# Homework Help: Satellite placements

1. Apr 2, 2005

### iambooboo

i have this lab i have to do for springbreak, heres the problem.

"Your and your partner have a consulting company, "SATELLITES AND ASSOCIATES", and you specialty is to determin satellite orbits. Your fims was approached by a colony of lunatics to find the most efficeint solution to their communication problem. Their budget allows for the purchase of three satellites. Your job is to determine if they should be place in low moon orbit or synchronous lunar orbit. In your lab report, i expect to see the folling information for each case to justify your conclusion. (mass of satellites= 500kg)

FBD(free-body-diagram), length of orbit, velocity or satellite, period of satellite. ac, gl and Fl. Analysis of the results, and conclusion. The lab report should be no more or less than 2 pages. Follow the following format: ..."

if someone can help me. can someone explain low moon orbit and synchronous lunar orbit? Which orbit are better? thank you for your time.

2. Apr 2, 2005

### Andrew Mason

Let me guess. This was handed to you on Friday morning?

AM

3. Apr 2, 2005

### iambooboo

yea how u know?

4. Apr 3, 2005

### Andrew Mason

Its an April Fool's joke.

AM

5. Apr 3, 2005

### tony873004

A low moon orbit is an orbit that is not too far from the surface of the moon. A lunar sychronous orbit is an orbit whose period matches the period of the rotation of the Moon. On Earth, Geosychronous orbit, the equivalent to lunar sychronous is the desired orbit for communication satellites. It allows them to hover over a fixed point on the equator. This way, people with satellite dishes on their houses don't need to keep re-aiming their satellite dishes depending on the time of day.

But it might be possible that there is no such thing as a lunar sychronous orbit like we have geosychronous orbits. The Moon takes a long time to revolve about its axis. If you want to give formulas, compute the distance a lunar sychronous satellite would have to be. Then Google for the formula for Hill Sphere. I think Wikipedia has a good one. Compare the distance to the Hill Sphere and you might quickly rule that possibility out.

If you don't want to do math, you can use a program I wrote called Gravity Simulator ( www.gravitysimulator.com ) and actually place satellites in all sorts of lunar orbits, make screen shots and print your results. (Use preferences to make a white background or you'll waste all your black ink).

Orbiter is another good program ( www.orbitersim.com ) to use to display your results, if you want more than just words on your 2 pages.

Are you allowed to choose medium moon orbits, or are you restricted to low and sychronous orbits?

Post here if you problems with this. Unless this really is an April Fool's joke!!

6. Apr 3, 2005

### jdavel

Andrew Mason,

Why do you think this is an April fool's joke? It's certainly solvable.

7. Apr 3, 2005

### Andrew Mason

Ok. Look at it:
1. It was handed out on the morning of April 1
2. It poses a fact situation that is silly
3. It poses a question without sufficient information (ie what locations do they want to communicate with?)
4. It asks for a lab report (of exactly 2 pages)
5. It asks high school students to do work over spring break.

AM

8. Apr 3, 2005

### ceptimus

6. The "ac, gl and Fl." part looks and reads (a bit) like April Fool.

9. Apr 3, 2005

### tony873004

If it's a joke, it's a cruel one. Why make students needlessly suffer through their spring break? With a joke, you should hold someone in suspense for a few minutes and then have your laugh, not needlessly cause them to chew up their spring break solving a problem that will not be graded. That crosses the line and is no longer a joke.

If I was in this class and I did the report, I'd be P***ED when I got back and found out that I stayed home one night solving this thing and it turned out to be a joke. And I'd demand a good bit of extra credit for solving it.

And a student who concludes it is a joke and returns to school to find out that it wasn't gets an F on a graded assignment. So your only option is to assume it's real.

10. Apr 3, 2005

### iambooboo

do anyone know the distance of the low moon orbit or synchronous lunar orbit? thanks for all the comments.

11. Apr 3, 2005

### tony873004

For Lunar sychronous, use this formula
$$r = (t / (2pi)) ^ {2 / 3} * (G * M) ^ {1 / 3}$$
r = distance from center of the moon
G=6.67e-11
M=mass of the moon
t = Moon's rotational period in seconds

Low lunar orbit is anything from just above the surface to a few hundred, maybe 1000 kilometers up, but not much more.

You could put your 3 satellites in the Moon's Lagrange 2, 4, & 5 points if your satellites had rockets on them to do stationkeeping burns. The Earth in a sense is lunarsychronous, so having communication platforms on the Earth might also be a solution.

12. Apr 3, 2005

### Andrew Mason

So what is the essential task that the question asks you to perform? What is the goal here? Who are these lunatics trying to communicate with? Where are they? Why would a lunar synchronous satellite be of any use here? (it would be a radius of about 87,000 km, I believe). Don't you think if the questioner was serious he/she would have addressed these things?

AM

13. Apr 3, 2005

### iambooboo

i think he wanted use to search the internet for help with physics. The teacher is alway talking about making a study group, and how he used to sneek into class rooms to do physics.