Author Topic: Deflecting or destroying dangerous asteroids  (Read 13763 times)

Online 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 »

Offline 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.

Offline 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

Offline 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.

Offline 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.

Offline 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 »

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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.


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.

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