An Interview with Sami Asmar
Meet Dawn Team Member, Sami AsmarThe following interview took place in Pasadena, California on March 26, 2010, between Sami Asmar, member of the Dawn team at JPL, and Education and Public Outreach team members Whitney Cobb (Mid-continent Research for Education and Learning—McREL) and Education and Public Outreach Manger, Joe Wise.
What is your team's role in the Dawn Mission and your role within that team?
SA: I'm a member of a multi-mission team at the Jet Propulsion Laboratory that investigates planetary gravity. I coordinate the gravity field analysis within the Dawn Science Team. Using a special technique, my colleague, Alex Konopliv, and I are specifically investigating the gravity fields of the two bodies the Dawn mission will visit, Ceres and Vesta.
WC: How is your job important to the mission's success?
SA: The key is achieving the primary science objectives. It's not gravity just for the sake of gravity—we will use gravity to explore the interior structure of the two bodies. I can't imagine a mission visiting a body, especially for the first time—possibly the only visit in our lifetimes—and not studying the interior structure.
WC: Please tell us more about the technique you mentioned.
SA: The best way to measure, determine, or investigate the internal structure of a planet is to land on the surface to place seismometers or drill for samples—and that's just not always practical. There are two techniques of remotely sensing what the inside is made of: one is to measure the magnetic field, and the other, our technique, is to measure the gravity field.
If a planet has a dynamo-type magnetic field, it generally has a liquid core and the motion of charged particles generates the magnetic field on the outside. There was a big surprise at Mars when the Mars Global Surveyor detected a magnetic field—suspecting that there was a dynamo and a liquid core, people got very excited. It turned out that there was a remnant magnetic field on the surface—just magnetized rocks. The thought is that Early in Mars history, Mars had a dynamo and the planet got magnetized. When the dynamo died (solidified), it maintained some remnant effect—which is what was measured.
Gravity is a more direct method to evaluate a solar system body's internal structure because you measure the actual effects in real time. Our technique is to measure the gravity by tracking the radio signal that the spacecraft transmits to a ground station on Earth. When a spacecraft flies by a body, or orbits a planet, the gravitational forces literally pull and push on the spacecraft. If it's carrying a good radio, hopefully there's a two-way transmission between a ground station and the spacecraft. The frequency of the radio signal is shifted by the Doppler Effect, which is proportional to the amount of forces acting on the spacecraft.
We measure the effect of the gravitational field, manifested as forces on the spacecraft, which in turn manifest themselves as a Doppler shift on the radio signal. That's what we measure on Earth and we work backwards translating how much force it would take to shift the signal that much. We're talking about very small numbers, so the instrumentation has to be very precise. That's our strong suit and my expertise; I'm the experimentalist. We work backwards measuring the gravitational field, from which we deduce models about the interior structure.
WC: What are some of the challenges of this aspect of this mission?
SA: We have to use the radio communications antenna on Dawn to get our data and transmit it from the spacecraft to Earth. So we prefer the antenna pointed in Earth's direction. The challenge is that we're competing with other instruments for where the spacecraft is pointed. Dawn's other instruments might want to be measuring surface features, gathering data for surface images, and other various effects, and it's not always suitable for those objectives to have the antenna pointed to Earth. So there's a little bit of a time share, a competition as the team develops a sequencing based on understanding and prioritization of the mission's varied objectives so that each investigation—including ours—can get its share fair of data.
WC: Is there a unique aspect of the Dawn Mission that is particularly compelling or interesting to you?
SA: It's probably the only mission I know of in deep space that will visit two bodies. Voyager 2 visited the four gas giants—but they were all fast flybys. To actually orbit a body, make measurements, spend an equivalent of a lifetime of what other missions would do, then decide, "Okay, we're done. Pack up, we're moving," and you fire up the engines then do it again—that is certainly unique. It is challenging and can be risky, but the project team has planned it well.
WC: Communication and writing are important to your job—we've heard so many times that communication is critical. Would you speak to that?
SA: I actually write a lot. I write for fun, and to be honest the scientists I work with tend to appreciate that skill. They're just so focused on the science, and they may have a hard time explaining what they're doing. I found myself able and interested in writing and communicating, and people valued that. I speak to schools occasionally and it's fun; I really enjoy the experience and the feedback I receive.
ADVICE TO ASPRING ENGINEERS OR SCIENTISTS
Can you describe what field of mathematics kids would pursue in order to study gravity?
SA: The final outcome of a gravity field measurement is described mathematically by something called spherical harmonics. This is a mathematical expansion of a function, very advanced mathematics. The closest association for anybody in high school is probably trigonometry, because spherical harmonic expansions are nothing but a series of sines and cosines. So that turns out to be the cornerstone of any math we work with—trigonometric functions. It's just amazing how much you can build on those.
So in a sense you're taking a signal and unpacking it mathematically?
SA: The easiest way to think about that—and that's taught in sophomore-level college classes as Fourier analysis—is if you have a square you're trying to represent with mathematical functions of sines and cosines They never fit because they're all rounded. One approximation wouldn't work, but two approximations come closer. If you have a bunch of them, smaller and smaller, then you can approximate a square better. So, for any arbitrary shape and feature, there is indeed a number of sines and cosines (and the number might be very large, depending on how odd the shape is), that can mathematically describe it. So, the tools we use are basic math.
What advice would you give to aspiring engineers or scientists?
SA: It goes back to my point about trigonometry and sine functions. It's amazing how much, at least as it appears on the outside, science seems to get really fancy and exotic. But the truth is that you'll never get there without having the fundamentals down. If a young engineer or scientist or student wants to get into this field, I would recommend studying math and basic physics and making sure you really understand that. It's amazing how the rest just falls in place automatically.
Everything I know about what I do today, I learned on the job. Yet, without what I learned in school—the basics, the math, the physics—I would never have picked up on what colleagues were telling me. When I read a newly published paper, I follow it because I have the basics. So there's no point just jumping into what appears to be advanced space science, and even astronomy to some extent, without having the fundamental math and physics. When my son is the right age, that's what I will emphasize to him.
WC: If there is one thing you wanted the younger generation to understand about space exploration, what might that be?
SA: That space exploration is risky and should not be taken for granted. Sometimes because of our successes, which we're blessed to have had, we start taking for granted that we can go to the next step—like taking humans to Mars. The reality is that it's far riskier than what many might appreciate. To get to that level of our national goals and ambitions, we have to go back to the basics and the fundamentals again, invest in a broad array of basic technologies to enable these endeavors.
WC: What are your leisure time activities?
SA: I'm very active in music, among other things, and writing—writing about music, and music about writing! I am active in the world music field, specifically music of the Middle East. I have an ensemble that I lead. We use ethnic instruments, and we utilize an Eastern structure of the scales that's very different from the Western classic tempered scale. It makes it very interesting to perform to audiences, and to educate them about it. Usually there is very positive feedback; people appreciate that the music can be very uplifting and percussive. But it also can be very meditative, especially flute, which is what I play. For me, it's a stress-release mechanism from work and life, and I can spend a lot of time doing that.
WC: What was your favorite book as a child?
SA: I liked so many books. The one title that jumps out is the Hitchhiker's Guide to the Galaxy [by Douglas Adams]. What I really liked about it that book was that it was scientific. You are in a space environment, and you have to use some scientific logic—even though it's science fiction. The author's writing style was just so funny—he could have been writing about cooking recipes for all I cared, I just loved that style. So that was fantastic. After reading the book, BBC radio had an associated series that I began listening to. So that one book sticks in my mind, and it was very relevant to what I ended up spending my adult life doing.
WC: Is there anything else that you'd like to share about the Dawn Mission?
SA: I think the team is an incredible group of people, starting from the top with Chris [Russell] and Carol Raymond. They're so good yet easygoing, and so open. I was not part of the original team. I was asked by my colleague Alex Konopliv, who is the lead gravity scientist, to help out and then ended up as the gravity working group chair. I felt right at home because they're just a very welcoming team.