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Life in the Planetary Aeolian Laboratoryby Greg Wilson
October 10, 1996
After two weeks of summer vacation in Germany and England, it was time to get back to work and the Planetary Aeolian Laboratory. I really like to travel, but it was time to get back to science and a full summer of research, presentations and proposal writing.
Upon returning home and getting over jet lag, I had to prepare the Mars Wind Tunnel for a series of experiments involving wind flows of sand dunes. Dr. Haim Tsoar, a geography professor from Israel, and a world authority on sand dunes, would be spending two months at the laboratory, and together we were hoping to explain why we don't see a particular type of sand dune on Mars. The dune type we were interested in is called a linear dune. They happen to be the most common form here on Earth, but we don't see them on Mars. Why? We think is has something to do with the thin atmosphere of Mars. With the help of Dr. Bruce White, a fluid mechanics professor at University of California, Davis, we developed a matrix of experiments where we simulated different Martian atmospheric conditions and wind directions. Hopefully this would answer our questions, but developing the instrumentation needed to measure the flow field in all the locations was going to be difficult.
We started by attaching, in a grid pattern, pieces of light string (tuffs) to the dune model in the tunnel. When the tunnel was turned on, we could see the flow directions and Haim explained to me the mechanism for how linear dunes were formed. If these mechanisms were not present on Mars, it would explain why we don't see them.
While this was going on, I had to prepare at talk on the physics of wind erosion and dust generation for a presentation in Lubbock, Texas. Not only did this take time away from the dune experiment, but I would be traveling for a whole week. I spent five years there during my graduate studies, and it was really great to see my old instructors and advisors again. The talk went well, but I couldn't help but worry about the experiments going on at the lab, and how we were going to get the measurements we wanted. I think being a scientist is a lot different than other jobs because you are always thinking about science and how to solve problems.
When I got back to the lab, Haim was tired of the "tuffs" and wanted to make measurements of the shear stress at different locations on and around the model. You see, it is the shear stress (energy of the wind) that moves sand grains and makes sand dunes, and measuring this would help prove our theories. We normally measure shear stress by measuring the wind velocity gradient near the surface with a pitot tube, but this technique does not work in separated flow, which was occurring down-wind of the dune model. I said, "Houston, we have a problem!"
One day, when I was walking down the hall of this building, I saw a poster of this supersonic (faster than the speed of sound) airplane wing and a simple technique of measuring skin friction on it. After doing some math, I learned that shear stress can be calculated from skin friction measurements. So I went to talk with Dr. David Driver, the author of the poster and he was more than happy to help me. The technique worked really well, except for the fact that small dust particles really mess up the measurements. Solution, wash out the entire wind tunnel and put a big air filter on it. This was not a fun job. But it was well worth it. And while the experiment is not complete yet, and Haim is back in Israel, we are really excited about the things we are going to learn and the many applications we have for this new technique. While all this was going on, proposals to do science with Mars Pathfinder were quickly becoming due. I worked on the wind tunnel experiment during the day, my nights and weekends were spent working on my proposal. I think it would be really exciting to operate a spacecraft on the surface of another planet, so I didn't mind giving up a lot of my personal time to try to make it happen.
As of October 10, the proposal is done and in the mail. It is time to sleep and relax a little. I still have the dune experiment to complete, other proposals to write, and other trips to take. As for now, I'm going to go backpacking in Kings Canyon, California this weekend with another planetary geologist here at Ames and my girlfriend.