PART 1: Galileo fact of the day
PART 2: ProbeSquash activity: Installment #7
PART 3: Recollections of the launch
PART 4: My week for AACS
PART 5: A radio experiment begins as Galileo disappears from Earth

A day on Jupiter is only 9 hours and 48 minutes long. Such fast
rotation causes Jupiter to be somewhat squashed due to centrifugal
force: its polar radius is 4000 km less than its equatorial radius (the
latter being 71,392 km). That means you'd weigh almost 25% more at
Jupiter's poles than at its equator, that is, if you could find a place to
stand! So a 100 pound person (on Earth) would weigh 230 pounds at
Jupiter's equator but 285 pounds at the pole! 

To recap, we suggest that after each Probe Squash installment, you
and your students make a prediction about how long the Probe's
mission will last.

Installment #7: Battery lifetime: electricity is vital
The Probe Battery: It Keeps Going, and Going, and Going.....

Before the Probe was released, it was able to draw power from the Orbiter.
Now that it's on its own, it relies on a battery. And not just any battery--the
Probe's lithium/sulfur dioxide batteries have to stand up to conditions far
tougher than anything that D cells from the supermarket are designed for.

Once the Probe separated from the Orbiter, the batteries provided the only
power source for the Probe during its almost 5 month long journey to
Jupiter. (A side note--one of the things that the Probe engineers had to be
very careful about while getting ready for Probe separation from the Orbiter
was to make sure that the batteries weren't accidentally discharged!)
Therefore, it was important to conserve energy on board the Probe, so
everything was turned off, with the exception of a timer that would "wake"
the probe six hours before entering the atmosphere. If the battery ends up
running down faster than expected, the Probe mission can't last as long. But
we won't know the battery's status until the Probe wakes back up.

When they're not being used (when they're not "under load"), the lithium
batteries have a voltage of 39 volts. Fresh out of the factory, they have a
total capacity of 21 ampere hours (an "ampere hour" is enough electricity to
keep a one ampere current flowing in a circuit for an hour), of which one
ampere hour will be lost as the battery ages (the battery, after all, is over 
six years old!); during the descent portion of the mission, an ampere-hour of
energy is used every 7 minutes). The Probe mission calls for the battery to
function for an hour after the Probe enters the atmosphere; by that time, the
Probe should use up about 18 ampere hours. With the remaining two
ampere hour margin, there should be enough power to last for at least 75
minutes after Probe entry, assuming that the Probe powers up no earlier
than scheduled.

(There are other batteries on board as well--two thermal batteries are used
for pyrotechnic events. You can hear the thermal batteries igniting, and smell
them after they ignite! Specifically,  thermal batteries are used for 1) the
mortar fire that will send out the pilot parachute, 2) the release of the Probe
heat shields, 3) extending the Nephelometer (or cloud sensor) arm, and 4)
activating the sharp cable cutters that will sever wires connecting the
Probe's outer protective shell to its inner capsule.)

To test the battery, a spare battery that was built at the same time as the
flight one (and therefore is just as old), and has been kept at the same
temperature as the flight battery, was hooked up to run under similar loads
and temperature. The loads are more severe than the actual Probe battery
will face. The test was run using the higher loads because this had been the
estimated load that, years earlier, before the exact loads on the spacecraft
were known, engineers had predicted the battery would face. To make it
easier to analyze the test results, the testing conditions weren't changed from
test to test over the entire lengthy history of the program.

Under this test, the battery lasted 68.5 minutes. After adjusting for the fact
that 1) the flight battery will experience smaller loads, and 2) the flight
battery will be some ten months older when called upon to do its job than
was the battery used in the test, Probe engineers are predicting that the
battery will be able to keep the Probe powered for 75.7 minutes. That will
take the Probe down to almost 30 bars of pressure, or about 193 degrees
Celsius.

Do you regard this as good news or bad news for the Probe's total lifetime?
And, something to think about for next time: so far, we've talked about how
to  keep the Probe "alive." But how do we get the Probe's data from the
hostile Jovian environment back to Earth?

1989 would be the big year for my project -- the year the Galileo
spacecraft would be launched. Even before launch, many years and
hundreds of careers had already been invested in the mission. By mid-
October, with launch imminent, most of the flight team members were 
visibly excited. Old-timers like me (by then, seven years on the project)
were more introspective; we had been here before.

When the project was approved in 1977, plans called for a 1982 Space
Shuttle launch along with a large booster rocket (its upper stage) to send 
Galileo off to Jupiter. Within a few years, delays in the Shuttle program
forced Galileo's launch to "slip" to 1984. Later, funding problems with the
upper stage forced a further delay, until 1985. In between, each new
federal budget seemed to threaten Galileo with outright cancellation and
each time Galileo managed to hold on. The engineers and scientists
working on Galileo, all coping with formidable technical challenges made
more complicated by each change to the mission, held on as well, hoping
each postponement would be the last.

When I joined Galileo in December 1982, launch had just slipped to May
1986. This seemed more secure than previous dates. By now, the Shuttle
had launched five times and funding for our upper-stage, the Shuttle-
Centaur, was firmly in place. Morale picked up as we began to assemble
and test the largest and most complex planetary explorer ever. In 1984, a
milestone had been reached -- two years until launch. We had never been
that close before!

By January 1986, I was spending most of my waking hours at work, 
preparing for Galileo's launch. Testing was complete and the spacecraft
had been shipped by flat-bed truck from JPL in Pasadena to the Kennedy
Space Center, where it become space shuttle Atlantis's prime cargo. Now,
among other duties, I was the systems engineer responsible for the first
maneuver Galileo would perform. This called for firing the spacecraft's
thrusters about 10 days after launch to assure that its course would take
it on a fly-by of the asteroid Amphitrite along the way to Jupiter. After
years of designing, testing, and trouble-shooting Galileo, I was on the 
team that would fly it. Unfortunately, there was no owner's manual in the
glove compartment.

Early on morning of January 28, 1986, the Galileo flight team assembled
in a large conference room for another in a long series of training lectures.
Some of us rubbed sleep from our eyes while others fidgeted, thinking of
the work remaining back at our desks. Overhead, the TV monitors were
all tuned to NASA's internal television network. Later that day, there
would be a press conference announcing Voyager 2's discoveries at the
planet Uranus. Meanwhile, the monitors showed preparations to launch
another Space Shuttle. For us, that launch meant that there would be only
one more to go before our own.

The lecture crept along, broken by many questions and clarifications.
Finally, someone suggested we take a short break to watch the shuttle
launch. We all looked up in time to watch the Space Shuttle Challenger
liftoff and clear the tower. Since the TV monitors had their sound off,
people chatted freely. Over my shoulder, someone said, "It's amazing how
that thing works every time."

On the screen above, Challenger was fading into the sky. By now, we knew
the shuttle launch sequence by heart. Soon the solid rocket motors would
burn out and separate. We were all startled when we saw what appeared
to be an early separation of the solid motors. As the seconds dragged, a
growing fireball filled the screen, showing many pieces dropping from the
sky. 

Without spoken commentary from the TV, no one knew for sure what was
happening.  

In some launch failures, the shuttle can return to the launch site for a
runway landing. Was Challenger on its way there now, out of sight of the
TV camera?

Someone said the monitors in the cafeteria next door might have sound.
About a dozen of us bolted for the doors. The cafeteria monitors were
silent also, but as we arrived, the NASA cameras had panned downward
to watch large pieces of debris hit the ocean. There was no sign of
Challenger gliding toward a runway.  


We all felt grief in our own ways. A few cried. Others stared vacantly at 
the screen, then slowly ambled away. The Astronaut Corps, the most
visible side of NASA, came to represent the many thousands of us that
worked in the space program. We lost family that day.

On the Galileo project, our actions, which a short time earlier were
energetic and purposeful, became lethargic and disjointed. Would Galileo
ever launch? Would there be planetary exploration at all in the near
future?

Within a day, our Project Manager, John Casani, returned from Florida
where he had been overseeing Galileo launch preparations. We assembled
in the cafeteria and John spoke atop a chair so he could be seen and heard
by everyone.  

He confirmed, as most had already assumed, that no one knew when to
expect another shuttle flight. In the meantime, our work to prepare for
launch and flight operations remained very important and we were all
expected to continue. Galileo would launch someday and the knowledge
required to fly it must be "captured" while this flight team remained
together. Meanwhile, others would go off to plan a new mission

1986 dragged on with new options considered and dropped almost
weekly. For a while, a 1987 launch seemed possible. Soon the new launch
date moved to 1988 and finally settled at October 1989. Our upper stage--
the Shuttle-Centaur booster, which used cryogenic liquid fuel--had been
canceled a few months earlier. The spacecraft was now going to use the
much smaller Inertial Upper Stage (IUS) booster. To get to Jupiter, Galileo
would have to take a six-year looping trajectory through the inner solar
system rather than a two-year direct flight. More importantly, the
spacecraft would have to be significantly modified to fly much closer to
the Sun than the original flight path called for. The added time was a
disappointment, but there was now so much more to be done.

By October 1989, the spacecraft was inside the Space Shuttle Discovery,
awaiting launch. A new flight team had been assembled, about an even
mix of new faces and old. This time, I was in charge of early cruise
activities to check out Galileo's operation  -- a "shake-out" to uncover
problems before the Venus fly-by next February when solar heating
would be at its worst. Depending on the day Galileo launched, my
command sequence would have to be adjusted (since the actual trajectory
would be somewhat different from the planned trajectory). Unfortunately,
that meant that during launch I would not be stationed in Galileo's
Mission Support Area (the MSA being Galileo's version of Apollo 13's
Mission Control - Houston). Rather, I would have to stay fresh to rework
my commands soon after Galileo was sent on its way.

This wasn't the happiest possible arrangement for me, but I accepted that 
responsibilities had to be divided and there were others who were more
qualified to do the monitoring. Besides, the last thing the MSA needed
were people standing around "just to be there" and obstructing other's
concentration.

In the weeks prior to launch, some friends and I conspired to make our
own personal statement on Launch Day. This project consumed most of
the precious personal time we had, but it seemed not to matter. How
many times does someone get to celebrate the start of a planetary
voyage?

Galileo's launch date was set by the positions of the planets. For a proper 
gravity assist, the spacecraft must approach Venus at precisely the right
time and in precisely the right direction and speed. Our upper-stage
would deliver most of the energy required for this; the rest would come
to launch and, on either side of it, days when you could get to Venus by
using more fuel. In hard terms, this meant Galileo *had* to be launched
sometime between October 12 and November 21, or the increased fuel
cost would force us to delay launch until the next favorable planetary
alignment six months later.

To make matters worse, the Space Shuttle had its own constraints that
determined what time of day it could launch. In the  middle of our launch 
period we might have a "launch window" lasting over an hour, but near
the beginning and end there would only be minutes to launch on each
day. A streak of minor problems or one large one could keep Galileo
earthbound until the following year.

As our launch period began, everyone waited nervously as the shuttle
prepared for launch. Minutes ticked away and then an announcement
came from Florida. The shuttle had a problem with one of its computers
and the launch that day was scrubbed.

A week later, with the computer repaired, our countdown began again.
This time, clouds rolled in over the launch site and weather forced
another cancellation.

October the 18th was a bright and sunny day in Pasadena. There were
still clouds in Florida, so many of us expected that day's launch would be
scrubbed also. Either that, or some other problem would cause a delay. 
Working on Galileo, we had learned to accept such things.

Friends in the MSA that morning tell me that when the launch clock
finally started ticking down to the single minutes, they looked at each
other with eyes wide. They were really going to do it!  In a conference
room in another building, I watched a TV screen with a roomful of other
Galileo personnel. There was a buzz of nervous chatter right up to the
final seconds before launch.  

Al Hoffman, our chief environmental engineer, kept a watchful eye on the
door to make sure latecomers had a view.

When the Space Shuttle cleared the launch tower, the room erupted with
cheers and applause. The noise subsided as the shuttle rose higher and we
remembered another launch three and a half years earlier. We held our
breaths as Discovery passed through one minute of flight and then two.
Cheers rose up again when we saw the shuttle's solid-rocket motors burn
out and fall safely away. 

Fists punched the air and hands slapped each other in "high-fives". Others 
slumped contentedly in their chairs, relieved that their wait was finally
over.  

With the shuttle, and our spacecraft, safely on its way to Earth orbit, Al 
Hoffman began handing out lapel pins commemorating Galileo's launch. It
was the first of many similar pins I would receive.

My co-conspirators and I looked at each other. The shuttle, with Galileo 
aboard, was in space at last. This was the right time.

We went to a utility closet and took the bundle of cloth, wood, and rope
that we had worked nights and weekends to prepare. On the roof, we
spread apart as planned and began to tie our rigging. Over the side we
hung our banner measuring about 10 feet high by 50 feet wide, all in
white with large blue lettering. "Galileo: WE'RE ON OUR WAY!", it said in
print large enough to be plainly seen from JPL's plaza, eight stories below.
Fluttering in the sun that clear fall morning, it was a beautiful sight.

Perhaps it was an extravagant gesture, but it spoke of the pride and 
satisfaction felt that day. We wanted to tell the world about it.

Whatever the future held, Galileo was earthbound no longer.

---------------------------------------------------------------------------

Bob Gounley went on to become a deputy team chief for Galileo's
engineering team and understands that it is against regulations to hang
banners off the sides of buildings without prior approval. Having recently
started work on a new project, he now observes the Galileo project from
afar. He looks forward to celebrating Galileo's arrival at Jupiter next week.

November 20, 1995
I am a subsystem engineer for the Attitude and Articulation Control
System (AACS). One of the things that makes my job so cool is that I get
to work on LOTS of different things. Here is the stuff I worked on this
week:

I have a computer program that I wrote that draws "Sphere plots." They
are kind of like drawing pictures on the surface of a computerized globe.
This turns out to be a very good way to look at geometry problems for
spacecraft because you can think of the globe as the sky and plot some
stars and planets on it, and then mark where the spacecraft is pointed
and the camera is looking.  

I used a program called SKYBALL a lot this week. On the 7th of December
we are  going to use a small antenna (called the Relay Radio Antenna, or
RRA for short) to pick up the science data from our probe as it enters
Jupiter's atmosphere. To make it all work, this antenna has to be pointed
at exactly the spot where the probe is. I was asked to make one last
quadruple check of the commands that the spacecraft will use to point
the antenna, so I used my Sphere Plot program to make a picture of
where the Earth and Sun and Jupiter will be on Dec. 7 and then plotted
where the spacecraft's spin axis was pointed and where the commands
will point the antenna. Everything checked out fine. 

I also used SKYBALL to see where one of the science instruments was
pointed to help the scientists understand their data better. I build lots of
little programs to plot or compute things,  so knowing how to work with
and program computers is very important for my job. My  little programs
are like a set of *tools* and I have a "toolbox" of my favorites that I use
and work to improve all the time. 

I went to a meeting to figure out how to use our not-quite-healthy tape
recorder to play back the  data we record from the probe. The meeting
was long and there was lots of heated debate  over the way to get the job
done. In the end the project manager put off the decision till later and
give the anomaly team (the group of people working on the problem) a
little more time to work. It's pretty common for "decision" meetings to
end this way.

I'm helping the tape recorder anomaly team by finding, plotting and
looking at lots of telemetry from the tape recorder (I'll write about how I
ended up doing this in another message).

I wrote a little program to look through a whole bunch of tape recorder 
telemetry (the signal that we receive from the spacecraft) and pull out
just the data when the recorder was playing or recording at its lowest
speed. Some folks are working on some new software for the spacecraft
that will automatically check to see if the tape  recorder is slipping or
acting funny. If it is, the new software will respond by stopping the
recorder. The people working need to know how  much power the tape 
recorder uses at different places on the tape and how much it changes
I also found some data on the pressure inside the recorder's sealed case.
It turns out that  the pressure also serves as a sensitive measure of the 
*temperature* of the recorder. This  is a good example of how we
sometimes have to use things (and data) in ways that were not originally
intended.  

Well, that's all the stuff I can think of at the moment. I'll write again 
soon...
                Steve

November 20, 1995

Well, the Radio Science crisis I described in my last journal has subsided.  
We discovered early last week that there were software changes in the
July upgrade which only the programmers knew about. We (the users)
didn't.  AAARGHHH!  So, now at least we know what the problem is (one
computer is too slow compared to another computer and so it is dropping
information in the process). Luckily, we do have some ways to work
around this.

It's almost 7 pm on Tuesday night before Thanksgiving and The Smiths are
serenading me as I type this. I just finished editing our Radio Science
Handbook. This is a resource document that our team puts together right
before every major experiment. We list useful things like phone numbers
and beeper numbers. We also explain the different parts of our
instrument (both the Deep Space Network (DSN) part and the spacecraft
part). We list the individual responsibilities of the members of the
Support Team. There's a section on references that we use and
monitoring systems that are useful to us. There's a section on procedures
that are common to all of our experiments. And, finally, we explain each
of the upcoming experiments including the appropriate setup for the
Radio Science System at the DSN ground stations. Well, I'm finally done
and tomorrow I will take it into the documentation section to be
photocopied. Whew!!  (See--language skills are very IMPORTANT!)

Have I spoken about our BIG experiment on December 8? Well, I'll just
tell you about it anyway (hee hee). On December 8, the day after we
reach Jupiter orbit, the spacecraft will go "behind" Jupiter as seen from
Earth. This is called an "Earth Occultation by Jupiter." As the spacecraft
begins to move behind the planet, the radio signal will begin to pass
through the Jovian atmosphere. The atmosphere acts like a lens and it
will bend (or "refract") the radio signal. We will record the signal at the
ground station (for this experiment, it will be the one in Madrid) using
special equipment. For radio science, we really are only interested in the 
center of the signal called the carrier. The equipment at the ground
station will sample the carrier at the rate of 5000 times per second and
we will record the signal for almost three hours.

Now, the navigation team knows the position of the spacecraft really well.
So, by combining the navigation information with the information from the
recorded radio signal, our Radio Science investigators can develop what's 
known as a refractivity profile (that is, they can show refraction as a 
function of height above the planet).  

The neat part is that we can actually use this information to examine
what's in Jupiter's atmosphere! The investigators have a pretty good--but
not perfect--idea of the composition of Jupiter's atmosphere. Different
mixtures of gases will have different refractive effects on the radio
signal. So, they'll fine tune their composition "model," changing around
the mixture of gases until the model gives them a refractivity profile like
what they see in the data. Then, based on gas physics, they can
determine temperature and pressure profiles along the path of the radio
signal--all from a distance far above Jupiter's atmosphere.

Pretty Cool, huh!!

The next two weeks will be spent making final preparations for the
Experiment. It actually begins at 2:02 AM on Friday, December 8 (yes,
that's 2 in the morning!). But, we have lots of things to do before then.
In fact, by the time it starts, we shouldn't have anything to do (if all
goes well)! We'll just sit back and watch as the station records our data.

Well, that's all for now. 

Ciao,
Randy G. Herrera

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