Re: How does the space shuttle orbit the earth and return?

Hi, Lauren,
I'm not sure exactly what you're asking, so if my answer doesn't help, please email me or send Mad Scientist Network a more detailed question, and I'll try again.

Nobody knows why gravity works, we only know what it does. From measurements, we can tell that every object pulls gravitationally on every other object. The more massive the object, the stronger its gravitational pull. The farther away you are from something, the less gravity you will feel. (It goes as the square of the distance, so twice as far away means one fourth as much gravitational pull.)

If we know where everything is, and how massive everything is, we can just calculate all the gravitational forces. When they launch the space shuttle, the gravitational force from the Earth is calculated carefully, and the rocket motors are turned on just long enough and in just the right direction to get into the desired orbit. It can't be "pulled into space" or anything because the only object close enough and large enough to do much pulling is the Earth, and it's pulling straight down, not up. The shuttle doesn't fall down because it "falls" around in a circle. To see how this works, try tying a string or a big rubber band to a ball or something, and swing it around. The ball moves in a circle, because the rubber band is constantly pulling on it. If you let go of the rubber band (so that it stops pulling), the ball flies off in a straight line. If you swing the ball around faster, the rubber band has to pull harder to keep it going in a circle. If you swing a little slower, the rubber band doesn't have to pull so hard. Orbiting the Earth works the same way, with gravity acting like the rubber band, and the space shuttle acting like the ball. If the shuttle is moving really fast, the Earth's gravity isn't enough to keep it moving in a circle, and the shuttle flies off. If the shuttle is moving too slowly, the Earth's gravity is too strong and the shuttle falls down towards the Earth. If the speed is just right, the shuttle keeps going around in a circle (an "orbit"). Because the gravitational pull gets stronger close to the Earth, you have to circle faster when you orbit close to the Earth than you do when you orbit far away. When the shuttle needs to change to a different orbit, or come in to a landing, they fire the rocket motors to speed up or slow down, as needed.

You can read more about gravity at NASA Ames gravity site and The Physics Classroom gravity site.

You can also read more about the Space Shuttle at the Future Astronaut's of America Foundation Space Shuttle site or NASA's Space Shuttle site.

-Steve Levin