How many parts are usually replaced on a Space Shuttle Orbiter between flights?
On average about 100 unplanned problem reports of the type requiring a removal or replacement of a Line Replaceable Unit (LRU) level part are initiated on every Space Shuttle orbiter between flights. These 100 LRUs are usually changed out due to failing a test, criteria or some measure of confidence, as part of the process that prepares the systems for a safe next flight. The parts consist of an assortment of items ranging from valves and regulators to major sub-systems such as actuators. The actual parts that fail, or in which confidence has been lost, will vary from flow to flow. The data shown below does not include 2 major sub-systems. One of these systems not included is the Space Shuttle Main Engine (SSME). This removal and replacement of whole engines is, nonetheless, a regular event between flights. The second major system not included in this data is the fragile Space Shuttle orbiter Thermal Protection System (TPS) components – tile, blankets, soft goods, and assorted parts. I
