Many of the people of Galileo have prepared biographical sketches
which can be found at the Online from Jupiter web site 
(http://quest.arc.nasa.gov/jupiter.html). Soon these will be available at 
the project gopher site (quest.arc.nasa.gov).

Many of these short reports include information about the childhood 
experiences which helped lead to a career in Spacecraft Operations.
Perhaps your students will find them interesting and motivational.

One Featured Activity for ONLINE FROM JUPITER is called
"Will the Probe Get Squashed" (or "ProbeSquash" for short).
This series of messages will provide details about the
paramaters which will effect how long the Probe will operate once it 
enters the nasty environs of Jupiter's atmosphere. To start, we'll
provide usage suggestions for teachers and the first installment.

Usage Suggestion:
If you are interested in using "Will the Probe Get Squashed?" as an 
ongoing classroom activity, you may want to have each of your 
students--or your entire classroom--keep a graph that will chart 
their predictions of the length of the probe mission, with a new 
prediction made at the end of each unit of ProbeSquash. The Galileo 
Orbiter mission limits the maximum length of the Probe mission to 
75 minutes, which puts a top limit on your student's graphs. There 
will be a total of 7-8 installments (and opportunities for predicting) 
during this activity.

Probe Squash #1: Launch Delays
Imagine that you are about to start on a long cross-country trip, 
driving a three year old car that, amazingly enough, has barely been 
used at all--it has less than 100 miles on the odometer! Even though 
the car hasn't been used too much, you probably wouldn't be able just 
to turn the key in the ignition and head out to the freeway: the 
battery would probably be dead, the lubricating oil would be sludgy, 
and the stereo might not be as nice as something you could buy 
today. You'd probably want to replace some parts, and repair others, 
just to make sure that you had no breakdowns on the road.

Galileo's atmospheric Probe went through a similar type of retrofit.  
Due to delays in the Galileo launch and lengthening of the mission 
from (roughly) two and a half to six years, several Probe components 
were replaced or rebuilt. These are the parachute, the mortar 
cartridge for chute deployment, and the lithium-sulfur dioxide 
batteries. The Net Flux Radiometer instrument also was rebuilt for 
improved performance. In addition, in the years before launch, all 
scientific instruments and subsystems aboard the Probe underwent 
detailed performance tests.

Be sure to tune in to the next segment of "Will the Probe Get 
Squashed," when we'll discuss the extreme entry conditions the 
Probe must survive before it can start upon its scientific mission!

Journal Entry:  October 10, 1995
Having finished up my vacation and caught up on my work for other 
projects, it's  time to get back to working on the Galileo Probe.

The Probe was separated from the Orbiter spacecraft this past July. It 
has no propulsion and will have no communications until after it hits the 
atmosphere of Jupiter. So it is simply falling towards the planet, being 
carried there by its initial momentum and the ever increasing 
gravitational pull of the giant planet. Once it gets there, it will turn 
itself on and collect data from above the atmosphere. Then when it hits 
the atmosphere it will decelerate from 100,000 mph to only 200 mph in 
just 4 minutes, losing nearly 200 pounds of mass from its heatshield in 
the process. Only after it has slowed down will it jettison the heatshield, 
deploy its parachute and begin to transmit data. 

Until then, we will not hear from it. And even then we will not be able to 
send commands to it. So thereUs nothing left to be done with the Probe 
itself. But there is still work! The equipment we use to hear the Probe, 
the Relay Radio Hardware (RRH), is still on the Orbiter and we need to be 
able to command it properly in order to get the Probe data back. The RRH 
includes an antenna that we use to receive the signal the Probe will be 
sending. The Probe will be much too far from Earth to catch the signal 
from here, so we will depend on the RRH to collect the Probe data, and 
then hand the data to the Orbiter to send it back to Earth. The first thing 
we had to do was to point the receiving antenna. We did this in August 
after a couple months of preparation to ensure that we knew how to 
command it properly and how to interpret the data it sent back to us. But 
we finally moved it to the proper location in 15 small steps, and all the 
preparation proved to be worthwhile when the antenna moved exactly as 
predicted! It's now perfectly pointed so that when the Orbiter gets to 
Jupiter and flies over the Probe (which will be descending through the 
atmosphere on its parachute), the receiving antenna will be pointed at the
Probe.

So now we turn our attention to other matters. Our ground engineers have 
finished putting together the computer networks we will use to 
distribute the data to the scientists over the Internet. Now we have to be 
sure that we have written procedures to tell us how to do this. Having a 
written procedure means there is less chance of someone making an error 
and delaying the distribution of the data. There will be a lot of 
excitement when the data finally comes in and when you have a lot of 
excitement, there's also a lot of confusion. The written procedure will 
help cut down on the confusion and will also help if someone on the 
ground team gets sick and we need to have someone new take over.  The 
first draft of the procedure has been written and we will all review it 
this week to see if it is clear and understandable. After that the final 
corrections will be made and we will each take turns practicing the 
procedure in case we have to be the one to do it for real in December!

Also, we have written a draft contingency plan which describes all the 
things we can think of that might go wrong, and what to do about each 
one. The contingency plan we wrote for the Probe release in July was 
quite complicated and took a long time to write because we had to worry 
about everything that might go wrong on the Probe. But with the Probe 
now safely on its way and beyond our reach, we only have to worry about 
the RRH, and there is very little that can go wrong with that hardware 
(or, at least very little that we can do anything about). So this time the 
plan will be relatively simple.  We will review this plan this week also, 
and then update it for the final corrections.

I hate it when my portable pager goes off. Typically, it happens at an
inconvenient place and time, like while watching a movie or at home in 
bed. A quick look at the beeper display is all it takes to tell if it is a 
nonsense phone number caused by someone making a wrong number.

That's the way it usually happens. The evening of Wednesday, 11 October 
would be different.

My friend and I were driving a freeway to Pasadena on our way to dinner 
and a lecture at Caltech. When my pager began its obnoxious chirping, I 
threatened, as on many previous occasions, to throw it out the window of 
my moving car if it was yet another false alarm. This time, I recognized 
the phone number. It was the Galileo Mission Support Area, the facility 
where data from the spacecraft is processed. When they page me, usually 
there's a problem on the spacecraft. This didn't feel like a false alarm.

The previous day, the spacecraft had snapped some pictures of Jupiter, 
the first of our approach images. Today we were to play the tape recorder 
back, buffering short segments of the picture and downlinking the raw 
bits to the ground. With our current software and data-rate, it would take 
several weeks to download the pictures, but before leaving the Galileo 
project in November I was looking forward to having a full-color picture 
of Jupiter to hang on my wall. Had something gone wrong?

Within a few minutes, I had reached a nearby supermarket and was 
talking to Jose' about the beeper message. It didn't sound good. Earlier 
that day, the tape recorded had been commanded to rewind back to the 
beginning of the tape in preparation for playback. This should move the 
tape at high speed until sensors in the recorder detect the transparent 
leader at the end; this signals the recorder to automatically stop the 
tape. The telemetry from the spacecraft showed that the capstan, the 
wheel that drives the tape, was turning at the expected rate. However, it 
should only have taken a few minutes to reach the beginning of tape. The 
capstan had kept spinning.

No one quite knew what this meant. Had the tape broken? Was the 
telemetry playing tricks on us? The Anomaly Recovery Team was being 
called and I would have to pull a story together. Dinner with my friend 
was out.

When I got to JPL, people had already begun to stream in. Jose' informed 
me that the tape recorder motor was still running. (At least it was when 
the radio signals with this information left the spacecraft 45 minutes 
earlier.) Several people were on telephone talking to hardware experts 
about what they were seeing. Everyone was very intent on what they were 
doing. The spacecraft was in trouble less than two months before the 
most important part of its mission.

By all indications, the tape recorder motors looked like they would go on
indefinitely waiting for that signal that the end of tape had been reached.  
The program on the spacecraft was supposed to command the recorder to 
play back sections of the tape, but the recorder was rejecting these 
commands because it hadn't finished its last task. We would have to radio 
a command to the spacecraft to tell the recorder to stop unconditionally.

Time was short. From the tracking station listening to the spacecraft
(Goldstone, out in California's Mojave desert), Galileo was a setting star 
in the sky.  Soon it would be too low on the horizon for the signal from 
the tracking station to get through. Ordinarily, we could call on the 
tracking station in Canberra, Australia to send the commands since 
Galileo would then be rising in its sky. Unfortunately, the transmitter at 
the station had failed only the week before and was down for repair. The 
station would be able to listen to Galileo, but not talk to it. The next 
station, in Madrid, Spain, wouldn't be in view of the spacecraft for nearly 
12 more hours.

No commanding had been planned during this time, so the Goldstone 
transmitter had been left off in order to improve reception of Galileo's 
weak signal. Getting the transmitter operational would take nearly an 
hour to warm up the high-power electronics and tune the signal so that 
the spacecraft could get the message clearly. Meanwhile, while the folks 
in Goldstone were busy getting their equipment ready, we here at JPL 
would prepare the commands for transmission, making certain that the 
instructions we send couldn't possibly make the situation any worse.

Soon I found myself in the Project conference room, briefing all 
assembled on the state of things. While speaking as clearly as possible, 
my words were going as quickly as they could go. The Project Manager 
understood and approved of the plan to stop the recorder and several 
engineers bolted out of the room to send the commands. They returned ten 
minutes later, glum and shaken. The transmitter at Goldstone had 
resisted attempts to turn it on quickly.  We had missed our opportunity!

That same night, other engineers where running a simulation of the 
Jupiter encounter on the Galileo Testbed. The Testbed is built from 
computers and other components identical to the ones on the spacecraft.  
We use it to be certain that the commands we send to Galileo will 
perform exactly as we expect. By some incredible stroke of fate, the 
testbed engineers discovered they were having a problem also. The tape 
recorder they were using, identical to the one flying to Jupiter, seemed 
to be moving without reaching the end of tape!  Whatever the problem 
was, we knew that at least the recorder on the ground could be opened up 
and examined for any clues that might explain our problems in flight.

That night, we made ready the commands that would be sent to the 
spacecraft from Madrid the following morning. None of us knew whether 
we would have a working tape recorder when this was over. No one talked 
about it, but continued in their preparations to be sure that everything 
would go smoothly tomorrow.

I drove home around midnight after first stopping at an all-night 
hamburger stand for that dinner I had missed earlier. A half billion miles 
away, the spacecraft I had worked on for nearly 13 years was suffering 
from a major glitch and there was nothing anyone could do but wait.

EPILOG:
The commands sent to Galileo the following morning stopped the 
recorder. Later, it was found that the problems with the tape recorder on 
the testbed only superficially matched those on the spacecraft. The parts 
that had failed on it could not have caused the flight equipment to behave 
in quite the way that it did.

Tape experts from the manufacturer and JPL identified several theories 
to explain the problem -- some of them recoverable and some not. About a 
week after the original problem, we sent a series of commands to the 
spacecraft to see if the tape could be made to move. It worked and the 
tape advanced exactly as instructed.

The anomaly will cause us to use the tape recorder more cautiously, but 
it now appears probable that we will still be able to use it to collect and 
store data for the life of the mission.

October 5 - October 22
It has been a long, exciting, and successful summer. We are now well into the
fall semester at the University of Idaho and I am teaching one four-credit
course. I am also teaching our department's research colloquium, a course
that meets once a week and has a wide variety of speakers from our
department, other departments at the University, other Universities, and
industry. Last week Marcie Smith, the Galileo Probe Project Manager from
NASA Ames was here to talk about the Galileo mission.

In my "free" time (that I don't seem to have nearly enough of) I am hard at 
work preparing, checking, and testing software for the Doppler Wind 
Experiment (DWE); this is the probe experiment for which I have primary 
responsibility. The DWE is designed to measure the winds at the location 
of the probe descent by looking at the Doppler Shift of the probe to 
orbiter signal frequency. To conduct this analysis requires that I know 
three things: 
1) the location and velocity of the orbiter during the probe mission
2) the location and velocity of the probe, and
3) the frequency measurements of the probe signal. 

Even without winds, there will be a Doppler Shift of the probe
signal due to the movement of the orbiter, the probe being carried 
eastward by the planet's rapid rotation, and the probe descending on its 
parachute. If it were possible to somehow know the exact locations and 
velocities of the probe and orbiter, and to know the precise frequency of 
the oscillator on the probe, in principle we could model the probe signal 
frequency exactly. But when we make this model we expect it will not be 
in perfect agreement with the measured frequency. This is due in small 
part (we hope!) to the fact that we do not know the precise orbiter and 
probe trajectories. If this error is small, the leftover error is due 
primarily to the winds. And it is from this small frequency error (called 
the frequency residuals) that the winds can be determined. So to measure 
the winds I will need to obtain the orbiter trajectory data (location and 
velocity) from the project navigation team.

Additionally, the navigation team will supply their best guess of the 
probe trajectory. However, we can't get the precise probe trajectory until 
after analysis of the probe data. Most importantly, we'll need the 
information we get from the Atmospheric Structure Instrument (ASI). The 
ASI will measure pressures, densities, and temperatures. Then, based on 
what we know about how the physics of atmospheres (things like "The 
Law of Hydrostatic Equilibrium" and "The Gas Law"), we can then 
calculate the distance the probe travels from the entry point to the 
vertical descent location (where it is on parachute and making 
measurements) and the speed of the probe as it is falling on its 
parachute. But this precise data will have to wait until the ASI scientists
have a chance to analyze the data - probably sometime in 1996. It is a
little disconcerting to know that my preliminary wind analyses will be 
based on a model atmosphere that might not be what the probe really 
finds. And if the atmosphere model is not very good, then I know that the 
probe descent velocity on the parachute will probably be incorrect. In 
addition, a probe descending through the real atmosphere (unlike a model 
atmosphere) will be bounced and buffeted around; also it may feel 
updrafts and downdrafts (like in a thunderstorm). So my early 
measurements may not be very accurate.

Finally, the last data set I will need is the probe signal frequency as
measured by the orbiter. Interestingly enough, out of these three data 
sets (the orbiter trajectory, the probe trajectory, and the frequencies), 
I should have the first two well before the probe arrives at Jupiter.
Although the Galileo Navigation team promised to get the orbiter 
trajectory to me sometime in September, things always seem to be a 
little bit late. Especially when I am anxious to get them. I have also been 
promised the probe trajectory sometime in September. And, as of late 
September, neither had arrived. Of course, nothing can take the place of 
the probe signal frequency data - for that I will have to be REALLY 
patient and wait until December!

Thursday, September 28 - Today I finally got the first of my long awaited
data sets. Following the probe release in July, and a detailed study of the
radio signal from the orbiter when the probe was released, it was 
possible for the Galileo Navigation team to put together a rather accurate 
prediction of the probe entry time, location, and where in the atmosphere 
of Jupiter the probe would be during its descent. According to the data I 
have, the probe will enter the atmosphere at about 4 minutes, 5 seconds 
after 3:00 P.M. (Pacific Standard Time) at a latitude of 6.54 degrees North 
of the equator. This is actually the time that we will find out, on Earth, 
that the probe has entered the atmosphere. The probe entry will actually 
occur about 1 hour earlier, but we won't know about it because Jupiter is 
so far away (the time for the radio signal to travel from the orbiter at 
Jupiter to Earth is 52 minutes). The entry location is slightly different 
from what I was told in July, so I have to start asking some questions to 
find out if this is a real change, or if my calculations are wrong.

It turns out that there's a problem with reading the data file that I got 
from the Navigation team.  This wasn't totally unexpected: if I write a 
program to read a data file, and then I actually try to use it to read the 
data file perfectly, often there are small but nettlesome problems. That's 
what happened to me. The data file I received happens to have a couple of 
extra spaces placed here and there, and where there used to be a space 
there is now the number '1'. So, now it is back to the computer to fix my 
program so that it can read the new data file. I think that this should be 
pretty easy to do.

Thursday, October 5 - Well, after a day of sending electronic mail to JPL 
and getting responses back every ten minutes (almost) I am now in 
possession of the second data set needed for the preliminary Doppler 
Wind Analysis. Interestingly enough, the orbiter trajectory file I am using 
is not based on the current orbiter trajectory, but describes the ideal 
trajectory. Every time they do a trajectory correction maneuver (TCM), 
the Navigation team at JPL tries to put the orbiter back on this ideal 
trajectory. And, since I don't want to get a new data file every time they 
do a TCM, I am using the trajectory they expect to be on when the orbiter 
gets to Jupiter. The final TCMs, called TCM28 and TCM28a, will be in late 
November.

Wednesday, October 11 - I am now at the annual Division for Planetary
Sciences conference. This year it is in Hawaii, which is a beautiful place
to hold a conference, but makes it hard to sit indoors with the beaches 20
feet outside the door!  But I overcame the temptation and I am returning 
to the mainland as pale as when I left.
Today we received a NASA press release outlining a possible problem 
with the Galileo tape recorder. While not yet panic stricken, I have to 
admit that I will have some trouble sleeping for awhile. Originally, the 
probe data was to be sent back to Earth in real time, with the tape 
recorder used as a backup. Since the High Gain Antenna failed to open, the 
probe mission was reconfigured so that the tape recorder was the 
location of primary probe data storage, and some spare memory in the
central computer on the orbiter was the backup. And, I remember being 
told several years ago that, if the tape recorder failed, then I would 
probably lose the frequency data that is used for the Doppler Wind 
Measurements, my experiment. I still have these concerns, but since we 
are only 57 days away from Jupiter my guess is (and this seems to be 
confirmed talking to the probe project manager) there is not enough time 
to reprogram the spacecraft in such a way so that my data is lost. So, 
assuming everything works as planned, my data should still be available. 
However, if (and this is a very big if) the tape recorder is really damaged, 
we do not have a backup for the probe data anymore, and we will not 
receive as much data as we had originally planned. I have to keep falling 
back on the fact that, if sending a spacecraft to Jupiter was easy, then 
1) someone would have done it before or 
2) it  wouldn't be worth doing.  
Well, we are almost to Jupiter and we are finding  out how difficult it 
really is.  Hang on, we are almost there!

Monday, October 16 - It is real difficult not to be somewhat pessimistic.
Again, no official word on the state of the tape recorder, but the last 
word I have is that it appears likely that it is a hardware failure - 
physical damage may have occurred. This is grim news and, if correct, the 
outlook seems to be very bleak. Sometimes it is very hard not to get 
discouraged, but either way there is a lot of excitement ahead.

Friday, October 20, 7:23 A.M. (PDT) - Some glimmer of good news received
yesterday. Although I am not privy to the exact failure analysis 
operations, rumors (which can be very dangerous) are that perhaps there 
has not been a total failure of the tape recorder. In the next day or two
(perhaps today) JPL will try to playback 30 seconds of tape from the tape
recorder to see if the tape is still intact. We may not get data - if the
tape heads are touching the leader. But if we get any rewind at all then I
interpret that as meaning the tape is still in one piece and all is not
lost.

Sunday, October 22 - The best possible news, for now. Yesterday I heard 
from the Probe project Scientist at Ames, Rich Young. He tells me that
preliminary indications are that the tape recorder is working. We were 
able to rewind the tape recorder and actually play a little bit of data.  
This was confirmed by a press release obtained today from JPL. Although 
we must still be cautious - obviously something went wrong, and we 
want to make sure that we understand exactly what, and how to prevent 
it from happening again - I am feeling quite a bit better than I have for 
the past ten days.  It looks like we may be on track again.  

Only 46 days to Jupiter!