2012

Donald Wegel, Lead Engineer, NASA Goddard Space Flight Center, Greenbelt, MD

NTB: Do you see other applications or uses for a tool like this?

Wegel: We mentioned in some earlier papers that this kind of tool could be used as a rapid retrieval system. On the Moon, if you just wanted to hop into a crater, grab a sample, and hop back out, you could imagine outfitting your system with a sample-collecting harpoon. It’s the same idea on Earth. Let’s say there’s a scenario similar to the nuclear disaster in Japan, where you send some kind of robot in, fire a harpoon, retrieve a sample, and come back out.  In reality, though, we’re focusing more on sample collection on comets and asteroids; however we have talked about modifying the system for Mars and maybe even Titan, one of Saturn’s moons.

NTB: The European Space Agency has the Rosetta Mission, which will use a harpoon to grapple a probe to the surface of a comet. Can you talk about the similarities and differences between the two missions?

Wegel: That’s actually one of our early inspirations, and what we look to closely. They spent a lot of time and effort and did a really impressive job on their harpoon grappling system. Using a tether is very challenging, especially in zero g. They behave very strangely and the possibility of getting tangled, especially when retrieving the sample, is a concern of ours. But Rosetta did a great job of designing a reel system that allows you to shoot into different densities, and not knowing what the density is to begin with, you can fire in, and the reel itself will have the clutch mechanism that throws the harpoon down if the comet doesn’t have enough density.

Some of these bodies have densities as low as cotton candy, so you can imagine firing a high-energy shot in, and nothing slowing the harpoon down, except for yanking the tether out of the spacecraft. [The ESA] has a really sophisticated tether design which avoids that, controls that, and allows retrieval of the harpoon. Also, they’ve done a lot of work with what I believe they call a “smart tether.”  Basically there is a data cable running down a tether, so not only is this tether mechanically important, but it also actually carries the signal and information back from the harpoon. So you’ll get temperature data and accelerometer data as the harpoons penetrate, and when they send back some of that data, that will help us significantly in knowing more about the comet they land on and what to expect.

NTB: What is most exciting to you about sampling a comet?

Wegel: I think by far the most inspiring possibility is finding the primordial ooze or the origin of life on earth. I can’t think of a more incredible thing to be a part of, to shed even any light on that, let alone prove some of that origin. That alone is what inspires me the most.

NTB: What still needs to be done with the harpoon?

Wegel: We’d like to start shooting harpoons from a greater distance. Right now, we’re shooting probably only two feet of free flight. It’s really not designed to fly freely. We can’t be as close to the surface as we wanted to be. We need to make sure that we can have these fly freely for a while, so whether we use rifling and have the harpoon spinning to maintain stability, or whether we use a slight drag with a tether to keep it stabilized, we need to basically fire the harpoon a longer distance. That’s quite a challenge because we need to have this test bed, which right now only shoots two or so feet. We would like to shoot closer to 10 or 20. We’re in the process right now of going to the next level on both longer free flight and a retrieval system, so we’ll play around with and design a tether system that can retrieve the sample cartridge.

NTB: What‘s a typical day for you?

Wegel: Fortunately, there is a lot of variety in this job, which I like a lot. I’m working on several other projects at the same time, but generally there’s one part of the day I spend using Pro/ENGINEER, which is a 3D CAD model program, and literally just design hardware. What I like the most about that is that you start with an idea sort of spinning around in your head, and you spend a little time getting that idea into the computer. You start to see this 3D model of what was in your head and now on the screen. And then you run a little analysis and find that “Well, this part needs to be a little different, this needs to be thicker, this should be thinner, sharper, or whatever,” and it starts to morph into the real part. Then you actually get 2D drawings, you hand somebody a piece of paper and or a file, and you eventually get an actual part that used to be spinning around in your head. You’re holding that piece of hardware in your hand. So that creative process, and actual creation process, I think, is what I like the most.

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