Total Organic Carbon Analyzer Monitoring Astronaut Drinking Water on ISS
Potable Water Analyzer
The Total Organic Carbon Analyzer (TOCA) is a potable water analyzer aboard the International Space Station (ISS). Most of the drinking water on the ISS is reclaimed, meaning wastewater must be cleaned with TOCA serving as a control to ensure the water has been successfully processed and is safe for astronauts to drink. The water analysis data collected by TOCA is sent to Mission Control and monitored by personnel at NASA’s Lyndon B. Johnson Space Center. Multiple TOCA Protoflight Units (PFUs) have flown aboard the ISS, from PFU1 to PFU4. TOCA PFU3 currently serves as the primary water analyzer downstream from the Water Processor Assembly (WPA) and is used weekly by astronauts aboard the station.
Lessons learned during the deployment of TOCA PFU1 influenced design changes that were instrumental in the development of PFUs 2-4; specifically, the implementation of a new non-toxic method of analyzing levels of Total Organic Carbon (TOC) present in water. TOCA PFU2 was assembled and tested in 2008-2009 and flew to the ISS aboard Space Shuttle Discovery’s 39th and final mission on February 24, 2011. PFU2 served as the primary TOCA from 2013 to 2022, almost double its required lifespan of five years. After spending 9 years in space and completing 527 water analyses, TOCA PFU2 was sent back to Earth when the ISS Program decided to refurbish the unit and bring it back to life.
With the primary TOCA PFU3 (and backup PFU4) on station, a plan was developed to rebuild PFU2. This involved replacing and refurbishing approximately 26 components within the custom designed chassis. Inside the chassis is a gas loop, liquid loop, and an electronics module connected with hundreds of feet of wires and tubing. The refurbishment process required precision disassembly and reassembly - navigating the complex design of a microgravity-capable TOC analyzer. The TOCA project is currently putting the refurbished unit through functional checkouts, which involves performing water analyses to ensure that the system can achieve its functional requirements. Once complete, TOCA PFU2 will serve as a spare for PFUs 3 and 4 for the remaining operation of the ISS.
Total Organic Carbon Analyzer
