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The ¬NED pin goes low on detection of a nuclear detonation [pdf]

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Re: The ¬NED pin goes low on detection of a nuclear detonation [pdf]

#21

Post by pjscott »

sjwright wrote: post #16
pjscott wrote: post #9

Earlier quoted context omitted.

Remember to declare ned_pin volatile. (Sorry to be pedantic, but I was getting physically uncomfortable about the possibility that it might not have been declared volatile.)

You're physically uncomfortable about indefinite 1999-esque partying? Do you have something better to do when !ned_pin?

Of course! When the !NED pin goes low, duck and cover like it's 1959.

(Fun fact: in a fairly large portion of the blast radius of a nuclear bomb, the main danger for people indoors is falling debris and broken glass from the pressure waves. Duck and cover actually works.)

Re: The ¬NED pin goes low on detection of a nuclear detonation [pdf]

#22

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Re: The ¬NED pin goes low on detection of a nuclear detonation [pdf]

#23

Post by JonnieCache »

They also sell something called the SCS750 which is apparently like a BeagleBoard IN SPAAAACE...

http://www.maxwell.com/products/microelectronics/product.asp...

Datasheet: http://www.maxwell.com/products/microelectronics/docs/SCS750...

Its CPU is in fact triply-redundant, like pjscott was saying. They run in lockstep, and they do some fancy stuff that involves dumping the CPU registers to memory, "scrubbing" the registers and then restoring them. I recommend having a look.

Space is cool. Even when it does have nuclear weapons in it.

Re: The ¬NED pin goes low on detection of a nuclear detonation [pdf]

#24

Post by kabdib »

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. :)

Re: The ¬NED pin goes low on detection of a nuclear detonation [pdf]

#25

Post by [deleted] »

kabdib wrote: post #24

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 al…

[deleted]

Re: The ¬NED pin goes low on detection of a nuclear detonation [pdf]

#26

Post by burgerbrain »

kprobst wrote: post #17
idoh wrote: post #8

So, my mom is a former Maxwell employee who now does her own defense contracting, and makes this same type of part. As I understand it, when there is a nuclear event, it generates x-rays followed by the EMP. The goal is to have warheads in flight to be able to continue to their target, so the strategy is to employ an NED. When an event is detected, the warhead shuts down its electronics for the duration of the EMP, a…

I thought EMP affected electronics regardless of whether they are powered at the time of the burst or not?

Perhaps the idea is to disengage delicate circuitry from long potentially antenna like circuits.

Re: The ¬NED pin goes low on detection of a nuclear detonation [pdf]

#27

Post by sliverstorm »

JonnieCache wrote: post #15
pjscott wrote: post #13

Earlier quoted context omitted.

Just think how much redundancy you could get, cheaply, with the advances that have been made with Moore's Law over the years. Computers for space probes don't need to be that fancy. It's totally feasible to build processors that use error-correcting codes in their entire datapaths, have tri-modular redundancy for all their functional units, and then are arranged alongside several other identical processors for ridicu…

Doesn't the difficulty/expense of keeping all those processors running in absolute cycle-for-cycle lockstep increase dramatically with the amount of redundancy? I vaguely remember being taught that this is the big problem developing real-time safety critical systems.

It could be that I just don't know enough about redundant system design, but I'm pretty sure the way Voyager worked was each computer ran independently and identically, and the result of computations was simply compared to the result on the other computers. In other words, you run it like Folding@Home or SETI@Home which send each job to multiple clients. That doesn't seem like a difficult problem to tackle.

Re: The ¬NED pin goes low on detection of a nuclear detonation [pdf]

#29

Post by tdicola »

kabdib wrote: post #24

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 al…

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

Re: The ¬NED pin goes low on detection of a nuclear detonation [pdf]

#30

Post by kabdib »

tdicola wrote: post #29
kabdib wrote: post #24

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 al…

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.

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