AFRL Demonstrates Pulsed-Thermography Inspection Capability for GLOBUS II

  • Published
  • By Heyward Burnette
  • Materials and Manufacturing Directorate
WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  AFRL performed an on-site pulsed-thermography inspection of the GLOBUS II radar cover, successfully demonstrating the utility of this new inspection technique and training site technicians in the process. As a result of AFRL's engineering expertise in nondestructive inspection (NDI) and thorough analysis conducted throughout the GLOBUS II program effort, the ongoing safe operation of the GLOBUS II radar system remains assured.

The US-developed GLOBUS II radar system serves as part of the 29-sensor, global space surveillance network that provides critical data to US Strategic Command. Located in Vardo, Norway, and operated solely by Norwegian personnel, GLOBUS II radar has proven effective at identifying more than 10,000 man-made objects orbiting the earth. The radar is sheltered by a composite fabric cover manufactured by Saint-Gobain Performance Plastics (Merrimack, New Hampshire). Fabricated in sections joined via hot bonding, the cover is secured to the structure that houses GLOBUS II but otherwise hangs above the radar so that no direct contact occurs. Pressurized air (with effects similar to those of a balloon) keeps the cover suspended over the radar.

AFRL's Structural Materials Evaluation Team supported the recent demonstration by devising and conducting a program to test a robust NDI procedure for evaluating the joined areas (hot-bonded sections) of the radar cover. The procedure employs ThermoScope®II, a pulsed-thermography inspection system manufactured by Thermal Wave Imaging, Inc. ThermoScope II consists of an inspection hood that contains an infrared (IR) camera and high-intensity flash lamps connected directly to a ruggedized laptop computer. During an inspection, the technician places the inspection hood directly on the surface area of interest and applies heat using the flash lamps. The system processes real-time (up to 300 frames per second) IR thermal data for the selected surface, with postprocessing and all applicable results displayed on the laptop. The collected data can effectively identify even subsurface areas that are not bonded; these potential problem areas are then subject to disposition by the responsible engineering authority for repair and/or recurring inspection. This pulsed, or flash-based, method represents the state of the art in thermography-based inspection techniques.

During the demonstration conducted on-site in Vardo, the newly trained Norwegian technicians (all of whom were also certified rope climbers) first assisted in many of the inspections and then went atop the radar cover (a height exceeding 100 ft) to inspect additional areas of interest. While inspection results indicated the presence of unbonded areas in the new cover, radar prime contractor ITT Industries subsequently determined that the size and location of the identified defects posed no threat to the cover's integrity. These specific defects, however, will continue to undergo periodic monitoring. Meanwhile, the entire cover is slated for annual inspection.