The interaction between the continuum flow of a Reaction Control System, or RCS, and the hypersonic rarefied flow around a spacecraft is not well understood. Uncoupled DSMC-CFD computational methods to accurately predict this type of flow are in development; however, the computational techniques being used have not been experimentally validated. A hypersonic wind tunnel and an optical measurement technique have been developed in order to provide experimental measurements necessary to validate the computational model. A previously developed planar laser-induced iodine fluorescence (PLIIF) measurement technique has been extended to measure temperatures in a range from 5 to 300K and pressures from 10-5 to 0.5 atm. This was achieved by including the nuclear hyperfme structure of iodine into the fluorescence model. The PLIIF technique was used to measure the temperature, pressure, and velocity for two situations: first, the free jet test section of the wind tunnel, and, second, a RCS flowfield consisting of a flat plate with transverse jet. The first data set was used to validate the newly developed PLIIF technique by comparisons with known relations for a free jet and to provide extensive data on the free jet test section. The RCS measurements represent the first experimental data set of their kind and will contribute to validation test cases for DSMCCFD codes in development. © 2001 by the American Institute of Aeronautics and Astronautics, Inc.