During the COLUMBUS C/D Phase, the suitable concentration (from 25 to 90 [ppm]) of antimicrobial Ortho-Phthalaldehyde (OPA) to be included into the Columbus Active Thermal Control Subsystem (ATCS) loop to minimize the risk of microbial growth and respectively the generation of a bio-film was defined.
A first coolant sample was returned to ground with Flight 1E. Its analysis showed an OPA content of 47.4 [ppm]. The analysis of a second coolant sample, returned to ground with the Flight 1JA revealed a maximum OPA level lower than 10.1 [ppm], far below the required minimum threshold of 25 [ppm].
This depletion, faster than expected, leads to the necessity of an anticipated OPA build-up into the Columbus water loop. This kind of activity was preceded by a proper preparation from configuration, hydraulic, logistic, operation and safety points of view and then actuated in November 2008.
Detailed hydraulic analyses were performed in the frame of the preparation phase to prevent any issue during the OPA replenishment and to assure an appropriate OPA dilution in all the ATCS loop branches. In addition, to face with the observed fast OPA depletion it was decided to waive the maximum concentration requirement through the release of a higher anti-microbial concentration (300 [ppm]). To support the waiver some material compatibility analyses were performed with successful results.
The equipment required for the OPA replenishment as well as the OPA itself, was provided by NASA.
The following paper provides an overview of the engineering evaluations developed to support the installation and usage of the Antimicrobial Applicator (AmiA) containing the OPA.