Radiation measurements in nonreflected shock tunnels

Atmospheric entry at superorbital speeds is associated with large amounts of radiation, often in nonequilibrium modes. This is a significant design issue for applications such as lunar return vehicles, aerocapture and for all missions to the gas giants. Analyzing such flows is complicated by a lack of both physical measurements from shock heated gases, and by our current understanding of the fundamental nonequilibrium processes involved. Shock tubes provide a useful means of obtaining realistic data from radiating gases under the same conditions as encountered in flight, and represent a powerful tool for the validation of advanced radiation models. This paper reports on work in progress to adapt expansion tubes to operate in the nonreflected shock tube mode to extend the range over which such data can be usefully obtained. The results of preliminary tests in the X3 facility are shown, and the possibilities for extending the measurements to a larger flight envelope are discussed.