Question Moving planets with rocket engines; is it possible?

[Andy44]

Even if the exhaust gets exoatmospheric and reaches escape velocity, it will be fighting gravity the whole way out. By the time it reaches the Earth's SOI boundary it will have lost so much velocity since leaving the nozzle that you are killing yourself in losses for very little gain.

 

[James.Denholm]

Maybe if the craft was large enough that the point of exhaust, for want of a better term, was outside the SOI boundary... Like a really, really big skyscraper with a rocket engine on top.

 

[Linguofreak]

On a mailing list I'm on, someone mentioned another detail about Jupiter hitting the Sun. It takes a long time (around 10 million years or so) for light to get from the core of the sun to the surface, because a photon will head in one direction for a bit, then hit a nucleus or electron and be absorbed, and then a bit later the particle it hit will emit another photon in another direction. So light basically random-walks its way to the surface, and spends a long time doing so. This means that about ten million years or so of the Sun's output is still working it's way towards the surface. Jupiter hitting the sun would stir up hot gas from deeper in, which would release some of the energy that's making it's way upwards. That would cause an even greater brightening. But still, the sun is really, really massive and even that would just be a temporary shaking up. Nothing near what you'd need to actually take the sun apart.

 

[T.Neo]

If the tides are speeding the Moon up and flinging it out, what about putting an asteroid in Earth orbit (yes, I know, risky), and flying it behind the Moon every so often, to lower it's orbit?

Would VASIMR type engines be able to give Phobos a boost?

 

[RisingFury]

You can't just expect to slow the Moon down by putting an asteroid or similar sized rock behind it. Our Moon is 5th largest Moon in the solar system if I remember correctly... and it's much larger then most asteroids, including both Mars' moons.

If you wanted to lower the Moon's orbit, you'd have to slam Phobos into it with quite a significant velocity... but even that would produce an elliptical orbit, which could bring up a hell of a lot of problems for Earth.

And to answer your question about VASMIR: No. No rocket engine, no propulsion system... nothing is anywhere near powerful enough to "move" the Moon, or Phobos out of Mars's orbit, for that matter. Phobos is significantly lighter... but still 10^16 kg.

And before someone asks about nuclear weapons, I doubt that'd work either. The energy from the reaction has to go somewhere, but since there is no air or atmosphere, you can't expect a blast wave to "push" the Moon.

 

[SlyCoopersButt]

The fact all that energy has to go somewhere is exactly why nuclear bombs can move low mass objects in space. Instead of moving air, The energy blast will move the object directly since you just cut out the atmospheric middleman. Project Orion would have used such blasts for Delta V. Of course I think you'd need anti-matter bombs before you can even think about moving anything larger than a few thousand meters.

 

[sputnik]

According to the documentation, clbkFastEphemeris is called on each simulation step.

YMMV, though--I've never written a planet DLL.

Me neither. But thanks for the pointer; I'd missed that one, and thought there was NOTHING that got called once a timestep. Thanks!

 

[T.Neo]

You can't just expect to slow the Moon down by putting an asteroid or similar sized rock behind it. Our Moon is 5th largest Moon in the solar system if I remember correctly... and it's much larger then most asteroids, including both Mars' moons.

And to answer your question about VASMIR: No. No rocket engine, no propulsion system... nothing is anywhere near powerful enough to "move" the Moon, or Phobos out of Mars's orbit, for that matter. Phobos is significantly lighter... but still 10^16 kg.

1. If I came across saying behind it permanantly (i.e. at one of the lagrange points), I said carefully orchestrated flybys which would, over time, slow the outward drift of the Moon.

2. Only to slow the gradual lowering of Phobos, Or is this not posible either?

I

 

[Talon1]

Okay...... New question, is it possible to make a planet sized ship that's land-able?
(sorry for missing anyone's posts, but I'm either, too lazy to read the posts or my brain keeps shutting down)

 

[Linguofreak]

If the tides are speeding the Moon up and flinging it out, what about putting an asteroid in Earth orbit (yes, I know, risky), and flying it behind the Moon every so often, to lower it's orbit?

There are probably ways that you could do it, if you were willing to wait long enough. If you're willing to operate on timescales of tens or hundreds of thousands of years, you could probably do a fair bit. The problem is, why? It will be quite a few million years before the moon's tidal recession moves it out far enough to have much effect here on Earth. By that time humanity will probably be gone from other causes.

Would VASIMR type engines be able to give Phobos a boost?

If you're willing to wait long enough, and put enough VASIMRs on it, probably. But once again, why?


-----Post Added-----

And to answer your question about VASMIR: No. No rocket engine, no propulsion system... nothing is anywhere near powerful enough to "move" the Moon, or Phobos out of Mars's orbit, for that matter. Phobos is significantly lighter... but still 10^16 kg.

If you're willing to wait long enough, and devote enough resources, you could probably move Phobos by a fairly significant amount. The moon is probably a bit far fetched, though. The question in either case is still "why?" The resources could be put to far better use.

 

[T.Neo]

The problem is, why? It will be quite a few million years before the moon's tidal recession moves it out far enough to have much effect here on Earth. By that time humanity will probably be gone from other causes.

If we are around by then, we will either have forgotten about the Earth entirly, or turned it into nature reserve. :lol:
If we are around and do care, we will certainly have the technology to do something about it. Maybe, by then, the Earth will be ruled by a race of superintelligent turtles. Don't rule out all possibilities.

If you're willing to wait long enough, and put enough VASIMRs on it, probably. But once again, why?

If we started to terraform Mars, or thicken the atmosphere, this may increase drag on Phobos, causing it to crash sooner. Also, if Phobos were to crash onto Mars while it was inhabited, that would be bad. Moving Phobos could also teach us how to deflect asteroids from hitting Earth.

The question in either case is still "why?" The resources could be put to far better use.

What uses?

 

[andysim]

Get some crazy new elastic bungey ropes and attach one end to the surface of earth and the other to a passing comet. :rofl::rofl:



Weeeeee!!

 

[Kaito]

Okay...... New question, is it possible to make a planet sized ship that's land-able?
(sorry for missing anyone's posts, but I'm either, too lazy to read the posts or my brain keeps shutting down)

I'm sure it is

Get some crazy new elastic bungey ropes and attach one end to the surface of earth and the other to a passing comet. :rofl::rofl:

Weeeeee!!

Oh yes, I'll just call the company:
"Hello, this is Bungee express, how may I help you?"
"Yes, I'd like 500 light years of super bungee, please"
"Okay, cash or credit"
"Cash"
"Your bungee will be ready in 24 hours. Please pay $14.95, unless you'd like it to be shipped directly to your house"

 

[Frogisis]

Physics is all just numbers - If you can get the numbers high enough, you can basically do whatever you want. But if you belonged to a civilization where that was possible, you probably wouldn't want to do whatever it was you were planning.