Exercise is a crucial ingredient for astronauts to maintain some semblance of their physiological well being and if you can combine that with exposure to artificial gravity then all the better. Enter the Human Powered Centrifuge (HPC), possibly destined for the International Space Station (ISS). It's an un-stationary bicycle that when pedaled spins around generating artificial gravity. Problem solved, right? Not so fast - nothing in space is that easy. When exercising, astronauts generate up to two times more carbon dioxide (CO2) than when relaxing and that level of CO2 could potentially cause problems for the sensitive ISS life support system. What to do? CFD to the rescue.

In the study "Computational Fluid Dynamics Ventilation Study for the Human Powered Centrifuge at the International Space Station", Chang H. Son performed a CFD analysis of the HPC in the presence of two CO2 generating astronauts - the exerciser and an observer. While increased levels of CO2 were predicted in and around the HPC, the action of the rotating bicycle was found to be beneficial in dispersing the CO2 of the exerciser. Unexpectedly it was the level of CO2 around the observer that was predicted to be the highest, but still well within comfortable limits.

There was no mention in the report about whether the exerciser might experience nausea spinning around in a confined space - no help from CFD there I'm afraid!