A reaction wheel—one of the heaviest parts of a space mission, its changing rotation used to shift a satellite's orientation—seen in a plasma wind tunnel belonging to the High Enthalpy Flow Diagnostics Group (HEFDiG) at the University of Stuttgart Institute of Space Systems (IRS). Arc-heated gas in the test chamber reaches speeds of several kilometers per second, reproducing reentry conditions, while the reaction wheel itself is being rotated, reproducing the tumbling that takes place as a satellite plunges through the atmosphere.