The Spacecraft Water Impurity Monitor (SWIM) seeks to provide enhanced analytical capability that enables NASA to send astronauts on long duration missions to the Moon and Mars without the possibility of returned water samples. The SWIM architecture consists of an Organic Water Module (OWM) and an Inorganic Water Module (IWM), that are independent analytical units but envisioned for complementary use. This paper describes the build and test of developmental hardware for the IWM portion of SWIM. IWM itself has two broad approaches for monitoring potential inorganic contaminants. The first is to develop a portable laboratory style capability that can search for a wide array of potential contaminants in samples, similar to what happens when bag samples are returned to the ground from the ISS. The second approach is to more narrowly focus on potentially high value indicators for continuous or near-continuous real time monitoring. The portable laboratory style capability fundamentally requires a separation science approach in order to specifically separate and detect a wide variety of compounds. IWM developmental hardware is based on capillary electrophoresis (CE) for species separation and capacitively coupled contactless conductivity (C4D) for detection. The CE-C4D hardware was used to broadly separate both common anions (chloride, sulfate, iodide etc.) and cations (sodium, potassium, ammonium, metals, etc.) with the same hardware and reagents. The real-time monitoring capability is based on microfluidic arrays of electrochemical sensors. Specifically, ion selective electrodes (ISEs) and conductivity sensors that can be mated into small volume (microliters) channels for fast measurements. The ISEs can have selectivity for potentially useful general indicators such as pH, sodium and ammonium as well as indicators that might be specific to ion bed breakthrough products like acetate and carbonate. Both capabilities are being matured towards technology demonstration missions and the developmental approach will be outlined.
Noell et al. (Sun,) studied this question.