Paul Steffes in lab. Photo by Jason Maderer.

Dr. Steffes was interviewed by Caitlin Buro in spring 2020.

When did you come to Georgia Tech and why did you come?

I came to Georgia Tech in the fall of 1982. The previous year Demetrius Paris had gotten the names of upcoming Ph.D. graduates from Stanford University, where I was completing my doctorate. He contacted me, asking if I was interested in an academic career and acquainting me with a new National Science Foundation (NSF) initiative to fund beginning academics. 

I applied and received a grant to support my initial research at Georgia Tech. So, thanks to Demetrius, I arrived at Georgia Tech in the then unusual circumstance of being able to reduce my teaching load and spend time focusing on developing a research program.


What were your initial impressions of Georgia Tech? Did you fit in?

The School was relatively small when I came—40 faculty administering to a student body of around 1,300 undergraduate and 300 graduate students. The major challenge facing Demetrius was to increase the number of faculty to accommodate the growing student body in terms of both instructional capacity and research funding for graduate student support. I think Demetrius felt that hiring faculty who did different things would broaden the research footprint and opportunity. His vision was to bring in new people who were not supplementary but complementary to the existing faculty, which he did very successfully.

My focus on the application of electrical engineering to planetary science fit that vision and fitting in was not an issue. However, there was only one staff member of the Georgia Tech Research Institute (GTRI) and one faculty member in Earth and Atmospheric Science and no one in Electrical Engineering doing related work. My intended research agenda represented an entirely new step for the School.

My instructional activities were initially teaching undergraduate electromagnetics courses. In my third year, 1985, I introduced my graduate course on satellite communications.


How did you become associated with NASA, and what was the focus of your work?

My NSF grant expired after one year, so I had to seek additional funding. The School supported me in visiting potential funding agencies, primarily NSF and NASA. My initial interview at NASA was not fruitful, but, almost by chance, I encountered a program manager who was familiar with my Stanford work. It was valuable, and they asked if I would be interested in continuing it. My response was, of course, a definite yes.

The NASA program manager went to lunch; I sat at his desk and wrote, by hand, my proposal summary on a T43 Form. When he came back from lunch, he had his secretary type it up, and he took it to a meeting that afternoon with NASA administrators. NASA liked the idea of supporting young faculty. At the time, they had two in Michigan, one in Arizona, and then me. By February of 1984, I was approved for the research grant and working on the "laboratory evaluation of the microwave properties of planetary atmospheres" part of the Venus and the Outer Planets Exploration Projects. That one grant lasted 32 years. It started in 1984 and existed until 2016.

In the meantime, I was supported to work on other projects involving NASA missions, which were much shorter-term projects. I worked on the Magellan Mission where the Magellan spacecraft was orbiting Venus, and we designed an experiment where we transmitted radio waves through the atmosphere from the Magellan telecommunications antenna. In another project, we used an older spacecraft orbiting Venus called "Pioneer Venus" to probe the atmosphere of Venus with microwave radio signals.  


What was the benefit of the research that you were doing with microwaves?

NASA was attempting to understand the makeup of various planets by probing the planet's atmosphere with microwaves, using sensitive receivers to record the reflected or refracted waves, and using the data to determine the atmosphere's constituents. One of the problems we were hoping to solve was that the environments on planets are very extreme, and using data from instruments calibrated under Earth conditions, using Earth as an analog, resulted in the wrong answer. What we did was create test chambers to simulate the conditions of the specific planet. We evacuated all the earth air, inserted the gases that existed on the particular planet, and then we placed the chamber into a temperature-controlled environment. Then, using equipment from either the radio telescopes or spacecraft to probe the known planetary environment as simulated in the chamber, we were able to accurately calibrate and interpret the data collected.

For example, when Pioneer Venus started orbiting Venus, the radio signatures they were measuring showed an unexpected and unexplained level of microwave absorption in the Venus atmosphere. Venus naturally has a very hot climate; temperatures on the surface average about 800 degrees Fahrenheit. So we designed experiments that allowed us to create a "Deep Venus atmosphere" by boiling or evaporating sulfuric acid (the material in the Venus clouds) to create sulfuric acid vapor in our test chamber. We were able to calibrate the data, and it was determined that what we measured on Venus was the sulfuric acid vapor that condensed to form clouds. Similarly, experiments conducted in our lab enabled the accurate determination of ammonia and water vapor constituents of the Jupiter atmosphere.


How did you get involved with the Juno Mission?

I had a history of doing lab work in support of NASA missions, and NASA knew they would need ultra-precise lab work to support the Juno mission. The lab work started in 2005, and we completed the first round in 2015.

The Juno mission was intended to develop a precise characterization of Jupiter's atmosphere. We had done work on a mission in the 1990s where a probe, Galileo, was dropped into the atmosphere of Jupiter (a gas giant) to measure the constituent elements of the atmosphere, but by bad luck, it landed in an especially hot and dry spot in the atmosphere. That was roughly analogous to an extraterrestrial trying to deduce the Earth's atmosphere by dropping a single probe on to the Sahara Desert. By contrast, the Juno mission employs a microwave receiver called a "microwave radiometer" (MWR) to measure the natural electromagnetic energy emitted from many different locations on Jupiter. The MWR measurements, properly calibrated, indicate the level of water vapor and ammonia on Jupiter at all different locations as the spacecraft orbits the planet. To support the mission, we designed and built an incredible system that could simulate the Jupiter atmosphere from very deep in the atmosphere to the uppermost part because we had to sense all the contributions from different layers. We spent a long time building the system, with several students working on it over the years as we developed a system able to provide the precision needed.

One of the things we learned early in the Juno Mission was that the Juno radiometer would sense emission emanating from much lower into the atmosphere than anticipated. So we are now designing a new system to simulate the Jupiter environment down to the lower elevations. This system will be much more complex and challenging to build than the first system, primarily because of the extremely high temperatures (900 degrees Celsius) and pressures (15,000 psi) in Jupiter's lower altitudes. And, because the system will have to use highly-flammable hydrogen which dominates Jupiter’s environment, it will have to be deployed at a remote location, yet to be determined.


What do you consider some highlights of your career?

The focus of my work has always been radio science using large antennas or spacecraft antennas to measure environments. I was fortunate to become associated with NASA doing work that was right in my wheelhouse. Our early work on the Pioneer Venus Mission provided NASA with the capability to do atmospheric sensing. This was a significant accomplishment, widely recognized within NASA, enabling atmospheric sensing to become a major aspect of subsequent Venus missions. It also led to continuing and increasing the involvement of our research team in subsequent programs.

On a personal level, the success of our work over time led to my also serving more as a consultant to NASA rather than just another university professor doing contract work, resulting in my participating in mission planning and analysis. My relationship with NASA and the recognition afforded by it is very satisfying and gratifying.

Another major highlight is my graduate students. As a university researcher, you are only as good as your students. It has been terrific having such high-quality students who have accomplished so much and produced truly remarkable achievements. A total of 23 students have received their Ph.D. degrees working with me. Most have gone on to achieve success in their own right. Jon Jenkins, one of my first graduate students, has been with NASA for over 30 years. John was involved in the creation of the Kepler mission, which has resulted in the discovery of 3,000 planets around other stars. Another graduate student, Joanna Joiner, is with Goddard Space Flight Center and responsible for several Earth sensing missions. She went from planetary work to monitoring the terrestrial environment and has been highly successful. I have had so many successful students.

I do as much planetary science as I do electrical engineering. When I first came to Georgia Tech, lip service was accorded to interdisciplinary work, but little was going on, and many thought it to be inappropriate. Dr. Demetrius Paris and his successor, Dr. Roger Webb, both viewed interdisciplinary work as integral to the success of the School and very successfully added faculty accordingly. The result has been that over the past 38 years, interdisciplinary work has become the bread and butter of the very robust School of ECE research program with attendant recognition as one of the top programs in the country. I am pleased to have been a participant and contributor to that evolution. 


What are your plans for retirement?

I will probably still support and direct graduate students, but I likely will not be instructing. I will still stay involved, mainly with mission Juno, because the mission entered Jupiter's orbit on July 4, 2016. Our prime mission will conclude at the end of 2021. Because the spacecraft has survived so well in orbit, and because there are other scientific objectives that we can achieve, we are proposing extending the mission to NASA. I will continue to be involved with the prime mission until the end of 2021, and, if approved, will be involved with the extended mission, which could last through 2025.