Bubble Growth from Permeation of Cabin Air into FEP Water Bladders Stowed on the International Space Station

Iodine-Compatible Contingency Water Containers (CWC Is) are used to transport water to the International Space Station (ISS) and store it on-board. The containers can be stored on-orbit for more than a year before their water is needed for use in the ISS potable water system (PWS).

Each CWC I is fabricated from two 18.5 by 22.5 inch 5 mil FEP Teflon sheets that are heat sealed to form a bladder. Each CWC I holds up to 21.3 liters of water.
Despite the fact that the CWC Is have minimal free air when launched, it has been found that more than 1 liter of air can be present in the CWC Is when their contents are needed. Because the potable water system cannot tolerate large amounts of air, the CWC Is must be vented by manually centrifuging the bag to agglomerate the air and locate it at the fill/drain port. The air is then be vented into a towel before the CWC I is attached to the PWS.

The present work explores the physics of the on-orbit air ingestion. The results of subscale ground and flight tests of air ingestion are combined with the physical analysis to predict the on-orbit CWC I air ingestion rate. The predicted air ingestion rate is found to agree well with on-orbit observations of CWC I air ingestion.