John W. Steele

Performance of the Extravehicular Mobility Unit (EMU) Airlock Coolant Loop Remediation (A/L CLR) Hardware

An EMU water processing kit (Airlock Coolant Loop Recovery A/L CLR) was developed as a corrective action to Extravehicular Mobility Unit (EMU) coolant flow disruptions experienced on the International Space Station (ISS) in May of 2004 and thereafter. Conservative schedules for A/L CLR use and component life were initially developed and implemented based on prior analysis results and analytical modeling. The examination of postflight samples and EMU hardware in November of 2006 indicated that the A/L CLR kits were functioning well and had excess capacity that would allow a relaxation of the initially conservative schedules of use and component life. A relaxed use schedule and list of component lives was implemented thereafter. Since the adoption of the relaxed A/L CLR schedules of use and component lives, several A/L CLR kit components, transport loop water samples and sensitive EMU transport loop components have been examined to gage the impact of the relaxed requirements. The intent of this paper is to summarize the findings of that evaluation, and to outline updated schedules for A/L CLR use and component life.

Selection of an Alternate Biocide for the ISS Internal Thermal Control System Coolant - Phase II

The ISS (International Space Station) ITCS (Internal Thermal Control System) includes two internal coolant loops that utilize an aqueous based coolant for heat transfer. A silver salt biocide had previously been utilized as an additive in the coolant formulation to control the growth and proliferation of microorganisms within the coolant loops. Ground-based and in-flight testing demonstrated that the silver salt was rapidly depleted, and did not act as an effective long-term biocide. Efforts to select an optimal alternate biocide for the ITCS coolant application have been underway and are now in the final stages. An extensive evaluation of biocides was conducted to down-select to several candidates for test trials and was reported on previously. Criteria for that down-select included: the need for safe, non-intrusive implementation and operation in a functioning system; the ability to control existing planktonic and biofilm residing microorganisms; a negligible impact on system-wetted materials of construction; and a negligible reactivity with existing coolant additives. Candidate testing to provide data for the selection of an optimal alternate biocide is now in the final stages. That testing has included rapid biocide effectiveness screening using Biolog MT2 plates to determine minimum inhibitory concentration (amount that will inhibit visible growth of microorganisms), time kill studies to determine the exposure time required to completely eliminate organism growth, materials compatibility exposure evaluations, coolant compatibility studies, and bench-top simulated coolant testing. This paper reports the current status of the effort to select an alternate biocide for the ISS ITCS coolant. The results of various test results to select the optimal candidate are presented.

Corrosion Testing of Brazed Space Station IATCS Materials

Increased nickel concentrations in the IATCS coolant prompted a study of the corrosion rates of nickel-brazed heat exchangers in the system. The testing has shown that corrosion is occurring in a silicon-rich intermetallic phase in the braze filler of coldplates and heat exchangers as the result of a decrease in the coolant pH brought about by cabin carbon dioxide permeation through polymeric flexhoses. Similar corrosion is occurring in the EMU de-ionized water loop. Certain heat exchangers and coldplates have more silicon-rich phase because of their manufacturing method, and those units produce more nickel corrosion product. Silver biocide additions did not induce pitting corrosion at silver precipitate sites.

Selection of Environmentally Friendly Solvents for the Extravehicular Mobility Unit Secondary Oxygen Pack Cold Trap Testing

SUMMARY BAD FOR GOOD FOR BAD FOR GOOD FOR BAD FOR GOOD FOR → NVR NVR NVR NVR NVR NVRBAD FOR BAD FOR BAD FOR GOOD FOR GOOD FOR GOOD FORFTIR FTIR FTIR FTIR FTIR FTIRBAD FOR GOOD FOR BAD FOR BAD FOR BAD FOR GOOD FORREACTOR REACTOR REACTOR REACTOR REACTOR REACTORFINAL FINAL FINAL FINAL FLUSH FINAL FINAL FLUSHFLUSH FLUSH FLUSH FLUSHClass I or II No No No No No YesODS?Initial HC – HC – Good HC – HC – Excellent HC – HC –Solvency Excellent (light HC) Excellent FC - Good Excellent ExcellentData Review FC – FC – FC - Good FC - Good FC - Good(HC & FC) Excellent ExcellentBackground 0.77 mg/100 < 0.01 0.54 mg/100 0.24 mg/100 ml 680 mg/100 < 0.01 mg/100NVR ml mg/100 ml ml (borderline) ml ml(pre- (appears todistillation) decompose)Background Totally High High Minimal Minimal MinimalIR at 2920 masks background background background background backgroundcm-1 (pre-distillation)Background 0.38 mg/100 < 0.01 N/A N/A Not done. N/ANVR ml mg/100 ml (appears to(post- Still too high, decompose)distillation) butdistillationshowspromise –but addssignificanttimeBackground Totally High High N/A N/A N/AIR masks. background. background.At 2920 cm-1 CH stretch CH stretch CH stretch(post- inherent in inherent in inherent in thedistillation) the base the base basemolecule. molecule moleculeOSHA TLV 200 ppm 600 ppm 50 ppm 25 ppm Not 1000 ppmJSC restricted JSC restricted Establishedmaterial list – material list – (health ratingwant to want to minimize = 1)minimize use use volume. 1 = minimalvolume. Reactor use concernReactor use undesirable.undesirable.GWP 806 397 9 9 Not(relative to Established 6000CO2) (low VP 10mm Hg)

Hydrophilic, Biocidal Coating for Condensing Heat Exchangers

Active environmental control systems for manned spacecraft and future lunar or planetary bases will need condensing heat exchangers to control humidity. Condensing surfaces must be hydrophilic to ensure efficient operation and biocidal to prevent growth of microbes in the moist, condensing environment. The coatings must be extremely stable and adhere to the condensing surface for many years. This paper describes the ongoing development of an innovative surface coating that has proven to be highly biocidal, hydrophilic, and stable. The coating can be applied to conventional heat exchanger structures. Early tests have shown excellent adhesion, stability, and biocidal properties. Long-term tests are underway to evaluate the coating’s behavior after exposure to simulated condensing environments.