Speakers
Description
On-orbit inspection of large space structures mostly relies on visual and video checks, which reveal only major visible damage. Subsurface damage such as micrometeoroid and orbital debris impacts, disbonds in thermal protection and solar-array stacks, and thermal-fatigue cracking stays hidden until it affects structural integrity. The ground-based NDT methods that could find this damage largely depend on an active excitation source: flash lamps, heaters, shakers. In orbit, that excitation is limited by the available power, mass and safety budgets. As an alternative, the NASA EVA infrared camera flown on the ISS in 2005 demonstrated that solar heating and shadowing can be used to build a through-thickness temperature gradient suitable for infrared thermography inspection.
This presentation examines whether the orbital thermal environment can act as the excitation for a full-field, non-contact, strain-sensitive inspection. The technique is shearography (speckle-pattern shearing interferometry), which measures surface displacement gradients at the microstrain level. When compared to thermography, shearography inspection results support the assessment of structural integrity and residual life.
Within the ESA OSIP ShearScope project, an orbital sunrise was replicated in the TU Delft Optical Metrology for Aerospace (OMA) laboratory using power-modulated halogen lamps, reaching a temperature change of up to 100 °C. Under this replicated passive excitation, a disbond in an aluminium-cork thermal protection panel and a delamination in a carbon-carbon plate were detected, together with bonding issues in solar-array panels. In addition, FEM analysis was made to support and guide the detection limits of the technique for these materials.
The project presentation is supported with two contributions by MSc researchers. The first addresses the orbital thermal environment and the resulting thermo-elastic response, comparing various orbits and the foreseen temperature gradients to feed a thermomechanical model. The second addresses the inspection of solar arrays, where an orbital heat-flux profile is applied as excitation to detect delaminations, trapped-air bubbles in the adhesive layers and voids in the composite facesheet of a solar-panel. Both MSc projects conclude with simulated shearography phase maps.
We would like to discuss with the thermal engineering community the realism of laboratory-replicated orbital heating, the flux profiles and possible orbital cases. Representative (space-grade) specimens and in-flight thermal data are very welcome to start new collaborations.
This research is performed as part of the ESA OSIP ShearScope project (No. 4000148089).