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OFJ97 Field Journal from Tal Brady - 2/10/97

I started this journal both for Online from Jupiter 97 and to write some memories for myself of the operation of the Galileo spacecraft that I have worked on for so many years. I'll see if I can keep the writing up even when Online From Jupiter 97 ends.

Galileo came out of solar conjunction (where the spacecraft is "behind" the Sun) about 2 weeks ago and seems to be working fine. I always worry when we're out of contact with the spacecraft for a while. You never know what can happen when you're not watching. Not that there's much I could do. Information about the health of the spacecraft is 6-12 hours old when we first see it anyway (this isn't just the time it takes the data to get to us--it's the time that it takes the spacecraft to send the data to us). Galileo is designed to stay healthy on its own for over a week if something goes wrong, but I still worry. Now it's back in contact and we even got some bonus realtime science data from the period when we did not know whether the telemetry would be good yet and were not willing to receive the tape recorded data (that's the higher priority data, and you want to make sure that it gets through).

All the CDS flight software--it is, essentially, the spacecraft's operating system, like MacOS 7 or Windows '95 is the operating system for most home computers) seems to be working fine. The last problem I was asked about turned out to be a misunderstanding about the way one of the science instruments gets its data moved in and out of the main data storage buffer. The tape recorder also seems to be working as expected, which is great news since a working tape recorder is the core of the software currently running on the Galileo. With continued good luck, we will never need the contingency software (what we call "Phase 3") that the flight software team is developing now (in case the tape recorder breaks down). I have even heard that the stuck Photopolarimeter instrument filter wheel was moved during the last attempt to free it, which is good news for the PPR team.

Looking at some of the pictures and information on the Galileo web pages. The images look great. We have a really good camera and the imaging people are using it really well. Callisto really has a rough bumpy looking surface. Europa's surface is much smoother and it looks like big and small pieces of newer stuff are overlaid on top of older stuff all over the place. Both Europa and Callisto look so different from Io and Ganymede, and from each other. Is it mostly caused by distance from Jupiter (Io and Europa are closer, Ganymede and Callisto further away) or are there other significant factors? I'll have to remember to ask the science team.

After two passes by Ganymede, the radio science team and fields and particles team were able to estimate its structure and determine that it has a magnetic field, which was completely unexpected. Don't know yet if there is a magnetic field around Europa. The Europa data looks less certain after one pass (E4, the last encounter last December), but maybe the second pass (E6, our current orbit) will firm up the data. Anyway, a lot of science data is coming back and the science people seem pretty happy with it. After all the hard work everyone on the Galileo project put in to design and implement the new, improved flight software, to see both the return of useful data and the return of surprising data such as Ganymede's magnetic field and Europa's active surface, is very gratifying. It means we did a good job.


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