Interview with Christine Hartzell, Associate Professor at University of Maryland

Interview:

Balamir: Could you please tell us about yourself?

Professor Hartzell: I am originally from Washington state. I did my undergraduate studies in aerospace engineering at Georgia Tech and went to graduate school at the University of Colorado at Boulder. I did internships at JPL and JAXA (the Japanese space agency). After receiving my PhD, I did a short postdoc at Caltech, before becoming a faculty member at the University of Maryland.

Balamir: Why did you want to become an aerospace engineer?

Professor Hartzell: Even as a young child, I was very interested in science and space, specifically. I really enjoy thinking about the microgravity environment, because it is so different than what we experience on Earth. I decided to pursue aerospace engineering because it seemed more employable (with just a bachelor's degree) than a pure science degree like physics.

Balamir: Your research is mostly directed towards space and spacecraft. What aspects of planets are you most interested in studying?

Professor Hartzell: I am most interested in studying small bodies in our solar system, specifically asteroids, comets and moons. I'm interested in these bodies because the gravity at their surface is very small. As a result, forces that are typically negligible on Earth (e.g. cohesion, electrostatics) start to become really important. That can make the surface dust and rocks behave in ways that are non-intuitive, which I find really exciting.

Balamir: How will studying this particular aspect of planets improve spacecraft design?

Professor Hartzell: NASA currently has several missions that are exploring asteroids. There is also some interest in mining asteroids. If you want to land on and collect sample from the surface of a small body, then it is advantageous to understand how the asteroid's surface is going to respond to the forces exerted by your spacecraft's thruster plume, scoop, drill, etc. For example, will you kick up a big plume of dust during landing and obscure your cameras? What is the best way to collect a sample on a body whose gravity is a million times smaller than Earth's?

Balamir: What are orbital mechanics? How can they be used in the design of spacecraft?

Professor Hartzell: Orbital mechanics is the study of trajectories or orbits. For example, orbital mechanics can answer questions like: Where is my satellite now? Where will it be in 25 minutes? What is the minimum fuel required to get a satellite into orbit around Mars? What is the path that a satellite will take when traveling from Earth to Jupiter, given a specific launch date and arrival date? Trajectory design is one of the first steps in the mission design process because we need to know *if* we can reach our destination body and how much time and fuel will be required.

Balamir: You also conduct some work in plasma dynamics. Can you explain some of your work in plasma physics?

Professor Hartzell: In addition to asteroids, I also study orbital debris (aka space junk). Currently, there is a population of very small (sub-cm) orbital debris that is too small to be detected using conventional methods, but can still pose a big risk to satellites (potentially causing damage to satellites if there is a collision). My students and I are working on a method to detect this small orbital debris by looking for a wave generated by the debris in the plasma environment around Earth. A plasma is like a very high energy gas where the electrons separate from the ions. The sun emits a plasma called the solar wind. Earth's magnetic field shields the surface from the solar wind. But the debris around the Earth is moving through this soup of ions and electrons that we call the ionosphere. We predict that the debris will cause a wave in this ionosphere plasma.

Balamir: You also utilize and do work with Granular mechanics. What are Granular mechanics? How can they be used to improve spacecraft design?

Professor Hartzell: Granular mechanics is the study of the behavior of collections of grains. Examples of granular systems include landslides, nuts in cans at the grocery store, and sand in an hourglass. Because the surfaces of asteroids are rocky and dusty, granular mechanics is a good tool to study these surfaces. We can simulate the interactions of spacecraft with the surfaces of small bodies using granular mechanics simulation methods.

Balamir: Since you also work on spacecraft design, can you explain some of the spacecraft design concepts that you are currently working on?

Professor Hartzell: One design concept we're working on is an instrument to measure cohesion of the dust particles on the surface of an asteroid. The instrument uses a charged plate to generate an electric field that would pull dust off the surface. By monitoring the size of the dust particles that detach and the electric field required to detach them, we can calculate the cohesive bond that had to be broken to detach the particles.

Balamir: I’ve also read that they’ve named an asteroid after you. Can you tell us about how you found or contributed to finding the Asteroid 9319? “Hartzell”.

Professor Hartzell: I didn't discover the asteroid that was named after me. People that discover asteroids can name them as they wish (with a few rules). Some discoverers (or spacecraft survey) have discovered many asteroids. In this case, a nomination for a name can be made to a committee. I was nominated by colleagues in recognition of my contributions to asteroid science.

Balamir: What has been your toughest accomplishment so far in your career?

Professor Hartzell: Every major accomplishment is difficult - that's what makes it a major accomplishment! Completing my PhD was a difficult accomplishment. Recently, I was awarded tenure. At universities, a professor's research and teaching accomplishments are evaluated after 6-7years at the university. If their accomplishments are viewed as sufficient, then the professor is awarded tenure and has a permanent position at the university. If tenure is denied, the professor must leave the university. The standards to achieve tenure are high (as they should be) so the process of getting tenure was a major and difficult accomplishment for me.

Balamir: What is a big milestone that you are looking forward to in your research?

Professor Hartzell: I'm looking forward to seeing observational evidence that small orbital debris do in fact produce the plasma waves that we have predicted with our mathematical simulations.

Balamir: To high schoolers like me and to younger generations that want to become aerospace engineers, what would be your advice to be successful in this career?

Professor Hartzell: My advice would be to continue to work hard in your math and science classes. Hard work is just as important, if not more important, than raw talent. Even if math is not your strongest subject, if you are willing to work hard, you can be a successful engineer. I would also encourage students to learn how to be a clear and engaging writer/communicator. Lots of engineers don't like writing, but writing is very, very important. If you do good technical work, but no one understands what you've written, then your work will not be valued or used by others.