3/4 of the safety mechanisms on a 4 megaton bomb failed over US soil.
I would hardly call this a breathless article.
What does "highly vulnerable" even mean? Could it have been triggered by the wind? If I'm the guy at the control panel, am I accidentally hitting that switch a couple of times per week? Maybe the only way that switch gets triggered is if I black out from the stress and my nose hits it on my way to the floor.
I get the significance of three/four barriers failing, but if the fourth one has a one-in-a-billion chance, is it really fair to say North Carolina was "dramatically close" to being nuked?
I would say its fair, would you feel safe if all bombs only had this switch from the 50s?
I suppose they could have neglected to put a fuse in the circuit which should have protected it against a surge that would damage some very expensive equipment (not to mention cause nuclear detonation.) But I don't know. I wasn't there to see and I didn't read the report. And we all know fuses fail as well - would that be the fourth out of five failsafes?
To answer your question, no - I honestly would not feel safe. But "dramatically close" is different altogether. When I think "dramatically close" I think about the time my kid ran into the street and I grabbed him from in front of a car... I needed to act urgently to avoid disaster.
I could be wrong though (and often am.)
That's not 1 in a million, that's 1 in 3.
Based on this tiny sample, here's the lottery analogy:
The lottery will flip 4 coins that have a 37.5% chance of being heads.
If you roll 4 heads lots of people die. So, just using this very inadequate sample from a single declassified document, you could estimate that a misfired bomb has a 2% chance of detonation (37.5%^4).
Obviously none of us know the real dataset, but my point is simply that it's not comforting that so many safety measures failed. (Which, as it happens, is also the opinion of the author of the original report in the article.)
That was exactly my point, that with such little data you cannot judge the probability.
Maybe the breeze of the wind is less potent than a impact of the drop of a heavy metallic object from an airplane.
The switch they're referring to is the arm/safe switch on the pilot's control panel. So the bombs didn't fail, one of them armed and tried to detonate exactly as designed when dropped from an aircraft. The only reason it didn't was because the pilot's arming circuit hadn't been activated. This isn't very reassuring because that arming switch may well have simply been a toggle switch under a cover, and even if it was better protected it still almost certainly boiled down to simply closing one or a pair of contacts, which can quite conceivably happen accidentally while bailing out of a spinning aircraft. Not exactly a one-in-a-billion chance.
There is a discrepancy between what TFA says (three out of four safety circuits) and what the wiki says (five out of six arming circuits) and I can't find anything to clear that up on my phone. Either way it's a disconcerting piece of history
The problem is that there are certain sorts of disasters where you really can't be sure you have the unknowns down well enough..... That's why aircraft components are rigorously tested. The only really safe solution I can think of is to try to anticipate the problem and sabotage the warhead first. For example one might, say, design warheads to destroy portions of the electronics if they get a signal that the pilot ejected.
So yes, it is probably possible. Is it possible to do so reasonably perfectly? I doubt it to be honest.
I don't know how big the primary on that bomb was, and can't find anything about that, but did find this (http://en.wikipedia.org/wiki/Castle_Koon) test of a fusion bomb where the primary didn't fizzle but the secondary nevertheless did not ignite. The primary there was 110 kilotons. So the primary on that bomb, not fizzling, is around 5 or 6 Nagasaki blasts.
According to Wikipedia, the Mark 15 had a real thermonuclear second stage that generated significant yield. However, its second stage was also packed with enriched uranium, and it obtained most of its energy from fission.
Essentially, it was a two-stage thermonuclear weapon that had a lower fusion fraction than most two-stage weaopns.
Summary of atomic weapons:
1. Pure fission. Fusion contributes 0% of yield.
2. Boosted fission: Fusion is used solely to improve the explosive yield of the fission. Fusion contributes 1% of yield.
3. Dirty two-stage thermonuclear: Fusion contributes between 1 and 50% of yield. Most of the yield comes from fissioning of the U-238 tamper by fast neutrons.
4. Clean two-stage thermonuclear: Fusion contributes 90-99% of yield. The U-238 tamper is replaced with beryllium or lead, which does not undergo fission when hit with fast neutrons.
5. Three-stage thermonuclear: Same as two-stage. Thermonuclear bombs are considered to be an "unlimited" design, because you can keep stacking stages on top of each other, until you've got enough to blow up the planet.
A fizzle in the Tsar bomba (a 100MT capable device) would not be expected to release 1MT of energy or even 1/10th that, it would still release likely very much less than even a single kiloton.
See http://en.wikipedia.org/wiki/Nuclear_weapon_design#Warhead_d...
Should assumes particular goals, and with almost any system you're looking at a trade off between safety and reliability. Like the sensors on a modern car; some cars refuse to start these days if the sensor's out.
The military's perspective is likely to be something like: We press a button, we want a mushroom cloud. Thank you very much. They're unlikely to want to introduce unnecessary points of failure in their system.
Timing systems, trigger mechanisms and the like will break, or be manufactured incorrectly. Nothing's perfect. Especially when you're designing something that's going to be thrown around a bit (slimmer margins.)
Which then gets weighed against the concern that that thing better not go off by itself.
I would imagine that the latter is why there were multiple safety devices on the weapon - reasoning that the chance of them all failing concurrently was very low.
Either way you do it, you're taking on some degree of risk of something - even if you make a system with a single point of failure, and make it fail safe as far as possible, that can never be entirely eliminated.
It seems rational to us that you'd err on the side of the thing not going off. But then again we're not in an arms race right now. Someone might well reason that if you introduce something that's going to introduce a certain failure rate into your system, that's going to mean you have to invest in more weapons to reach the degree of force you want. Especially if they're reasoning in a very constrained space - i.e. they primarily think about the threats they're used to - and just don't think of things like bombers going down, (which in any case they're going to find themselves encouraged not to do since it implies fault on their part) that's going to be a very easy rationalisation for them to make to themselves.