It is well know that the elevated satellite operating temperature causes the unused catalyst material in the Room Temperature Vulcanized materials (RTV) to volatize, which can then re-deposit or condense onto other spacecraft surfaces. In the presence of sunlight, this Volatile Condensable Material (VCM) can photo-chemically deposit onto optically-sensitive spacecraft surfaces and significantly alter their original, beginning-of-life (BOL) optical properties, such as solar absorptance and emittance, causing unintended performance loss of the spacecraft. This has been studied in vacuum environments simulating geosynchronous orbits, but never to our knowledge in atomic oxygen environments simulating low earth orbit. In this work we present an initial study of the effect of an atomic oxygen environment on the optical properties of previously photofixed material as well the effect of an atomic oxygen environment on the photofixing process. We will employ spectroscopic ellipsometry to characterize films deposited from the outgassing of DC93500, RTV566, SCV2590, CV2568 and SCV2590-2.
DC-93-500, SCV-2590 and SCV-2590-2 silicone/siloxane based co-polymers serve as adhesive components of
satellites and other spacecraft. It is well known that out gassing of these materials is a major source of
contamination. For the past several years we have been optically characterizing the condensates and their photofixed
films via in-situ ellipsometry and quartz crystal microbalance (QCM) measurements. We have identified several
common outgassed components in each of these materials via FTIR, including polydimethylsiloxane (PDMS), and
Tetra-n-propylsilicate (NPS). We have studied the optical properties of the photofixed films produced at various
wavelengths of incident light , as well as when mixtures of these films are employed as the outgassing source via
variable angle spectroscopy ellipsometry. We can relate the photofixed material optical properties to the bulk liquids
and to the films produced by the outgassssing of the actual co-polymers mentioned above. This work may lead to
the evaluation of the optical properties of the photofixed effluents of actual adhesives by evaluating a few basic
components
Room Temperature Vulcanized (RTV) materials, such as silicone adhesives, are commonly used to bond components of
communication satellites and other types of spacecraft. The elevated satellite operating temperature causes the unused
catalyst material in the RTV to volatize, which can then re-deposit or condense onto other spacecraft surfaces. This
Volatile Condensable Material (VCM) can condense onto optically-sensitive spacecraft surfaces and significantly alter
their original, beginning-of-life (BOL) optical properties, such as solar absorptance and emittance, causing unintended
performance loss of the spacecraft. Knowledge of the optical impact of VCM's is therefore a major concern of spacecraft
designers and spacecraft-contamination engineers. In view of this we have employed in-situ spectroscopic ellipsometry
to monitor in real time the optical constants of the condensed effluent of RTV-566, SCV-2590-2 and SCV-2590 as
function of condensation temperature from 120 K to 180 K. The film is condensed directly on to a QCM crystal. Thus
the QCM generated deposition trajectory and thickness can be correlated to the optical trajectory and thickness, yielding
the film density. We will present the optical constants, n and k, as a function the condensation temperature.
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