Background
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, or IBA, will support inspection of the Shuttle's thermal protection system.
General information
The Inspection Boom is based on preexisting hardware from the Shuttle arm program and is essentially the same design except the arm joints are replaced with aluminum transitions, effectively freezing the joints in place. The tip of the boom is 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 is roughly the same dimensions as the Shuttle's remote manipulator Canadarm. Thus, the IBA fits 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 can pick up the IBA using grapple fixtures.
Description of the IBA
The IBA is comprised of the following parts.
Transitions
Each subassembly component or joint of the IBA (known as the forward, mid, and aft transitions) is made up of a cylindrical aluminum extrusion that has been machined to a very fine tolerance. These transitions serve as the structural support between the two booms, as well as the mechanical interface to the grapple fixtures and the sensor suite.
Booms
Graphite-epoxy booms link the forward, mid, and aft joints to the upper and lower arm booms. The upper arm boom is 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 is about six metres long comprising and a third of a metre in diameter with 11 plies of graphite-epoxy and weighing 22 kilograms. Each boom is protected with a Kevlar cover (the same material used in bulletproof vests) to prevent dents or scratches.
Wiring Harness
Just as the arm booms link the forward, mid, and aft transitions mechanically, the electrical cables (wiring harness) links the power systems. The wiring harness routes electrical power, data and video to the sensor suite on the aft joint. This link continues back to the cabin of the Space Shuttle, where astronauts control the actions of the Shuttle's robotic arm.
Grapple Fixtures
The IBA design makes use of existing grapple fixtures on both the forward and the mid transitions. The forward transition sports a modified Electrical Flight Grapple Fixture as an interface to the Shuttle arm. The mid transition has a Flight Releasable Grapple Fixture as an interface to the Space Station arm.
Closed Circuit Televisions (CCTV)
The IBA has no cameras installed along the boom. The Shuttle arm, however, has one at the elbow joint and one at the wrist joint to monitor clearances. The CCTV cameras are used to aid the astronauts in the positioning of the arm and IBA.
Control System
The movement of the IBA is controlled uniquely by the Shuttle arm, which is in turn controlled by the Space Shuttle's general-purpose computer. The hand controllers used by the astronauts tell the computer what the astronauts would like the arm to do. Built in software examines what the astronauts commanded inputs are and calculates which arm joints to move, what direction to move them in and how fast to move them. As the computer issues the commands to each of the joints it also looks at what is happening to each joint every 80 milliseconds. Any changes inputted by the astronauts to the initial trajectory commanded are re-examined and recalculated and updated commands are then sent out to each of the joints. Arm control software parameters are tailored for optimal scanning performance of the IBA operations.
The Shuttle arm control system is continuously monitoring its health, and should a failure occur, the computer will automatically apply the brakes to all joints and notify the astronaut of a failure condition. The control system also provides a continuous display of joint rates and speeds, which are displayed on monitors located on the flight deck in the orbiter. As with any control system, the computer can be overridden and the joints can be operated individually from the flight deck by the astronaut.
Thermal Protection System
The IBA is entirely covered with a multi-layer insulation thermal blanket system, which provides passive thermal control. This material consists of alternate layers of Kapton, Dacron scrim cloth and a Beta cloth outer covering. In extreme cold conditions, thermostatically controlled electric heaters (resistance elements) attached to critical electronic hardware are automatically powered on to maintain a stable operating temperature.
Mission Overview
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