Design of an On-orbit Point-of-use Adsorbent Filter for the Extravehicular Mobility Unit Influent Feed-water

Trace film-forming organic contaminants in water have historically been shown to adversely impact EMU (Extravehicular Mobility Unit) Sublimator performance. EMU feed-water quality requirements and strict controls over wetted materials used for feed-water storage and transfer are in place to minimize the risk of introduction of such contaminants. These controls are becoming increasingly difficult to manage for the ISS (International Space Station) mission where the EMU hardware must be repeatedly recharged on-orbit for up to 6-years with feed-water, most of which will be generated or provided from new sources. The supply of water on orbit that was previously transferred from the Space Shuttle to PWR (potable water reservoir) storage containers had previously been under increased scrutiny due to water quality concerns. In one case, EMU hardware (SEMU 3015) feed-water was found to have out-of-family contaminants (polyamides, siloxanes, organic acids) in water supplied from on-orbit stored water. SEMU 3015 experienced Sublimator performance problems on its first EVA which led to the hardware being returned to the ground for refurbishment after only one use The source of the polyamides, siloxanes and organic acids was never determined, but the on-orbit storage containers and transfer lines remain candidates for the source of the contaminants. Efforts are underway to develop an on-orbit scrubber bed for EMU feed-water to circumvent such risks in the future. The scrubber bed is envisioned as being external to the EMU and used to purify all water as it is charged into the EMU feed-water bladders. A sorbent or sorbents would be selected to remove relatively high molecular weight film-forming organic compounds of the type known to adversely impact Sublimator performance. The intent of this paper is to provide a status of efforts to identify the optimal adsorbent material/materials for this application and to detail the design activity underway relative to implementation.