# Accelating a Planet

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If we took all the nuclear weapons ever made (we will just say 70,000 for the sake of it) and located them in one spot 1 mile by 1 mile

and for the sake of it built a de laval nozzle 5 miles high 1 mile wide out of unobtainium. Could we from a purely velocity postion change the orbit of earth.

Yes all the nukes are detonated at the same time

Diameter of the throat of the nozzle is 0.5 miles at an alitiude of 1.5 miles

Also as a side conversation what would be the ramifications of such a detonation.

I should mention that all the nukes are 0.2 miles away from the nozzle so the shock wave will hit the nozzle and go out like a gas

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Net thrust in this situation is zero, everything is stopped by the atmosphere before it can escape (hypervelocity shrapnel is vaporised in lower atmosphere, moving gases are stopped even quicker). To push a planet with reaction force, your exhaust has to escape Earth's gravity altogether, if it falls back, theres no net thrust. Similarly, you cant speed up Earth's rotation with a horizontal rocket - the thrust is absorbed by the atmosphere and transferred back to the ground via drag quite efficiently.

Note: on top of that, difficult to extract thrust from a shockwave as the net movement of mass is very low, its a wave, not a continuously moving block of air. When you push a wave through a "slinky", the centre of mass of the slinky stays pretty much where it is.

Ummm, do people still know what a "slinky" is?

Edited by p1t1o

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1980, ~13 000 Mt in total

Earth mass = 6*1024 kg.

13000 * 4.2*1015 / 6 * 1024 = 10-5 J/kg

Need moar nukes.

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1 minute ago, kerbiloid said:

1980, ~13 000 Mt in total

Earth mass = 6*1024 kg.

13000 * 4.2*1015 / 6 * 1024 = 10-5 J/kg

Need moar nukes.

Wow

MOAR nukes are we are already at 13 K Mt

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If you are planning on destroying the world, please at least use the appropriate metric prefix: 13000 Mt = 13 K-Mt = 13 Gt.

If you want some idea of the other effects of a large  nuclear detonation, take a look at NUKEMAP. It can only calculate up to 100 Mt, but it is still really interesting to the magnitude of effects of such a blast.

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If you could get the exhaust gases to escape Earth you could accelerate it slightly.

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Just now, cubinator said:

If you could get the exhaust gases to escape Earth you could accelerate it slightly.

Why would then need to escape earth exactly. I mean if you fire a rocket upside down on earth it does move it earth (barely) but still

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3 minutes ago, Cheif Operations Director said:

Why would then need to escape earth exactly. I mean if you fire a rocket upside down on earth it does move it earth (barely) but still

Reread the 1st response to you question. The same reason you cannot lift yourself off the ground by pulling up on your shoes.

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7 minutes ago, Cheif Operations Director said:

Why would then need to escape earth exactly. I mean if you fire a rocket upside down on earth it does move it earth (barely) but still

Firing a rocket to accelerate something is like throwing a rock while on a skateboard. If you throw the rock, you will accelerate in the opposite direction. But if you move the rock as if you were to throw it, then pull it back towards you with your arms, your net change in velocity will be zero. In this scenario, Earth's atmosphere and gravity are like the force of your arm pulling the rock back after you throw it. In order for Earth to accelerate, the reaction mass from the nukes has to get out of the atmosphere and out of Earth's gravity well, just like the rock which has to leave your arms, or else the two will be pulled toward each other equally and Earth's net acceleration will be zero.

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41 minutes ago, Cheif Operations Director said:

Why would then need to escape earth exactly. I mean if you fire a rocket upside down on earth it does move it earth (barely) but still

No a rocket fired upside down wont produce any thrust either. Gas experiences drag just like solid objects do, high velocity exhaust is slowed very quickly in air.

So lets remove the atmosphere and do it on an airless Earth.

Earths escape velocity is 11.2km/s - that is the speed you need to have at the Earths surface, to escape the influence of its gravity.

Average kerolox exhaust velocity is on the order of 5-6km/s, so even in vacuum, the exhaust will reach some altitude, and fall back to Earth.

As difficult to accept as it seems, it is the gravity of the exhaust products acting on the Earth that negates the thrust.

Exactly the same as when you jump of the ground a little. On takeoff, you actually do exert thrust on the Earth, and it moves a little (less than the width of a proton IIRC). When you fall back to the Earth, the Earth actually rises slightly to meet you, that is your gravity acting on the Earth to negate the thrust you imparted. Does it seem like the force exerted by your legs is much much greater than your gravitational influence? It is, but your gravity acts on the entire mass of the Earth, whereas your legs are only accelerating a few kg.

Its weird but the maths adds up.

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A rocket engine requires mass to use as a reaction medium. Simply detonating every nuke in a large combustion chamber would only throw the mass in that chamber. Even accelerated to near light speed that amount would be insignificant compared to the mass of the planet.

To change the velocity of the planet by 1km/s, you'd need to throw about 20,000 trillion tonnes of material off at the speed of light.

A typical ion thruster has an exhaust velocity in the 20-50km/s range. So let's assume the exhaust leaves Earth's gravity well at 30,000m/s because that's a fraction of the speed of light and makes things easier. The mass required just increased another 10,000 times. 200 quintillion tonnes required.

That's about 40 million times the mass of the entire atmosphere by the way. At that scale I'd expect the rocket exhaust to be wide in proportion to the thickness of the atmosphere. Basically the portion of the atmosphere over the rocket exhaust would get blasted off into space and the drag around the exhaust perimeter would be negligible.

The energy required would be 1.6e32J. 1 Megaton is roughly 4e15J. 4e16 Megatons of nuke required.

We have approximately 6400 Megatons of nuke. Their combined yield of channeled into a perfectly efficient ion thruster could alter the velocity of earth by 0.16nm/s.

Or not enough that anyone would notice.

I may have misplaced a few factors of a thousand here or there, so it could be worth checking.

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9 hours ago, p1t1o said:

Ummm, do people still know what a "slinky" is?

Also, this project would be deadly, because nuclear stuff is deadly, so are explosions, and if we somehow survived that, then the new orbit would be deaddlly,.

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3 hours ago, Nightside said:

please at least use the appropriate metric prefix: 13000 Mt = 13 K-Mt = 13 Gt.

Prefixes are arbitrary, so both notations are correct. But Mt is used more widely in this context.

Quote

If you are planning on destroying the world

Vice versa, I was trying to show that our efforts are insufficient.

3 hours ago, Nightside said:

If you want some idea of the other effects of a large  nuclear detonation, take a look at NUKEMAP. It can only calculate up to 100 Mt, but it is still really interesting to the magnitude of effects of such a blast.

Nukemap is just a toy.
Alas, forum rules about copyrights restrict me in suggesting of a set of pdfs and an old DOS program with more complex math model of weapon effects and warplan.

But 10-5 J/kg is in any case too weak to significantly effect the Earth orbit.

Edited by kerbiloid

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if you want to accelerate a planet, i would reccomend A LOT of gravity tractors

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Spoiler

Like this one.
(Pay attention to the anchor. It holds the Earth attached.)

Edited by kerbiloid

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2 hours ago, insert_name said:

if you want to accelerate a planet, i would reccomend A LOT of gravity tractors

Or a moon

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6 hours ago, Nightside said:

The same reason you cannot lift yourself off the ground by pulling up on your shoes. ﻿

The hell I can't.

But I guess it does require a staircase and a helmet.

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If you want to move the earth, it would be simpler to just build a open ended tube filled with vacuum a couple of kilometers across that goes all the way to space, then use thousands of coilguns to fire a significant fraction of the earth's mass at greater than escape velocity. Of course, you can only run it for a little bit of each day.

Side effects:

Depletion of fossil fuel reserves assuming you don't build a massive amount of solar first.

Bankruptcy of whoever attempted this.

Likely massive effects on the ecosphere from: disruption of wind patterns, massive amounts of waste heat, destabilized crust where ever you're taking your rock from.

Accelerated global warming if you're using fossil fuels, followed by either extreme global cooling or heating as the earth's new orbit takes it either further away from or to closer to the sun.

Bottom line: Why did you do this?

You could also build a Dyson swarm and power a laser with it that you aim at a mirrored band orbiting earth.

Or better yet just build a stellar engine and use the sun to pull earth along with it.

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If you have that much nuke, I think the easiest way woulf be to split a chunk of Earth' crust off into space.

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Make a small blackhole near/above the Earth surface and accelerate particles throwing them out of the Earth gravity, This will be a jet.

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2 hours ago, kerbiloid said:

Make a small blackhole near/above the Earth surface and accelerate particles throwing them out of the Earth gravity, This will be a jet.

Yeah, just like throwing stuff with rocket engines.

Except you get to be ripped apart by tidal forces.

And the black hole will pull earth around it.

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1 minute ago, Xd the great said:

Except you get to be ripped apart by tidal forces.

If the hole will be enough small, the process of ripping can last for eons.

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15 hours ago, kerbiloid said:

Alas, forum rules about copyrights restrict me in suggesting of a set of pdfs and an old DOS program with more complex math model of weapon effects and warplan.

No reason I cant post this link, do you mean these?:

For estimating fireball size, thermal effects and shockwave strength, Nukemap is actually pretty good, it is based on the mathematics shown in the famous document  "The Effects of nuclear Weapons" which I presume is one of the documents you refer to (and if it isnt, it should be). If you ask me the weakest part of it is the googlemaps API because it takes a 2D calculated estimate and plops it down in the real world, whereas the true results would be nowhere near as neat.

Fact is, things like moisture content of the air (variable in 3D and over time), the direction the wind is blowing (variable in 3D and over time), temperature (varia...you see where Im going) amongst other factors, not to mention the topography of the land, can make very significant changes to the effects of a particular detonation and just try and calculate that!

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10 minutes ago, p1t1o said:

do you mean these?:

Yes, this program.
But NRDC pdfs which are its description (the last one of them) are now not for free. (Maybe never were, but I didn't know.)
(Though its script files are very readable, too.)

10 minutes ago, p1t1o said:

fireball size

Simplified formulas (from another source)
Air blast: r = 52 Y0.4, surface blast r = 68 Y0.4. Yield in kt, radius in m.

Edited by kerbiloid

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New sum!

It's estimated that there is about 100 trillion tonnes of Uranium in earth's crust.

Of that, approx 0.72% is fissionable U235.

That's approx 720 trillion kg of fissionable U235.

U235 releases 83 trillion joules per kg when fissioned.

So all the uranium in earth's crust could produce about 60,000 trillion trillion joules.

Earth weighs about 6 trillion trillion kg, therefore we've released about 10,000J/kg.

1kg with a kinetic energy of 10,000J would be travelling at 140m/s, so the velocity of earth powered by uranium fission can't exceed this.

Therefore NERVAs can't significantly move the earth.

Hydrogen bombs and nuclear fusion is required for anything greater.

Edited by RCgothic

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