# Which spot on earth would have the fewest # of satellite's visible?

1. Oct 21, 2009

### bigmac

1. The problem statement, all variables and given/known data

I'm suppose to explain that....

2. Relevant equations

none...

3. The attempt at a solution

Well I tried to explain it but I'm not sure if its right. I think that if you are near the south pole, there would be less satellites visible because the population that uses the satellite technology the most is in the northern part of the globe? lol can someone help me with this.

One more question:

1. What do you notice about the mean motion and the inclination of geosynchronous satellites? Explain why each value is what it is.

I don't get that question at all....any help! thanks!!!

2. Oct 21, 2009

### D H

Staff Emeritus
Suppose a satellite is directly over the North pole. What spot on the Earth will be directly underneath the satellite half an orbit later?

3. Oct 21, 2009

### bigmac

umm the spot between the north and the south pole? I'm not sure if I understood you correctly...

4. Oct 21, 2009

### bigmac

anything???

5. Oct 21, 2009

### D H

Staff Emeritus
Halfway between the north and south pole is the equator, and that is where it will be in a quarter of the orbit, not half an orbit.

6. Oct 21, 2009

### bigmac

So, you're saying that the fewest sats are visible when they are at the equator??? can you explain it please! thanks!

7. Oct 21, 2009

### kellenm

I would think the fewest would be viewed at the poles.

8. Oct 21, 2009

### mgb_phys

Wouldn't all geostationary satelites be visible from the pole while only half of them would be visible from the equator?

9. Oct 21, 2009

### D H

Staff Emeritus
No, I'm not saying that. I am trying to help you do your own homework. Our job here is to help you do your homework, not do it for you. Begging for answers is not a good ploy here.

A satellite's orbit is in the shape of an ellipse with the center of the Earth at one focus of the Earth. A circular orbit is even easier to imagine: It is a circle with the center of the Earth at the center of the orbit. Satellites can be in equatorial orbits because the equator forms a circle around the Earth with the center of the Earth at the center of the circle.

A satellite in an equatorial orbit will never be over the North Pole. What does a circular orbit that passes over the North Pole look like? What point is diametrically opposed to the North Pole?

10. Oct 21, 2009

### D H

Staff Emeritus
This is homework, mgb_phys.

Geostationary satellites are not visible from the poles. Why not?

11. Oct 21, 2009

### kellenm

I know, pick me.

12. Oct 21, 2009

### D H

Staff Emeritus

13. Oct 21, 2009

### kellenm

I know....

14. Oct 21, 2009

### bigmac

I wasn't begging for an answer. I just didn't understand it....I'm still confused

15. Oct 21, 2009

### DaveC426913

This is key.

16. Oct 21, 2009

### D H

Staff Emeritus
A couple more hints:

A satellite cannot be permanently stationed over the North Pole, or over Washington DC, or over Mexico City. Why not?

A truly geostationary satellite must necessarily be in an equatorial orbit. Why?

17. Oct 21, 2009

### mgb_phys

GSO is 36,000km above the equator so the pole is at an angle above the plane of:
asin ( Earth radius / Earth radius + 36,000km ) = 8.8deg

But then I had a m / km swapped in the rule for the distance to the horizon, so they would be above the horizon if you were 1.7km tall !

18. Oct 21, 2009

### DaveC426913

That 8.8 deg: positive or negative?

19. Oct 21, 2009

### D H

Staff Emeritus
Hey! This is a homework problem you guys are dorking around with.

Stop that!

20. Oct 21, 2009

### mgb_phys

It's a dumb question.

From a point on the equator you can see roughly half of the Geostationary band but these aren't uniformly distributed around the equator - do you need to check the current positions? Are dead satelites counted.

Anything like GPS or Iridium is going to have even coverage over all points on Earth.
Same with a sun synchronous earth resources platform.

A Molniya orbit is going to spend most time visible from the north are you supposed to take into account time averaging?