Oh.
Hi there.
Hi.
I'm NASA astronaut
Nick Hague,
living and working
aboard the International Space Station.
Stability in spacecraft is important.
It's what keeps satellites
and space
telescopes oriented
in the right direction
to make observations
and send data back down to the ground.
Here on the International Space Station,
stability keeps the bottom of the station
pointed toward the Earth.
And our solar panels
pointed toward the sun
so we can charge up. and we have power.
Let's face it.
None of us
want to spend our entire time on orbit
feeling like we're on a gigantic
carnival ride constantly tumbling around.
Though, I got to say,
you know, it's fun
to do every now and then.
Never gets old.
But we have to stay stable somehow.
Although the space station
is equipped with thrusters
to give us little nudges here and there,
they require fuel.
And that's not very efficient.
A more efficient way
to keep us pointed in the right
direction is through
using rotational stability
from gyroscopes.
Today
we're going to explore
rotational stability
and how gyroscopes
can be used to keep objects pointed
where we want them.
Every object
has its mass distributed
in different ways.
How the mass of an object
is spread out affects
how it rotates around
each of its three principal axes.
For example,
spinning an object around its minor axis
where its mass is closest
to its axis of rotation is stable.
This is what keeps a spiraling
football stable as it flies.
Rotating an object
around its major axis,
where its mass is concentrated around
the perimeter, is also stable.
This is what keeps a spinning top upright
and a Frisbee stable in flight.
Finally, if
you spin an object around the third axis,
called its intermediate axis,
it will be unstable.
Even the slightest amount of imbalance
will cause it to flip or tumble.
This is called
the intermediate axis theorem.
When an object like a t handle
or a wingnut is spun
on its intermediate axis
and then allowed to move freely
in the microgravity environment of space,
at first it appears stable.
But as the instability
in its axis of rotation
increases, there's
a sudden shift in its inertia,
snapping it around 180 degrees
where the process begins all over again.
While this might look cool,
it is not something
we would want to have happen
on a spacecraft
To keep spacecraft stable,
we use gyroscopes.
A gyroscope is a spinning
wheel with its mass
concentrated far
from its axis of rotation.
As they spin,
they resist rotation along any axis
other than their spin axis.
The International Space Station
has four different Control
Moment Gyroscopes, or CMGs.
They consist of steel wheels
at different orientations
that spin at a constant
speed of 6600 revolutions per minute.
Not only do the CMGs
keep the station stable,
but we can also reposition them
to induce a gyroscopic force
to change the orientation of the station.
Here I have a simple model
of the gyrostat
or device
used to test gyroscopic control.
It's very easy
to make and consists of a gyroscope
placed in the middle of sheets
of cardboard.
As you can see,
we've colored one half of each side,
so it helps us keep
track of the orientation
of the gyroscope.
So there it's spinning around
its minor axis
and it's stable.
Nice and stable
on this major axis.
I'm going to set it up
so that I spin it
around its intermediate axis.
This is the one that goes through here.
And there you can see it
tumbles around
another axis as it rotates.
No matter how hard I try
to get it to only spin around one axis.
Now let's see if we can make the gyros
that spin with stability by spinning up
the gyroscope.
With the axis of the spinning gyroscope
in the same direction
as the rotation of the intermediate axis,
the gyro step.
It's now stable,
even is irregular as a camera.
You can try to find where its axis,
major, minor, and intermediate axis are.
This looks pretty stable.
No, no twist.
There.
And if I'm right,
it's going to turn around
and the camera's going to point
towards you here shortly.
And it's going to turn around
and point toward me.
And it just keeps repeating.
So every object's got it.
Well,
I hope you enjoyed this demonstration
and learned a little something new
about rotational dynamics
and gyroscopic stability.
Now you go give it a try.
Make your own gyrostat just like mine.
Thanks for joining me here
on the International Space Station.