Is It Time to Reconsider Anti-Nuclear Laws?

[malawi_glenn]

Hi there nuclear lovers!

Myself lives in sweden, and here it is illegal to do research in nuclear power (experimental), and to build new reactors, research in new fissible nuclides and so on.

And also barley no money is invested in the reactors we do have, so they are not in good shape.. So it has become a very bad "spiral" in our country regarding nuclear power.

Do you know if any other countries have this "twisted" law against better and more safe nuclear power?

My self think it is the same as forbidding research in better medicines. Many people get killed every year due to this, that the medicines have bad effects on some etc...but not one single person has been killed due to nuclear power in our country.

 

[engineroom]

Check out the N laws of New Zealand. There is a very stong stand in that country against N weapons and many of the same sentiments exist about N power.

I'm not sure if N power is outlawed or just that the compliance costs would be that high its not worth it.

Funny considering Lord Rutherford was from New Zealand.

 

[Morbius]

Check out the N laws of New Zealand. There is a very stong stand in that country against N weapons and many of the same sentiments exist about N power.

I'm not sure if N power is outlawed or just that the compliance costs would be that high its not worth it.

Funny considering Lord Rutherford was from New Zealand.

engineroom,

Yes - New Zealand and certain ports in Japan don't allow nuclear reactors in their
jurisdiction. This creates a bit of a problem for the US Navy because the vast majority
of our aircraft carriers are nuclear powered.

Recently, when Admiral Mullens, the current Chief of Naval Operations; was named to
be the next Chairman of the Joint Chiefs of Staff; C-SPAN ran the video of the Senate
confirmation hearings from a year ago when Mullens was named CNO.

There was concern by Sen Nelson of Florida about the aircraft carrier U.SS. John F.
Kenndedy. Evidently the Kennedy was in need of some refurbishment, and it was
stated that the Navy keeps the Kennedy around so that they have a conventionally
powered aircraft carrier in case they need to station a carrier in a port with a "no-nuke"
policy.

Dr. Gregory Greenman
Physicist

 

[Andrew Mason]

Making laws based on imperfect, incomplete or incorrect information can be very destructive. Good intentions are irrelevant. The Swedish nuclear laws may be a case in point.

The world prohibition against all use of DDT may have been another. DDT is still the most effective means of controlling mosquitos and the malaria they carry. A reasonable program for careful use of DDT might have saved millions of lives. Millions died directly due to the DDT ban. We are only now realizing that and reintroducing DDT in a measured and careful manner.

The bottom line: if you oppose something, you have an obligation to understand it thoroughly. If you do, you will rarely advocate that a complete ban is the best solution. If something is not economic, you don't have to pass a law to ban it.

AM

 

[StuMyers]

I've always been a very enthusiastic supporter of nuclear power, but I have to admit to a certain degree of apprehension regarding naval reactors. Bottom line is, they're classified and I don't know how they work. I read that they are PWR designed, but before I let them into my harbor I'd want to study the details.

 

[engineroom]

engineroom,

Yes - New Zealand and certain ports in Japan don't allow nuclear reactors in their
jurisdiction. This creates a bit of a problem for the US Navy because the vast majority
of our aircraft carriers are nuclear powered.

Recently, when Admiral Mullens, the current Chief of Naval Operations; was named to
be the next Chairman of the Joint Chiefs of Staff; C-SPAN ran the video of the Senate
confirmation hearings from a year ago when Mullens was named CNO.

There was concern by Sen Nelson of Florida about the aircraft carrier U.SS. John F.
Kenndedy. Evidently the Kennedy was in need of some refurbishment, and it was
stated that the Navy keeps the Kennedy around so that they have a conventionally
powered aircraft carrier in case they need to station a carrier in a port with a "no-nuke"
policy.

Dr. Gregory Greenman
Physicist

Actually New Zealand banned any ship equipped with N weapons but this has extended to N power and ships carring N waste. As the US navy have a neither confirm or deny policy concerning whether their ships have N weapons on board or not they can't enter New Zealand waters. A conventional powered US navy ship that is declared as not being N weapons capabity is welcome to enter a NZ port.

After the French government committed an act of international terrorism in a New Zealand port by bombing the Rainbow Warrior vessel the public opinion of New Zealand became entrenched towards a No Nuclear viewpoint.

New Zealand has been very consistant in its approach to Nuclear weapons and consisitly objects and protects anytime a test is (was) conducted. About 5 years ago a shippment of N watse was moved from France to Japan and this shipment was not allowed in New Zealand waters, I think the NZ navy shadowed the ship while it was close to NZ waters to be sure they stayed out.

It is fair to say that the antinuclear laws in New Zealnd are more a philispocial ideal than a technical problem.

 

[engineroom]

Making laws based on imperfect, incomplete or incorrect information can be very destructive. Good intentions are irrelevant. The Swedish nuclear laws may be a case in point.
AM

Just because one can should one?? I don't mean the law by that statement.

Swedish & New Zealand nuclear laws are reflecting strongly held opinions of the majority of the population in those counties - demoracy in action. Laws against N power, N waste & N weapons are never going to be bassed on technical reasons but moral reasons. These laws are quite different to laws that place technical paramenters and restictions on the how or where. These laws ask and challenge the fundamental why?

 

[StuMyers]

How can producing electricity be a moral issue?

It seems that the problem is an entire generation whose first word association after the word 'nuclear' is the word 'bomb'.

Maybe the NucE's need a re-branding? Call it plasma-power or something, rather than next-gen nuclear. Seems to be working for NASA... nuclear pulse propulsion is re-branded external pulsed plasma propulsion. No sign of the words 'bomb' or 'nuclear'.

 

[Azael]

Just because one can should one?? I don't mean the law by that statement.

Swedish & New Zealand nuclear laws are reflecting strongly held opinions of the majority of the population in those counties - demoracy in action. Laws against N power, N waste & N weapons are never going to be bassed on technical reasons but moral reasons. These laws are quite different to laws that place technical paramenters and restictions on the how or where. These laws ask and challenge the fundamental why?

Not quite. In sweden the laws came into place after a referendum where you could vote no to nuclear power in three different ways. But there was no wat to vote for more nuclear power.

The options was.

1. Keep it as long as it is needed until it can be replaced by renewables. Finish the reactors currently beeing built, prohibit building new ones.
2. Was basicly the same as 1 except some minor twists.
3. Shut down all reactors withint 10 years.

The results where
1. 18.9%
2. 39.1%
3. 38.7%

Obviously the referendum was a big pile of ****. Atleast a overwhelming majority wanted to keep the existing reactors. But there is no telling how many wanted more nuclear power.

Today 31% wants to build new reactors, 48% wants to keep the existing ones as long as possible and 19% wants to shut it all down.

The reason things haven't changed in sweden is because 2 small parties are keeping the entire energy policy in sweden hostage. The big left wing party(social democrats) are not quite big enough to get there own majority, so they have to cooperate with the communist party and the green party. But the commies and the greens want to get rid of nuclear power. The greens and commies togheter get around 10% of the votes.

On the right side 3 of the parties want to build more nuclear power while the fourth has strong roots in the anti nuclear movement. The fourth party gets around 7-8% of the votes.

So a 18 % minority is keeping sweden stuck on a nuclear phase out that has no public support anymore. Doesnt matter if right or left wins elections, it the same bull**** on both sides.

On the bright side it is no longer illegal to fund research into new reactors(previously only waste management research was legal and that included transmutation). Its also no longer illegal to make a economic comparison betwen nuclear and other energy sources. So all the brainwashing laws are gone.

 

[malawi_glenn]

Azael:

Indeed, much have been better in our country, but still far away from what many other countries have.

Good post!

 

[StuMyers]

Not quite. In sweden the laws came into place after a referendum where you could vote no to nuclear power in three different ways. But there was no wat to vote for more nuclear power.

The options was.

1. Keep it as long as it is needed until it can be replaced by renewables. Finish the reactors currently beeing built, prohibit building new ones.
2. Was basicly the same as 1 except some minor twists.
3. Shut down all reactors withint 10 years.

Number one is kind of interesting. Exactly what makes a 'renewable'? 5 billion year supply? 600 million? 500,000? From what I understand, there is a nearly limitless (on human life scales) supply of uranium and thorium.

 

[Azael]

Number one is kind of interesting. Exactly what makes a 'renewable'? 5 billion year supply? 600 million? 500,000? From what I understand, there is a nearly limitless (on human life scales) supply of uranium and thorium.

It seems like it is up to the green fanatics to decide what is renewable or not Imo splitting energy production into renewable and non renewable is utterly pointless. Anything lasting more than 200 years should be sufficient. The whole concept of renewable is laughable since it hides what's most important. How much polutants the energy source release into the environment. I hate to se biomass burning counted as renewable energy despite its negative environmental and health consequenses.

Offcourse the greens are trying there best to fool the public that uranium will run out within 50 years. I don't know how many debate articles I have seen in swedish newspapers where the biggest swedish environmental group is pushing that message. Getting a rebuttal printed in same papers are all but easy.

 

[Morbius]

It is fair to say that the antinuclear laws in New Zealnd are more a philispocial ideal than a technical problem.

engineroom,

It's neither a "technical problem", or "philosophical ideal"; it's just plain popular
ignorance and stupidity!

Hey, if New Zealand doesn't want to allow a Nimitz carrier into their ports - it's their loss.

The US Navy has tried to be accomodating - that's one of the reasons for keeping the
conventionally powered U.S.S. John F. Kennedy. It is well known that the USA has
nuclear weapons in its inventories that will fit on aircraft that the Kennedy supports.

However, I believe that the US Navy has stated that surface ships no longer routinely
carry nuclear weapons. The only Navy vessels that routinely carry nuclear weapons
are the Trident subs. The Navy ackowledges that the subs have the Trident missiles;
they just decline to confirm whether those missiles actually have nuclear warheads
installed in them. [ Like who doesn't know it - but that's the policy ]

Since the Kennedy could carry nuclear weapons, but routinely doesn't - do you know
if New Zealand would welcome a visit by the Kennedy?

The USA doesn't owe New Zealand anything. Most nations welcome the
US Armed Forces because that puts them under the USA's military "umbrella".

Do you know if the New Zealanders are so ignorant as to also exclude radio-pharmeceuticals?

Dr. Gregory Greenman
Physicist

 

[Morbius]

These laws are quite different to laws that place technical paramenters and restictions on the how or where. These laws ask and challenge the fundamental why?

engineroom,

I would bet that if the former USSR had designs on New Zealand; they wouldn't have had
ANY PROBLEM with the USA showing up with nuclear arsenal in hand.

The USA was the only power that could force the then expansionistic USSR to back down,
and stay in line.

The present day Russia retains and maintains the nuclear stockpile of their former
incarnation - the USSR. There are other powers out there with nuclear weapons also.

As a counter to that - there stands the USA - so nuclear armed expansionistic powers
can not use their nuclear arsenals to advantage.

Dr. Gregory Greenman
Physicist

 

[Morbius]

Obviously the referendum was a big pile of ****.

Azael,

Yes - you can tell that from the way the referendum was constructed - they give the
pro-nukes two options in order to spilt their votes. That way a minority position can
win.

It's no different than having an election with 3 candidates - two of which are of the same
political philosophy. Even if a majority of voters are of one political opinion - they split
their votes between the two choices - and the minority view will win because they have
only one choice.

You can truly tell that that referendum was authored by some political shills that wanted
to foist their view on the populace - so they "rigged" the election in the manner I describe
above.

Some demonstration of Democracy. NOT!

Dr. Gregory Greenman
Physicist

 

[Morbius]

Number one is kind of interesting. Exactly what makes a 'renewable'? 5 billion year supply? 600 million? 500,000? From what I understand, there is a nearly limitless (on human life scales) supply of uranium and thorium.

StuMyers,

There's enough to last a VERY LONG time.

Long before we run out of fission fuel; scientists will have mastered nuclear fusion.

Then 1 out of every 6,000 or 7,000 atoms of hydrogen in the ocean will be nuclear fusion
fuel. That's an awful lot of energy that could carry the world until the Sun becomes a
red giant star and incinerates the Earth.

That's another thing - solar and wind don't offer our species the ability to escape the
certain destruction when the sun becomes a red giant. Nuclear power would be our
only hope for mankind to survive into the indefinite future.

Dr. Gregory Greenman
Physicist

 

[malawi_glenn]

StuMyers,

There's enough to last a VERY LONG time.

Long before we run out of fission fuel; scientists will have mastered nuclear fusion.

Then 1 out of every 6,000 or 7,000 atoms of hydrogen in the ocean will be nuclear fusion
fuel. That's an awful lot of energy that could carry the world until the Sun becomes a
red giant star and incinerates the Earth.

That's another thing - solar and wind don't offer our species the ability to escape the
certain destruction when the sun becomes a red giant. Nuclear power would be our
only hope for mankind to survive into the indefinite future.

Dr. Gregory Greenman
Physicist

And nuclear bombs will protect us from asteriods :) [from Bruce Willis - Armageddon]

 

[russ_watters]

Laws against N power, N waste & N weapons are never going to be bassed on technical reasons but moral reasons. These laws are quite different to laws that place technical paramenters and restictions on the how or where. These laws ask and challenge the fundamental why?

How can producing electricity be a moral issue?

This is the engineering forum, but I would say it is quite clearly morally wrong to subject your populace to pollution, war, and even higher prices based on an irrational fear of the unknown. Killing people because you don't understand the alternatives should not be morally acceptable.

 

[Morbius]

And nuclear bombs will protect us from asteriods [from Bruce Willis - Armageddon]

malawi_glenn,

Yes - actually if the orbit of the asteroid is eccentric enough so that we won't have
a large lead time - a nuclear bomb is the ONLY thing that might save us.

If the orbit of the asteroid is such that it is near by and we determine that it is going to
hit many, many orbits in the future - and hence many years in the future; then there are
a number of technologies that can be employed; because we have many, many years
to give the asteroid a gentle push.

However, if an asteroid comes screaming out of the Ort Cloud beyond the orbit of Pluto;
and this is the first we see it, and it is going to impact the Earth on THIS orbit - then
we don't have many years to give it a gentle push. We have to give it a BIG push NOW!

We have to provide the ENERGY that is needed to put this asteroid into a different orbit.

If it is a big asteroid, what is the one thing that can carry a LOT of energy in a package
that is light enough for us to send into space? A nuclear bomb!

You also have to understand HOW a nuclear bomb is used. Don't listen to the idiots
in the media that say "Oh - nuclear bomb - you're going to blow it up and that's going
to make matters worse". Those people are IDIOTS!

The idea with a nuclear bomb is you want to PUSH the asteroid into a new orbit; just like
the rockets and gravity tractors. You explode the bomb NEAR the asteroid. The
radiation from the bomb ablates the surface and pushes the asteroid. The push will
work even if the asteroid is a "rubble pile" because all the pieces are irradiated. [ You
can't push on a "rubble pile" with a rocket that "docks" with the asteroid.]

So YES - nuclear weapons may be our only hope!

Let's just hope that the asteroid is not too big for a nuke to push!

Dr. Gregory Greenman
Physicist

 

[Andrew Mason]

However, if an asteroid comes screaming out of the Ort Cloud beyond the orbit of Pluto; and this is the first we see it, and it is going to impact the Earth on THIS orbit - then we don't have many years to give it a gentle push. We have to give it a BIG push NOW!

We have to provide the ENERGY that is needed to put this asteroid into a different orbit.

If it is a big asteroid, what is the one thing that can carry a LOT of energy in a package that is light enough for us to send into space? A nuclear bomb!

You also have to understand HOW a nuclear bomb is used. Don't listen to the idiots in the media that say "Oh - nuclear bomb - you're going to blow it up and that's going to make matters worse". Those people are IDIOTS!

The idea with a nuclear bomb is you want to PUSH the asteroid into a new orbit; just like the rockets and gravity tractors. You explode the bomb NEAR the asteroid. The radiation from the bomb ablates the surface and pushes the asteroid. The push will work even if the asteroid is a "rubble pile" because all the pieces are irradiated. [ You can't push on a "rubble pile" with a rocket that "docks" with the asteroid.]

So YES - nuclear weapons may be our only hope!

Let's just hope that the asteroid is not too big for a nuke to push!

Interesting possibility.

Here is a quick calculation to see if it is possible:

Let's assume that an asteroid is about 1 km in radius and has the density of iron. I calculate that it would have a mass of about 3x10^13 kg. (4x10^9 m^3 at 8000 kg/m^3).

Let's also suppose that it is moving toward the Earth at a speed of 25 km/sec (2.5x10^6 m/sec)

In order to move it an Earth radius (6x10^6 m) from a path heading for the centre of the earth, at a distance from the Earth of 2.5 lunar orbits (10^12 m), you would have to move it that far in 10^12/2.5x10^6 seconds = 4x10^5 seconds. So you would have to make it move at an average speed (perpendicular to its path) of 6x10^6/4x10^5 = 15 m/sec.

That means imparting an energy of .5mv^2 = .5*3x10^13*(15)^2 = 3*10^15 Joules.

Now, assuming that a nuclear explosion is 1% efficient in converting nuclear energy into actual kinetic energy of the asterioid, you would need a bomb that produced on the order of 3x10^17 Joules of energy. Considering that the bomb dropped on Hiroshima released about 5.2 x 10^13 Joules of energy, you would need a bomb roughly 10,000 times as powerful to move the asteroid.

I hope my calculation is wrong, but I am afraid that even nuclear bombs might not do the trick.

AM

 

[Morbius]

.
Now, assuming that a nuclear explosion is 1% efficient in converting nuclear energy into actual kinetic energy of the asterioid, you would need a bomb that produced on the order of 3x10^17 Joules of energy. Considering that the bomb dropped on Hiroshima released about 5.2 x 10^13 Joules of energy, you would need a bomb roughly 10,000 times as powerful to move the asteroid.

I hope my calculation is wrong, but I am afraid that even nuclear bombs might not do the trick.

Andrew,

A 1 Megaton H-bomb puts out an energy of 4.186 x 10^15 Joules.

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

You are low on your estimate of the energy conversion. The asteroid is going to
subtend a certain solid angle with respect to the bomb - and any radiation from the
bomb that is in that solid angle is going to be absorbed by the asteriod. That energy
is going to end up as "blow-off".

In any case, if a nuclear weapon doesn't have enough energy to deflect the asteroid;
nothing else is going to have enough energy.

Dr. Gregory Greenman
Physicist

 

[Andrew Mason]

Andrew,

A 1 Megaton H-bomb puts out an energy of 4.186 x 10^15 Joules.

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

You are low on your estimate of the energy conversion.

Actually, I think I am high. Most of the energy will be in the form of heat. Assuming that it is reasonably efficient in converting heat into kinetic energy of the bomb mass - 50%, and half the bomb mass strikes the asteroid (the other half has to blast off into space), that means that 1/4 of the energy of the bomb is converted into kinetic energy of matter striking the asteroid.

If the bomb weighs 4 tonnes, then 1 tonne of matter containing 10^15 joules of kinetic energy strikes the asteroid. This means the asteroid received an impluse of:

mv = m\sqrt{\frac{2KE}{m}} = M\Delta V (M = mass of asteroid; V = speed of asteroid)

\Delta V = \frac{m}{M}\sqrt{\frac{2KE}{m}} = \frac{10^3}{3x10^{13}}\sqrt{\frac{2x10^{15}}{{10^3}}} = 3x10^{-10}*1.4x10^6 =4.2\times 10^{-4} \text{m/sec.}

It will barely move the asteroid at all.

AM

 

[Morbius]

Actually, I think I am high. Most of the energy will be in the form of heat.

Andrew,

You have to be careful which formulas you use. A lot of the formulas from the
weapons effects handbooks tell you how much heat is put out by a bomb exploding
here on Earth.

However, a lot of that heat actually started life as radiation. It was transformed into
heat as a result of interactions with the air.

However, in space; there is no air - so the radiation component will be higher than
what is usually quoted.

Dr. Gregory Greenman
Physicist

 

[Morbius]

If the bomb weighs 4 tonnes, then 1 tonne of matter containing 10^15 joules of kinetic energy strikes the asteroid. This means the asteroid received an impluse of:...

Andrew,

The mechanism is not the bomb mass hitting the asteroid.

The mechanism is that the radiation from the bomb ablates the material of the
asteroid itself, and the blowoff of that material is what gives the asteroid the
impulse.

Dr. Gregory Greenman
Physicist

 

[Morbius]

It will barely move the asteroid at all.

Andrew,

Depending on when and where you alter the asteroids orbit; even a very small change
in velocity can alter the orbit enough to miss the Earth.

Dr. Gregory Greenman
Physicist

 

[Andrew Mason]

Andrew,

The mechanism is not the bomb mass hitting the asteroid.

The mechanism is that the radiation from the bomb ablates the material of the
asteroid itself, and the blowoff of that material is what gives the asteroid the
impulse.

Ok. I can see why.

That would require putting the bomb inside the asteroid. I suppose that you could have a bunker buster type of bomb blast into the asteroid and then detonate the nuclear bomb. That might work but you would need to blast a large portion of the asteroid and you would need a very large nuclear device.

AM

 

[Azael]

Ok. I can see why.

That would require putting the bomb inside the asteroid. I suppose that you could have a bunker buster type of bomb blast into the asteroid and then detonate the nuclear bomb. That might work but you would need to blast a large portion of the asteroid and you would need a very large nuclear device.

AM

The idea is to blast it outside the asteroid. The radiation will vaporise the surface and that will work as rocket engine pushing the asteroid of its current trajectory. You don't need or want to put the bomb inside the asteroid.

If you do it when its far enough from Earth the nuke doesn't have to be that big. A gentle nudgle when its far away is as effectiv as a massive blast when its close.

 

[Morbius]

Ok. I can see why.

That would require putting the bomb inside the asteroid. I suppose that you could have a bunker buster type of bomb blast into the asteroid and then detonate the nuclear bomb. That might work but you would need to blast a large portion of the asteroid and you would need a very large nuclear device.

Andrew,

NOPE - you don't have to put the bomb in the asteroid at all.

You explode the bomb above the surface of the asteroid, and let the
radiation illuminate the surface. When the material on the surface
absorbs the radiation, it will get hot and ablate or vaporize. The
resultant reaction from the vaporization of the surface material will
give you a force that deflects the asteroid.

This is the same way that ICF - Inertial Confinement Fusion works.
The radiation interacts with the material on the surface of the fusion
pellet - and results in a force. However, in the case of ICFl, the
radiation is all around the pellet - so the resultant force implodes it.

Dr. Gregory Greenman
Physicist

 

[Morbius]

You don't need or want to put the bomb inside the asteroid.

Azael,

You got it exactly correct. I see you know your Physics.

Dr. Gregory Greenman
Physicist

 

[Andrew Mason]

The idea is to blast it outside the asteroid. The radiation will vaporise the surface and that will work as rocket engine pushing the asteroid of its current trajectory. You don't need or want to put the bomb inside the asteroid.

If you do it when its far enough from Earth the nuke doesn't have to be that big. A gentle nudgle when its far away is as effectiv as a massive blast when its close.

I don't think that would really work. Ultimately, it is the momentum of the radiation that would give you the impulse. The vaporizing surface could not give back more kick than the incoming radiation.

The only way to increase the momentum of the asteroid by absorbing radiation, vaporizing its surface and then expelling that vapour backward, is to build up vapour pressure and then release it suddenly in a burst, creating a jet-effect. But I don't see how that would happen unless you made a cavity and detonated the bomb inside it.

AM

 

[Morbius]

I don't think that would really work. Ultimately, it is the momentum of the radiation that would give you the impulse. The vaporizing surface could not give back more kick than the incoming radiation.

Andrew,

WRONG - it's NOT the momentum of the radiation that gives you the impulse.

Why do you think the momentum of the blowoff is constrained by the incoming radiation?
The two don't have ANYTHING to do with each other.

NOPE - when the radiation vaporizes the surface of the asteroid, it is going to throw
matter that was once part of the asterioid off at high speed. That's going to give you the
impulse.

Read up on how Inertial Confinement Fusion works! It's NOT the radiation pressure
due to the fact that the photons have momentum. It's the momentum of the blowoff
that gives the impulse. This is all VERY WELL understood physics from the
inertial confinement fusion programs.

http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/finert.html

"Directed onto a tiny deuterium-tritium pellet, the enormous energy influx evaporates the
outer layer of the pellet, producing energetic collisions which drive part of the pellet inward."


Dr. Gregory Greenman
Physicist

 

[Andrew Mason]

Andrew,

WRONG - it's NOT the momentum of the radiation that gives you the impulse.

Why do you think the momentum of the blowoff is constrained by the incoming radiation? The two don't have ANYTHING to do with each other.

NOPE - when the radiation vaporizes the surface of the asteroid, it is going to throw matter that was once part of the asterioid off at high speed. That's going to give you the impulse.

Read up on how Inertial Confinement Fusion works! It's NOT the radiation pressure due to the fact that the photons have momentum. It's the momentum of the blowoff that gives the impulse. This is all VERY WELL understood physics from the inertial confinement fusion programs.

http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/finert.html

"Directed onto a tiny deuterium-tritium pellet, the enormous energy influx evaporates the outer layer of the pellet, producing energetic collisions which drive part of the pellet inward."


Dr. Gregory Greenman
Physicist

In the example you gave, enormous energy is concentrated into a small space (using lasers) and this creates large pressure (energy build up) inside these pellets. You need highly concentrated (low entropy) energy to start with. Radiation from an atomic weapon may have a large amount of energy but it is not going to be that concentrated.

Unless energy is allowed to build up in the target, the energy of the vapourized molecules in the target cannot exceed the momentum of the radiation or matter particle striking them. The odd one might get hit by two or more incident particles and end up with more momentum than either ofthe incoming particles, but I think that would be the exception. It seems to me that a laser pulse striking the asteroid could vapourize molecules on the surface of the asteroid and create a jet effect. That would be much easier to deliver than a several tonne nuclear bomb.

As an aside here, on this inertial confinement model, has anyone tried using a heavy transparent outside layer and a tiny inner space occupied by tritium/deuterium? That way, an brief but energetic pulse absorbed by the water would heat the water on the inside. It would be, at least momentarily, confined to a very small space and possibly achieve fusion, if it was hot enough.

AM

 

[Morbius]

In the example you gave, enormous energy is concentrated into a small space (using lasers) and this creates large pressure (energy build up) inside these pellets. You need highly concentrated (low entropy) energy to start with. Radiation from an atomic weapon may have a large amount of energy but it is not going to be that concentrated.

Andrew,

You don't know what you are talking about. The radiation from a nuclear weapon even
at a considerable distance is VERY, VERY, VERY...MUCH LARGER than what we
are able to get from a laser - even if we concentrate it.

Unless energy is allowed to build up in the target, the energy of the vapourized molecules in the target cannot exceed the momentum of the radiation or matter particle striking them. The odd one might get hit by two or more incident particles and end up with more momentum than either ofthe incoming particles, but I think that would be the exception.

WRONG! WRONG! WRONG!

Where do you get the idea that the momentum of the radiation is some kind of limit?

Let's say the asteroid is moving in the Z-direction - we use this to define our coordinates.
Therefore, the momentum of the asteroid in the X-direction is ZERO!

Now we blow up a nuclear device above the X-surface of the asteroid. The asteroid
absorbs the radiation - the surface material is vaporized and blows off - some of it
in the X-direction - outward from the asteroid. The momentum of this material is
positive in our chosen coordinate system.

However, by conservation of momentum - the total momentum of the system has to
be ZERO in the X-direction. Therefore the asteroid HAS TO RECOIL in the negative
X-direction in order to conserve momentum. Now how is the momentum of the
recoiling asteroid limited by the momentum of the radiation?

THINK ABOUT IT! You command of the physics here has been TERRIBLY SHODDY!

It seems to me that a laser pulse striking the asteroid could vapourize molecules on the surface of the asteroid and create a jet effect. That would be much easier to deliver than a several tonne nuclear bomb.

This "jet effect" from the laser is what the bomb does. Lasers are TERRIBLY
inefficient. You get only a few percent of the input power out as laser energy.
Additionally, the frequencies that you get from a laser are NOT the frequencies
that you want for absorption by the asteroid. You want energy in the X-ray spectrum.
It's difficult to get lasers to operate there - but that is precisely the region that nuclear
weapons radiate.

Andrew - I'm NOT making this stuff up off the top of my head. In the early '90s
there was a workshop held at Lawrence Livermore National Laboratory - the
"Planetary Defense Workshop" in which the best scientists in the field were brought
together to work on the problem of asteroid deflection.

You are pooh-poohing the conclusions of a gathering of the best scientists in the
field! Why don't you LEARN about this - rather than pooh-poohing it.

As an aside here, on this inertial confinement model, has anyone tried using a heavy transparent outside layer and a tiny inner space occupied by tritium/deuterium? That way, an brief but energetic pulse absorbed by the water would heat the water on the inside. It would be, at least momentarily, confined to a very small space and possibly achieve fusion, if it was hot enough.

NOPE - won't work because the density is too low. You need to get to a MUCH
higher compression. You aren't going to get fusion at the low densities without
compressing the fusion fuel.

Take a look at the reaction cross-section as a function of density to see that you don't
have to do an experiment - it's a LOSING IDEA from the start.

Dr. Gregory Greenman
Physicist

 

[Andrew Mason]

Andrew,

You don't know what you are talking about. The radiation from a nuclear weapon even at a considerable distance is VERY, VERY, VERY...MUCH LARGER than what we are able to get from a laser - even if we concentrate it.

Of course the energy from a laser pulse from Earth will be many orders of magnitude less than the energy from a nuclear bomb detonated next to the asteroid. My point was that it might be a more efficient mechanism for transferring energy into asteroid momentum.

WRONG! WRONG! WRONG!

Where do you get the idea that the momentum of the radiation is some kind of limit?

I didn't say that. I said that unless the energy is allowed to build up in the target, the kick delivered by the release of vaporised asteroid matter cannot exceed the change in momentum of the incident radiation and matter.

Now there may be something inherent in the process of absorption of radiation by the asteroid that creates such a build up of thermal energy in the asteroid that then causes an explosive release of matter. But I don't know that. All I am saying is that that is what is required.

Let's say the asteroid is moving in the Z-direction - we use this to define our coordinates. Therefore, the momentum of the asteroid in the X-direction is ZERO!

Now we blow up a nuclear device above the X-surface of the asteroid. The asteroid absorbs the radiation - the surface material is vaporized and blows off - some of it in the X-direction - outward from the asteroid. The momentum of this material is positive in our chosen coordinate system.

However, by conservation of momentum - the total momentum of the system has to be ZERO in the X-direction. Therefore the asteroid HAS TO RECOIL in the negative X-direction in order to conserve momentum. Now how is the momentum of the recoiling asteroid limited by the momentum of the radiation?

THINK ABOUT IT! You command of the physics here has been TERRIBLY SHODDY!

It seems to me that it depends on how energy is transferred from the incident photons to the atoms in the asteroid.

If the absorption of radiation energy produces heat in the asteroid and that causes a build-up of pressure of asteroid matter that is subsequently released as a burst of vapour from the asteroid, you are absolutely right that the incident momentum is immaterial.

But if it is simply a matter of individual incident photons knocking off atoms from the surface, I don't see how the atoms can receive an impulse from an incident photon that exceeds the change in momentum of the incident photon.

This "jet effect" from the laser is what the bomb does. Lasers are TERRIBLY
inefficient. You get only a few percent of the input power out as laser energy. Additionally, the frequencies that you get from a laser are NOT the frequencies that you want for absorption by the asteroid. You want energy in the X-ray spectrum. It's difficult to get lasers to operate there - but that is precisely the region that nuclear weapons radiate.

Andrew - I'm NOT making this stuff up off the top of my head. In the early '90s there was a workshop held at Lawrence Livermore National Laboratory - the "Planetary Defense Workshop" in which the best scientists in the field were brought together to work on the problem of asteroid deflection.

You are pooh-poohing the conclusions of a gathering of the best scientists in the field! Why don't you LEARN about this - rather than pooh-poohing it.

I am not pooh-poohing it at all. I am just saying that it requires a build-up of heat in the asteroid followed by a release of vapour.

NOPE - won't work because the density is too low. You need to get to a MUCH higher compression. You aren't going to get fusion at the low densities without compressing the fusion fuel.

Take a look at the reaction cross-section as a function of density to see that you don't have to do an experiment - it's a LOSING IDEA from the start.

You may be right that it is a losing idea - I was just tossing it out. But losing ideas sometimes have surprising turns, so tossing out a losing idea isn't necessarily a bad thing.

AM

 

[russ_watters]

Andrew, the energy from a nuclear bomb is omnidirectional, so sure, it isn't as "concentrated" as a laser. Still, if you detonate the bomb near an astroid, almost half of the energy will be captured by the asteroid. Maybe that's how you define efficiency (50% vs 100%), but since there is no laser that comes anywhere close to the power output of a nuclear bomb, you still get much more oomph from the nuclear bomb - efficiency really isn't a relavant concept here. [and that's without considering the efficiency of generating the laser]

To get an idea of the scale difference, the worlds largest laser, (actually a collection of 192 lasers) will have a total energy capacity of 346mj (it is still under construction). That's .000008256 kilotons. So you'd need to fire it one hundred twenty thousand times to impart the same amount of energy on an asteroid as a small nuclear bomb. [someone check my math...]

http://www.specialtyphotonics.com/knowledge_base/newsletter/0707/largest_laser.html

 

[Andrew Mason]

Andrew, the energy from a nuclear bomb is omnidirectional, so sure, it isn't as "concentrated" as a laser. Still, if you detonate the bomb near an astroid, almost half of the energy will be captured by the asteroid. Maybe that's how you define efficiency (50% vs 100%), but since there is no laser that comes anywhere close to the power output of a nuclear bomb, you still get much more oomph from the nuclear bomb - efficiency really isn't a relavant concept here. [and that's without considering the efficiency of generating the laser]

But my point is that it is not the efficiency by which the asteroid absorbs energy. That should be very high. It is the efficiency by which it converts energy into asteroid momentum.

Let's take an example. I fire a bullet into a soccerball. Let's assume that the soccerball is designed so that it absorbs 100% of the bullet's energy (and momentum).

In the first case, it stops the bullet by heating up a clump of matter inside the ball and it simply converts the energy into warming the ball. The momentum of the ball will be equal to the loss of momentum of the bullet.

In the second case, the bullet pushes on a plate that comresses the air in the ball. The compressed air is allowed to build up pressure until the bullet is stopped. Then the compressed air is released in a rearward direction through the hole made by the bullet. In this case, the momentum of the ball is equal to the momentum of the bullet + the momentum of the air that is directed rearward through the hole. The momentum of that air has nothing to do with the bullet momentum. It is a function of the energy of the bullet and the "efficiency" by which that energy is converted into momentum of the escaping air.

To get an idea of the scale difference, the worlds largest laser, (actually a collection of 192 lasers) will have a total energy capacity of 346mj (it is still under construction). That's .000008256 kilotons. So you'd need to fire it one hundred twenty thousand times to impart the same amount of energy on an asteroid as a small nuclear bomb. [someone check my math...]

http://www.specialtyphotonics.com/knowledge_base/newsletter/0707/largest_laser.html

Given the logistics of getting a nuclear bomb near an incoming asteroid, perhaps developing a laser to move asteroids might be a better investment.

If a laser is significantly more "efficient" in converting photon energy into asteroid momentum - as I suggest that it may be but I don't know that - you would not need to deliver nearly as much energyas a nuclear bomb in order to achieve the needed asteroid momentum change.

AM

 

[quetzalcoatl9]

WRONG! WRONG! WRONG!

Where do you get the idea that the momentum of the radiation is some kind of limit?

if i may butt in here, why exactly is Andrew wrong on this?

assume a perfect transfer of energy from the radiation to the material of the asteroid. then the molecules of the asteroid will be kicked into an excited state. let's assume that all of that energy is kinetic, and so by conservation of energy the surface molecules of the asteroid (the ones that were resonant with the radiation) will then be blasted off of the asteroid (that is, "asteroid" being the part of the material that is still in the ground state). the kinetic energy of the leaving molecules will be equal to the amount of energy transferred from the radiation.

the energy of the radiation will be be related to it's (in this case rather high) frequency, or by the de Broglie relation, the photon's momentum. This momentum, unless I am missing something, will be a limiting factor in the momentum imparted to the asteroid.

What is wrong with this?

Q

 

[NeoDevin]

The ENERGY is the limiting factor, not MOMENTUM. Any material vaporized from the asteroid will have momentum in the opposite direction, allowing for a push of arbitrarily large momentum, given sufficient energy, even though the bomb is not actually touching the surface (if there even is one) of the asteroid. This method works whether the asteroid is a single solid piece, or a large collection of small bits of debris.

Putting the bomb inside the asteroid would be less effective at imparting momentum (ie. almost no net momentum change at all), plus there would be the chance that you would break the asteroid into pieces and then have an even bigger problem heading towards the earth.

 

[Andrew Mason]

if i may butt in here, why exactly is Andrew wrong on this?

assume a perfect transfer of energy from the radiation to the material of the asteroid. then the molecules of the asteroid will be kicked into an excited state. let's assume that all of that energy is kinetic, and so by conservation of energy the surface molecules of the asteroid (the ones that were resonant with the radiation) will then be blasted off of the asteroid (that is, "asteroid" being the part of the material that is still in the ground state). the kinetic energy of the leaving molecules will be equal to the amount of energy transferred from the radiation.

the energy of the radiation will be be related to it's (in this case rather high) frequency, or by the de Broglie relation, the photon's momentum. This momentum, unless I am missing something, will be a limiting factor in the momentum imparted to the asteroid.

What is wrong with this?

It is kinematically possible for vapourized matter from the surface to provide a greater impulse to the rest of the asteroid than the momentum received from of the incident radiation. In fact, it is possible for that vapour to provide an impulse in a completely different direction. In the soccer ball example I gave, if the pressurized air is released out the front of the ball, the ball could recoil toward the incident bullet with greater momentum than the incident bullet. The limiting factor is the energy of the incident bullet.

My point is that whether this occurs depends on the actual mechanism. There has to be a build-up of vapour pressure within the asteroid before the vapour escapes from the the surface. Now there may be a mechanism by which pressure within the vapourizing surface will build up. One would have to study the actual physical process.

AM

 

[Andrew Mason]

The ENERGY is the limiting factor, not MOMENTUM. Any material vaporized from the asteroid will have momentum in the opposite direction, allowing for a push of arbitrarily large momentum, given sufficient energy, even though the bomb is not actually touching the surface (if there even is one) of the asteroid. This method works whether the asteroid is a single solid piece, or a large collection of small bits of debris.

The direction of the kick provided by the vapour does not have to be away from the bomb. You could have an asteroid in which the far surface (ie opposite to the surface facing the nuclear bomb) was covered in ice. If the asteroid was thin enough, it might be possible for the heat from the radiation to evaporate water under the ice and build up vapour pressure until the ice burst causing a sudden release of vapour away from the far surface and pushing the asteroid toward the nuclear bomb.

Putting the bomb inside the asteroid would be less effective at imparting momentum (ie. almost no net momentum change at all),

There can be no change of the total momentum, but that is the case whether the bomb is inside or outside the asteroid. You are only interested in the bulk of the asteroid. An exploding bomb could easily propel some of the asteroid matter. If the bomb were to propel large chunks of asteroid outward into space, the rest of the asteriod would have to recoil in the opposite direction.

plus there would be the chance that you would break the asteroid into pieces and then have an even bigger problem heading towards the earth.

Or more smaller ones.

AM

 

[russ_watters]

But my point is that it is not the efficiency by which the asteroid absorbs energy. That should be very high. It is the efficiency by which it converts energy into asteroid momentum.

[snip] If a laser is significantly more "efficient" in converting photon energy into asteroid momentum - as I suggest that it may be but I don't know that - you would not need to deliver nearly as much energyas a nuclear bomb in order to achieve the needed asteroid momentum change.

But both the nuke and the laser primarily fire EM radiation at the asteroid and both will mostly just heat it. So what's the difference?

I understand what you mean about the laser being more efficient (a refleced photon imparts twice momentum as an absorbed photon, for example), but we're not talking order of magnitude differences so the laser would still need to be on the same order of magnitude in energy as the nuclear bomb. And at that energy, the laser is still going to be vaporizing part of the asteroid anyway, so I'm not convinced the mechanism would even be fundamentally different.

Bottom line, it would be more efficient energywise to use the laser (at the very least, more than half the energy of the nuke is going in the wrong direction), but certainly not more than a single order of magnitude more efficient and that just isn't enough to be worthwhile.

Given the logistics of getting a nuclear bomb near an incoming asteroid, perhaps developing a laser to move asteroids might be a better investment.

The logistics of getting a nuke to an asteroid were perfected in the early 1960s. Today, we can pretty much use off-the-shelf components to send a nuclear bomb to anywhere in the solar system we want on short notice (under a year to launch, certainly) - you could almost literally rip the payload off a rocket on the pad in Florida and replace it with an ICBM warhead and guidance package. And since and lasers powerful enough to match don't exist, I'd bet on the nuke getting there first!

The NIF is costing $1.2 billion to build and I don't know how much it would cost to fire it a hundred thousand times. The second (ie, no development costs, just construction and launch costs) rover we sent to Mars cost $200 million to build and send to Mars.

So with choice A, we need technology that doesn't exist, a lot more money, and a lot more time to make it happen than choice B. It just doesn't make sense.

 

[quetzalcoatl9]

The ENERGY is the limiting factor, not MOMENTUM. Any material vaporized from the asteroid will have momentum in the opposite direction, allowing for a push of arbitrarily large momentum, given sufficient energy, even though the bomb is not actually touching the surface (if there even is one) of the asteroid. This method works whether the asteroid is a single solid piece, or a large collection of small bits of debris.

Putting the bomb inside the asteroid would be less effective at imparting momentum (ie. almost no net momentum change at all), plus there would be the chance that you would break the asteroid into pieces and then have an even bigger problem heading towards the earth.

i kindly disagree on all points.

1) whether we talk of momentum or energy here is mostly irrelavant. the energy imparted will be proportional to the square of the momentum so i could equally argue that it is the momentum of the radiation (i.e. the inverse wavelength weighted by a factor of Planck's constant)

2) if it were possible to blast the asteroid out from the center, that would not necessarily be detrimental since it is possible that those pieces will all "radiate" from their trajectory and miss the Earth completely.

 

[Andrew Mason]

But both the nuke and the laser primarily fire EM radiation at the asteroid and both will mostly just heat it. So what's the difference?

As I said, I am not sure that a laser would be any more efficient in converting energy into momentum. I just thought it would be quicker to deliver and more accurate, as well as delivering a more concentrated energy. I may be wrong on that last point as Morbius points out. The energy of the radiation in the xray/gamma ray part of the spectrum is much higher than light, energy/unit area might be higher even if the number of photons/unit area is lower.

I tend to agree with you that a nuclear weapon would actually be more effective. The radiation would heat the asteroid vapourizing the surface molecules, but the enormous shock wave from the blast would also compress the vapour, allowing for a buildup of vapour pressure that would then be released when the blast pressure subsided.

AM

 

[Morbius]

I didn't say that. I said that unless the energy is allowed to build up in the target, the kick delivered by the release of vaporised asteroid matter cannot exceed the change in momentum of the incident radiation and matter.

Andrew,

Which is where you are 100% WRONG!

Consider the following. Suppose the asteroid is traveling in the "Z" direction; and we
bury some explosive charges on the "X" side of the asteroid. Because the asteroid
direction defines the Z direction; the momentum in the X direction is ZERO.

Now we detonate the high explosive so that we propel a bunch of the matter that was
once a part of the asteroid into the +X direction. That matter represents momentum
in the +X direction. However, conservation of momentum requires that the total
momentum of the entire system, asteroid plus blow-off material has to be ZERO;
which is what it was before the detonation. Therefore, the asteroid has to recoil
in the -X direction. That's the ONLY way that the total momentum can be ZERO.

It seems to me that it depends on how energy is transferred from the incident photons to the atoms in the asteroid.

If the absorption of radiation energy produces heat in the asteroid and that causes a build-up of pressure of asteroid matter that is subsequently released as a burst of vapour from the asteroid, you are absolutely right that the incident momentum is immaterial.

YES - that is EXACTLY what happens. The absorption of radiation produces heat and
vaporizes the material of the asteroid. This material "blows-off" or "jets-off" and by
necessity to conserve momentum - the asteroid has to recoil in the opposite direction.

As I stated before - this is EXACTLY the mechanism that is being used in laser fusion
for example. The lasers are directed in a hohlraum where the build-up of laser energy
causes the hohraum to radiate X-rays. Those X-rays impinge on the surface of the
spherical fusion pellet and the ablation of the surface causes the pellet to be compressed.
The pellet is "recoiling" in response to the blow-off of the surface.

But if it is simply a matter of individual incident photons knocking off atoms from the surface, I don't see how the atoms can receive an impulse from an incident photon that exceeds the change in momentum of the incident photon.

As I have stated REPEATEDLY - that is NOT the mechanism. The asteroid is NOT
recoiling due to the momentum of the photons [ consider that to be zero, if you like ];
the recoil is produced by the ABLATION of the surface due to the absorbed energy.

I am not pooh-poohing it at all. I am just saying that it requires a build-up of heat in the asteroid followed by a release of vapour.

Which is EXACTLY what happens when you irradiate the material with intense X-rays!

Dr. Gregory Greenman
Physicist

 

[Morbius]

Andrew, the energy from a nuclear bomb is omnidirectional, so sure, it isn't as "concentrated" as a laser. Still, if you detonate the bomb near an astroid, almost half of the energy will be captured by the asteroid. Maybe that's how you define efficiency (50% vs 100%), but since there is no laser that comes anywhere close to the power output of a nuclear bomb, you still get much more oomph from the nuclear bomb - efficiency really isn't a relavant concept here. [and that's without considering the efficiency of generating the laser]

To get an idea of the scale difference, the worlds largest laser, (actually a collection of 192 lasers) will have a total energy capacity of 346mj (it is still under construction). That's .000008256 kilotons. So you'd need to fire it one hundred twenty thousand times to impart the same amount of energy on an asteroid as a small nuclear bomb. [someone check my math...]

Russ,

You are EXACTLY correct - "efficiency" means NOTHING here. [ You see this all the
time - people get "hung up" on efficiency when that's not the important metric ].

What you want is to impart a force, and hence momentum and energy to the asteroid.
That's ALL that counts.

If you impart 10 kilotons worth of energy to the asteroid using a 1 megaton nuclear bomb;
who cares if the process if 1% efficient?

Would imparting 0.00001 kilotons of energy with 100% efficiency be better? If that amount
of energy is insufficient to deflect the asteroid enough - who cares that it can be done
with 100% efficiency.

That's one of the hallmarks of a good scientist - to know what metrics are important; and
which are NOT! Here efficiency is meaningless; all that matters is how much momentum
and energy can be imparted to the asteroid, and will it produce sufficient deflection.

Dr. Gregory Greenman
Physicist

 

[Andrew Mason]

Andrew,

Which is where you are 100% WRONG!

Consider the following. Suppose the asteroid is traveling in the "Z" direction; and we bury some explosive charges on the "X" side of the asteroid. Because the asteroid direction defines the Z direction; the momentum in the X direction is ZERO.

Now we detonate the high explosive so that we propel a bunch of the matter that was once a part of the asteroid into the +X direction. That matter represents momentum in the +X direction. However, conservation of momentum requires that the total momentum of the entire system, asteroid plus blow-off material has to be ZERO; which is what it was before the detonation. Therefore, the asteroid has to recoil in the -X direction. That's the ONLY way that the total momentum can be ZERO.

Morbius, we seem to be talking at cross purposes. You are giving an example of what I have been saying is required.

If you blow off part of the asteroid, the rest of it must receive an impulse in the opposite direction. I agree. That is exactly what is required: an explosive release of matter from the asteroid.

You are saying that you don't need to do that directly. You can do it indirectly using radiation from the bomb to heat the asteroid to vaporize the surface to such a temperature that it blows off. Ok. It is not sufficient to just have radiation just knock atoms off the asteroid. I think we both agree on that.

All I am saying is that in order to provide the explosive impulse, there has to be some containment before the vapour is released. I am just not sure of the mechanism by which that occurs. One way to do that would be to produce a heat gradient within the asteroid with the greatest heat just below the surface. Another might be to have the pressure from the explosion shock wave contain the vapor as the heat is building up.

AM

 

[Morbius]

All I am saying is that in order to provide the explosive impulse, there has to be some containment before the vapour is released.

Andrew,

NOPE - you don't need to have any type of containment.

The radiation flux from a nuclear bomb is going to be much higher than if you took the
most powerful laser and contained it!

You don't need to concentrate the radiation from a nuclear bomb - it is so intense even
without containment or any type of concentration; that it will do the job of providing the
impulse to do the deflection.

That's all that matters - do you put enough radiation on the target to blow off enough
material. If you are thinking in terms of lasers or other radiation sources - I can see
where you would want to contain and concentrate the radiation.

However, for a nuclear bomb - that containment and concentration is just NOT
necessary.

Dr. Gregory Greenman
Physicist

 

[russ_watters]

All I am saying is that in order to provide the explosive impulse, there has to be some containment before the vapour is released.

I read once that it has been considered as a means to propel airplanes to spray raw fuel on their wings...

Anyway, I think we've beaten this thread to death.