It has long been known that high levels of carbon dioxide (CO2) in a confined space can be dangerous. But what is often less known is that elevated CO2 levels can increase headaches and lethargy while lowering the ability to concentrate on high-level tasks.
The International Space Station is the epitome of a confined space.
On Earth CO2 is 0.04% of the air’s content (400ppm). NASA had previously set a long-duration spacecraft maximum allowable CO2 concentration of 0.7% (similar to submarines). It was important for them to know what impact this would have on the crew.
While CO2 levels are constantly monitored via wall monitors on the International Space Station (ISS), NASA scientists proposed wearable CO2 monitors for the astronauts to study the effect of long-term exposure to increased CO2 levels over time.
The challenge for NASA scientists was to create a personal CO2 monitor each astronaut could wear for an extended period. There were several key criteria that a wearable CO2 sensor would have to meet:
- It would need long battery life so that data could be logged for an extensive period without recharging.
- The sensor would have to be compact and have a low mass for comfort and convenience.
- A simple data interface would make the data acquired easy to access, while keeping the system development process as short and uncomplicated as possible.
After a comprehensive survey of what products were on the market, NASA scientists chose a solution from SST Sending Ltd and Gas Sensing Solutions (GSS). The two companies worked with NASA during the prototyping phase, providing detailed performance information on the industry-leading CozIR CO2 sensor so that this device could be used with maximum effectiveness in space agency’s personal CO2 monitors.
The CozIR sensor brought several strengths to the table. These low power, high speed non-dispersive infra-red (NDIR) devices can read 0 to 5000ppm (parts-per-million) CO2 with ±5% sensor accuracy. They comfortably support an operational lifespan of 10 years. Important to their suitability was their low power requirements, drawing only 3.5mW at 2 samples per second. Another advantage was the ease of connectivity – with a convenient serial connection facilitating data transfer.
Once the prototype was complete, NASA constructed a custom board for the CozIR sensor. This provided power, processing, data storage and wireless connectivity. The team also designed a housing that could be 3D printed and easily clipped onto the astronaut’s clothing with the sensors worn on their collars.
Using these personal CO2 monitors, it will be possible for simple and unobtrusive tracking of the astronauts’ individual CO2 exposure over an extended period of time. Astronauts can view their own CO2 data via a custom iPad application. In addition, all crew data will be saved and studied by researchers to get a better understanding of the long-term effect of heightened CO2 exposure during space travel. Not only could this prove highly beneficial to the ISS crew, but also for potential future missions to Mars.
The personal CO2 monitors that were developed for this project were transported to the ISS in the spring, with the crew completing proof-of-concept demonstrations soon after. The process of gathering data is now underway, with initial analysis due to take place towards the end of the year.