TOPICS > Science

Deep Impact

July 4, 2005 at 12:00 AM EDT


RAY SUAREZ: This Fourth of July, NASA put on a fire works display of cosmic proportions when the Deep Impact probe collided with a speeding comet. NASA hopes the collision will give us a peek at ice and rock left over from the early solar system.

The two-part probe, about the size of an SUV, took off on Jan. 12 from Cape Canaveral on a winding 268 million mile journey. One part of the probe collided early this morning with its target, the comet Tempel 1, at 23,000 miles per hour. The impact left a hole that may be as wide as a football stadium and 14 stories deep. The second part of the probe zoomed past the comet and continues to relay images back to Earth.

To walk us through the project is one of Deep Impact’s chief engineers, Rick Grammier. Welcome. Now that you’ve had a couple of hours to sift through your early photographs and some of the images and data that’s being sent back from the flyby craft, can you say now that everything went as planned?

RICK GRAMMIER: We can say that it went better than we planned. It is absolutely phenomenal how well it went. We didn’t have to exercise any of our contingency options and the science we’re getting back is phenomenal.

RAY SUAREZ: That smaller craft that was meant to collide with the comet, once you lined it up and it was on track to smash into it, what happened then? It was just a situation where then it was time at JPL to sit back and let it happen?

RICK GRAMMIER: No, not at all. Actually it was quite tense. We let it go 24 hours before impact. We put it on an impact trajectory, which it was basically in free flight then for 22 hours, but we had always planned that during the last two hours the auto navigation software would kick in and we would have to perform up to three, what we call impact trajectory maneuvers. In fact that’s exactly what we did. The first maneuver was computed and fired at 90 minutes prior to impact. It then assessed where it was, computed another solution and fired at 35 minutes before impact and then finally 12.5 minutes out it performed its last maneuver which is basically to offset it so that it could be viewed by the flyby spacecraft. And it performed flawlessly.

RAY SUAREZ: The pictures of the approaching surface of the comet are really stunning. Until how close to impact time was that smaller craft taking pictures?

RICK GRAMMIER: Actually, the last picture we got back was three seconds prior to impact, which is phenomenal. We had thought that we’d be lucky if we could get one 30 seconds. That was our goal. To get one 30 seconds prior to impact but we were concerned about the dust particles when we fly through the coma that would be knocking the Impactor spacecraft back and forth and may cause it to have its optics stand blasted. It just kept taking it all the way in.

RAY SUAREZ: What did the other craft that was watching all this going on see?

RICK GRAMMIER: Well, the flyby obviously was standing back a little bit per the plan. We had slowed it down just long enough so that it could get 13 minutes of imaging, of the actual impact and the crater formation. And it, in fact, had its own algorithms that targeted that exact same spot which was one of our concerns as well, that it wouldn’t be able to see the impact site if it didn’t compute it right. And it performed again flawlessly.

It actually captured the impact, the resulting bright flash which was just fantastic. It captured the crater formation and the debris that was thrown out. Then as it passed under and started looking back, it could still see the cratering debris that was being illuminated by the sunlight so it actually captured just some fantastic images.

RAY SUAREZ: This early on before you’ve really had a chance to go over your data, what observations can you make just based on what you’ve been able to see so far?

RICK GRAMMIER: Well, that’s a good question because we haven’t had much time to actually evaluate the data. What we can say is we’re definitely positive that we created a crater that was larger than a house. If you’ll recall we thought maybe up to the size of a football stadium. They’re still trying to sort that out. We’re still trying to get the data down so we know that we created quite a crater. We believe that it penetrated quite deeply which means we’ll get a very good look at the interior and also throughout some of the interior composition into the resulting impact debris.

We do know or feel that the surface is likely very soft crust on the surface and that it was definitely — looks like it might have been layered. We can’t say that for sure. The scientists are still trying to figure that out. But what I can tell you is we just have a wealth of scientific information to go through in the next months.

RAY SUAREZ: That spray of debris that came from the cratering, is any of that being collected? Is any of it capturable or is this really an observation mission?

RICK GRAMMIER: This is really an observation mission. It’s unlike Star Dust that went through Velt-2 to capture or collect some of the particles coming off the coma. This was strictly to create the impact crater and observe the ejecta as well as how the crater forms which tells the scientists a lot about the material properties and constituents of the actual comet itself. There are observation platforms obviously orbiting the Earth like Hubble and Spitzer and Chandra that are observing these in various regimes of the spectrum as well as observatories on Earth.

RAY SUAREZ: Once the craft tells you everything it knows about this morning’s event, is there any work left for it to do or is it just hanging out there in space.

RICK GRAMMIER No. There’s not much work left to do after that. Basically we’ll spend the next couple of weeks, 10 days, getting all the data off of it. It was continuing to image per the plan after it flew by, it would periodically turn back image and then turn back so it could relay the data down. We’re quite full on board on our memory right now from all the data that we have taken. We’re playing that back. When that is completed, then we’ll basically moth ball the flyby spacecraft.

RAY SUAREZ: Will you ever be able to see Tempel 1 again in the future from any other observation point?

RICK GRAMMIER: Well, certainly this is one of the periodic comets so it comes into the solar system about every five-and-a-half years. It’s observable via the observatories on the ground or if they wish to observe them from the orbiting platforms, they can do that as well. But we don’t have another plan to send another spacecraft there.

RAY SUAREZ: Rick Grammier, thanks for being with us.

RICK GRAMMIER: Thank you. I appreciate it. Happy Fourth of July.

RAY SUAREZ: Same to you.