NASA and other space agencies with personnel onboard the ISS (International Space Station) have been dealing with reports from astronauts that they were getting , having trouble sleeping, and other performance problems. After significant research, agencies found this was due to elevated carbon dioxide (CO2) levels on the station. Because of the technological demands and costs associated with lowering CO2 to non-headache-inducing levels, astronauts have been told they will just have to accept these higher levels and the consequences that come with them.

Carbon Dioxide Levels on the International Space Station

When we breathe in, we are primarily trying to take in oxygen (O2), and expel CO2. Our body uses O2 to burn food in our body for energy, taking carbon from our food and turning it into CO2. On the space station, there are many people in a confined area, which leads to a buildup of CO2.

The ISS removes CO2 from the air with three atmosphere processors, two built by NASA and one by the Russians. These atmosphere processors are completely renewable and can run continuously. The only limits on their function are energy demands and wear on the equipment.

With 6 crew members on the ISS, they found that the levels they had been running the processors at was too low, and the CO2 levels regularly exceeded partial pressures of 4 mm Hg (mercury), sometimes for an entire day and reaching short-term levels of 9 mm of Hg. This resulted in increased headaches.

To reduce the incidence of headaches, scientists decided to target an average value of 4 mm Hg of CO2 , hopefully lowering the headache risk from 3.3% per week to 1.6% per week. This decision was made as a compromise. Although one atmosphere processor is capable of keeping CO2 at survivable levels for up to 9 crew members, reducing CO2 levels has costs in terms of resource use, especially power and wear in the equipment. It was determined that reducing the headache risk to 1% would require dropping the CO2 level to 2.5 mm Hg. Although this is technically possible, NASA decided that attaining levels below 3 mm Hg was impractical, so headaches are going to have to come with the job (as they do for many of us who work on screens all day , though those are more likely to be TMJ headaches, which can be treated).

The Coming Headache Plague?

Some of you may be concerned that rising CO2 levels on Earth will lead to increased headaches. This is possible, but it may be a long way off.

Currently, the CO2 levels on Earth just passed 400 ppm (parts per million), which translates to about 0.3 mm Hg. Currently, levels are rising at about 0.7% per year. At this rate, it would take us about 280 years to reach the 1% headache risk threshold of 2.5 mm Hg.

The only problem with this is that the rate at which CO2 levels are increasing is increasing as well. From 2012 to 2013, CO2 levels rose by about 0.4%. If CO2 increases keep increasing at that rate, in just ten years we would be increasing at a rate of about 4% per year. At that rate, we will reach the headache threshold in 55 years, and in 66 years we would have higher levels of CO2 on Earth than on the ISS.

And that would be a big headache.