# Calculate the orbital period of a spacecraft around the moon

1. During an Apollo lunar landing mission, the command module continued to orbit the Moon at an altitude of 100km. How long did it take to go around the Moon once?

2. T= 2(pi)(r^3/2) / root (GM)
mass of moon = 7.35 X 10^22
radius of moon= 1.74 X 10^6

3. I think that is the correct equation, and I've tried plugging all the values in. I know that the radius will have the 100km (100,000m) added on to it...right?

## Answers and Replies

Andrew Mason
Science Advisor
Homework Helper
1. During an Apollo lunar landing mission, the command module continued to orbit the Moon at an altitude of 100km. How long did it take to go around the Moon once?

2. T= 2(pi)(r^3/2) / root (GM)
mass of moon = 7.35 X 10^22
radius of moon= 1.74 X 10^6

3. I think that is the correct equation, and I've tried plugging all the values in. I know that the radius will have the 100km (100,000m) added on to it...right?
Your equation is correct. What are you using for the radius of the orbit?

AM

Last edited:
HallsofIvy
Science Advisor
Homework Helper
Be sure to include that the radius of the orbit is 100+ radius of the moon in km.

Ouabache
Science Advisor
Homework Helper
Welcome pinkerpikachu to PF forums!! You will find this is a great forum for interactive discussion on all kinds of topics.

In your question, you are off to a good start. It would be useful to show us the results of your calculations (and the steps you made to get there). This will enable us to see if you are on the right track.

I'm working on the same problem, can you help me understand how you derived your initial equation?