This effort is focused on the design, calibration, and implementation of a high temperature heat flux sensor for thermal systems research and testing. The High Temperature Heat Flux Sensor (HTHFS) was designed to survive in the harsh thermal environments typically encountered in hypersonic flight, combustion and propulsion research, and large-scale fire testing. The sensor is capable of continuous use at temperatures up to 1000 â ¦C. Two methods for steady-state calibration of the HTHFS at elevated temperatures have been developed as a result of this research. The first method employs a water-cooled heat flux sensor as a reference standard for the calibration. The second method utilizes a blackbody radiant source and a NIST calibrated optical pyrometer as the calibration standard. The HTHFS calibration results obtained from both methods compare favorably with the theoretical sensitivity versus temperature model. Implementation of the HTHFS in several types of transient thermal testing scenarios is also demonstrated herein. A new data processing technique is used to interpret the measurements made by the HTHFS. The Hybrid Heat Flux (HHF) method accounts for the heat flow through the sensor and the heat storage in the sensor, and thus renders the HTHFS virtually insensitive to the material on which it is mounted. The calibrated output of the HTHFS versus temperature ensures accuracy in the measurements made by the sensor at high operating temperatures. / Ph. D.