Asteroid Defense Systems

[Cadet_BNSF]

I was just reading about how NASA is planning a test run of some initial planetary asteroid defense systems, and I saw a link to the DART system. In that article, it mentions that nuking an asteroid would be a bad thing. The only reason I have heard for not nuking asteroids is that it creates a lot of smaller asteroids. But, here's the thing, those smaller asteroids are more likely to burn up in the atmosphere than the one giant one is. So why isn't blowing up the asteroid an option?

Conceptual view of the DART spacecraft

[Mitchz95]

Because 200,000,000 asteroid fragments burning up in the atmosphere at the same time would create a firestorm and incinerate anything beneath them. That's assuming that nuking the asteroid actually destroys it: nukes don't have a lot of power in space since there's no air to carry the blast wave, so all the damage will be done through heat.

[Bill Phil]

Nukes in space are just radiation sources. Albeit a huge amount of radiation. Could vaporize the roid, but that's a stretch. You'd be better off just pushing it with an Orion than blowing it up.

[kerbiloid]

A nuke could penetrate before it explodes. Then it would crash the asteroid rocks from inside exactly like on the Earth.

[Nikolai]

8 hours ago, Bill Phil said:

Nukes in space are just radiation sources.

Truth.  A nuclear explosion detonating near an asteroid's surface doesn't "push" the asteroid with a shockwave so much as emit enough X-rays to boil off a decent amount of asteroid material, and the reaction to the mass boiling away "pushes" the asteroid in the opposite direction.

8 hours ago, Bill Phil said:

Could vaporize the roid, but that's a stretch.

Also true.  Rock is surprisingly resistant to being vaporized.  And nukes are powerful, but not magically powerful.  You need somewhere on the order of ten gigajoules delivered to a cubic meter of rock to vaporize it.

http://www.madsci.org/posts/archives/mar2002/1015040902.Es.r.html

[magnemoe]

If you nuke an asteroid you would perferably use an orion drive charge, https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion#/media/File:Orion_pulse_unit.png

Drive charge deliver momentum to asteroid, this will still be an kick but will affect the entire hemisphere, reducing the risk of breakup and will move all fragments in one direction if happens.

7 hours ago, Mitchz95 said:

Because 200,000,000 asteroid fragments burning up in the atmosphere at the same time would create a firestorm and incinerate anything beneath them. That's assuming that nuking the asteroid actually destroys it: nukes don't have a lot of power in space since there's no air to carry the blast wave, so all the damage will be done through heat.

Would still be better, first you intercept in deep space an shattered asteroid spread out and the force would be radial to change trajectory, Majority of pieces will miss, the other would be very spread out as in over the entire world. Main issue would be large fragments, worst case would be lots of large fragments, all the junk in the cloud would make it hard to get in additional interceptors. 
This would only be an issue if it was an dinosaur killer sized asteroid and still far better than an global catastrophe 

[Spricigo]

Imagine you are guarding a large glass windows and somone throw a brick towards that window.  You options:

A) Move the window out of the way

B) Throw a net at the brick

C) Detonate a nuclear device near the brick.

 

 

[Urses]

The biggest no way to use a nuke on asteroids is the film "Armageddon" cool action but scientificaly nonsense.

To split the asteroid with a nuke you have to find the point of most stress within. And as smaller the remaining parts have to be the more energy you have to pump in. The nukes have many energy but the most damage is produced through atmospheric effects, like Shock and Sound wafes and radiation like heat and EMP.

Asteroid is atmosphereless so no Shockwave or sound Vibrations, is a material bulkage immune to emp (otherwise it would be a space ship with electronicks?) and will get a lill' smelted on the outside. 

It is like to hammer on a rock. If you are not realy lucky to hit a stress point, you only split some fragments off without any realy effect?

[kerbiloid]

If a nuke penetrates into the upper layer of an asteroid (meters-tens meters) and blast, it will be a camouflet which will partially evapourate, partially throw out the asteroid substance, making a jet which will push the asteroid into the opposite direction, changing its orbit.

P.S.
There are many asteroids, but only one Bruce Willis.

[wumpus]

I'm pretty sure you would get some measurable delta-v by strapping a nuke to an asteroid and setting it off.  Hopefully within time that such would be enough to miss the Earth (the key is always early detection).  I doubt that chemical rockets could provide as much delta-v, although in the end time frames would be pretty similar (you would need months if not years in advance to nudge the orbit enough).

I love pushing ion engines, but while they might manage more delta-v, expect it to take years to apply such (it takes years to apply those massive delta-vs to tiny probes, tiny delta-vs to massive asteroids could even take longer).

 

 

[cratercracker]

When somebody says that we need to nuke an asteroid:

[Spricigo]

1 hour ago, wumpus said:

I doubt that chemical rockets could provide as much delta-v

As much deltaV as what? In real life we have no reliable option.

Nuclear rockets? Banned.

Ion propulsion? Pitfully weak.

Solar sails? Experimental.

 

[magnemoe]

4 hours ago, Spricigo said:

Imagine you are guarding a large glass windows and somone throw a brick towards that window.  You options:

A) Move the window out of the way

B) Throw a net at the brick

C) Detonate a nuclear device near the brick.

A) would be moving Earth, no more comment. 
B) This is an good idea for stopping an ballistic missile in space, as the relative speed is more than 10 km/s it will destroy the missile even if you used an thin fishing net and the large diameter increases chances to hit over an tiny projectile. Against an large asteroid  it would have minimal effect. 
Yes you could match speed with it, wrap it then move it, dV requirement would be idiotic, you would need animater, fusion or orion pulse nuclear, yes nuclear salt water would also work
This is in an clear and present danger situation, an 100 meter astroid will probably hit earth in 100 year and it could work with ion, but in that case I would rater capture it. 
c) 2 KM in 2 years scenario. 

 

[p1t1o]

I dont know why everyone is bashing nukes all of a sudden. They are still the best shot we have, everything else is either hypothetical or requires new technology.

Obviously of less use against so-called "rubble pile" asteroids, but we wont be firing bunker-busting penetrators, they will be detonated at a distance they will ablate enough mass to give a useful push.

Also the idea being intercepting it quite far away, so if you do blast it to pieces, it is extremely unlikely that many, or even any of them will still be on the same course.

We are a tiny target, if there is a rock on a collision course, and we explode it into a cloud of smaller rocks, very little of that mass will remain on said collision course.

Unlike the movies, the interception is not likely to occur within the Moons orbit with the Earth looming large in front of it.

But we arent going to explode it, we;re just going to ablate it a little and change its course by a few arc-seconds years before it comes anywhere near us.

So if it is about the only thing we have with the required power, and blasting rocks to bits is not really the problem it seems, what exactly is the problem?

 

[magnemoe]

2 hours ago, wumpus said:

I'm pretty sure you would get some measurable delta-v by strapping a nuke to an asteroid and setting it off.  Hopefully within time that such would be enough to miss the Earth (the key is always early detection).  I doubt that chemical rockets could provide as much delta-v, although in the end time frames would be pretty similar (you would need months if not years in advance to nudge the orbit enough).

I love pushing ion engines, but while they might manage more delta-v, expect it to take years to apply such (it takes years to apply those massive delta-vs to tiny probes, tiny delta-vs to massive asteroids could even take longer).

The nice this of an orion drive charge nuke is that you don't have to match speed with the asteroid, you want some distance and its no need to be stationary, the speed difference can be compensated for if an issue at all. One issue with an high speed intercept is that junk around the asteroid will hit hard, yes you can shield yourself, you could even detach the shield plates to fly in front of you for added security. 

[magnemoe]

9 minutes ago, p1t1o said:

I dont know why everyone is bashing nukes all of a sudden. They are still the best shot we have, everything else is either hypothetical or requires new technology.

Obviously of less use against so-called "rubble pile" asteroids, but we wont be firing bunker-busting penetrators, they will be detonated at a distance they will ablate enough mass to give a useful push.

Also the idea being intercepting it quite far away, so if you do blast it to pieces, it is extremely unlikely that many, or even any of them will still be on the same course.

We are a tiny target, if there is a rock on a collision course, and we explode it into a cloud of smaller rocks, very little of that mass will remain on said collision course.

Unlike the movies, the interception is not likely to occur within the Moons orbit with the Earth looming large in front of it.

But we arent going to explode it, we;re just going to ablate it a little and change its course by a few arc-seconds years before it comes anywhere near us.

So if it is about the only thing we have with the required power, and blasting rocks to bits is not really the problem it seems, what exactly is the problem?

 

Finally some who get it, and yes nukes is the nuclear option, if its an far future issue its something you plan to deal with in the future. 

Anyway it don't look like its any very dangerous asteroids, comets on the other hand, they come in far faster an are pretty stealthy if inbound.
Shoemaker levy gave us an 2 year warning and it was in Jupiter orbit, impact speed was 60km/s with 21 kilometer sized bodies. 

[LordFerret]

From the sound of things, this 'exercise' is merely going to monitor and track TC4; As if we're not going to do that anyway. Exactly what planetary defense systems do we or anyone have anyway?

TC4: How NASA Plans to Test its Planetary Defense Systems on Close-Approach Asteroid

[DDE]

28 minutes ago, LordFerret said:

Exactly what planetary defense systems do we or anyone have anyway?

None.

All of the current systems are early-warning. No actual tools.

[Spricigo]

3 hours ago, magnemoe said:

A) would be moving Earth, no more comment.

No, the Earth will be fine. It go hit several times before and is still there. WE are the window that will be destroyed if proper measures are not taken in time.

 

3 hours ago, magnemoe said:

B)... Against an large asteroid  it would have minimal effect. 

Point is, if we intercept the asteroid early enough we just need a minimal effect. Our current problem is ensure we identify the threat early enough. (After figuring out how to detect it)

 

3 hours ago, magnemoe said:

Yes you could match speed with it, wrap it then move it, dV requirement would be idiotic , you would need animater, fusion or orion pulse nuclear, yes nuclear salt water would also work

Intercept and rendezvous is well within the capacity of chemical rockets. (Already done). The move it part depends entirely on how much of leading time we have. (It can be quite insignificant in terms of deltaV but the point is how much mass of equipment is necessary to this. )

 

4 hours ago, magnemoe said:

c)

C) is a moronic idea.

[LordFerret]

Moving anything will be risky business. Early detection is one thing, determining its precise orbit another, trying to account for perturbers another, and where in heaven's name will it end up going in its new orbit once it is moved the biggest question.

[Spricigo]

9 hours ago, p1t1o said:

I dont know why everyone is bashing nukes all of a sudden. ...

.... what exactly is the problem?

 

What could possible go wrong? 

Theoricaly (1), we are just taking a weapon of mass destruction (2)that uses radioactive material (3) putting it on top a huge tank of explosives (4) igniting those explosives (5) to deploy our WMD on an asteroid we have little information (6) precisely positioning it (7), so we can detonate our WMD remotely (8) and effectively use the explosive energy (9) to overcome gravitational (10) and structural (11) bonding forces, turning the big asteroid in multiple (12) radioactive (13) smaller asteroids while also ensuring that the whole thing (14) is deflected from its collision course with the Earth. (15). 

Maybe we get in a desperate enough situation to go with that madness anyway. 

[Urses]

The most reliable idea with the nukes and asteroids would be a orion drive for this lill rock... and as more nukes you let go off as more you generate a nocele on the asteroid. First ones do little to nothing to the orbit of this asteroid but produce a crater. The following will be fired in the crater and generate a vectored trust. We don't destroy the asteroid but we are able to change the traejectory far enough to fling the asteroid on the upper atmospheric layers maybe.

[PakledHostage]

Something to bear in mind for a realistic ELE type impact scenario is that we may not have any option other than to detonate nukes as the object whizzes by at ludicrous speed.

All the near earth objects over 1 km in diameter have been identified via the WISE probe's whole sky survey (within a reasonable degree of confidence) and none of them other than maybe 1950DA are on a collision course with us. The dinosaur killer has been estimated to have been on the order of 10 km in diameter, so we can be quite confident that we won't get blind sided by something like that. 

What we have to worry about, on the other hand is something like comet C/2013 A1 Siding Spring that passed close to Mars in 2014. It was only about 18 months from when it was discovered until it passed Mars, and initial computations of its orbit suggested that it might hit. Worse yet, it was on a retrtograde trajectory and would hit at ~60 km/sec. It wouldn't have to be very big to do a lot of damage at that speed. And we don't have any rockets with enough delta-V to reach and land anything on something like that enough in advance. All we could do is send nukes on flyby trajectories and detonate them at closest approach in the hopes that they deflect it enough (via the ablation method mentioned above) to miss us.

Edited October 7, 2017 by PakledHostage

[kerbiloid]

An option: redirect with nukes a small asteroid to crash into a dangerous big asteroid and disintegrate it.

[Spricigo]

2 hours ago, PakledHostage said:

Something to bear in mind for a realistic ELE type impact scenario is that we may not have any option other than to detonate nukes as the object whizzes by at ludicrous speed.

Which don't  make it a reliable options.  

Right now on such scenarios we may have no option PERIOD. (e.g. asteroid detected too late) Or we may have some  chance to rush out a risk plan to deal with the threat.

But definitely we don't have a clear idea of how to deal with such scenario and have a good survival.