Author Topic: Deflecting or destroying dangerous asteroids  (Read 9617 times)

Offline catdlr

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Re: Deflecting or destroying dangerous asteroids
« Reply #20 on: 07/17/2017 04:37 AM »
NASA plans to deliberately crash DART spacecraft into an asteroid

Tech Insider
Published on Jul 16, 2017


Large asteroids colliding with Earth is extremely rare. However, if that happens, it could mean the end of civilization as we know it. NASA isn't taking any chances. It is currently developing DART, a small spacecraft that will crash into an asteroid to deflect it from Earth.

https://www.youtube.com/watch?v=KYy0t93lEMs?t=001

Tony De La Rosa

Offline stefan r

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Re: Deflecting or destroying dangerous asteroids
« Reply #21 on: 07/17/2017 06:13 PM »
A better (and far simpler) means of deflection is to direct a nuclear weapon at the incoming asteroid. The goal would not be to destroy the asteroid, but to detonate the weapon sufficiently close to the surface to pick up mass from the asteroid and blast it away (causing thrust in the opposing direction), thereby deflecting the asteroid from its original course.


using wikipedia for the radius of underground nuclear tests we could melt from 40 to 120 meters of rock per megaton yield.  It may not be realistic or desirable to bury the nuke.  A surface explosion would ablate and vaporize rock and would melt much less rock than the subsurface test.  The cracked zone is 800 to 1200 m/Mt1/3

Shock waves do not propagate through porous material the same way they propagate through crystalline solids.  Water ice transforms into liquid when compressed.  An explosion under a glacier will behave differently than an explosion under rock.  Underground nuclear tests do not give a precise model even if we could land and place the bomb.

If we have a 500m rubble pile and detonate a 1Mt nuclear device then we have a 499m rubble pile.  It becomes several pieces if the chunks are not bound tightly. 

4.184 x 1015J is one megaton.  A 500 meter asteroid (6 x 107 m3 could weigh in at 1011kg.  If we got 100% conversion of energy to thrust we would get 200 m/s change in direction.  I am not sure how to calculate the thrust from a surface explosion.  But I would guess less than 1%.  Which leaves 1 or 2 m/s.  Earth's radius is 6.3 x 106m so you need the explosion more than 2 months before the asteroid contacts earth. 

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #22 on: 07/17/2017 08:06 PM »
Which leaves 1 or 2 m/s.  Earth's radius is 6.3 x 106m so you need the explosion more than 2 months before the asteroid contacts earth. 
Note this is a very short timescale by planetary defense standards. The goal is to have years or decades of warning, and for the majority of the risk, this is achievable. For smaller objects, shorter warning can be used to evacuate the affected area instead.

FWIW, there were several presentations on the deflection in the conference videos I linked earlier. The first two in session 4 here discuss the nuclear option:



Offline gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #23 on: 07/18/2017 06:17 AM »
A better (and far simpler) means of deflection is to direct a nuclear weapon at the incoming asteroid. The goal would not be to destroy the asteroid, but to detonate the weapon sufficiently close to the surface to pick up mass from the asteroid and blast it away (causing thrust in the opposing direction), thereby deflecting the asteroid from its original course.


using wikipedia for the radius of underground nuclear tests we could melt from 40 to 120 meters of rock per megaton yield.  It may not be realistic or desirable to bury the nuke.  A surface explosion would ablate and vaporize rock and would melt much less rock than the subsurface test.  The cracked zone is 800 to 1200 m/Mt1/3

Shock waves do not propagate through porous material the same way they propagate through crystalline solids.  Water ice transforms into liquid when compressed.  An explosion under a glacier will behave differently than an explosion under rock.  Underground nuclear tests do not give a precise model even if we could land and place the bomb.

If we have a 500m rubble pile and detonate a 1Mt nuclear device then we have a 499m rubble pile.  It becomes several pieces if the chunks are not bound tightly. 

4.184 x 1015J is one megaton.  A 500 meter asteroid (6 x 107 m3 could weigh in at 1011kg.  If we got 100% conversion of energy to thrust we would get 200 m/s change in direction.  I am not sure how to calculate the thrust from a surface explosion.  But I would guess less than 1%.  Which leaves 1 or 2 m/s.  Earth's radius is 6.3 x 106m so you need the explosion more than 2 months before the asteroid contacts earth.

Which is actually a very good result. And if not, there is this novel idea of having more than one 1Mt nuke ready.

After all, we managed to make thousands of damn things for the purpose of killing each other, surely we should be capable of maintaining just a few dozens to save us all?

Offline mikelepage

Re: Deflecting or destroying dangerous asteroids
« Reply #24 on: 07/19/2017 09:13 AM »
A better (and far simpler) means of deflection is to direct a nuclear weapon at the incoming asteroid. The goal would not be to destroy the asteroid, but to detonate the weapon sufficiently close to the surface to pick up mass from the asteroid and blast it away (causing thrust in the opposing direction), thereby deflecting the asteroid from its original course.


using wikipedia for the radius of underground nuclear tests we could melt from 40 to 120 meters of rock per megaton yield.  It may not be realistic or desirable to bury the nuke.  A surface explosion would ablate and vaporize rock and would melt much less rock than the subsurface test.  The cracked zone is 800 to 1200 m/Mt1/3

Shock waves do not propagate through porous material the same way they propagate through crystalline solids.  Water ice transforms into liquid when compressed.  An explosion under a glacier will behave differently than an explosion under rock.  Underground nuclear tests do not give a precise model even if we could land and place the bomb.

If we have a 500m rubble pile and detonate a 1Mt nuclear device then we have a 499m rubble pile.  It becomes several pieces if the chunks are not bound tightly. 

4.184 x 1015J is one megaton.  A 500 meter asteroid (6 x 107 m3 could weigh in at 1011kg.  If we got 100% conversion of energy to thrust we would get 200 m/s change in direction.  I am not sure how to calculate the thrust from a surface explosion.  But I would guess less than 1%.  Which leaves 1 or 2 m/s.  Earth's radius is 6.3 x 106m so you need the explosion more than 2 months before the asteroid contacts earth.

Which is actually a very good result. And if not, there is this novel idea of having more than one 1Mt nuke ready.

After all, we managed to make thousands of damn things for the purpose of killing each other, surely we should be capable of maintaining just a few dozens to save us all?

I'll quote this whole post of mine, but I do like to refer back to this table every now and then. 1% conversion to kinetic energy from an 8Mt stand off explosion is probably being conservative.

Something about the scenario mentioned doesn't quite square up for me.  The scenario was a simulated impact date of September 20th, 2020, with astronomers being able to determine with 100% likelyhood that impact would occur by May of 2017.  And then they say:

"While mounting a deflection mission to move the asteroid off its collision course had been simulated in previous tabletop exercises, this particular exercise was designed so that the time to impact was too short for a deflection mission to be feasible"

Really? 3 years is too little time?  For a gravity tractor, definitely, but I'd like to think somebody would put a nuclear warhead on a rocket.

I ran some numbers assuming a nuke equivalent to 8 MegaTons of TNT (mass about 2 metric tons) which is on the upper edge of this plot:



and (assuming 1% of the warhead's energy is converted to kinetic energy) I calculated how big a dV this might cause in various sized impactors (assuming spherical comets/asteroids) and how long that dV would need to cause an Earth width deflection:



Pretty rough working I know, and I'm sure it's been done more precisely elsewhere, but we know a Falcon 9 can put DSCOVR in Sun-Earth L1 in 100 days and could be ready in under 6 months. SE-L1 is 1.5 million Km from Earth (or about 20 hours for a comet moving at 20km/s).

So to deflect a 250m impactor that they're talking about, you'd need the nuke to meet the rock at least that far away from Earth (probably more depending on trajectory).  A falcon 9 could certainly put a 2 ton payload at least that far out in 4 months.

Maybe it would take another 8 months to get through the legal implications of putting a nuke on a rocket, but honestly, if that was the only way to do it, I'd like to think it would happen.  In any case, I'm not sure I see why it need take much longer than 18 months?

It doesn't really help us if we had a dinosaur-killer comet coming in from outside the ecliptic like comet sliding spring, but for <1km impactors with >2 years warning, surely we could make it work...


« Last Edit: 07/19/2017 09:13 AM by mikelepage »

Offline mikelepage

Re: Deflecting or destroying dangerous asteroids
« Reply #25 on: 07/23/2017 05:08 AM »
Whitelancer64 points out to me that the most common US nuke developed for missile deployment is the W87, which has a yield of 475kT (updated from 300kt - see wiki), or ~17x less than my hypothetical 8Mt nuke.  However they are also lighter at ~250kg.

It's hard to believe that only one would be sent at a time (they were designed to be sent 12 at a time which is easily with the capability of an F9), but if it were, one would have to adjust the numbers in my table up (can't find the original table so just doing this by hand).  Again assuming 1% conversion to kinetic energy.

Time to deflect asteroid by one earth diameter for 1x W87, or 12x W87:
12km (Dino killer): 4930 days (13.5 years), 411 days
4km: 949 days (2.59 years), 79 days
1km: 117 days, 9.7 days
250m: 14 days, 1.2 days

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #26 on: 07/24/2017 02:28 AM »
... Again assuming 1% conversion to kinetic energy. Time to deflect asteroid by one earth diameter for 1x W87, or 12x W87:
250m: 14 days, 1.2 days
1) Where are getting the 1% conversion assumption? Is that based on vaporization of surface material?
2) After the Chelyabinsk meteor, Russia declared a single Dnepr (RS-36) with ten warheads (550-750kt each) would obliterate a 100m object with only a few hours notice. Impacting converts the majority of energy into kinetic - as opposed to simply brushing the surface with radiation. Having "bunker buster nukes" already designed for impacting is a bonus, unless you're the target.

Offline mikelepage

Re: Deflecting or destroying dangerous asteroids
« Reply #27 on: 07/24/2017 05:57 AM »
... Again assuming 1% conversion to kinetic energy. Time to deflect asteroid by one earth diameter for 1x W87, or 12x W87:
250m: 14 days, 1.2 days
1) Where are getting the 1% conversion assumption? Is that based on vaporization of surface material?
Nothing so sophisticated.  The way I thought of it is that the explosive energy radiates evenly in all directions, and you don't necessarily want to explode a rubble pile so much as shift it.  You would probably perform a stand off explosion at some distance from the asteroid so the energy front from the bomb is roughly unidirectional.

Surface area of a sphere is 4πr2, (or 41253 square degrees) so 1% conversion to KinE assumes that the asteroid takes up about a 20 x 20 degree patch of sky relative to the bomb.  Or in other words, for a 250m asteroid, if the bomb is detonated 731m away, that means 1% of the energy from the bomb reaches the asteroid.  You could go closer, but you're more likely to break it up into multiple impactors.  1% was a nice round number.

Quote
2) After the Chelyabinsk meteor, Russia declared a single Dnepr (RS-36) with ten warheads (550-750kt each) would obliterate a 100m object with only a few hours notice. Impacting converts the majority of energy into kinetic - as opposed to simply brushing the surface with radiation. Having "bunker buster nukes" already designed for impacting is a bonus, unless you're the target.

Yeah but for anything in the 200m-1km range, you just break the asteroid into multiple impactors, which makes it way more likely that one of them hits a populated area.  Even a largish tsunami from a single ocean impact (that could be prepared for/evacuated from) would spread the damage out more than multiple chaotic airburst explosions on top of a heavily populated continent. 

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #28 on: 07/24/2017 07:30 AM »
Surface area of a sphere is 4πr2, (or 41253 square degrees) so 1% conversion to KinE assumes that the asteroid takes up about a 20 x 20 degree patch of sky relative to the bomb.  Or in other words, for a 250m asteroid, if the bomb is detonated 731m away, that means 1% of the energy from the bomb reaches the asteroid.
Fun fact: There's no mass (air) in space and thus no means for the energy of a nuke to become kinetic. It's nothing but radiation with a couple pounds of broadly dispersed atoms. Hence my comments on "brushing the meteor with radiation to vaporize its surface" - that vaporization is the only thrust a standoff nuke would have and no more effective than pointing a laser at a meteor (which has also been proposed).

Offline gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #29 on: 07/24/2017 11:33 AM »
Surface area of a sphere is 4πr2, (or 41253 square degrees) so 1% conversion to KinE assumes that the asteroid takes up about a 20 x 20 degree patch of sky relative to the bomb.  Or in other words, for a 250m asteroid, if the bomb is detonated 731m away, that means 1% of the energy from the bomb reaches the asteroid.
Fun fact: There's no mass (air) in space and thus no means for the energy of a nuke to become kinetic. It's nothing but radiation with a couple pounds of broadly dispersed atoms.

Try "tons". A 6 MT device has at least a ton of fusion fuel. Initial fusion shock wave velocities are on the order of 100 km/s, and without atmosphere there is nothing to slow them down. To get you a handle on that number, total conversion of that much momentum can impart some 50 m/s to a kilometer-sized asteroid.

Even though most of the explosion energy is indeed in the radiation pulse, you should not disregard effects of bomb debris.

Offline Zed_Noir

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Re: Deflecting or destroying dangerous asteroids
« Reply #30 on: 07/24/2017 03:33 PM »
Surface area of a sphere is 4πr2, (or 41253 square degrees) so 1% conversion to KinE assumes that the asteroid takes up about a 20 x 20 degree patch of sky relative to the bomb.  Or in other words, for a 250m asteroid, if the bomb is detonated 731m away, that means 1% of the energy from the bomb reaches the asteroid.
Fun fact: There's no mass (air) in space and thus no means for the energy of a nuke to become kinetic. It's nothing but radiation with a couple pounds of broadly dispersed atoms. Hence my comments on "brushing the meteor with radiation to vaporize its surface" - that vaporization is the only thrust a standoff nuke would have and no more effective than pointing a laser at a meteor (which has also been proposed).
Nothing that several sub-kilo tonne yield nukes before the follow on multi mega tonne yield nuke cannot solved.



Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #31 on: 07/24/2017 05:35 PM »
Fun fact: There's no mass (air) in space and thus no means for the energy of a nuke to become kinetic. It's nothing but radiation with a couple pounds of broadly dispersed atoms. Hence my comments on "brushing the meteor with radiation to vaporize its surface" - that vaporization is the only thrust a standoff nuke would have and no more effective than pointing a laser at a meteor (which has also been proposed).
Do you realize that the people at the national labs responsible for these weapons have done detailed studies and simulations of this particular problem? A couple of them talk about it in video I linked above.

Your off-the-cuff speculation is unlikely to be more accurate than the work of people who have spent entire careers on the problem. If you care about it, take some time to familiarize yourself with the work that has already been done.

« Last Edit: 07/24/2017 05:46 PM by hop »

Offline stefan r

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Re: Deflecting or destroying dangerous asteroids
« Reply #32 on: 07/25/2017 12:52 AM »
Do you realize that the people at the national labs responsible for these weapons have done detailed studies and simulations of this particular problem? A couple of them talk about it in video I linked above.

Your off-the-cuff speculation is unlikely to be more accurate than the work of people who have spent entire careers on the problem. If you care about it, take some time to familiarize yourself with the work that has already been done.

This is clearly an open field with ongoing research.  At 15:23 in your video:
Quote
Thats a great question.  I have looked at that for kinetic impacters.  To sensitivity for different locations on a shaped model.  But I haven't done it for nuclear ablations though.  It would be nice to do a suite of simulations for that.
The units on her graph is cm/s.  So the energy yield to deltaV conversion likely to be much lower than 1%.

She basically said very similar things to what was posted.  They made a model.  Bigger nuke does more than small nuke.  Bigger asteroid harder than small asteroid.  Her assessment that it would work was based on a 10 year warning time.  Earlier warning/response is better than delayed. 

At 25:20 he puts up a chart were the delta V is 1.6 cm/s.  Compare to 8:40 where she has 100 cm/s.  Both are using 1 Mt nukes.  Robert's asteroid has double diameter.  Megan has maximum delta V for a proximity burst.  He has a 50 m optimum distance. 

Thank you for linking the video. 

Nothing so sophisticated.  The way I thought of it is that the explosive energy radiates evenly in all directions, and you don't necessarily want to explode a rubble pile so much as shift it.  You would probably perform a stand off explosion at some distance from the asteroid so the energy front from the bomb is roughly unidirectional.

Surface area of a sphere is 4πr2, (or 41253 square degrees) so 1% conversion to KinE assumes that the asteroid takes up about a 20 x 20 degree patch of sky relative to the bomb.  Or in other words, for a 250m asteroid, if the bomb is detonated 731m away, that means 1% of the energy from the bomb reaches the asteroid.  You could go closer, but you're more likely to break it up into multiple impactors.  1% was a nice round number.
The energy from the bomb is ionizing radiation.  The surface heats and explodes.  That explosion moves the asteroid. 
Gunpowder is an explosion we get to play with more frequently than nukes.  As a child a friend and I set fire crackers next to rock and various toys.  The distance the rock moved was disappointing.  The effect of gunpowder on bullets is similar.  A shorter barrel generates a lower velocity even though the mass of the bullet and gunpowder is the same.  As the barrel length goes toward 0 the bullet is quite slow.  In order to compare to a nuke/asteroid you would have to have no casing and detonate the explosive in a vacuum.

The total momentum of the material that ablates from the surface of the asteroid will be much higher than the force on the asteroid itself.   

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #33 on: 07/25/2017 01:11 AM »
Try "tons". A 6 MT device has at least a ton of fusion fuel. Initial fusion shock wave velocities are on the order of 100 km/s, and without atmosphere there is nothing to slow them down. To get you a handle on that number, total conversion of that much momentum can impart some 50 m/s to a kilometer-sized asteroid.
1) Where are you getting a 6MT warhead and how are you sending it to space?
2) At what range are you calculating the 50m/s on a kilometer-sized object?

Even though most of the explosion energy is indeed in the radiation pulse, you should not disregard effects of bomb debris.
Actually, I should disregard the initial mass and pressure created by a standoff blast. For example;
Surface area of a sphere is 4πr2, (or 41253 square degrees) so 1% conversion to KinE assumes that the asteroid takes up about a 20 x 20 degree patch of sky relative to the bomb.  Or in other words, for a 250m asteroid, if the bomb is detonated 731m away, that means 1% of the energy from the bomb reaches the asteroid.

If p2=p1(r1/r2) and the initial blast from a 50cm sphere (approximate size of an 800lb, 475Kt W88 warhead);
 - The 1% impacting is 8lbs (~1/5 DART's momentum) and with dispersion at 731m of 0.27lb/m2.
It's nothing but radiation with a couple pounds of broadly dispersed atoms.

Only around 50% of a nuclear blast is pressure, 40% thermal, gamma and neutron radiation and 10% nuclear decay. http://www.atomicarchive.com/Effects/effects1.shtml
If p2=p1(r1/r2) and the initial blast is calculated from 475Kt x 50% and the same radii as above;
 - The TNT equivalent at 731m is 81t dispersed, or 812kg TNT equivalent against the 1% surface.

Radiative pressure is similarly diminished by distance. As a whole, standoff nukes are worthless against meteors, comets, etc. If a nuke, or salvo of them are to be used it would either be a near-surface push or sub-surface blast to focus as much of the pressure and energy onto the object.
This brings up the problem of debris, which brings up the greatest error many make - there's no point trying to deflect a meteor, only decelerate it. A salvo fired at the leading face could include four direct impacts and 4-8(depending on missile) pincer blasts, forming a pressure wave that slows the object enough to miss Earth and containing ejected or rebounding debris.

Do you realize that the people at the national labs responsible for these weapons have done detailed studies and simulations of this particular problem? ... Your off-the-cuff speculation is unlikely to be more accurate than the work of people who have spent entire careers on the problem.
You flatter me, Hop - suggesting my "off the cuff speculation" is as accurate as those in national labs who've devoted their lives to the issue. It may not be the instance here, but thank you anyways.  8)

Edit: Forgot to check my values and made a dumb math error.
« Last Edit: 07/26/2017 04:29 AM by Propylox »

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #34 on: 07/25/2017 05:56 AM »
As a whole, standoff nukes are worthless against meteors, comets, etc.
This is contradicted by a large body of work, including some of the talks I linked earlier. Most people in the field regard standoff nukes as a technically viable option, and standoff is generally the preferred nuclear option when circumstances allow.

This is like to your earlier claim that 20 meter space telescopes are required, when in reality the people actually looking for threats would be quite happy with something like the 0.5 meter NEOCam proposal.
Quote
You flatter me, Hop - suggesting my "off the cuff speculation" is as accurate as those in national labs who've devoted their lives to the issue. It may not be the instance here, but thank you anyways.  8)
No flattery involved: "Unlikely to be more accurate" does not imply "likely to be as accurate".

To be blunt: Your posts make it clear that you are unfamiliar with the subject. I'm suggesting you spend some time fixing that rather than continuing to post stuff that is very obviously at odds with the facts.

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #35 on: 07/25/2017 08:02 AM »
As a whole, standoff nukes are worthless against meteors, comets, etc. 
This is contradicted by a large body of work, including some of the talks I linked earlier. Most people in the field regard standoff nukes as a technically viable option, and standoff is generally the preferred nuclear option when circumstances allow.
Because "most people" in a group believe something's a good idea and have written so, that makes it so? Well praise geocentrism! Too bad the math, facts and common sense contradict their work. Sincerely, Copernicus

No one in the field has called for a 20m space telescope for asteroid detection, the most serious proposal is for a quite modest IR telescope.
That's because members of "the field" are 1) broke, and 2) telescope designs haven't improved in 350yrs so the idea of a 20m 'scope seems impossible. If I showed a 20m scope at the cost, packaging and weight of a 1.5m scope, "the field" would be all over it as necessary to their work.  ;)
« Last Edit: 07/25/2017 08:08 AM by Propylox »

Offline gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #36 on: 07/25/2017 11:38 AM »
The way I thought of it is that the explosive energy radiates evenly in all directions

Actually, for nukes in space it's quite easy to make energy release directional. Fusion weapons use carefully designed radiation channels with complex geometry for optimal implosion of the secondary. People in weapon labs spend decades and billions to learn all ins and outs of controlling intense gamma radiation inside high-Z-lined cavities.

It should be easy for them to design a space nuke with a casing which has a thinner section which is eaten through by gammas first, and most of the bomb energy is then radiated in one direction.

Online tyrred

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Re: Deflecting or destroying dangerous asteroids
« Reply #37 on: 07/25/2017 04:23 PM »
Casaba Howitzer is such directed effect nuclear device.  1Mt Casaba Howitzer could theoretically impart 0.2TJ/m^2 with detonation 1km distant from target.  Enough to deflect dangerous asteroid?

From http://toughsf.blogspot.com/2016/06/the-nuclear-spear-casaba-howitzer.html :

Large Casaba Howitzer (1000kg)
0.001 radian directivity (0.0057 degrees)
1Mt yield, 5% efficiency: 0.2PJ
Distance 1km: Irradiance = 0.2TJ/m^2
Distance 10km: Irradiance = 24GJ/m^2
Distance 100km: Irradiance = 200MJ/m^2
Distance 1000km: Irradiance = 2.09MJ/m^2

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #38 on: 07/25/2017 04:43 PM »
Because "most people" in a group believe something's a good idea and have written so, that makes it so?
When those people are experts in the field, and their work is backed up by rigorous study, it's a lot more likely to be true than random individuals idle speculation.

Quote
Well praise geocentrism! Too bad the math, facts and common sense contradict their work. Sincerely, Copernicus
The practice of science has advance significantly since Copernicus. If you want to convincingly dispute the work of the people who have done detailed analysis of nuclear weapon effects on asteroids, you need to actually demonstrate that their match is wrong, not just say "nuh uh!"
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That's because members of "the field" are 1) broke, and 2) telescope designs haven't improved in 350yrs so the idea of a 20m 'scope seems impossible.
This is just totally wrong, again. Telescope design has improved tremendously in the last 350 years (seriously, does that really even need to be said?!), and while 20 m is probably out of budgetary reach in the next couple decades, people right now are working on designs for 10 m+ space telescopes to follow Hubble and JWST. (HDST, LUVOIR etc)

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If I showed a 20m scope at the cost, packaging and weight of a 1.5m scope, "the field" would be all over it as necessary to their work.  ;)
Not for asteroid surveys, because a 20 m scope is not required to find the objects that pose a significant threat. The reality is that continued operation of existing surveys with planned upgrades + LSST + NEOCam  is probably enough to meet the 90% of 140m NEOs goal, or at least come fairly close.

Here's a recent paper on the NEO size distribution https://arxiv.org/abs/1707.04066
There's still a fair bit of uncertainty in the tens of meters range, but over 100m we have a pretty good idea what the population looks like.
« Last Edit: 07/25/2017 04:49 PM by hop »

Online whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #39 on: 07/25/2017 05:14 PM »
*snip*
As a whole, standoff nukes are worthless against meteors, comets, etc. If a nuke, or salvo of them are to be used it would either be a near-surface push or sub-surface blast to focus as much of the pressure and energy onto the object.
This brings up the problem of debris, which brings up the greatest error many make - there's no point trying to deflect a meteor, only decelerate it. A salvo fired at the leading face could include four direct impacts and 4-8(depending on missile) pincer blasts, forming a pressure wave that slows the object enough to miss Earth and containing ejected or rebounding debris.
*snip*

Just to correct a misconception you have - deflection can be done in any direction. Slowing down an asteroid, pushing it to the side, or speeding it up would all work equally well to cause it to miss the Earth.
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