[X] My Assistant

[tty]

You definitely do NOT want to use any violent technique that might break an impactor up into small fragments. Remember that according to recent research the main killing mechanism of the Chicxulub impact was the vast cloud of dust-sized secondaries that deposited enough energy in the stratosphere to cause wordwide fires and fry unprotected organisms.

That, paradoxically, is one reason I think using nuclear charges would be safer than a series of "deep impacts". The shock wave from a directed-energy nuclear weapon set off some distance from an impactor would act more or less in parallell and equally on all parts of it and therefore run less risk of breaking up an "orbiting rubble pile".

Safest of all (but very slow) is of course "gravity tugs", which apply an equal force on each atom of an impactor.

tty

[ugordan]

That, paradoxically, is one reason I think using nuclear charges would be safer than a series of "deep impacts". The shock wave from a directed-energy nuclear weapon set off some distance from an impactor would act more or less in parallell and equally on all parts of it and therefore run less risk of breaking up an "orbiting rubble pile".

Except that would be a very cost ineffective way to divert an object. Probably wouldn't work, either. Some 80% percent of the energy released by a nuclear weapon is soft x-rays, the rest being mostly kinetic energy of the fragments. Were you to arrange detonation some distance away from the object, the surface area of the expanding debris that did useful work would diminish rapidly. In essence you'd waste a large fraction of the bomb's yield on nothing. It's arguable that the fragments would push upon the object with any significance when they hit. Let's say you set the bomb off so 10% of the spherical debris cloud impacted the object - a fairly close burst. Given a warhead in the (conservative) range of 1 ton, that's 100 kg of material pushing on a kilometer or so sized object. Even given the high nucleus speeds (something like thousands of km/s) that wouldn't do much. The fragments would still deliver a shock to the object, the front being parallel wouldn't help much. As for the bulk of the energy released - the x-rays, I imagine they'd be rapidly absorbed by the first couple of millimeters of surface regolith which would explosively flash into steam, generating some impulse thrust and producing a shock wave on its own in the object, in advance of the much slower fragment debris cloud that is yet to arrive. The x-ray generated shock wave shape wouldn't be dependant on whether the bomb went off near or far -- what angle the x-rays were absorbed wouldn't matter as the material would blow-off vertically to the surface at that point. There's really no easy way to convert the sudden release of many megatons into a gentle push.
A nuclear charge would basically only be good at destroying an object and we don't want that. Moving the detonation point away from the object will rapidly diminish your return, if any.

BTW, what's a directed-energy nuclear weapon?

[nprev]

Actually, I meant putting threatening bodies in accessible heliocentric orbits that would require little more than cislunar delta-V to reach for future use. I agree that putting the things in orbit around the Earth would be WAY risky given the current state of the art & our limited knowledge about these bodies.

[dilo]

Agree with you, nprev. Also considering that, in order to put such a body in Earth orbit, you need an high delta-V impressed in a relatively small time frame with further technological issues and asteroid-integrity risk.
Unless you want to use airbraking in Earth atmosphere!

[nprev]

Thanks, Dilo. I think it's prudent to save these objects when feasible rather than destroy them. Our civilization will shortly have an exponential appetite for resources...better to keep any such handy, no matter how remote the application!

EDIT: BTW, I personally witnessed the 10 Aug 1972 'aerobraking' of an NEO over western Montana...gotta say that it definitely looked both risky & nerve-racking, can't imagine initiating such an event voluntarily... This pic isn't mine on the link (I was only 9 yrs old & had no camera), but it passed right over my local zenith & produced two impressive sonic booms...brr.

http://gep.alien.de/ifo/images/ifo_meteor01.jpg

[tty]

BTW, what's a directed-energy nuclear weapon?

It is not well known, but it is possible to build a fission weapon so that nearly all the energy is concentrated into two relatively narrow cones (conversely it should also be possible to concentrate it into a "sheet", though I don't know if this has ever been verified experimentally). Of course this would considerably increase the efficiency of the energy transfer to an impactor.

tty

[nprev]

Personally, I think it'll be a long, long time (if ever) until the 1967 UN Treaty on Outer Space is amended to allow thermonuclear devices in space even for peaceful purposes, so I don't see this as a feasible alternative.

Given global proliferation of both nuclear technology & launch capability, that's probably a genie best left in the bottle anyhow. We sure don't need a new trigger for major political crises to cloud space development. However, I'm not sure if manufacturing steering bombs from, say, indigenous lunar resources is expressly prohibited by the Treaty; if I recall correctly, most of the relevant language is focused on launching weapons into Earth orbit.

[tuvas]

It is not well known, but it is possible to build a fission weapon so that nearly all the energy is concentrated into two relatively narrow cones (conversely it should also be possible to concentrate it into a "sheet", though I don't know if this has ever been verified experimentally). Of course this would considerably increase the efficiency of the energy transfer to an impactor.

tty

It hasn't been completely tested, but I can tell you that most nuclear weapons (At least to my knowledge) were shaped to exert more force towards the central parts, to give more force along the ground and not so much up and down. I do know it's possible if you have something the shape of a tuna can or even more exagerated to essentially release the force in a forward and backward direction, which would increase the efficiency considerably.

As to allowing the peaceful use of nuclear weapons in space, I'm sure something could be ammended if it's outside of the moon's orbit, as I recall, no law is valid beyond that point (I could be wrong...)

[nprev]

As to allowing the peaceful use of nuclear weapons in space, I'm sure something could be ammended if it's outside of the moon's orbit, as I recall, no law is valid beyond that point (I could be wrong...)

Nope...there are a number of provisions in the UN agreements that apparently extend into infinity. For example, no nation can make a territorial claim on the Moon "or any heavenly body" greater than (I think) a 50 km radius around a permanent base. A lot of it was based on the treaties that cover Antarctica.

I don't know if asteroid mining has ever been directly addressed in the UN, but I'm sure that it'll be a real dogfight someday if & when any real profit potential becomes evident.

[ugordan]

It hasn't been completely tested, but I can tell you that most nuclear weapons (At least to my knowledge) were shaped to exert more force towards the central parts, to give more force along the ground and not so much up and down.

Where did you hear this? By up and down you mean ground or?

[tuvas]

Where did you hear this? By up and down you mean ground or?

Basically the explosion of a typical nuke expands outwards. I did a research study on Nuclear Pulse Propulsion some time ago, it was in one of the sources I found, basically the explosion for a typical nuke looks like a "pancake" for lack of a better word. It's more eliptical, but there is more explosion going to the ground level then up and down. Just a thought, that's all.

[ugordan]

If you're referring to the Mach stem where the shock wave reflected off the ground produces a "skirt" when combined with the direct wave, enhancing the ground damage, then yes. As far as directed energy weapons go, they probably do exist for special purposes, but once that energy (x-rays and fragments) exits the bomb casing and hits the atmosphere it loses this directional component. From there on you have a classic spherical fireball which quickly evens out an irregular energy distribution. Apart from gamma rays and neutrons that is, which interact poorly with the air and can largerly travel freely.

[Nyx]

This is my first post, so welcome everybody!! And happy new year!

May we say that 2006XG1 is more dangerous than Apophis?, or what is the level of danger we should expect from this asteroid as compared to other know NEAs... As a physicist, I can answer that, comparing fly-by distances or Torino scale, 2006XG1 is more dangerous, but Apophis' orbit seems to be more Earth-close that the other one, because of the apogee distance. What do you think about?

[nprev]

I think the jury's still out, but there's no significant risk; it'll probably come in as less risky than Apophis, if for no other reason than there's only one potential encounter. The latest update as of today has increased the probable miss distance to 0.72 Earth radii and the sigma LOV is decreasing, so the asteroid's orbit is becoming better known.

EDIT: just to cap off this thread, it's now down to a Torino 0 with a miss distance of 0.93 Earth radii & a 1 in 15 million chance of impact...no surprise!