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OFJ97 Field Journal from Dave Atkinson - 2/11/97

It's hard to believe that more than a year has passed since we arrived at Jupiter. At 3:15 P.M. on Saturday, December 7 I thought back over the excitement of one year ago, and the activities that have followed. After receiving the wind experiment data in bits and pieces following the arrival of the probe at Jupiter, the wind analysis was completed between press conferences, professional conferences, and writing papers. There was also a lot of travel. Right after the probe mission, I was going to a conference or meeting every month all over the world: San Jose, Houston, The Netherlands, England, to name a few.

For me, however, the best part has been sharing the thrill of going to Jupiter. In the past 15 months I have been to many, many elementary schools, astronomy clubs, high schools and colleges throughout Idaho, Washington, California, and Arizona. Since the whole purpose (and the most exciting part) of science is sharing what is learned, I am hoping to continue visiting schools and groups for a long time.

The culmination (although not the end) of these trips was in early January, more than a year after our arrival at Jupiter. A conference was held in Padova, Italy to celebrate Galileo the scientist, Galileo the spacecraft, and Galileo the Telescope (The Galileo National Telescope, which is being built in Italy). On the last day of "The Three Galileos" Conference, we all visited the Vatican where we had an audience with Pope John Paul II and a tour of the Vatican Observatory.

Throughout the year there have been many occasions where I have had to sit back, catch my breath, and think to myself that we made it to Jupiter! We were *really* there - tasted it, touched it, smelled it, saw it. It is sometimes difficult for me to completely comprehend what was accomplished in December, 1995, and what is still being accomplished now as the orbiter continues to study the planet and its moons.

So, in between being philosophical and sentimental, I have had some work to do. For several reasons it has been difficult to make sense of the wind measurements. First, to determine the speed at which the probe was drifting in the winds, I needed to know the speed at which the probe was falling on its parachute through the atmosphere. This is easy to calculate (sort of) if you know how fast the atmospheric pressures and temperatures are changing. Fortunately, these measurements were made by the Atmospheric Structure Instrument (ASI). Unfortunately, like the rest of the probe, the ASI got much, much hotter than it was supposed to. Imagine putting a radio into your oven and turning it to 300 degrees Farenheit (Kids - don't let your parents try this at home!). Your radio wouldn't last very long!

The inside of the probe is thought to have reached about this temperature (300 degrees) before it stopped working. So before we could completely understand the probe data, including the radio frequency of the probe signal used for the wind measurements as well as the ASI data, we had to go back and see how the instruments worked at very hot temperatures. During the spring, summer, and into the fall we took some spare instruments and put them into ovens at NASA Ames Research Center to see how well they worked as the temperatures got higher. It has only been in the past several months that we finally decided we understood how well the probe instruments were working and felt confident that the wind measurements were correct.

So - what are the winds? It looks like we have had a big surprise - the winds don't get weaker as we go further beneath the cloud tops. They get *stronger*. At the cloud tops the winds are about 100 m/s (this is a breeze of about 220 miles per hour). As we go down the winds start picking up, reaching some nice kite flying weather of about 175 m/s (about 385 miles per hour).

So, is the work finished? No - there is still more to do. When the effect of the wind is subtracted away from the probe signal frequency, we are left with the "left-over" frequency (the frequency residuals). This is due to probe motion caused by something other than the winds. In the frequency residuals I think I can see the effect of the probe spinning, and the swing of the probe under the parachute. There is some turbulence causing the probe to bounce and this is probably in the frequency residuals as well. So I now get to start analyzing the residuals, and, once I am finished, I should know exactly how it would have felt to sit on the probe as it plunged deeper into Jupiter's atmosphere. Every swing, sway, bump, and turn the probe made during its final hour will be discovered.

What now? Of course, Galileo still takes much of my time. I am currently on a research sabbatical from my university in Idaho and spending a warm winter at the Lunar and Planetary Laboratory in Tucson, Arizona. My work now is concentrating more and more on the next great exploration - the Cassini mission to Saturn and its largest moon Titan. I am once again involved in measuring winds, this time on Titan. My guess is that the exploration of Titan and the discovery of what lies beneath its atmospheric haze - mountains and glaciers? Seas and lakes? - will be one of the most exciting chapters in the history of solar system exploration. Mark your calendars - we leave for Saturn next October (1997) and arrive in July, 2004.


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