stopping the moon from escaping the orbit of the Earth?

Question

I am writing a story that takes place in the future and i was wondering how to stop the moon from escaping the orbit of the Earth via mining material from the asteroid belt and bringing it to the moon. What are the mathamatical equations needed for such a feat?

example.-- how many cubic tons would it take to halt the moon from traveling any farther from the Earth and stabilizing in a fixed orbit and yet not having the gravitational pull to send it hurtling back at Earth and killing all life as we know it?

Answer 1

Very lsightly altering its velocity woudl do it. You would have to put a massive thruster on it to slow it down a little.

Affecting its mass will do nothing- changing the mass of the Earth would, but orbital velocity is independent of the mass of the satellite (odd, but true).

Answer 2

One way would be to slow the Earth's rotation rate so that one face of the Earth always faced the Moon.

In fact, that's the reason the Moon is moving further away from the Earth. The Moon's pull on the Earth causes tidal friction which slows down the rate of the Earth's rotation. The overall angular momentum of the Earth-Moon system has to stay constant since it's the Moon acting on the Earth's rotation instead of an outside force. The Moon's orbit expands to absorb the angular momentum lost as the Earth slows its rotation rate.

Of course, something had to expand the orbit of the Moon. Conservation of angular momentum is an observation, not a cause. Thanks to an equal and opposite reaction, the Moon speeds up as it slows the Earth's rotation rate down (ie - the Moon is equally attracted to the tides as the water in the tides are attracted to the Moon). Speeding up the Moon adds energy to the Moon's orbit and makes it larger.

Of course, if conservation of angular momentum is going to apply, the force slowing down the Earth's rotation rate can't come from outside the Earth-Moon system. You would have to do something like increase the amount of water that moved with each tide.

Thinking about it, zaphod's right. It should be the evil scientist trying to stop the Moon from moving any further from the Earth, since you'd basically be creating natural disasters in the way of super high tides to slow the Earth's rotation. Plus the slower rotation would create some unbearably hot days and some unbearably cold nights.

Answer 3

Sorry. Altering the MASS of the moon would not affect its orbit. You would need to alter its angular velocity or the radius of the orbit. And a large change in either of those would be required to make the moon leave orbit.

As there is no existing cause for the moon to escape its orbit, there is no basis for your story, anyway. The moon's orbit expands by a few inches per year, which means a noticeable change will require millions of years. The sun will die and both the earth and the moon will be destroyed long before the moon's orbit would become significantly larger.

Good luck finding another story idea.

Answer 4

aviophage is right. the moon is moving away, but oh so slowly. perhaps a new direction for your story would be that over mining the moon would change its orbit for the worse, and we poor saps never saw it coming. so now we must fix the NEW problem, not that the moon is going away, but now its in danger of deteriorating its orbit and "killing all life as we know it".

however, any change in lunar mass would begin to have noticeable effects on earths ocean tides. this would disrupt huge ecosystems and effect shorelines, shipping routes, world economy, etc. sounds like a disaster already.

for more science, check out :

http://en.wikipedia.org/wiki/Moon_orbit

Answer 5

is the Moon going somewhere?

hey, i mean, if i was staying over at your house, sleeping on your sofa and told you i was gonna leave (yeah!)... one inch a year...

wouldnt you think I wasn't really leaving?