How are nukes detonated? And how are they canceled?

Question

So i know that nukes have bits of uranium separated, on detonation they combine and uranium reaches critical mass and everything go boom. And I know that nukes are detonated in the air, several hundred meters above ground.

So my questions are:
– how is the detonation carried out, does the nuke auto detect when its ~1000 meters above ground and detonate itself? What’s the mechanism?

– is there a way to cancel the detonation by clicking an off button somewhere? Surely there has to be an off switch, it would be stupid not to.

– if there’s an off switch, what happens afterwards, does the nuke fly back or does it still hit the target and not detonate?

– lets assume a nuke is close to the target but the off button is pressed, so detonation has been canceled, but it still hits the ground at whatever high speed nukes travel at, can it still go off just because of the impact or are they very durable?

In: Physics

Answer 1

So the kind of bomb you’re talking about is a “uranium” or “gun-type” bomb and it’s the oldest and simplest kind of design. Modern bombs generally use a hollow plutonium sphere that gets compressed by timed high explosive charges because that gives you a better kaboom:weight ratio.

Anyway, triggering mechanism: A bomb can trigger based on any number of things. It could have a simple timer, an altimeter, a radar, an inertial navigation system, or a GPS to tell it where it is. Modern weapons likely have combinations of many triggers to make sure they work.

There’s no off switch. Some missiles *might* have the capability to self-destruct in-flight if ordered to, but that’s all kept very secret. And once the actual warhead is separated it is going to go boom whether you like it or not.

You don’t “cancel” a detonation. If there’s an “off button” it’s in the form of an explosive charge that blows the missile apart, or a command that sends the missile into the ground/ocean.

An impact or explosion won’t set off a modern nuclear bomb. They need a very precise series of timed detonations of their explosives to make the core go nuclear. Smashing the weapon into the ground just makes a lot of radioactive junk go flying everywhere.