# Orbital Motion Question

1. Jan 13, 2012

### billybobay

I'm not asking for you to do my homework but can you help me on it?! I have no idea how to even attempt it. Any help would be greatly appreciated!

The International Space Station (ISS) just celebrated its 10th anniversary of human habitation. During that time it has been orbiting the earth at an altitude of 350 Km.

a. If the radius of the earth is 6,370 Km, what is the period of orbit for the ISS?
b. Does the orbiting speed of the ISS depend on its mass?
c. Suppose the ISS is in a stable orbit when the space shuttle brings in a new component for attachment. This increases the mass of the ISS. Do the astronauts have to adjust the speed of the shuttle to maintain the same orbit? (hint: momentum is always a factor in our universe) Explain your reason for your answer.
d. If the ISS were to be moved to a geosynchronous orbit (always staying above the same point on the earth), What would the new altitude of the ISS have to be?

2. The attempt at a solution

a. 6370+350=6720 km is the period of orbit? is that correct?
b. I need a lot of help!
c. I need a lot of help!
d. I need a lot of help!

2. Jan 13, 2012

### BruceW

hmmm, if your teacher is setting you this homework, then I guess he/she has already taught you the relevant concepts? The important topics for this question are: Newton's law of universal gravitation, circular motion and centripetal acceleration. look back at your notes, and hopefully it will start to make sense. Also, has your teacher gone through these types of questions in class with you yet?

3. Jan 13, 2012

For a, the orbital period is the time it takes for the object to do 1 complete orbit.

4. Jan 13, 2012

### bigfooted

a) period is the time it takes to complete a circle around the earth. It is in units of time. you just calculated the radius of the orbit, which you will need to calculate the orbital velocity.
Orbital velocity v=sqrt(Gm/r). Do you know G,m and r? When you have the velocity, you can calculate how long it takes to traverse a circle with radius 6720 km.
b) Is the mass of the ISS in the equation for the period?
c) what does the hint mean?
d) When the ISS is always above the same point above the earth, what is the period of the ISS compared to the period of the earth?