Space junk aficionado: Carolin Frueh
It’s hard to pick up garbage when the trash keeps moving in orbits subject to hard-to-calculate gravitational pulls from the Earth and Moon. Carolin Frueh, associate professor in Purdue Engineering’s School of Aeronautics and Astronautics, is putting her considerable mathematical prowess to the test of solving dilemmas that a sanitation department on Earth would never have to contend with. Purdue Engineering Review talked with her about her work.
Why the fascination with space junk?
There are two motivations. For one, there is a strong environmental protection component — tending to what others discard and trying to improve the situation, and, hey, doing that in space to keep space a resource we can use, how fascinating is that? The even greater fascination is that the problem is difficult. Assumptions that might hold for natural bodies are not valid for human-made objects like spacecraft. Also, you get the full gush of always being too far away in your measurements, you are usually measurement-deprived, and there are non-linear dynamics and significant interaction with non-conservative forces that depend on path. It’s all good fun.
You studied in Germany and Switzerland. How do things differ?
I found that the research itself, what constitutes good science and engineering, and educational goals within science and engineering are fairly similar. This is not surprising, as science and engineering are global fields and international exchange and collaboration are highly valued. Cultural differences come to bear in how personal interactions are conducted, how constructive critique is formulated, and what metaphors are used to brand or explain concepts. In the U.S., there tends to be more incentive for high risk-high gain projects, as well as an emphasis on creating new centers or research facilities from scratch. On the other hand, in Germany, for example, there is more focus on how sustainable a new concept is and whether it can leverage existing infrastructure. Of course, those are all general tendencies, and I want to emphasize that they are not true for single cases.
What can you say about the culture at Purdue’s College of Engineering?
The research environment at Purdue has been very supportive, with a high level of collegiality, which should not be taken for granted. This is especially true for the School of Aeronautics and Astronautics and extends across the entire College of Engineering. Within the college, the topic of the sustainable use of space has gained more attention, and an important aspect in the education of our students is to make them fit for jobs in the space industry.
What is your philosophy of teaching?
I try to teach the students the fundamentals that will make them successful as aerospace engineers. While there is lifelong learning, I think if you are missing some of the essentials, it can be hard to acquire that follow-on training after graduation. Ideally, I give them the tools that enable them to follow the careers of their dreams. My classes are not easy, as many students will tell you, but I try to make them interesting, highlighting applications and fostering student interaction with questions and presentations; sometimes students make short video clips for class. I try to always improve and find new ways for conducting the classes and interactions. In my graduate class, I often have professionals from the field come in and teach a lecture in their specialty. I think it is a privilege to teach, and I am very proud of all of my students; all of them work very hard.
What’s the future of traffic control and garbage collection in space?
Future traffic control has to limit haphazard approaches, like just launching very large constellations of spacecraft in an already crowded space and relying on collision avoidance. Rather, we have to focus on critical densities and maximal orbital years per single entity. Fast deorbiting soon after mission completion is key; 25 years in low-Earth orbit (LEO) and graveyard orbits in geostationary orbit (GEO) are not sufficient. At the moment, we see public pressure for compliance with outdated measures. We have seen much progress with the deorbiting of upper stages, but more effort is needed in deorbiting more of the actual satellites. We also still see significant fragmentation events, for which the cases are not always clear; more research is needed there. Additionally, I think we will see active debris removal missions in the future. We must intensify the steps we take to ensure that space debris considerations become a vital part of the mission design. And of course, the focus of space debris is now not only on the near-Earth space but also expanding into the cislunar region (between the Earth and the Moon) and deep space.
What are the national security considerations of all this?
Every space operation also naturally touches upon security considerations. A satellite can be sweeping over several countries and continents within minutes. With anti-satellite actions and GPS spoofing, the security aspect of satellites and satellite services is very apparent. Therefore, it is key to have space domain awareness, so that there is information on where space objects are and are going to be, and what their action space is. In recent years, cybersecurity for the active satellites has also become increasingly important. At the moment, more and more missions are planned for the cislunar space, where the objects are farther away — a very different dynamic than in near-Earth space. Thus, a lot of our work is to understand how to establish space domain awareness in this larger region.
Is there a particular math problem you would like to answer?
Ah, there are many. At the moment, I am fascinated, for example, by the inversion problem of shape, attitude and materials of a space object over large distances from a single, easily accessible measured quantity, the reflected light. To solve it, one needs not only the math of inversion and theory of estimation, but also how orbital dynamics couples into all of it, in near-Earth and in cislunar space. The other problem would be to devise alternative concepts to the probability of collision that would have more useful information content. Both of those topics are directly affected by how and where do we, and can we, collect measurements on Earth or in cislunar space; how do we extract information from noise-affected measurements; and how do we determine orbits from short sequences of observations? Given the information and parameters that we have, how can we define and quantify how many objects are there, and also how many are too many for a sustainable use? Plenty of interesting questions, and hard problems to solve.
Any advice to young people with an interest in engineering and space?
Follow your passion and what interests you. Try to be as good as you can at what you are doing (and hopefully there is some fun in it).
Would you share with readers a small window into yourself?
I like to ride my bicycle in my spare time; I am not very fast, but at least my bike looks cool. My favorite color is black. And btw, the skull I keep in my office is not real, of course — I think … mmm.
Related Links
NBC News: ‘The U.S. is getting serious about space junk’
Expert on space junk: When spacecraft explode, answers may be left in the debris left behind
Space.com quotes Professor Carolin Frueh on ‘Space debris: More storm clouds ahead in orbit’
Using sunlight to save satellites from a fate of ‘space junk’
