Deputy Principal Investigator Discusses Dawn Asteroid Mission

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Deputy Principal Investigator Discusses Dawn Asteroid Mission
07.02.07
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SCHUBERT
From the Kennedy Space Center in Florida, I'm Corey Schubert.
NASA's upcoming mission to study a pair of asteroids is gearing up for a launch aboard a Delta 2 rocket. How will Dawn study these compelling asteroids? Deputy Principal Investigator for the mission Carol Raymond joins us now with more....welcome!
RAYMOND
Thank you Corey, I’m glad to be here.

SCHUBERT
What is your role in the Dawn Mission and how will your role change after the spacecraft is launched?

RAYMOND
I’m the Deputy Principal Investigator for Dawn and I’m also a scientist at the Jet Propulsion Lab. My role in the mission is really to look after the science of the mission. Working with the team that is building the spacecraft that’s designing the ground operations structure and planning the operations and I basically try to keep track of all of the activities and make sure that the science needs are being met before the mission gets off the ground and then after launch my role will change to be more involved in analyzing the science data that comes back from the bodies. That’s the real payoff for the scientists on the mission obviously.

SCHUBERT
Tell us about the ion engine and what does it do for the spacecraft?

RAYMOND
Well, the ion engine basically pushes the spacecraft out into the asteroid belt that’s its main function. The ion engine is a very new type of propulsion system which has flown a few times now on other missions but we’re using it to do a historic first and that’s to go out into the main asteroid belt and go into orbit around one asteroid, leave it and then go to another asteroid and this is a very, very exciting mission itinerary.
So the reason we can do that is that the engine is kind of like maybe “Tang” to astronauts in the sense you can take a full tank of Xenon and then the engine allows you to use sunlight to turn that Xenon into thrust. We ionize it into a plasma, the plasma is accelerated towards grids that also have an electric charge and as the particles exit the spacecraft they exert a very small force which eventually in the vacuum of space builds up, up to a tremendous speed. So what we’re really doing is really driving out to the asteroid belt, out to the objects in the asteroid belt. We’re constantly thrusting, but at a very low level, compared to traditional chemical thrust missions.

SCHUBERT
Why does it take so long to get to the asteroids?

RAYMOND
Well they’re really far away, is one answer. We’re going to the main asteroid belt and that’s beyond the orbit of Mars, it’s between Mars and Jupiter. There is also a near-Earth asteroid belt which is between Earth and Mars and that has been visited by the NEAR spacecraft that went to Eros.
So we have to go beyond Mars and because we’re using this low-thrust ion engine it takes longer, but it also allows us to visit two objects because the spacecraft is so much smaller and we get so much power out of the propellant that we do bring. So it does take us four years to get to Vesta, our first target and then it will take us another three years to get to Ceres which is a bit farther out but till not all the way to the of the asteroid belt.

SCHUBERT
What are the instruments aboard Dawn and what they will show us?

RAYMOND
Dawn has three instruments and one system which provides us science data. The three instruments are framing cameras which are provided by the Max Planck Institute in Germany and the framing cameras are giving us images of the surface in eight color filters so we have color mapping of the surface of the bodies. We also have visible an infrared mapping spectrometer which is provided by the Italian Space Agency. And this is another way to look at the surface through a special lens which gives you information about the wavelengths that are being emitted from the surface and those are diagnostic of what kinds of materials there are. So with that instrument we are looking for the minerals that make up the rocks and we’re essentially doing something like a geologist would do when they go out in the field and map units.
Our third instrument is provided by the Los Alamos National Lab and it’s a Gamma Ray ad Neutron detector, and in this case we’re exploiting the cosmic ray high energy particle flux onto the surface of the body to examine what elements are at the surface and slightly below the surface and the way that works is that the particles interact with the molecules and the elements on the surface and by looking at the energy of the particles coming in and the energy as they are leaving from the interaction with the surface we can use a diagnostic tool to find out what was there that it “bumped into” essentially and it’s very diagnostic of hydrogen and that instrument will tell us about how much water is on the surface, either bound up in clay minerals or other types of materials and how much water there is perhaps water ice under the surface.
It will also provide complimentary data to the mapping spectrometer to tell us about the minerals that are on the surface as well.
Now our last instrument is not an instrument per se, but a system and that’s the telecommunications system. We have a large high-gain antennae and we use it to communicate with Earth. And by measuring the position of our spacecraft we can map the gravity field of the bodies because we are looking at how the gravity field of Vesta and Ceres are tugging on the spacecraft going in orbit around in orbit around the bodies and by doing this over and over again as the spacecraft is at different places around the body we can map out the gravity fields. And what we do with gravity is to understand more about what’s inside the center of the bodies.
So it’s a way to look remotely into the center of the body and understand more about its structure.

SCHUBERT
What is the most exciting day for a principal investigator or deputy investigator?

RAYMOND
Well there are lots of exciting days. Launch will be a very exciting day because it’s amazing to see something that you’ve been working on so long actually leave the Earth, heading off towards the targets. But I’m sure that the most exciting day for me and this mission is going to be when we get our first pictures back from Vesta which is our first target. Because it’s obviously the reason we’ve worked so hard on this for so long is that are wanting to look at those bodies.

SCHUBERT
How much do we know already about these asteroids?

RAYMOND
We have very blurry images of both Vesta and Ceres from telescopic observations. We’ve looked at both the bodies using Hubble data and those are the best images we can obtain from the ground. But still, they don’t reveal the detail that we need to understand the surface of the body to understand the processes which have shaped them and what kind of materials they are made of which is what we are really after in this mission.
We also have a lot of pieces of Vesta on the Earth because a lot of the meteorites that have fallen to the Earth have come from Vesta and we know this because of doing this matching of spectra of rocks that have been analyzed in the laboratory the meteorites to the telescopic spectra of Vesta.
So we are doing somewhat of a reverse sample return mission in that we can look and examine these rocks in great detail. Which we think some of them come from deep in the interior of Vesta and go look at the body and put those pieces together to understand it in a very complete way.

SCHUBERT
Why visit two asteroids as opposed to just one?

RAYMOND
Well that’s really what the mission is really all about. This mission is a comparative planetology mission meaning that; we want to understand why these two bodies in the asteroid belt exist as such different bodies today. They began in similar position within our solar system. They’re at the dividing line between the drier rocky terrestrial planets and the outer gaseous giant planets. They are remnants of the earliest epoch of solar system formation and their formation was stopped when Jupiter began to exert so much force that it disrupted their ability to grow any larger. It also disrupted the interactions in the asteroid belt, such that many bodies that may have been growing large were shattered.
However; these two bodies were large enough that they escaped those catastrophic collisions and so they essentially exist as little time-capsules from this very, very early period of solar system formation. And Vesta being very dry and differentiated and basaltic and being similar to our moon and Mars as in contrast to Ceres, looks more like a moon of the outer solar system. It retained a lot of water and organics and has not melted internally, it asks the question, did these two objects end up in this state because of their initial conditions? Was there a gradient in the chemistry of the material or was it a thermal gradient that caused them to follow these two very different evolutionary paths? And by asking and answering that question we expect to shed some light on why we have the diversity of objects in our solar system that we see today.

SCHUBERT
How did Dawn get its name?

RAYMOND
Well, Dawn is a journey in space and time. And we feel that we are going back to the dawn of our solar system. So, that’s why we named it Dawn.

SCHUBERT
Besides visiting different targets, how will history compare this mission with past missions such as Pioneer, Voyager and New Horizons?

RAYMOND
Well, I guess that question would be answered by the people writing the history books. But I would guess that this mission is very similar to those missions in the sense that we are on a reconnaissance quest to look at two very new worlds, very unlike things that we have visited so far in the solar system.
And we’re beginning reconnaissance of a part of our solar system which is fairly unknown, but it’s likely a key to putting together the whole puzzle of how it all came to be. So I think that with the New horizons mission to Pluto, with the Messenger mission to Mercury and Dawn to the main asteroid belt we’re really completing now a very detailed exploration of our entire planetary neighborhood.

SCHUBERT
Carol, thanks so much for joining us.

RAYMOND
It’s a pleasure to be here.

SCHUBERT
For more on the Dawn mission, visit nasa.gov.
I'm Corey Schubert.
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