Fun fact: the actual programs in the spacecraft were stored in core rope memory, an ancient memory technology made by (literally) weaving a fabric/rope, where the bits were physical rings of ferrite material.
"Core" memory is resistant to cosmic rays. The state of a core bit will not change when bombarded by radiation in Outer Space. Can't say the same of solid state memory.
I worked on core memory computers in the 60's. You had 16K, tape drives (no disks) and FORTRAN. What a gas!
At a low level your correct, but you can use error correction and a lot of redundancy to prevent cosmic rays from corrupting solid state memory and still have a lot more than 16K of storage space for a long time.
...which involve error correction and a lot of redundancy. But I assume you meant radhard electronics boxes, which lets you run whatever you want within a cosmic-ray shielded box.
Hubble, the ISS and other low-orbit satellites are affected by the South Atlantic Anamoly, which funnels down charged particles from the Van Allen belts.
(This /was/ a surprise to the folks who designed Hubble, but the spook satellite people apparently knew all about it . . . and didn't tell the Hubble folks, not even over beer or something. Great win for national security, guys </sarcasm>).
I didn't see an opening bracket for sarcasm so I assume it's before 'Great win'. Were they really surprised by this? Also are they same people that didn't know putting hard drives in space would fail because of the lack of air and had to replace them with SSDs?
I think it's just an understanding of how the underlying physics work. Alpha and beta radiation will cause bits to flip in solid-state devices, because the state is held with electrons. Whereas core rope memory stores that state as magnetic fields in ferrite cylinders. So radiation will basically just bounce right off the giant ferrite cores (giant relative to solid-state semiconductors, that is).
*I am not a physicist, someone correct me if I'm grossly wrong.
Hmm, it's more like any ionizing particle (charged) creates pairs electron/hole, many of them, so that the charge distribution in the pn junctions are altered. Sometimes gamma photons generate Compton electrons in the material that act as delta rays, to the same effect. Heavy particles can alter the crystal structure, inducing defects that may change its properties. Magnetic storage devices don't have polarised junctions and could withstand all this if they didn't include solid state electronics. Radiation hardening techniques and shielding can help a lot.
Its more a cause of the radiation ionizing the underlying semiconductor material. For instance when an electron tunnels into a transistor it can cause strange effects. Look up single event upset and single event latch-up for more information. The SEL is interesting as it causes a transistor to act as a double transistor and start drawing tons of power. At least that's how I understand it.
Great! Texting LOL to my grandmother suddenly has a whole new meaning. I love it! She often complains her memory is getting old so it works even better!
"It is first appropriate to briefly describe the Apollo Guidance Computer (AGC). This processor is a general purpose, sequential, digital machine. Its word length
is 16 bits including parity. The random access memory consists of 2048 words of
destructive, read-write memory, called erasable, and 36,864 words of non- destructive read-only memory called fixed memory. The memor’y cycle time (MCT) is slightly less than 12 microseconds, with two MCI’s required to execute an add
and four MCTs to execute a multiply. As is typical of real-time control computers, this machine has a set of special input-output channels with which it controls the
spacecraft and observes the state of its environment. The interrupt structure consists of ten program interrupts with associated priorities, which are used for program
control transfers. In addition, twenty-six counter interrupts with associated priorities allow for input-output servicing. The instruction set consists of forty-two
regular instructions and nine involuntary instructions. Figure 1 indicates the number and diversity of systems with which the AGC interacts"
Bugger is not common, but also not uncommon American slang. It has rather lost it's original meaning. I have heard little old American ladies use it, probably having heard it in a movie, with the intention of a meaning derived from to bug (bother). I don't think any slang dictionary has ever caught up with this usage.
I've used bugger since the first of the Austin Powers movies. My friends and I used it until one of them married a South African girl and she made us stop being as it was incredibly impolite and rude apparently. I started again last year after watching Top Gear and then recently got yelled at by a new accounting manager who moved into the office across from my cubicle. Once again, I was being crude but in all honesty, for me, the word is no different than saying frag, frell, crude bunnies, etc.
Very commonly used in New Zealand, its used on TV with no problems, heres the iconic Toyota ad using the word bugger to good effect: http://www.youtube.com/watch?v=TKY_OysWu3k
Quick correction: if you read your link you'll see that glitches have been called bugs since the 1930s or earlier. The Mark II team didn't originate the term but they were very amused to see the literal manifestation.
The note by that moth in the log book says "First actual case of bug being found." Other text on that page reinforces the idea that the word "bug" was in use before that particular bug, not least the quote from Thomas Edison.
Now that the shuttle program has ended, it would be nice to get the supposedly perfect code produced by the On-board Shuttle Group as well. I wonder if a FOIA request has been made.
A very interesting book, written by Frank O'Brien and published by Springer, The Apollo Guidance Computer: Architecture and Operation, is definitely worth the read. Fun fact: The unit weighed 70lbs (32kg).
The AGC has spawned a pretty active cult of hardware hackers that have built the AGC from scratch - including the core memory.
looking through some of those documents a couple things stand out to me:
1) learn your maths people if you want to do rocket science stuff
2) the amount and detail of the documentation they wrote back then is unreal
3) the simple webapps I write for big bucks at local megacorp pale in comparison to those programs that frickin landed people on the moon!
Because the odds are that the simulator with which someone will run around yelling about the bug they found (which will get them links on HN and other fun perks) will have had less than 1% of the time spent on creating it than the code that was actually sent into space, and on the balance, given the observation of a defect in the combined simulator+Apollo code the highest probability locus is the new, untested code that was probably rushed out for publicity's sake and had no lives ever depend on it.
You seem to have misinterpreted my post as me saying I would never believe it was a bug in the Apollo code, despite me making very sure to explicitly disclaim that.
http://en.wikipedia.org/wiki/Core_rope_memory