Pioneer Robot to image-map Chernobyl nuclear unit
On April 26, 1986, the worst nuclear accident in history occurred in Reactor Unit 4 of the Russian Chernobyl power station in the Ukraine, killing 31 people and irradiating thousands. Now, more than ten years later, Unit 4 is still structurally deteriorating. Consequently, it is scheduled to be visually examined by a movable robotic-vision system to scan, detect, and identify structural problems.
To provide a safe, reliable, and effective means to document the state of the reactor, researchers at the Jet Propulsion Laboratory (Pasadena, CA), NASA Ames Research Center (Mountain View, CA), and the Robotics Institute of Carnegie Mellon University (Pittsburgh, PA) have teamed with RedZone Robotics (Pittsburgh, PA) to develop the Pioneer Robot, a remotely controlled machine-vision system for examining the structure of the Chernobyl reactor building.
Scheduled for deployment later this year, the Pioneer Robot consists of a tracked vehicle operated by electric motors that can climb slopes of up to 45. An on-board stereo vision system is slated to acquire range data and color images of two rooms in the reactor facility.
To digitize these stereo images, three CCD cameras are mounted in an L-shaped configuration, protected from radiation by lead shielding. Each camera has an 8-mm-focal-length lens, which, combined with a 1/3-in. CCD sensor, results in an approximately 35 field of view.
"CCD technology has several advantages over competing technologies such as laser scanners, radar sensors, and structured light rangers," says Mark Maimone of the Jet Propulsion Laboratory. "Such systems operate passively and require no moving parts, which makes them better suited for the radiation environment," he adds.
Designing the system to meet the highly hazardous radiation of Chernobyl is a complex task. Each camera is shielded with 1.25-cm-thick lead, which covers the CCD-board camera, lens, and mirror. "This thickness of lead results in a 4X reduction in incident gamma radiation onto the camera," says Maimone. To reduce further the radiation hazards to the CCD, a mirror is placed at a 45 angle in front of the CCD. Incident radiation in the optical path is then reflected off the mirror into the optics, which reduces the incident radiation strength by another four times.
After the stereo images are acquired, they are delivered over a 100-m-long vehicle tether cable to a PC-based frame grabber for digitization. An Onyx graphics workstation from Silicon Graphics (Mountain View, CA) is used for stereo processing and display using software developed by the NASA Ames Research Center and the University of Iowa. The primary goal of the workstation-based cartography system is to integrate an entire set of range and intensity imagery from multiple mapping positions and merge them into a textured, three-dimensional rendering of the target space.
