“What goes up must come down” is a well-known axiom of physics which describes the law of gravity. However, when it comes to the task of designing probes and other spacecraft which can withstand re-entry into the Earth’s (or any planet’s) atmosphere, “what goes up must come down” becomes more a question of “What shape will it be in when it comes back?”
“We’re essentially talking about something coming in really, really fast and that has to stop without crashing,” says Dr. Alexandre Martin, one of the newest faculty members to UK’s Department of Mechanical Engineering. Modeling re-entering space vehicles is Dr. Martin’s primary area of research. “I’m attempting to calculate from the aerodynamic outside of the vehicle the amount of heat coming into the vehicle. We have to get rid of the heat so the humans or instruments or whatever is in the vehicle doesn’t blow up.”
Somewhat ironically, Dr. Martin’s work in aerospace engineering arose out of discontentment with the field of physics. “I got tired of with dealing with things you can’t touch,” he says. After beginning a master’s program in engineering, Dr. Martin started working with large industrial circuit breakers. Specifically, he modeled the electric arc interactions which transferred heat to the walls and caused them to break down—a process called ablation. From there, his research on heat transfer and ablation led him to study those processes as they apply to spacecraft. In 2005, Dr. Martin received his Ph.D in Mechanical Engineering from École polytechnique in Montréal and then moved to Lyon, France to begin his post-doctoral work. In 2007, his research led him to the University of Michigan in Ann Arbor where he remained until being invited to join the Department of Mechanical Engineering at UK in late 2010.
The good news, says Dr. Martin, is that the Earth’s atmosphere removes more than 95% of the heat as a vehicle re-enters it; however, the remaining 5% must be dissipated if human beings and instruments are to survive the energy buildup from the speed at the time of re-entry. That doesn’t even consider if the probe is trying to land on Mars or one of the moons orbiting other planets. “If you design your vehicle for the Earth’s atmosphere, it accounts for certain types of gas but if you’re going to Mars, it’s a completely different kind of atmosphere so you have to rethink and redo everything,” explains Dr. Martin.
Change the planet, change the mission, change the size or speed of the vehicle, and the engineer has to change the design of the vehicle to account for ablation. Reducing the margin is one area Dr. Martin claims could use substantial improvement. “With the last Apollo mission, about 15% of the mass of the vehicle was the ablative heat shield. So we sent something of which 15% wasn’t usable payload—basically useless. If you’re trying to build a station on Mars, well…it gets expensive.”
What Dr. Martin enjoys most about teaching is the interaction with the students and the chance to work together on challenging projects. In addition, Dr. Martin sees the geographical proximity to nearby Air Force bases and NASA research centers as an attractive draw for students interested in aerospace engineering. The NASA Glen Research Center in Cleveland, Wright-Patterson Air Force Base near Dayton and Arnold Air Force Base in Tennessee are cutting-edge research locations within relatively short distances, not to mention local aerospace companies like Lexington-based Advanced Dynamics, Inc. “There are great resources for students who want to study aerospace engineering without leaving the area.”