TESSELLATOR
The FRC has developed an autonomous inspection and servicing robot for NASA's space-shuttle fleet to inspect and rewaterproof the shuttle's Thermal Protection System (TPS) Tiles.
The scenario envisioned was one of a fully robotic inspection and rewaterproofing of the underside tiles in the Orbiter Processing Facilities (OPFs) at Keenedy Space Center:
The Thermal Protection System was identified as one of the major areas that automation could assist current work flows. Kennedy Space Center is NASA's major launch facility and also performs ground processing for launch vehicles such as the Space Shuttle. The Shuttle is a complex vehicle requiring thousands of inspection, repair and retrofitting tasks. There are 30,000 Tiles covering the orbiter. These tiles protect the orbiter from the extreme heat of re-entry. The type of tile used is determined by heat levels they are subjected to during re-entry. Bottom surface tiles are a ceramic core that can withstand 2000F, wing and aileron edges are composed of a carbon-carbon material and uppersurfaces are covered by ceramic fabrics. A large number of inspection and repair tasks occur when the shuttle arrives back at KSC and enters the Orbiter Processing Facility, or OPF. Technicians carefully inspect gaps and steps between adjacent tiles, replace chipped and damaged tiles, and check for charred materials between tiles. Man-weeks of effort are required for complete inspection and repairs to be completed. The bottom-side tiles are extremely porous. To prevent water absorption the tiles are injected with a chemical through a re-waterproofing process. The chemical is hazardous and requires the use of safety clothing and respirators. It currently takes four days for the rewaterproofing process to be completed and the process occurs every landing of the orbiter. We have identified the re-waterproofing task as the initial application for high payoff automation activity in ground operations. Rationale for process automation includes increase of personnel safety, reduction of tedious manual tasks, process time reduction, reliability increase and paperwork reduction through automatic tracking and updating of tile information. Additionally, these particular tasks were selected because automation will decrease work time, they are step and repeat processes and enabling technologies exist. The robot system was designed for minimal facility impact, the ability to operate in different facilities,and to be easily transported between facilities. The device must be able to handle different process specific tools and sensors and be able to position and orient these devices with respect to the orbiter. The system design is comprised of task specific sensors and tools, a positioning system, navigation sensors, and a control system. We have developed a mobile base with arm, tooling and sensing with SRI and RI, capable of the re-waterproofing tasks and extensible to future TPS work. It is capable of high maneuverability, long reach, precise navigation and accurate positioning of end-of-arm tooling and sensing. The base provides integral power systems for day long operations, a controller system for on-board control and guidance of the robot. The manipulator provides motions outside the footprint of the mobile base to work over obstructions that lie on the floor of the OPF. A telescoping device provides vertical excursion for a planar two degree-of-freedom manipulator holding sensing and tooling. The navigation sensor provides information to the base for accurate positioning within the facility and thus with respect to the orbiter which is fixed in position in the OPF. The use of retroreflective targets and an active scanning device atop the mobile base will provide enough information to locate the base accurately to a desired tile. Onboard sensing will then provide the position lock-in to a specific tile. For local obstacle detection and avoidance low-level bump and proximity sensing have been used. Sensors on the toolplate provide 3-D measurements necessary for characterizing dimensions between tiles. Critical dimensions include the step, or height difference, and gap between tiles. SRI has developed a system consisting of cameras, and structured light devices for this purpose. Preliminary investigation currently shows that structured light provides the best results in comparing resolution, speed, quality, and technology availability. Rockwell International developed the rewaterproofing tool. The system will be delivered to NASA's KSC by summer of 1994, where it will be demonstrated and spend at least an additional year going through the certification process for GSE equipment in Class I, Division II environments. In-service operations for the system are expected by the end of 1995.
