The Inspection Boom and the Laser Camera System
The Inspection Boom by MacDonald, Dettwiler and Associates Ltd. (MDA): A Critical Canadian Tool that Served the Return to Flight and Beyond
Following the Columbia shuttle accident in early 2003, the Columbia Accident Investigation Board (CAIB) was formed to mandate improvements to the Shuttle Program. One of the requirements was a way for NASA to inspect the underside of the Shuttle before reentry.
Building on the technology and experience acquired by MDA in building several generations of space-borne manipulators, MDA developed an extension to the Space Shuttle's robotic arm to perform on-orbit inspections of the Shuttle's thermal protection system. The Inspection Boom Assembly's (IBA) main role was the inspection of the Shuttle's thermal protection system.
The Inspection Boom was based on preexisting hardware from the Shuttle arm program and is essentially the same design except that the arm joints were replaced with aluminum transitions, effectively freezing the joints in place. The tip of the boom was designed to accommodate and interface with a suite of sensors to assess the Orbiter's thermal protection system.
Weighing 211 kilograms (excluding sensors), and nearly 15 metres long, the IBA had roughly the same dimensions as the Shuttle's Canadarm. Thus, the IBA fit neatly on the starboard side of the Shuttle, where a holding mechanism was originally designed to support a second arm. Once in orbit, the Shuttle arm and the Space Station's Canadarm2 would pick up the IBA using grapple fixtures.
Description of the IBA
Each subassembly component or joint of the IBA (known as the forward, mid, and aft transitions) were made up of a cylindrical aluminum extrusion that had been machined to a very fine tolerance. These transitions served as the structural support between the two booms, as well as the mechanical interface to the grapple fixtures and the sensor suite.
Graphite-epoxy booms linked the forward, mid, and aft joints to the upper and lower arm booms. The upper arm boom was about five metres long by a third of a metre in diameter comprising 16 plies of graphite-epoxy (each ply is a millimetre thick) for a total weight of about 22 kilograms. The lower arm boom was about six metres long and a third of a metre in diameter with 11 plies of graphite-epoxy and weighing 22 kilograms. Each boom was protected with a Kevlar cover (the same material used in bulletproof vests) to prevent dents or scratches.
Just as the arm booms linked the forward, mid, and aft transitions mechanically, the electrical cables (wiring harness) linked the power systems. The wiring harness routed electrical power, data and video to the sensor suite on the aft joint. This link continued back to the cabin of the Space Shuttle, where astronauts controlled the actions of the Shuttle's robotic arm.
The IBA design made use of existing grapple fixtures on both the forward and the mid transitions. The forward transition sported a modified Electrical Flight Grapple Fixture as an interface to the Shuttle arm. The mid transition had a Flight Releasable Grapple Fixture as an interface to the Space Station arm.
Closed Circuit Televisions (CCTV)
The IBA had no cameras installed along the boom. The Shuttle arm, however, had one at the elbow joint and one at the wrist joint to monitor clearances. The CCTV cameras were used to aid the astronauts in the positioning of the arm and IBA.
The movement of the IBA was controlled by the Shuttle arm, which in turn was controlled by the Space Shuttle's general-purpose computer. The hand controllers used by the astronauts told the computer what the astronauts would like the arm to do. Built-in software examined what the astronauts commanded inputs were and calculated which arm joints to move, what direction to move them in and how fast to move them. As the computer issued the commands to each of the joints it also looked at what was happening to each joint every 80 milliseconds. Any changes inputted by the astronauts to the initial trajectory commanded were re-examined and recalculated and updated commands were then sent out to each of the joints. Arm control software parameters were tailored for optimal scanning performance of the IBA operations.
The Shuttle arm control system was continuously monitoring its health, and should a failure have occured, the computer would automatically apply the brakes to all joints and notify the astronaut of a failure condition. The control system also provided a continuous display of joint rates and speeds, which were displayed on monitors located on the flight deck in the orbiter. As with any control system, the computer could be overridden and the joints could be operated individually from the flight deck by the astronaut.
Thermal Protection System
The IBA was entirely covered with a multi-layer insulation thermal blanket system, which provided passive thermal control. This material consisted of alternate layers of Kapton, Dacron scrim cloth and a Beta cloth outer covering. In extremely cold conditions, thermostatically controlled electric heaters (resistance elements) attached to critical electronic hardware were automatically powered on to maintain a stable operating temperature.
Neptec's Laser Camera System
Neptec's Laser Camera System (LCS) was installed on the end of Canadarm's extension boom for the Return to Flight mission in 2005 and all subsequent shuttle missions. It was a wide angle, high-speed, high-precision, laser scanner that was used to inspect hard-to-reach areas on the underside of the Shuttle that could not otherwise be viewed from the Shuttle. The scanner gave NASA the ability to detect even fine cracks in the thermal tiles that would have proven fatal to the Shuttle during re-entry from orbit.
The LCS used a synchronized scanning technique, patented by the National Research Council of Canada, to generate high precision three-dimensional data. At distances of up to 10 metres, it would create a model of any object accurate to a few millimetres. The LCS was the first three-dimensional laser scanner to be space-qualified. The LCS was developed by Neptec from a scanner that was originally tested in 2001 on Shuttle flight STS-105.
The LCS offered a significant advantage over a traditional video camera because it not only provided full three-dimensional surface information, but it was also immune to the effects of changing lighting conditions. This immunity was very important since the sun rises and sets 16 times a day in low-Earth orbit.
The LCS's range of space applications also included the ability to track and calculate the position and orientation of objects in space. In this mode, the LCS could be used to guide space robots such as the Canadarm and Canadarm2, or as a sensor to guide spacecraft as they manoeuvred to dock with one another in space.
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