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Comment by kabdib | Hacker News Reader

I've wondered about the following:

The firmware controlling a nuke has to have, at some point, a bit or control register it sets that causes the explosion to go off:

    *pKaboom = true;

or something like that. My question is: What is the line of code after that?

    *pKaboom = true;
    /*NOTREACHED*/

I suspect it's more complicated than that (there's an infinite loop of some kind that keeps retrying the command sequence). I also suspect I will never know, short of some very hush-hush software being open-sourced someday. :)

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GCC has a noreturn pragma for this sort of thing. It lets you mark functions as never returning, which can in turn help the optimizer generate code leading up to that function's call sites.

  ...
  exit(EXIT_SUCCESS); // or maybe failure, if we reach this point? :)

I doubt the warhead has code to control its activation--more likely it's something like an altitude sensor that controls detonation.

Think cruise missile. Some code looks at a map, looks at GPS, looks at altitude and velocity, and decides "Yup, this is the spot."

It's probably a lot more prosaic than I imagine.

I'm fairly certain that ICBM's use inertial guidance with predefined/computed coordinates (http://en.wikipedia.org/wiki/Inertial_guidance). There's no software involved, its all physical. Detonation is (probably) trigged by a combination of altimeter, accelerometer and other telemetry systems.

Yeah, GPS doesn't work so well through the plasma sheath around a reentry vehicle. And you don't have a whole lot of time to acquire GPS lock, or steer, when you're still traveling at hypersonic speeds and it takes maybe half a minute to hit the ground after first encountering the upper atmosphere.

Cruise missiles, on the other hand... Well, let's just say there are eye-witness accounts of one flying down the street and turning the corner at an intersection before detonating in a tiny radius. All the was left of the target was a single shoe, IIRC.

Oelewapperke posted a long and detailed reply to this post, and yet it will go ignored because all his posts are automatically killed without him being aware of it. His posts may not be perfect, but I still find this kind of false positives terrible.

It's not a false positive. He's hellbanned. Hellbanned users don't know they're hellbanned - their posts appear to them "not dead." If you look at his posting history, all of his posts starting 160 days ago are dead, and it seems to have started at a post from 175 days ago.

I know about hellbanning -- I've actually complained about this before:

http://news.ycombinator.com/item?id=1256772

But the post was killed...

oelewapperke: I hope you're reading this, because your reply to this comment is not visible. You've been hellbanned.

http://www.codinghorror.com/blog/2011/06/suspension-ban-or-h...

It happened 175 days ago, when you made an unwise comment about killing children. All your comments since then have not been visible, or upvotable. This is why you're supposed to put contact information in your profile.

I hesitated before posting this, since from your older comments you appear to be a bit of a reddit user, and the comment itself contains several significant technical errors regarding the design of nuclear weapons, (American nuclear weapons haven't been of the "gun" type for 60 years now) which casts a poor light on the comment as a whole; but I don't think you're completely beyond hope.

Make a new account. Try not to be an asshole with it.

Perhaps not for an ICBM, but GPS is definitely a possibility on a missile. You could even build a DIY one with this http://arduiniana.org/projects/the-reverse-geo-cache-puzzle/

ICBM's use inertial and (in the case of Trident) star mappers.

The reason they don't use GPS is that you would (hopefully) only start throwing ICBMs around if you are in "nucular combat toe to toe with the Rooskies" - and the way you know you are in a proper war is that all your GPS satellites have just been destroyed by the other side.

Some missiles run a proprietary operating system for which one has to buy a license per missile. I always found it funny that those instances of the OS were going to destroy themselves.

I guess there might be some code for mis-firing. Detonating this kind of stuff is tricky.

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