Radiation Testing of Thermal Control Thin Films
Christian Ranzenberger
RUAG Space GmbH, Vienna, Austria
Abstract
Multi-layer insulation (MLI) forms to a great extent the outer barrier of a satellite towards space. Thin Polymer foils, which are used in MLI blankets, have to endure the harsh space environment for mission duration often lasting well above ten years. Thermo-optical but also mechanical properties suffer or change because of radiation exposure.
Complete MLI stacks, which were composed of thicker outermost layers and up to seven thin internal layers separated by non-woven spacers, were irradiation tested.
After initial screening tests on individual foils, space environmental tests were performed. The campaign involved vacuum thermal-cycling and exposures to UV-radiation, electrons and protons simulating a 15 year GEO mission.
Outer layer test candidates were an alternative 25µm black Polyimide (PI), a white PI, 25µm Polyether-ether-ketone (PEEK) and Kapton HN as the reference material.
For materials composing the internal MLI stack 6µm aluminized (VDA) PET -i.e. Mylar®- foil and an 8g/m² polyester spacer were chosen. These two standard internal MLI materials were compared to their thinner derivatives consisting of 3µm VDA/PET/VDA and a 4g/m² polyester spacer as well as to novel thin films made of 3µm VDA/ Polyethylennaphthalat (PEN) /VDA and 6µm VDA/PEEK/VDA.
Solar Absorptance was measured at the beginning and end of test, as well as at various stages in-situ during the exposures. Thermal emittance was measured ex-situ. Out of the tested MLI stacks samples were tensile tested to determine exposure influence on foil mechanical properties by comparison to pristine and reference materials.
This presentation outlines the test campaign performed, the test results achieved and discusses the conclusions derived.