How Can We Effectively Destroy An Asteroid Headed for Earth?

[Morbius]

Would fixing some rocket engines on to the asteroid help to deflect it? Just use a joystick to save earth. I guess the hard part would be getting on the surface with the engines, then positioning properly.

baywax

Depends on the orbit of the asteroid, how big it is...

Basically, it depends on how much energy would it take to deflect it, and how much
time you have.

If the asteroid is very massive, and it will hit us on its current orbit; then you may need to
put so much energy into it that NO chemical rocket could put that much energy in. There
would be NO chemical rocket that is powerful enough to deflect it.

There might even be an asteroid too massive for a nuclear weapon to deflect.

In which case, the Earh is doomed.

Dr. Gregory Greenman
Physicist

 

[Morbius]

The primary objective, naturally, is deflection.

However, it would also be beneficial to get rid of the damn thing for good. Is it plausible to do precise enough dynamical calculations ahead-of-time in order to not only deflect an obejct from near earth, but ensure that its orbit takes it into either the sun or one of the gas giants?

Sojourner01,

All depends on how much energy is required. These are massive objects, and we really
don't have a lot of energy available.

In cosmological terms; the forces of Nature at our command are pretty puny.

Dr. Gregory Greenman
Physicist

 

[Sojourner01]

Well, what I'm getting at is that assuming you can deflect the object from earth, are our computational methods precise enough to ensure that its new trajectory will put it where we want it? I'm sure the answer to this question will depend on where in the risky trajectory you choose to act - further away from Earth you don't need as much of a jolt, but that also puts it further away from its intended destination. I ask because I'm aware that astronomers can't say with complete certainty whether or not a particular object will strike us in the future; there's a 'window' limited by their ability to compute the dynamics of all the bodies involved ahead of time. Waht I'm asking is, does this inaccuracy extend to us altering the path of a large object, assuming we're practically able to?

 

[Morbius]

Well, what I'm getting at is that assuming you can deflect the object from earth, are our computational methods precise enough to ensure that its new trajectory will put it where we want it?

Sojourner01,

Oh sure to the computational methods.

Take, for instance, the Cassini mission. We had insufficient propulsion systems to launch
Cassini directly to Saturn; so it was launched in a trajectory that caused it to make TWO
fly-bys of Venus, in order to pick-up momentum via the "sling-shot" effect; before it went
to Saturn.

http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1997-061A

If we can accurately "hit" the rings of Saturn by making two "bank-shots" off of Venus;
then we can calculate how to deflect the asteroid.

Dr. Gregory Greenman
Physicist

 

[mr200backstrok]

this is a little off topic, but is there an upper limit for the yield of thermonuclear bombs?

 

[joema]

this is a little off topic, but is there an upper limit for the yield of thermonuclear bombs?

To my knowledge, there is no upper yield limit. In principle, by cascading fission/fusion/fission stages, any size weapon could be constructed. I believe 50,000 megaton devices have been studied: http://en.wikipedia.org/wiki/Nuclear_weapon_yield

However there is a limit to the yield per unit weight. The absolute maximum theoretical yield is 166 kg per megaton, and that's just for the nuclear material itself. Actual achievable yield from real-world warheads is closer to 350-400 kg per megaton.

Stated differently, the maximum yield ratio thus far achieved is 5.2 megatons per metric ton, so a 200 megaton device would weigh 38.5 metric tons (84,877 lbs).

The Saturn V payload to lunar escape velocity was about 47 metric tons, so largest bomb it could lift on that trajectory would be "only" 244 megatons.

An asteroid intercept would likely require a higher energy trajectory, which means lower payload. Just guessing, say about 100 megatons on a Saturn V.

 

[Morbius]

this is a little off topic, but is there an upper limit for the yield of thermonuclear bombs?

mr200backstrok,

Unlike fission weapons, there is no upper limit nor lower limit to the yield of a
thermonuclear bomb [ provided you can ignite it ].

Consider the lower limit. The small fusion pellets that would undergo thermonuclear
fusion in ICF - Inertial Confinement Fusion are, in essence; small thermonuclear "bombs".
The problem is it takes an awfully large machine, like a laser the size of a football stadium
to ignite it.

In fission bombs; there is a lower limit because there is a "critical mass". You don't get
a self-sustaining fission reaction until you have a certain minimum amount of material,
called the "critical mass". Once you get the fission reaction started in a fission bomb
by having the minimum amount of bomb fuel - then you have enough fuel there for a
yield that is very sizeable compared with conventional chemical explosives.

In practice, the thermonuclear bombs are "triggered" by a fission bomb; so there is a
minimum possible yield to a real thermonuclear bomb because there is a minimum yield
for the device that triggers it.

The largest bomb ever designed was the "Tsar Bomba" - "King of the Bombs" - which
the Russians designed to have a yield of 100 megatonnes. They actually tested a
reduced yield version of this bomb with a yield of 54 megatonnes. That test was the
largest yield nuclear test ever conducted.

Dr. Gregory Greenman
Physicist

 

[Morbius]

To my knowledge, there is no upper yield limit. In principle, by cascading fission/fusion/fission stages, any size weapon could be constructed. I believe 50,000 megaton devices have been studied: http://en.wikipedia.org/wiki/Nuclear_weapon_yield

joema,

You're off by a factor of 1,000!

The table in the Wikipedia article you reference gives the yield of the Tsar Bomb as
50,000 in units of KILOTONS. That would be 50 Megatonnes; not 50,000 Megatonnes.

Dr. Gregory Greenman
Physicist

 

[joema]

...You're off by a factor of 1,000!...The table in the Wikipedia article you reference gives the yield of the Tsar Bomb as
50,000 in units of KILOTONS. That would be 50 Megatonnes; not 50,000 Megatonnes...

Sorry, I was referring to theoretical weapons which have been studied, not actual detonations. I referenced the article to show the basic principles of nuclear weapon yield, and the chart which shows there's a yield-to-weight limit but no upper yield limit: http://en.wikipedia.org/wiki/Image:US_nuclear_weapons_yield-to-weight_comparison.svg

I don't have the ref, but I believe in the 1950s and 60s, Rand Corp. studied unitary Cobalt-salted devices with yields up to 50,000 megatons. They concluded there was no upper yield limit, and then-current engineering would allow construction.

However from an asteroid deflection standpoint, there's no way to deliver such a device, as it's far too heavy for even the largest launch vehicle. It would take a vehicle at least 100x the payload capacity of a Saturn V.

 

[mr200backstrok]

Sorry, I was referring to theoretical weapons which have been studied, not actual detonations. I referenced the article to show the basic principles of nuclear weapon yield, and the chart which shows there's a yield-to-weight limit but no upper yield limit: http://en.wikipedia.org/wiki/Image:US_nuclear_weapons_yield-to-weight_comparison.svg

that one is measured in kt. if you look at the left side of the chart, it says "yield (kt)".

That kind of power is insane...

 

[joema]

that one is measured in kt. if you look at the left side of the chart, it says "yield (kt)"...

Yes, I know it says yield in kt. But just as the horizontal axis shows weight in kg up to 10^5 kg, there is in fact no upper weight limit, nor any yield limit.

 

[Morbius]

I don't have the ref, but I believe in the 1950s and 60s, Rand Corp. studied unitary Cobalt-salted devices with yields up to 50,000 megatons. They concluded there was no upper yield limit, and then-current engineering would allow construction.

joema,

Rand Corp. doesn't design nuclear weapons; or even know how the current ones work.

There are ONLY two places in the USA where the design knowledge for thermonuclear
weapons exists; and that's at Los Alamos and Lawrence Livermore.

So I wouldn't put any credance in anything out of Rand when it comes to nuclear
weapons design.

Dr. Gregory Greenman
Physicist

 

[joema]

joema,

Rand Corp. doesn't design nuclear weapons; or even know how the current ones work...

Thanks for the correction. Maybe it wasn't RAND.

True LANL and LLNL are the centers of actual weapon design, and past RAND research focused more on weapon effects than design. However RAND participants have included former Los Alamos and Lawrence Livermore physicists. Two examples:

- Harold L. Brode, physicist, and pioneer of numerical simulations of nuclear explosions
- Samuel Cohen, inventor of neutron bomb

None of this changes the answer to the poster's question: there's no upper limit to the maximum size of a nuclear warhead, but the yield-to-weight ratio imposes a practical limit based on current launch vehicle payload capacity.

 

[Morbius]

- Harold L. Brode, physicist, and pioneer of numerical simulations of nuclear explosions

Harold L Brode was a physicist at RAND that simulated nuclear weapons effects -
NOT the bomb itself. The only places where the nuclear weapon itself is simulated
in the USA is at Los Alamos and Lawrence Livermore.

- Samuel Cohen, inventor of neutron bomb

Cohen is the "self-proclaimed" inventor of the neutron bomb.

However, the devices that were once in the USA's stockpile called "neutron bombs"
dating from the '70s were the W-79 Mod 0 artillery shells and they
were invented by scientists at Lawrence Livermore; NOT Cohen.

None of this changes the answer to the poster's question: there's no upper limit to the maximum size of a nuclear warhead, but the yield-to-weight ratio imposes a practical limit based on current launch vehicle payload capacity.

There's no theoretical upper limit to the yield of a thermonuclear weapon.
A fission weapon does have lower and upper limits.
However, since a thermonuclear weapon needs to be "triggered" by a fission weapon, and the fission weapon
has a lower yield limit; the thermonuclear weapon has an effective lower limit, because its trigger does.

BTW, check your Physics Forum Private Messages.

Dr. Gregory Greenman
Physicist

 

[xllhawksllx]

Thats a horrible idea, as you said it would send thousands of pieces towards earth. Most likely, the solution would be to push the asteroid out or somehow detonate it where it would split into and somehow well that remains to be figured in how to deal with the remaining pieces.

 

[Morbius]

Thats a horrible idea, as you said it would send thousands of pieces towards earth. Most likely, the solution would be to push the asteroid out or somehow detonate it where it would split into and somehow well that remains to be figured in how to deal with the remaining pieces.

xllhawksllx,

You don't understand how you use a nuclear device to deflect an asteroid.

You don't "blow up" the asteroid. You detonate the nuclear weapon at a stand-off
distance from the asteroid. The radiation from the nuclear weapon ablates the surface
of the asteroid, which causes it to recoil.

The nuclear weapon PUSHES the asteroid; it doesn't "blow it up".

For a large asteroid, a nuclear weapon may be the ONLY HOPE; because only a
nuclear weapon has enough energy to deflect a large asteroid in a package that
is light enough for us to launch into space.

Dr. Gregory Greenman
Physicist

 

[James Essig]

Extreme Size of Thermonuclear Devices for Space Based Planetary Protective Measures

There are a number of ways extremely large nuclear devices could be fabricated for any of a wide variety of extreme planetary defense scenarios.

The first such scenario involves destroying a distant but inward bound asteriod or planetary body of extreme size. Note that the destruction of such a large body is possible if given enough time to fabricate a large enough nuclear device in Earth or Solar orbit. One can consider an extreme but rather absurd case wherein a global society might want to construct a thermonuclear device comprising 10 EXP 15 metric tons of fusionable material of simmilar construction to a fission-fusion-fusion device. Such a device would have a yield of approximately 10 EXP 23 tons of TNT or about 50 times the mass of the Earth in TNT which is roughly equivalent to the heat of vaporization of a typical mass of solid ordinary planetary materials with total mass equal to (n)(50)(Me) where n ranges from unity to 10 and depends on the materials and Me is the mass of the Earth. Such a device, if utilizing a dense hydrogenic compound for fusion fuel such as Lithium Dueteride, would have a diameter on the order of 100 kilometers.

The fusionable fuel for such a device would have to be collected from Earth and/or other planetary bodies and perhaps comets which comprise a large percentage of their material in the form of low atomic number exothermically fusionable elements. Thus such a large device would not be practicable nor possible to construct rapidly enough to respond to near term planetary emergencies such as the near term threat of a huge asteriod collision.

A more likely scenario for the use of devices this large and larger would involve the threat of extraterrestrial biological organisms such as may exist within a interstellar dust cloud in the form of exotic dangerous micro-organisms or any other simmilar interstellar threat. Such a threat in unlikely to be discovered any time soon and such a discovery would probably entail the ability and infrastructure in possession of future humanity to travel throughout interstellar space for which there have been suggested and studied numerous propulsion techniques that do not require any fundamental physics beyond what has already been commonly excepted and utilized on a wide scale in industry and research throughout the Globe.

One can, for instance, imagine the collection of cometary material from say the Kuiper Belt and/or the Oort cloud by intentionally directing comets in relatively slow collisions amongs themselves until a planetary body sized collection of low atomic number elements and their various isotopic forms has been accumulated. A means for purifying the collected material to form a planet sized nuclear device of precisely manufactured material content might be required to produce a workable thermonuclear device or perhaps the collected material could be ignited without refinement. In the later case, perhaps one or more large enough secondary nuclear devices could be used to initiate the
fusion of the collected mass at various locations wherein the process of fusion would quickly spread throughout the entire planetary mass until all of the collected fusionable material has fused. As another option, perhaps one or more large shaped charged nuclear fusion devices could produce the critical pressures required to initiate self propagating fusion reactions throughout the collected material. Note that a nuclear fusion device with the mass of the Earth would have a yield of roughly 10 EXP 29 tons of TNT or roughly the mass of TNT of two orders of magnitude greater than the approximate 10 EXP 27 metric tons mass of the Sun.

Although larger devices would seem to have no obvious conceivable purposes, one can even imagine as a very, very long term stellar engineering project, the very gradual construction of a thermonuclear device with the mass of a white dwarf star wherein the materials of construction would be supercooled at the construction site and gradually assembled and with a means for radiative heat exhaustion whereby the collection of matter could be built up in such a manner that it would not ignite and form a star. Obviously, a means would have to be devised to cope with the extreme gravitational forces on the surface of the growing orb which would eventually become, in a sense, a white dwarf as its increasing mass caused gravity induced self compression into white dwarf like matter densities.

As yet an even more extreme case, one can imagine the construction of a huge toriodal ring with the diameter of our planetary solar system comprising a mass of 10 EXP 5 to 10 EXP 6 solar masses of fusionable fuel wherein the torus would be gradually spun up as it is constructed in order to prevent gravitational collapse of the device as its mass increases. Accordingly, the device could be constructed at symmetrically disposed locations about a circle in either a discreet or continuous fashion. As the device neared completion, its final rotational velocity would be several hundreds of kilometers per second and the rotational velocity of the device would be designed along with the major diameter, thickness, and mechanical strength of the material composition of the torus in such a manner that the tidal forces acting on portions of the torus between locations at different radial distances from the center of the torus would have minimal effect. The torus when fully constructed would preferably be dense enough so that, even given its extreme size, its density would be close to that of a white dwarf inorder to provide a potentially much more stable and thin torus. For a torus having a 10 EXP 10 kilometer circumference, a mass of 10 EXP 6 solar masses, and a thickness of 10,000 kilometers. the density of the torus would approach that of a white dwarf.

Much larger torus shaped nuclear devices may be possible, but at the risk of boring the reader with absurdity, these more extreme versions will not be discussed here.

The point to be made here is that, literally speaking, there is no upper limit to the mass of a thermonuclear device. Why would mankind choose to produce the extreme sized devices described above is amyones guess. However, it may be useful to point out that the cosmos over long time frames is a metaphorical shooting gallery. One has to merely recall the event that supposedly wiped out the dinosaurs and realize that over a long enough time period, most probably, even larger threats will present themselves. If we are going to plan for the survival of mankind for the next thousand years, why not plan for our survival essentially for eternity.

 

[Astronuc]

The point to be made here is that, literally speaking, there is no upper limit to the mass of a thermonuclear device.

Um - there is a practical limit in which the yield is limited by the size, such that it would be impractical to build a large device. In addition to the yield, there is the matter of delivering the device. The bigger the device, the larger the propulsion system necessary to deliver it.

Pardon me, but a device based on 10¹⁵ metric tons of fusionable material is absurd!

 

[James Essig]

Hi Astronuc;

Thanks for the feedback.

A much more practical 1,000 megatons to safety destroy a 1/4 mile wide or even a 1/3 mile wide asteriod might be doable providing at least one third of the bombs energy can be deposited within the asteriod's material composition. 1,000 megatons of TNT releases the energy required to completely vaporize 2 cubic kilometers of water ice and because of the relatively lower specific heat and heat of vaporization of many solid minerals and metals roughly, an equal volume of rock and metal may be vaporized depending on the minerals and metals in question. Note that even though it is relatively easy to bring water from freezing to boiling, the heat of vaporization of water is about 1.85 megajoules/kilogram as opposed to the 0.420 megajoules/kilogram necessary to heat liquid water just above freezing to boiling temperature. The specific heat of water and its heat of vaporization is about as high as they come for ordinary materials.

Note that a 1 megaton nuclear warhead detonation in a surface blast will produce a crater 1,000 feet across and 200 feet deep in granite. Much of the ejected material would be vaporized in a surface blast and much of the remainder that is not vaporized will be pulverized into dust and or grainular pebble sized material. Based on the 1/3 route scaling of crater depth with yield, a 1,000 megaton device would produce a crater 10,000 feet across and 2,000 feet deep. Even based on the perhaps more precise EXP 0.31 dependence of crater size with incremental yield increase where the depth of the crater for a nuclear device detonated at Earth's surface scales as the EXP 0.31 incremental yield increase, we are still talking about a crater depth of at least 1/3 of a mile.

A good question would be how to effectively couple the bombs blast energy to the asteriodal material without causing it to break into smaller pieces. Perhaps using a robust deep asteriod penetration mechanism simmilar to the robust deep Earth penetration techniques studied within the U.S. defense establishment could be used to produce a much greater coupling between the bomb energy and the asteriodal material. Note that as big as the craters produced by surface detonations of nuclear weapons are, much of the weapons total energy is reflected back upward away from the ground so that more effective coupling of the blast energy to the ground as in a sub-surface burst produces a crater of considerably greater dimensions.

Another option would be to use a 1,000 megaton device in the form of a directed energy nuclear device such as a shaped charged nuclear device that would produce directed energy in the form of a much hotter, much higher pressured, and much higher velocity jet in a simmilar manner utilized by conventional shaped charged explosive devices used to defeat heavilly armoured vehicles. Some publically available sources quote the maximum potential explosive energy flux density from such a device as much as 6 orders of magnitude greater than that achievable by a traditional spherically symmetric nuclear detonation. Just as an interesting aside, this upper range for shaped charged nuclear explosives corresponds to a kinetic energy of protons within the explosion of about 10 TeV. This is within the range to be studied by the upgraded LHC of CERN in an attempt to discover the Higgs Bosons which are believed to be the quanta of the Higgs Fields which according to the Standard Model of Particles and Fields, is the mechanism responsable for mass generation and inertia for all known particles having mass in our universe.

The mattergy jet produced by a nuclear shaped charge device of 1,000 megaton yield might be just the right mechanism to effectively couple the blast energy to the asteriod providing that a large portion of the total energy of the blast can be incorporated within the jet.

For larger asteriods, larger devices could be constructed. Note that the approximate alledged 400 kilograms per megaton as the maximum mass specific yield of a nuclear device might not be valid if a large enough supply of fusionable fuel can be appropriately disposed around the fission primary of the thermonuclear device. Note that just one kilogram of hydrogen fully fusioned via the proton proton reaction cycle has a yield of about 200 kilotons. If such a reaction could propagate through a 100 metric ton thermonuclear device that is mostly hydrogen with about 95% or greater efficiency, then a 100 metric ton device based on the proton proton cycle could have a staggering yield approaching 20,000 megatons or a whopping 20 gigatons. I would think that this size of a device could be developed and llifted into low Earth orbit by the ARES V booster under development to lift into orbit the components of the CEV that will take mankind back to the Moon by about the year 2020. The large rocket propulsion system to accellerate this monster device to target an asteriod could be seperately lofted by another ARES V booster wherein the two components would be assembled in low Earth orbit.

Best Regards;

Jim

 

[James Essig]

I would like to wish all of the readership of this site and your families and loved ones a great New Year and many more to follow.

Regards;

Jim

 

[LURCH]

Thanks Jim.
Interestuing that this thread should get resurected now. I just read an article about a possible impactor headed for Mars. All scenarios for defending Earth from an impact rely no the early detection and accurate prediction f the impending impact event. If the asteroid 2007 WD5 hits Mars, it will do so within the month, and still nobody can say for sure. Not a very promissing sign.

 

[baywax]

Thanks Jim.
Interestuing that this thread should get resurected now. I just read an article about a possible impactor headed for Mars. All scenarios for defending Earth from an impact rely no the early detection and accurate prediction f the impending impact event. If the asteroid 2007 WD5 hits Mars, it will do so within the month, and still nobody can say for sure. Not a very promissing sign.

How accurately was the Shoemaker-Levi event predicted?

 

[James Essig]

Hi LURCH and baywax;

Thanks for your comments and feedback.

Given that a one megaton nuclear warhead releases the energy to fully vaporize 2 million metric tons of water ice or 2 million cubic meters of ice, and by virtue of many minerals' and metals' much lower heat of vaporization and specific heat compared to water, an equal volume of many of these much denser minerals and compounds could be vaporized by a one megaton device. I would have to say that if the energy of a one megaton nuclear detonation could be evenly distributed throughout a 450 foot diameter asteriod, the asteriod could be completely vaporized by such a device.

Note, that a surface detonation of only a one megaton nuclear warhead will produce a crater 200 feet deep and 1000 feet wide in hard rock, even in consideration that much of the blast energy of a surface nuclear detonation is instantly reflected back away from the ground. I would have to say that a robust deep asteriod penetrating one megaton nuclear warhead should be able to vaporize completely at least a 100 meter diameter asteriod. A 100 meter diameter asteriod would have a mass on the order of 1.5 million tons.

Such an asteriod hitting the surface of the Earth at a typical 20 Km/Sec would have a yield of (1.5 x 10 EXP 6)((7) EXP 2) tons of TNT or about 75 megatons which is almost as powerful as the most powerful publically agknowledge H-Bomb design of the former U.S.S.R. at 100 megatons. Such a 75 megatons explosion would be catastrophic if it happened in New York City, Mexico City, Tokyo, Beijing or other very large metro area.

Note that the thermal pulse of the Russian 58 megaton Tsar Bomba tested in 1961 in an airburst over a remote Arctic island location would have caused fatal third degree burns in humans at a distance of 100 kilometers from the blast epicenter. Although detonated 2.5 miles above the ground over the island, the rock crust beneath the blast was turned to ash. A woman who later visited the test side was amazed when she saw and noted that the blast zone was licked clean and shinny like an ice skating rink, all traces of uneveness in the rocks where melted and swepted away. Such an explosion's thermal pulse is large enough in the extent of its effects to completely set ablaze the entire land mass of many smaller nations and several of the smaller states within the U.S..

Clearly even only a 100 meter diameter asteriod, although not able to wipe out the human race, could produce totally unacceptable losses of property and human life. A direct nuclear strike by a typcial 0.475 megaton to one megaton yield warhead may be our only option in dealing with 100 meter diameter class asteriods on relatively short notice. Note that perhaps a couple to a few W-88 nuclear warheads such as those stationed aboard U.S. Ohio Class SSBM boats could probably do the job. The yield of one W-88 warhead is about 0.475 megatons or 475 kilotons.

Much larger asteriods might be destroyable with nuclear devices of much higher yield given enough lead time to construct and/or deploy such devices. Super large asteriods could be deflected potentially with a high yield stand off neutron bomb detonation wherein the intense neutron flux would penetrate several meters into the asteriod vaporizing the surface layer of the asteriod thus allowing the momentum imparted to the asteriod for course correction to be maximized by the recoil produced by the reaction between the hot very high pressured vaporized surface layer in gaseous form and the bulk of the remaining asteriod.

Best Regards;

Jim Essig

 

[baywax]

Hi LURCH and baywax;

I would have to say that if the energy of a one megaton nuclear detonation could be evenly distributed throughout a 450 foot diameter asteriod, the asteriod could be completely vaporized by such a device.

How does one evenly distribute the energy of a one megaton nuclear detonation throughout an asteroid?

Do we get someone like Bruce Willis out there drilling holes for and even distribution?

 

[James Essig]

Hi baywax;

Thanks for the response.

You make an excellent point. If one is going to go through the trouble of bringing the hardware and/or explosives such as dynamite to drill a hole to the center of the asteriod, why not just attach a large effecient chemical rocket to nudge it out of the way. Perhaps on relatively short notice, a assemblage of powerful chemical rockets might do the job. Assumming that perhaps 2000 metric tons of rocket propellent would be used wherein the energy of propellent to asteriod velocity vector changing kinetic energy would be equal to 50 %, one can imagine the rocket system pushing on the asteriod to change its velocity by as much as about 100 meters per second which is very significant giving enough lead time assumming that the mass specific energy release for the combined masses of the rocket fuel components is roughly equal to that of TNT detonation. At the very least, the asteriod might be directed into a mid-ocean environment or to the middle of Antartica where it would likely do much less harm than if it hit a populated area.

Another draw back of nuking asteriods at very close range is the spread of the radioactive fallout cloud or a significant portion of it composed of radioactive gas, condensed particles, and soot from the destroyed asteriod. The whole planet could receive an unsafe dose of radioactive fallout at best.

Personally, I kind of like the huge chemical rocket idea in part because we understand chemical rockets very well. Scaling them up to huge proportions however would take some doing. But, better safe than sorry.

Thanks;

Jim Essig

 

[stewartcs]

At the very least, the asteriod might be directed into a mid-ocean environment or to the middle of Antartica where it would likely do much less harm than if it hit a populated area.

Everything I've seen on the Discovery channel about asteroid impacts seem to indicate that it wouldn't matter where it hit, the subsequent damage would be propogated around the earth. I also remeber seeing something about the force of impact traveling through the center of the Earth and causing greater damage on the other side. Of course the size and velocity of the asteroid would dictate how much damage was done.

CS

 

[DaveC426913]

I also remeber seeing something about the force of impact traveling through the center of the Earth and causing greater damage on the other side. Of course the size and velocity of the asteroid would dictate how much damage was done.

CS

As for the planetoid that hit Mars and made the giant http://www.davesbrain.ca/whims_mars_atlas.php?map=altitude&labels=on" *, just ask the former residents of the Tharsis bulge and the Valles Marineris.

* sorry, IE only.

 

[baywax]

As for the planetoid that hit Mars and made the giant http://www.davesbrain.ca/whims_mars_atlas.php?map=altitude&labels=on" *, just ask the former residents of the Tharsis bulge and the Valles Marineris.

* sorry, IE only.

Yes, it is also possible that an impact also took half of Mar's crust off.

Hemispheres Apart: The Crustal Dichotomy on Mars
Thomas R. Watters,1 Patrick J. McGovern,2 and Rossman P. Irwin III1
1Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, D.C. 20560; email: watterst@si.edu

2Lunar and Planetary Institute, Houston, Texas 77058

Abstract The hemispheric dichotomy is a fundamental feature of Mars, expressed by a physiographic and geologic divide between the heavily cratered southern highlands and the relatively smooth plains of the northern lowlands. The origin of the dichotomy, which may have set the course for most of the subsequent geologic evolution of Mars, remains unclear. Internally driven models for the dichotomy form the lowlands by mantle convection, plate tectonics, or early mantle overturn. Externally driven models invoke one giant impact or multiple impacts. Areal densities of buried basins, expressed by quasi-circular depressions and subsurface echoes in radar sounding data, suggest that the dichotomy formed early in the geologic evolution of Mars. Tectonic features along the dichotomy boundary suggest late-stage modification by flexure or relaxation of the highlands after volcanic resurfacing of the northern lowlands. Subsequent deposition and erosion by fluvial, aeolian, and glacial processes shaped the present-day dichotomy boundary.

http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.earth.35.031306.140220

 

[baywax]

Hi baywax;

Thanks for the response.

You make an excellent point. If one is going to go through the trouble of bringing the hardware and/or explosives such as dynamite to drill a hole to the center of the asteriod, why not just attach a large effecient chemical rocket to nudge it out of the way. Perhaps on relatively short notice, a assemblage of powerful chemical rockets might do the job. Assumming that perhaps 2000 metric tons of rocket propellent would be used wherein the energy of propellent to asteriod velocity vector changing kinetic energy would be equal to 50 %, one can imagine the rocket system pushing on the asteriod to change its velocity by as much as about 100 meters per second which is very significant giving enough lead time assumming that the mass specific energy release for the combined masses of the rocket fuel components is roughly equal to that of TNT detonation. At the very least, the asteriod might be directed into a mid-ocean environment or to the middle of Antartica where it would likely do much less harm than if it hit a populated area.

Another draw back of nuking asteriods at very close range is the spread of the radioactive fallout cloud or a significant portion of it composed of radioactive gas, condensed particles, and soot from the destroyed asteriod. The whole planet could receive an unsafe dose of radioactive fallout at best.

Personally, I kind of like the huge chemical rocket idea in part because we understand chemical rockets very well. Scaling them up to huge proportions however would take some doing. But, better safe than sorry.

Thanks;

Jim Essig

Pretty complicated James! But, the big rocket idea seems more plausible than the idea of drilling into an asteroid and precisely planting a nuke for max. even distribution of energy. Besides, Bruce Willis probably isn't willing to risk his neck again for this one (re: the movie: Armageddon, 1998)

How about building boosters on Earth to get us out of the way!? Either way, I think there are groups who have dug themselves in for an occasion such as this. They've stashed their gold, oil, food, SUVs and swimming pools deep under the Rockies etc... Too bad they'll be the only ones representing the human race when all the dust, ash and crust settles.:-(

 

[James Essig]

Hi stewartcs and DaveC426913;

In fact I heard on the Discovery Channel that an asteriod of the size of that which blasted out the Yucatan Peninsula and perhaps killed off the dynosuars may have turned the entire atmosphere of planet Earth into a broiler thus killing any dynosuars that would have survived the initial blast wave as it circled the globe. Accordingly, there would be so much glowing red hot and white hot debris shot out into orbit around the Earth that the black body thermal emmissions from such debris would have roasted the surface of the Earths land mass and might have even caused ponds and shallow lakes to begin bioling. The animals that survived would be of the types that could borrow underground or dive underwater to take advantage of the thermal inertia of the ground and deep water.

Hi baywax;

I not sure what we could do if we saw a 6 to 10 mile wide asteriod heading for Earth and due to impact in a couple of weeks wherein the asteriod was of dark surface color and therefore missed by astonomers until a few weeks before doomsday. I suppose I would break out my grill or try to buy an outdoor turkey smoker and cook some real good final barbecued food. In such a case, mankind might have to impart on a crash course to produce as many nuclear warheads as we could and of unprecedented yield and let the asteriod have it either by many simultaneous and/or repeated direct hits or via stand off blasts that would gradually nudge the sucker out of the way via the surface layer high pressure gas prooducing ablative effects of the stand off nuclear detonations. In this scenario, short of this, I can't see what else we could do. In such a case, I completely agree with you that, unfortunately, all that humanity would have left to represent us after the smoke, fire, and dust settled out would be those folks hold up deep underground with those SUVs, oil depos, gold, food, and swimming pools: a rather scary thought!.

Thanks;

Jim

 

[stewartcs]

Hi stewartcs and DaveC426913;

In fact I heard on the Discovery Channel that an asteriod of the size of that which blasted out the Yucatan Peninsula and perhaps killed off the dynosuars may have turned the entire atmosphere of planet Earth into a broiler thus killing any dynosuars that would have survived the initial blast wave as it circled the globe. Accordingly, there would be so much glowing red hot and white hot debris shot out into orbit around the Earth that the black body thermal emmissions from such debris would have roasted the surface of the Earths land mass and might have even caused ponds and shallow lakes to begin bioling. The animals that survived would be of the types that could borrow underground or dive underwater to take advantage of the thermal inertia of the ground and deep water.

That was my point! It wouldn't matter where it hit on Earth if it was big and fast enough.

CS

 

[DaveC426913]

... an asteriod of the size of that which blasted out the Yucatan Peninsula and perhaps killed off the dynosuars may have turned the entire atmosphere of planet Earth into a broiler thus killing any dynosuars that would have survived the initial blast wave as it circled the globe. Accordingly, there would be so much glowing red hot and white hot debris shot out into orbit around the Earth that the black body thermal emmissions from such debris would have roasted the surface of the Earths land mass and might have even caused ponds and shallow lakes to begin bioling.

To my ear this sounds like quite an exaggeration of generally plausible and accepted events, but I can not be sure.

 

[baywax]

Hi baywax;

I not sure what we could do if we saw a 6 to 10 mile wide asteriod heading for Earth and due to impact in a couple of weeks wherein the asteriod was of dark surface color and therefore missed by astonomers until a few weeks before doomsday. I suppose I would break out my grill or try to buy an outdoor turkey smoker and cook some real good final barbecued food. In such a case, mankind might have to impart on a crash course to produce as many nuclear warheads as we could and of unprecedented yield and let the asteriod have it either by many simultaneous and/or repeated direct hits or via stand off blasts that would gradually nudge the sucker out of the way via the surface layer high pressure gas prooducing ablative effects of the stand off nuclear detonations. In this scenario, short of this, I can't see what else we could do. In such a case, I completely agree with you that, unfortunately, all that humanity would have left to represent us after the smoke, fire, and dust settled out would be those folks hold up deep underground with those SUVs, oil depos, gold, food, and swimming pools: a rather scary thought!.

Thanks;

Jim

Its interesting that you noted the low reflectivity and high light-absorbency of some asteroids... to the point of only reflecting 4 percent of the light hitting them.

That makes them particularly scary. These are called "ghouls" by some astronomers. Very hard to detect and therefore a cause for the learned types to be paranoid at all times.

Why not strike up the BBQ every day or the equivalent since it could be any day of the century that this impact could happen, with no one the wiser... except the outlandishly paranoid types who, at this very moment, are living underground, in artificial light, because they know there is very little warning about a bollide event taking place and being caused by a "GHOUL"!

This is an interesting topic, mind you, and I think we could come up with a solution that would favour the people of the Earth if we really put some effort into it. Your multiple hits from all angles by nukes is a good start. It would just have to be far enough away from Earth to help us avoid the radon clouds etc..

Another disconcerting thought is... we have never, overtly, exploded a nuke in space so we need to know what those effects are before we do. Who knows, it might cause a chain reaction of black holes sucking our solar system into another universe... beam me up Scottie!

 

[James Essig]

Hi baywax;

Thanks for the interesting info regarding the actual reflectivity of the GHOULS and related nomenclature.

It is hard to be certain what the extreme effects of space based nuclear detonations could be. I have heard of quasi-scientific notions that such effects could by chance produce electromagnetic space time bridges to other locations in space time including into the past or future. The result accordingly would be an electromagnetic wormhole produced by the device's low frequency electromagnetic pulse. If such could be produced, it might perhaps be dangerous for our civilization or life on Earth if the electromagnetic wormhole provided a link between the present and the past wherein energy or information could be transmitted into the past into the Earth wherein it might pose the possibility of changing the present in drastic ways.

Certain theories on the possible pluasibility of time travel suggest that a temporal causality censorship principle would prevent the travel into the past by persons, information, or energy form interfering with the present even in consideration of free will in the sense of actions not being completely determined by their causes. One version of such a conjecture holds that if a time traveler tried to change the present by changing the past freely or was in positions to perform a deterministically constrained act that could do such, nature would act to prevent such from happening such as by causing the time traveler to suddenly pop back into the present time and location from whence he left.

Another possibility is that such a time traveling act would result in the chance in the present to be realized in a parallel history of the type simmilar to those conjectured to exists in the "Many Worlds Interpretation" of quantum theory in which each act of the collapse of a wavefunction causes a branch of parallel history to be formed. Accordingly. there are ensembles if not infinities of new complete parelell histories forming all of the time as a result of each naturally occurring quantum act of decoherence even on microscopic particle levels.

If such electromagnetic wormholes are possible by remote chance, perhaps brought on by a chance electromagnetic low frequency radiation pattern of flux distribution, there is a real possibility that it could be very dangerous.

I think I remember that in the original "Planet of the Apes" series of books and movies, such an electromagnetic time warp is what caused the fusion powered long duration flight relativistic starship launched from Earth to enter a time portal and travel a few hundred years into the future wherein the crew members that survived the suspended animation process eventually came to realize that they had landed back on Earth in the distance future wherein the civilization that they had left behind was destroyed in a global nuclear holocuast.

I don't know if such electromagnetic time portals can exist but I can think of some additional ways that they might be realized although only in a general sense although I have no idea how one would actually be produced in detail either artificially or naturally. One way to view the electromagnetic force is that it is a fundamental force just like general relativistic gravity for which there is mounting mathematical and theoretical evidence that wormholes into the past, future, cosmically remote locations in space time within our universe can exist, and perhaps also travel into other universes or Big Bangs that remain at least causally weakly coupled to our universe or wherein such causality and information exchange ability, even if normally dorment, can be activited by rare natural or perhaps be artificial general relativistic gravity based wormholes on demand.

This, however, is a very fascinating subject to me as well.

Thanks;

Jim

 

[baywax]

Hi baywax;

Thanks for the interesting info regarding the actual reflectivity of the GHOULS and related nomenclature.

It is hard to be certain what the extreme effects of space based nuclear detonations could be. I have heard of quasi-scientific notions that such effects could by chance produce electromagnetic space time bridges to other locations in space time including into the past or future. The result accordingly would be an electromagnetic wormhole produced by the device's low frequency electromagnetic pulse. If such could be produced, it might perhaps be dangerous for our civilization or life on Earth if the electromagnetic wormhole provided a link between the present and the past wherein energy or information could be transmitted into the past into the Earth wherein it might pose the possibility of changing the present in drastic ways.

Certain theories on the possible pluasibility of time travel suggest that a temporal causality censorship principle would prevent the travel into the past by persons, information, or energy form interfering with the present even in consideration of free will in the sense of actions not being completely determined by their causes. One version of such a conjecture holds that if a time traveler tried to change the present by changing the past freely or was in positions to perform a deterministically constrained act that could do such, nature would act to prevent such from happening such as by causing the time traveler to suddenly pop back into the present time and location from whence he left.

Another possibility is that such a time traveling act would result in the chance in the present to be realized in a parallel history of the type simmilar to those conjectured to exists in the "Many Worlds Interpretation" of quantum theory in which each act of the collapse of a wavefunction causes a branch of parallel history to be formed. Accordingly. there are ensembles if not infinities of new complete parelell histories forming all of the time as a result of each naturally occurring quantum act of decoherence even on microscopic particle levels.

If such electromagnetic wormholes are possible by remote chance, perhaps brought on by a chance electromagnetic low frequency radiation pattern of flux distribution, there is a real possibility that it could be very dangerous.

I think I remember that in the original "Planet of the Apes" series of books and movies, such an electromagnetic time warp is what caused the fusion powered long duration flight relativistic starship launched from Earth to enter a time portal and travel a few hundred years into the future wherein the crew members that survived the suspended animation process eventually came to realize that they had landed back on Earth in the distance future wherein the civilization that they had left behind was destroyed in a global nuclear holocuast.

I don't know if such electromagnetic time portals can exist but I can think of some additional ways that they might be realized although only in a general sense although I have no idea how one would actually be produced in detail either artificially or naturally. One way to view the electromagnetic force is that it is a fundamental force just like general relativistic gravity for which there is mounting mathematical and theoretical evidence that wormholes into the past, future, cosmically remote locations in space time within our universe can exist, and perhaps also travel into other universes or Big Bangs that remain at least causally weakly coupled to our universe or wherein such causality and information exchange ability, even if normally dorment, can be activited by rare natural or perhaps be artificial general relativistic gravity based wormholes on demand.

This, however, is a very fascinating subject to me as well.

Thanks;

Jim

I was going to suggest using sonic energy to break a bollide apart but... sound can't travel in space.:-, (and that wouldn't suit the Nuclear Engineering section of PF anyway!)

 

[binzing]

Dunno if its been said already. Discover did a similar article about satellite destroying, and the science channel has done a show on it.

 

[baywax]

Pentagon prepares to destroy defunct spy satellite

The US Navy isn't going to launch a nuke at the broken spy satellite but this is a first for the the Pentagon. After criticizing China for blowing up one of its own worn satellites, the Pentagon has decided its the only option for this one or have it raining down rocket fuel on potential, earth-bound victims.

So I thought this story was along the lines of this thread in the terms that there will be a launch and it will be aimed at an orbiting body in space.

http://news.yahoo.com/s/ap/20080214/ap_on_go_ca_st_pe/dead_satellite

 

[James Essig]

Hi baywax;

Thanks for providing the above link. I should be an interesting test of the missile's capabilities.

Regards;

Jim Essig

 

[Astronuc]

The US Navy isn't going to launch a nuke at the broken spy satellite but this is a first for the the Pentagon. After criticizing China for blowing up one of its own worn satellites, the Pentagon has decided its the only option for this one or have it raining down rocket fuel on potential, earth-bound victims.

So I thought this story was along the lines of this thread in the terms that there will be a launch and it will be aimed at an orbiting body in space.

http://news.yahoo.com/s/ap/20080214/ap_on_go_ca_st_pe/dead_satellite

Apparently the missile to be used to intercept the satellite is a Standard Missile 3, a product of Raytheon. I uses a conventional warhead, not a nuclear warhead.

http://www.globalsecurity.org/space/systems/sm3.htm

 

[James Essig]

Hi again;

It occurred to me inorder to completely avert the risk of material hitting the ground, perhaps the interceptor missle could be fitted with a 1 kiloton to 5 kiloton nuclear device that detonates a few meters away from the sattelite via proximatety sensor to completely ionize the sattelite. There might be some radiation risk but not as much radioactive fallout as a ground burst would produce.

Thanks;

Jim Essig

 

[baywax]

The mission to destroy the failing US spy satellite was a total success according to Pentagon officials.

http://news.yahoo.com/s/ap/20080221/ap_on_go_ca_st_pe/dead_satellite

 

[carstensentyl]

(A moderate asteroid is between a thousand and a million Gigatons. Does that put it in perspective?)

That is far more than the combined mining blast fragmentation on the planet. That's a special thing to consider when nuclear warheads are occassionally used to fragment bedrock for mining operations.

If a giant meteor is headed, we had better divert it (can our weapons even nudge it in another direction?) because we stand no chance of destroying most meteors, when our mining can't even tickle the thin crust of the planet we live on.

 

[James Essig]

Hi carstensentyl;

Thanks for the feedback.

Note that there is no limit to the size of a thermonuclear warhead theoretically.

A thermonuclear warhead with a mass of 10 EXP 15 metric tons or a with diameter of 100 kilometers would produce enough blast, ionizing radiation, and thermal energy, in short its energy yield, to completely vaporize 50 planets with the mass of the Earth that were frozen to the core considering the heat capacity, latent heat of fusion, and latent heat of vaporization of the materials out of which Earth is composed.

A thermonuclear warhead with the mass of the Earth could completely vaporize 100 million such planets.

A artificially produced white dwarf massed thermonuclear warhead could completely vaporize (150,000)(100,000,000) or 15 trillion planets with the mass of the Earth.

A larger thermonuclear device involves another more far out idea to gradually construct a huge white dwarf densitied thermonuclear device with the mass of about 10 EXP 6 solar masses wherein the finished product would be a rotating toriod with a diameter of about 6billion kilometers. The device could be gradually spun up until it reached the end of construction and a rotation velocity on the order of several hundred kilometers/second would prevent it from undergoing gravitational collapse before detonation. White dwarf dense toriodal material would allow for a thin aspect ratio toriod to reduce gravitational/rotational induced tidal forces which otherwise could tear the ring apart. A rotational velocity of say 500 km/second would permit the fusion energy yield to be efficiently stored at about 5,000 times greater than that of the rotational kinetic energy.

This baby would have a yield of 1,000,000 carbon detonation supernova and could completely vaporize 15 million trillion such planets or 15 x 10 EXP 18 such planets.

A still larger version of a ring 600 billion kilometers in diameter would have a yield of 100,000,000 carbon detonation supernova and would produce enough yield energy to completely vaporize 1.5 x 10 EXP 21 such planets. If one out of every 30 stars in our observable universe has a planet like Earth orbiting it, the number of all of such planets in the observable universe with the mass of the Earth would be about 1.5 x 10 EXP 21.

Using matter/antimatter toroidal configurations or concentric matter and antimatter toruses made of nuetron dense forms of matter and antimatter such as solid neutronium and antineutronium, devices with a mass of 10 EXP 14 solar masses with a sub black hole enclosed volume density and a radius of 20 lightyears would produce enough energy upon matter antimatter annihilation completely vaporize 1.5 x 10 EXP 29 planets with the mass of the Earth frozen to the core. This is equivalent to the entire baryonic mass within the observable universe. However, such a device would be ridiculous to construct because it would produce a great enough hard gamma ray flux to potentially kill of all extraterrestrial civilizations within the observable universe with a current radius of 13.7 billion lightyears. However, given a billion years of ever increasing human population within the universe and growth of our space based materials production and manufacturing infrastructure, we could probably build such a device.

I can think of possibly even much larger yield thermonuclear and matter antimatter devices composed of a layered arrangement of fusion or matter antimatter fuels and an exotic theoretical material known as negative mass which has yet to be discovered let alone produced. With judicious layering of fuels and negative mass in an onion like arrangement, in theory devices with infinite mass and infinite yield could be constructed given an infinite amount of time to construct them. If the life time of protons turns out to be finite, one could simply use eternally stable forms of quarkonium, a theoretical material with a density as great as 1,000 times that of the atomic nucleus in the construction of the cosmic onion.

In short, there really is no theoretical limit to the size and yield of the devices we can construct.

On the lighter side, a pure fusion thermonuclear device with the mass of a modern nuclear powered aircraft carrier would have a diameter of only about 200 feet and yet could completely vaporize an asteroid with the mass of (1/2)(100,000)(200,000,000) metric tons or 10 trillion tons. A cubic mile pure fusion device with an average density of water could completely vaporize a (1/2)(1,000,000,000)(200,000,000) metric ton asteroid or an asteroid with a diameter of 425 kilometers.

Note that if efficient mass drivers in the form of electromagnetic guns can be developed to launch payload after payload into Earth orbit, there is no reason why a highly efficient billion ton fission fusion fusion nuke could not be assembled in low Earth orbit in 10 to 20 years and used to attack any asteroid conceivable given enough lead time. Huge chemical rockets could set the nuke on course to ablissimate any conceivable asteroid.

Regards;

Jim

 

[baywax]

In short, there really is no theoretical limit to the size and yield of the devices we can construct.

On the lighter side, a pure fusion thermonuclear device with the mass of a modern nuclear powered aircraft carrier would have a diameter of only about 200 feet and yet could completely vaporize an asteroid with the mass of (1/2)(100,000)(200,000,000) metric tons or 10 trillion tons. A cubic mile pure fusion device with an average density of water could completely vaporize a (1/2)(1,000,000,000)(200,000,000) metric ton asteroid or an asteroid with a diameter of 425 kilometers.

Note that if efficient mass drivers in the form of electromagnetic guns can be developed to launch payload after payload into Earth orbit, there is no reason why a highly efficient billion ton fission fusion fusion nuke could not be assembled in low Earth orbit in 10 to 20 years and used to attack any asteroid conceivable given enough lead time. Huge chemical rockets could set the nuke on course to ablissimate any conceivable asteroid.

Regards;

Jim

Is there a record of what happens when you detonate a nuke in space?

 

[carstensentyl]

Baywax. I think nukes are actually stronger in space, but I could be mistaken since I know nothing about nuclear fission.

Jame's post has some very interesting pointers about how much destruction a nuclear weapon can cause. However, I do not agree that we will have the technology to send anything larger than a conventional space shuttle into space any time soon. I suppose that the parts could be assembled in space.

Do we have a means of detonating a large nuclear device? Isn't there some limit to the amount that we are capable of detonating?

 

[DaveC426913]

Baywax. I think nukes are actually stronger in space, but I could be mistaken since I know nothing about nuclear fission.

I doubt it. Much of the destruction is due to the pressure wave that is transmitted through the air. In space, all you'd get is the primary shock, which is limited tot he mas of the bomb itself.

Do we have a means of detonating a large nuclear device? Isn't there some limit to the amount that we are capable of detonating?

Well, since we don't have the means to build one, I'm not sure how we don't have the means to detonate one...


However, it is a chain reaction, so there's no reason why it should be particularly difficult.

 

[Astronuc]

Dave is correct. The detonation of a nuclear device has to do with it's architecture, not the environment surrounding it.

A large nuclear device would be thermonuclear in which the fusion assembly is triggered with a fission device (trigger). In the case of a satellite it would be overkill.

In the case of an asteroid, the objective would be to get the warhead as close as possible to the asteroid (and possibly in contact or shallow penetration). The nuclear explosion would be used to rapidly heat (via radiation) one side of the asteroid and use the effect of ablation to deflect the asteroid.

The approach may be dependent on the composition of the asteroid, e.g. ice vs stoney/metal.

 

[baywax]

Dave is correct. The detonation of a nuclear device has to do with it's architecture, not the environment surrounding it.

A large nuclear device would be thermonuclear in which the fusion assembly is triggered with a fission device (trigger). In the case of a satellite it would be overkill.

In the case of an asteroid, the objective would be to get the warhead as close as possible to the asteroid (and possibly in contact or shallow penetration). The nuclear explosion would be used to rapidly heat (via radiation) one side of the asteroid and use the effect of ablation to deflect the asteroid.

The approach may be dependent on the composition of the asteroid, e.g. ice vs stoney/metal.

So, because there is no atmosphere to transfer a lot of the energy from the blast to the object (in space) the device is going to work better if its embedded in the material. Like one of the bunker buster-type shells with a delayed detonation time?

 

[carstensentyl]

There has got to be some sort of limit to the size of the explosion. Jam-packing more material into the bomb just doesn't seem to do it for me. There must be a maximum detonation velocity. Of course, we can always create a bigger explosion with multiple warheads...

 

[Astronuc]

So, because there is no atmosphere to transfer a lot of the energy from the blast to the object (in space) the device is going to work better if its embedded in the material. Like one of the bunker buster-type shells with a delayed detonation time?

Nuclear weapons produce a tremendous quantity of radiation in a broad spectrum, not only in gamma and X-ray, as would be expected in a nuclear explosion, but also in UV, visible and infrared. Many people in Hiroshima and Nagasaki received burns from the bright light, as well as receiving UV, X-ray and gamma radiation which penetrated the skin and body according to energy level.

If a nuclear warhead is detonated near an asteroid, it would receive a burst of radiation which would heat some volume and cause some material to ablate.

If the warhead impacted, then detonated, then there would be some explosive removal of the asteroid material.

There has got to be some sort of limit to the size of the explosion.

Yes, there is an optimal yield-size relationship, but that details would not be discussed in a public forum.