OFJ97 Field Journal from Tal Brady - 2/20/972-20-97
The encounter with Europa is still moving along OK. Talked to some of the science team about the realtime science data results, which is the non-image science (e.g. information about the magnetic field). The realtime data is slowly coming in and looks good, but some analysis time will be required before they can tell if the data shows any surprises. The operations monitors had a display of the "Doppler" data, which shows the spacecraft's velocity change at the point of Europa closest approach. I was there watching and it looked really fine as it tracked the actual change against the predicted. (Readers might want to look up the Doppler effect on electromagnetic radiation to see how the radio telemetry received from the Galileo can be used to track spacecraft velocity changes.) I think some of this display was on the web page. [ed. note: yes, it was; "Doppler" data during each encounter is often broadcast "live" to the Galileo Countdown pages]
Now that we've done the Europa closest approach, the schedule says there will be Jupiter and Ganymede science tonight and tomorrow, then Jupiter and Callisto science Saturday. This encounter seems to have a little of each major science objective. Sort of a casserole; put in some Europa and some Jupiter, then add a little Ganymede, Callisto and Io for spice. Playback of the recorded image and approach science should start late Saturday night (PST). Looks like another good encounter. Maybe the most trouble free yet. It's a good sign for the mission lifetime if there are fewer problems past the halfway point. It means that things are pretty stable on the spacecraft.
As far as my own work goes, we had to restart the Phase-3A software testing on the testbed again this morning. Yesterday's test found that the new camera software didn't "load" the right way. Today's test has both of the new software loads running correctly. However, it looks like testing is showing that the CDS software and the camera software are having some problems working together--exactly what I was worried about. The problems may be fairly small because the test is still running and is producing telemetry packets containing image data. Since the test hasn't crashed, and since we are actually getting data, this indicates that most of the software is working properly. Still, it definitely looks like we will have to make some changes to the flight software based on these results. We should have more complete results by Monday, and then we can get started on any required changes to the software.
Noticed in the operations schedule that they took an image last night of Amalthea (one of Jupiter's smaller moons) later than expected. But, it looks like it got recorded OK. I'll have to remember to keep an eye out during playback for that image showing up on the web [ed. note: you might have to watch for awhile: it can sometimes take months before images are ready to show up on the web!]. The encounter "record" period, during which image data are recorded onto the tape player for later playback of the data to Earth, looks to finish about 6:00 PM Saturday and Playback to start about 7:00 PM (PST). I wonder if there will be anything from the new playback on the Web by Monday or Tuesday. The people who put images on the web page will probably kill me for that thought. That's probably way too early. Oh well, off to see 'The Empire Strikes Back' with some friends tonight.
Playback has started and it's going fine, Yaaah! I was right, it's way too early for new pictures, but there is a nice Galileo Today article that talks about what is happening about now. The Empire Strikes Back was great; big crowd, lots of fun.
Got some bad news today. The Magnetometer instrument software seems to have stopped running prior to the encounter and so their realtime science data from the encounter is probably not good. Their recorded data may be OK. We'll just have to wait and see. Fortunately, the problem is most likely to be a temporary memory error caused by the high radiation environment around Jupiter; Europa's pretty close in to Jupiter, so it sits in a lot of radiation. Although we use special "radiation hard" (i.e. resistant to radiation damage) memory on Galileo to protect against this kind of problem, we expect to have this kind of failure every once in a while,and we have seen a similar problem on one other instrument in the earlier encounter with Europa last December. If the problem is temporary, we can read out the Magnetometer's memory, send it back to Earth, compare it to the copy of the program that we have at JPL, find the bad part, and send up commands to the spacecraft to write a copy of good code over the bad part. Then we can just restart their computer with a command; a lot like rebooting a home computer after a crash. If we do the extended mission, there will be several more Europa passes, so if we were going to lose any science, this encounter is not the worst place to do so. Though I doubt that the magnetometer people would agree with me!
In the CDS Flight software development area the system test results from the new Phase-3 software do, as I expected, indicate errors in the way the CDS software interfaces (talks to) the camera software. There are two, I think, and one will require another system test later this week in order to determine if the problem is best fixed in my Control and Data Subsystem software or in the camera software. Also, both in the system test and in our development integration tests a small number of errors were found. The software is being changed to fix these errors during the first few days of this week. The changes required look pretty straight- forward. Only the one needing the additional test is of any concern.