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.
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.
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?
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.
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.
Sure, we detected the Chelyabinsk meteor - as it happened. Well done!
It was only a 400-500kt blast that fortunately detonated at +25km altitude due to a shallow trajectory.
Fortunately we know of every kilometer-sized object and apparently have operational capability to deflect "very large objects", according to Hop.
Unfortunately that leaves a lot of 1km-20km craters, airblasts equal to armageddon and the extinction of humanity.
As previously stated,QuoteUnless 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.
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.
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.
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.
Quote from: whitelancer64 on 07/13/2017 07:57 pmA 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.
Quote from: stefan r on 07/17/2017 06:13 pmQuote from: whitelancer64 on 07/13/2017 07:57 pmA 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?
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...
Quote from: mikelepage on 07/23/2017 05:08 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?
... 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
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.
Quote from: mikelepage on 07/24/2017 05:57 amSurface 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.
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.
Quote from: mikelepage on 07/24/2017 05:57 amSurface 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).
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.
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.
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.
As a whole, standoff nukes are worthless against meteors, comets, etc.
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.
The way I thought of it is that the explosive energy radiates evenly in all directions
Because "most people" in a group believe something's a good idea and have written so, that makes it so?
Well praise geocentrism! Too bad the math, facts and common sense contradict their work. Sincerely, Copernicus
That's because members of "the field" are 1) broke, and 2) telescope designs haven't improved in 350yrs so the idea of a 20m 'scope seems impossible.
If I showed a 20m scope at the cost, packaging and weight of a 1.5m scope, "the field" would be all over it as necessary to their work.
*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*
...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....
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.
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.
And still no ability to see objects small enough to deflect; no means to deflect objects we could possibly see.
but there's no means to find objects of that size or down to the 20-30m range equivalent to ICBM blasts.
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.
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.
none acknowledge the impossible distance, impossibly high number of warheads required or any means to implement
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.
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.
Quote from: hop on 07/25/2017 04:43 pmThe 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.
The practice of science has advance significantly since Copernicus.
Quote from: meberbs on 07/26/2017 07:24 pmSo 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.
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.
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.
I have not questioned others' credentials,
only their conclusions and pointed out credentials don't matter.
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.
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.
In the complete absence of actionable data, but a wealth of irrelevant glad-handing and statistics,
we can realistically only rely on the total vaporization of a meteor as defense. 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.
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.
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.
First and foremost; all studies to date are without merit as the physical properties of meteors is unknown
Nukes are insufficient.
So if a nuclear mass generator was a viable / non-fictional concept,
I'd guess that would be more practical than the above two concepts (nukes & tethers).
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.
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.
Quote from: as58 on 07/29/2017 03:39 pmIf 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.
Quote from: as58 on 07/29/2017 03:39 pmIf 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.
Quote from: hop on 07/28/2017 04:50 pmWe 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/Quote from: meberbs on 07/28/2017 02:27 pmSince 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.Quote from: hop on 07/28/2017 04:50 pmStatistics 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.Quote from: meberbs on 07/28/2017 02:27 pmCredentials 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.
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.
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.
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?
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?
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 wouldn't cross the minefield, duh. I also wouldn't play Russian roulette or buy into a "~90% completion in ten years" scheme.
Why, when small asteroids are the only ones we can stop?
I think nukes are insufficient because of the overall business case.If there are an unknown quantity of objects to annihilate
The probabilities of successfully achieving the outcome is uncertain. The cost is too much.
The global politics is just too complex.
The risk of failure is high.
Previously I mentioned telescopes haven't advanced in 350years - the date when reflection replaced refraction in large scopes.
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.
Quote from: Mr. Scott on 07/29/2017 04:20 pmHowever, 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.
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 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.
Note several other things: IR is *not* necessarily better or necessary for detection.
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.
Quote from: jg on 07/30/2017 02:06 pmQuoteWe 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/1707.04066It's notable that estimates for the >100 m class seem to be converging pretty well.QuoteNote several other things: IR is *not* necessarily better or necessary for detection.
QuoteWe 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/1707.04066It's notable that estimates for the >100 m class seem to be converging pretty well.QuoteNote several other things: IR is *not* necessarily better or necessary for detection.
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
Active optics? Myth.
Quote from: Propylox on 07/29/2017 12:24 pmDr. 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."
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/
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.
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.
Re1) In the real world, there's always choice and if you think it's either/or, you haven't found all the options.
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.
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.
<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).
Quote from: jg on 07/30/2017 02:06 pmBigger 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.
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.
Quote from: jg on 07/30/2017 02:06 pmIR 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.
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.
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?
Quote from: as58 on 07/29/2017 04:32 pmThere 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 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.
Quote from: Propylox on 07/31/2017 04:26 amPlease 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.
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.
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.
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.
Quote from: Propylox on 07/31/2017 05:34 amSecondly, 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.
Quote from: hop on 07/31/2017 05:08 amQuote from: Propylox on 07/31/2017 04:26 amPlease 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.
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.
Quote from: Propylox on 07/31/2017 06:32 amYes, 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.
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.
*snip*Quote from: whitelancer64 on 07/29/2017 06:11 pmQuote from: Propylox on 07/29/2017 12:24 pmDr. 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.
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.
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.
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].
I agree nothing should be done. The threat is imaginary and overplayed.
Extinction events are only circumstantial evidence.
Earth apparently survived five extinction events.
Quote from: daveklingler on 07/30/2017 04:40 pmI 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.
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.
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.
Quote from: whitelancer64 on 07/31/2017 03:54 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.
... 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. ...
Quote from: meberbs on 07/31/2017 08:02 am... 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.
... 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
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.
Spectroscopy does tell you what its made of. That's literally what spectroscopy does.
...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.
You can only observe the size of an asteroid if it makes a close approach to Earth.
Spectroscopy does tell you what (an asteroid's) made of. That's literally what spectroscopy does.
@hopSome 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.
@hopChelyabinsk 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!
*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?
From afar, surface observations cannot determine internal composition.
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".
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.
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?
Quote from: JasonAW3 on 08/02/2017 03:24 pmsnips 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.
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.
Quote from: whitelancer64 on 08/02/2017 04:45 pm... 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.
... So to answer that last question, Yes.
(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.
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.
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.
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.
There haven't been any tests of nuclear systems in space nor are any planned.
Nobody has any idea if the effectiveness is worth the effort!
Let's just say there are 24 Chicxulub class asteroids headed this way.
Quote from: daveklingler on 08/01/2017 04:55 amMy 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.
There have been nuclear weapons tests in space.
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.
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).
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?
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'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.
... if you can build a >10m space telescope for the cost of NEOCam, you should probably submit a proposal to NASA.
Quote from: hop on 08/05/2017 07:16 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.
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.
Could you please describe how this telescope design that you keep alluding to would work?
[. 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.
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
Quote from: RonM on 08/05/2017 09:20 pm... 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 JWSTPoint 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.Quote from: Jim on 08/05/2017 09:54 pm...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.
... Hubble "only" has a 2.4m mirror.
...ESA doesn't even come close and has worse "problems".
Quote from: Propylox on 08/05/2017 09:05 pmNEOCam 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.
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???
Let's not psychoanalyze each other, k?
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.
Quote from: puttelino on 08/21/2017 09:20 amOn 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.
Quote from: hop on 08/21/2017 05:40 pmQuote from: puttelino on 08/21/2017 09:20 amOn 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?
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.
On the other hand, in space, to my knowledge, a nuclear bomb could not cause a blast, a shock wave because of the absence of air.
Hello, when a nuclear bomb explodes on Earth it causes a blast, a shock wave that can blow and repel objects.On the other hand, in space, to my knowledge, a nuclear bomb could not cause a blast, a shock wave because of the absence of air.So how could a nuclear bomb deflect an asteroid ?Thanks !
Would the radiation pressure be sufficient?I have always had the image of radiation pressure as the very weak force pushing a solar sail.I read about the orion project and if I understood correctly they would have used a nuclear bomb where the radiation is converted into heat with a material opaque to the radiation and then this heat is directed towards a tungsten plate which vaporizes and the plasma resulting from this vaporization would have hit the thrust plate which would have created the thrust. So he wasn't using the radiation pressure to push her, not directly.I don't know if the radiation pressure alone would have been enough to create enough thrust.
So if I understand correctly a nuclear bomb without a tungsten plate which would explode near an asteroid would only produce radiation (ignoring the vaporized bomb shell) and it would produce radiation pressure on the asteroid (like light sun on a solar sail) but I imagine that this radiation pressure alone would create such weak thrust on the asteroid that it wouldn't deflect it? On the other hand, if this same bomb explodes close enough to the asteroid, the radiation from the bomb could heat the surface of the asteroid enough to cause it to vaporize and transform part of it into gas or plasma which, by escaping from the surface of the asteroid, asteroid would cause significant thrust and deflect it.
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 days4km: 949 days (2.59 years), 79 days1km: 117 days, 9.7 days250m: 14 days, 1.2 days
Quote from: Propylox on 07/24/2017 02:28 amQuote from: mikelepage on 07/23/2017 05:08 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.Quote2) 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.
You have it right, but the other answer is also more or less correct. The asteroid would act as a pusher plate and be deflected by the plasma from the explosion of an Orion type shaped charge. Even though the asteroid is probably not a very good pusher plate, but it's basically action and reaction Newtonian physics.To increase the effectiveness you might want to detonate the nuclear charge close enough to the asteroid to vaporize some of the asteroids material into a gas, or even into a plasma. Depending on how effective the coupling is, and how the hole dug into the asteroid shaped itself, you would end up with a short lived but very energetic jet that would push the asteroid onto a new course.If the asteroid was not strong enough, then it might break itself into smaller bits, and some of these might still be on the original trajectory. So there probably is an art to it.
Thing is, W87 is off the shelf more or less, but what we actually want is a nuclear shape charge like a Casaba Howitzer. for high directionality.
If the asteroid is of the "rubble pile" type, and the warhead is fairly rugged, what if it is just pushed or impacted INTO the asteroid some meters. I'm thinking of the recent probe experience, where it gently sank into the rubble. Would it impart enough "thrust" through the ejecta to alter the orbit enough to avoid a collision with Earth months down the line? Or, perhaps a penetrating conventional warhead (bunker-buster), followed by a nuclear device into the hole or crater created?Fun with explosives!
Quote from: Asteroza on 08/24/2022 11:09 pmThing is, W87 is off the shelf more or less, but what we actually want is a nuclear shape charge like a Casaba Howitzer. for high directionality.The point of using an "off the shelf" W87 is that you don't need some special design, very highly classified, shaped charge. You can do asteroid deflection with basic "vanilla" nuclear warheads, of which there are thousands available.
Quote from: whitelancer64 on 08/25/2022 06:07 pmQuote from: Asteroza on 08/24/2022 11:09 pmThing is, W87 is off the shelf more or less, but what we actually want is a nuclear shape charge like a Casaba Howitzer. for high directionality.The point of using an "off the shelf" W87 is that you don't need some special design, very highly classified, shaped charge. You can do asteroid deflection with basic "vanilla" nuclear warheads, of which there are thousands available.IIRC there was just over 500 W87's manufactured. The new Sentinel ICBM system(LGM-35A) will initially deploy with the same W87-0(300kt) while the newer W87-1(475 kt) is developed.Since the W87 series is the ICBM warhead to be used for USA/NORAD/NATO defense, wouldn't it make sense to use the larger 1.2 mt B83 gravity bomb? Esp. since the B83 is only cleared for usage from the B-2 Spirit as it has been withdrawn from b-52H payload in 2017 IIRC and the B-1B since 1995. Not all B-83s are the full 1.2 mt versions though, I'm not sure of the breakdown of each variant.Or maybe we as humans are destined to go the way of the dinosaur/Dodo bird?