We all have heard that the smartphone you play Candy Crush on, has more computing power than what was used to put man on the moon.
While true, It was only possible with specific technical requirements that ran 30 volumes and 40,000 pages. A single change required more paperwork than a phone-book ! There were also 4 identical computers that had to agree on every millisecond decision !
At the on-board shuttle group, about one-third of the process of writing software happens before anyone writes a line of code. NASA and the Lockheed Martin group agree in the most minute detail about everything the new code is supposed to do — and they commit that understanding to paper, with the kind of specificity and precision usually found in blueprints. Nothing in the specs is changed without agreement and understanding from both sides. And no coder changes a single line of code without specs carefully outlining the change. 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.
………
As the 120-ton space shuttle sits surrounded by almost 4 million pounds of rocket fuel, exhaling noxious fumes, visibly impatient to defy gravity, its on-board computers take command. Four identical machines, running identical software, pull information from thousands of sensors, make hundreds of milli-second decisions, vote on every decision, check with each other 250 times a second. A fifth computer, with different software, stands by to take control should the other four malfunction.
