What is wrong with my math, or are asteroids just that impossible to move.

[pizzaoverhead]

Idea: how fast can asteroid rotate before breaking up? I guess its out of question for iron ones, but ice?

The asteroid itself can spin without breaking away much faster than the layer at the surface that your thrusters would be attached to.

[peadar1987]

Surely if the asteroid was spinning, you'd set up the engines only to fire when they're facing the right direction. Sure, you'd need longer overall, and your thrusting would be less efficient, but given plenty of time, it shouldn't be a massive issue.

[Accelerando]

THE POINT IS THAT IF YOU WANT PEOPLE TO HELP YOU ITS BENEIFCAP DO MAAAK E SUR E THAT THEUY CAN REDA IT EASILYU INSTEAD OF FEEDING HTME HART RRO TEAD TEXT THAT TAKES A LOT OF EFFORT TO DECIPHER IT IS ACTUALLY IN ONES OWN BENEFIT TO KOMMMUNICATGE CLEARRYL INSTAD OF DOING OTHER SMAKE THE WORK FOR THEM BUT APPARENTLHY THAT DOESNT' TMATTER AND YOU CAN JUST RELXHA AND TYPE WITHOUT CARING IF IT LOOKS OK OR IS EASY TO READ TO ME THAT IS NOT THE RIGHT WAY TO ASK PEOPLE TO BE KIND OENOGH TO ANSWE A QUESTION BUT OBVIOUSLY I AM WRONG THE GOOD THING IS THAT IT SIS GOING TO SAVE HME A LOT OF WORK BWNE TYPEING HERE THANKS YOU COFR POINTNG THAT OUT

Whoops I noticed I left my capslock on. Well it's easier and quicker to leave it this way.

Whining and moaning like an upstart child is the standard now instead of just getting over some little formatting discrepancy? How interesting. I would have expected more from someone interested in "careful and better".

[PakledHostage]

Idea: how fast can asteroid rotate before breaking up? I guess its out of question for iron ones, but ice?

I wasn't able to find a concise article to link to, but there is an observed spin rate barrier.

[vger]

Maybe I've been overlooking something whenever I hear ANYONE mention the idea of using nukes against an asteroid. I always find myself asking the same question: how does anyone expect to get a chain reaction when there's no atmosphere for the nuke to work with?

[Accelerando]

Maybe I've been overlooking something whenever I hear ANYONE mention the idea of using nukes against an asteroid. I always find myself asking the same question: how does anyone expect to get a chain reaction when there's no atmosphere for the nuke to work with?

Atmosphere is important to generate a shock wave, not for the explosion itself.

[jwenting]

Why all the hard to read 10^13 notation?

Why not just write 10¹³?

Unless you want people just to ignore the post and what you're writing because it looks messy, of course.

because not everyone is more interested in the looks of things than about the content...

Myself, unless I'm being paid to write something, I'm not going to spend hours fine tuning the formatting of the text.

[peadar1987]

Maybe I've been overlooking something whenever I hear ANYONE mention the idea of using nukes against an asteroid. I always find myself asking the same question: how does anyone expect to get a chain reaction when there's no atmosphere for the nuke to work with?

Because nukes don't work like some other explosives, all the energy is already contained inside the warhead, and it just needs to be detonated. Doesn't need to react with anything external.

[PakledHostage]

Maybe I've been overlooking something whenever I hear ANYONE mention the idea of using nukes against an asteroid. I always find myself asking the same question: how does anyone expect to get a chain reaction when there's no atmosphere for the nuke to work with?

And because you don't need a pressure wave to nudge the asteroid. In principle, the nuclear bomb blast heats the surface of the asteroid causing surface material to ablate away on the side facing the detonation. That ablation results in a change in momentum in the asteroid. It doesn't even matter that much if the asteroid is rotating because it all happens so fast. Personally, I think it is an important experiment to try. I realise that there are political obstacles to that type of testing but we should have some sense of how well it works (if at all) before we need it.

[OTehNoes]

As far as I can tell, this math is assuming that all of the explosive force is imparted perfectly efficiently into the kinetic energy of the asteroid, which is most certainly Impossible.

Bingo, the bomb WOULD make that much energy, but most of it would be wasted in directions away from the asteroid, the amount that went towards it would be much less.

[vger]

Ah, yeah, that makes sense. Alternatively, I sort of like the solar sail idea. In the case of a rotating rock, the sail would only alter the asteroid's trajectory when it's pointing towards the sun, thereby giving a push more or less in just one direction.

Wasn't there a plan in place to hit an asteroid with a nuke? I remember reading about it within the last year or two, but now can't find a thing on it. Or has the nuclear situation on Earth become too volatile again, with NK thinking it was heading for them, even if it was going in the opposite direction?

[Holo]

So I was bored, I wanted to find what effect it would have if the strongest nuclear bomb ever made (The Tsar Bomba) was used to slow an asteroid. This is what I got:

The density of a stony meteorite is 4.5 g/cm³

=4.5 t/m³

The size of an asteroid is 8 km × 1 km × 1 km

This equals 8 000 000 000 m³

=3.6×10¹⁰ metric tonnes

=3.6×10¹³ kilograms

The orbital velocity of an asteroid is 20 km/s

Kinetic Energy = ½ × m × v²

=12 000 000 000 000 000 000 000 J

=12×10²¹ J or 12×10¹⁷ GJ

Energy of 1 ton of TNT is 4.184 GJ

The Tsar Bomba is 50 Mt

50 000 000 × 4.184 = 209 200 000 gigajoules

Tsar Bomba Energy ≈ 209 200 000

The energy after the explosion is the energy of the asteroid - the energy of the bomb

½ × 6x10¹³ × v² = 11999790800000000000000

= 6×10¹³ × v² = 23999581600000000000000

=v² = 399993026.67

=v = 19999.83 m/s

There, I fixed the formatting of the OP. It took nowhere near hours; it's about 6-7 minutes after I started. So nice straw man.

Why do you also talk about looks and content as if they are mutually exclusive? Anyway, content doesn't matter if it's unpleasant to read.

Edited February 27, 2014 by Holo

[Accelerando]

People being served eviction notices probably don't find them pleasant to read, but the importance of their content is no less diminished.

The point is that either way it's such a trivial difference; and even if it can be whipped up in a few minutes, what's the matter other than to please some nitpickers who value tiny changes over the gist of a post? OP's post isn't a term paper, it's a question that can be understood and answered without a whole mess of deep thought.

[Aghanim]

For superscript against ^ notation: Probably OP doesn't know how to do superscript

But this small nitpicking is more effective deflecting this thread trajectory than the largest nuke ever made...

Nuking the surface isn't as effective as putting it in a drilled hole

And you don't need some exotic alloy to create nuclear shaped charge : http://www.projectrho.com/public_html/rocket/enginelist.php#shapedcharge

[peadar1987]

Also, if you catch it soon enough, a delta-V of less than 1m/s could quite easily be enough to change the orbit by several hundred kilometers by the time it reaches earth, which could make all the difference.

[Albert VDS]

You mean change it's speed in a given direction.

Only a few mm/s would be enough to change it's course drastically.

[LLlAMnYP]

Firstly, you let some typos creep into your calculations. It should be

7.2*10^21 J = 7.2*10^12 GJ for the KE of this rock.

As far as the rest of the discussion goes, you haven't specified an inertial frame of reference to talk about 20 km/s. Without it there is no point in discussing the energy output of the Tsar Bomb and comparing it to the energy of the asteroid in an arbitrary reference frame. What also is needed, is a mechanism through which the energy of the bomb works "against" the kinetic energy of the asteroid. X-ray radiation for instance would hardly make a dent, if that's all of the energy output of the bomb - it would be along the lines of 10 um/s delta-v.

PS

Guys, I can see your point on superscripts... but symbols? That sweet little multiplication cross, for instance. I don't see a character table for commonly used math symbols here in the forum editor, do you really expect someone to dive into the built-in Windows Character Map every time he needs to post anything more than a smiley with "10char" attached?

The tl;dr is, that WYSIWYG editors for math notation drive me into a state of rage (especially when they're not really suited to the task), but I promise to start using proper superscripts 'n' all as soon the forum starts parsing LaTeX input :-)

Edited February 27, 2014 by LLlAMnYP