Nathaniel Ruhl stands in front of a wall, smiling.

What They Learned: Nathaniel Ruhl ‘22

The physics major developed a method of autonomous spacecraft navigation, by which satellites can pinpoint their own location.

Have you ever wondered how spacecraft navigate their paths through space? Many spacecraft use Earth-based navigation systems, whereby they communicate with Earth via large radio antennas. However, as the spacecraft leave our solar system, the time it takes to send these signals back and forth becomes far too great.

Nathaniel Ruhl sought to find a solution to this problem in his thesis. The physics major and French minor developed a method of autonomous navigation, by which spacecraft are able to determine their own location without communicating with Earth. He dubbed his method, intended specifically for satellites that are orbiting planets with atmospheres, the Horizon Crossing Navigational Method (HCNM).

Ruhl explained that for satellites using HCNM, a telescope on the satellite watches an X-ray star as it crosses the planet’s horizon. Using X-ray data and software Ruhl developed, the satellite is then able to determine its own position.

Ruhl credited his advisor, Professor of Physics and Astronomy Andrea Lommen, with whom he has been working since summer 2020, with much of his success.

“[Andrea] is really good at breaking down large and complex problems into feasible steps that don’t seem so scary,” he said. “I believe that her guidance with these complex problems is one of the reasons that I was able to make so much progress.”

Additionally, Ruhl was encouraged by Lommen to regularly present his work to a working group of astrophysicists, of which she is the chair. He explained that the opportunity to present his work on multiple occasions, and receive helpful feedback from other astrophysicists, aided in his project.

Ruhl will be studying mechanical engineering at the University of Pennsylvania this fall as part of Haverford’s 4+1 program with the university. He will be staying involved with his thesis work, however, as it is continued at both Haverford’s labs, as well as at the Advanced Space Technology Research Labs (ASTER).

What are the implications for your thesis research?
We are currently working with ASTER Labs, Inc. to implement the “horizon crossing measurement” as an additional measurement into their navigational filter. Hopefully, horizon crossings will be used on the next mission that supports X-ray navigation.

What is your biggest takeaway from the project?
My biggest takeaway is learning how to approach a novel problem, how to ask the right questions grounded in fundamental physics, and how to explore these questions and ideas with computer programming. Although nobody has ever used horizon crossings for navigation before in the same way as I am doing it, I also learned how to gain inspiration from past research on related topics and use those ideas to help me develop new techniques.

“What They Learned” is a blog series exploring the thesis work of recent graduates.