Profile: Martin Ross, Senior Project Engineer, Commercial Launch Projects

Rockets, Soot, and the Stratosphere

Marty Ross outside


Could rocket launches be regulated in the future because rocket engines emit soot into the stratosphere? That is the question Marty Ross and fellow scientists are striving to answer with their research into rocket emissions and climate, research that has caused a stir in the aerospace and space tourism industry. Many have interpreted their widely published research to mean that scientists want to regulate rocket launches, but Ross said that’s not how science works. And in fact, in this case, the opposite is true—if anything, Ross and his colleagues want to reduce the risk of unnecessary regulation.

“Ultimately, I’m a space cadet,” Ross said. “I want to see daily launches. What worries me is that the vision of daily launches is put at risk if we don’t pay attention to emissions and the possibility of regulations. So, that’s why we want to do this—to look at this work as risk reduction. That’s a big part of what we do at The Aerospace Corporation—risk analysis. The idea is to gather the data and the understanding so that when the regulator comes knocking at the door, we can say we know exactly what our emissions do to the atmosphere—and they are relatively small. The failure mode is that rockets unnecessarily get swept up in global regulation.”

How Science Works

Ross, a senior project engineer and scientist in Aerospace Civil and Commercial Launch Projects, joined The Aerospace Corporation in 1988. Since then he has published more than 50 papers on a variety of space and atmospheric science and engineering subjects. His recent work has involved studying black-carbon particles, or soot, released by rockets into the stratosphere. (See his article in this Crosslink issue.) “We made some reasonable assumptions that are neither crazy speculation nor overly conservative — just middle-of-the-road assumptions. We drop these assumptions into models of the atmosphere and pull out a single number—the amount of increased heating in the atmosphere. And at first glance it seems significant, kind of an important result. The details and uncertainties will have to be explored later on with direct measurements of soot emissions from rockets.”

He believes that their research is often misunderstood, that people interpret their conclusions as saying they are predicting exactly what’s going to happen. “We’re not saying that at all. We don’t know exactly what is being emitted because of a lack of data and models so we’ll make reasonable guesses about soot and carbon dioxide and water vapor. When you do, you derive a range of numbers regarding the atmospheric effects of rockets—and some of that range falls above a level where the effects become significant. So clearly, we need to look a little more closely and reduce the uncertainties so we can reduce the risk of unwarranted regulation.”

To get at the real numbers, researchers must obtain funding, then gather instruments to measure the size and shape of the soot particles, carbon dioxide, water vapor, and other gases emitted by rockets. They will put the instruments on a high-altitude research aircraft and fly through the stratospheric plumes of various hydrocarbon-fueled rockets and actually make the measurements. Ross thinks the required plume and modeling data could be collected in a few years.

Into the Plume

This is not his first research using high-altitude planes. Ross and other scientists in the early 1990s worked with NASA and used the agency’s WB-57F to get measurements inside the plume of an Air Force Titan IV solid-rocket motor. The collaboration produced measurements that showed it unlikely that rockets constitute a serious threat to global stratospheric ozone. The effort, funded by the Titan IV program, helped demonstrate the scientific value of the WB-57F, which has since become one of the key aircraft for NASA airborne science. “We saw a lot of interesting data, enough to say that solid-rocket motors were not the threat that some were speculating about before they collected actual data. We clearly saw significant ozone loss, but it wasn’t catastrophic,” Ross said.

That research was the beginning of the RISO (Rocket Impacts on Stratospheric Ozone) program that Aerospace established at the request of the Air Force to collect data regarding the effects of solid-rocket-motor emissions on the atmosphere. In 1999, RISO joined forces with NASA, the National Oceanic and Atmospheric Administration, and the National Center for Atmospheric Research to form ACCENT (Atmospheric Chemistry of Combustion Emissions Near the Tropopause). ACCENT provided a common set of atmospheric measurements from shared payloads on the high-altitude aircraft to serve the interests of both NASA and the Air Force. (See “Rockets and the Ozone Layer,” by Ross and Paul Zittel in Crosslink, Vol. 1, No. 2.)

Looking Forward

Ross is concerned about the lack of an institutional connection between the rocket business and science community. An established ongoing mechanism for the aircraft engineers to interact with the atmospheric scientists provides much information about how airplanes affect the atmosphere. “But that connection doesn’t exist for rockets. The rocket engineers—the propulsion people—don’t really have an appreciation for the science, and the scientists don’t realize what rocket engines can do.” He regards his own role as working to see this connection grow.

Most recently, he suggested that Aerospace should import an established climate model—a three-dimensional computer representation of Earth’s atmosphere from the surface to the outermost layer so that Aerospace could begin to directly contribute to climate research and apply the model to long-term customer needs. For example, the upper atmosphere may cool and shrink as the surface warms in coming years, causing the density of the air at orbital altitudes to decrease, possibly resulting in less drag and a longer stay in orbit for spacecraft, spent hardware, and debris. Climate change could affect Air Force future requirements for meteorological sensors. And rocket emissions affect more than just climate and ozone—for example, they influence GPS signals. “A researcher in Japan recently was able to track a foreign missile by using GPS receivers because the signals were affected by holes created by the missile exhaust. He was able to track the trajectory by looking at GPS signals,” Ross said. “This is something we need to be expert about.”

Acquiring a climate model would not be out of the ordinary for Aerospace but would require an initial push internally, Ross said. “Within the company, Aerospace is quite entrepreneurial. If you do good work—even for research that is maybe fringe, not mainstream—if it’s objective and technically sound, that gets rewarded. And if you demonstrate credibility, you can carve out a niche. You see different levels of support over the years for that kind of activity, but in the long run, Aerospace is a pretty neat company. We look forward while keeping an eye on the past.”

Space Scientist

Ross first learned about The Aerospace Corporation at the University of Michigan, where he earned his B.S. in aerospace engineering. “When we were all graduating, doing interviews with companies, if you could snag an interview with Aerospace, well, that was the cream of the crop. Nobody knew much about it. What exactly did they do? So coming aboard Aerospace after grad school was incredible for me.” His M.S. and Ph.D. degrees in planetary and space physics are from UCLA.

“I’m not so smart that I can give advice to young engineers, but I would tell them—based on my 30 years of experience as a student, researcher, and professor—load up on mathematics, learn it as a language. Once you’ve got a language telling you how the universe works, everything else can be made to seem simple. I’ve been studying The Road to Reality, a book by Roger Penrose, an English physicist. He starts with the most elementary mathematics and works up to quantum mechanics and cosmology. Every day, I read a few pages of Penrose and try to get through it—not just skip over the rough stuff—to really understand what’s going on. And I realized that if you know the mathematics, everything else follows along.”

Ross has been interested in science and astronomy since a child. “My earliest memory is crawling up in a big recliner with my dad and he would read You Will Go to the Moon. I had my first telescope at 7, and at 16, I delivered newspapers to put up an observatory in our backyard. I built a concrete platform and a structure and shelter for a 12-inch telescope because it was too big to move. There was no question that I was going to do the space thing. And I still just kind of poke around the edges and try to look around where people just haven’t looked yet.”

—Donna Born

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