Whoa! A close shave next year.

[RIPTIDE]

second because Nukes dont cause a sockwave in space, only a very hot dot. Sending it againts a big rock wouldnt do any more than a smudge Im afraid.

A very hot dot... lmao.

 

The sun is a very hot dot. :)

 

The nuclear detonation BTW is supposed to cleave off a small part of an object. By radiated heat, and subsequent expansion shock within the material. Conservation of momentum should make the parts change direction. The other way (the way I prefer) is to have a large enough detonation that will flash a substantial portion of the object to gas which will generally move away in a vector perpendicular to the side of the object that is flashed. Again conservation of momentum does the rest. The reason I like this method the best is because it doesn't require a closest (read: more risky) rendezvous with the object. All that is required is a enormous detonation.

Edited March 10, 2012 by RIPTIDE

[Pilotasso]

A rendevous is not so risky as you might expect, It has been done before (yes, a landing on an asteroid), plus it can be attempted with many vehicles simultaneously. Sending one nuke would be the risky option, and the efect much smaller (specially if it of metallic composition) with a bigger buble of uncertainty.

 

Oh and BTW the SUN has lasted 4 billion years and its a fusion combustion phenomena. A nuke lasts only a fraction of a second and its caused by fission, the exactly opposite nature. :)

 

Could you find any worse comparison?

Edited March 10, 2012 by Pilotasso

[asparagin]

You can nuke with both processes.

[EtherealN]

Well, to be precise, thermonuclear weapons do use both - typically you would use the spherical implosion method on a plutonium primary within a reflective casing and use that to ignite the hydrogen secondary. (And depending on design, you might actually have some fission of uranium in the secondary as well, using the pressure from the hydrogen secondary to compress and fission a uranium tamper within it.)

[Glowing_Amraam]

Yeah hopefully this one will miss the U.S.A. and hit Norway, where it will only kill fjords and mountains :huh:

 

Haha, well I better go hide then ;)

[asparagin]

Haha, well I better go hide then ;)

 

Don't worry, all calamities happen in the US, don't you watch movies?

[Speed]

A rendevous is not so risky as you might expect, It has been done before (yes, a landing on an asteroid), plus it can be attempted with many vehicles simultaneously. Sending one nuke would be the risky option, and the efect much smaller (specially if it of metallic composition) with a bigger buble of uncertainty.

 

Oh and BTW the SUN has lasted 4 billion years and its a fusion combustion phenomena. A nuke lasts only a fraction of a second and its caused by fission, the exactly opposite nature. :)

 

Could you find any worse comparison?

 

You're incorrect. Nukes work just fine in space. When nukes explode, saying they produce heat is simplifying things way too much. Nukes produce high speed neutrons and fission products, neutrinos and lots of high energy electromagnetic radiation like gamma rays. These energetic products of nuclear fission and fusion quickly get absorbed by the atmosphere and the surrounding environment, and THOSE things heat up drasticly, and start a rapid outward expansion.

 

In space, there the radiation keeps travelling till it hits something. Like an asteroid.

 

So your idea that nukes are just a "hot point in space" doesn't make sense. So nukes produce no energy in space, but tons of energy on the ground?

 

If you still don't believe me, there is another way to understand it.

 

Photons carry energy, hence they carry mass (yes, mass- just not rest mass, they have relativistic mass), and hence, photons carry momentum. In fact, the momentum they carry is very easy to calculate from a cliche equation we all know and love:

 

E = mc^2

Momentum is mass times velocity, so:

mometum of a photon = mc = E/c.

 

When photons strike a surface, they transfer momentum to this surface, and they thus exert a pressure. This pressure is known as radiation pressure. And nukes produce radiation pressure. ALOT of radiation pressure.

 

So what does the nuke release that doesn't carry momentum? High velocity fission fragments- check. Very high energy electromagnetic radiation- check. Neutrinos- check, but no check. Yes, neutrinos have momentum, but the absorbtion coefficient of neutrinos is incredibly very low even in solid lead. The vast majority of neutrinos pass right through the earth like it's not even there.

 

In fact every single ounce of energy that a nuke releases to the environment here on the ground will also occur in space, and any body that is close to the nuke will be blasted by high energy radiation that it will absorb the momentum of. Now, this momentum isn't just converted into a momentum change of the total body, yes, much of it is goings into changing the momentum of the individual molecules with respect to each other-a change in heat energy. But some of it WILL go into changing the total momentum of all the asteroid's constituent atoms.

 

If you want a break down of what kinds are energy exactly are produced by nuclear explosives, see this site:

http://nuclearweaponarchive.org/Library/Fission.html

 

So, let's just do a little calculation. Explode a 500 kt nuke 300 meters away from a 45m wide asteroid (which is pretty far away, we can easily get closer than that). The nuke releases its high velocity fission fragments and high energy photons that the asteroid absorbs the energy (and momentum) of.

 

Assuming that the asteroid is spherical, then it subtends a solid angle of roughly:

 

pi*(22.5/300)^2 = 0.018 sr.

 

Dividing that by 4*pi, the total steradians in a sphere, we get:

1.4x10^-3

 

So the asteroid covers a little over 1.4 thousandths of the sky as seen from the nuke. Assuming that all the useful, non-neutrino energy impinging upon the asteroid by the 500kt nuke are is absorbed by the asteroid, then the asteroid absorbs:

 

500kt*1.4x10^-3 = 700t. It's as if 700tons of dynomite went off on the surface of the asteroid. Knowing that 1 ton dynamite = 4.184GJ, then the asteroid absorbs about 2.9 TJ of energy, and the amount of energy absorbed per square meter on the side of the asteroid directly facing the explosion will be:

 

2.9TJ/pi*(22.5)^2 = 1.85x10^9 J/m^2. All of which will be deposited in a fraction of a second. It's like every square meter of the asteroid will have 1000 pounds of TNT exploding on it. That mother**** is going to ablate like crazy- the surface is going to vaporize and provide significant thrust to the asteroid.

 

Assuming the worse-case scenario, it's made of solid nickel-iron, then the asteroid will mass something like:

 

(4/3)*pi*(22.5 meters)^3 * (7.8x10^3 kg/meter^3) = 3.7x10^8kg.

 

Now assume that just 1% of the energy absorbed by the asteroid is absorbed as kinetic energy, then you get a total delta V of:

 

 

KE= 0.5*m*v^2

0.01*2.9TJ = 0.5*3.7x10^8*v^2

 

v = 12.6 meters/sec. Now, assuming the asteroid will hit earth in dead center, then this delta-V will be enough to make the asteroid miss if the asteroid is hit this much time before impact:

 

radius of earth/v = 6,400,000m/12.6 = 508,000 seconds = 1410 hours = 59 days.

 

Anyway, I hope you see... nukes work. And we could have nuked it from the surface instead, but this example nuked it from 0.3km away.

Edited March 10, 2012 by Speed

[Pilotasso]

A complex explanation for something that is really simple. An asteroid, specially one of metallic compositions doesnt care less about radiation emmited :D

 

You only going to heat it up on a smaller area, for something that has been blazed by the sun and interstellar gamma rays and the like for billions of years and has a heat differential of 200 degrees between night and day. RIPTIDE mentioned ejectying material out of it, but it would only do something for ice bodies that evaporate when they get close to the sun anyway (or get blown on the upper atmosphere should they collide).

 

Our discussion here was only about knoking them out of the way, and not how a bomb dissipates its energy, or how bad it affects life on a place that doesnt have any. :)

Edited March 10, 2012 by Pilotasso

[RIPTIDE]

A rendevous is not so risky as you might expect, It has been done before (yes, a landing on an asteroid), plus it can be attempted with many vehicles simultaneously. Sending one nuke would be the risky option, and the efect much smaller (specially if it of metallic composition) with a bigger buble of uncertainty.

 

Oh and BTW the SUN has lasted 4 billion years and its a fusion combustion phenomena. A nuke lasts only a fraction of a second and its caused by fission, the exactly opposite nature. :)

 

Could you find any worse comparison?

Yes it has been done before and if it had failed, no-one was going to get killed because of its failure. IN this scenario, it's different. Landing something on the surface of an asteroid is far riskier than just needing to approach it.

 

The most powerful Thermonuclear weapons are Fusion based in their main operation, just like the Sun. Nobody would waste a payload on a mere fission-only bomb.

 

Obviously the comparison was missed on you completely. So I'll explain it. The Sun is a hot dot in the sky, and the reason you get hot from that hot dot is by Radiated heat. And in my scenario, it is how most of the energy will be transferred.

[Speed]

A complex explanation for something that is really simple.

Which you obviously didn't read a single word of.

 

If you want to debate me on this, why don't you try to refute my arguments with actual physics rather than just what you believe. If someone pulls out math and shows how you're wrong, you can't just say "no, YOU'RE wrong"..... If you really know so much about this, prove to me where I went so terribly wrong in my math.

Edited March 10, 2012 by Speed

[159th_Viper]

Deflecting-Asteroids-by-Means-of-Standoff-Nuclear-Explosions.pdf

[Pilotasso]

I read it, and you must be kidding me thinking radiation pressure lasting a fraction of a second would affect a body weighting millions to billions of tons. The cosmic sources pump much more radiation to any asteriod in the course of eons than a Nuke could ever do. and their orbits are stable enough to be predictable.

 

Also what you havent underestood in my previous post is that I didnt say nukes dissipate any less energy in space. The dissipation is done through a showave on an atmo , and that is what most peaople are familiar with. In space it only produces radiation.

[Speed]

[ATTACH]63701[/ATTACH]

 

Thanks Viper..

Some relevant quotes:

A standoff nuclear explosion produces a change in the momentum of an asteroid primarily by means of material that is evaporated or spalled (by rapid thermal expansion) from its surface due to the deposition of energy. This energy is transmitted from the explosion mostly by means of neutrons and X rays.

 

Which is exactly what I implied as well.

[Speed]

I read it, and you must be kidding me thinking radiation pressure lasting a fraction of a second would affect a body weighting millions to billions of tons. The cosmic sources pump much more radiation to any asteriod in the course of eons than a Nuke could ever do. and their orbits are stable enough to be predictable.

 

Also what you havent underestood in my previous post is that I didnt say nukes dissipate any less energy in space. The dissipation is done through a showave on an atmo , and that is what most peaople are familiar with. In space it only produces radiation.

 

Sorry but with what do you back up your claim: "you must be kidding me thinking radiation pressure lasting a fraction of a second would affect a body weighting millions to billions of tons.". What equation tells you this?

 

Anyway, it's not really the radiation pressure anyway. Like I said, you didn't read my post, I didn't say it was the radiation pressure that did it. What I said was this:

500kt*1.4x10^-3 = 700t. It's as if 700tons of dynomite went off on the surface of the asteroid. Knowing that 1 ton dynamite = 4.184GJ, then the asteroid absorbs about 2.9 TJ of energy, and the amount of energy absorbed per square meter on the side of the asteroid directly facing the explosion will be:

 

2.9TJ/pi*(22.5)^2 = 1.85x10^9 J/m^2. All of which will be deposited in a fraction of a second. It's like every square meter of the asteroid will have 1000 pounds of TNT exploding on it. That mother**** is going to ablate like crazy- the surface is going to vaporize and provide significant thrust to the asteroid.

Look, I'm not going to waste any more time on this. You have to back up your claims with solid physics, or they have no weight at all. Explain why the experts (such as the one Viper quoted in the paper) are wrong. And "I just can't believe it" is not a valid argument.

Edited March 10, 2012 by Speed

[Pilotasso]

No, but if your short of time and desperate enought to use existing technology as the paper says, then your not going to have enough time to acess the composition and structure of the asteroid either. According to the paper composition affects the ammount of energy converted to motion. Which basically means you wont know nothing how youll be affecting its trajectory untill you try it. Thats risky.

[RIPTIDE]

[ATTACH]63701[/ATTACH]

123456789

 

CONCLUSION

If an Earth-threatening asteroid is discovered in

the near future, it is likely to be roughly in the size

range of the above examples. (Approximately 80% of

the near-Earth asteroids discovered in 2003 are between

40 m and 1100 m in diameter.) Therefore, the

examples show that deflection of typical asteroids by

means of standoff nuclear explosions is practical.

[asparagin]

Jumping to conclusion(s) ey?

 

You're lucky this paper has a one written for mortals, most conclusions (in renowned papers) force you to drop laziness.

[Speed]

No, but if your short of time and desperate enought to use existing technology as the paper says, then your not going to have enough time to acess the composition and structure of the asteroid either. According to the paper composition affects the ammount of energy converted to motion. Which basically means you wont know nothing how youll be affecting its trajectory untill you try it. Thats risky.

 

I'll grant you that it's far better to use something with less uncertainties like a gravity tractor.

 

I will also grant you that perhaps my initial statements about radiation pressure were a bit confusing, however, they are not incorrect. My point is, electromagnetic radiation carries momentum. When electromagnetic energy strikes a surface the molecules will either reflect it back (which actually will double the radiation pressure), or absorb it. If they absorb it, then they heat up, and emit more and more radiation in the effort to cool back off, according to Planck's law. This radiated exits the surface, giving the surface a thrust. That's one way to look at it, at least. There are others.

 

I do believe that if you have heated an object to a uniform temperature, and it reflects no incident radiation (a black body), then it will have zero net thrust from radiation pressure as the re-emitted radiation will be in all directions. I could be wrong though.

 

Anyway, a nice example of the effect that solar radiation pressure can have on asteroids is this:

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

As I mentioned earlier (I didn't call it the "Yarkovsky effect" though because I couldn't remember the name though), utilizing this effect could be used for deflecting asteroids (though it will take a lot longer).

Edited March 11, 2012 by Speed

[RIPTIDE]

Jumping to conclusion(s) ey?

 

You're lucky this paper has a one written for mortals, most conclusions (in renowned papers) force you to drop laziness.

 

Well thanks for telling me how lucky I am. :megalol:

 

[asparagin]

Well thanks for telling me how lucky I am. :megalol:

 

[Pilotasso]

I just droped by to apologise for the tone of my messages yesterday. I have been inconsiderate torwards the data you provided and lashed out frustration from my RL here.

 

 

Sorry. :)

[Speed]

I just droped by to apologise for the tone of my messages yesterday. I have been inconsiderate torwards the data you provided and lashed out frustration from my RL here.

 

 

Sorry. :)

 

I think we've all been there. In fact, some of my replies to you were far too hostile and I had to edit them down, and even after that, I still ended up feeling like I had been a jerk.

[Speed]

Anyway, based off of Ethereal's reply, I may not be the only amateur astronomer/space buff on these forums. Anyone else? Personally, I've been at it for about the last 18 years. Over that time, I graduated up to a large aperture dobsonian (truss) design. I like observing the bright eye candy stuff, but most of the time, I go after really faint challenging objects- very faint planetary nebulae, diffuse nebulae, and distant galaxy clusters out to 3 billion light years or so. Texas has some dark skies :)

[EtherealN]

Not sure I'd call myself an amateur astronomer. I have a robotic 8-inch celestron but don't use it enough to really call myself an astronomer of any sort. Been thinking about giving it a sort of permanent housing with retractable roof and control from the computer indoors though - over here we have very little night-time during the summer, and in the winter it's awful cold. :P

[Speed]

New article up at space.com this morning: http://www.space.com/14857-asteroid-nuclear-bomb-explosion-video.html

 

Scientists at Los Alamos claiming that supercomputer simulations show how a 1 Mt nuclear blast would be fairly effective against a 500meter wide rubble pile asteroid. A relevant quote:

Scientists at Los Alamos National Laboratory, a United States Department of Energy facility in New Mexico, used a supercomputer to model nukes' anti-asteroid effectiveness. They attacked a 1,650-foot-long (500-meter) space rock with a 1-megaton nuclear weapon — about 50 times more powerful than the U.S. blast inflicted on Nagasaki, Japan, to help end World War II.

 

The results were encouraging.

 

"Ultimately this 1-megaton blast will disrupt all of the rocks in the rockpile of this asteroid, and if this were an Earth-crossing asteroid, would fully mitigate the hazard represented by the initial asteroid itself," Los Alamos scientist Bob Weaver said in a recent video released by the lab.

 

Also, like I said, this is your last resort, when you don't have time to build and deploy or deploy, a better deflection means. If this 45 meter wide asteroid were going to hit us next year, and impact in a populated area, the nuclear option would be our only option, which is the only reason I've been talking about it so much.

Weaver stressed that nuclear bombs would likely be deployed only as a last resort, if an impact loomed just months away. And other researchers caution that a nuclear blast might have negative side effects, such as sending a hail of many small space rocks toward Earth instead of a single big one.

 

Again, what I wonder is, why couldn't they just set a second nuclear blast off a few seconds after the first? That way, you might be able to deflect like 80% of the remaining debris. Anything that is still going to hit earth, should be at or very near the position of where the initial object would have been, had it not been hit by the first blast. Right?

 

Just send up two nukes. Russia and the US get to draw straws as to who gets to hit the asteroid first :D Maybe the UK, France, and China get to draw straws for a third nuke. Free nuclear tests!

Edited March 12, 2012 by Speed