Kapton as a standard for atomic oxygen flux measurement in Leo ground simulation facilities: How good is it?

A common method for assessing the Atomic Oxygen (AO) flux in LEO ground simulation facilities is measuring the mass loss of attached Kapton coupon and assuming a known erosion yield of 3x10(-24) cm(3)/O atom. However, in most ground simulation facilities additional components, e.g., UV radiation, excited and ionized oxygen atoms and molecules or reactive volatile products of degraded samples might be involved in Kapton-AO interaction. The present work studies the effect of simultaneous irradiation of AO and other reactive species on the Kapton etching rate. The Kapton mass loss was measured in-situ using Quartz Crystal Microbalanace (QCM). The etching rate was assessed as a function of AO and either VUV radiation, ions, various feed gases, sample temperature or reactive volatile products. X-ray photoelectron spectroscopy (XPS) and Atomic Force Microscopy (AFM) were also applied in order to understand the erosion mechanism involved in the etching rate alteration. The study shows that reactive species (other than AO) present in the ground simulation facilities could lead to substantial errors in the AO flux evaluation. The validity of the use of Kapton as a reference material for ground simulation testing (of spacecraft candidate materials for LEO applications) should be critically reassessed in the context of the present findings.