Author Topic: Deflecting or destroying dangerous asteroids  (Read 17908 times)

Offline drunyan8315

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Deflecting or destroying dangerous asteroids
« on: 07/13/2017 07:29 PM »
I have tried to search for other posts on this, but have been unable to figure out how to search within this forum, where it clearly belngs, so here goes.

Protection against Earth-approaching asteroids is a topic that comes to mind every time we see headlines about a "surprise" close approach of a wandering hunk of rock, but then fades for most of us. But what about the surprise that turns out to have our name on it - and won't go away? What are the impediments to deploying a serious protection system against those?

For one, there is the "giggle factor", but I think it is diminishing with each new "surprise" visit. Probably the remaining big factor is the assumption that any defense system would be staggeringly expensive, requiring a diversion of investment that could be used in more "productive" ways. The assumption here is that such a system would have no other use than to protect us from the "nasty surprise" that may never come, and would otherwise sit idle.
Maybe there is a way around this objection - if not to significantly reduce the cost, to at least derive some secondary benefit from it. Recent attention to asteroid capture missions got me to thinking about the possibility of "fighting fire with fire"... or in this case fighting asteroids with asteroids!
My first thoughts were occasioned by the concept of capturing an asteroid in lunar orbit... could it be stored there as a mass to be directed into the path of a dangerous visitor? I soon realized that to direct even a smallish asteroid out of lunar orbit (rather suddenly, on demand) would require prodigious amounts of force that would probably require development of thrusting engines orders of magnitude greater than we have now.
Then I considered whether an asteroid could be maintained in a co-orbital trajectory (figure-8?) around Earth AND Moon. Would this allow an orbital velocity to be maintained that was much higher than that required to orbit either body? The mental picture I had was of a mass using the deep gravity well of the Earth to continuously return to the Moon's shallower one, to be returned toward Earth, etc. Of course the mass could approach the Moon quite closely without an atmosphere to interfere. Might it be possible to use relatively small trajectory changes to cause the mass to be ejected from this co-orbit, to smack an unwelcome visitor?
Now even if the basic mechanics would work (and I am becoming more skeptical that they would), this situation would require constant fine-tuning to avoid either losing the mass into space, or having it impact one or the other of its "parents", potentially causing the kind of destruction it was meant to prevent! The investment in keeping this monster pinball game under control might not be sustainable, either.
But what about a sling, perhaps at a Lagrange point? Would it be possible to connect two asteroid masses and spin them around each other?! The required potential energy could be raised gradually with more or less known technology, but released suddenly as kinetic energy with an explosion to sever the connection between the two masses. Yes, the connection would have to be formed from materials suitable for a space elevator, at least! And of course, the "recoil" would consist of the "other" mass flying away just as rapidly, hopefully into deep space.
And what about the "real-world" secondary benefits I suggested would be necessary? Well, a space probe manufacturing / launch facility on one or both of the masses would enjoy artificial gravity, and to launch... just kick the probe over the edge! Getting ON this giant merry-go-round might be trickier than getting OFF however!

Okay, this is my bizarre idea.  Have at it!

Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #1 on: 07/13/2017 07:57 PM »
For the record, figure 8 orbits are possible, but they are not stable, since any perturbation would deflect it from the orbit. Given that the Moon is moving around the Earth and the Sun also exerts gravitational force on the asteroid, it would probably not remain in a figure 8 orbit for more than one orbital period before being deflected off-course.

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.

The primary problem with this is it must be done a long time in advance, so prior warning is required, on the order of years of lead time.

There are multiple other proposals for deflecting away an asteroid, but they would require even longer lead times to prepare and execute, such as albedo change, and gravity tractor.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline drunyan8315

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Re: Deflecting or destroying dangerous asteroids
« Reply #2 on: 07/13/2017 09:32 PM »
Thanks for your comment, and I am not surprised an Earth-Moon orbit is not stable. Do you have any insight into whether the "pumping" of energy into an object in such an orbit could be effected the way interplanetary probes use planet flybys, assuming the stability of the orbit is maintained through other active measures?

Interesting that you mention the problem of known methods of deflection requiring long lead times, because they exert gentle continuous forces. This is the specific problem I was addressing with the double-asteroid sling, although I did not articulate it explicitly. This approach seems to me to potentially allow for the storage of large amounts of energy, accumulated gradually with not-too-advanced technology, but released instantaneously. It seems like it would be able to deliver a HARD hit relatively quickly, and at a distance, either deflecting the target or perhaps even shattering it. Thoughts?

Ps. I am not convinced of the validity of the arguments that are made against disruption of the asteroid - that it would make the problem worse by multiplying the number of objects.

Offline gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #3 on: 07/13/2017 09:50 PM »
Nukes would work. Relatively modest development needed.

Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #4 on: 07/13/2017 10:40 PM »
Thanks for your comment, and I am not surprised an Earth-Moon orbit is not stable. Do you have any insight into whether the "pumping" of energy into an object in such an orbit could be effected the way interplanetary probes use planet flybys, assuming the stability of the orbit is maintained through other active measures?

Interesting that you mention the problem of known methods of deflection requiring long lead times, because they exert gentle continuous forces. This is the specific problem I was addressing with the double-asteroid sling, although I did not articulate it explicitly. This approach seems to me to potentially allow for the storage of large amounts of energy, accumulated gradually with not-too-advanced technology, but released instantaneously. It seems like it would be able to deliver a HARD hit relatively quickly, and at a distance, either deflecting the target or perhaps even shattering it. Thoughts?

Ps. I am not convinced of the validity of the arguments that are made against disruption of the asteroid - that it would make the problem worse by multiplying the number of objects.

A figure 8 orbit wouldn't "charge up" an asteroid, as probes do with a gravitational assist, if it gained speed it would be ejected out of the figure 8 orbit. Spinning two asteroids tethered together would, but that would be very difficult to aim thanks to gyroscopic effects. You'd also have to very, very, very precisely time the breaking of the tether to have any chance of hitting a target, and that's not likely, even minute errors would cause it to miss, in other words, there's no good way to aim such a system. Even our most precise rocket launches have scheduled course corrections to get our probes to their targets accurately.

Breaking apart an asteroid is undesirable for a few reasons. If done at close range you, to quote Independence Day, "risk turning one dangerous falling object into many."

However, when done a great distance away, most of the bits might miss Earth entirely, but then they a. would be much harder to track and b. would form a debris cloud heading towards Earth. The danger to our satellites would be pretty high even if all the bits were small enough to burn up in Earth's atmosphere.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Offline Ludus

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Re: Deflecting or destroying dangerous asteroids
« Reply #5 on: 07/14/2017 03:54 AM »
There will be a lot of money invested in learning to redirect asteroids as part of asteroid mining. The main issue is deltaV for very massive objects. It doesn't really solve anything to imagine hitting one very massive object with another. If you can produce so much delta V for one object as to precisely redirect it to do that, you could much more easily deflect the problem asteroid using the same techniques.

Asteroids don't have to be nudged very much to make them NOT intersect with the earth. To shove around one asteroid enough to make it precisely intersect with another's path is WAY harder.

One possible technique that could do quite a lot is to land a combination of an automated drill (maybe plasma) a big solar array and an EM catapult. This would be hundreds of tons but may be doable by SpaceX ITS Cargo Version. The setup would use Solar power to fling pellets at high speed away. It would very slowly consume the sateroids mass as propellant using Solar power. This kind of setup operating continuously to do some pretty impressive Asteroid herding.

Offline sanman

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Re: Deflecting or destroying dangerous asteroids
« Reply #6 on: 07/14/2017 04:27 AM »
Could the so-called "3rd/4th generation" nuclear weapons, which are in theory supposed to be able to asymmetrically direct their explosive power like a shaped charge, be more useful for this situation?

How could a nuclear blast be shaped to impart maximum effect on a target asteroid?

Would existing nuclear warheads be easily repurposed to this task, or would there have to be any special customizations / modifications?




Online tyrred

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Re: Deflecting or destroying dangerous asteroids
« Reply #7 on: 07/14/2017 08:39 AM »
"Casaba Howitzer" would not be prohibitively difficult to field at close range to Earth, kludged onto an existing ICBM.  Creates a collimated beam of nuclear plasma, a directed energy weapon.  Not exactly "off the shelf" asset (as far as is public), but the studies for project Orion showed that at least theoretically it was possible... And that was decades ago.  Range and targeting could be a challenge, as the target trajectory needs to be deflected enough to miss Earth and it's constellation of satellites without reducing the target to a rubble pile of buckshot.  Most likely this approach would still be too little, too late.  We must first have the eyes to see where to direct the defense.

Online M.E.T.

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Re: Deflecting or destroying dangerous asteroids
« Reply #8 on: 07/14/2017 09:57 AM »
I don't understand the standard response that blowing up the asteroid with a nuclear weapon is not feasible, because the cloud of resultant debris is supposedly just as dangerous as the single massive rock.

Surely it is the size of the single rock that makes it able to penetrate the protective blanket of the atmosphere, which means that a million smaller pieces will burn up in the atmosphere instead of impacting the ground and creating mega tsunamis or gigaton sized explosions.

Smaller is therefore better, in my view. So blowing it up would be a valid option.

Offline jgoldader

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Re: Deflecting or destroying dangerous asteroids
« Reply #9 on: 07/14/2017 01:10 PM »
The incoming has KE and gravitational PE, and that's all going to be dissipated.  It could happen all in one place, or in several.  A 20 meter piece can make a very powerful airburst with heat and shock wave (ref: Chelyabinsk).  Imagine a hundred of those, all at once, spread over a ~1500 km diameter area.  Figure one or two for every major European or US city, say.  Are you *sure* that's better than a single impact?

Until we better understand the physical properties of NEOs, and there are likely to be many different classes (from metal chunks to loosely-bound aggregates), it's not easy to figure out what to do.  And we might not have the luxury of time to investigate a possible impactor far enough in advance to really tailor a response.
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Offline RonM

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Re: Deflecting or destroying dangerous asteroids
« Reply #10 on: 07/14/2017 01:43 PM »
Big question is how far in advance of impact do we detect the object and when can it be intercepted. If there's very little time, as in the OP scenario, blowing up the asteroid won't work since all of the debris cloud will still hit the Earth. If we can hit the asteroid a year in advance then we don't need to blow it up, just a little thrust will cause it to miss. If it's too late to move the asteroid, but there's enough time for most of a debris cloud to dissipate and miss the Earth, then blowing it up will work. There's no one size fits all solution.

Offline ppnl

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Re: Deflecting or destroying dangerous asteroids
« Reply #11 on: 07/14/2017 09:58 PM »


One possible technique that could do quite a lot is to land a combination of an automated drill (maybe plasma) a big solar array and an EM catapult. This would be hundreds of tons but may be doable by SpaceX ITS Cargo Version. The setup would use Solar power to fling pellets at high speed away. It would very slowly consume the sateroids mass as propellant using Solar power. This kind of setup operating continuously to do some pretty impressive Asteroid herding.

High speed projectiles would waste energy which may be your most limited resource. Instead use massive projectiles at low velocity. Maybe some reasonably small multiple of its escape velocity. Also less wear on your launcher.

Offline gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #12 on: 07/14/2017 10:13 PM »
The incoming has KE and gravitational PE, and that's all going to be dissipated.  It could happen all in one place, or in several.  A 20 meter piece can make a very powerful airburst with heat and shock wave (ref: Chelyabinsk).  Imagine a hundred of those, all at once, spread over a ~1500 km diameter area.  Figure one or two for every major European or US city, say.  Are you *sure* that's better than a single impact?

Yes, I'm sure.

A thousand 20 meter meteors airbursting at ~20 km up over an entire hemisphere can break a lot of glass and kill maybe 2000 people, in total, by shards etc.

An equivalent single 200 meter bolide won't be significantly slowed by atmosphere and would make a 5-10 km diameter crater. It's easily a city killer, or can create ocean-wide tsunamis 50 m in height.
« Last Edit: 07/14/2017 10:15 PM by gospacex »

Offline jgoldader

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Re: Deflecting or destroying dangerous asteroids
« Reply #13 on: 07/14/2017 11:41 PM »
Obviously, either would be "not good."  I wonder if a single impactor yields both the worst case scenario in terms of fatalities (probably a water impact w/tsunami) and the fewest, via a land impact in some very remote area. I tried to conjure the worst "multiple small impact" case I could imagine; in a "real" case, most of the little pieces wouldn't hit major cities.  But don't underestimate a Chelyabinsk airburst over a big city; it could well shatter pretty much all the glass in a major city, bring down building facades... I wouldn't want to be downtown.  And if that happened in many cities, well, not good.

But I do agree that a single impactor should give the worst-case scenario.  If I had to choose between one big impact in the ocean or the "shotgun" effect of a nuked parent body, I'd go for the latter.  It would be, as you suggested, at worst tens of thousands of deaths vs. potentially tens of millions.

Either way, not a good outcome.  And a circumstance I hope we don't face any time soon.
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Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #14 on: 07/15/2017 05:57 PM »
I don't understand the standard response that blowing up the asteroid with a nuclear weapon is not feasible, because the cloud of resultant debris is supposedly just as dangerous as the single massive rock.

Surely it is the size of the single rock that makes it able to penetrate the protective blanket of the atmosphere, which means that a million smaller pieces will burn up in the atmosphere instead of impacting the ground and creating mega tsunamis or gigaton sized explosions.

Smaller is therefore better, in my view. So blowing it up would be a valid option.

then they a. would be much harder to track and b. would form a debris cloud heading towards Earth. The danger to our satellites would be pretty high even if all the bits were small enough to burn up in Earth's atmosphere.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #15 on: 07/15/2017 10:33 PM »
There is a large body of literature on planetary defense, based on actual calculations and experiments.

Presentations from the recent planetary defense conference in Japan may also be of interest.
https://www.youtube.com/channel/UCpq_pj8aLeFu-0i4Je8_JsQ

But all this is irrelevant. Anything small enough for us to redirect is too small for us to see in time while anything we can see in time is too large to redirect. Unless we start putting +20m telescopes in space there's no point in developing redirect capabilities. Better just to make peace with and live your days.
This is completely wrong. We routinely detect asteroids too small to be a concern, and objects capable of creating larger than city-scale devastation are readily detectable without 20m space telescopes. Very large objects can be deflected with enough advance warning.

Long period comets are much harder to deal with, but they are only a moderate fraction of the overall risk.

We may not be able to eliminate the threat, but with modest effort we can significantly reduce it. In fact, we already have, the survey of >= km scale NEOs is nearly complete.

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #16 on: 07/16/2017 04:17 AM »
Sure, we detected the Chelyabinsk meteor - as it happened. Well done!
We have also detected lots asteroids smaller than Chelyabinsk that did not impact. Impact risks are a numbers game. You don't have to identify every single one to reduce your overall risk.
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It was only a 400-500kt blast that fortunately detonated at +25km altitude due to a shallow trajectory.
In the grand scheme of things, Chelyabinsk wasn't a big deal. Even Tunguska size objects aren't unless they hit near a population center. Sure, we'd like to detect and prevent these kinds of things, but in the worst case it's a disaster like a major hurricane, earthquake or tsunami, not a civilization killer. (edit: To be clear, I'm referring to Tunguska size events, not impacts in general!)
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Fortunately we know of every kilometer-sized object and apparently have operational capability to deflect "very large objects", according to Hop.
That's not even remotely what I said. We have discovered most of the > 1km NEOs. We know that in principle, current technology is sufficient to modify their trajectories on multi-decade timescales.
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Unfortunately that leaves a lot of 1km-20km craters, airblasts equal to armageddon and the extinction of humanity.
This is not accurate. See http://impact.ese.ic.ac.uk/ImpactEffects/ for example. The reason Congress initially gave NASA a mandate to find ~1km and larger objects is because those were the ones judged to be civilization killers. They later extended the goal down to 140m, because those pose serious regional risks. While the 90% goal for >140m NEOs won't be met soon with current resources, LSST and existing surveys are expected to reach  ~70% https://arxiv.org/abs/1706.09398

Discovery efficiency follows a curve, so completeness for, say >500m objects will be significantly higher.
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As previously stated,
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Unless we start putting +20m telescopes in space there's no point in developing redirect capabilities.
Better just to make peace with and live your days.
This is still a completely incorrect statement. Again, this is a well developed field of research, read the literature! 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.
« Last Edit: 07/16/2017 04:36 AM by hop »

Offline jg

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Re: Deflecting or destroying dangerous asteroids
« Reply #17 on: 07/16/2017 10:45 PM »
Please take a look at http://fallingstar.com/home.php about the ATLAS project.

The first two ATLAS telescopes are coming on line this year.  You can see the discoveries on the minor planets center (or follow @fallingstarIfA for discoveries).  The discovery rate is about to go up a factor of 5 (the original corrector plates were defective, and new ones are/will be installed shortly).

This will get us good stats on small threatening NEO asteroids for the first time.

John Tonry (the PI) is a friend, and I can ask questions of him if the fallingstar web siteis unclear.

Note this is not a panacea: 40% of the sky is too near the sun to be observed.

Online catdlr

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Re: Deflecting or destroying dangerous asteroids
« Reply #18 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 #19 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 #20 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 #21 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 #22 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 #23 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 mikelepage

Re: Deflecting or destroying dangerous asteroids
« Reply #24 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.

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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 gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #25 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 #26 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 #27 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 #28 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:
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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.   

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #29 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.
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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 gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #30 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 #31 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 #32 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.

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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 »

Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #33 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.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #34 on: 07/25/2017 07:47 PM »
Somewhat related news today: There seem to be more large long period comets than previously estimated.

Large, Distant Comets More Common Than Previously Thought
https://www.jpl.nasa.gov/news/news.php?release=2017-197
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...
NASA's WISE spacecraft, scanning the entire sky at infrared wavelengths, has delivered new insights about these distant wanderers. Scientists found that there are about seven times more long-period comets measuring at least 0.6 miles (1 kilometer) across than had been predicted previously. They also found that long-period comets are on average up to twice as large as "Jupiter family comets," whose orbits are shaped by Jupiter's gravity and have periods of less than 20 years.
...

Paper (paywalled) Debiasing the NEOWISE Cryogenic Mission Comet Populations
« Last Edit: 07/25/2017 07:48 PM by hop »

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #35 on: 07/25/2017 09:08 PM »
Regarding the effectiveness (or otherwise) of nuclear deflection, here's a paper from Bruck Syal et al in 2013 which reviews the subject:

Limits on the use of nuclear explosives for a steroid deflection (PDF via google scholar search for that title http://www.planetary.brown.edu/pdfs/4747.pdf)

An interesting bit on the energy deposition question:
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The simulated nuclear explosive was selected for optimized neutron output (high fusion to fission yield), as the cross-section of energetic neutrons is nearly independent of composition for materials between carbon and iron. This results in a penetration depth of 17g/cm^2, heating substantially more mass than the same flux of x-rays and providing a larger impulse for the same amount of incident energy.

On survey efficiency, supporting my earlier WAG about NEOCam and LSST
Modeling the Performance of the LSST in Surveying the Near-Earth Object Population - Tommy Grav, Amy Mainzer, Tim Spahr
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We further show that while neither LSST nor a space-based IR platform like NEOCam individually can complete the survey for 140m diameter NEOs, the combination of these systems can achieve that goal after a decade of observation.
No 20m telescopes required  ???

Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #36 on: 07/26/2017 03:43 PM »
As noted in several posts above, it is possible to deflect massive asteroids, but more lead time is required to do so. We are in no way limited to only the deflection of 100 meter or smaller asteroids.

There have been many, many studies on asteroid deflection - not idle speculation by random people. Hop has cited some of them.

Why haven't you cited any studies to show you are correct? hmm...
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #37 on: 07/26/2017 04:10 PM »
And still no ability to see objects small enough to deflect;  no means to deflect objects we could possibly see.
You seem quite sure of this. How small is "small enough to deflect"? Are the calculations, models and assumptions this is based on published somewhere? Is this based on particular deflection methods or warning times?

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but there's no means to find objects of that size or down to the 20-30m range equivalent to ICBM blasts.
Do you have specific calculations showing that the overall risk from 20-30m asteroids is significant compared to that posed by 140+ meter bodies?
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Of course a 20m telescope would and do so in a couple years, not decades, while non-regular (new) orbits threatening Earth would be readily identified.
What size range would this 20m space telescope completeness >90% for, and how did you arrive that conclusion? How much is overall risk reduced by completing the survey in a "a couple years" rather than decades? Does this "couple years" account for construction time of the 20m telescope?

Also, your previous argument was not that smaller telescopes would be too slow, you said
Anything small enough for us to redirect is too small for us to see in time while anything we can see in time is too large to redirect. Unless we start putting +20m telescopes in space there's no point in developing redirect capabilities.
(my bold)
Taken at face value, this seems imply that you believe anything less provides no useful reduction of risk. Again, is this based on specific models or calculations? If not, why are you so confident that it's true?

edit:
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none acknowledge the impossible distance, impossibly high number of warheads required or any means to implement
Which specific scenarios in Bruck Syal et al paper linked above require "impossible" distance or warhead numbers? What models or calculation did you use to come to the conclusion that these scenarios are "impossible"?
« Last Edit: 07/26/2017 08:33 PM by hop »

Offline meberbs

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Re: Deflecting or destroying dangerous asteroids
« Reply #38 on: 07/26/2017 07:24 PM »
Hop, May I suggest some consistency in your claims, or at least acknowledge the lack of consistency in "the field" of so-called experts ...

Yeah, I'm not sure how you can call them "experts" without proving they have a clue or their "rigorous studies" can even agree - Without arguing their case or disputing mine, only asserting so. Position, authority and quoting such does not equate to truth.

There's no need to "convincingly dispute" their claims when they effectively do so to each other. What you've shown appears as "random individuals idle speculation" which you copy/pasted and declared as fact.
So now you are reduced to disputing the credentials of the people who study this for a living.

There is plenty of need to convincingly dispute their claims, even if they did it to each other, you would have to show where these supposed contradictions are. If you bother actually reading these studies such as the one hop linked about LSST performance, you will see they compare their results to other researchers and explain causes for any differences.

Your arguments are equivalent and just as wrong as the people who doubt that the Earth is getting warmer, and use arguments such as "two scientists using different models didn't get the exact same answer, therefore their models are worthless and wrong so the opposite of what they say must be true and the Earth is cooling" ignoring that the data all agrees that the Earth is warming, and the differences are part of the known uncertainty, which isn't large enough to change the result that the Earth is warming.

In citing "experts" working nuclear deterrence, including lectures of remedial information, none acknowledge the impossible distance, impossibly high number of warheads required or any means to implement. They're of no practical, actionable use - only speculative theory to support minimally effective actions.
These aren't the people responsible for designing rockets, and there are others out there working on building bigger, better rockets. Their studies are necessary of course for figuring out whether we have a big enough rocket for a given deflection mission.

The practice of science has advance significantly since Copernicus.
Unfortunately the intellectual integrity of those that follow science, and seem to enjoy citing others' work, apparently has not. If you understood the topic, not just recite it, you'd question your assertions as well.
If YOU understood the topic, you wouldn't question their work unless you had something specific to question about it.

Online tyrred

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Re: Deflecting or destroying dangerous asteroids
« Reply #39 on: 07/28/2017 07:14 AM »
So what is your plan to gain 100% certainty, and how will you convince others to fund and field it, if all others have failed?

Offline meberbs

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Re: Deflecting or destroying dangerous asteroids
« Reply #40 on: 07/28/2017 02:27 PM »
So now you are reduced to disputing the credentials of the people who study this for a living. ... Your arguments are equivalent and just as wrong as the people who doubt that the Earth is getting warmer ... If YOU understood the topic, you wouldn't question their work unless you had something specific to question about it.
Did I just get called a GW-denier? Stay classy.
No, I said you are using the exact same kind of horribly wrong anti-science arguments as them.

They may have great credentials and spent their lives on the topic, but that doesn't make them right - only the truth can do that.
It makes them more likely to be right than you, especially when you don't actually point to specific things they say that are wrong.

I have not questioned others' credentials,
Questioning their credentials is exactly what is implied when you put the word expert in quotes.

only their conclusions and pointed out credentials don't matter.
Credentials don't matter? Lets go ask a 5 year old to resolve this for us then.

I'll also point out hop, like other topic pundits, have led you astray with false promises, flawed reasoning, worthless studies and his inability to defend those subject/quotes is proof of his ignorance of it.
You are the only one here doing any of the things you said. There generally has been nothing to defend the quotes because you haven't been providing any specific arguments against them. Your lack of specific arguments against them "is proof of your ignorance of it" (to paraphrase you)

To your credit, you at least attempted specific criticisms in this post even if they take the exact form that I just explained was utterly wrong: Calling an entire field of research worthless due to known uncertainties.

First and foremost; all studies to date are without merit as the physical properties of meteors is unknown - specifically their tensile strength, shear strength and elasticity. Shoemaker-Levy 9 disentigrated from tidal forces that are comparatively minor, suggesting anything but compressive forces with containment or minute forces over decades would be disasterous. But making assumptions about how to affect them would be like making environmental or atmospheric predictions without actually knowing the atmosphere's composition. DART will fill some voids current "experts" ignore while making speculative and uneducated theories.
More evidence you don't read any of the papers, scientists tend to be quite explicit with their assumptions. We do have some data, and that includes that there are a variety of types of asteroids. Even if a study only applies to some of them it is far from worthless.

In the complete absence of actionable data, but a wealth of irrelevant glad-handing and statistics,
Did you just say that statistics aren't data?

we can realistically only rely on the total vaporization of a meteor as defense. That limits our defense to 100m or less,
It is almost certainly pointless to ask, but do you have any calculations or data to back up this assertion? What assumptions did you make?

Obviously one of your assumptions was to ignore options like the gravity tractor.

but the path of parliamentarians and statisticians has concluded we should only focus on larger objects, with fungible "completeness" or "risk reduction" assertions. In truth nothing has been accomplished as no defense -from any size or distance- has been made. Only empty, and foolish promises.
Since the only thing you count as progress is successfully deflecting an asteroid, we should give up all searches for asteroids and research into deflection methods right now, because none of them are producing progress. Then if we somehow notice something on a collision course anyway, we can send a last minute thrown together mission and cross our fingers.

Or maybe you might want to reconsider using absolute words such as "nothing."

Edit: mis-placed quote tag and minor typos
« Last Edit: 07/28/2017 04:55 PM by meberbs »

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #41 on: 07/28/2017 04:50 PM »
That limits our defense to 100m or less, but the path of parliamentarians and statisticians has concluded we should only focus on larger objects, with fungible "completeness" or "risk reduction" assertions. In truth nothing has been accomplished as no defense -from any size or distance- has been made. Only empty, and foolish promises.
So, all the specific assertions you made earlier were not based on any specific calculations or model? Yet somehow, you are certain that 20 m space telescopes are required, and that standoff nukes are "useless", and that diverting >100 m asteroids is "impossible"

If you haven't done any calculation or experiment, why do you believe these specific things are true? Why should we believe your assertions over people who spent decades at NASA and national labs working on this stuff in a rigorous manner?

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Moreover, "completeness" under 100% isn't complete and even if it was, wouldn't actually be complete just like "risk reduction" doesn't actually reduce the risk of a city or planet being anhiliated. These are meaningless statistics used by people who don't understand the problem, but like to justify their participation.
This is just total innumeracy. Statistics are a fundamental and extremely successful part of science, and impact risk is based on quite simple statistics. If you have to cross a mine field, and have a choice of knowing where ~90% of the mines are, or not knowing where any are, which do you chose?
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First and foremost; all studies to date are without merit as the physical properties of meteors is unknown
This is just totally, obviously incorrect: We have in-situ data for multiple asteroids and comets, surface data from Rosetta and Hayabusa (soon to be joined by OSIRIS-Rex and Hayabusa 2) and impact data from Deep Impact. We have observations of many hundreds of thousands of asteroids, and many of these provide significant insight into their structure and physical properties. We also have literally tons of asteroid material from meteorites, and observation of thousands of objects entering the atmosphere.

Physical properties are a significant source of uncertainty, but to say we know nothing just shows total ignorance of the field. The data we have puts significant constraints on the range of properties we are likely to encounter.

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #42 on: 07/29/2017 02:12 AM »
Nukes are insufficient.
In what way are nukes insufficient? The big problems are political: Pretty much everyone would probably be OK with nukes if a major catastrophe was imminent, but you'd really like to do some tests before you need them, and that opens up a big cans of worms. Even laying the groundwork to have them ready could get very touchy.

There are cases where you wouldn't get enough warning to effectively use nukes, but other methods generally require even more warning, so that's not really a problem with nukes specifically.
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So if a nuclear mass generator was a viable / non-fictional concept,
It's not, at least not any anything above atomic scales. Any civilization that could produce significant macroscopic mass from energy would have plenty of ways to divert asteroids.

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I'd guess that would be more practical than the above two concepts (nukes & tethers).
I'm not aware of tethers being a serious deflection option. There have been some suggestion of "harpooning" passing comets / asteroids as a way of saving fuel (e.g. https://www.space.com/30451-nasa-comet-hitchhiker-concept-mission.html), but it's a pretty far out concept that is far from being available in the real world.

Kinetic impactors and various slow push methods like gravity tractors tend be the most common alternatives to nukes. The 2007 report to congress has a good overview https://cneos.jpl.nasa.gov/doc/neo_report2007.html  (although of course a lot of work has been done since, and many of the dates have slipped)

Offline Hog

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Re: Deflecting or destroying dangerous asteroids
« Reply #43 on: 07/29/2017 11:31 AM »
What size of fission fission/fusion device would be need?
Would the current less than 1mT devices be sufficient, or would we need to revisit some 9-15mT weapons of the past?

I can see the difficulty in testing for such devices, or even attempting to procure the materials and engineer the actual nuclear portion of the device.
Paul

Offline as58

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Re: Deflecting or destroying dangerous asteroids
« Reply #44 on: 07/29/2017 03:39 PM »
Actually I said we should focus on finding asteroids/meteors we can currently stop (100m down to 20m equivalent to ICBMs) that can cause massive destruction, while awaiting data (DART) to inform us on the properties of asteroids instead of wildly speculating on
what to do, how effective it would be, calling it "expertise" and trying to con Congress into funding it. Notably, finding 20m meteors means we found the 20mi ones as well and provides more future options to test redirect concepts.

Why? Studies (and history) show that risk of lives lost due to ~20m meteors is very low, while detecting them is extremely difficult (=expensive). If one is spending money to save lives and property, concentrating on finding small asteroids/meteors makes very little sense from cost/benefit point of view.

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #45 on: 07/29/2017 04:03 PM »
If one is spending money to save lives and property, concentrating on finding small asteroids/meteors makes very little sense from cost/benefit point of view.
Why, when small asteroids are the only ones we can stop? Programs to find large meteors have no benefit as we have no actions against them. And the cost of finding small asteroids is almost no different than finding large ones if the cost of scaling up a telescope is minimal. Previously I mentioned telescopes haven't advanced in 350years - the date when reflection replaced refraction in large scopes. Sure, we've managed to ease production and reduce weight by combining multiple mirrors into a larger primary and surface-coat rather than back-coat the mirrors, but that's embarrassingly minor for 31/2 centuries.

Building better telescopes is something everyone can get on board with. From asteroids, to the Solar system and deep space - even downlookers want better scopes. That's the squeaky wheel which actually benefits mankind and identifies smaller, more numerous asteroids to test redirect methods on in the future.
« Last Edit: 07/29/2017 04:15 PM by Propylox »

Offline RonM

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Re: Deflecting or destroying dangerous asteroids
« Reply #46 on: 07/29/2017 04:24 PM »
If one is spending money to save lives and property, concentrating on finding small asteroids/meteors makes very little sense from cost/benefit point of view.
Why, when small asteroids are the only ones we can stop? Programs to find large meteors have no benefit as we have no actions against them. And the cost of finding small asteroids is almost no different than finding large ones if the cost of scaling up a telescope is minimal. Previously I mentioned telescopes haven't advanced in 350years - the date when reflection replaced refraction in large scopes. Sure, we've managed to ease production and reduce weight by combining multiple mirrors into a larger primary and surface-coat rather than back-coat the mirrors, but that's embarrassingly minor for 31/2 centuries.

Building better telescopes is something everyone can get on board with. From asteroids, to the Solar system and deep space - even downlookers want better scopes. That's the squeaky wheel which actually benefits mankind and provides smaller, more numerous options to test redirect methods in the future.

We don't have to "stop" asteroids. A slight change in course will cause them to miss hitting the Earth. The earlier they are detected, the better because it will take less of a push. Even very large asteroids can be deflected with a few years advanced warning.

Since you believe telescope technology hasn't advanced in 350 years, you obviously don't know what you're talking about.

Asteroid survey telescopes don't need to large, but it would help if they were in space. Orbital wide field of view IR telescopes are needed.

Offline as58

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Re: Deflecting or destroying dangerous asteroids
« Reply #47 on: 07/29/2017 04:32 PM »
If one is spending money to save lives and property, concentrating on finding small asteroids/meteors makes very little sense from cost/benefit point of view.
Why, when small asteroids are the only ones we can stop? Programs to find large meteors have no benefit as we have no actions against them. And the cost of finding small asteroids is almost no different than finding large ones if the cost of scaling up a telescope is minimal. Previously I mentioned telescopes haven't advanced in 350years - the date when reflection replaced refraction in large scopes. Sure, we've managed to ease production and reduce weight by combining multiple mirrors into a larger primary and surface-coat rather than back-coat the mirrors, but that's embarrassingly minor for 31/2 centuries.

Building better telescopes is something everyone can get on board with. From asteroids, to the Solar system and deep space - even downlookers want better scopes. That's the squeaky wheel which actually benefits mankind and provides greater options to test redirect methods in the future.

Just because we can (with great expense) deflect ~20 m asteroids doesn't necessarily mean that trying to detect all of them is a worthwhile goal. I believe a much better cost/benefit would come from almost any much more down-to-earth investment in public safety.

Saying that telescopes haven't advanced in 350 years needs some strange definition of what counts as a (significant) advancement. But I'm not sure what kind of development you are hoping to happen. There are laws of physics to contend with and only in New Physics section can wishful thinking overcome them. Or perhaps your posts are a prelude to a sales pitch for large-scale diffractive lenses?

Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #48 on: 07/29/2017 06:11 PM »
We have observations of many hundreds of thousands of asteroids, and many of these provide significant insight into their structure and physical properties. ... Physical properties are a significant source of uncertainty, but to say we know nothing just shows total ignorance of the field.
No, you really don't know anything. Six months ago the 40-90m asteroid "2017 BS5" was discovered in an orbit nearly identical to Earth's and flew past last weekend. This is an obvious orbit to detect, like a dim star following the Earth, and yet it wasn't detected until the point no redirection theories could have avoided a possible collision, only total vaporization of the object at the last minute. Fortunately it missed.
Thankfully pundits and "the field of experts" who focus on "risk reduction and completion" have enough "studies" of the physical properties to handle this, right?
Dr. John S. Lewis - "Until we know what the body is made of, hazard projections are nonsense. It could be a dustball, a snowball, a loose collection of rocky rubble, a monolithic soft rock, a monolithic hard rock, a giant steel cannonball, et cetera. It could, at the extremes, fall apart into dust at high altitudes or penetrate hundreds of meters into Earth’s crust and explode like World War III." http://deepspaceindustries.com/asteroid-profile-2017-bs5/

Since the only thing you count as progress is successfully deflecting an asteroid, we should give up all searches for asteroids and research into deflection methods right now, because none of them are producing progress.
Actually I said we should focus on finding asteroids/meteors we can currently stop (100m down to 20m equivalent to ICBMs) that can cause massive destruction, while awaiting data (DART) to inform us on the properties of asteroids instead of wildly speculating on what to do, how effective it would be, calling it "expertise" and trying to con Congress into funding it. Notably, finding 20m meteors means we found the 20mi ones as well and provides more future options to test redirect concepts.

Statistics are a fundamental and extremely successful part of science, and impact risk is based on quite simple statistics. If you have to cross a mine field, and have a choice of knowing where ~90% of the mines are, or not knowing where any are, which do you chose?
I wouldn't cross the minefield, duh. I also wouldn't play Russian roulette or buy into a "~90% completion in ten years" scheme. I'd actually try to identify all the hazards, find out their properties and remove the threat rather than waltzing through with my fingers crossed, waiving a study and professing expertise.

Credentials don't matter? Lets go ask a 5 year old to resolve this for us then.
and Did you just say that statistics aren't data?
If someone's entirely wrong and peddling myths, credentials only show who was foolish enough to give them credentials. If a 5yr old had credentials, does that make them right? And no, statistics aren't real data. Observed, recorded information is valuable, but not after it's gone through a blender with ample assumptions, categorization and reconfigurations to become stats, marketing or whatever you want it to be.

One quote you missed from that very same article... says we can determine the composition of an asteroid.

"JSL: There are, as yet, no useful data to characterize what 2017 BS5 is made of. The close fly-by this weekend will give Earth-based astronomers a great opportunity to get a good spectrum and tell us what class of meteorite it is most closely related to, what the dominant minerals are, and what economic value it might have."

Nobody in this thread would ever say that we should stop looking for asteroids. Long lead-times are essential for a deflection attempt. Where you go wrong is your claim that we can't deflect any unless they are ~100 meters in diameter or smaller.

Do you have any sources you can cite that shows the people who have done asteroid deflection studies are "entirely wrong and peddling myths"?
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #49 on: 07/29/2017 08:42 PM »
What size of fission fission/fusion device would be need?
Would the current less than 1mT devices be sufficient, or would we need to revisit some 9-15mT weapons of the past?
Check out the paper or PDC talks I linked earlier for some examples. These are based on detailed simulations done by people working at weapons labs, unlike some other claims in this thread.

In the paper, they estimate ~300kt is sufficient to disrupt a ~270m asteroid and  ~1mt for ~1km, both on relatively short timescales (<=year before impact)

For deflection scenarios (stand-off or low yield surface burst), it's a trade-off between warning time, yield, and how much energy you can deposit before the body starts to disrupt. The latter is important because if you disrupt the body, you want to be sure that it's fully disrupted.

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #50 on: 07/29/2017 09:11 PM »
I wouldn't cross the minefield, duh. I also wouldn't play Russian roulette or buy into a "~90% completion in ten years" scheme.
In the real world, you don't get that choice. Many real world risks are a numbers game, and resource limits dictate that you can't defend against all of them.

There is a non-zero probability that a km scale asteroid ejected from another solar system could impact the earth at > 100 km/s. On average, that probably happens less than once in the life of the solar system, but it's a real thing that could happen tomorrow. Anyone with a shred of common sense should be able to see that effort spent defending against that scenario is a worse investment than defending against events we expect to happen every few thousand years.

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Why, when small asteroids are the only ones we can stop?
You keep claiming this, but it's just totally, trivially, wrong. With sufficient warning, we can deflect km scale asteroids. The physics is really not that complicated, and the engineering is all based on stuff we already know how to do.

The key is finding them early, and we're doing that. If you look at https://cneos.jpl.nasa.gov/stats/totals.html you'll see that the number of known ~1km asteroids has been nearly flat since 2010, despite significant upgrades to the surveys.  From https://cneos.jpl.nasa.gov/stats/site_km.html you can see that discoveries of these peaked around 2000, with LINEAR  (using 1m and 0.5m telescopes) being the most productive. The current most productive surveys (PAN-STARRS and Catalina) use 1.8m and 1.5m scopes respectively and have much better cameras, yet their discovery rate of km class asteroids is much lower and is declining.

That's a very good indication that we've found most of them.
« Last Edit: 07/29/2017 10:42 PM by hop »

Offline jg

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Re: Deflecting or destroying dangerous asteroids
« Reply #51 on: 07/30/2017 02:06 PM »
Big asteroids can be discovered years/decades in advance of any possible impact.  We now have a pretty good idea of most of those given the surveys that have been under way for quite a few years (e.g. PanSTARRS, etc).  We can potentially do something about those, and discussion of what to do about those is very much underway, here and elsewhere.  But changing the economics of getting to space is essential.

The problem with small asteroids is that you can't see them in time to do anything (except to provide warning). We don't even know how common they are.

The closer to earth you discover them, the more you would have to really mess with them to get them to miss the earth (relatively easy to do with big asteroids that you know about long in advance, where even "small" amounts of force can move the orbit enough to avoid impact).  If you disrupt an asteroid, then you get a shotgun effect, that makes the situation worse.  Many of these incoming rocks are much more like a ball of loose rubble than a nice solid nickle iron asteroid. This is the principle of MIRV nuclear weapons: you get a bigger effect by N small explosions than one big explosion.  You don't have much time to try to figure out what kind of rock, or how solid it is, that is about to fall on someone's head, and therefore what will happen if you try to divert or otherwise destroy it.

What you can do is provide warning of small asteroids that will take out a city or small region of the planet, in time that people can get out of the way (or be warned to be away from windows, as in Chelyabinsk).  That's what ATLAS is beginning to do, as its telescopes are coming on line. http://fallingstar.com/home.php.  It currently has two .5 meter telescopes, hopefully to be expanded to a full network of 6 in the future.

Note several other things:  IR is *not* necessarily better or necessary for detection.  The quantum efficiency of CCD's is extremely high, and goes into the near IR (your every day CCD camera has a filter to keep the near IR out).  Detectors further in the IR are: 1) much lower resolution, 2) much lower quantum efficiency.  Remember, asteroids are "sun lit".

Bigger telescopes are not a feature: what you need to do is observe the whole sky multiple times/night (something ATLAS is doing), so you can distinguish asteroids from stars.

ATLAS should be able to give between a day and a couple weeks warning for incoming "Chelyabinsk" kinds of asteroids (and get us finally really good statistics on the number of small rocks that may fall on our heads).

Is ATLAS a panacea?  no, it can at best give you 60% coverage of incoming asteroids.  This is due to the Sun; not only the closer you get to the sun, the more the sky light interferes, but that less of the asteroid is reflecting light.

But it's a serious start, and statistics from it will determine how much urgency there may be for planetary defense asteroid detection from orbit, once we know how common incoming rocks are.

If you want to know of incoming rocks, subscribe to ATLAS's twitter feed (or the minor planet center announcements).

https://twitter.com/fallingstarIfA

ATLAS just really getting on line in a serious way. I need to check with my friend John Tonry if the new corrector plates are all set (last newsletter said installation in April), which are/will increase its detection rate a factor of five from the early results.

Happy rock ducking...







Offline gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #52 on: 07/30/2017 04:04 PM »
I think nukes are insufficient because of the overall business case.

If there are an unknown quantity of objects to annihilate

You expect _dozens_ of km-scale asteroids to appear out of nowhere, all crossing the Earth? Why?

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The probabilities of successfully achieving the outcome is uncertain.  The cost is too much.

However, the conditional probability of most of us dying, if a ~2 km asteroid is to impact anywhere on Earth, can be fairly well estimated to be  close to 100%.

I'm willing to pay "high" cost of having several dozen megaton-class warheads and corresponding spacecraft to be stored and ready to nuke it, if it will be found.

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The global politics is just too complex.

What is actually a problem? We right now have THOUSANDS of ~300kt class ICBM warheads on alert, ready to kill us all. A few dozens more don't change this picture significantly.

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The risk of failure is high.

The risk of doing nothing is higher.
« Last Edit: 07/30/2017 04:04 PM by gospacex »

Offline gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #53 on: 07/30/2017 04:17 PM »
Previously I mentioned telescopes haven't advanced in 350years - the date when reflection replaced refraction in large scopes.

There are no Ritchey–Chrétien designs.
There are no three-mirror anastigmat designs.
There are no Dall–Kirkham designs.
Off-axis designs (Schiefspiegler, Stevick-Paul) also do not exist.

No advances in hollow-core mirror manufacture happened, it's a myth.
Computer-controlled off-axis mirror polishing? Fantasy!

Ultra-low expansion glass? Does not exist! (Corning is obviously lying about it on their website)
Metal mirrors and special technologies to create those (powder HIP metallurgy, multi-stage polish and annealing)? No, no no.

Active optics? Myth.
Natural guide star adaptive optics? Lies.
Artificial guide star adaptive optics? Did not happen.

Optical interferometers also do not exist.

Nothing has changed in last 350 years. Sure!

Offline daveklingler

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Re: Deflecting or destroying dangerous asteroids
« Reply #54 on: 07/30/2017 04:40 PM »
I see NEOs as tremendous resources.  I'm hopeful that within the next few years we can begin discussing them in those terms, rather than strictly as hazards.  With the appropriate orbital infrastructure, we can begin pulling material off of asteroids each time they cross, which will lead us to more infrastructure, which in turn will increase the demand for more material. 

I think that even relatively soon, as technology and orbital populations develop, most of what's considered dangerous now will be repeatedly and incrementally redirected into more useful orbits where it can be whittled down into nothing.  Something we see as a potential planet killer in the next few hundred years may be eyed closely by corporate planners in another fifty. 

So...deflect, destroy or use?

Offline gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #55 on: 07/30/2017 06:31 PM »
I see NEOs as tremendous resources.  I'm hopeful that within the next few years we can begin discussing them in those terms, rather than strictly as hazards.  With the appropriate orbital infrastructure, we can begin pulling material off of asteroids each time they cross, which will lead us to more infrastructure, which in turn will increase the demand for more material.

More like "build infrastructure on the NEO", this would save on raw material transportation costs.

But anything like this is at best ~50 years in the future. Even if you crack the financing problem, just R&D on space manufacturing would take many iterations and many decades.

Offline jg

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Re: Deflecting or destroying dangerous asteroids
« Reply #56 on: 07/30/2017 07:08 PM »

However, the conditional probability of most of us dying, if a ~2 km asteroid is to impact anywhere on Earth, can be fairly well estimated to be  close to 100%.

I'm willing to pay "high" cost of having several dozen megaton-class warheads and corresponding spacecraft to be stored and ready to nuke it, if it will be found.

The big asteroids, the "world killers" are easy to see years in advance, and are now a mostly known topic.  People are seriously discussing the best way to deal with them, which is more complex than it appears on the surface, as disrupting a ball of rubble is a very bad idea.

But you have a lot of time to deal with the big asteroids, since you can find them years in advance.  Due to the time before impact, you only have to give them (relatively) small nudges, potentially over a long period to miss Earth; in fact at a low enough rate that their minimal internal gravity may keep a asteroid that is a rubble ball together.

Whether nukes will be a piece of the asteroid solution, is not clear to me (I've not studied the problem).  There are serious people trying to figure that out, and meetings and proceedings you can study. Both Bomb Builders from the national labs, astronomers and others are trying to figure that out.

But firing a nuke at a small asteroid nearby earth, on one of the last days before impact, will require large impulse.  This seems very likely to often result in turning the small asteroid into a MIRV that would inflict more destruction than a single, larger impact.  That this is a serious issue, is clear from videos of the incoming Chelyabinsk (and other smaller entries into Earth's atmosphere of asteroids).  Just take a look at the fireballs.  These asteroids often fall apart.

So hold your nukes: it isn't clear yet they can/should play an role.

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #57 on: 07/30/2017 08:05 PM »
The problem with small asteroids is that you can't see them in time to do anything (except to provide warning).
This isn't quite correct. You can't see them in time to do much if they are on an impact trajectory at the time of discovery, but the vast majority have near misses before impact. In that case, you can figure out whether they pose a threat on subsequent orbits. A good recent example of this is 2012 tc4 https://uanews.arizona.edu/story/upcoming-asteroid-flyby-will-help-nasa-planetary-defense-network

If you look at https://cneos.jpl.nasa.gov/stats/size.html almost 50% of known NEOs are in the < 100m categories, and a substantial number are in the < 30m. Of course, this is a tiny fraction of the population, but we do already discover and track NEOs in this size range.

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We don't even know how common they are.
The error bars are large, but it's not totally unconstrained. We know the rate of impacts of very small bodies from nuclear weapon monitoring and fireball networks. Populations can also be estimated from surveys that only see some of them, as long as we have a good understanding of the efficiency and biases. The DECam paper I linked earlier is a good example https://arxiv.org/abs/1707.04066

It's notable that estimates for the >100 m class seem to be converging pretty well.

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Note several other things:  IR is *not* necessarily better or necessary for detection.
One thing mid IR is good for is characterization. With just optical, you don't know whether it's a large, dark body or a small reflective one. The difference between a 30m and 100m is a big deal if it's going to impact. The downside of course is that it has to be in space, but being in space has it's own significant advantages for discovery.

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Bigger telescopes are not a feature: what you need to do is observe the whole sky multiple times/night (something ATLAS is doing), so you can distinguish asteroids from stars.
I would disagree with this a bit, both large and small telescopes have their place. All else being equal, large telescopes let you discover the same size object sooner. LSST is an obvious example where a large telescope will make a big contribution.

Offline jg

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Re: Deflecting or destroying dangerous asteroids
« Reply #58 on: 07/30/2017 08:23 PM »

Quote
We don't even know how common they are.
The error bars are large, but it's not totally unconstrained. We know the rate of impacts of very small bodies from nuclear weapon monitoring and fireball networks. Populations can also be estimated from surveys that only see some of them, as long as we have a good understanding of the efficiency and biases. The DECam paper I linked earlier is a good example https://arxiv.org/abs/1707.04066

It's notable that estimates for the >100 m class seem to be converging pretty well.

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Note several other things:  IR is *not* necessarily better or necessary for detection.


We'll know *alot* more about size distribution within the next few years, as ATLAS comes on line and builds a good sample set. The uncertainties will drop dramatically.

LSST's cadence is one scan of the observable sky every 4 days.  ATLAS is 4x a night.  And I won't go into the cost of LSST relative to ATLAS.  You need a high cadence to catch/discover small nearby asteroids.  Once every 4 days, and all you get is one dot unless the rock is far away.  LSST will do great at finding distant big rocks indeed.  In fact, I was asked to review the software project to get alerts of new discoveries out of LSST last year.

Once you discover the incoming/nearby asteroid, you immediately want to followup to confirm/refine the orbit, and get it's reflectance spectrum.  That tells you a lot about what flavor rock.  I used to to build equipment to do such things in the 1970's in MIT's Planetary Astronomy Lab ;-); you can do very well in the optical/near IR....

In this case, small systems designed to serve the purpose specifically will do much better than general purpose big telescopes (which are very expensive).

The big issue I see is that survey projects such as LSST, ATLAS and other surveys don't yet get the timely followup they need.  Something I'm noodling on quite hard at the moment, as a result of having to think about the LSST Antares project I reviewed.
« Last Edit: 07/30/2017 08:38 PM by jg »

Offline gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #59 on: 07/31/2017 12:37 AM »
But firing a nuke at a small asteroid nearby earth, on one of the last days before impact, will require large impulse.  This seems very likely to often result in turning the small asteroid into a MIRV that would inflict more destruction than a single, larger impact.

This was already discussed. Many smaller impacts from fragments in almost all cases is less damaging than the impact of a intact body. One reason, for example, is that smaller fragments dissipate more of their energy in the air, before impact.

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That this is a serious issue, is clear from videos of the incoming Chelyabinsk

How did you conclude that? Those videos did not contain two events, one of a fragmented meteorite and another a similar but intact one.

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #60 on: 07/31/2017 04:26 AM »
Active optics? Myth.
Oops, forgot that. It is an advancement worth recognition and doesn't just apply to telescopes.

Dr. John S. Lewis - "Until we know what the body is made of, hazard projections are nonsense. It could be a dustball, a snowball, a loose collection of rocky rubble, a monolithic soft rock, a monolithic hard rock, a giant steel cannonball, et cetera. It could, at the extremes, fall apart into dust at high altitudes or penetrate hundreds of meters into Earth’s crust and explode like World War III." http://deepspaceindustries.com/asteroid-profile-2017-bs5/
One quote you missed from that very same article... says we can determine the composition of an asteroid. ... Long lead-times are essential for a deflection attempt. Where you go wrong is your claim that we can't deflect any unless they are ~100 meters in diameter or smaller.

"JSL: "There are, as yet, no useful data to characterize what 2017 BS5 is made of. The close fly-by this weekend will give Earth-based astronomers a great opportunity to get a good spectrum and tell us what class of meteorite it is most closely related to, what the dominant minerals are, and what economic value it might have."
You need to explain how waiting until an asteroid's upon us to identify its composition jives with the long lead time you say is necessary to stop it, and how you plan to stop any such meteor of (well)over 100m if you a) have lead time, but no knowledge of its composition -or- b) wait until its upon you.

1) In the real world, you don't get that choice. 2) Many real world risks are a numbers game ...

The key is finding them early, and we're doing that. If you look at https://cneos.jpl.nasa.gov/stats/totals.html you'll see that the number of known ~1km asteroids has been nearly flat since 2010, despite significant upgrades to the surveys.  From https://cneos.jpl.nasa.gov/stats/site_km.html you can see that discoveries of these peaked around 2000, with LINEAR  (using 1m and 0.5m telescopes) being the most productive. ...
3) That's a very good indication that we've found most of them.
Re1) In the real world, there's always choice and if you think it's either/or, you haven't found all the options.
Re2) Nothing is a numbers game other than actual numbers games unless all you can comprehend is numbers.
Re3) It's a very good indication that it was either a waste of time/money that found nothing of importance -or- that you've only found the irrelevant ones and missed everything you were supposed to.

In the paper, they estimate ~300kt is sufficient to disrupt a ~270m asteroid and  ~1mt for ~1km, both on relatively short timescales (<=year before impact)
For deflection scenarios (stand-off or low yield surface burst), it's a trade-off between warning time, yield, and how much energy you can deposit before the body starts to disrupt. The latter is important because if you disrupt the body, you want to be sure that it's fully disrupted.
Please clarify the word "disrupt" as deflection or disintegration and how you "know" how much energy an asteroid can absorb per m2 or kg when the composition is a guess and its physical properties are completely unknown until a mission like DART actually tests an asteroid.
« Last Edit: 07/31/2017 04:31 AM by Propylox »

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #61 on: 07/31/2017 05:08 AM »
Re1) In the real world, there's always choice and if you think it's either/or, you haven't found all the options.
This is just so obviously false it's hard to imagine you are being serious. You didn't address the example I provided in that post, but here are a few more examples of this kind of "logic":
1) If you can't totally eliminate the risk of cancer, you might as well smoke 10 packs a day!
2) If a vaccine is only 95% effective, you are just as well off not using it!
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Re3) It's a very good indication that it was either a waste of time/money that found nothing of importance -or- that you've only found the irrelevant ones and missed everything you were supposed to.
Complete non-sequitur. In the 1990s, when this search started, we did not know if there were any ~1km scale NEOs that posed a near term impact risk. The majority of 1km NEOs have now been found, so that potential risk is mostly eliminated. Yes, it turns out there were none that we need to deflect right away (yay!) but we could not have known that without looking.

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Please clarify the word "disrupt" as deflection or disintegration and how you "know" how much energy an asteroid can absorb per m2 or kg
I provided a link to the paper. You probably should have read it before declaring the results were impossible.
Quote
when the composition is a guess and its physical properties are completely unknown until a mission like DART actually tests an asteroid.
It's simply false to claim that the properties of asteroids are completely unknown. DART will further improve our understanding, but we already know a whole lot.

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #62 on: 07/31/2017 05:34 AM »
<parsed> We'll know *alot* more about size distribution within the next few years, as ATLAS comes on line and builds a good sample set. ... You need a high cadence to catch/discover small nearby asteroids.  Once every 4 days, and all you get is one dot unless the rock is far away. ... In this case, small systems designed to serve the purpose specifically will do much better than general purpose big telescopes (which are very expensive).
As far as survey work, ATLAS is an excellent design for complete coverage at low cost - but I question its defensive merit, its ability to detect dim objects of small size, low albedo or at viable distance.
I question its ability to gather enough photons in time for action.

Bigger telescopes are not a feature: what you need to do is observe the whole sky multiple times/night so you can distinguish asteroids from stars.
I would disagree with this a bit, both large and small telescopes have their place. All else being equal, large telescopes let you discover the same size object sooner.
It's not an either/or answer, it's both and then some. How "good" an asteroid telescope would be depends on how fast it can gather photons from the entire sky (FoV - f and/or speed of traverse) and how many photons from every point (telescope size and/or exposure). A 180 field of view in SSO on endless exposure would see most everything, but at poor resolution compared to a very large scope traversing quickly. I'd use the later, acknowledging lightweight requirements for traverse speed, launch and budget.

IR is *not* necessarily better or necessary for detection. The quantum efficiency of CCD's is extremely high, and goes into the near IR. Detectors further in the IR are: 1) much lower resolution, 2) much lower quantum efficiency.
One thing mid IR is good for is characterization. With just optical, you don't know whether it's a large, dark body or a small reflective one.
Due to the poor resolution of IR, requirements for in-space operation and long exposure, I don't see any advantage as an initial survey, only a follow-up on objects of interest, investigation or threat. As there's already IR scopes in space (not all publicly) in addition to the upcoming JWST that can characterize these, there's no advantage to launching another tiny one that can't really do anything.

There are laws of physics to contend with and only in New Physics section can wishful thinking overcome them. Or perhaps your posts are a prelude to a sales pitch for large-scale diffractive lenses?
Good engineering doesn't contend with the laws of physics, it masters them. And there's no sales pitch as you couldn't have my work at any price  ;D though if members wish to discuss a Very Large Space Telescope in its own thread, I'll dust off and update (if necessary) my decade-old designs. ie; Whatever size scope you planned, use that dimension for the secondary mirror and add 25% mass for the entire telescope.
« Last Edit: 07/31/2017 05:40 AM by Propylox »

Offline as58

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Re: Deflecting or destroying dangerous asteroids
« Reply #63 on: 07/31/2017 05:53 AM »
There are laws of physics to contend with and only in New Physics section can wishful thinking overcome them. Or perhaps your posts are a prelude to a sales pitch for large-scale diffractive lenses?
Good engineering doesn't contend with the laws of physics, it masters them. And there's no sales pitch as you couldn't have my work at any price  ;D though if members wish to discuss a Very Large Space Telescope in its own thread, I'll dust off and update (if necessary) my decade-old designs. ie; Whatever size scope you planned, use that dimension for the secondary mirror and add 25% mass for the entire telescope.

Yes please, I'd love to hear about your design.

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #64 on: 07/31/2017 05:54 AM »
Please clarify the word "disrupt" as deflection or disintegration and how you "know" how much energy an asteroid can absorb per m2 or kg when the composition is a guess and its physical properties are completely unknown until a mission like DART actually tests an asteroid.
I provided a link to the paper. You probably should have read it before declaring the results were impossible. It's simply false to claim that the properties of asteroids are completely unknown. DART will further improve our understanding, but we already know a whole lot.
You used a word ambiguously (twice in two different ways) and I'd like you to clarify it. If you don't understand the material enough to recognize that and just copy/posted it, that's OK too. Secondly, the composition of all asteroids is known - it's a bit of everything, never the same and the composition and physical properties of any one asteroid is a complete unknown.
What merit does your nuke papers have against any specific threat, not just as useless generalizations? How will you determine the physical properties of a specific threat to conclude the amount of energy per m2 or kg that could or should be used. It's OK to admit you and "the field" haven't a clue and offer empty promises.
« Last Edit: 07/31/2017 05:56 AM by Propylox »

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #65 on: 07/31/2017 06:15 AM »
Due to the poor resolution of IR, requirements for in-space operation and long exposure, I don't see any advantage as an initial survey, only a follow-up on objects of interest, investigation or threat. As there's already IR scopes in space (not all publicly) in addition to the upcoming JWST that can characterize these,  there's no advantage to launching another tiny one that can't really do anything.
You don't see the advantage, but the people who actually do this stuff do:
1) https://neocam.ipac.caltech.edu/
2) The 2007 NASA report recommends an IR space telescope https://cneos.jpl.nasa.gov/doc/neo_report2007.html

Finally, JWST really isn't good for fast moving inner solar system stuff.

Quote
Secondly, the composition of all asteroids is known - it's a bit of everything, never the same and the composition and physical properties of any one asteroid is a complete unknown.
Yes, meteorites and spectra and radar just don't exist ::)
« Last Edit: 07/31/2017 06:23 AM by hop »

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #66 on: 07/31/2017 06:32 AM »
Secondly, the composition of all asteroids is known - it's a bit of everything, never the same and the composition and physical properties of any one asteroid is a complete unknown.
Yes, meteorites and spectra and radar just don't exist ::)
Yes, WL64 made the same suggestion - just wait until the asteroid's about to hit Earth to find out what it is and have decades to divert it. No that didn't make sense, but at least he didn't recommend waiting for it to become a meteorite. Friggin' genius.

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #67 on: 07/31/2017 06:41 AM »
Yes, WL64 made the same suggestion - just wait until the asteroid's about to hit Earth to find out what it is and have decades to divert it. No that didn't make sense, but at least he didn't recommend waiting for it to become a meteorite. Friggin' genius.
You completely missed the point. Meteorites are asteroid samples. They give us a very good idea of the range of compositions we are likely to encounter, and we can identify asteroids with similar composition using spectra.

Offline meberbs

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Re: Deflecting or destroying dangerous asteroids
« Reply #68 on: 07/31/2017 08:02 AM »
Please clarify the word "disrupt" as deflection or disintegration and how you "know" how much energy an asteroid can absorb per m2 or kg when the composition is a guess and its physical properties are completely unknown until a mission like DART actually tests an asteroid.
I provided a link to the paper. You probably should have read it before declaring the results were impossible. It's simply false to claim that the properties of asteroids are completely unknown. DART will further improve our understanding, but we already know a whole lot.
You used a word ambiguously (twice in two different ways) and I'd like you to clarify it. If you don't understand the material enough to recognize that and just copy/posted it, that's OK too.
I found nothing ambiguous about his use of disrupt. It seemed to me to be a fairly dictionary standard use of the word. In this context it is close to a synonym for deflection.

What merit does your nuke papers have against any specific threat, not just as useless generalizations? How will you determine the physical properties of a specific threat to conclude the amount of energy per m2 or kg that could or should be used. It's OK to admit you and "the field" haven't a clue and offer empty promises.
No one would admit what you just said because it is false. You might as well have said "I didn't read the paper because I like ignorance."

The paper literally discusses the effects of different material properties, and contrary to your repeated claims we should have at least some idea of the asteroid's properties. Also, there is no reason the spacecraft carrying out the mission couldn't have instruments on it to take additional measurements on approach to use for fine tuning detonation distance.

As for the specifics of how to determine the properties, I am not an expert on that (what I do know is a combination of spectroscopy, radar, optical images, and the fact that asteroids are not just random, but tend to fall into specific categories) , but if you want the details you can do some research yourself:
https://scholar.google.com/scholar?q=determination+of+asteroid+properties

Offline gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #69 on: 07/31/2017 11:51 AM »
Yes, WL64 made the same suggestion - just wait until the asteroid's about to hit Earth to find out what it is and have decades to divert it. No that didn't make sense, but at least he didn't recommend waiting for it to become a meteorite. Friggin' genius.

You completely missed the point. Meteorites are asteroid samples. They give us a very good idea of the range of compositions we are likely to encounter, and we can identify asteroids with similar composition using spectra.

No matter how many times you point out to this guy that he makes one grave mistake in his logic after another, he won't stop arguing, adding more nonsense.

There's a solution to it: we can stop replying.
« Last Edit: 07/31/2017 11:51 AM by gospacex »

Offline Hog

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Re: Deflecting or destroying dangerous asteroids
« Reply #70 on: 07/31/2017 02:04 PM »
What size of fission fission/fusion device would be need?
Would the current less than 1mT devices be sufficient, or would we need to revisit some 9-15mT weapons of the past?

I can see the difficulty in testing for such devices, or even attempting to procure the materials and engineer the actual nuclear portion of the device.


Is there anyone with the opine that perhaps nothing should be done? Perhaps humans are destined to go the way of the dinosaurs?
Paul

Offline Hog

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Re: Deflecting or destroying dangerous asteroids
« Reply #71 on: 07/31/2017 02:11 PM »
https://www.nasa.gov/planetarydefense

NASAs Planetary Defense Coordination Office operates on $4million per year  I wonder what that would swell to in the event of an early warning of oncoming danger.

Could space telescopes at distance enveloping the Earth, similar to the DEWS used by NORAD?
Paul

Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #72 on: 07/31/2017 03:54 PM »
*snip*
Dr. John S. Lewis - "Until we know what the body is made of, hazard projections are nonsense. It could be a dustball, a snowball, a loose collection of rocky rubble, a monolithic soft rock, a monolithic hard rock, a giant steel cannonball, et cetera. It could, at the extremes, fall apart into dust at high altitudes or penetrate hundreds of meters into Earth’s crust and explode like World War III." http://deepspaceindustries.com/asteroid-profile-2017-bs5/
One quote you missed from that very same article... says we can determine the composition of an asteroid. ... Long lead-times are essential for a deflection attempt. Where you go wrong is your claim that we can't deflect any unless they are ~100 meters in diameter or smaller.

"JSL: "There are, as yet, no useful data to characterize what 2017 BS5 is made of. The close fly-by this weekend will give Earth-based astronomers a great opportunity to get a good spectrum and tell us what class of meteorite it is most closely related to, what the dominant minerals are, and what economic value it might have."
You need to explain how waiting until an asteroid's upon us to identify its composition jives with the long lead time you say is necessary to stop it, and how you plan to stop any such meteor of (well)over 100m if you a) have lead time, but no knowledge of its composition -or- b) wait until its upon you.

Your claim was that it is not possible to know an asteroid's composition. This is patently false.

It should be obvious that long lead times will allow for many, many observation of the incoming object, which provides for very precisely calculating its orbit as well as determining its composition, and possibly even its internal structure. It would likely be the most intensely scrutinized object in the solar system.

There are multiple means of deflection. A nuclear blast is just one way, but it's by far the easiest way to give an asteroid a precisely measured push. Gravity tractor is another, albedo change is another, impact, laser ablation, and so on. The longer lead time we have the more options are available.
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Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #73 on: 07/31/2017 05:55 PM »
I found nothing ambiguous about his use of disrupt. It seemed to me to be a fairly dictionary standard use of the word. In this context it is close to a synonym for deflection.
FWIW, I was specifically referring to the "fragmentation" cases in section 2.2:
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When the time before impact is short (less than a decade), the necessary speed change becomes a significant fraction of the escape speed, even for large bodies, and fragmentation may be difficult to avoid. If fragmentation occurs near the Earth, allowing a sizable fraction of the material to impact, this can worsen the event. How ever, if the time to impact and the dispersal speeds are sufficient to cause most of the material to miss the Earth, fragmentation can achieve substantial mitigation, and smaller bodies may be fragmented into pieces unable to penetrate the atmosphere.
(I mis-remembered the authors using "disrupt" here when I replied to Propylox, so it was slightly less clear than I intended, but it's pretty obvious they didn't read the paper.)

And of course, as you note they specifically describe the material properties used for these cases:
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Fragmentation was examined for both a 1 km body (about a billion tons) and an Apophis-sized, 270 m body (a bit over 20 million tons). As before, the structures consisted of a higher density core (ρ=2.63 g/cm^3 ) and a lower density mantle (ρ=1.91 g/cm^3). An equation of state for tuff (soft, porous rock that forms from compacted volcanic ash) was implemented in the mantle region. The bulk density of the structures was 1.99 g/cm^3, close to that measured for asteroid Itokawa (ρ=1.95 g/cm^3) [10].

Finally, I don't mean to suggest this study is the definitive word on the subject. It's a publicly accessible example, which shows (in agreement with a lot of other work) that various nuclear options appear viable under physically plausible assumptions.

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #74 on: 08/01/2017 03:59 AM »
I agree nothing should be done.  The threat is imaginary and overplayed.
You can argue over the cost/benefit, but the threat is clearly not imaginary. There are plenty of large impact craters on earth, and historically Chelyabinsk and Tunguska are obviously significant impact events.
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Extinction events are only circumstantial evidence.
This is incorrect. There is clear, direct evidence for both extinction events and large impacts (not all extinction events are associated with impacts, and not all impacts cause mass extinctions) There is some debate over how much other factors were involved in the extinction of the dinosaurs, but the catastrophic effects of the impact are not in question.
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  Earth apparently survived five extinction events. 
"Extinction event" means a lot species died out suddenly around the same time. The fact that we have no evidence of global sterilization events is irrelevant.
« Last Edit: 08/01/2017 04:00 AM by hop »

Offline daveklingler

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Re: Deflecting or destroying dangerous asteroids
« Reply #75 on: 08/01/2017 04:55 AM »
I see NEOs as tremendous resources.  I'm hopeful that within the next few years we can begin discussing them in those terms, rather than strictly as hazards.  With the appropriate orbital infrastructure, we can begin pulling material off of asteroids each time they cross, which will lead us to more infrastructure, which in turn will increase the demand for more material.

More like "build infrastructure on the NEO", this would save on raw material transportation costs.

But anything like this is at best ~50 years in the future. Even if you crack the financing problem, just R&D on space manufacturing would take many iterations and many decades.

There's a mental  paradigm shift necessary before any of this can happen.  People need to first be able to see non-planetary destinations as desirable for permanent habitation, and secondly that creating artificial 1G gravity is simple and relatively inexpensive.

Given 1G gravity, space manufacturing can (often) use conventional, mass-produced terrestrial machinery, and NEOs become resources much sooner.

My own preference would be to work on deflecting dangerous (and non-dangerous, but accessible) asteroids into orbits that leave them accessible for future development.  I believe that if we can deflect them, we can do this.
« Last Edit: 08/01/2017 05:03 AM by daveklingler »

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #76 on: 08/01/2017 06:03 AM »
My own preference would be to work on deflecting dangerous (and non-dangerous, but accessible) asteroids into orbits that leave them accessible for future development.  I believe that if we can deflect them, we can do this.
Capturing is much harder. To avoid an impact, you only need velocity change on the order of millimeters per second if you have decent (years to decades) warning. Getting a random NEO into orbit will be more likely be in the kilometers per second range.

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #77 on: 08/01/2017 10:44 AM »
Let's move away from theoretical to actionable.

An asteroid has been discovered on a collision course with Earth, the size and distance of which doesn't matter. We can observe its size, orbit, surface material and it's center of mass based on tumble. We cannot determine its total mass as G is irrelevant at these scales, thus we cannot determine its density. We cannot determine if that mass is homologous or concentrated in one or more areas.

Assumptions can be made on composition based on origination, therefor assumptions can be further made on its physical properties such as mass, momentum, cohesive strength and melting point. Ample theoretical studies have been done on how this asteroid will respond to deflection techniques including warheads.

Humanity gets one shot at this. Should we trust all those assumptions and theories or disregard them and instead determine facts about the asteroid, then devise a course of action? I sincerely hope we don't follow speculative assumptions with minimal accuracy.
As such, all the theories/studies to date are worthless as an actual situation would require its own study - based on actual facts - and the theories/studies to date cannot even provide a reliable, actionable roadmap for such a study. It'd be a square one, all on the line.

Offline RonM

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Re: Deflecting or destroying dangerous asteroids
« Reply #78 on: 08/01/2017 02:30 PM »
Let's move away from theoretical to actionable.

An asteroid has been discovered on a collision course with Earth, the size and distance of which doesn't matter. We can observe its size, orbit, surface material and it's center of mass based on tumble. We cannot determine its total mass as G is irrelevant at these scales, thus we cannot determine its density. We cannot determine if that mass is homologous or concentrated in one or more areas.

The distance is very important. You can only observe the size of an asteroid if it makes a close approach to Earth. If impact occurs on this pass, it's too late for action. If it speeds by and will hit on a later orbit, there's time to develop a strategy to deflect.

Quote
Assumptions can be made on composition based on origination, therefor assumptions can be further made on its physical properties such as mass, momentum, cohesive strength and melting point. Ample theoretical studies have been done on how this asteroid will respond to deflection techniques including warheads.

Humanity gets one shot at this. Should we trust all those assumptions and theories or disregard them and instead determine facts about the asteroid, then devise a course of action? I sincerely hope we don't follow speculative assumptions with minimal accuracy.
As such, all the theories/studies to date are worthless as an actual situation would require its own study - based on actual facts - and the theories/studies to date cannot even provide a reliable, actionable roadmap for such a study. It'd be a square one, all on the line.

The studies are useful because we have examined potential scenarios and developed potential deflection options. We already have an idea of what to do if an asteroid fits one of those scenarios. It will take less time to develop a response since we've previously considered theoretical options. The theories are not worthless.

With enough lead time we could send a mission to the asteroid to determine its composition, mass, etc. and then be able to develop an effective plan.

Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #79 on: 08/01/2017 03:14 PM »
... It should be obvious that long lead times will allow for many, many observation of the incoming object, which provides for very precisely calculating its orbit as well as determining its composition, and possibly even its internal structure. It would likely be the most intensely scrutinized object in the solar system. ...
Surface observations such as optical, IR and spectroscopy will only tell you where the asteroid's been, not what it's made of and certainly not its internal structure. Penetrating radar will highlight density dispersion and whether it's essentially dusty rubble, a dirty icecube or a dense metallic mass with mantle, but this can't be performed at vast distances and assumptions would only misinform.

Spectroscopy does tell you what its made of. That's literally what spectroscopy does.

Radar observations can penetrate the surface, as you say, and and finding out whether it's a solid body or a rubble pile, etc. is determining its structure.

You're talking out of both sides of your mouth here.
Quote
... we should have at least some idea of the asteroid's properties. Also, there is no reason the spacecraft carrying out the mission couldn't have instruments on it to take additional measurements on approach to use for fine tuning detonation distance.

As for the specifics of how to determine the properties, I am not an expert on that (what I do know is a combination of spectroscopy, radar, optical images, and the fact that asteroids are not just random, but tend to fall into specific categories) , but if you want the details you can do some research yourself:
https://scholar.google.com/scholar?q=determination+of+asteroid+properties
Unfortunately, we wouldn't have any idea of the asteroid's properties if it was new - no matter how many pundits and "experts" like to say/think so. Any interceptor spacecraft would absolutely need to quantify the asteroid with optical, radar, gravitational and seismic measurements before any attempted action.

Moreover, detonating a single warhead is a fool's errand at any range or composition (but I got these studies!) unless the meteor is small enough to be completely vaporized by it.

Again, you make this claim, and again, it's still wrong.

Even a few centimeters per second of dV is enough to deflect an asteroid if done sufficiently in advance.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #80 on: 08/01/2017 03:26 PM »
Let's move away from theoretical to actionable.

An asteroid has been discovered on a collision course with Earth, the size and distance of which doesn't matter. We can observe its size, orbit, surface material and it's center of mass based on tumble. We cannot determine its total mass as G is irrelevant at these scales, thus we cannot determine its density. We cannot determine if that mass is homologous or concentrated in one or more areas.

Assumptions can be made on composition based on origination, therefor assumptions can be further made on its physical properties such as mass, momentum, cohesive strength and melting point. Ample theoretical studies have been done on how this asteroid will respond to deflection techniques including warheads.

Humanity gets one shot at this. Should we trust all those assumptions and theories or disregard them and instead determine facts about the asteroid, then devise a course of action? I sincerely hope we don't follow speculative assumptions with minimal accuracy.
As such, all the theories/studies to date are worthless as an actual situation would require its own study - based on actual facts - and the theories/studies to date cannot even provide a reliable, actionable roadmap for such a study. It'd be a square one, all on the line.

This would be like a general saying "Let's disregard all previous intelligence, as well as all our weapons, strategy, and tactics and fight the next war making things up as we go along.

Who knows? Maybe a massed charge of spears, with support from bows and arrows are better than machine guns and bombs. After all, we don't know what weapons the enemy will have, where they are concentrated, or what the terrain will be."
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #81 on: 08/01/2017 05:50 PM »
Spectroscopy does tell you what its made of. That's literally what spectroscopy does.
Indeed.

Another thing that Propylox neglects is that the range of plausible configurations is limited. There's a limited number of general asteroid classes (stony, carbonaceous, metallic...) and physical configurations (monolithic blocks, rubble pile, blocks mantled with rubble) and anything we encounter will almost certainly fall into one of those categories. We have a lot of information about each class from space missions, meteorites and remote sensing. As long as we can classify the target, we can say a lot about the likely properties without much direct observation of the specific target.

Finally, we don't need absolute knowledge of all the asteroids properties. We just need to know the uncertainties and how they affect the available deflection options. If a given deflection method works for both solid rock and rubble piles, we don't need to know which a given target is.

For anyone who wants a comprehensive scientific review of what we actually know about asteroids, chapters of the recent book Asteroids IV can be found on arxiv using this search: http://arxiv.org/find/all/1/co:+AND+ASTEROIDS+IV/0/1/0/all/0/1?skip=0
« Last Edit: 08/01/2017 06:26 PM by hop »

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #82 on: 08/01/2017 06:38 PM »
...
1) The studies are useful because we have examined potential scenarios and developed potential deflection options. We already have an idea of what to do if an asteroid fits one of those scenarios. It will take less time to develop a response since we've previously considered theoretical options. The theories are not worthless.

2) With enough lead time we could send a mission to the asteroid to determine its composition, mass, etc. and then be able to develop an effective plan.
Re1) Yes, but all the studies are on mythological asteroids of neatly derived categories. How many asteroids have been visited, thoroughly analyzed, their internal structure mapped and deconstructed? And that highly variable group, including 67P, don't fit with the assumed categories - unless contorted like the proverbial square peg / round hole. Keeping one's math sharp is always a good idea, but none of the scenarios - the theoretical options, represent what we have found or will likely find. As Napoleon, Tyson and countless coaches have said, everyone has a plan until it matters (the first shot's fired, punched in the mouth, the ball's snapped).

Re2) I not only agree, but suggest it would be essential to send a craft to the subject asteroids to quantify it as current speculations are both fundamentally naive and proven false. Even our best measurements at distance cannot, and have not provided enough information to plan course of action - much less claim nuclear solutions.
« Last Edit: 08/01/2017 06:40 PM by Propylox »

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #83 on: 08/01/2017 07:48 PM »
You can only observe the size of an asteroid if it makes a close approach to Earth.
Directly resolving the asteroid isn't the only way to determine the size. The absolute magnitude is known essentially as soon as the orbit is determined, and gets within a factor of a few. See https://cneos.jpl.nasa.gov/tools/ast_size_est.html

Knowing the spectral type reduces the plausible range for the albedo. Thermal IR provides further constraints, within 10% or so. See https://neocam.ipac.caltech.edu/page/whyinfrared

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #84 on: 08/02/2017 12:51 PM »
Spectroscopy does tell you what (an asteroid's) made of. That's literally what spectroscopy does.
From afar, surface observations cannot determine internal composition. It will actually misrepresent.
ie; An icy object is discovered, ejecting water vapor as it nears the Sun on its orbit. Must be a comet, a KBO and primordial body - right? So a mission is sent to analyze it and it turns out it's a Jovian asteroid that dropped out of orbit. That was ESA's Rosetta blunder and a repeated mistake in classifying asteroids, comets or the middle-ground of "Main Belt Comets" or "Active Asteroids".

If a deflect/destroy mission is sent based on surface observations it will inaccurately assume the objects density. Comet Borrelly is as dark as a rock, but only because it's so old it lost all its ice and is actually incredibly porous (180kg/m3). Comet Temple 1 (620kg/m3) and Rosetta's asteroid 67P (533kg/m3) have similar orbits, but 67P is relatively young and dumps so much water each orbit it's now less dense than the ancient Temple 1.

The density, or porosity of these are only known after they were intercepted. Any attempted deflection would have to reach and study the object first, as making assumptions based on appearance is the same as flying blind on pride. Making prior assumptions about composition or structure is equally foolish.
PS - Asteroid 67P's trail of molecular oxygen and very high deuterium levels can only come from the inner orbits of Jupiter or Saturn, which is where it originated - not from beyond the gas giants as is required to be classified as a comet. If the ESA can't tell the difference between a comet and asteroid, do you really think "studies by experts in the field" can readily classify threats and plot a solution?
« Last Edit: 08/02/2017 12:55 PM by Propylox »

Offline as58

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Re: Deflecting or destroying dangerous asteroids
« Reply #85 on: 08/02/2017 02:23 PM »
@hop
Some have concluded that it may not have been asteroid or meteor at all.  It could be plausible that Tunguska was caused by ejected material from a Earth volcano (Krakatoa) that reached orbit and eventually decayed. 

This just might be the most bizarre attempted explanation of the Tunguska event that I've ever seen.

Offline JasonAW3

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Re: Deflecting or destroying dangerous asteroids
« Reply #86 on: 08/02/2017 03:24 PM »
@hop

Chelyabinsk also has no impact crater.  If the object fell anywhere it was in a lake.  There were no deaths.  Just broken windows.

This is the problem with the asteroid stuff, It is just totally over played!  Just another global warming hoax story where the data has been hyped beyond belief for political purposes.

There are no volcanic stone objects known to be in orbit at this time!


First; Chelyabinsk was an asteroid both too small and of the wrong composition to actually impact and cause additional damage.  Had it been slightly larger, or of a slightly different composition, it's likely that it could have made it to about half the altitude it did, and obliterated Chelyabinsk completely.

      Just because an asteroid makes an air burst, rather than an impact, doesn't make it any less dangerous.  Tunguska is a prime example of that.  (As to how many were killed in that blast, this is open to conjecture, as the area was, at the time, largely uninhabited.  It is possible that others were killed, but their remains were destroyed or consumed by local wildlife.  It was a number of years before an expedition was able to go to that area to examine what had happened.  A lot of environmental recovery happened in the interim).

Second; No, the risk is NOT overplayed.  There are a number of, mostly, smaller impacts that happen on Earth on a fairly regular basis.  (Not just airbursts, but actual impacts).  As most of these are fairly small and happen out to sea, very little is actually heard about those.

      The problem is, although large, disastrous impacts are fairly rare, the odds are high enough and the potential damage and loss of life is high enough, that it is a concern that should be addressed.

      That none of the known NEOs, asteroidal or cometary, are currently in a high risk of collision of collision with the Earth, this could easily change due to some very minor changes, induced in their orbits by the gravity of one or more planets, moons or even other NEOs.

      I suggest, rather than ranting about how "Fake News" the whole Asteroid Impact Threat is, you should do a bit more research and learn the true odds and possible outcomes of ignoring such threats.
« Last Edit: 08/02/2017 06:16 PM by JasonAW3 »
My God!  It's full of universes!

Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #87 on: 08/02/2017 04:45 PM »
*snip*

Any attempted deflection would have to reach and study the object first

*snip*

do you really think "studies by experts in the field" can readily classify threats and plot a solution?

That would be ideal, certainly. That's one reason why early detection is important. With, say, 10 years or more of lead time, we could study the crap out of it, send probes. Tailor-make a precision deflection mission.

But it's not 100% essential. If we don't have that much time, a deflection effort based on what data is available from Earth-based observations could still proceed. It wouldn't be as precise of a deflection, but deflection is still possible.

So to answer that last question, Yes.
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Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #88 on: 08/02/2017 04:54 PM »
From afar, surface observations cannot determine internal composition.
This is wrong for most NEO asteroids. If you see S type spectra, you can be pretty confident that represent the bulk composition of the object, because there's no mechanism to form small differentiated NEOs. If you see C type, it's almost certainly C type all the way through. It might have been a comet at one point, but if it's in a near earth orbit and doesn't show activity, most of the volatiles are probably gone.
Quote
ie; An icy object is discovered, ejecting water vapor as it nears the Sun on its orbit. Must be a comet, a KBO and primordial body - right? So a mission is sent to analyze it and it turns out it's a Jovian asteroid that dropped out of orbit. That was ESA's Rosetta blunder and a repeated mistake in classifying asteroids, comets or the middle-ground of "Main Belt Comets" or "Active Asteroids".
If you are suggesting that 67P isn't a comet, or that it's composition (edit: I mean bulk composition here, not isotope ratios) was some huge surprise, that's just flat out wrong. There were plenty of surprises in the details, but it's still a comet and broadly in line with the things we expect of comets.

The fact that boundary between comets and asteroids is fuzzy isn't some big failure or surprise, that's what happens when you try to force nature into rigid categories.
Quote
The density, or porosity of these are only known after they were intercepted. Any attempted deflection would have to reach and study the object first, as making assumptions based on appearance is the same as flying blind on pride. Making prior assumptions about composition or structure is equally foolish.
This is totally wrong, again. Whether uncertainty in the composition and density matters depends on the deflection method and the range of uncertainty. If fragmentation is the goal, just send a nuke big enough for the worst case and call it good. If you are using a gravity tractor, budget enough power for the highest plausible mass.

Sure, in an ideal world you'd like to have perfect knowledge of the target. In the real world, you try to know your uncertainties and make sure your plan accounts for them.

Edit:
not from beyond the gas giants as is required to be classified as a comet. If the ESA can't tell the difference between a comet and asteroid, do you really think "studies by experts in the field" can readily classify threats and plot a solution?
This isn't how comets are defined. A comet is a comet if it exhibits cometary activity. Where it formed is not part of the definition.

edit 2:
and should hardly need to be said that the D/H ratio and presence molecular oxygen are not particularly relevant to planetary defense.
« Last Edit: 08/02/2017 05:34 PM by hop »

Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #89 on: 08/02/2017 05:14 PM »
snips No, the risk is NOT overplayed. ...
1) The problem is, although large, disastrous impacts are fairly rare, the odds are high enough and the potential damage and loss of life is high enough, that it is a concern that should be addressed.
2) That none of the known NEOs, asteroidal or cometary, are currently in a high risk of collision of collision with the Earth, this could easily change due to some very minor changes, induced in their orbits by the gravity of one or more planets, moons or even other NEOs.
Don't get me wrong, I'm all for identifying NEOs and means to deflect them, but the risk is overplayed.
Re1) The "odds" don't represent the declining possibility of impacts eon after eon. While it's possible for something to come hurling at Earth, its more likely those days have long passed. There's no large impending meteors after years/decades of observations, only the physical proof of past events. Like zits, a young Earth probably had high occurrence while today's risk is low - though the "odds" of zits/yr would remain constant. This is the "overstatement" of risk.
Re2) Gravitational constant is almost irrelevant at these scales as is the likelyhood of high-speed orbital collisions between small objects that could significantly alter an orbit. Objects already gravitationaly bound to other planets are even more unlikely reach escape velocity. The possibility exists a comet could play billiards or Trojans/Centaurs fling loose after a slight bump, but the steady motion of orbits and vastness of space makes disturbances resulting in a major event here extremely unlikely in the coming millennia.

1. The Odds of a large impact in any given year is low, but the Risk is high because the consequences of an impact could be disastrous. A Tunguska over New York, or London, or Mexico City, or Beijing, etc. would result in millions of casualties.

While we do know of nearly all the predicted population of NEOs larger than 1 km in diameter, and none are on a collision course with Earth, we don't know of about half of asteroids that are larger than 250 meters, and only a small fraction of those larger than 100 meters. Those could deliver regional devastation or destroy cities.

And our knowledge of asteroids that orbit closer to the Sun than the Earth is limited to a handful of examples.

2. He's talking about gravitational perturbation, not the gravitational constant. We're good at predicting perturbations from planets and other large bodies, but a close-range interaction with an undiscovered body would be an issue.

Quote
... So to answer that last question, Yes.
To shoot blind with naivete and pride is your choice. But I previously pointed out if the world's on the line that kind of arrogance, primarily from a field of ignorant "expertise", is as dangerous as the meteor threat itself - possibly moreso when they make things worse. As a society, allowing and supporting such bad science makes us no different than geocentrist, yet with much greater consequences.

It wouldn't be shooting blind. It would be a deflection effort with the best information available. If the lead time is limited, that's all you're going to get.

Doesn't matter what you, in your arrogance, think is naive or what your opinion is of the experts that would direct such a mission.
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Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #90 on: 08/02/2017 06:01 PM »
(snips) ... you can be pretty confident that represent the bulk composition ... almost certainly C type all the way through. ... but it's still a comet and broadly in line with the things we expect of comets.
Bulk composition and broad assumptions is not an understanding of their composition. That requires knowledge of mass, dispersion, material, porosity, etc. and how those traits react to forces.
Whether uncertainty in the composition and density matters depends on the deflection method and the range of uncertainty. If fragmentation is the goal, just send a nuke big enough for the worst case and call it good. If you are using a gravity tractor, budget enough power for the highest plausible mass.
You've offered the bookends of minute and massive, but left out the bulk of possibilities.
Whatever a meteor is made of, they're all composed of chunks and fluff loosely held together. Their density and composition (layering, including a rocky shell around a dusty mantle, harbouring mountainous core seeds like 67P) determines if the level of force used to deflect makes them behave as a monolith, rubble pile or dustball. Classifying them in neat categories is a rudimentary addresses of one trait. If the density and composition are unknowns, it's physical properties (strength, elasticity, rebound, etc.) cannot be known and predicting how it responds to varied levels of force is guesswork.
« Last Edit: 08/02/2017 06:14 PM by Propylox »

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #91 on: 08/02/2017 09:44 PM »
If the density and composition are unknowns, it's physical properties (strength, elasticity, etc) cannot be known and predicting how it responds to varied levels of force is guesswork.
What you seem to ignore is real threats will most likely lie in the very broad space between 100% guesswork and 100% certainty.

If you see an asteroid with similar size and spectra to Itokawa (for example) you know it's going to be mostly stony, most likely with a significant fraction of rubble and possibly some large monolithic blocks. This is just an illustrative example, there's actually a lot more that can be derived from basic ground based observations and knowledge of the overall population. Go read the book I linked earlier if you want to actually want to get an idea what the state of the field is.

The point is that uncertainties can be constrained. Everyone would rather have detailed knowledge from a precursor mission, but in the end what we really want is to have high confidence the chosen solution will work within range of uncertainty. That depends on the uncertainty and how sensitive the solution is to the uncertainty

For example, the Bruck Syal et. al paper I linked earlier concludes a 1 Mt surface burst should fragment a km class stony asteroid such that (given sufficient lead time) the majority of fragments will miss the earth. If we are faced with an Itokawa analog (~ 0.5 x 0.3 x 0.2 km), using a full 1 Mt should give a very healthy safety factor for any plausible composition and physical structure. As long as devices with sufficient yield are available, the only penalty for overkill with this method is launch mass.

Offline spacenut

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Re: Deflecting or destroying dangerous asteroids
« Reply #92 on: 08/02/2017 10:10 PM »
Yes, you don't have to destroy a large asteroid, just deflect it.  A nuke blast to the side of one might just push it out of earths path and make it a close flyby.  Maybe even several along the path, to deflect, as long as we detected it in time.  Atlas V with its Centaur upper stage might be able to push a nuke toward the asteroid.  If not a Delta IV heavy should. 

Offline Lar

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Re: Deflecting or destroying dangerous asteroids
« Reply #93 on: 08/03/2017 12:10 AM »
Weeds alert.

Tunguska cause isn't on topic. There are asteroids out there that will need deflection or they will cause much unfun.

This thread needs to dial back the snark a bit too.
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Offline Lar

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Re: Deflecting or destroying dangerous asteroids
« Reply #94 on: 08/03/2017 04:38 AM »
What part of "off topic" were we struggling with? More posts removed.
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Offline Kansan52

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Re: Deflecting or destroying dangerous asteroids
« Reply #95 on: 08/03/2017 05:26 PM »
There have been nuclear weapons tests in space.

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #96 on: 08/03/2017 05:32 PM »
The boundary conditions say that the only that's are large objects (10+ km Diameter, more or less.. the colors is to prevent Chicxulub II ).  All other objects are either too big to deflect or too small to worry about.
This is totally wrong. Go play with http://impact.ese.ic.ac.uk/ImpactEffects/ and decide what is acceptable in your back yard / country / continent.

Congress and NASA settled on >= 140 meter as the kind of thing we want to be able to try to do something about (see https://cneos.jpl.nasa.gov/doc/neo_report2007.html). Because small asteroids are more common and we have already spotted most of the large ones, the most likely impact scenarios involve things at the lower end of this range.

Quote
There haven't been any tests of nuclear systems in space nor are any planned. 
This is not correct. The US and USSR both tested multiple nuclear weapons in space.

Quote
Nobody has any idea if the effectiveness is worth the effort!
This is incorrect. We know a great deal about weapons effects and asteroids, and we can make detailed calculations to get an good idea of the effectiveness. I provided links to work on this subject earlier in the thread.

Given sufficient warning, there are numerous other viable approaches to deflecting asteroids.

Quote
Let's just say there are 24 Chicxulub class asteroids headed this way.
This is an absurd scenario. There is not a single Chicxulub class asteroid that presents any near term impact risk. A comet impact of this size is possible, and we almost certainly wouldn't be able to do anything about it, but this scenario is an extremely small fraction of the overall risk.

Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #97 on: 08/03/2017 05:39 PM »
We've found more than 90% of the predicted population of near-Earth asteroids 1 km or larger in diameter. This is the size of asteroid that would cause destruction on a global scale. Objects larger than 100 meters in diameter would cause regional destruction, and larger than ~20 meters would be city killers. We've found about half of the predicted population of near-Earth asteroids larger than about 250 meters, and only a fraction of those that are smaller.

Any size asteroid can be deflected, given enough lead time.

The impactor that created the Chicxulub crater was probably on the order of 15 km in diameter.

There have been tests of nuclear weapons in space, several series of tests done by both the USA and the USSR from 1958 to 1962. The Partial Test Ban Treaty of 1963 prohibited the further testing of nuclear weapons in space (as well as underwater and in the atmosphere).
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Offline gongora

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Re: Deflecting or destroying dangerous asteroids
« Reply #98 on: 08/04/2017 02:57 PM »
Thread trimmed (again).

Offline daveklingler

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Re: Deflecting or destroying dangerous asteroids
« Reply #99 on: 08/04/2017 08:27 PM »
My own preference would be to work on deflecting dangerous (and non-dangerous, but accessible) asteroids into orbits that leave them accessible for future development.  I believe that if we can deflect them, we can do this.
Capturing is much harder. To avoid an impact, you only need velocity change on the order of millimeters per second if you have decent (years to decades) warning. Getting a random NEO into orbit will be more likely be in the kilometers per second range.

As the asteroid miners begin to exert influence over asteroid mitigation debates, the number of strategies will begin to correlate with the number of types of asteroid bodies and the market for various compositions.  Rather than choosing a mitigation strategy that makes a given resource economically unaccessible, a potentially dangerous body could be non-destructively placed into a less hazardous orbit.  Another choice might be a more accessible orbit that would allow chunk-by-chunk dismantlement or just continual orbital adjustment.  Many of these bodies are also scientifically very valuable, once the number of robotic asteroid exploration spacecraft begins to proliferate.

You can separate NEOs into two classes:

1.  The ones we've catalogued, none of which look like imminent threats right now.
2.  The ones we haven't catalogued, none of which look like imminent threats right now.

Either way, it's desirable to begin preparing deflection and destruction technologies but premature to try to choose one.  The potential for mining and science should reasonably be part of the discussions.

My point overall is that the way we're looking at NEOs is changing to include new stakeholders, or rather that stakeholders actually exist other than the entire planetary population.

Offline Hog

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Re: Deflecting or destroying dangerous asteroids
« Reply #100 on: 08/05/2017 09:49 AM »
There have been nuclear weapons tests in space.
Yes, the largest was a W-49 1,400,000 tonnes of equivalent yield of TNT at an altitude of 400kms. Electrons from the blast were detectable for 5 years afterwards.  The Starfish Prime detonation was the best instrumented of the USA tests.
There were concerns for orbiting American astronauts.

Yucca 28 April 1958, 1.7 kt, 26.2 km
Teak, 1 August 1958, 3.8 Mt, 76.8 km
Orange, 12 August 1958, 3.8 Mt, 43 km

United States USA – Argus – South Atlantic Ocean
Argus I, 27 August 1958, 1.7 kt, 200 km
Argus II, 30 August 1958, 1.7 kt, 240 km
Argus III, 6 September 1958, 1.7 kt, 540 km (The highest known man made nuclear explosion)

USA – Dominic I – (Operation Fishbowl) – Johnston Atoll, Pacific Ocean
Bluegill, 3 June 1962, failed
Bluegill Prime, 25 July 1962, failed
Bluegill Double Prime, 15 October 1962, failed
Bluegill Triple Prime, 26 October 1962, 410 kt, 50 km
Starfish, 20 June 1962, failed
Starfish Prime, 9 July 1962, 1.4 Mt, 400 km (The largest man made nuclear explosion in outer space)
Checkmate, 20 October 1962, 7 kt, 147 km
Kingfish, 1 November 1962, 410 kt, 97 km

USSR – 1961 tests – Kapustin Yar
Test #88, 6 September 1961, 10.5 kt, 22.7 km
Test #115, 6 October 1961, 40 kt, 41.3 km
Test #127, 27 October 1961, 1.2 kt, 150 km
Test #128, 27 October 1961, 1.2. kt, 300 km

USSR – Soviet Project K nuclear tests – Kapustin Yar
Test #184, 22 October 1962, 300 kt, 290 km
Test #187, 28 October 1962, 300 kt, 150 km
Test #195, 1 November 1962, 300 kt, 59 km

"The worst effects of a Soviet high-altitude test occurred on 22 October 1962, in the Soviet Project K nuclear tests (ABM System A proof tests) when a 300 kt missile-warhead detonated near Dzhezkazgan at 290-km altitude. The EMP fused 570 km of overhead telephone line with a measured current of 2,500 A, started a fire that burned down the Karaganda power plant, and shut down 1,000-km of shallow-buried power cables between Aqmola and Almaty."

What I find hugely surprising is the amount of actual high altitude nuclear tests that occurred during the Cuban Missile Crisis. 4 Soviet and 2 American.  That's a LOT of missile and nuclear activity occurring when Strategic Air Command is at DEFCON-2 and the rest of the USA contiguous forces are at DEFCON-3. SAC remained at DEFCON-2 until November 15,1962. The only other time DEFCON-2 was ordered was during Desert Storm for Gulf War#1. The Sept 11 2001 attacks caused Donald Rumsfeld the Sec of Def to raise the Defense Condition to DEFCON-3 and to prepare for a possible increase to DEFCON-2.

 

Readiness condition     Exercise term        Description                   Readiness
DEFCON 1 COCKED PISTOL    Nuclear war is imminent                Maximum readiness
DEFCON 2 FAST PACE Next step to nuclear war Armed Forces ready to deploy and engage in less than 6 hours
DEFCON 3 ROUND HOUSE Increase in force readiness above that required for normal readiness Air Force ready to mobilize in 15 minutes
DEFCON 4 DOUBLE TAKE Increased intelligence watch and strengthened security measures  Above normal readiness
DEFCON 5 FADE OUT                Lowest state of readiness               Normal readiness


I wonder if there would be any sort of DEFCON adjustment for an imminent meteorite hit?

I would think that detonating a warhead at an altitude of 400km would be very different than the distance from Earth that would be required to affect to course of the meteor, or to deflect it from a collision with Earth?  I would think, the greater the range, the better.


Pic #1 Starfish Prime The debris fireball stretching along Earth's magnetic field with air-glow aurora as seen at 3 minutes from a surveillance aircraft.

Pic#2 The flash created by the explosion as seen through heavy cloud cover from Honolulu 1,445 km away




« Last Edit: 08/05/2017 09:50 AM by Hog »
Paul

Offline meberbs

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Re: Deflecting or destroying dangerous asteroids
« Reply #101 on: 08/05/2017 02:30 PM »
I just want to note that the chart that Propylox posted above is dated "2015", but in my attempts to find an updated version, I discovered that it appears the data in that chart was actually from 2014.

The National Near Earth Object Prepardness strategy from December 2016 uses what appears to be the same data. Unfortunately this makes me think there isn't an updated chart available.

It did lead me to what appears to be the original data source. This presentation is from March, 2014. I find the specific date signficant, because since then, we have been discovering asteroids at a rate of over 1000 per year.

I also attached a slide from the original source which is interesting because it shows the projected completion curve for once the 90% of > 140 m goal is met.

I estimate about 40% completion at that point for > 60 m. The authors estimate about 1/3 of Tunguska size and 10% of ones large enough to make it to the ground (>25 m) at that point.

also of note:
Quote
Current surveys have almost a 50% chance of detecting a “death plunge” small object with enough time for civil defense measures; future surveys have the potential to do even better with appropriate observing protocol.

I'd really like to see updated current data, but the original study makes it pretty clear you can't just add in the new detections, you also should make use of the additional data to refine the population size estimates.
« Last Edit: 08/05/2017 02:34 PM by meberbs »

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Re: Deflecting or destroying dangerous asteroids
« Reply #102 on: 08/05/2017 07:16 PM »
In a decade, if everything planned works out, we might be able to see half the objects the size of Asteroid 2017 001, which was only discovered three days after it skimmed Earth, and 10% of the objects similar to the Chelyabinsk air-blast (which could have easily leveled counties or impacted the ground).
This is incorrect.  Chelyabinsk size objects have no potential to "level counties", and if it had survived to the ground (edit: unlikely for bodies of this size), it would have had the effect of a medium sized nuke and made a small crater. Bad day if it happens in your neighborhood, but not a regional or global catastrophe.

When you calculate the risk of small objects like this, you have to include the probability it will hit something of value. 70% of the Earth's surface is ocean (and things in this size range are far too small to create a tsunami risk) and only a tiny fraction is densely populated.

Again, see http://impact.ese.ic.ac.uk/ImpactEffects/ for a rough idea of what the effects are.
Quote
Why even bother financing such a program if it's to be so completely ineffective, especially with volunteer options like ATLAS doing just as much?
ATLAS gets NASA funding (http://www.fallingstar.com/nasa_funding.php) and only addresses a narrow section of the overall risk.

Why bother? Detecting 90% of the >140m accounts for a huge fraction of the overall risk.

Quote
If it's to be a funded project we should build 10m-70m telescopes, whatever is necessary (size is neither cost nor payload confined as a Hubble/WFIRST-type mission could support over a 110m telescope), to actually do the job while also cataloguing pretty much the entire asteroid belt, solar system, it's moons and much of the Kuiper Belt.
I'm having trouble parsing this, but if you can build a >10m space telescope for the cost of NEOCam, you should probably submit a proposal to NASA. Good luck...
« Last Edit: 08/05/2017 11:17 PM by hop »

Online hop

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Re: Deflecting or destroying dangerous asteroids
« Reply #103 on: 08/05/2017 07:37 PM »
I'd really like to see updated current data, but the original study makes it pretty clear you can't just add in the new detections, you also should make use of the additional data to refine the population size estimates.
The DECam paper I linked earlier (https://arxiv.org/abs/1707.04066) has recent estimates of the size distribution, with comparison to previous work. Figure 8 attached.



« Last Edit: 08/05/2017 07:38 PM by hop »

Offline Propylox

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Re: Deflecting or destroying dangerous asteroids
« Reply #104 on: 08/05/2017 09:05 PM »
... if you can build a >10m space telescope for the cost of NEOCam, you should probably submit a proposal to NASA.
NEOCam is planning a 0.5m primary, which if reground as a secondary would suggest a primary collecting diameter around 7m and associated 25% increase in launch mass. But why would I submit such a proposal to NASA considering the poor state of their current programs (SLS, ISS, Commercial), their planned ones (DSG and..?) and their dysfunctional administrative system (program management, selection, budgeting, etc).
If they got better, better options like this and others will both become available and be selected. For now NASA's still better than ESA, but still not worth the time nor effort or expectations.
« Last Edit: 08/05/2017 09:11 PM by Propylox »

Offline as58

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Re: Deflecting or destroying dangerous asteroids
« Reply #105 on: 08/05/2017 09:14 PM »
... if you can build a >10m space telescope for the cost of NEOCam, you should probably submit a proposal to NASA.
NEOCam is planning a 0.5m primary, which if reground as a secondary would suggest a primary collecting diameter around 7m and associated 25% increase in launch mass. But why would I submit such a proposal to NASA considering the state of their current programs (SLS, ISS, Commercial), their planned ones (DSG and..?) and their dysfunctional administrative system (program management, selection, budgeting, etc)? If they got better, better options like this and others will both become available and be selected. For now it's still better than ESA, but still not worth the time nor high expectations.

Could you please describe how this telescope design that you keep alluding to would work?

Offline RonM

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Re: Deflecting or destroying dangerous asteroids
« Reply #106 on: 08/05/2017 09:20 PM »
NEOCam is planning a 0.5m primary, which if reground as a secondary would suggest a primary collecting diameter around 7m and associated 25% increase in launch mass.

No, that's not how it works. A 7m mirror would have nearly 200 times the surface area of a 0.5m mirror. How could you possibly build a 7m telescope that only masses 25% more than a 0.5m? Hubble "only" has a 2.4m mirror.

We don't need large space telescopes to find asteroids. Multiple NEOCam missions would be nice to speed up the survey.

Please do some research before you post.

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Re: Deflecting or destroying dangerous asteroids
« Reply #107 on: 08/05/2017 09:45 PM »
Could you please describe how this telescope design that you keep alluding to would work?
Seconded, but in it's own thread, please!

Offline Jim

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Re: Deflecting or destroying dangerous asteroids
« Reply #108 on: 08/05/2017 09:54 PM »
[. But why would I submit such a proposal to NASA considering the poor state of their current programs (SLS, ISS, Commercial), their planned ones (DSG and..?) and their dysfunctional administrative system (program management, selection, budgeting, etc).
If they got better, better options like this and others will both become available and be selected. For now NASA's still better than ESA, but still not worth the time nor effort or expectations.

Wrong on all counts.  All unsupported opinion.
There is no "poor state" of the science programs.  It is healthy.

"dysfunctional administrative system"? You really don't know what you are talking about.  The proposers run most of the missions.

NASA is the only show around.  ESA doesn't even come close and has worse "problems".


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Re: Deflecting or destroying dangerous asteroids
« Reply #109 on: 08/05/2017 10:22 PM »
NEOCam is planning a 0.5m primary, which if reground as a secondary would suggest a primary collecting diameter around 7m and associated 25% increase in launch mass. But why would I submit such a proposal to NASA considering
If you can't propose it yourself, there's a whole lot of people in the field who would love to be able to propose a 7m telescope on a Discovery budget! Or better yet, a 2m telescope on an even smaller budget.

NEOCam was proposed for Discovery, which is a competitive, PI-lead, cost capped program. That means the PI proposes the mission, NASA and outside experts evaluate the technical credibility and science value, and if it's selected, NASA pays for it. NEOCam wasn't selected in the last round, but it did get additional development funding. An otherwise equivalent, much larger telescope for similar cost would be very competitive indeed.

Furthermore, the community is currently studying concepts Hubble follow-on visible / near IR  / UV telescope in the 8-16 meter class (ATLAST / HDST / LUVOIR etc.) This is expected to be flagship cost (i.e. several to many billions) mission. If it could be done on a Discovery budget (~0.5 billion) that would be a game changer for the entire field.

(but again, if you want to discuss how you think this can be done, it really deserves it's own thread)
« Last Edit: 08/05/2017 11:15 PM by hop »

Offline gongora

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Re: Deflecting or destroying dangerous asteroids
« Reply #110 on: 08/06/2017 01:17 AM »
... Hubble "only" has a 2.4m mirror.
Sorry, ft to m SNAFU. 43ft ~ 6.5m for Kepler , 110ft ~ 33.6m for WFIRST , 294ft ~ 91m for JWST

Point being very large telescopes aren't the financial and technical hurdle so many assume. And if such telescopes were available, they'd be requested for missions such as asteroid detection. Which is in itself proof that the current proposals aren't based on mission demands, but the low bar of beggars. So I ask what's the point of a project that will take forever, be incomplete when "finished" while not addressing the most likely source of impacts and only one we can stop: small meteors - especially when good options are available?
If you're going to do something, do it right. Don't offer snails, call it gourmet and demand hundreds of $millions.

...ESA doesn't even come close and has worse "problems".
On that, we're in complete agreement. I'd add it's not just their space program, but entire scientific endeavours.

What the hell are you talking about?  What are those numbers in your post supposed to mean, and why do you think it's trivial to build space telescopes an order of magnitude larger than anything that's been flown?

Offline gospacex

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Re: Deflecting or destroying dangerous asteroids
« Reply #111 on: 08/06/2017 08:49 AM »
NEOCam is planning a 0.5m primary, which if reground as a secondary would suggest a primary collecting diameter around 7m and associated 25% increase in launch mass.

No, that's not how it works. A 7m mirror would have nearly 200 times the surface area of a 0.5m mirror. How could you possibly build a 7m telescope that only masses 25% more than a 0.5m? Hubble "only" has a 2.4m mirror.

We don't need large space telescopes to find asteroids. Multiple NEOCam missions would be nice to speed up the survey.

Please do some research before you post.

It's some 5th time you and others said this to him. He will not.

Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #112 on: 08/07/2017 02:55 PM »
This is the Dunning–Kruger effect, he obviously thinks he knows what he's talking about, but he doesn't actually know enough about these topics to know that he's wrong.
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Offline Lar

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Re: Deflecting or destroying dangerous asteroids
« Reply #113 on: 08/07/2017 08:42 PM »
Let's not psychoanalyze each other, k? Some posts ought to be edited or deleted.
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Offline meberbs

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Re: Deflecting or destroying dangerous asteroids
« Reply #114 on: 08/09/2017 12:44 AM »
One of the points I have been trying make lately is that it takes a space telescope to really ascertain asteroid threats.  JWST is so late and overcost ($10B+ and climbing) it really makes you wonder about the impact Will be if it fails.

There is no way the telescope of JWST is 91m. More like 6.5m.

Does JWST have specific goals to monitor asteroids or inbound comets that are Earth grazing?  I always (or 17 years ago) got the impression it was to be used for deep sky surveys using a variety of IR cameras/sensors.  Are there dedicated space telescopes for asteroids flying now???
JWST is really irrelevant to the thread. While it is capable of observations inside the solar system, it is really not designed for searching for NEOs, and in most cases is incapable of pointing in a way to see them. It could be used for some IR characterization of comets or certain NEOs, but even without the pointing restrictions, it would be a terrible choice for a survey to discover new objects. It is intended for long dwells at objects within a narrow field of view. Details about the intra-solar system capabilities are at the link below.

https://jwst.nasa.gov/faq_solarsystem.html

As for space based telescopes, there was the NEOWISE mission, and NEOCAM is in the planning stages. JWST is a gigantic, complicated telescope mostly for looking far away. JWST is just not a relevant baseline (cost, schedule, or complexity) for discussing space based telescopes for NEO asteroid searches.

P.S. you are right about the size of JWST, but seem to have misstated the cost, $10 billion is the current estimate of the final bill including international contributions and operation, and this number hasn't really changed since the last re-plan years ago. It is not the amount that has been spent so far, and it is not climbing.

Offline Nomadd

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Re: Deflecting or destroying dangerous asteroids
« Reply #115 on: 08/09/2017 12:56 AM »
Let's not psychoanalyze each other, k?
Why do you think you feel that way?

Re: Deflecting or destroying dangerous asteroids
« Reply #116 on: 08/21/2017 09:20 AM »
What if you combined the nuke and the impactor mission?

And for this proposal, you have to understand i'm a complete newb at this :)

If we know well in advance that a large stone has our name on it. Im counting on red tape going out the window. So does economical issues.

Do the proposed impactor mission at high initial speed. On top of the impactor we put a smaller version of the proposed Orion damper with a large nuke behind it. The impactor now has a high delta-V. Just Before impact, we detonate the nuke and give the impactor at huge boost in speed. Plus any energy the nuke itself Projects around the plate.

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Re: Deflecting or destroying dangerous asteroids
« Reply #117 on: 08/21/2017 05:40 PM »
On top of the impactor we put a smaller version of the proposed Orion damper with a large nuke behind it. The impactor now has a high delta-V. Just Before impact, we detonate the nuke and give the impactor at huge boost in speed. Plus any energy the nuke itself Projects around the plate.
What do you gain by transferring energy from the nuke, to the impactor and then to the target? Why not cut out the middle man?

In general, nukes have the highest energy density, so launching a combination of nukes + kinetic impactors gives you less capability than using the same mass of nukes alone. Kinetic impactors are technically and politically simpler, so they are attractive in cases where they provide sufficient energy in a reasonable launch mass.
« Last Edit: 08/21/2017 05:40 PM by hop »

Offline bradjensen3

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Re: Deflecting or destroying dangerous asteroids
« Reply #118 on: 08/21/2017 10:58 PM »
Assuming for the moment that the hypothesis that Ceres has a layer of ice under its surface, and ice volcanoes that lead to the surface, put a water NTR on the asteroid, then send it automated rockets full of water from Ceres for months or years to refill the NTR's reaction mass.

If there is no large amount of water on Ceres, please forget this suggestion was ever made.

If you know the path of the asteroid years in advance, you do not have to deflect it to the side. Any increase or decrease in its velocity is going to change the orbit enough that it won't show up at the appointed time.

Re: Deflecting or destroying dangerous asteroids
« Reply #119 on: 08/22/2017 08:25 AM »
On top of the impactor we put a smaller version of the proposed Orion damper with a large nuke behind it. The impactor now has a high delta-V. Just Before impact, we detonate the nuke and give the impactor at huge boost in speed. Plus any energy the nuke itself Projects around the plate.
What do you gain by transferring energy from the nuke, to the impactor and then to the target? Why not cut out the middle man?

In general, nukes have the highest energy density, so launching a combination of nukes + kinetic impactors gives you less capability than using the same mass of nukes alone. Kinetic impactors are technically and politically simpler, so they are attractive in cases where they provide sufficient energy in a reasonable launch mass.

Yes, really should have thought about that. How ever I read only 40% of the nukes energy is radiation and what not. If we put a gas between the impactor and the nuke. Could we also harwest the pressure wave in som manner and get more energy out of it?

Offline whitelancer64

Re: Deflecting or destroying dangerous asteroids
« Reply #120 on: 08/22/2017 04:17 PM »
On top of the impactor we put a smaller version of the proposed Orion damper with a large nuke behind it. The impactor now has a high delta-V. Just Before impact, we detonate the nuke and give the impactor at huge boost in speed. Plus any energy the nuke itself Projects around the plate.
What do you gain by transferring energy from the nuke, to the impactor and then to the target? Why not cut out the middle man?

In general, nukes have the highest energy density, so launching a combination of nukes + kinetic impactors gives you less capability than using the same mass of nukes alone. Kinetic impactors are technically and politically simpler, so they are attractive in cases where they provide sufficient energy in a reasonable launch mass.

Yes, really should have thought about that. How ever I read only 40% of the nukes energy is radiation and what not. If we put a gas between the impactor and the nuke. Could we also harwest the pressure wave in som manner and get more energy out of it?

NASA has a small side project called Hypervelocity Asteroid Intercept Vehicle (HAIV), which proposes sending an impactor and a nuclear device along the same mission. The impactor hits first, creating a small crater which the nuclear device then detonates in. Similar to your idea.
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Re: Deflecting or destroying dangerous asteroids
« Reply #121 on: 11/16/2017 09:34 PM »
NASA has released a report on the current status of planetary defense efforts https://www.nasa.gov/feature/new-report-assesses-status-of-detecting-near-earth-asteroids

I haven't read it yet, but the summary suggests the big picture hasn't changed too much.

Offline dustinthewind

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Re: Deflecting or destroying dangerous asteroids
« Reply #122 on: 12/10/2017 10:03 PM »
Something neat I have seen recently they want to make was a space based phased array that could superheat a point.  With enough energy the rock can be vaporized and acts like a rocket via the vaporization.  The object can be diverted with out much delay as the energy travels at the speed of light.  I think they also suggested other uses for it such as photon propulsion for spacecraft and moving asteroids for mining, power transport. 

I had pondered an earth based array that used atmosphere correction similar to some telescopes.

I guess it is the DE-STAR project. 
« Last Edit: 12/10/2017 11:31 PM by dustinthewind »

Offline LMT

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Re: Deflecting or destroying dangerous asteroids
« Reply #123 on: 12/11/2017 02:08 AM »
Something neat I have seen recently they want to make was a space based phased array that could superheat a point.  With enough energy the rock can be vaporized and acts like a rocket via the vaporization.  The object can be diverted with out much delay as the energy travels at the speed of light.  I think they also suggested other uses for it such as photon propulsion for spacecraft and moving asteroids for mining, power transport. 

I had pondered an earth based array that used atmosphere correction similar to some telescopes.

For an estimate of deflection capability, Zhang et al. 2016 quantifies expected deflection for asteroids and comets, using stand-off DE-STAR and also the smaller stand-on DE-STARLITE.
« Last Edit: 12/11/2017 02:09 AM by LMT »

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