Orbital velocity (also called circular velocity) is the speed of a satellite in orbit around a planet. The formula for circular velocity is given in the text as:
where r is the distance from the satellite to the center of the
planet, M is the mass of the planet and G is a
fundamental constant of nature, given as 
.
The two most important things to remember are: (1) be sure to work with
distances in meters or the units won't work out, and (2) add the radius
of the planet to the distance of the satellite above the surface.
Example:
What is the orbital velocity of a satellite in orbit 10,000 km above the
surface of the Earth? The mass of Earth is 
kg
and the radius of the Earth is 6378 km. Add this to the height of the
orbit to get r = 16,378 km = 
. Plugging these
numbers (plus G) into the circular velocity formula gives:
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