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OFJ Field Journal from Randy Herrera - 12/7/95

Well, it's 11:30 pm on Thursday, December 7.....what a day!!! I arrived here at the Lab around 2:00 pm this afternoon. The first thing I hear is that some reporter is looking to interview me....WOW!!! Anyway, I went down to Von Karman Auditorium and talked to the gentleman for about 15 minutes. He is writing a story for a radio electronics magazine so Radio Science would really interest the readers.

We had four big events today: Io Closest Approach, Jupiter Closest Approach, Probe Relay, and Jupiter Orbit Insertion. All of them were nearly perfect. Now, the work begins for our Team. Our experiment begins at 2:02 am and will continue to 8:13 am (PST). Ours will be the FIRST SCIENCE DATA TO BE RECEIVED IN THE ORBITAL TOUR!!! (Even before the Probe data...(smile))

One of our colleagues was in charge of bringing in supper for us and she brought plenty...so we're all sitting around right now feeling like stuffed piggies.

The first event that will take place (tonight) as we approach our experiment is that the Navigation Team will provide us with an update on the trajectory. More specifically, the time of ingress. (Ingress is the time that the spacecraft slips behind the planet during an occultation.) If the time of ingress has shifted by a small amount from what was predicted earlier, we'll leave things as they are. If it's greater than a minute, we'll think about having the Deep Space Network station make some small changes to help correct the predicts (which basically predict what the frequency of the spacecraft's radio signal frequency will be at any time--useful if you want to pick up the spacecraft's signal).

Making those predict files is a lot of work. We sent one set of predicts out to the station on Monday night. Then, we sent another updated set of predicts out to the station on Wednesday night. Each time, the Navigation Team delivered an updated trajectory file to us and we calculated a set of predicts. The DSN Operations (or Ops) personnel also calculated a set of predicts on their own. We then compared the our predicts with the DSN predicts. If the difference between the two predictions of the spacecraft radio frequency is less than some small amount (30 Hertz, in this case), then the DSN predicts are used during the actual pass. The reason that we used two trajectory updates is that we need the best possible predicts for the experiment. We can't be too far off from the expected frequency or we might miss the signal entirely.

It's now 12:25 am on Friday and we just heard from the Nav Team. The difference between the predicts from Wednesday and the update from the Nav Team is about 25 seconds so we've decided that we SHOULD NOT attempt to compensate for the slightly-in-error predicts. We might be off on the exact frequency of the spacecraft's radio signal by about 37 Hertz, but we think we can absorb that in the bandwidth we're using (the bandwidth--the range of radio frequencies over which we will receive signals--covers about 2500 Hertz, so even if we're in error by 37 Hertz, the signal should still be picked up. ). We'll start getting data in about 1/2 hour. Wish us luck....



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