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Daniel Guggenheim School of Aerospace Engineering
Daniel Guggenheim School of Aerospace Engineering
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ItemInverse estimation methodology for the analysis of aeroheating and thermal protection system data(Georgia Institute of Technology, 2013-11-06) Mahzari, MiladThermal Protection System (TPS) is required to shield an atmospheric entry vehicle against the high surface heating environment experienced during hypersonic flight. There are significant uncertainties in the tools and models currently used for the prediction of entry aeroheating and TPS material thermal response. These uncertainties can be reduced using experimental data. Analysis of TPS ground and flight data has been traditionally performed in a direct fashion. Direct analyses center upon comparison of the computational model predictions to data. Qualitative conclusions about model validity may be drawn based on this comparison and a limited number of model parameters may be iteratively adjusted to obtain a better match between predictions and data. The goal of this thesis is to develop a more rigorous methodology for the estimation of surface heating and TPS material response using inverse estimation theory. Built on theoretical developments made in related fields, this methodology enables the estimation of uncertainties in both the aeroheating environment and material properties from experimental temperature data. Unlike direct methods, the methodology developed here is capable of estimating a large number of independent parameters simultaneously and reconstructing the time-dependent surface heating profile in an automated fashion. This methodology is applied to flight data obtained from thermocouples embedded in the Mars Pathfinder and Mars Science Laboratory entry vehicle heatshields.
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ItemInverse Estimation of the Mars Science Laboratory Entry Aerothermal Environment and Thermal Protection System Response(Georgia Institute of Technology, 2013-06) Mahzari, Milad ; Braun, Robert D. ; White, Todd R. ; Bose, DeepakThe Mars Science Laboratory entry vehicle successfully landed the Curiosity rover on the Martian surface on August 5, 2012. A phenolic impregnated carbon ablator heatshield was used to protect the spacecraft against the severe aeroheating environments of atmospheric entry. This heatshield was instrumented with a comprehensive set of pressure and temperature sensors. The objective of this paper is to perform an inverse estimation of the entry vehicle's surface heating and heatshield material properties. The surface heating is estimated using the flight temperature data from the shallowest thermocouple. The sensitivity of the estimated surface heating profile to estimation tuning parameters, measurement errors, recession uncertainty and material property uncertainty is investigated. A Monte Carlo analysis is conducted to quantify the uncertainty bounds associated with the nominal estimated surface heating. Additionally, a thermocouple driver approach is employed to estimate heatshield material properties using the flight data from the deeper thermocouples while applying the shallowest thermocouple temperature as the surface boundary condition.
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ItemA Reconstruction of Aerothermal Environment Thermal Protection System Response of the Mars Science Laboratory Entry Vehicle(Georgia Institute of Technology, 2013-02) Bose, Deepak ; White, Todd R. ; Mahzari, Milad ; Edquist, KarlAn initial assessment and reconstruction of Mars Science Laboratory (MSL) entry aerothermal environment and thermal protection system (TPS) response is performed using the on-board instrumentation suite called MSL Entry, Descent, and Landing Instrumentation (MEDLI). The analysis is performed using the current best estimated trajectory. The MEDLI suite in part provides in-depth temperature measurements at seven locations on the heat shield. The temperature data show the occurrence of boundary layer transition to turbulence on the leeside forebody of the entry vehicle. The data also suggest that the TPS recession is lower than nominal model predictions using diffusion limited surface oxidation. The model predictions of temperatures show an underprediction in the stagnation and apex regions, and an overprediction in the leeside region. An estimate of time-varying aeroheating using an inverse reconstruction technique is also presented. The reconstructed aeroheating is sensitive to the choice of a recession model.
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ItemPreliminary Analysis of the Mars Science Laboratory's Entry Aerothermodynamic Environment and Thermal Protection System Performance(Georgia Institute of Technology, 2013-01) Mahzari, Milad ; Braun, Robert D. ; White, Todd R. ; Bose, DeepakThe Mars Science Laboratory (MSL) entry vehicle successfully landed on the Martian surface on August 5, 2012. A phenolic impregnated carbon ablator heatshield was used to protect the spacecraft against the severe aeroheating environments of atmospheric entry. This heatshield was instrumented with a comprehensive set of pressure and temperature sensors. The objective of this paper is to present the thermal flight data returned and provide a preliminary post-flight analysis of MSL's aerothermal environment and heatshield thermal response. The flight temperature data are compared with the thermal response predictions by the same analytical models used in heatshield design. In addition to this direct comparison, a preliminary inverse analysis is performed where the time-dependent surface heating is estimated from flight-measured subsurface temperature data.
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ItemInitial Assessment of Mars Science Laboratory Heatshield Instrumentation Flight Data(Georgia Institute of Technology, 2013-01) Bose, Deepak ; White, Todd ; Santos, Jose A. ; Feldman, Jay ; Mahzari, Milad ; Olson, Michael ; Laub, BernardThe Mars Science Laboratory (MSL) Entry Descent and Landing Instrumentation (MEDLI) suite on MSL entry vehicle heatshield has successfully returned pressure, temperature, and thermal protection system (TPS) ablation data acquired during entry. This paper provides an initial assessment of MEDLI thermal instrumentation data that is comprised of in-depth temperatures in the TPS made of Phenolic-Impregnated Carbon Ablator (PICA). Temperatures are measured in-depth at seven different locations on the surface. The thermal sensor plugs are also characterized in arc jet facilities to quantify measurement uncertainties and biases. The assessment of flight data provides key insights into boundary layer transition to turbulence, surface recession, turbulent heating augmentation, stagnation point and apex laminar heating, and in-depth thermal response. A preliminary comparison with model results highlights inadequacies in our predictive capability. The peak temperature measured by near surface thermocouples was found to be 1049 C in the vicinity of apex region. Initial estimate of peak surface temperature with nominal model settings is about 1575 C. The peak heat flux was found to be on the leeside of the vehicle as predicted, but its value is sensitive to the recession model.
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ItemIntegrated Trajectory, Atmosphere, and Aerothermal Reconstruction Methodology Using the MEDLI Dataset(Georgia Institute of Technology, 2012-06) Dutta, Soumyo ; Mahzari, Milad ; White, Todd R. ; Braun, Robert D.The Mars Science Laboratory (MSL) mission’s instrumentation will enable accurate reconstruction of the vehicle’s entry, descent, and landing (EDL) performance including the trajectory, the observed atmosphere, aerodynamics, aeroheating, and heatshield material response. The objective of this paper is to develop methodologies for an integrated approach to the reconstruction of the vehicle’s EDL performance. Two estimation approaches are presented: Serial and Concurrent. The serial approach is demonstrated by application to the Mars Pathfinder flight data and estimating trajectory and aeroheating performance.
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ItemReconstruction of Mars Pathfinder Aerothermal Heating and Heatshield Material Response Using Inverse Methods(Georgia Institute of Technology, 2012-06) Mahzari, Milad ; Braun, Robert D. ; White, Todd R.The Mars Pathfinder probe entered the Martian atmosphere in 1997 and contained instrumentation that provided measurements of the SLA heatshield subsurface temperature at different locations during the entry sequence. These measurements represented the first Martian aeroheating flight data since the Viking Lander missions. The objective of this paper is to reconstruct the Pathfinder entry vehicle's aerothermal heating and heatshield material response using updated modeling tools and approaches in both direct and inverse manners. The direct approach consists of performing updated Computational Fluid Dynamics (CFD) calculations on a newly reconstructed entry trajectory to characterize the vehicle's heating environment. From the calculated heating boundary conditions, the heat shield in-depth temperature response is computed using an updated thermal response and ablation model for the SLA material. These predictions are compared directly to the flight data. In addition to the direct comparison approach, inverse methods are used to estimate boundary conditions that result in a closer match between the flight data and subsurface temperature predictions. The unblown surface heat transfer coefficient is reconstructed as a function of time using whole-time domain least-squares methods in conjunction with regularization techniques.
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ItemTime-dependant Estimation of Mars Science Laboratory Surface Heating from Simulated MEDLI Data(Georgia Institute of Technology, 2012-06) Mahzari, Milad ; Braun, Robert D.There are substantial uncertainties in the computational models currently used to predict the heating environment and the Thermal Protection System (TPS) material response during Mars entry. Flight data is required to quantify and possibly reduce such uncertainties as well as improve current computational tools. The Mars Science Laboratory (MSL) Entry, Descent and Landing Instrumentation (MEDLI) suite will provide a comprehensive set of flight data which will include subsurface temperature measurements of its PICA heat shield at different locations. Accurate reconstruction of MSL surface heat flux from the flight data is a critical step in reducing these uncertainties. The purpose of this paper is to investigate the time-dependent estimation of MSL surface heating from simulated MEDLI subsurface temperature data using inverse methods in the presence of random and bias measurement and model errors. The surface heat flux is indirectly reconstructed by estimating the discretized surface heat transfer coefficient profile as a function of time. Whole-time domain least-squares methods in conjunction with the Tikhonov regularization technique are applied to this problem. The analysis is performed for the instrument plugs at the lowest and highest heating locations. The performance of the estimation methods and the accuracy of the reconstructed surface conditions are investigated under different types of errors in the measurements such as random noise and thermocouple lag. Furthermore, the effect of material property bias on the estimation of surface conditions is also studied.
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ItemA Statistics-Based Material Property Analysis to Support Ablation Simulation UQ Efforts(Georgia Institute of Technology, 2012-04) Copeland, Sean R. ; Mahzari, Milad ; Cozmuta, Ioana ; Alonso, Juan J.Accurate characterization of Thermal Protection System (TPS) material properties is an important component in modeling and simulating the response of the material under heating. Unfortunately, for many common TPS materials, especially ablators, these material properties are not always well known and contribute a source of aleatory uncertainty to thermal simulations, impacting the safety and reliability of entry systems. Furthermore, efforts to capture these uncertainties have been hampered by a lack of suitable experimental data to establish proper input statistics, necessitating the use of ad-hoc methodologies to fabricate input PDFs. In this work, new ablator material property data from the Mars Science Laboratory (MSL) program is used to construct experimentally-based material property PDFs for use in non-deterministic ablation simulations. A standard UQ propagation, sensitivity analysis and uncertainty contributor breakdown analysis is performed using the revised input set in the anticipated MSL aerothermal environment. Lastly, a problem is formulated to quantitatively establish the relationship between errors in input statistics and errors in output quantities of interest.
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ItemProposed Analysis Process for Mars Science Laboratory Heat Shield Sensor Plug Flight Data(Georgia Institute of Technology, 2011-06) Cozmuta, Ioana ; White, Todd R. ; Santos, Jose A. ; Laub, Bernard ; Mahzari, MiladThe Mars Science Laboratory (MSL) mission is scheduled to enter the Martian atmosphere in August 2012. Aboard the heatshield is the MSL Entry Descent and Landing Instrumentation (MEDLI) system that includes a series of embedded sensor plugs to measure in-depth response of the thermal protection system (TPS). The general objectives of the MEDLI system are to assess the TPS performance and reconstruct the aerothermal environment experienced during entry. Some specific objectives, such as measuring TPS temperature, can be addressed with direct measurements. Other objectives, such as determining surface heating, must be inferred using measurements combined with analytical tools. This paper describes the specific objectives, the expected sensor responses to the entry environment based on aerothermal and material response simulations, and the reconstruction analysis process being developed for the flight data.