[dpitkin]

I think I read this from HN but I use this as the best example of mission critical software, the Space Shuttle at NASA.

The most important things the shuttle group does -- carefully planning the software in advance, writing no code until the design is complete, making no changes without supporting blueprints, keeping a completely accurate record of the code -- are not expensive. The process isn't even rocket science. Its standard practice in almost every engineering discipline except software engineering.

http://www.fastcompany.com/28121/they-write-right-stuff

[JoeAltmaier]

But most engineering projects don't have hundreds of millions of moving parts. At that scale, standard practice becomes intractable.

The Space Shuttle went up the first time with a few K of core memory. The software effort was really pretty trivial compared with systems today.

[dpitkin]

The article is from 1996 but even then they were far beyond a few K.

"Take the upgrade of the software to permit the shuttle to navigate with Global Positioning Satellites, a change that involves just 1.5% of the program, or 6,366 lines of code. The specs for that one change run 2,500 pages, a volume thicker than a phone book. The specs for the current program fill 30 volumes and run 40,000 pages."

[JoeAltmaier]

The brain of NASA’s primary vehicle has the computational power of an IBM 5150, that ’80s icon that goes for $20 at yard sales. According to NASA and IBM, the shuttle’s General Purpose Computer (GPC)—which controls, among other things, the entire launch sequence—is an upgrade of the 500-kilobyte computer the shuttle flew with until 1991.

  --  http://www.popsci.com/node/31716

[JoeAltmaier]

My point exactly. That process can't work unless you have millions to spend.

[roedog]

This process results in low bug counts. But, even then, NASA still programs the software to accept patches as they fly.

I don't know how applicable the NASA way is to commercial firms. They have different goals. National Mission Success vs. shareholder returns. The commercial firms are still making money and happy shareholders with a lot of bugs. While a single unit conversion bug on the Mars Climate Orbiter resulted in the loss of a multi-billion dollar spacecraft.