# Physics: How To Get In and Out of Orbit

On my science blog, I shared my general thoughts on the wonderful movie Hidden Figures.  On this post, I want to answer the one question I've received the most - how do you even get something into orbit around the Earth? And how do you leave orbit entirely?

As with all of my posts, you can skip the diagrams if you want - the text should give you the general idea. Now on with the show!

# Getting to Orbit

When we say a satellite is in orbit around the Earth, we mean that the satellite is traveling at the exact speed to counteract the force of gravity pulling it down. This means that the satellite is constantly falling, but its going fast enough so that it stays the same height above the Earth.  This results in the satellite traveling in a circular motion.  There are two forces acting on a satellite in this case:

1. The centripetal force.  For circular motion to occur, this force must point inward toward the center of the circle
2. The gravitational force.  This force exists between any two objects in our known galaxy.  It is directed between the centers of both objects (in this case, the satellite and the Earth)

For our satellite to stay in a circle, both of these forces must be the same.  This means that we can set the centripetal force equal to the gravitational force.  Solving this equation gives us a velocity of approximately 8 kilometers per second, or 17,682 miles per hour.  This is the speed that any satellite (including the International Space Station) has to achieve to be able to stay in orbit.  It's also why satellite launches tend to curve right after leaving the launchpad - they need to get to the orbital speed and be parallel to the Earth's surface so they can be pulled into circular obit.