The Orbiter Boom Sensor System (OBSS) is a 50-foot boom carried on board NASA's Space Shuttles. The boom can be grappled by the Canadarm and serves as an extension of the arm, doubling its length to a combined total of 100 feet. At the far end of the boom is 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 suspect potential damage to other areas, as evidenced in imagery captured during lift-off or the rendezvous pitch maneuver, then additional regions may 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 since. It is used to inspect the shuttle for damage to the heatshield, officially called 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 a shuttle was destroyed due to damage inflicted to the heatshield during lift-off. The OBSS is central to focused inspections of the TPS, not only because it carries all the instruments necessary for detailed measurements and observations, but also because without it the Canadarm is too short to reach to all the areas that need to be surveyed.

Description

The boom is 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 2.5 inches (6.3 centimeters) 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 are required.

STS-120 ISS repair

During STS-120 the OBSS was used as an extension boom for the space station's Canadarm2, something it was never designed to do. During this mission the P6 solar array had become damaged during the redeploy. Canadarm2 grabbed the arm on its center grapple fixture and then astronaut Scott E. Parazynski was mounted at the end of the boom to make the repair. Because Canadarm2 is unable to power the OBSS it was without power many hours more than it was designed to handle, but because it was heated up considerably before the start of the repair it stayed undamaged.

Future of OBSS on ISS

Due to the benefits for spacewalkers from the extended range provided by connecting an OBSS to the International Space Station's robotic arm, NASA has approved a plan for leaving an OBSS behind on the ISS following the last space shuttle flight. The plan calls for a number of modifications to the OBSS, including the modification of the Shuttle grapple fixture on the end of the boom with a SRMS-compatible PDGF.

References

1. NASA: Shuttle in Shipshape: Part II
2. CSA: Inspection Boom by MDA: One of critical Canadian tools that serves the return to flight

External links

• NASA -Space Shuttle page