In Part 2, I found the velocity required for circular orbit was

where *G* is the gravitational constant, *M* is the mass of the body being orbited, and *r* is the distance to the center of that mass. I tested this on the ISS’s orbit and found the velocity matched quite well. Now, I’m interested in looking at orbital periods, and calculating aspects of some common orbits.

**Problem:**Calculate the velocity and periods for some typical circular orbits.