The space shuttle, for example. I saw this question on another forum. Wish I hadn't. Now I'm curious and confused.

Once in orbit, it travels at about 17,500 mph around the earth. What propels it at that speed? I thought that once it begins to orbit, it (as well as most other things in orbit, including space junk and debris) is stationary and does not need to be propelled or powered along by thrust.

In trying to understand this, I keep reading that the space shuttle is rotating or revolving or orbiting around the earth at 17,500 mph and that a collision with some space debris could be disastrous.

And then there's the astronauts who go outside the shuttle and float around like in a vacuum and make adjustments and repairs.

And I can understand the shuttle (in orbit), is in a fixed position above the earth and because of the earth's gravitational pull, is literally "falling" off the edge or curvature of the earth. Nevertheless, according to what I read, the shuttle is moving a speed of 17,500 mph!

What is propelling it? Jet engine thrusters, etc. :confused:

Thanks in advance...

This site (http://www.zyra.net/orbit.htm) may help with some insight.
Also you must bear in mind Earth's rotational speed (http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970401c.html).
As to what is propelling it, well as there virtually no friction in space, then there is nothing to slow the shuttle down.
So once this spedd is reached then it will continue to move at this rate for ever, or near enough anyway.
An interesting science fact of note is a new propulsion system NASA are looking into for long distance travel.
Ion Propulsion (http://nmp.nasa.gov/ds1/tech/ionpropfaq.html) has relatively slow acceleration, but is capable of sustaining this acceleration for years on end. Hence attaining an incredably fast overall velocity.

I hope this has given you more to think about and you fine the links interesting.