Sandblasting Craters for Future Space Landings

Coincidentally, I got a message today from my colleague Dr. Phil Metzger asking me about research I had done during my grad school days at UCF in 2012. Phil is now a researcher at Florida Space Institute based out of UCF, but at the time, he was a research scientist at NASA's Kennedy Space Center in a lab that is now known as Swamp Works.

As I wrote in my previous entry, I spent much of my research at UCF conducting experiments in vacuum chambers. So what was I do to when my vacuum chamber broke and needed a replacement part that would take two months to obtain? Summer vacation? No, find other work to do. With the help of Phil and the Florida Space Grant Consortium, I spent much of the summer working in Phil's lab.

Similar to my marble into regolith impact experiments, Phil had done some work sandblasting regolith with jets to mimic a retrorocket landing on a planetary body to understand how craters are formed. We wanted to continue those experiments using varying jet width sizes, intensities, and heights above the regolith. We also used several types of granular materials, including many light ones such as plastic confetti and corn cob pieces to simulate a reduced gravity environment such as Mars.

We conducted the experiments in clear boxes with half of the jet of gas shooting in and half out in order to capture a cross section of the experiment. We recorded the blasts and looked at the way the crater formed and how the granular material moved due to the gas, studying the videos frame by frame. Similar to my marble impact experiments, the ejecta or ejected material (the splash) and the crater rim also mattered.

What I thought was the coolest (aside from blasting stuff at high velocities, of course) was the way the crater walls formed. The regolith along the sides of the craters spun like caught in a bad wind storm, creating multiple little vortices (or vortexes, if you prefer). The crater walls seems to move upwards in waves against the direction of the current. Just like blowing air through a straw into a drink, the liquid needs to move up and over, out of the way of the incoming air, and the air bubbles carry the liquid up. Granular materials act a lot like a liquid despite being made of many small solid pieces. It's fascinating to watch.

I also got to play with microscopes. I took magnified photos of the materials I used. I think amber is the coolest material to image close up out of the ones I used. I needed to understand the properties of the materials and measure the angles of repose, that is, the steepest angle that I could pour the grains into a pile without the side of the pile sliding down.

One summer isn't long to do much research and Phil is continuing the experimentation. Best of luck to Phil and the students who take this work on!