“An internship at NASA is both a dream come true and a challenge,” says Jan Skácel from the Department of Plasma Physics and Technology.

What project did you work on during your internship?

My work was in the field of fundamental physics. I contributed to modeling kinetic boundary conditions in the Arc Jet Complex facility. In this device, gas is heated by an electric arc to extremely high temperatures and then accelerated to supersonic or even hypersonic speeds. The hot gas stream is directed onto the surface of a test sample. This makes it possible to simulate the conditions that spacecraft face during atmospheric entry. The Arc Jet Complex has a rich history spanning 55 years. For example, materials for thermal protection were tested here for missions such as Apollo, the Space Shuttle, and Mars Pathfinder. Today, the facility is primarily used for testing materials for planned missions to the Moon and Mars, where spacecraft are expected to decelerate with the assistance of Earth’s atmosphere during return, or to be directly captured by the Earth’s atmosphere. Our task was to understand and describe in more detail the physical processes occurring near the electrodes, at the points where the electric arc originates, and on this basis to propose modified boundary conditions that NASA could use in its simulation codes for a more accurate characterization of the arc.

What software or code do you use for modeling?

At the von Karman Institute (VKI), where I also work as part of my PhD, we are developing our own simulation code called Pantera (PArticle Numerical Tool for non-Equilibrium Reacting Aerodynamics), together with our Italian colleagues Pietro Parodi and Federico Bariselli. Pantera is an open-source software designed for the simulation of non-equilibrium gas and plasma dynamics. It uses special numerical methods such as Direct Simulation Monte Carlo, Particle-in-Cell, and Monte Carlo Collisions. The plasma or gas is represented by macroparticles that move, collide with each other, and are accelerated by forces coming from other charged particles in the simulation or from external sources. This particle-based, statistical approach allows us to represent, in a very illustrative and faithful way, the complex physical processes taking place in the gas or plasma, including the detailed modeling of plasma–wall interaction. This software we used at NASA to simulate the interaction of the plasma arc with the electrodes. One of the key physical processes that needed to be considered and implemented into Pantera was thermionic emission. It is a process in which strong emission of electrons occurs from surfaces heated to very high temperatures. This process is very important for sustaining high-temperature arcs. In addition, we implemented a more efficient method for calculating particle collisions in a gas with multiple components of different concentrations. In this way, we managed to significantly improve the model of physical processes in the plasma arc of the Arc Jet Complex. With the help of this improved model, our task was then to determine how the electrode is affected by the plasma under different arc parameters, and to create a kind of map of boundary conditions that can be generalized from the very detailed kinetic scale, which we simulated using Pantera, to a macroscopic—more simplified—one, which NASA can then directly incorporate into its own models and codes.

What does collaboration with NASA mean to you?

The greatest benefit I see is the opportunity to make contacts and get to know a team of top experts. In addition to us, there were also students from French schools, so it was truly an international environment. I learned how similar projects are carried out elsewhere in the world and gained experience that I will use in my further scientific work. For me personally, the internship is a dream come true—I have been interested in astronautics since I was fourteen, and I never expected that one day I would make it all the way to NASA.

How did you get into physics?

What ideas did you have about your future profession when you were young? It was always expected of me that I would rather become a designer, because I come from a town where Siemens was located, and my grandfather was a technician. In the family, it was kind of assumed. But then, sometime in the last year of high school, something switched in me. Suddenly I became interested in completely different things—I started to enjoy physics, even though I didn’t realize it for a long time, it just happened naturally. It was only before the final year that I told myself I wanted to study physics. So, then the path led to the Faculty of Science. Gradually, I met interesting people, and everything started to develop from there.

What role did our faculty and your supervisor here play in this journey?

Within the topics of bachelor theses, I first encountered the issue of electric propulsion for satellites, which really surprised me a lot, because I had no idea that something like this was being done here. I had the opportunity to talk about this topic with my future supervisor, Zdeněk Bonaventura, and I decided to devote myself to this field. From that time on, everything slowly started to develop: as part of my master’s thesis I began working on the development of fluid models of plasma, and in my spare time, also with the support of my supervisor, I tried out particle models for simulating the transport of charged particles in gas. That proved very useful later on when I began working with Pantera. Thanks to Dr. Bonaventura’s contacts, I was able to go to the von Karman Institute in Belgium for a research internship under the supervision of Prof. Thierry Magin and PhD student Giuseppe Gangemi, where I worked on the development of a multi-component plasma model. This model describes the motion of plasma containing several types of particles as the motion of a single fluid but composed of multiple components. Each component within the fluid has its own so-called diffusion velocity. This approach is promising because it makes it possible to reduce the number of equations that need to be solved. Gradually, we also began to focus on the issue of modeling satellite charging. This is a very current and interesting topic that examines the influence of plasma and the residual Earth’s atmosphere on satellites. As satellites orbit the Earth, they become electrically charged due to interactions with the surrounding environment (plasma). This can lead to malfunctions and instabilities in their trajectories because of momentum transfer between the satellite and the environment. In a worse case, it can even cause damage by electrical discharges if significantly different charges build up on different parts of the satellite. At present, I am pursuing a PhD on this topic under joint supervision: at Masaryk University, where my supervisor is Dr. Zdeněk Bonaventura, and at Université Libre de Bruxelles, where my supervisor is Prof. Thierry Magin. As part of my PhD, I also continue to work at VKI.

Could you explain what the von Karman Institute focuses on?

The von Karman Institute is dedicated to research in the fields of fluid dynamics, aerodynamics, and propulsion for aviation and space. For example, they study the atmospheric entry of satellites, test new materials for aerospace, and have laboratories for simulating extreme conditions, like those at NASA. I have been collaborating with VKI for almost three years, first within an Erasmus+ internship, which I undertook from MUNI during the third semester of my master’s studies, and now also as part of my PhD.

What did your everyday work at NASA look like?

I worked closely with the NASA research team on specific physical problems that needed to be considered in our model. For example, we tried to find a way to account in the model for the evaporation of the electrode surface, which occurs due to the extremely high temperatures present at the point of contact between the plasma arc and the electrode surface. At the same time, I had space for my own research, which consisted mainly in expanding and testing the physical models implemented in Pantera. A great advantage was the possibility of personal consultations with NASA mentors, who were available to us whenever we needed expert advice or assistance.

I also had the opportunity to consult with a truly seasoned expert who had been working on various physical and technical problems for NASA research for more than 40 years. But besides work, we also had plenty of extracurricular activities. Right next to our office was the Spacebar, where we could always end a demanding day pleasantly over a glass of beer. We also organized several dinners together with colleagues. On weekends, I took the opportunity to explore the beauty of California, and I am still thrilled about my trip to Yosemite National Park.

How did you get the internship at NASA?

It all started thanks to the contacts between the von Karman Institute and NASA. Similar collaboration had taken place in the past, but it was interrupted during COVID. After the pandemic, it was successfully restarted, and the opportunity to apply opened up again. We first had to propose a project topic that we would work on and that would also be of interest to NASA. In the end, we came up with the topic of the already mentioned modeling of kinetic boundary conditions in the plasma arc. I was lucky to be selected within the Erasmus+ program at VKI to work on this project directly at NASA.

Looking back, how do you evaluate the entire stay?

I met many interesting people with whom I could discuss the physics of electrical discharges. I have to say that throughout the whole internship I made full use of the knowledge I had gained from lectures at our faculty. Thanks to this, I was able to actively participate in discussions on the given issues. I was also very glad that I could involve my supervisor, Zdeněk Bonaventura, in these discussions, as he provided us with very useful advice, which helped us improve our simulation models for electrical discharges. Thanks to this, we were able to achieve very good results during the NASA internship. I am pleased that NASA was so interested in our project that we are planning to continue working together on this topic in order to bring it all the way to the actual kinetic boundary conditions.

Thank you for the interview.

Photo: Jan Skacel´s archive