1.Sputnik I, the first artificial satellite to circle the planet (October 1957) had a mean orbital radius of 6957 km. Compute its period in seconds 2. I am using the equation T^2 = R^3/C 3. I converted 6957 km to AU's which equals 4.638 E-5. When I plug in the numbers, and convert it to seconds, I come up with 9.96 seconds. Am I using the correct formula? Thanks for your help.