Gas flow over an object when there are few molecules in a given volume must be studied with different equations than with “thicker” gases. Aerospace engineers must take this into account when they are designing spacecraft that will enter a planet’s upper atmosphere at hypersonic speeds. Assistant Professor Thomas Schwartzentruber (Aerospace Engineering and Mechanics) and his research group have developed a new molecular-simulation tool that allows modeling under these conditions. The image on the left, above, shows a sample of this molecular simulation result for hypersonic flow over a satellite geometry resembling the MIR space station. The image to the right shows a simulation of hypersonic flow over a reentry capsule, with the contours showing the temperature increase through the shock wave ahead of the vehicle. It also shows the degree of surface heating, a maximum near the capsule shoulder. An article about this research appears in the Spring 2012 Research Bulletin.