Schematic of the optical sensor for measuring pretreat concentration. (Image: NASA)

Innovators at the NASA Kennedy Space Center have developed a new optical sensor for measuring concentration in a liquid solution. The sensor was designed for measuring the pretreat solution concentration within the Universal Waste Management System (UWMS), a specialized toilet designed for the International Space Station (ISS) and other future missions. The sensor was developed to replace the current pretreat concentration sensor within the UWMS that uses electrical conductivity instead of light-based methods.

Typical concentration sensors, like the one initially used in the UWMS, rely on changes in electrical conductivity to measure the concentration of a solution. These measurements using conductivity are prone to voltage drift over time, leading to unreliable measurements as the sensor ages. The optical sensor developed here uses light scattering to measure the solution concentration without the issue of voltage drift.

In this sensor, light from a green LED is passed into the sensor housing where it hits a first detector (i.e., a photodiode) to establish a reference of the amount of light before scattering. Simultaneously, the light from the LED scatters through the pretreat solution and then hits a second photodiode to measure the amount of light after scattering. The difference between the amount of light measured by the two detectors is used to calculate the concentration of the pretreat solution (based upon Beers Law).

The optical concentration sensor has been demonstrated to effectively measure pretreat concentrations in both still and flowing liquid conditions and is resistant to contamination issues as necessitated by the UWMS. Using established methodologies and commercial components, the new sensor can precisely measure the concentration or pretreat within the waste treatment solution using the light passed through and scattered by the solution. The optical sensor can be adapted to measure the concentration of solutions across various industries.

NASA is actively seeking licensees to commercialize this technology. Please contact NASA’s Licensing Concierge at This email address is being protected from spambots. You need JavaScript enabled to view it. or call at 202-358-7432 to initiate licensing discussions. For more information, visit here .