Enabling Mammalian Cell Culture on ISS

The Atmosphere Control Module (ACM, also known as the CO2 Incubator Controller) is a SABL-insert that adds functionality to control the SABL experiment volume atmosphere to 5% CO2 which is the typical concentration used in Earth-based mammalian cell culture.  The development of ACM has been a major enabler for multiple cell culture studies performed on ISS. Although ambient CO2 levels are typically ~0.04% on Earth and ~0.5% on ISS, the 5% CO2 environment provided by ACM serves two major functions:

  • Moderation of pH. In combination with bicarbonate ions provided in the growth culture, 5% CO2 provides an effective mimic to the bicarbonate pH buffering system found in mammalian blood streams. The buffer system keeps the cell culture pH at a nominal level in the absence of other pH regulating systems, such as the kidneys.
  • Replication of the high CO2 environment found within mammalian body tissue. This high concentration is fundamentally caused by a combination of cellular metabolism and the limited gas transport capability of the blood stream. High concentrations of CO2 can impact cellular metabolism due to competitive enzymatic reaction dynamics (hemoglobin is a well-known example).

The first ACM units flew to the ISS on SpX-9 in 2016. Each ACM unit includes CO2 storage cylinders that periodically release CO2 to maintain the specified atmospheric conditions. New freshly-filled ACM units are flown on a continually-rotating basis as the older ACM CO2 supplies are depleted from experiment usage. At any given time, it is typical for 2 to 3 ACM units to be on-orbit with several more on the ground undergoing refurbishment or supporting R&D work in our lab.


  • Controllable CO2 concentration ranging from ambient (0.5%) up to 8% CO2 (5% typical)
  • Fast CO2 refills following incubator door openings
  • Circulation fan to ensure homogenous CO2 distribution within the experiment volume
  • Environmental monitoring for CO2 and rH
  • Capable of long-term autonomous operation on the order of months before requiring replacement