Browse Publications Technical Papers 2001-01-2337
2001-07-09

Preliminary Assessment of Microbial Adhesion on the Surface of Materials from the ISS Internal Thermal Control System: Results of an Accelerated 60-d Study 2001-01-2337

The internal thermal control system (ITCS) in the International Space Station (ISS) is a closed loop that circulates an aqueous fluid that provides a constant temperature coolant supply to the equipment, payloads, and the avionics loop. The ITCS fluid was formulated to perform this function without compromising the health of the crew in the unlikely event of a leak into the cabin. It was also designed to control the microbial population by maintaining a high pH (approximately 9.4), limiting the amount of total organic carbon (<5 ppm), and using silver (approximately 2 ppm) as a biocide. A flight-like test facility for conducting a 3-yr study was developed by NASA Marshall Space Flight Center (MSFC) to simulate the conditions in the ISS moderate temperature ITCS. The 3-yr study, begun in August 2000, will provide information about the long-term effects of microbial growth on representative ITCS material.
In addition to the 3-yr study, a short-term test to evaluate the effects of microbial attachment on the ITCS materials was developed by MSFC and Altran Corporation. For this test, coupons of the materials of construction were exposed to test fluids for a period of 60 d. Open cell potentials were monitored daily and cyclic polarization data were obtained at d 0, 30, and 60. This provided information on the susceptibility of the coupons to pitting-type corrosion upon exposure to the test solutions (with and without bacteria). Scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDS) was performed on coupons to provide quantitative information on topography, corrosion-product formation, and metal loss. Total and viable bacterial assays, as well as total biomass assays (carbohydrate and protein), were performed on a biweekly basis, providing a measure of fouling potential under simulated in-use conditions. This paper addresses the test setup, procedures, and results of the 60-d study of the ITCS material.

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