Reduction in the Iodine Content of Shuttle Drinking Water: Lessons Learned

Iodine is the disinfectant used in U.S. spacecraft potable water systems. Recent long-term testing on human subjects has raised concerns about excessive iodine consumption. Efforts to reduce iodine consumption by Shuttle crews were initiated on STS-87, using hardware originally designed to deiodinate Shuttle water prior to transfer to the Mir Space Station. This hardware has several negative aspects when used for Shuttle galley operations, and efforts to develop a practical alternative were initiated under a compressed development schedule. The alternative Low Iodine Residual System (LIRS) was flown as a Detailed Test Objective on STS-95. On-orbit, the LIRS imparted an adverse taste to the water due to the presence of trialkylamines that had not been detected during development and certification testing. A post-flight investigation revealed that the trialkylamines were released during gamma sterilization of the LIRS resin materials. The LIRS effluent water quality was not completely tested after gamma sterilization as previous experience and limited testing suggested that gamma irradiation would not degrade the resins. In addition, concerns about microbial contamination ruled out testing of the flight hardware following sterilization. The lessons learned from the experience were that experiments with the potential to impact the Shuttle life support system should be classified as critical hardware, and that certification testing of all hardware parameters must be carried out in the final flight configuration.