anyone agree with me that the prospect of a meteor causing a doomsday belongs in pseudosci?

No. There is obvious precedence. In no other time in our history, that we know of, have we been able to avoid a disaster such as a meteor strike. That fact that we choose not to use our resources on that, and instead put them to studying whether cows methane produces a noticible increase in temperature (or other silly projects) is ludicrous to me. All research has its place. But I feel a good defense system should be first.

It is very real science.

-AntonK

Antonk, you know some researcher got grant money a couple years back to study the physics involved in why buttered toast seems to allways land face down. Yet we have only mapped some 3% of all possible NEO's, last I heard. We have our priorities straight, yep-ers.

I think that there should be a defence system against asteroids.

The best spots would be in orbit around the earth or on the moon.

We don't want to end up like to dinosaurs do we!:bugeye:

There is a reasonably good chance that a meteor strike could wipe out a city at some stage. We really should be doing more to catalogue objects which will cross the Earth's orbit in the future, so that we can plan ahead.

We do have a defence against asteroids. We call it Jupiter. . . though if one gets past that and is headed our way I guess we're out of luck. . . unless the moon decides to take one for the team.

Anyway, what can we do if something like that were to happen, really? I guess our best bet would just be to launch a bunch of nukes at it, and who knows how well that'll work, but then what better strategy could we devise, really?

As far as defences go theres alot of them.

One is it put solar sails on the asteroid. But this only works if theres a large amount of time before the asteroid hits because solar sails have a low out put.

Another is to put small engines on the asteroid. But again needs alot of time due to fairly low output of engines.

Still another one is where pieces of the asteroid are shot of the asteroid with some catipult type thing. This there by changes the speed and direction of the asteriod as though it were an engine.
And again it would take a long time.

So if an asteroid were only 1 year from hitting the Earth these would due zip! :eek:

But nuclear weapons might due something. Although they are actually weak compared to the asteroid. But they could bump it a bit and maybe save us.:D

What could we do? Very little. These things come in very fast (up to 70km/sec!), and are quite large (Meteorite that crashed into the Yucutan peninsula is estimated at 6 miles wide!).

So, interception, well, luckily, it's a very big target, hooray! But unluckily, it's moving, really, really fast. Current state of the art technology is having a hard time performing boost phase intercept of ICBMs, so I doubt we'd be able to accurately lob nukes at any incoming.

And because of the lack of accuracy, and relatively weak yield of a nuke, compared to the momentum of a 6 mile wide lump of rock at that speed, you got another dilemma;

Shoot early, when it's trajectory isn't that well established, and it might miss us, but risk nudging it _on_ course, or wait, until we know it's going to hit us, but then any course alterations have less effect.

The Hollywood films on this subject were a good laugh, if unfortunately very distant from reality.

Of course, we also have to weigh up the danger of launching Megaton nukes into space, even the most reliable launch vehicles (Delta, Arianne, Soyuz) are only about 95% successful. Not all have dramtic endings, but some of the failures leave cold dead satellites in orbit to burn up when the final stages fail to ignite. Fine if all you have is a small nuclear powered thermocouple onboard, but an environmental disaster if it contains a lot of fissionable material.

So basically, for all our technology, we could still go the way of the dinosaurs. Assuming we last as long as they did, of course. We're still newcomers and upstarts comparatively speaking. If we last as long as them, without killing ourselves off, I'd be impressed.

Anyway, the only living thing to have been killed recently by a meteorite was that Shepherds dog at Nakhla, supposedly. We have perhaps enough to worry about from the rain of small objects, than one big one, .....

Knock 'em into orbit and mine 'em.

Gifted has the right approach; these Near Earth Objects are the most valuable resources in space, as they are close enough to Earth to utilise, and in low gravity so they don't need to be dragged out of a planet's gravity well.
Together with water from comets these rocks could be recast into habitats for thousands of people, and produce thousands of space craft to exploit the rest of the solar system.

But most importantly they should be owned; if an owned asteroid comes anywhere near the Earth the owners would be responsible for adjusting the object's orbit.

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Not only does our solar system rotate around the center of our galaxy, it also make an up and down sine motion in a regular pattern. Every tens of millions of years our solar system enters a more dense star populated layer of the galactic disc.
this recurring event needly co-incides with several past extinctions of species on earth. Apparently the gravity tides offset several Kuiper/Oort belt objects....

Jupiter usually acts as a shield to catch a lot of hits for us, but when it really rains we get wet also and we have seen that it causes extinctions of species after wich other species emerge and become dominant. Without the galactic shower shuffling the deck of cards humans might not even have evolved in the first place!!!!

But this time the unique oppertunity presents itselve to break the cycle and build umbrellas with technology. The weak human will probably beat the mighty dinosaur with his one outstanding feature called a brain (that is if humans do not nuke themselve back to stoneage before the next cosmical threat presents itselve):bugeye:

Your right about the up and down movement of the solar system and the way Jupiter blocks alot of asteroids for us.

From what I heard the up and down movement happens every 30 million years or and it takes about a million years for the asteroids to reach earth from the Ort Cloud.

Also right now one of these system shifts is supposed to be happening!:eek:

So right now we are in more than average danger from asteroids.

We should develop better defences against asteroids now so well have another 30 million years before we have to really worry about it again.:)

A large probe is built in orbit, several is better. This probe has high thrust engines, carries a variety of sensor gear, and perhaps a dozen nukes. When a collision course is detected, the probe goes out to the asteriod. Detailed scans are transmitted back to arth, and anylized by scientists who tell the probe where to put a nuke. The explosion alters the asteriod's course, and the probe hangs out until the asteriod is deflected to a suitable trajectory, or it uses up its nukes, at which time it returns to earth orbit for replenishment, refurbishment, and to wait for the next asteriod.

Thats a good idea!

Another thing that could be done with this would be having a small base on the moon made just for these probes.

If it was made self reliant or automatic the anti asteroid probe base could function for years and if developed enough protect the earth for many generations.:)

Originally posted by Gifted
A large probe is built in orbit, several is better. This probe has high thrust engines, carries a variety of sensor gear, and perhaps a dozen nukes. When a collision course is detected, the probe goes out to the asteriod. ...The explosion alters the asteriod's course, .

Sounds feasible if you say it fast enough, but like I stated in my post, these things are big, and really fast. Timing the detonation of a nuke would be critical, when they travel at several kilometres per second. You'd need a detonation very close to the surface so ablated material formed a jet and that momentum causes the trajectory change.

And thetre's the yield of your nuke vs the size of the object. The Tunguska Meteorite/Comet delivered about 15megatons. The dinosaur killer at the Yucutan Peninsula, about 100 megatons.

And how big would a meteor be that delivered say, 20megatons? Just 30 metres in diameter. So you have to aim your nuke, to detonate on the correct side of a small object, travelling at incredible speed, and make sure that detonation occurs within about 100metres of the surface, to make sure as much force and heat is transferred. 100m, at say, 15km/sec, means a firing solution accurate to 1/150th of a second, dependant on sensors that can track the objects distance accurately at that speed.

So if you can do this, you can deflect small meteorites, as long as you can make an autonomous nuke to intercept it a long long way away.

But how far? a rough calculation says you'd be hard pushed to give a 30m meteor a speed fo 1ms with a 10megaton yield nuke detonated 100m from the object. You waste a lot of impulse as most is lost on such a small object at that distance.

So, 1ms. the earth has a radius of 6,400,000m. Assuming it would hit dead centre, that means you need more than 3,200,000 seconds notice. at 15Km a second, that object has to be hit 48,000,000 km away. Can we see 30m wide objects that distance away?

But wait, it gets worse, that's your collision point. You have to get your nuke there first. The fastest man made object, Voyager 1, covers about a million miles in a day. So it would take a month (ignoring launch time, and orbital manouvering to slingshot to aquire this speed) to reach that intercept. So, where does that put our 30metre rock. Well, one month, and another 38,880,000km away. So we have launch at keast a month in advance, when this rock is 8.7million km away. So we have to see it and notice it's a threat, and have plotted it's course well before that. How long would that take? What are we going to see it with? It's a small dark bit of rock, over 8.7million km away. Not Hubble.

So we can't see it, can't launch a rocket fast enough to intercept it, if we could, and then have a really tricky firing solution, to attempt to dump as much impulse on it as possible, to perhaps move it at 1ms so it misses earth.

Of course, if it's bigger or faster (some travel at 70km/s) you can adjust the maths accordingly.

It's just not feasible.

Feel free to do some calculations and show me why you think it is though.

We can and must calculate the orbit of every object with an Earth crossing orbit; we have calculated 2400 so far, and more are being found each day; the closest approach to Earth found so far is in 2880AD.
To adjust the orbit of an object given eight hundred years notice would take a relatively small series of detonations.
More objects are found every month; soon we will have 24 thousand, no doubt; they represent valuable resources in space- what we need is all these objects to be acquired for mining, then they will become the property of the mining company.
No mining company would risk such large objects falling onto Earth, because of lawsuits.
The only objects which we won't be able to stop, because of insufficient notice, will be the ones coming from the Oort cloud; comets, mostly.
They are sometimes visible from long distances, due to outgassing- but it would be hard to stop one, as you say.
Good luck is what we need, with comets, for the foreseeable future; until we can map the Oort cloud as well.
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But wait, it gets worse, that's your collision point. You have to get your nuke there first. The fastest man made object, Voyager 1, covers about a million miles in a day. So it would take a month (ignoring launch time, and orbital manouvering to slingshot to aquire this speed) to reach that intercept Your assuming I'm not using nuclear rockets and such, but I see your point. Because the probe would match speed with the NEO, I don't think accuracy would be a problem. Smaller objects like you describe, could posibly be cuase to detonate in the upper atmpsphere, Considering that we can put a warhead in a two-foot circle 10,000 miles away, I again don't see accuracy as a problem. I think an atmospheric intercept would require less warning(not saying it wouldn't require any), and possibly easier to do. Bigger ones, the mass extinction ones, would get the probe.

Most NEO searches in the midwest are now done by automatic search. Those discovered for the largest part are found through such searches. I have an internet friend, who is an amateur astronomer. While he is an amateur, he does have his own observatory. Among the folks he has met during the Messer parties held every year, are also some who host the auto-searches for NEO's. For the largest part, they too, are amateurs.

NEO's were elevated to a government concern in England, where there is now a government backed effort to identify NEO's and a panel trying to decide what actions would be most effective to the prevention of a NEO impacting the earth. Mostly, what has come out here is what they have held as being the most effective methods to deal with a NEO that becomes more than a NEO.

As for the necessity of worrying about NEO's, one only has to look at the moon to see what impact they can have. Or do a bit of research for deep impacts on the internet. They have been turning up in the most suprising places, mostly in the ocean but still there are those on the land surfaces too.

One of the best platinum sources in Canada comes from a large impact site. It is so good that for years it has been the #1 source for platinum for the world.

Fears of a deep impact in the ocean causing world wide tidal waves has been a concern for a long time.

The thought of using NEO's for resources has also been a consideration for some time. It seems that a lot of the good ice bodies are NEO's. The ices are speculated to be both a resource for oxygen and for fuel. Rather than pull them into orbit for mining I think we would be better off to mine them where they are. Much less of a chance of something going wrong. Not to mention the amount of fuel it would take to change the orbit of one of them.

As far as sending, say a nuclear charge towards a body in space, it is not as simple as from point to point on the face of the earth. For one thing, almost all of our locator devices now use satellites for positioning. That is good only for the surface of the earth, not beyond orbit. When you leave the geo-orbit height you also leave the ability to measure down to meters when locating an object.

Many of our probes have had cameras that navigate by star location. These probes are build as one of a kind. There are none on the shelf and the lead time to make them is on the order of years. Something we may not have the luxury of having is time.

A lot of the NEO's are dark in color and do not pickup well to visual observation. Those NEOs on the return flight from the sun are also hard to spot as the suns glare does hinder us from finding them. Many of these NEOs were found only after they had gone past us and not before when we would have had the time to do something about it.

Something causes disruption in the Oort cloud. This something, what ever it is, sends a rain of bodies into the inner system every-so-often. We are nearing the time span that this should occur again if historic records have any say in it. Jupiter is estimated to clear out all but a 1/4 or less of these bodies. It is that last 1/4 that we have to worry about.

I am not a fan of the Planet X theory. If Planet X were there we would have found some indication of it by now. Even if it were out of the plane of orbits. It is possible that galactic rotation brings something close enough to disturb these bodies but the jury is out right now on that. Your guess is as good as mine.

Originally posted by Gifted
Your assuming I'm not using nuclear rockets and such, ...

Considering that we can put a warhead in a two-foot circle 10,000 miles away, I again don't see accuracy as a problem.

I think an atmospheric intercept would require less warning(not saying it wouldn't require any), and possibly easier to do.

Bigger ones, the mass extinction ones, would get the probe.

Well, right now, we only have chemical rockets to play with. Launching nukes on a nuclear powered rocket is a long way off. Getting clearance to fly that sort of set up will take a long long time.

Yes, we have that level of accuracy when aiming at a static terrestrial target using GPS. But intercepting something moving at 15km/s takes much, much more. We can't catch up with an object moving that fast, so we'll end up coming at it head on most likely, so that closing speed is something special. Nudging things in know orbits sounds easy, but that assumes the thing that is going to get us is a known object. If it's extra solar, we're buggered.

Atmospheric detonation, fine in principal, but you still have that closing speed issue. You need to detonate real close to deliver your impulse, 1/150th of a second late, and your nuke gets smashed to bits before it has a chance to detonate. I don't know what the 'lock time' for a nuclear device is, anybody know? How reliable is the timing from initiation of reaction to delivery of blast? How long does it take?

The probe, for extinction sized objects. well, we're going to make a dent in a six mile wide bit of rock with a 20Megaton weapon?

Maths please on this one, I need to see numbers!

These probes are build as one of a kind. There are none on the shelf and the lead time to make them is on the order of years. Something we may not have the luxury of having is time. I thought I said that thesewould be built ahead of time. Phlogistician, your assuming again that I'm launching from earth's surface. You have valid points, that's why we should start now to find ways around them. The atmospheric intercept idea I thought up in two minutes. The math is not the obstacle here. It's the time to do the math and get it right. I agree, 20Mt is way too small.Many of our probes have had cameras that navigate by star location. The MIRVs I was refering to used this to get accuracies of a few meters. Dependign on whether your going to detonate the bombs in space or on the asteriod, laser guidance is accurate enough. To clarify something: the probe(not really the best word) will match velocities with the asteriod, and then launch the bombs from there.

I don't think being in orbit, ready, saves much time, earth to LEO takes how long? Eight Minutes? Nukes need servicing, and space is a hostile environment, so it may be safer to keep the 'probe' on the ground until it's needed, rather than risk repeated launches of nukes.

So you plan to fly your nuke into the path of the meteor, turn stop, accelerate in the direction of travel, allow the meteor to catch up, land on it and detonate? Removes some difficulties from firing solution, but you now have a fuel requirement, and need to decellerate and accellerate a nuke plus flight body to the same speed as the meteor. So to 10km/s or more. Now Beagle-2 is currently running away from us at 11.4km/s, so it is achievable, but Beagle-2 only weights 65Kg. A small ICBM payload is nearer 500kg, so you're talking a lot more fuel.

Intersting ideas, keep them coming. Next, though, we need a far higher yield nuke, and it needs to be much lighter. How are we going to get that?

One thing that might not have been thought of here. How do you predetermine the size of the rock you are going to have to hit?

This will determine what we need to use. The size of the bomb, the mass of propellent needed to get it there, and what speed it needs to be going at to catch it.

It wouldn't do to have to hit a 300 yard rock with a 1000 megaton nuke. A 1 kiloton wouldn't have much effect on a 6 mile or better. This is assuming you have the fuel to get it there and match the trajectory. It is possible that no matter what we do that we don't have the time to do this or that the trajectories are so out of whack that it will take a time to do gravity assist to catch the object.

As mentioned, both the nuke and the rocket need maintaince. What was not mentioned was the threat on micrometorites and man made trash in orbit, either of which could do a number on any stationary launcher in orbit.

Why not put a giant adjustable mirror in either earth orbit or sun orbit or moon base. Mirror would be able to focus suns energy on to asteroid and create a side stream of hot particles which will nudge asteroid off track.

Giant mirror could be a frensnel construction or a giant cylindrical drum with a mylar adjustable surface. On the moon a solar reflector could be made out of thousands of adjustable mirrors.

Such a weapon could also be used against the Earth, so proper precautions would have to be taken to avoid that.

Yes, lasers might be useful, at various wavelengths and for various purposes;
Using lasers as lidar can locate objects all over a volume of space, and the doppler shift of the reflection will give an indication of velocity; this method of scanning is very energy intensive- but if you want to live in space, you have got to be prepared to use energy; the Sun gives out a trillion times the Earth's current usage, and it is likely that a space economy will need a large part of it. It might not be a good idea to stare in the direction of a lidar sensor when active.

some objects, particularly icy objects might be persuaded to change course by off centre targetting by high energy lasers; problems with this approach include the spread of the beam which can seriously weaken even a high powered laser at great distances.

Also the vapourisation of the surface of the object causes an outgassing which instantly cuts down the effectiveness of the laser.

Perhaps by firing short bursts of high powered short wavelength laser this effect can be mitigated.

space junk objects may also be good targets for high powered lasers- with enough power small objects could be vapourised; which admittedly does not get rid of the mass, but could make the larger objects small enough to be dealt with by kevlar dust shielding or similar.
You only get one shot though before you have to scan again.

It has also been suggested that lasers can be used to charge dust particles to allow deflection or collection by magnetic fields;
this may be possible,
and the magnetosphere of the Earth is an example of how such deflection of charged particles might work; it is another energy hungry process, and could seriously disrupt unshielded electronics.
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The question at this point in time is not what is most efficient, but what is cheapest and fastest to build and deploy.

As far as cost and current technology go the only thing that is readily avaliable for deflecting asteroids is nuclear weopons.

And if a asteroid was heading directly for us and would hit in a few months the only technology that is advanced enough to do anything is nuclear weapons.

So until laser technology or any other technology is further developed nuclear weapons are are only hope against asteroids.

Something that could be developed would be nuclear powered engines that could push the asteroid away and wouldn't cost a whole lot more than current technology.

So when deflecting asteroids its clear that it should be nuclear. :D
At least until the other technologys are developed. :)

"anyone agree with me that the prospect of a meteor causing a doomsday belongs in pseudosci?"

That depends on the size of the meteor. Small objects, i.e. 500m or less in size, will probably not cause anything more than 'local' damage (unless they hit the ocean), exploding with an energy of 100-1000 megatons (100-1000 H-bombs). An impact of this magnitude would certainly wipe out a big city or small province, but would not ruin an entire country.

Of a bigger worry are objects 1km in size and above. With these sorts of objects (and there are probably something like a million that cross Earth's orbital plane) the impact energies begin to approach the level at which human civilisation will be threatened at a global level, either due to the direct effects of the impact (explosion, blast wave, tsunami, etc) or from the indirect effects (climate change, disruption to agriculture, etc). Objects of 10km size and above are 'dinosaur-killers'-these will almost certainly cause a mass extinction that will wipe out a large proportion of all living species, terrestrial and marine, and there is little chance anything bigger than a shrew or a rat will survive in the aftermath. It is now well-established that the impact in the Yucatan (Chixulub) some 65 million years ago, which was of an object of this size, played a key role in wiping out the dinosaurs (as well as about 75% of all other species then alive).

This, I regret to say, is one area where the 'fear of the skies' is justified.