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Cryodeposit Mitigation and Removal Techniques for Radiometric Calibration Chambers


OBJECTIVE: Develop materials and instruments for cryodeposit mitigation and removal in radiometric calibration chambers. DESCRIPTION: A better understanding of the cryodeposition process is required such that techniques can be developed to successfully remove cryodeposits that can be such a problem in test chamber performance. Water ice layers on the order of 100nm (and greater) can significantly affect the performance of an optical component. At some thickness (highly dependent upon temperature) there is a conversion from a transparent film to a highly scattering form. If the transition is thermally induced due to an increase or decrease of the substrate/film temperature, it may be correlated to a phase change in the ice from amorphous to a crystal state or from one crystal state to another which leads to a density gradient in the ice, while a non-thermally induced (i.e. thickness induced) transition could be the result of stresses from the changing density of the ice and the difference in elastic properties between ice films and the underlying substrate. Prevention of cryodeposits could possibly be accomplished by various means that minimize the sticking coefficients of critical surfaces (hydrophilic coatings, helium curtain, electromagnetic fields, etc.). Removal of water cryodeposits can be accomplished by desorption of the water molecules. There are different types of desorption including, among others, thermal and photo-induced (using various wavelength regions) that have been evaluated. Other techniques may exist that can also accomplish the removal of these cryodeposits. The removal of other, more complex contaminants shall also be investigated. A removal system is needed that will not contaminate the chamber directly through its use, and can be used in the chamber"s cryogenic environment. The removal process can be utilized during the cryo pumpdown, but only at non-test times when radiometric data are not being acquired. The system must be of such a size that it does not impact the optical or other chamber systems. It must not contaminate or otherwise damage the targeted optical element or the System Under Test (SUT). PHASE I: Identify cryodeposition mechanisms and phenomenology specific to optical and mechanical substrates used in cryo-vacuum test chambers. Investigate prevention mitigation, and removal techniques. Develop plan for prevention, mitigation, and removal. PHASE II: Develop materials and instruments to minimize and address cryodeposit formation in cryo-vacuum test chambers. Demonstrate technology in cryo-vacuum test chamber environment or facsimile (<77 K, 10-6 Torr) for water and complex molecules (hydrocarbon or silicone) deposition. PHASE III: Transition technology to Air Force cryo-vacuum test chambers. Other transition partners might include: NASA, Raytheon, Ball Aerospace, Kinetic Kill Vehicle-in-the-Loop Simulator (KHILS), Johns Hopkins University Applied Physics Lab, MIT Lincoln Labs, Alliant Techsystems, Inc (ATK). REFERENCES: 1. Andersson S. and van Dishoek E.F. Photodesorption of Water Ice [Journal]. - Leiden : Astronomy and Astrophysics, 2008. - Vol. 491. 2. Drobyshev A. [et al.] Thermal Desorption and Spectrometric Investigation of Polyamorphic and Polymorphic Transformations in Cryovacuum Condensates of Water [Journal]. - Almaty : Low Temperature Physics, 2007. - 5 : Vol. 33. 3. Focsa C., Chazallon B. and Destombes J.L. Resonant Desorption of Ice with a Tunable LiNbO3 Optical Parametric Oscillator [Journal]. - Lille : Surface Science, 2003. - Vol. 528. 4. Krasnopoler A. and George S.M. Infrared Resonant Desorption of H2O from Ice Multilayers [Journal]. - Boulder : Journal of Physical Chemistry B, 1998. - Vol. 102. 5. J. Labello,"Water Ice Films in Cryogenic Vacuum Chambers,"Ph.D. Dissertation, The University of Tennessee Space Institute, Dec. 2011.
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