PART 1: Overview of the discuss-jup mailing list
PART 2: Design a spacecraft to test for life on Europa
PART 3: One simple question raises many more not so simple ones
PART 4: Studying a cassette tape several hundred million miles from Earth
PART 5: Journals for memories
PART 6: Subscribing/Unsubscribing: How to do it

Online from Jupiter 97 Participants:

For this update, we've got some news that we think you'll find interesting and useful. The discuss-jup mailing list is ready and waiting for discussion! This list provides a forum for the discussion of issues, concerns, teaching strategies, useful resources, project collaboration opportunities and suggestions for the OFJ97 project.

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We've got an exciting new activity online relating to the possibility of life on Europa. This activity challenges students to design a spacecraft that will travel to Europa, one of Jupiter's moons, and test for the presence of life. Students should take into account various factors affecting the design of a spacecraft travelling to the outer solar system as well as develop tests to determine if life is present on Europa. For example, the spacecraft will have to dig through thick ice to find a liquid ocean. The designs can be submitted to the NASA K-12 Internet Initiative to be posted online. A discussion list will be established to provide a forum for discussion among students regarding different designs. NASA experts will also provide their opinions of the designs and general observations about the task-at-hand.

This should be a very exciting and intriguing activity and we are anxious to begin receiving work so we can post it on the OFJ97 website!

http://quest.arc.nasa.gov/galileo/features/life.html

[Editor's Note: Todd Barber is a propulsion engineer working with the Retro Propulsion Module (RPM). The RPM is a complex rocket propulsion system that provides all the trajectory correction and pointing control capability for the Galileo spacecraft.]

Hi, folks on the net! It is very nice to be back again talking about the privilege of working on Galileo as a propulsion engineer. I continue to very much enjoy learning about our propulsion system as the orbital tour unfolds.

Since the tour began, my two German colleagues (Fritz and Klaus-Peter) and I have had to adjust to challenge of performing a propulsive maneuver every 2-3 weeks, much more frequently than during interplanetary cruise. However, this is offset by the fact that these maneuvers have become quite routine (especially when contrasted with the uniqueness of each of the three main engine (what we refer to as the 400-Newton, or 400-N) firings!). A more mundane mission with respect to propulsion is certainly fine with Fritz, Klaus-Peter, and me, since the mission now is truly an odyssey of scientific discovery.

And, yet, intertwined with the routine there are always new challenges! Just today I sat in on a meeting looking at the problem of insufficient power near the end of the proposed Galileo Europa Mission (or GEM; this would keep Galileo active for another two years). As the spacecraft's radioactive main power sources continue to decay, there is less and less power available for the electrical and heating needs of the spacecraft. So, we need to examine ways to conserve power so that we can continue to run the spacecraft. We received some very interesting questions this morning, some of which follow:

"Can we turn off the 5 Watt heater on the 400-N engine to save power?"

This is a great way to save 5 Watts, but we have to ponder this carefully. The temperatures at the 400-N engine (which still contains fuel and oxidizer "upstream" from the valve seats) would plummet many tens of degrees in this scenario. In fact, propellant freezing near the 400-N engine is a certainty in this case; that's why we have a heater to begin with. Incidentally, the valve seats of which I speak are basically teflon (plastic) sealing devices that are opened and closed to control the flow of propellant to the main engine.

We have many questions about the "best" (read: safest) way to turn off the 400-N engine heater, should it prove necessary. Should we dump the propellant just upstream of the engine before freezing (by firing the 400-N engine ever-so-briefly with closed latch valves), or is this action more risky than just freezing the propellant already there? What will happen to the valve seats at the 400-N engine when their temperatures plunge below any previously tested limits?

It's interesting, isn't it? One seemingly innocuous question ("can we turn off the 5 Watt heater on the 400-N engine to save power?") has given rise to other, more provocative questions that are not easily answered. This is not unlike the challenges tackled by our science teams! Frequently, a new scientific discovery from Galileo answers one question (perhaps one posed twenty years ago after interpreting Voyager results), but raises many others! To me, this is one of the indescribable thrills of both science and engineering.

Another question from this morning, "Can the RPM [RetroPropulsion Module] transducers [sensors] be turned off towards the end of the GEM mission?" This action would save some 3.8 Watts, but again this inquiry raises further questions that Fritz, Klaus-Peter and I will have to try to answer. What are the chances that the transducers would never turn on again after being turned off? Could turning them off then on again affect their performance and calibration?

Without these transducers, we would not be able to monitor the pressures or temperatures for any of the RPM hardware. This is certainly a little discomforting, since we count on that data to check the RPM performance and any potential problems. However, this may be an acceptable risk near the end of GEM.

Other than asking these types of questions, I have kept busy looking at thruster performance during various types of spacecraft maneuvers (to be specific, spin corrections (S-thrusters), balanced turns (P-thrusters) and unbalanced turns (Z-thrusters)). This performance assessment nicely complements the work Fritz does in analyzing thruster performance during another type of spacecraft maneuver known as Orbit Trim Maneuvers (OTMs). Thruster performance continues to be excellent, generally with a small consistent overperformance of a few percent (vs. ground test levels) for each of the 12 small thrusters. We have to be concerned when the thrusters perform *too* well, in addition to when they don't perform up to snuff.

The three of us are also preparing a paper entitled "Final Galileo Propulsion System In-Flight Characterization" to be presented in Seattle this July. Disseminating information about the very interesting Galileo propulsion system performance to a knowledgeable audience in the beautiful "Emerald City" will be very rewarding and useful.

Thanks for your interest in the Galileo propulsion team! We'd like to take this opportunity to congratulate all science teams on Galileo as their ongoing discoveries continue to astound and baffle us. Truly Galileo is placing itself firmly and proudly in the rich history of planetary science.

[Editor's Note: Laura Barnard is an Engineering Aide for the Science Planning and Operations Team.]

Finally Friday!!! Yeah! It has been a long week. I have fixed half of the damaged data files, and I have several things going on today that are urgent, so I will have to fix the rest Monday or Tuesday of next week. It is a huge task that takes a lot of time to do. I have to "merge" several different types of files together and model them with a special type of software that we have. The software actually counts all of the resources, and accounts for what capabilities the spacecraft has. It then can generate reports that show overuse of the tape recorder, conflicts with too much data in the downlink data stream, and conflicts between instruments. Actually loading the files into the software isn't just a simple matter of sticking the files together either; all of the various parts have to be in the right time order, and all of the general file types have to be loaded in a certain order as well. I then generate reports from the models. The final reports and files will be put on CD-ROM disks for archiving so that in case this happens again we have a CD to restore the files.

Another part of my job is responding to all the pleas for help. The color printer doesn't work, my computer didn't back up last night, my monitor won't turn on... the list is fairly endless! I sometimes know how to fix the problem, but there are times when it is just easier to call someone else. The team could do that too - but I think that they like asking me first because it is one easy step. They call me, and I keep bugging people until the problem is fixed. Sometimes it is something simple, and sometimes it requires a part that won't get here for two weeks. Today I had to find out why people were not getting their computers backed up at night. We have a system that during the night while we are gone, contacts the Mac computers and backs them up (a different set of people each night). One person didn't have the software loaded correctly, and the others were all on Wednesday night backup. Apparently the tape didn't load correctly, so it didn't work that night. Finding out all of this information and correcting it took an hour of my time with the help of the system administrator.

Seeing how it is Friday - and a payday - several of us rode the local shuttle and went off lab for lunch. There were nine of us that day. Sometimes that group is smaller, but as the days are nice and the work is exhausting more of us leave the lab for a break!

When I got back I did a job that is very complex and gives me nightmares. First, you have to know that earlier in the mission the tape recorder got stuck and didn't move when we commanded it to move. We really thought that the tape was broken. This was going to be a *serious* problem, since we needed the tape recorder to store our data--if the tape recorder didn't work, we'd receive far less data. Not a pretty picture! Luckily when the tape cooled after several days of not being used, we sent commands to move it backwards. The extra tension helped the tape came loose. Since then we are *very* careful with conditioning the tape, and what it does in every sequence.

So what is my nightmare job? Basically I keep track of what the tape (on that tape recorder) is doing. This means figuring out what the tape will be doing during the sequences that we are planning, as well as the history of what the tape did in the past. Everytime that we stop the tape, move it, etc. we make a note of that motion. A spreadsheet program then calculates the risk involved in getting stuck. My report goes directly to the Mission Director and the Science and Sequence Office Manager. That's what gives me nightmares! I always worry that I will do the calculations and make some mistake, and the tape will actually stick even though my report said that it wouldn't!

Well - the weekend is starting so I better head home.

[Editor's Note: Tal Brady designs and programs the flight software for the Control and Data Subsystem (CDS) computer.]

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.

2-12-97
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.