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OFJ97 Field Journal from Duane Bindschadler - 2/19/97

Tomorrow is the the E6 flyby of Europa. Galileo will whiz by Europa at less that 600 km above the surface. From my point of view as a coordinator for the magnetometer (MAG) and dust detector (DDS), it's the busiest day for us in the whole orbit. Here's what's going to happen:

At about 9:30 this morning (about 30 minutes from now) the dust detector (DDS) will be "reconfigured" (which means that certain settings on the instrument are changed). DDS is sensitive to certain kinds of radiation. This radiation becomes more intense the closer we get to Jupiter. At about 18 times the radius of Jupiter, the radiation is intense (strong) enough to cause problems for the DDS electronics. Basicially, it makes DDS think that it's measuring dust particle impacts when there is no dust around. It's like static on the radio interfering with your favorite song. Only in our case, the "music" is data about small dust particles around Jupiter. Reconfiguration helps to cut down on the static.

About 24 hours from now, at 8:00 tomorrow morning, the magnetometer (MAG) will also be reconfigured. Unlike DDS, it is not really bothered by the radiation. MAG is being reconfigured to account for changes in the strength of Jupiter's magnetic field. Like Earth, Jupiter has its own magnetic field. This field is generated deep inside Jupiter, and the closer Galileo gets to Jupiter, the stronger the magnetic field it feels.

MAG has several different sensitivity settings. It can measure small changes in magnetic fields, but only if the overall field strength is small. It also has a setting at which it can measure changes even if the field is very strong, close to the cloud tops of Jupiter. But in this setting, it can only detect relatively large changes in the magnetic field. And it has a third setting, somewhere between the other two.

You can think of the first setting as being like a small ruler, which you would use to measure things that are a few inches, or less than an inch across. The second setting is more like a long tape measure, which can measure the width of a room, or the distance between two houses on a block.

As we approach Europa, MAG will be set to its intermediate sensitivity.

At 8:37 am, data from MAG, DDS, and the other fields and particles instruments will begin to be recorded onto the tape recorder. Most of the time, these instruments send data to Earth, but at a low transmission rate. The instruments can make measurements at a much greater rate than Galileo can send the data back to Earth. So most of the time, they collect data, and then compress and edit it before sending it on to Earth. But now, for 45 minutes, all these instruments will collect their data and write it to Galileo's tape recorder at the highest possible resolution. In that 45 minutes, as we pass above the surface of Europa, we will collect as much data as we normally do in a week!

MAG will measure the changes in magnetic field strength and direction, and DDS will collect information on very small dust particles in the vicinity of icy Europa. It will take less than an hour to collect this data, but we will have to wait almost one month before we can play it back off the tape recorder and send it down to Earth. And it will take several days to play back data that took 45 minutes to record. I wonder what we'll find.



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