Gravitational Pull Problem

Tychu · Post by **Tychu** » 2006-09-23 03:25am

Since before time began (6 years old) I have been making a sci-fi fantasy saga. One day i will be compiling it and attempting to make a book series
You guys will be the first to have a copy

But i have one question.

If at all
How far does a satalitte of a planet (a moon) have to be from its planet that it orbits it but can have its own moon without the planet having a gravitational pull that will pull the moons moon away from it?

Ford Prefect · Post by **Ford Prefect** » 2006-09-23 06:33am

Dpends on the mass of thep lanet in question. You need to give more in the way of detail - mass of the planet, mass of the moon.

Singular Quartet · Post by **Singular Quartet** » 2006-09-23 10:40am

Ah, good old orbital mechanics... Simple answer: Mass does have something to do with it, yes, but another factor is orbit speed. The faster the orbit, the closer the moon can be to it's planet. Granted, this makes no comments about the stability of the planet (The closer together they are, the more the moon is going to effect the planet's orbit)

Force of Gravity between two objects is dictated by Gravitational constant *( (Mass of planet * Mass of moon) / distance between centers^2

As I recall, rotational force (the force you want to use to overcome the force of gravity) is something like Force = Mass * rotational acceleration, but I can never remember how to find rotational acceleration (it's been about three years since I've had to cover this topic...)

Tychu · Post by **Tychu** » 2006-09-23 11:28am

ok oops im sorry. If you notice i posted at what 3 in the morning, tired

say the planet was a gas giant like the size of Saturn or Uranus.
I always wonderd why we never really see a moon have a moon in Sci-Fi
6 suns but no moon of moons

Master of Cards · Post by **Master of Cards** » 2006-09-23 07:56pm

Tychu wrote:ok oops im sorry. If you notice i posted at what 3 in the morning, tired

say the planet was a gas giant like the size of Saturn or Uranus.
I always wonderd why we never really see a moon have a moon in Sci-Fi
6 suns but no moon of moons

Define how big you want the second moon we have sats orbiting the moon

Tychu · Post by **Tychu** » 2006-09-24 01:15am

I never heard that we have satalites orbiting the moon. Maby flyby space probes but not satatlites.

but anyway im talking about natural occuring sized chunks of rock. Say Earth was a moon of Jupiter can Earths moon orbit Earth without being pulled into Jupiter

Silver Jedi · Post by **Silver Jedi** » 2006-09-24 12:56pm

Well, it is possable. Afterall, what is earth but a 'moon' of the sun? As others have said however, it would have alot to do with the relative masses of the three bodies and their orbital speeds. If I had to guess, I'd say that speed and trajectory would be the determining factors in wether the Moon's moon would stay in orbit, and it's mass would determine it's effect (if any) on the first moon and the planet. However, there are probably people here that are much more knowlagable about the subject than me.

Winston Blake · Post by **Winston Blake** » 2006-09-26 05:35am

Hill sphere. Formulae after intro.