269 DAY IN THE LIFE: IN-FLIGHT MAINTENANCE CHAPTER 16 function properly. Examples of such components include hatches, portable breathing masks, and other emergency equipment. Finally, hardware may simply break unexpectedly and will need to be fixed for a certain component or system to be returned to operational use. When hardware fails on the space station, the way it fails or breaks may not have been envisioned when the hardware was being designed. All of this work falls in the realm of in-flight maintenance (IFM). IFM occurs both inside and outside of the ISS. The primary focus of this chapter is the internal IFM, which is managed by the Operations Support Officer (OSO) console. External maintenance, which might include replacing a cooling pump or installing power cables, is managed by the extravehicular activity (EVA) console and is discussed in detail in Chapters 17 and 18. The three categories of IFM include: Preventive Maintenance, Corrective Maintenance, and Diagnostic Maintenance. Preventive Maintenance entails all of the regular cleanings and inspections that are performed to ensure the proper operation of the hardware or system. Corrective Maintenance involves repairing or replacing hardware that has stopped working either because it is a consumable at the end of its life (e.g., a filter) or because it has broken unexpectedly (e.g., a light bulb or computer). Sometimes, hardware or equipment breaks and it is not obvious what has broken, especially in electronic equipment. In these cases, Diagnostic Maintenance is first required to determine where faults might be located, and to help ground teams establish the best way to repair the hardware or situation. Maintenance Methodology To the maximum extent possible, all ISS maintenance procedures are thoroughly reviewed and validated on mock-ups or flight-like hardware before the crew performs any procedures. OSO flight controllers, assisted by the necessary engineering specialists, develop methods and procedures for all maintenance tasks inside the ISS—from accessing and cleaning a filter, to the complicated replacement of a valve in the Carbon Dioxide Removal Assembly. Whenever possible, these procedures are tested on the ground prior to being given to the crew to ensure the correct tools are called out and that no unexpected problems occur while accessing certain areas, and to look for any hidden “gotchas” throughout the maintenance activity. Such procedures “walk” the ground teams and the crew through every aspect of maintenance activities. The general flow of these procedures is to gather the needed tools and spare parts, turn off the power to the equipment, access the equipment being maintained, perform the maintenance, clean up and close out the workspace, and finally turn everything back on and ensure the hardware is functioning properly. Some aspects of ISS maintenance are similar to the maintenance done at home, or in automotive or aircraft repair facilities. Crews use standard hand tools to remove bolts and other fasteners to access broken components. They remove failed components and replace them with spare parts, then put the equipment back together using a torque wrench to ensure every fastener is tightened properly. In some instances, a good pair of pliers will help move a stubborn panel or a bent fastener. Given that astronauts all have varying degrees of experience in tools and maintenance, each crew member participates in maintenance training lessons that range from tool identification to performing complex maintenance operations on jet aircraft hardware. They also receive instruction on soldering, sewing, using a rivet gun, replacing Ethernet connectors, and creating wire jumpers and splices, not to mention the use of items such as a tap and die kit, driver drills and impact drills, and screw extraction kits. The ISS is stocked with a wide variety of spare parts and tools because resupply from Earth is difficult, expensive, and time consuming. The tool inventory on board includes an array of hand tools, repair kits, and a number of specialty tools such as multimeters, pressure and temperature monitors, oscilloscopes, borescopes, and fiber optic diagnostic systems. Table 1 provides a summary of the maintenance tools and kits available for use in the US Segment of the ISS. Maintenance and system upgrades on Earth often generate stories worth retelling, both when things go right and when things do not go quite as anticipated. What follows are a few of these stories to describe the implementation of some of the different types of maintenance performed on the space station.