Development of inverse methods for reconstruction of flight environments on ablators
Obtaining measurements of flight environments on ablative heatshields is both critical for spacecraft development and extremely challenging due to the harsh heating environment and surface recession. Thermocouples installed several millimeters below the surface are commonly used to measure the heatshield temperature response, but an ill-posed inverse heat conduction problem must be solved to reconstruct the surface heating environment from the embedded thermocouple measurements. The material properties of typical ablators make the reconstruction process more challenging when the measurements are deep, but measurements often must be located deep to allow for surface recession. Compounding the complexity of the surface reconstruction problem, surface recession can contribute substantially to the measurement response, but it is generally poorly predicted. Two methods are proposed in this dissertation to address these issues. To address reconstructions of deeply located measurements, a hybrid sequential/whole domain algorithm called the sequential subdomain algorithm is presented and demonstrated to show improved performance for applications similar to common low density carbon ablators used on the NASA Mars Science Laboratory and Orion capsules. To address uncertainty in surface recession prediction, a method for decoupling the surface recession evaluation from the inverse heat conduction problem is presented to allow more rapid and detailed analysis of different recession models. The decoupled method is shown in verification exercises to provide reconstructions of equivalent accuracy to the traditional coupled method but with reduced computational effort. These methods are applied to reconstruct the environments on the Mars Science Laboratory heatshield using several kinetically limited recession models.
Lyrintzis, Purdue University.
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