The Orbiter Boom Sensor System (OBSS) was a 50-foot (15.24 m) boom carried on board NASA's Space Shuttles. The boom was grappled by the Canadarm and served as an extension of the arm, doubling its length to a combined total of 100 feet (30 m). At the far end of the boom was an instrumentation package of cameras and lasers used to scan the leading edges of the wings, the nose cap, and the crew compartment after each lift-off and before each landing. If flight engineers suspected potential damage to other areas, as evidenced in imagery captured during lift-off or the rendezvous pitch maneuver, then additional regions could be scanned. The OBSS was introduced to the shuttle fleet with STS-114, the "Return to Flight" mission executed by Discovery, and was flown on every mission after that until the retirement of the Space Shuttle fleet in 2011. It was used to inspect the shuttle for damage to the heat shield, officially called the Thermal Protection System (TPS), that could jeopardize the shuttle during re-entry. The decision to perform focused inspections of the TPS was prompted by the Space Shuttle Columbia disaster, in which Columbia was destroyed due to damage inflicted to its TPS during launch. The OBSS was central to focused inspections of the TPS, not only because it carried all the instruments necessary for detailed measurements and observations, but also because without it, the Canadarm was too short to reach to all the areas that needed to be surveyed. Description The boom was essentially the same design as the Canadarm itself, except that the articulatory joints are fixed. OBSS arms for the three remaining orbiters were manufactured relatively quickly, primarily because some spare parts for the Canadarm system were used. Two instrumentation packages are installed at the far end of the OBSS. Sensor package 1 consists of the Laser Dynamic Range Imager (LDRI) and an Intensified Television Camera (ITVC). Sensor package 2 is the Laser Camera System (LCS) and a digital camera (IDC). The sensors can record at a resolution of a few millimeters, and can scan at a rate of about per second. It is also fitted with handrails, so that the boom could be used to provide spacewalkers with access to the shuttle's underbelly in case in-flight repairs were required. STS-120 ISS repair During STS-120 the OBSS was used as an extension boom for the space station's Canadarm2,