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Emily LakdawallaJuly 1, 2005

Deep Impact encounter minus 3 days

Jul 1, 2005 | 09:34 PDT | 16:34 UTC: I'm on location for Deep Impact

OK, I'm in...I arrived at an unusually empty Jet Propulsion Laboratory this morning in advance of the first Deep Impact encounter press conference. (It's empty because most JPL employees have Friday and Monday off for Independence Day Weekend -- no such luck for me or the Deep Impact team.) I've gotten my Enormous Bright Orange Badge identifying me as MEDIA and I seem to have pretty good wireless Internet access, so I am ready to write and tell you everything I find out about what's going on with this mission.

Just to set things up: Deep Impact is about to split into two pieces, sending one on a collision course for comet Tempel 1. The mission is designed to expose fresh materials from the interior of a comet to human eyes for the first time. Not only will Deep Impact be watching, but so will a dozen spacecraft and more than a hundred telescopes (many hundreds if you count all the amateurs who are making real contributions to the impact observations).

The impact is scheduled to take place at 22:52 Pacific time on Sunday July 3 (05:52 July 4, UTC), plus or minus three minutes. (Here's the complete timeline.) This morning's press conference is the first for the weekend. Then there is a quiet period, on Saturday -- which is when I'll take my holiday weekend, thank you very much! -- and then things get busy on Sunday, beginning with a press conference at 11:00 Pacific time. Then, at 8:30 in the evening, NASA TV coverage begins continuously, through the impact, and finally they plan a press conference at 1:00 in the morning on July 4 (08:00 UT). I'll be here at JPL through all those events, letting you know what's going on with the mission as I get the news.

Everybody cross your fingers that Deep Impact hits the target and we see a spectacular impact event!

Jul 1, 2005 | 09:57 PDT | 16:57 UTC: Butterflies for Deep Impact

Before the press conference started I had a quick chat with Peter Schultz, the Brown University impact scientist on the mission, and a former professor of mine. I asked him if there was anything that he's done that has compared with the size of Deep Impact. The biggest "boom" he's made involved a 7-kilometer-per-second projectile, only about 2/3 as fast as the Deep Impact collision will be. And the biggest crater he's made experimentally is about a meter across. He commented that he's probably made a bigger splash belly flopping into a swimming pool!

Jul 1, 2005 | 10:44 PDT | 17:44 UTC: Quotes from the Deep Impact press conference

This first press conference is about engineering and mission operations. Science comes in the next hour.

Of five people on the press panel, the only one who smiled when he was introduced was Monte Henderson, who is the rep from Ball Aerospace. There's nothing more he can do to make this work, so he's relaxed! The other managers looked much more nervous.

JPL head Charles Elachi said: "We are going to hit a bullet with another bullet while watching with a third bullet. And to make it more challenging we are trying to hit it from the shiny side. And to make it more difficult, it as never been done before. But the payoff would be worth the risk. For the first time in thousands of years, instead of fearing comets, we will be able to know what they are made of." Elachi is speaking from a position of great strength, citing the successes of the rovers, Cassini, and Spitzer.

Program Manager Lindley Johnson gave an overview, talking about why comets are fascinating. The graphic he chose was of Hale-Bopp -- a spectacular, enormous comet. Tempel 1 is much smaller!

Rick Grammier, Project Manager: mission status: 'All systems are nominal. We have uploaded the final products for the sequence and execution of the encounter. The ground operations team is sitting on the edge of their seats. If I could bottle all the adrenaline I've seen flowing in the last day I probably wouldn't sleep for a year." He shows a funny picture of PI Mike A'Hearn with the "business end" of Deep Impact, the "317-pound copper slug." Grammier gave an overview of the mission, narrating the new Dan Maas animation, which follows the timeline I've outlined before.

Henderson, Program Manager from Ball Aerospace, walked over to a 1/4 scale model to describe its parts. I like this guy -- but it sounds like he's giving a sales pitch to Defense Department representatives! "The armored Humvee of space exploration"?? Some interesting tidbits: the High Resolution Imager on the flyby spacecraft is one of the largest telescopes ever sent to deep space.

There's no question this needs to be a pretty heavily shielded spacecraft because of all the debris in the neighborhood around the comet. Five overlapping copper shields are designed to stop particles up to the size of 1/4 of a gram, or, Henderson said, 1/4 the size of an M&M candy. "These two spacecraft have been designed to accomplished something that the best fighter pilots in this country could not do." That's the bullet-watching-a-bullet-hitting-a-bullet thing Elachi was talking about -- the speeds involved in this mission are so high that human reflexes would have no hope to make the navigation work. Spacecraft have navigated themselves autonomously, at least to some extent, for a long while. Cassini can even point its cameras autonomously. But the speeds involved here are really extreme.

Henderson just mentioned Send Your Name to A Comet -- and pointed out the spot on the impactor where the CD is mounted. That CD is about to be vaporized.

Dave Spencer, Mission Manager at JPL: everything is nominal. "The flyby spacecraft is taking images of the comet every 9 minutes, for both navigation and science -- its size, shape, and rotational characteristics."... "All systems checked out perfectly, and we are ready to go Saturday night." ... "As the comet approaches the sun, it becomes active. Each jetting event changes the orbit of the comet slightly, and Deep Impact has to account for that."

Jennifer Rocca: "For encounter and impact, we follow a strategy of 'live for the moment,'" sending back the highest priority data before the spacecraft's closest approach. Another interesting tidbit: the High Gain Antenna isn't much bigger than typical residential TV satellite dishes. Data rate is 200 kbps. "All commands required to proceed with nominal encounter have already been transmitted to both craft. We have timed the encounter for a period of overlap between 70-meter antennas at Goldstone and Canberra."

The formal presentation is over. Time for press questions now. One press person asked about the complicated dynamics...it is very confusing. I'll try to go through that in a later entry.

Dave Perlman, of the San Francisco Chronicle, is sitting next to me and asking a question. I spent a little quality time with Dave in Darmstadt at the Huygens event -- it's nice to see a familiar face. The group of people who cover space missions is pretty small.

Ooh -- a tough question about how last minute outbursts could affect the mission. Grammier answers: "When we first saw this outburst we wanted to know whether this represented a problem from a mission viewpoint; but the overall impact is pretty minimal. There seems to be an outburst about once every 4 or 5 rotational periods. We had another one this morning." So there likely shouldn't be another one before the mission, he said. "The outburst represents only 20% of the brightness of the nucleus," so it shouldn't fool the AutoNav. "We can only guesstimate at danger to the flyby craft. That depends on how violent the outburst is. As we flyby at only 500 kilometers," he said, you couldn't predict the events; but an outburst wouldn't affect the plan for the mission.

Why was copper chosen for the impactor? Henderson: Science community wanted "as much of a noble metal as possible: gold, silver, or copper, since these were not likely to be present in the comet." Copper was an obvious choice from an expense point of view, he said.

Grammier: "There's not much we can do from a ground control standpoint" to affect the outcome of the mission. The mission depends on the Impactor Trajectory Correction Maneuvers, which will be autonomously navigated. At the speeds involved, and with the 8-minute one-way light time between the Earth and the spacecraft, ground command on Earth would be impossible.

A BBC reporter asked about contingencies. Spencer: "If the impactor doesn't separate, then we'll send ground commands to try to separate. If none of that works, we will take the entire spacecraft and impact the comet that way. That will supply us with fantastic images, and we have an armada of others taking data, so we'll get a lot of data from that." They also have different imaging sequences to accommodate an unexpectedly bright or dim comet.

Another typically tough BBC question: Possibility of no impact? Grammier: "That depends upon our computer models of the comet. We have varied the parameters within our models, and used that to test our systems to see how are systems are sensitive to those parameters. We think we have covered a broad spectrum of possibilities. In the end, though, we still don't know what this comet has in store for us. What science will we get if we have a miss of the nucleus? In that case we will still get very good resolution of the comet nucleus itself, better than we have had before."

That's it for the engineering press conference. Science will be up in 20 minutes....

Jul 1, 2005 | 11:45 PDT | 18:45 UTC: Quotes from the Deep Impact science press conference

A second conference, and second panel, of scientists instead of engineers this time. The conference hasn't started yet but there is already humor. Mike A'Hearn, the Principal Investigator (PI), is in the middle of the panel and they've just powdered his balding dome as he laughed with embarassment. A scientist in the audience behind me joked "they don't like specular reflection!" You know you're a geek when you laugh at stuff like that. (I'm sad to report that I did laugh.)

Who smiled this time? Nobody. They all sort of smirked. I sure wish people would smile when they are introduced on these press panels! However, it was a pretty punchy group. Don Yeomans especially was cracking all kinds of silly jokes throughout the conference.

Tom Morgan, Program Scientist from NASA HQ (the only one wearing a jacket and tie): "5 billion years is a long time," he joked, as it took a while to get the video up showing the formation of the solar system, which he showed in order to explain why comets are important -- because they represent a "small remnant" of the Icy Parent Bodies that formed the ingredients for the solar system formation.

Don Yeomans, Co-Investigator, from JPL: makes the point that the comets that we see in the middle of the solar system are "middle aged" because of the experience they have had in the inner solar system, losing their volatiles. He keeps calling it the comet "nu-cyoo-lus." He emphasizes the resolution we'll get from Deep Impact. Giotto best resolution on Halley was 100 meters, "the length of a football field." ... "In planetary science, better resolution is better." Deep Space 1 best resoluion at comet Borelly was 50 meters, "half a football field." More recently, Stardust best resoluion on Wild 2 was 25 meters, "a quarter of a football field. Our mission is going to resolve objects on the surface about the size of the football, a huge leap forward in resolution."

Mike A'Hearn, Principal Investigator (PI), University of Maryland: "Where are we now? We are still very far from the comet, but we're closing very rapidly. We're already getting very good science results out of the mission. This is one of the very few occasions where we've had continuous viewing of a comet, and we can begin to understand what drives these. They are very short, not much stuff comes out, and they dissipate very quickly. Sneezes. The coma expands very rapidly over half a day. It dissipates rapidly enough that there is no issue for spacecraft hazard at all," which probably isn't quite true overall. I think maybe he meant that yesterday's outburst is of no concern to the spacecraft. A'Hearn emphasized that the Dan Maas video is an artist's conception, "one of many possible scenarios." ... "The events will unfold over days, so we need a worldwide distribution of observers."

Jessica Sunshine, Co-Investigator, from Science Applications International Corp (SAIC), is a spectroscopist (and another former Brown student). "We have almost a thousand different colors of light that we are going to be looking at," in the infrared. Rosetta will be looking in the ultraviolet. Jessica had the bravery to show "squiggly lines," a spectrum of the comet; press officers don't usually like showing spectra because they think the public won't understand them. Jessica is a really good explainer -- I'll get her spectrum and show it to you in a later note.

Jessica continued, rhapsodizing about the spectra she showed: "It was exciting to see anything, 10 days before the encounter. We can identify water, complex hydrocarbons, CO and CO2, and what is refreshing, we can compare to what we have seen previously from the VEGA mission to Halley, and we are seeing almost the same kinds of materials -- but we were 300 times farther away from Tempel 1 than when VEGA was at Halley. We are getting signals 50 times brighter now than even what you see here. From looking at data, we were able to tell that water in the outburst was double what it had been prior to the outburst."

Jessica said that Deep Impact will see unique stuff. "From telescopes, we mostly see the outer coma or atmosphere. But the materials that come out of the comet are short-lived. They react with each other and with solar radiation to make secondary materials, and that's what we see from far away. But with Deep Impact we will be able to see the primary materials as they come out. We are trying to see materials that are on the inside. Like any good geologist, we take our hammer and we hit it, to see how hard it is and see what's inside. These materials have not seen the light of day for 4.6 billion years. That is what we're waiting to see. These materials are going to pass in front of the spectrometer and we are going to see the compositional variation on the inside of the comet." A crater has inverted stratigraphy, so that "the materials that were deeper are now on top. I'm fond of our impactor, our geologic hammer."

Pete Schultz, Co-Investigator, Brown University. "My students call me the 'Master Blaster.'" [They called him lots of other things too, but I won't repeat those here.] "We know how big it is, but we don't know the nature of the comet. Our strategy is to explore the various options -- not just to look at the crater at the end, but to study the materials as they come out, all the way to the initial flash." He shows pictures of the NASA Ames Vertical Gun Range, which is a really, really, really cool experimental device. I envy Pete's students the chance to create impacts at many kilometers per second in a vacuum chamber. "Every time I do one of these experiments, I am surprised. I think that is the best-case scenario -- that we will be surprised."

Now it's time for press questions.

Dave Perlman asked whether the spectrometer could detect rock as well as ice composition. Jessica answered: "Our spectrometer was specifically designed both for the coma and the geology, both for ices and tars, and for silicates, the rock-forming minerals. It's going to be quite a challenge to unravel it all, but if it's there, we're going to see it."

Someone asked if they know what causes the outbursts. A'Hearn: Ideas for outbursts "include the ideas that they come from impacts, transitions from amorphous ice into crystalline ice, and a variety of other things. By looking at the changes in chemical composition in a natural outburst, I think we will be able to pin down the many mechanisms responsible." He emphasized again the benefits of the intensive observing plan, which is unusual for a comet. Latest outburst was yesterday morning, not today as Grammier had said earlier, A'Hearn clarified.

Are we seeing unusual activity at Tempel 1 since it's close to its perihelion (closest approach to the sun)? A'Hearn: "The overall activity of Tempel 1 had been observed at previous perihelion passages. The overall activity peaks a few months prior to perihelion, so the overall activity is decreasing. So it's basically a seasonal effect -- it's summertime where the active part of the comet is. Some comets are active before, some after perihelion. In detail, each one is different. The biggest outburst doubled the amount of water in the coma -- but we haven't worked out the numbers yet."

Someone asked Jessica what the minimal success criteria were: "We certainly want to hit the comet and watch what happens, and as Pete said, we hope to see some surprises."

Will Deep Impact help in defending Earth against cometary impactors? A'Hearn: "It sure is easier to change the course of something if you know what it is that you are changing the course of. You cannot design a sensible defense system if you do not know what the impactors are."

I'll be writing these two press conferences up into a more formal news story, which I'll post later today.

Read more: mission status, Deep Impact

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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