PART 1: Galileo fact of the day
PART 2: Quest is in trouble
PART 3: Extension of the Probe Symbol Storage
PART 4: Reprogramming the computers and sequences
PART 5: Configuring the Deep Space Network

Roughly 60 percent of Galileo's radiation dose will be received
within an hour of Jupiter closest approach. Unshielded, 15 minutes
would be fatal to a human being. Your average PC probably
wouldn't do a lot better. We've had to use some special computer
chips and a lot of shielding to protect our computers. (The attitude
control computer has so much shielding around it that the
compartment it goes into has been nicknamed "the Brinks Bay"
after the people who build safes for banks.) 

December 7, 1995
Wednesday I returned from a week's trip to Florida for Tel-Ed95,
a K-12 networking conference. It was a great show with lots of the right
people. And Ft. Lauderdale is nice this time of year. So I was relaxed
as I came back to work. 

In checking my messages the day before, I had heard that Quest (Online
from Jupiter's Unix computer) had crashed..."a bunch of files had been
lost, but they were mainly from a section of the disk that once housed
computer accounts since deleted".  Not so!  My account (marc@quest)
had also been hosed.  So, anxious to do some journal editing and Email
catch-up (I'm now at 2200 messages), instead I stared at a screen that
showed not one Online from Jupiter file. Oh my stars!

I turned to our Webmaster Alan for help.  Although he is rich with
relevant computer experience, Alan had only been on the job for six days.
Our normal System Admin named Ted was away for the week and his boss 
and backup named Larry was home sick. So it was up to Alan (with a 
little help from me with pointers to the right people) to resolve the
problem.

The top Quest priority is our Web server which was operating OK. Also
operating nominally was the mail system, including the majordomo list
handler that sends out these updates. But when Alan tried to do some
minor crash repair work, the system had a tendency to crash. That's not 
good.

Another problem was the system we have in place for students to send
Email questions of the Galileo people. It's no longer functioning. That's
bad. In order to fix it, we will have to tackle the underlying problem.  
But in tackling the project, we'd crash the system.  Although we had
announced this capability on the Web, we hadn't yet announced it on this
list. So it wasn't that busy yet.

Alan worked to get the system into a safe mode by making sure that all the
relevant backups were done. He did some trouble isolation and together
we ran around trying to figure out how to get hardware repairs done
within our bureaucracy. By the end of the day we hadn't resolved the
problem completely. We were a bit wary of pushing too hard since we
risked having Quest crash and not wake up. So together Alan and I
decided to leave the system in its present mode until after Jupiter
Encounter today.  We'll try again to repair the system on Friday
(hopefully Larry will be back until then).  So for now you will not be 
able to send questions to the question-jup@quest address. (Once we are
recovered, I'll make a full announcement of this feature).

With my recent luck, it is a good thing I am not directly involved 
with the spacecraft.

Your network pal,
Marc

November 17, 1995
Things keep moving fast on this project!  It's certainly exciting, but it 
can also be very frustrating sometimes.

>From our Probe perspective, watching JPL deal with the tape recorder 
problem has been interesting, but it didn't involve us directly.  In 
fact, during the early part of this ... 'incident' ... I was doing 
my civic duty by serving on a jury in municipal court (we convicted).  
What did affect us though, was the extension  of Probe symbol storage.

What is Probe symbol storage?  Well, about three years ago or so, when 
we first found that the Orbiter's big antenna was stuck and that we 
would have to record the Probe data for later replay, we realized that 
we were entirely dependent on the tape recorder working properly.  
If it were to fail, we would lose all the Probe data!  We couldn't 
send it back to Earth in real-time without the big antenna, and there 
was no place else to store it except on the tape recorder. So we 
scratched our chins and thought about it a bit, and came up with an idea.

The spacecraft has the tape recorder to store data temporarily, while it 
waits for an opportunity to send it back to Earth.  The size of this 
tape recorder is rather large, much like a hard disk on your computer.  
But the spacecraft also has a relatively small amount of random access 
memory (RAM) which is uses to store its software.  Again, just like 
your typical desktop computer.  Now, the full set of Probe data is 
about 4MB (megabytes), which fits easily onto the tape  recorder.  
But the Orbiter's RAM is only about 0.4MB.  How could we get around this?!

Well, as it turns out, much of the full Probe data set is overhead.  That 
is, it's coding that helps the data get to the ground cleanly, and 
information about  the quality of the radio signal received from 
the Probe.  If this overhead is stripped away (with the result 
that what's left is more prone to having errors in it), the data 
actually being sent from the Probe is only about 0.3MB.  Would 
this much fit into RAM?  Certainly the RAM was large enough, 
but there still had  to be room to store the spacecraft's software.  
Eventually, we found that we could fit about half of this stripped 
Probe data set, or 147KB (kilobytes)  into  the spacecraft RAM.  
We refer to this as Probe symbol data because it consists of 
only the symbols (coded bits) actually transmitted by the Probe, 
without all the overhead.  Although this was only about half of 
the data that the Probe would be sending, it was by far the most 
important information.  Of course then the spacecraft CDS software 
engineers still had to figure out away to do all this data stripping 
onboard the spacecraft, but it was eventually accomplished and we 
could relax.

"There!" we said to ourselves.  "Certainly the tape recorder will work 
just great, but even if something goes terribly wrong with it, we have 
our most important data backed up!"

Of course, then came October 11th and the Great Tape Recorder Snafu.

Immediately we decided that trusting the tape recorder may no longer be 
the wise  thing to do, and we looked to see if there was anything else 
that could be done to improve the Probe data backup.

The thing that helped us here was that with nobody trusting the tape 
recorder all of a sudden, the mission management decided to scrap all 
the science observations that were planned to be done as Galileo neared 
Jupiter.  All these observations were supposed to be accomplished by 
software stored in the RAM, and  the results would be stored on tape 
to be read out through the RAM.  Since this software was no longer 
needed, and since the tape recorder would not need to use  the RAM 
for a while, we suddenly found that there was more RAM available to 
store Probe data.  Our original plan was to store both "strings" of 
Probe symbols in RAM for 31 minutes, and then only one "string" for an 
additional 8 minutes, getting us down to 39 total minutes (the Probe 
sends two simultaneous streams of data, or "strings," up to the Orbiter).  
Now an extra 61KB was suddenly available and we were able to store even 
more Probe symbols--now we could save up to 72 minutes on a single string.

Once again, however, it's the implementation that made it all interesting!

Storing the data is one thing, reading it out is another.  At first blush, 
having all this RAM for storage makes things easy.  In fact, too easy!  
After changing Galileo's software to allow us to store some original data, 
we found that another planned change will write over some of the RAM that 
we will have just stored, erasing it.  So this data has to be moved to 
another part of RAM before it's overwritten.  And with RAM now so full of 
Probe data, there's not much left for everyone else.  So a high priority 
in January (after the spacecraft comes back around from behind the Sun) 
will be to read out some of the Probe symbols, and send them back to Earth 
and free up the memory.

This week we've been struggling with the question of how to tell whether or 
not the symbols have been read out successfully before we overwrite them, 
because we  don't want to write over any data until we're absolutely sure 
that it has been safely read out.  The strategy right now is to read out 
the symbols three times,  and then compare the three read outs.  We will 
do a vote of best two-out-of- three on each bit of data: if two of the 
readouts agree on a value, and the third readout disagrees, majority rules, 
and we'll assume that the third readout  was wrong.  But there will likely 
be some cases where we will have an "outage" (we don't get the data for 
some reason, e.g. the spacecraft's signal is too "noisy" for the Deep 
Space Network antennas to receive properly)  and not get the third read out.   
And then we'll  find that there is a disagreement between the two bits we 
do have, so now what do we do?.  These are the kinds of details we 
are working on right now.

But this problem will be resolved soon.  The issues that are still looming 
up ahead are the timing of the data, and all the arrangements for the 
actual work in December.  Getting close now!!!

November 29, 1995
We've been working very hard lately trying to figure out what changes we 
had to make to the central computer system on board the spacecraft in 
order to work around the tape recorder problem that we have a few months 
ago. It's been challenging for two reasons.  First, we have to design a 
new software system in a very short amount of time and second, we have to 
be creative to figure out how to make sure that the system works while 
keeping as much science as possible.  This process is coming to a close, 
however, and the actual work to really make the changes is starting up in 
full force!  My part, as a representative for a science instrument, is 
winding down for the moment.  I will have a lot of work in the next six 
months however, because all of the pre-designed science sequences that 
we had planned to use for every orbit have to be updated to reflect these 
design changes.

On a different note, we are all getting excited about the upcoming JOI - 
short for Jupiter Orbit Insertion - that will occur on December 7th.  
In fact, I am a member of a group of people who put on skits and songs at 
various project functions.  We jokingly call ourselves the "Not Ready for 
Real- Time Players."  We are busy (in addition to our other work!) planning 
the skits and songs that we'll perform on December 7th for the flight 
team and associated friends and family.  We usually take the opportunity 
to poke fun at various teams on the project or various project managers!  
People seem to really enjoy our performances, but the best part about being 
a member of this group (for me) is the rehearsals. We make a lot of jokes 
and laugh a lot while trying to write the pieces and put the program 
together. I'm looking forward to performing on December 7th!

November 29, 1995
Last night it hit me... SMACK... right in the face... eight days,  EIGHT DAYS! 

You see, on the west side of JPL, right near the main entrance, there is a 
mall and in that mall there is a billboard-sized sign.  The sign currently 
contains trajectory information for Galileo and Ulysses*, showing the 
solar system (out to Jupiter), so people can see the locations of the 
spacecraft.  As Jupiter Orbit Insertion (JOI) day got closer, the public 
affairs people added an "Orbit Insertion" countdown to the Galileo section 
and went from weekly updates (every Monday) to what looks like daily 
updates.  Last night, as I walked out to my car, I glanced over at that 
sign.  It is not like I was looking for something new or different.  
I had seen that sign hundreds of times, but this time it hit me...  
EIGHT days to ARRIVAL!

About a week ago, the January 1996 issue of Astronomy magazine showed up 
in my mailbox  (Isn't it weird how when you subscribe to a magazine you 
get your issues one to two months before it hits the newsstands?  I've 
already received my February issues of my surfing and bodyboarding mags, 
but..). Galileo got the cover.  I recall thinking "cool, the cover," and 
proceeded to read the article.

It was a good article, but that was the end of it.  No big deal.  But then 
it was prior to the Thanksgiving holidays, so maybe that had something to 
do with it.  I guess there was too much going on between then and 
Arrival Day, but now...  eight days, wow.  I've only been waiting for 
this for two years, but for some people, the wait has been a couple of 
decades.

I also saw a fawn grazing on the grass just a few steps from that sign. JPL 
sits at the base of some mountains, and when there isn't enough food or 
water, the deer will come down onto the Lab for a little snack.  I had 
heard about this, but had only seen one once before.  It was pretty cool.  
Maybe it was some kind of symbol.  Maybe Galileo is like that fawn, which 
looked like it was out on its own for the first time, and we're also about 
to cross one of the big steps in our....

Nah, I don't think so.  Galileo has a team of close to 300 people looking 
out for its well being, so that can't be it.

So, what have I been doing since my last journal entry?  Well, a little bit 
of this, a little bit of that.  That is the nature of being in the 
Mission Planning and Outreach Coordination Office.

For the mission planning part of my job, I spent the last few weeks applying 
what we had recently learned about telecom performance (basically, how well 
we can "hear" the spacecraft) to the Arrival Day time period.  Just a few 
days ago, we issued the final decisions on how we'll be configuring the 
Deep Space Network and telecom from the end December 5th through the 
beginning of the 9th of December.  The configuration for Arrival Day itself 
is of particular importance.

On Arrival Day, Galileo will perform some of the most important activities 
for the mission:  Io Torus science data collection, the Probe entry and 
relay of its data, and the JOI.  We had a very complicated set of 
requirements to juggle:  we have to maintain the best real-time 
visibility into spacecraft operations (that is, get as strong a radio 
signal as possible), send real-time commands to the spacecraft at specific 
times, and get navigation data so that we can see how the JOI burn went 
(this information is needed so that the nav team can start the design of 
"cleanup" maneuvers, specifically the first Orbit Trim Maneuver which is 
only about a day and a half after orbit insertion).  If you recall my 
previous journal, two-way antenna setups are needed for sending commands 
to the spacecraft and for getting navigation data, while one-way setups 
provide the best real-time visibility ("best" as in giving higher radio 
signal strength for locking onto Galileo's signal).  There is even a 
special one-way setup called "ultracone" which provides even better 
real-time visibility (this configuration is only available at the 
Canberra antenna, see below).  Well, what did we end up with?

Fortunately, two of the three antennas that we are using on Arrival Day 
have overlapping "view periods" (view periods are the times when a 
particular antenna can point at Galileo and receive its signal).  
The 70-meter diameter antennas that we use are in Madrid, Spain;  
Canberra, Australia;  and Goldstone, California.  The view periods of 
the antennas at Goldstone and Canberra overlap for 4 hours.  The layout 
of activities to antennas goes kind of like this:  Io Torus Science and 
preparation for Relay occurs over Goldstone only, Relay occurs over the 
Goldstone / Canberra overlap and JOI occurs over Canberra only.  The 
best real-time visibility possible is required (or highly desired) during 
this whole period.  Commanding is required all the way from just after 
the Io Torus science collection through just prior to the end of JOI and 
then stops for awhile and, depending on the how the spacecraft is doing, 
could start back up a few hours after JOI.  Navigation data, again 
depending on how the spacecraft is doing, is required for a couple of 
hours, starting a few of hours after JOI. Juggle away!

The commanding requirements forced us to set up Goldstone in two-way mode. 
Fortunately, the Goldstone view period was long enough and the timing on 
the commands was such that we were able to schedule the transmission of 
all the required commands over the Goldstone antenna, even those for just 
after JOI (you see, it takes the commands about 52 minutes to get to the 
spacecraft, so even though JOI does not occur over Goldstone, we can still 
send commands from Goldstone because they'll get to the spacecraft right 
around when JOI will be near completion).  The two-way configuration for 
Goldstone did hurt our visibility for Io Science collection and preparation 
for Relay, but doing all of the commanding over Goldstone allowed us to 
set up the Canberra antenna using the "ultracone," which will provide 
the best visibility possible for Relay and JOI.

But, what about the commanding and navigation needs *after* JOI?  If 
Canberra is in ultracone mode, we can't meet those requirements, can we?  
Yes, yes we can: antenna configurations can be changed in the middle of 
a "track" ("track" is just another name for a view period, except it is 
called a track once it gets allocated to Galileo by the antenna time 
planners - officially called Resource Allocation Team via the Resource 
Allocation Process - get it, RATs that RAP - I know, it's bad).  The key 
is that these requirements are dependent on how the spacecraft is doing.  
The idea is the following: after JOI, once we are convinced that the 
spacecraft is in good health, we will change the setup of the Canberra 
antenna from ultracone to 2-way.  That allows us to collect navigation 
data and send commands.  After those requirements are met, we will switch 
the antenna back to one-way mode (but not back to ultracone because 
switching in and out of ultracone causes a 30 minute gap in our data and 
we already have had one of these gaps to be able to get into 2-way mode) 
to once again boost the signal strength as high as possible.  Pretty fancy, 
huh?  Well, it took *many* hours of work from *many* people to convince 
ourselves that this was the right thing to do.  The good thing about it 
is that it is flexible and it meets all our requirements.  And that is 
what mission planning is all about.

So that was a little bit of this, what about a little bit of that?  
My other tasks have been in the outreach section of the office (I don't 
know why I am calling it a section since our office has only 3 people 
in it).  In order to get ready for Arrival Day, there is a lot of 
information that has to be transformed and compiled into summaries and 
non-detailed descriptions of the events that will be occurring... around 
here we tend to call it "putting something in human-readable form." So, 
I am producing a time-ordered listing for Arrival Day that will list 
orbiter, probe and antenna events starting from the 7th of December 
at 1 o'clock in the morning (Pacific Standard Time) through the 8th of 
December at 8 o'clock in the morning.  The listing will be used by many 
different people, but mainly by the Public Information Office as a guide 
to what important events are occurring during the day.  One other product 
I am currently working on is a Post-JOI Sequence of Events.  This is a 
chart that shows the events that take place in the week after JOI.  
Most importantly, it shows when the first Orbit Trim Maneuver and the 
first Probe Symbol return are scheduled.  I understand that these 
charts will be used at Arrival Day press conferences.

Well, that is enough about work.  I am really looking forward to tomorrow.  
My sister and a cousin are coming into town.  We plan to go to Disneyland 
on Sunday and up to San Francisco to visit some other cousins the weekend 
of the 9th. They will be staying in LA with me until the 13th of December 
which is when my holiday vacation starts.  We will be going out to Thailand 
for 3 weeks.  I have brother who works for an oil company out there and he 
wasn't going to be able to make it home for the holidays (for the second 
straight year).  We decided that we would go out and visit him and his 
family instead.  It should be a blast.

As far as my sporting activities, WE WIN, WE WIN, we finally won a 
basketball game.  It has been a hard season, we lost most of our games 
in the final minutes, but yesterday we managed to keep it together for 
the whole game.  The tournament play is scheduled for the weekend of 
the 9th, but I will not be able to play due to my trip to San Francisco.  
I'll find out how we do when I get back.  Volleyball and Softball 
seasons are over.  I am looking forward to when they start up again 
in January.  As far as surfing, we finally have been getting some good 
swells.  They are winter swells out of the west.  I guess the south just 
didn't want to produce anything this past summer.  Last weekend I went 
out at Zuma Beach in Malibu.  It was Saturday and I had missed the bulk 
of the swell that hit the coast on Thanksgiving day, but the waves were 
still tasty.  Water: 61-63 degrees F, chilly, full suit for sure.  I 
caught this really good "right" (that's a wave that peels to the right).  
Had to paddle hard for it, but once I caught it I was in surf heaven.  
It had good size and was peeling nicely and was pretty long.  No surf 
in Thailand, or so my brother says.  Maybe we will take some trips to 
the surrounding islands.  Some of the best surf in the world is in that 
part of the globe.

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* The Ulysses Mission is the first spacecraft to explore interplanetary 
space at  high solar latitudes. Ulysses is a joint endeavor of the 
European Space Agency (ESA) and the National Aeronautics and Space 
Administration (NASA) of the USA.