaches of the Solar System and all of
the planets and moons in between, or even if we just want to live
in the orbit of our own planet, then we are going to need to
sacrifice our own bodies or develop some kind of artificial gravity replacement. Because we
know that the only way to create true gravity is with extreme concentrations of mass.
The best we could possibly do with something as simple as a spaceship is
to create a force that might simulate the effect of gravity. Luckily for us,
Albert Einstein figured out how to do this a very long time ago.
All we need to do is accelerate at a rate that is equivalent to the
force of Earth's gravity, which in this case would be an acceleration of nine
point eight meters per second squared. This is also an oversimplification, but we've
done just about enough bad physics lessons for one video. According to Einstein,
if you could accelerate linearly at this exact rate, then the downward force you
would experience from acceleration would be identical to the force of gravity experienced on the
surface of the Earth. So why don't we do that? Well, Accelerating
at nine point eight meters per second squared is incredibly rapid. It would take
an outrageous amount of rocket fuel to achieve this kind of acceleration with a conventional
rocket, and we have to remember that this is not a speed that you
can coast at. This formula demands that you continuously accelerate at a rate of
nine point eight meters per second squared, which would pretty quickly get you up
to a velocity that approaches the speed of light. You'd enter the next galaxy
within a few years. You could probably even reached the edge of the known
universe within your lifetime. Meanwhile, everything not moving at near light speed would
experience billions of years of passing time, So the Earth, the Sun,
and even the entire Milky Way galaxy would all have grown old and died.
You'd have accelerated yourself right to the end of infinity, whatever that is.
But time is even weirder than gravity, so let's stop talking about it before
we all have an existential meltdown. So with Einstein's theory out, that leaves
us with one final way to mimic the effect of Earth's gravity spinning in a
circle. I'm pretty sure these things are illegal now, but if you're an
adult over the age of thirty, then you've probably experienced one of these playground
merry go round things. A bunch of sadistic children would spin this nightmare up
to terminal velocity until kids started flying off and vomiting everywhere. It was great
fun, and that is the exact kind of effect that we are trying to
replicate in space, just hopefully with less crying and vomiting. This is where
rotating space stations come into the picture. We've seen a ton of these things
in science fiction media over the years, but would they actually work as advertised
in the real world. The reason that those old playground toys had such devastating
effects on our tiny little bodies was down to the radius being too small and
the rate of rotation being too fast for the brain and the inner ear to
handle. Very smart people have done a bunch of really interesting studies where they
stuck people into centrifuge machines, which are basically very large equivalents of our playground
merry go round, and they monitor what happens to the lucky subjects. From
that, we've figured out that the average person can sustain around one revolution per
minute without becoming nauseous or disoriented, So that's not very fast. If we
know the desired revolutions per minute and we know the target force of one G,
then all we need to do is find our radius for our circular space
station and we should be all set. The biggest problem we face is that
the slower the desired rotation, the larger the space station needs to be.
For example, if we wanted to spin something the size of the existing iss
to generate one g of force, then it would need to rotate once every
ten seconds, so obviously the result would be a vomit comet. It's generally
accepted that to achieve a force of around one g at around one rpm,
we would need a structure that is at least one kilometer across, So this
is one gigantic circle. But that's not even all that we have to consider
here. Remember we figured out that the Earth's surface is over six thousand kilometers
away from its gravity well, and that's why we don't experience different amounts of
gravity at different elevations on the surface. Even in a one kilometer diameter ring,
you are now relatively close to your center point, which in that case
the center of the ring would be a point of zero gravity and the full
one G force would be located on the outside of the ring. That means
that the gradient between zero G and one G is going to be steep.
So just standing up straight on the floor, you may experience a perceptible difference
in the force of gravity acting on your head than what you feel at your
feet. Best case scenario, this could be very strange, but worst case
it could be straight up disorienting. This is also problematic if you want to
have multiple levels in your space station, as each level would have a reduced
force of gravity as you went up, and even more extreme gradient between the
force of gravity at the ceiling and g force at the floor. Though climbing
any kind of stairs or ladder would be nearly impossible. Yet another force that
we have to consider here is the Coriolis effect, which is pretty much the
effect of our rotational momentum on objects inside the station. We have this on
the Earth, but because the Earth rotates so slowly, the Coriolis effect is
imperceptible in our daily lives. The force of gravity significantly overpowers the rotational momentum,
so it only really has an effect on high level weather patterns. This
is what causes storm clouds and hurricane to rotate. But on a much smaller,
much faster spinning station, the Coriolis effect is going to be a regular
force to contend with. It basically means that nothing will ever go in a
straight line. So if you tried to throw a baseball inside a rotating space
station, the ball would immediately curve over to the side. If you tried
to pour a drink into a glass, the liquid would go flying out at
an angle, trying to take a shower would be a major challenge because the
water would never fall straight down. Now you've probably already noticed that building a
gigantic space station ring one kilometer across is going to be nearly impossible from a
logistical standpoint. That's the kind of thing that will definitely require some asteroid mining
and a whole manufacturing industry on the Moon and stuff like that. But we
could have a more feasible solution. We don't actually need the entire ring.
All we need is the diameter and the rotation. So you could have two
space station modules that are connected together by a one kilometer long truss and then
set it into rotation. This would achieve that force of roughly one G in
each of the modules. So in theory, all we would really need to
figure out is a relatively basic microgravity three D printing operation to build out that
trust structure. We could then use two large vehicles like SpaceX starships or cr
space inflatable life modules, and we could have the first artificial gravity station.
This is at least conceivable with the technology that we have available right now.