How Do Spacecraft Orbit Earth? Angular Momentum Explained By NASA

Space.com

How is it possible for the ISS to stay in orbit? Learn more about the science behind orbiting Earth and more in this NASA "STEMonstrations" video.   Credit: NASA Johnson Space Center

Transcript

00:00Hello, my name is Sultan Alniadi and I'm an astronaut living and working aboard the International

00:20Space Station.

00:22Any idea how it's possible for the space station to continuously orbit Earth 250 miles above

00:27the surface?

00:29And why at 17,500 miles per hour?

00:33What would happen if the station sped up or slowed down?

00:35We are going to explore those questions and more by investigating the connection between

00:40the angular momentum and the orbits in our microgravity environment.

00:45But first, you need to know a couple of other terms.

00:49Let's get started.

00:52Before we dive into centripetal force, it's important to look at Newton's first law of

00:56motion, which states that an object will continue moving with a constant velocity along

01:00a straight path unless acted upon by a net external force.

01:05This means that the space station will move along a straight path if it weren't for one

01:09key external force acting on it, Earth's gravitational pull.

01:14Another name for this external force is centripetal force.

01:18A centripetal force is any net force that keeps an object moving along a circular path.

01:24Gravity, in this case, is a centripetal force because it is the force that is keeping our

01:28space station moving in its circular path around Earth.

01:32Okay, now you know that gravity constantly pulls a moving object with linear momentum

01:41inward just enough to cause it to travel in a curved path, making its momentum angular.

01:49The International Space Station maintains this balance between gravity and linear momentum

01:53by traveling at the required 17,500 miles per hour to maintain an altitude of 250 miles.

02:01This is considered low Earth orbit.

02:03It is high enough to encounter very little interference from the atmosphere but low enough

02:07to be relatively easy to travel to.

02:10Let me show you some examples of angular momentum being conserved in the microgravity environment

02:15aboard the station.

02:16I will apply a force to set this yoyo in motion.

02:19The force of tension is transferred through the string, which is a centripetal force keeping

02:24this yoyo revolving around my hand.

02:26But what happens when I let go of the string?

02:28Once the tension from the string is removed, the object continues to follow Newton's first

02:33law of motion.

02:34It keeps moving at a constant velocity along a straight path relative to the space station.

02:40Now what happens to the motion of the yoyo if we increase the centripetal force by increasing

02:44the tension in the string?

02:46As I'm holding the string between two fingers on one hand to keep the axis of the rotation

02:50stable, I'm going to pull the string with my other hand, increasing the tension and

02:55centripetal force and decreasing the radius of the yoyo's orbit.

02:59As the radius of the yoyo's orbit decreases, its velocity increases.

03:04Angular momentum is the product of an object's velocity, mass, and the radius of its orbit

03:09from an object's center.

03:11If you only have centripetal force, angular momentum must also be conserved.

03:15So if the radius of its orbit decreases, its velocity must increase in order to maintain

03:20its angular momentum.

03:23Let's try this again, but this time I'll decrease the tension on the string, lowering the centripetal

03:29force and increasing the radius of the yoyo's orbit.

03:34If you thought the velocity of the yoyo would decrease, you were right.

03:38Since angular momentum must be conserved, if the radius of an orbit is increased, the

03:43velocity of the yoyo must decrease.

03:48As you can see, there is an inverse relationship between the radius of the orbit and the yoyo's

03:53velocity.

03:54I was able to change the velocity of the yoyo by increasing and decreasing the centripetal

03:58force in the system.

03:59We can't do this with the orbit of the station or other satellites because we can't change

04:04the pull of gravity exerted by Earth.

04:06Instead, to keep the station in a stable circular orbit, we used thrusters that can help maintain

04:12the constant speed of 17,500 miles per hour.

04:18To learn more about these topics, check out the corresponding classroom connection to

04:21conduct your own experiment and discover other ways angular momentum plays a part in your

04:26daily life.

04:27Thank you for exploring some physics with me today, and see you soon.

Category

Transcript

Recommended