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Before every flight, Ted Keller, the senior technical manager of the on-board shuttle group, flies to Florida where he signs a document certifying that the software will not endanger the shuttle. NASA knows how good the software has to be. Even the smallest error in space can have enormous consequences: the orbiting space shuttle travels at 17,500 miles per hour a bug that causes a timing problem of just two-thirds of a second puts the space shuttle three miles off course. Every time it fires up the shuttle, their software is controlling a $4 billion piece of equipment, the lives of a half-dozen astronauts, and the dreams of the nation. The group writes software this good because that’s how good it has to be. In fact, the SEI based it standards in part from watching the on-board shuttle group do its work.
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They work for the “on-board shuttle group,” a branch of Lockheed Martin Corps space mission systems division, and their prowess is world renowned: the shuttle software group is one of just four outfits in the world to win the coveted Level 5 ranking of the federal governments Software Engineering Institute (SEI) a measure of the sophistication and reliability of the way they do their work. This software is the work of 260 women and men based in an anonymous office building across the street from the Johnson Space Center in Clear Lake, Texas, southeast of Houston. Commercial programs of equivalent complexity would have 5,000 errors. The last 11 versions of this software had a total of 17 errors. Consider these stats : the last three versions of the program - each 420,000 lines long-had just one error each. It is perfect, as perfect as human beings have achieved.
What makes it remarkable is how well the software works. When the software is satisfied with the shuttle’s position in space, it orders the main engines to shut down - weightlessness begins and everything starts to float.īut how much work the software does is not what makes it remarkable. It keeps track of where the shuttle is, orders the solid rocket boosters to fall away, makes minor course corrections, and after about 10 minutes, directs the shuttle into orbit more than 100 miles up. The software throttles the engines to make sure the craft doesn’t accelerate too fast. The software gives the orders to gimbal the main engines, executing the dramatic belly roll the shuttle does soon after it clears the tower.