CHAPTER 6 DAY IN THE LIFE: “BRAIN TRANSPLANTS” ON THE INTERNATIONAL SPACE STATION 110 Flowchart showing the 1-year process required to plan and execute a software upgrade to the major systems on the International Space Station. Each block represents a milestone. The upper-left box indicates how far in advance of the transition (T) the activity should start. The upper-right box indicates when the activities should be complete. In this example, the actual completion dates for the Release 14 update (described below) are indicated in red above each box. Terrestrial computers need to be periodically updated to accommodate new features, fix bugs, or address compatibility issues as other systems evolve over time. Software on the International Space Station (ISS) is no different in that way. Where the software on the ISS does differ is that every vital function of the space station is controlled by a computer and cannot be suspended while software is changed. Critical ISS systems cannot afford to simply wait while updates are applied and computers are rebooted. The two main reasons for updating space station software are to install upgrades for new features and to fix problems. The development of the software was staggered over time, particularly over the ever-changing configuration of the ISS during its construction. There was no point in having software that performed a function—say, controlling a cooling loop or module—when that loop or module was to be installed years down the road. It takes years to design the code to control the space station, and additional years to write and test the software before it is installed. Furthermore, errors can arise from a simple typo when the code was written. Rigorous testing catches the vast majority of these problems. Other errors come from how the coders interpreted a software requirement, or are due to evolution of the team’s thinking as the system matured. If an error is critical, the code will be updated before it is loaded on the space station computers. The update to fix bugs that have a noncritical impact or that the flight team can work around may be made in a subsequent release so as to not impact the schedule. Considerable care in terms of testing, planning, and execution is taken when ISS computers are updated. If done properly, the crew hardly notices any changes. The ISS software was first upgraded in October 2002. At the time, it was the largest software upgrade ever