scott wrote:

>> I read an article somewhere that before any program change is made, 
>> there are meetings upon meetings.
> 
> I think that happens for a lot of software development, not just in 
> space shuttles.
> 

Some, but definitely not all. Many places a small fix-up may not need a 
day's worth of meetings, but with the shuttle, not a single line of code 
can be changed.

I think this is the article: 
http://findarticles.com/p/articles/mi_m0ISJ/is_n1_v33/ai_15103437

>> I'm sure there are glitches in the firmware of cars, you probably 
>> don't notice, or think its something mechanically wrong.
> 
> It's extremely unusual though, almost unheard of, for there to be any 
> noticeable glitch in the core software running a car.  It's simply 
> because the consequences are so great, that the effort is put in to 
> ensure that no glitches ever can occur.  Especially nowadays with all 
> the stability, engine and other control stuff run by software, it would 
> be a total disaster for any company if their cars suddenly did something 
> stupid under certain conditions.

I seem to remember a glitch in the ABS system for certain GM vehicles 
many years ago.

>> Entertaining -- it ramped the current up high enough to fry the motor 
>> coils. Oops. I've personally stripped toothed belts bare because of a 
>> software error.
> 
> But if you knew your software was to control something like a car or 
> plane with people in it, you would have course checked and tested your 
> software more thoroughly.  That's my original point, ditto with Andrew's 
> order, if they really cared enough they would have systems in place to 
> make sure that incorrect orders could not be delivered.

In this case it didn't make it to production until it was corrected. We 
really didn't want our customers to have to constantly replace bearings 
and motors. ;)

>> Oh, and most avionics have direct linkage to the controls. The drives 
>> AFAIK are only used in autopilot, so that can be disengaged if 
>> something goes awry.
> 
> Maybe on very small civilian aircraft, but on any passenger carrying jet 
> or military jet the control system is totally electronic with no 
> mechanical linkages.  I suspect it would be near impossible for a person 
> to manually control most planes mechanically, both because of the high 
> forces needed, and the lack of an electronic controller to help keep 
> things stable.
> 
> But usually there are 4 totally separate controllers, so they do have a 
> high degree of redundancy.

Ah, I figured the avionics linkages would be hydraulic, not computer 
controlled.

> about to switch it on, and then as he flicked the switch, the mass moved 
> extremely quickly to point B, past point B, kept accelerating and 
> smashed off the end of the demo. Everybody laughed.

Heh. Ouch...

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