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Modeling radiation key component to landing safely on Mars

4/9/2021

Debra Levey Larson

heat shield and back shell for NASA's Mars 2020 mission. Credit: NASA
The heat shield (left) and back shell (right) comprise the aeroshell for NASA's Mars 2020 mission. Credit: NASA

In 2015, AE Professor Marco Panesi received a NASA Early Career Faculty award to study radiation in the back shell of entry capsules. On February 18, 2021, we witnessed his research findings in action as Perseverance landed safely on Mars.

During the entry into a planetary atmosphere space objects, traveling at very high speeds, become very hot. Understanding how hot is critical for the design of the thermal protection system that prevents the vehicle from burning up. Under these extreme conditions, the gas radiation accounts for more than half of the total heat on the back shell.

The model used to compute the radiation environment encountered during the entry into Martian atmosphere was developed by Panesi and his former student Amal Sahai, who is now a researcher in the aerothermodynamic branch at NASA Ames Research Center. 

Panesi’s ECF research project aimed to develop methods to model the shock layer radiation for Mars entry vehicles and incorporate the effects of non-equilibrium chemical processes. Panesi and Sahai used novel methods to describe the microscopic kinetic state of molecules in the vicinity of the back shell, and to drastically accelerate the calculation of the radiation heat-loads in the wake of the spacecraft, without sacrificing the physical fidelity of the model.

Marco Panesi
Marco Panesi

“The ECF has been one of my most successful, yet challenging projects, and it gave me the opportunity to work very closely and learn from the most brilliant scientists at NASA Ames and NASA Langley Research Centers.” Panesi said. “This work would have not been possible without the collaboration with Dr. Richard Jaffe and the group of computational chemistry, and Dr. Christopher O. Johnston, one of the world’s leading experts in radiation modeling for hypersonic flows.”

In the wakes of vehicles traveling at hypersonic flows, the cooling of the gas results in a recombination of the carbon dioxide molecules and the formation of highly energetic but transient molecules that can release radiant energy.

“Modeling the energy states of these non-equilibrium gas molecules represented a significant challenge, as hundreds of thousands of possible energy states are theoretically possible for a single molecule,” Panesi said. “Modeling each possible state for all the molecules that could contribute to the thermal heating model of a Mars vehicle is computationally intensive.”

Panesi and Sahai constructed a more efficient model for chemical kinetics and radiation using a coarse-grained method. They examined several groups of energy levels, or bins, which were defined using a novel adaptive method based on entropy maximization.

The methods and models developed within the project were used by Christopher O. Johnston at NASA Langley to compute the radiation heating in the back shell of the vehicle during entry. In collaboration with Panesi, further development and refinement continue within the NASA Entry Systems Modeling Project.

Panesi’s ECF project was entitled, “Reduced Order Modeling for Non-equilibrium Radiation Hydrodynamics of Base Flow and Wakes: Enabling Manned Missions to Mars.”

Related work includes:

“Comparative analysis of reduced-order spectral models and grouping strategies for non-equilibrium radiation,” written by Amal Sahai, Christopher O. Johnston, Bruno Lopez, and Marco Panesi, is published in the Journal of Quantitative Spectroscopy and Radiative Transfer.

"Reduced-order Non-Boltzmann Modeling of Coupled CO2 Thermochemistry and Radiation in Mars Entry Wake Flows," by Amal Sahai, Christopher O. Johnston, Bruno Lopez, and Marco Panesi Physical Review Fluids.