**FTS-NASA-VOICE**

**Moderator: Trina Ray**

**March 28, 2006**

**1:00 pm CT**

Coordinator: Excuse me, at this time I\'d like to inform all
participants that today\'s call is being recorded. If you have any
objections you may disconnect at this time.

And I\'d like to turn today\'s call over to Miss Trina Ray. Thank you.
You may begin.

Trina Ray: Thank you. Well I\'d like to welcome everybody to the CHARM
telecon for this month. We\'ve got a fantastic topic today. It\'s one
that you all suggested when I took ideas a few CHARM telecons ago. I
wrote down a whole bunch of suggestions and one of them was a spacecraft
tutorial.

And today we\'re joined by Julie Webster, who is the Cassini Spacecraft
Operations Manager. And she\'ll have a wonderful talk for us on the
spacecraft.

Just a few reminders about the telecon. If you don\'t have mute
capability on your phone, that\'s okay. Just press star six at any time
to mute and unmute. If you have any trouble at all press star 0 and the
operator will come on and help you.

And Julie is welcome to take questions during the actual talk. And with
that, I will go ahead and turn it over to Julie.

Julie Webster: Okay, this is, of course, my favorite subject. I\'ve been
working on Cassini since 1995. I started back in the assembly, test and
launch operations phase. So I hope today - I\'ve got a few unique
pictures for you that were taken during that time to just kind of give
you a different perspective.

You know, when the scientists put out their beautiful pictures and
things like that and the engineers look at all the wiring and
electronics and the assembly that had to be put together to take that
picture.

So I tried to arrange it with picture/words, picture/words and I\'m
going to try to use the words to talk to the picture before. If this
works out. In hindsight, I should have probably done it the other way.
But this, this will go.

Man: Julie, I\'m sorry to interrupt but you have a bad connection.

Trina Ray: I was going to ask you\...are you on a...

Julie Webster: Okay.

Trina Ray: \...are you on a hand - you know, on a phone or can you\...

Julie Webster: I was.

Trina Ray: \...can you pick up the handset?

Julie Webster: I just picked up the handset. Is that better?

Trina Ray: Oh, much better.

Man: It's pretty much the same.

Julie Webster: Oh, good. Okay.

It\'s pretty much the same?

Man: It\'s still bad.

Julie Webster: Oh.

Man: It\'s much better here.

Trina Ray: It\'s much better here too. You know what Julie, hold on a
second. Let me go ask the operator if she can see any problem. Let\'s
just hold on for a sec.

Julie Webster: Okay.

Man: I don\'t think it\'s the telecon. (See what happens when) you have
engineering problems?

Julie Webster: Especially on telecommunications. It stops everything.

Man: Especially once you have - if you\'re in a wonderful situation. It
certainly got better. I mean, it\'s perfect here. I guess maybe it\'s
not so good up where the other - I think if you\'re on a speakerphone
sometimes it\'s not so good. I don\'t know.

Julie Webster: Yeah. She told me to pick up the handset but apparently,
it\'s not much better.

Man: I think it\'s better but it\'s not like, you know, it\'s not
perfect. There\'s still some kind of crackling that you hear.

Man: Is that what the other person is experiencing? The crackling?

Man: I was getting some crackling too; it seemed like when she went to
the handset it got better.

Man: Yeah, I agree with both statements.

Julie Webster: Okay, well let\'s hope Trina solves the crackling or
handset problem.

Man: See if she can bring some cookies too.

Trina Ray: Okay, the operator is going to come take a look at it.

Man: It\'s pretty marvelous that this could even happen.

Trina Ray: It\'s amazing.

Well, the entire Cassini mission is basically driven by telecon. We have
so many telecons because our scientists are spread out all over the\...

Man: World.

Trina Ray: \...all over the world. All of the engineers are co-located
at JPL and - basically in one building. But even, I mean, I routinely
from my office will call into a telecon that is just, you know, down the
hallway.

Julie Webster: Do you want to try again?

Trina Ray: Okay. Do you want - are you working with the operator Julie?

Julie Webster: No. Was I supposed to?

Trina Ray: She was going to take a look at your line.

Julie Webster: Okay.

Trina Ray: And see if, whether she though you should call back in or
whether she thought\...

Julie Webster: I can certainly do that. That\'s easy.

Trina Ray: Yeah. I wonder what she would recommend. I guess we can hold
on a sec.

Julie Webster: Okay.

Man: It\'s interesting because the local lady in Southern California, I
guess or wherever, her voice is much clearer than Julie\'s. So there is
a difference for some reason. Of...

Trina Ray: That\'s because I\'m calling from home. I am sure it\'s just
the whole atmosphere. Calling from home you get a better connection.

Man: And maybe that\'s why I\'m hearing you better too.

Trina Ray: I have to say Julie calls in from her office to telecons that
are right down the hallway too. I know. I\'ve seen it happen.

(Jane): Trina, this is (Jane). A lot of people when they mute on and
off, also, you know, if they go back and forth a lot, that creates a
little blip. And actually, when we\'re writing the transcripts, that
makes it almost impossible sometimes. Because the Operator - the
transcript - all they hear is the blips all the time.

So people should try to also just keep the mute on when they\'re
listening to the talk and then ask questions at the end or whatever.

Man: Okay, so we\'ll save our questions for the end?

Trina Ray: No, I don\'t think so. We can ask\...

(Jane): Well, if you do, just be sure that you mute, you know, not with
frequency.

Man: All right.

(Jane): Who is this asking all these questions?

(Ron Ignelsi): Oh, (Ron) - I didn\'t ask all of them but I asked a lot
of them - (Ron Ignelsi).

(Jane): And are you a Solar System Ambassador?

(Ron Ignelsi): Yes.

(Jane): Great. Thanks.

Trina Ray: So (Jane), were you hearing Julie okay before or\...

Julie Webster: I was hearing Julie just fine. I think we should just go
ahead and\...

Coordinator: Excuse me, this is the coordinator. I have placed Ms.
Webster back to conference. And her line is much better at this time.

Trina Ray: Oh, excellent. Do we need to start the recording over?

Coordinator: I can\...

Trina Ray: Or is it still going?

Coordinator: It\'s still going right now.

Trina Ray: Would it be okay if we sort of stopped it and restarted it so
that it\'s a nice clean recording? Is that possible?

Coordinator: Yes, we can go ahead, I can go ahead and we can disconnect
that. And go ahead and re-do it after the call is ended. And we\'ll just
go ahead and record it now. And then we can go ahead and fix that for
you.

Trina Ray: Oh, okay.

Coordinator: Okay?

Trina Ray: That\'s fine also.

Coordinator: Okay, all right and then you can go ahead and\...

Trina Ray: We\'ll just let Julie go ahead. And then once you start over,
we can figure that\...

Julie Webster: Okay. Do I need to start all over or can you just cut out
all the conversation about bad telecon?

Trina Ray: I guess we should just start from scratch.

Julie Webster: Okay.

Again, I\'ve been on Cassini since 1995. So I started back in the
assembly, test and launch operations phase. And what I was trying to
show with the pictures today, I hope I got some unique pictures, was how
engineers look that the spacecraft in terms of the buildup of it instead
of just the pretty pictures.

So anyway, on page 3, we are the largest outer planetary spacecraft ever
built. I believe - and I have never verified this and I\'ve given this
in many, many talks - that Phobos, the Russian spacecraft that went to
Mars, that had problems in the late \'80s was actually a larger
spacecraft.

At launch we weighed 507 - almost 5,600 kilograms. And of that, 3100
kilograms was just pure propellant. Today we are down to just 422 of
that 3132 left, after three major maneuvers and dozens of smaller
maneuvers.

We do have 58 microprocessors on board, which is pretty amazing. Every
instrument has its own microprocessor. Several of the attitude control
systems have microprocessors. And of course, there\'s microprocessors
that run the computer and the ... attitude flight computer.

The 12 science instruments - and the only thing I want to put out here
on the picture is the optical remote sensing, the things that you get
most of the times on these telecons are the pictures - and the four
cameras are collocated on what they call the remote sensing pallet, in
the picture. So the cameras are all facing collinear so you get, you can
get pictures from all four of the cameras for one spacecraft pointing.

The fields and particles instrument are mostly collinear - well, over on
the fields and particles pallet. But they are also spread out around the
spacecraft. So they are a little bit different there.

The electronics in the spacecraft is mostly in - there is a 12 sided bay
that\'s the upper equipment module where the louvers are shown. And
I\'ll have a better picture of that later. JPL has almost always built
their spacecraft in a bay configuration. I think we started out with an
8 bay for Voyager. And some of the Mariners, I think were like 6 six
bays.

We were up to 12 bays, so I think we have the most bays in terms of a
kind of circular configuration that JPL has ever flown.

Okay so\...

Man: A bay is a side?

Julie Webster: It\'s a side. You know, like an octagon, like an 8 sided
would be like a stop sign?

Man: Okay.

Julie Webster: And so we are a 12 sided. A dodecahedron, is that
correct? Or is that 20?

Man: Yes.

Julie Webster: I never can remember.

Man: You\'re right. But are we looking at the picture on page\...

Julie Webster: Page 2. Yes.

Man: Okay, thank you.

Julie Webster: I\'ll go into quite a bit of details in a second on the
next grouping.

There\'s three of the radioisotope thermoelectric generators. And those
are shown in the cartoon around the bottom. And they have shields on the
top of them to stop some of the heat from going back in in a different
way from what we wanted, on the spacecraft.

So I\'m going to go on to page 4.And\...

(Ken Kramer): Julie, could I ask you, ask you a question about\...

Julie Webster: Sure.

(Ken Kramer): \...a propellant, please? It\'s (Ken Kramer) from
Princeton, New Jersey.

About the propellant, have you used - or how much have you used in the
past years since the Saturn orbit insertion?

Julie Webster: Let me see, I\'ve got that detail written right over
here.

In the past year, we\'ve used a fair amount because we did what we call
Periapsis Raise Maneuver. And I\'ll show that in a later slide. We were
about two-thirds down in propellant before that Periapsis Raise
Maneuver. And so I\'ll go through a little bit of detail on that.

If you want some additional details, I can also email you those kind of
things.

(Ken Kramer): I will ask you that then. Just one last question, about
the instuments - basically everything is functioning normally on the
spacecraft, right? There are no problems at this time?

Julie Webster: There are no problems on this. It\'s been the most
amazing spacecraft I ever worked on.

Okay, page 4 is the picture of the radioisotope thermoelectric
generator. Page 5 is the details.

We started out with three, what we call RTGs. We had about 875 watts of
power at launch. If you think about it, that\'s less than half of your
hairdryer. Of course, that\'s a little misleading because your hairdryer
is on a 110 volt system and we are on a 30 volt system. But it still is
an amazing amount of - not very much power to run this whole spacecraft.

The RTGs themselves, we get heat from the radioactive decay. And that
heat is turned into power. And of course, the more they decay, the less
heat they produce. So we lose about one watt a month. So we\'re down to,
today, about 721 watts. So we\'ve lost 150 watts since the launch. And
we\'ll continue to lose that. It\'s about 9 watts a year starting around
2007.

The excess power - we still have, out of all of that, out of that small
amount of power - we still have excess power. And that\'s distributed
out to a (shunt) radiator. And I\'ll point that out in one of the later
pictures. I think that solar thermal vac has a good picture of the
(shunt) radiator. And that is just radiated out to space.

One of the major upgrades on Cassini, as opposed to like a Galileo or a
Magellan or the Voyagers, or some of the earlier Earth spacecraft, is
that we have - the power is distributed to the electronics and the
instruments through 192 solid state power switches. And the solid state
power switches are like little circuit breakers.

This, for me, this was a major step forward in the engineering because
relays - we used to use relays. So you know, if you had a critical
thing, you would put four relays on it. And you would have to close two
different relays to get the power through the electronics. And relays,
we were always worried about relays sticking, or relays frying together,
or other things about faulty relays.

So these power switches have been a major upgrade for us. They - the
critical loads, you know, we tried to make the spacecraft idiot proof,
even for us. So all the critical loads have redundant switches an
automatic turn on circuitry. So if the spacecraft is on, they\'re on-
and a lot of things that we\'ve never turned off since we first powered
the spacecraft at launch.

There is special fault protection involved. We\'ve worried about these
switches occasionally, if they\'re off or on, they tend to just trip
off, not for an over current situation but because of a faulty design.
And we\'ve uploaded special fault protection for these cases.

The other thing that is unique about the power system is we don\'t have
enough power to keep all the instruments on all the time. We keep 10 of
the 12 at any given time but not all 12. The radar and radio science
guys, tend to be high power draws so we go into certain operational
modes to be able to carry.

So we say if you want radar on, these instruments have to be in sleep,
these instruments have to be off, et cetera, et cetera.

Let\'s see, I don\'t think there\'s anything else. I\'m on to page -
with the next page is a picture of the 1750A processor the
microprocessor that is actually the main computer chip on the
spacecraft. So the engineering flight computer, the command and data
system, we have two identical flight computers.

Of course, when you send an asset, a spacecraft like this out to Saturn,
we do all lot of redundancy. Almost everything that is a critical item
has a redundant.

So we have a redundant computer, we have a redundant bus that
distributes the computer out to the different electronics and the
science subsystems. It\'s, I think it\'s always kind of amazing that we
only take 512 - these computers are only 512K of RAM. There isn\'t - you
don\'t need all lot of processing power to run a spacecraft.

We upload background sequences about every 3 to 6 weeks. So we put
everything that is needed for the computer to fly for the next 3 to 6
weeks. And then sometimes we still need real-time commands so those are
up-linked during downlink passes that we\'ll talk about in a little
while.

Let\'s see, we do process all the telemetry for the spacecraft
engineering subsystems, and the instruments, the instruments - when
we\'re not in sight of a downlink station - we store the information,
and the pictures and the science data, on two solid state recorders.

And each solid state recorder is the 2.3 gigabits; 2.1 is available for
telemetry. On any given day, we only downlink probably a little bit less
than 2 gigabits a day.

And going on to the - the next is the propulsion system. And maybe I can
answer some more prop questions on this one. We have two completely
different, two completely isolated systems.

One is a mono propellant system which is hydrazine. And hydrazine is put
through a heated catalyst bed to rapidly expand and get us this small
thrust.

These are one Newton thrusters. We have 4 thrusters per cluster. And the
cluster, if you look in the photograph, those are the lower items that
look like little squares that are out on the black supporting struts.
And there\'s one in each corner. We have - we only use 8 at a time. And
there are 2 downward facing and 2 outward facing in the Z direction.

And in between the down and Z, between the downward facing and the
outward facing in one direction, we can thrust the spacecraft in any
direction that we need to go.

These small thrusters, are used in what we call a blowdown mode. That
means that they\'re pressurized to a certain thing using helium as a
pressurant at launch. And since launch, they\'ve been - of course, every
time they thrust, they lower the pressure just a little bit.

We - and because there\'s less gas in there, we started out with these
at one Newton thrusters and we\'re down now to about .65 Newtons today.
And the reason that I\'m going into a little bit of detail on this, is a
week from next Monday, on April 10, we\'re actually going to fire - oh,
I just drew a blank here.

We\'re actually going to fire a pyro device. And if you look at the
pictures, there is a small ball - and I have a helium recharged tank for
mono prop - there is a small ball on the lower right part of the
picture. We\'re actually going to fire a pyro that will open up that
small ball of highly pressurized helium. And it will go back in to the
large mono prop ball. And it will pressurize these thrusters back up to
one Newton.

That gives us more attitude control authority for going very close to
the Titan passes. So that we have more thrust capability to overcome
Titan (torques).

Let\'s see, what else can we talk about that? Oh, we have a complete
backup system. All of those thrusters have a redundant thruster with
them. We have never gone to the backup redundant system in flight. The
spacecraft has been remarkably performing well.

The other system that is a larger thrust is the bi-propellant system.
It\'s nitrogen tetroxide and (monomethyl) hydrazine. And it - we have
main engines. The picture is not a very good picture for the main
engines - I\'m hoping that I\'ll have a better picture later on -
because of the support cages are in the way. But they are kind of the
blue-gray nozzles down at the bottom of the picture, if you look
carefully.

These are 445 Newtons engines, or just large thrusters. And they\'re
used to - there\'s only one engine that we\'ve ever used. We\'ve only
used engine A. But because you go out to Saturn, after 7 years, you
don\'t want an engine failure to stop you from going into orbit, we
carried a backup engine. And we still have that backup engine available
to us should anything happen with the main engine.

The bi-prop also is mostly used in a blowdown mode in terms of that it
was pressurized, except for real long burns. For long burns, for large
burns like a Saturn Orbit Insertion or the Periapse Raise Maneuver, or
the Deep Space Maneuver that are very, very long, over several minutes,
you know, 5 up to maybe 90 minutes burn, those are all done in a
regulated mode. And we have a regulator that provides a constant
pressure to the engines so that we get the same thrust throughout the
maneuver.

Let\'s see, the engines, almost - it wasn\'t really an afterthought, but
late in the design game, they came back with some worry about these two
engines kind of hanging out in the breeze during the asteroid crossing,
was our original concern. And so we put on an articulated baby buggy,
baby buggy cover that is a, it has metal stays, and thermal blanket
material, several layers of thermal blanket material. And we actually
articulate, or you know, baby buggy this over the main engines during
any dust hazards.

We kept the engine covered almost all the time in cruise, and only
opened it when we wanted to do a trajectory correction maneuver. In
tour, we tended to do just the opposite. We leave it open except for
dust hazard crossings where we get near the E-ring, I believe. And when
we go in to the closer rings where we\'re worried about dust hazards,
we\'ll close the cover at that time.

Man: Julie, you would begin to, obviously, have a problem if the dust
cover never opened. Do you take special precautions to make sure it will
open under (all) circumstances?

Julie Webster: Absolutely. Engineers are nothing if not cautious.
There\'s two motors, there\'s two driving motors for this. You can use
either motor A or B, or you can use both if there\'s an issue with
driving the material.

And in the worst case conditions, since it\'s easier to avoid dust
hazards than it is to not fire a trajectory, you can also blow this off.
We can blow this cover off with a pyro fire should we need to. And we
always keep that option in the back of our mind.

Man: Thanks, (that was) my question, if you\...

Julie Webster: And\...

Man: \...to not chance things.

Julie Webster: And actually, in \'88 - not \'88, gosh, 10 years too
early - in 1998/1999 we actually had quite a change in where the cover
opened to because of the stiffness of the material after it\'s been out
in flight for a while. And we watch that very closely. Since then it\'s
kind of settled into the same. It opens up about 2/3 of the way. It
doesn\'t get quite all the way up, like it used to, anymore. And that\'s
still good enough to fire the main engines. But we watch that every
single time when we close and open the cover.

All right. Let\'s go on. Now the workhorse subsystem, of course every
subsystem thinks they are the most important subsystem, but attitude
control is the essential thing for science. We have to be able to point
the spacecraft reliably, we have to be able to point it accurately, and
we have to point it very stable, should we need to.

That attitude control system, the picture is kind of showing that the
attitude control system is distributed all over the spacecraft. At the
top, and I don\'t think I wrote that in the words, but there\'s two
holes in the high gain antenna. And those are where the sun sensors go.

So the very first thing the spacecraft does, if it doesn\'t know where
it\'s at, - the flight software on board tells it to go find the sun. So
it will turn the spacecraft in a slow motion around until it gets the
sun in the field of view of the sun sensors going through the high gain.

And then it tries to find stars. So the actual attitude determination is
done by what we called stellar reference units. And what these are, are
basically very, very fancy cameras with CCDs, charge coupled devices.
Where they have, they are comparing against, all the time, against an
onboard star catalog.

We have about a 3500 star catalog. So it takes a picture. It picks out
the four or five brightest stars in the field of view at any given time
and it tries to match them up to its star catalog to make sure that it
knows where it\'s at.

If it can\'t find more than three stars, it starts a search program that
it will continue to try and move around until it can find those four or
five brightest stars at any given time.

Now, the stellar reference unit, still, it can be spoofed on occasion if
there\'s bright bodies, like Saturn is a bright body, Titan is a bright
body, even the reflection of the rings is considered a bright body. So
it can be spoofed into seeing brighter bodies than the stars that we
want it to see.

So during that time, we may tell it not to look for stars for a few
minutes, to a few hours. And we hold the attitude control by gyroscopes
or inertial reference units. And we have two, although we only used one,
hemispheric resonator gyros. And that\'s how we hold the attitude if we
can\'t pick it up with the SRU.

And then the attitude rates are supplied by the gyros all the time. And
if the stellar reference unit is working, it updates the attitude rates
and determination into the gyros constantly.

The attitude control, there\'s two ways to hold the spacecraft stable.
We are a three axis stabilized spacecraft. And we can either stabilize
the spacecraft and hold the pointing control with the thrusters, the
little thrusters - and we tend to thrust around what they call a
deadband. So we normally use a 2 milliradian, what they call a deadband.

So for plus and minus 2 milliradians - remember 17 milliradians is a
degree, so it\'s an 1/8, less than 1/8 of a degree or so between a 1/4
of a degree by the time you go plus or minus 2 - we tend to bounce back
and forth. So we let the spacecraft drift. And then if it comes up
against the edge of being 2 milliradians off its perfect pointing, it
will fire a thruster to force it back towards the ideal position that we
want.

And then it will go back the other way and we\'ll fire a thruster the
other way. And we\'ll kind of dead band. We\'ll just bounce back and
forth between those two areas. That\'s perfectly okay for a lot of
spacecraft and science data taking, but it\'s not usually good enough
for the cameras.

And for the cameras, we go on - the reaction wheel control. There\'s
three reaction wheels and they\'re around the - basically there\'s three
spaced around the bottom of the spacecraft. And there\'s one that was up
on the upper equipment module that was a spare reaction wheel.

The reaction wheels are nothing but - the are kind of a spinning magnet.
They the kind of make a heavy, if you think of it as a top, you know,
where tops always try to correct to an attitude. And we put electronic
impulses in to these RWAs to cause a torque, to cause torque and to
cause it to change attitude per the, per whatever the spacecraft is
supposed to point at, at the time.

These reaction wheels are, as you see in the pictures, they are
incredible. They provide better than 100 microradians. Usually it\'s
down in the 50 to 60 microradian region, over 1,000 seconds. And that is
even in fact if the spacecraft is going several kilometers per second,
we still hold that pointing control with the reaction wheels.

I mentioned the fourth wheel, we carry a spare. We didn\'t carry three
spares, because of the expense and the weight. But we carried one spare
that could be moved into position to replace any one of the three prime
wheels. And in July of 2003, we actually had to do that.

We had a wheel that, the bearings on it started rattling and causing us
a lot of friction, kind of like a hot spot on your (unintelligible). And
we saw enough degradation that we went to the fourth wheel. We put it
into the place of the third prime wheel. And we\'ve been running on that
combination of 1-2-4, since July of 2003.

Is there anything else that I didn\'t tell you about the attitude
control system? The attitude control system has its own flight computer.
It talks to the command and data system to receive commands from that.
And also to send it back its telemetry. But the other flight computer,
that attitude flight computer, takes a complete care of attitude
control. And it can run, basically, on its own, once its given a target
to go to.

Man: Hi Julie, I have a question about a reaction wheel? In other
spacecraft, we often hear that when that fails, that\'s the end of that
mission. And it\'s a mission critical assembly. It\'s also one of the
few things that seems to have to be a mechanical solution to a need in a
spacecraft.

Is there some thing in the future that may replace reaction wheels that
you can envision?

Or do you think this is what we\'ll be using for generations to come?

Julie Webster: Boy, not that I know of. I think that the reaction wheels
are going to be basically used for generations to come. I think the
trick is in the manufacture and how good - they are getting better with
the lubricants. Cassini had some stabilizing chemicals put in its
lubricant to make it last longer and work better.

There\'s, you know of course with any ball bearing assembly, it\'s
absolutely critical how well you polish the ball bearings, is how well
they work in flight. So I don\'t know of anything that is coming down
the pike to replace reaction wheels, I do know that they ought to be a
good chunk of your budget.

Because you are right. When they fail - if we were to lose another
wheel - well now, let me back up a second. To us, it looked like we had
some problems. We never, ever with wheel 3 had a pointing control issue.
It\'s just that it was chattering more than we wanted it to.

And we\'ve got lots of telemetry on these wheels, probably more than
most spacecraft. We actually watch a lot of the friction spikes that
most spacecraft don\'t even have instrumented.

So we could actually go back to reaction wheel 3 and use it. We just
assumed that its life span, you know, has been degraded. But you are
right. They are a limiting factor.

Now, we could drop to an all thruster mission but it would shorten the
length of the mission and it would certainly degrade the pictures, quite
a bit.

Okay, the next picture - I\'m an old telecom engineer, so I always do
more on telecom than I do on any other subsystem. This picture, on Page
12, is one that was taken during the assembly and test phase.

They actually, at the time, you can see the technicians that are
squatting, are actually installing part of the radio plasma wave system,
which those red canisters were the covers before flight of the radio
RPWS antennas.

But what I wanted to show here, was that this is a four frequency
antenna. So this is used by the engineering subsystem for the
commanding, sending up commands and getting back telemetry. It\'s used,
the Doppler on the X-band is used by navigation to navigate the
spacecraft.

And we also have an (S-band) frequency that is used for radio science.
It is in the neighborhood of about 2 gigahertz. The X-band, which is the
workhorse frequency, is about 8 gigahertz.

But you also have the KA-band to which is another radio science
experiment, which is again, about four times higher than the X-band
which is about 20/32 gigahertz.

And then radar, radar also uses the high gain as the antenna for them.
They use a different, they don\'t - they use the parabolic dish slightly
differently. And the little things down in the middle that looks like
the two wings that are little five darker gray spots, those are
actually - there\'s five on each side - those are actually the beams
that send out the radar pulse and then receive the echo. So I was trying
to kind of show you that.

On top of the high gain antenna, is the low gain. The struts are holding
out the low gain, which is basically a choked wave guide. And we use
that for emergency communications.

The next page that I wanted to describe is how we get command and data
back from the earth. You have probably have had, or know some talks on
the Deep Space Network.

But just to remind you, that the Deep Space Network comprises of,
there\'s three complexes, one in Barstow, California, one in Madrid,
Spain, and one outside of Canberra, Australia.

And each complex has the big 70 meter antenna. And then they each have
multiple of 34 meter antennas. The 34 meter antennas are the workhorse.
And on any given day, we mostly have a nine hour pass where we point the
spacecraft to the Earth and have one of these 34 meter antennas receive
the signal.

That - I wrote in words on this picture quite a bit - but the most
important thing is on the tracking and navigating the spacecraft. The
DSN has a hydrogen controlled maser standard. And so it has, its knows
time, very, very exactly; and therefore, it knows frequency very, very
exactly.

So they send up a signal to the spacecraft. And in the spacecraft, a
transponder turns the signal around. It multiplies it by an exact
amount, in this case it\'s 880 over 749. And it forms a coherent
downlink. And so that gives the radio and navigation, the radio science
and navigation, a very, very precise two way coherent Doppler in order
to navigate the spacecraft.

Let\'s see, the two low gain antennas. We have one low gain antennas
that I pointed out on top of the high gain. The other low gain antenna
is located just below the probe. The probe is now missing and the
picture shows that it is not there anymore. The low gain two, when we
were in inter-cruise, which I\'ll show you in just a few minutes, we had
to use - the high gain was used as a sun shield. And so we had to
communicate out through the two low gain antennas. And so they were 90
degrees apart, on the spacecraft.

This is a classic - its a Cassini model - but it is a classic Deep Space
transponder, Motorola built Deep Space transponder, where the uplink bit
rates can go from 7. 8125, up to 500 in an exact multiple, so it\'s 500,
250, 125 et cetera.

The downlink rates can be anywhere from 14 - not the 22 I have on the
page - 14 to 165 kilobits, but if we fall to the low gain at Saturn
ranges, we have to drop down to 5 bits a second to - in order to receive
the signal on the ground.

Let\'s go to the next page. The next page is the Cassini spacecraft
being readied. This is a classic picture. I\'m sure you\'ve all seen it,
if you\'ve looked at the website at all. We were getting it prepared for
solar thermal vac. The solar thermal vacuum test, that is the most
important test for the whole spacecraft. If you pass solar thermal
vacuum, that\'s when you\'re really, what we consider flight space
qualified.

And this chamber, this 25\' circular chamber that this Cassini
spacecraft is inside, there\'s big doors - after they get finished
preparing it, and they close - and they can turn on, and they turn on
huge arc lamps down in the basement.

And then they focus them very precisely with mirrors at the top of this
chamber. And this can be made to simulate anywhere from sun at Saturn,
which is like a 1/10th of the sun, or it can simulate 2.3 suns like a
Venus.

And of course, since we had to go to both Venus and Saturn, we had to be
prepared for both. They close the chamber, lock it down, bring it down -
they form a vacuum in there so they draw out all of the ambient air -
and then they start running liquid nitrogen down those black panels,
those black panels that surround it, they start running liquid nitrogen
down that wall to simulate a space environment.

Now, even the liquid nitrogen in there wasn\'t cold enough for some of
the targets for the cameras. For example, the CIRS telescope had to be
colder than the liquid nitrogen. So during solar thermal vacuum tests,
we put in a very special helium cooled target, to get a liquid helium to
get down to the almost absolute coldest we could actually get.

To maintain these, there\'s a thermal system involved. And what we have,
there\'s two parts of this thermal system. There\'s the passive
components, which is the thermal blankets and the surface treatments
like the optical surface reflectors, that are like mirrors that would
reflect back any heat. And then there\'s the radiators that I just
described that would face cold sky - that needed the liquid helium
target to verify that it functioned correctly.

And the active components, if you look very carefully up on the 12 sided
bay area, there\'s the shiny metal things that kind of look like curtain
slats. Those are the louvers that are on some of the electronics bays.

And they are louvers that work exactly like your thermal thermostat in
your house. If it gets too warm, they open the louvers to outer space.
If it gets too cold, they closed the louvers and hold the heat in within
the spacecraft.

So, there\'s two really big things on this spacecraft that were a major
step forward. And the thermal system is one of them. It\'s amazing, but
from Venus distances all the way out to Saturn distances, we\'ve
maintained the temperature of the that 12 sided bay within 10 degrees of
room temperature at all times.

So it\'s run - in degrees centigrade - it\'s run anywhere from 20, to
35, degrees the whole time in flight. And that\'s pretty amazing. I\'ve
worked on spacecraft that that had thermal problems. And it\'s hard to
work with once they get stuck.

There is an autonomous thermal control that, where they turn on if they
get too cold and turn off if they get too hot. And then because the
instruments get turned on and off by operational modes or just the time
in flight, we also have replacement heaters to keep them - because they
tend to be more decentralized from the central body of the spacecraft,
we have replacement and supplemental heaters to keep them from getting
too cold.

We use - I was pointing out the RTG, the radio thermal generators. The
sun shades, those are to keep the waste heat from the RTGs from going
back into the spacecraft and radiating more heat than the instruments
want to see.

We also use the waste heat to come back into the center core and keep
the propellants warm. And that was another, like I said, major design
for us on this spacecraft.

Okay, so we\'re back up. I just threw the launch picture in because I
like the launch picture.

(John Bittel): Excuse me, I have one question.

Julie Webster: Sure.

(John Bittel): Was - This is (John Bittel). I'm a solar system
ambassador in Park Ridge, Illinois. Was Huygen\'s, the probe in the
spacecraft, rated the same planetary protection category?

Julie Webster: That\'s a good question. I don\'t know that exactly
because the planetary protection for the probe itself was handled by the
Europeans.

Trina, do you know on that on that one?

Trina Ray: No. I don\'t. I can only assume that the probe, because you
knew it was landing on Titan, and you knew that Titan is very
interesting from a planetary protection point of view, had very high
standards, that I would not assume that the orbiter had.

But, you know, I don\'t know that for sure. And I\'m not even sure who
to ask. Maybe (Spehalski).

Julie Webster: Yeah, there are some planetary protection information. If
you email Trina, we\'ll get that information out to you.

(John Bittel): Great. Because I know that it\'s listed as category 2 but
with - I\'m getting a lot of questions with the water being discovered
on Enceladus. So I just wanted to make sure that I knew what the story
was.

Julie Webster: Yeah, one of the things, with the Enceladus water, just
like the Io on Jupiter, we\'ll be very careful at the end of Cassini\'s
life, that we don\'t or can\'t encounter or hit any of the other moons
for that exact reason. Because they are interesting scientifically, and
we don\'t want to contaminate them in any way.

Okay. So we had this incredibly long 7 year cruise. And you think, well
gosh, what do you do for 7 years? But it turns out, that we actually
wound up with a lot to do. We launched with fairly minimal flight
software because we knew that we had 7 years to develop it.

We started out with a spacecraft that had pretty simple command and
telemetry systems. Not real fancy, we couldn\'t go back and forth, in
what we call ping-pong, on one SSR to the other SSR. We only ever used
one SSR at a time. We could only do thruster control. We didn\'t have
the flight software to control the reaction wheels. And we didn\'t need
to because there wasn\'t that much we were doing in early cruise.

One of the things that we\'ve done - four times in flight with that
attitude control system, and three times in flight with the CDS, with
the command data system - is we have actually switched operating systems
on the spacecraft on the fly.

And those of you that change operating systems on your computers know
what a nerve wracking system that is. Imagine having to do that at long
distance and just hoping that it works when you can hear it back. One of
the things - the very first thing that they did, when they first came to
me and said they were going to do this, I said they were nuts. But
within three days of launch, we had switched both prime CDS and AACS
computers to change from launch to cruise parameters.

So we kind of did a - I\'m a Macintosh person - so we did an OS 9, to
9.1, at that time. And then we had to stay on the low gain again because
the high gain was - had to be pointed at the sun at all times. So we
used the two low gains to communicate with Earth, which kept our bit
rates very, very low.

During most of the first three years of cruise, we were at 40 bits a
second or lower of data. And we also, in the early check out, we had a
lot of launch latches that held instruments. We had to puncture
(membranes). We had to deploy the radio plasma antennas. We had to check
out the backup units and make sure they were viable.

We did a probe check out within the first three months to make sure that
the probe was functioning and had survived launch. And we did an
instrument check out.

We did - of all the instruments except the Ion and Neutral Mass
Spectrometer because it required a cover release that we were not going
to do until much, much later. In fact, just before Saturn orbit
insertion was when we finally did that one. And the radiofrequency, the
radio science system, because that required the high gain.

Okay, then our trajectory, of course we were too heavy to go on a direct
path to Saturn. And so we had to do this fancy Venus/Venus, Earth,
Jupiter gravity assist. So the first thing we had to do, as soon as we
launched, we had to fly and catch up with Venus. And then swing by Venus
very close so that they would give us a gravity assist, kind of a boost
in speed.

And we did this on April 26 of 1998. We flew above Venus at an altitude
of 284 kilometers and we did some science calibrations. One of the
things that we engineers assumed - incorrectly as it turned out but for
the good of us all - is that we were going to fly a rock. We\'re going
to be very, very careful on this and the weren\'t going to do of a lot
of science.

And of course, as the scientists, as soon found out that we had an
incredibly healthy spacecraft, and everything was working well, they
wanted to take science calibrations. And so we did radar and radio
plasma at Venus.

And then, the Venus, the first gravity assist gave us quite a boost but
we had to come back in to catch the second Venus gravity assist. So we
were flung out along the red path, in the interplanetary trajectory
picture, after Venus 1. And so when we got out to the furthest place
away from the sun that we were going to in that orbit, we actually fired
the engines in the Deep Space Maneuver to slow ourselves down so that we
could fall back into Venus 2.

We actually did a 90 minute regulated burn to hold constant pressure on
the bi-propellant system. And that gave us confidence that we could do
Saturn orbit insertion and also get us back on the main trajectory. So
we did a - there was a serendipitous time where Earth was in front of
the sun from the spacecraft.

And at that time we were allowed to turn - and of course, the high gain
was still facing the sun - but the Earth was right there so we could use
the high gain. And at that time, that\'s when we checked out the high
gain data rates and the K-band, and the S-band for the first time.

And a year and two months later, we went by a Venus the second time on,
in June of 1999, with some more science calibrations. And then less than
two months later, six weeks later, we flew by the Earth. We did a pretty
fancy Earth avoidance.

So we actually had to it zigzag our way in to flying by Earth. We would
a zigzag in an then we would zigzag back out. And then we would zig in
and then we would zig out, just to make sure that we were not going to
accidentally hit the Earth if things didn\'t work right.

It was 2000, before we actually switched on the permanent high gain. We
were finally past all of the, we were well past the Earth at that point.
And we could actually switch and use that high gain as pointing at the
Earth instead of the sun. And that is when we could finally use of the
science data rates.

And then at that time, we were ready with a whole new operating system
for both AACS and CDS, to give the reaction wheel capabilities. So we
didn\'t actually turn the wheels on and use them to control the
spacecraft until March of 2000. Of course, at that time, once we had the
reaction wheels, the scientists were really clamoring for lots of
pictures of Jupiter.

And so we started a chance to use the tour sequencing capabilities and
the scientists took pictures for plus or minus, yeah I guess a six month
campaign, plus or minus three months before and after Jupiter, taking a
lot of the fancy pictures that I\'m sure you\'ve seen on the Website if
you followed Jupiter.

And then from, you know, January 2001 to July 2004 we were just out,
taking the rest of the orbit. I think - oh, we did another flight,
another operating system software load, in February and April of 2004.
And then we did it again in 2005.

Let me go on to the picture\...

Man: I have a question about the Venus fly-by?

You mentioned that in that chamber, it went to up to I guess, 2.3 suns.

Julie Webster: Yeah, 2.3 suns. That\'s what Venus sees compared to our
sun.

Man: Okay. So the heat is really from the sun itself and not from
Venus\'s atmosphere?

Julie Webster: That\'s correct. We never, we didn\'t actually go close
enough to get into their atmosphere enough to get much heating from
them.

Man: Thank you.

Julie Webster: Yeah. It was mostly from the sun\'s effects.

Okay, once we went into orbit in July of 2004 then the very first thing
we had to do was to get back and get ready for the probe mission. So as
you see, and this was the question about the bi-propellant in the firing
of the main engines - let me see if I found my notes in the meantime on
that.

Right, so the Periapse Raise Maneuver - so we got into orbit but now we
were flung into this very long 170/180 day orbit. And we got out to
orbit 1 in 23 August 2004 and did the Periapsis Raise Maneuver. And for
that, we actually, again, it was to raise periapse. We didn\'t want to
go that close to Saturn again, like we did the first time. We didn\'t
want to go through those rings like we did the first time.

We had to go through the rings in order to let Saturn\'s gravity catch
us and fling us into an orbit; but we never wanted to go that close
again. So we got way out on Periapsis Raise Maneuver, and again, fired
our engines to slow ourselves down so that we would fall back into a
smaller orbit.

We were actually, at Saturn, we were going thousands of kilometers per
second. And at Periapsis Raise Maneuver, we were actually measuring
tens, and hundreds of meters per second. That\'s how slow we were in
that orbit.

We came back around again and we started doing several things. We did a
(Titan A) and a (Titan B) but - what this picture on Page 23 is really
trying to show is that we did very special maneuvering to try and get to
the probe targeting, to get the probe targeting maneuver so we could
release the probe.

And then we had to clean up out of that probe separation on the 24th of
December. And then we had to do an orbit deflection because remember, we
had to put the whole spacecraft and the probe where we would both hit
Titan.

And then we released the probe so that it became this flying saucer that
landed on Titan. But we didn\'t want to hit Titan so we did an Orbit
Deflection Maneuver, that is what the ODM stands for, for us to come out
and fly by Titan at a much greater distance.

We actually went by Titan at 60,000 kilometers, if you remember, there
was a problem with the radio on the probe. And we had to take out the
effects of Doppler. We\'d originally planned to fly by at like 1300
kilometers and whiz by with the Doppler. Instead, we had to go to a very
large, high Titan maneuver, to stay away from, in order to knock off the
Doppler affects, when we took that probe data.

Okay, so\...

Trina Ray: Julie, I have a question.

Julie Webster: Sure.

Trina Ray: This is Trina.

I always have told people - and I don\'t know if it\'s true, so you can
tell me right now if I\'ve been lying for years - but in the history of
the mission, we were only on a collision course twice, with a body.

Once was the one you just mentioned, a collision with Titan. But when we
launched, we were deliberately put on a collision course with Venus
before, so that if we had completely lost control of the spacecraft it
wouldn\'t have come around and smacked into the Earth. So we were
deliberately put on a collision course with Venus.

Is that right?

Julie Webster: Pretty close. Because we actually only did two trajectory
corrections to get past Venus. And that trajectory correction maneuver,
one, was just to raise as up a little bit away from Venus.

And then we didn\'t have to do another course correction. So we actually
really weren\'t on a Titan, I mean a Venus impact (tour) for very long.

Trina Ray: But we were?

Julie Webster: We were for\...

Trina Ray: (See, it makes for a good story).

Julie Webster: For about a month, we were. We were a Venus impactrr for
about a month.

Trina Ray: There you go. See, it makes for a very good story.

Julie Webster: Yes it does. You\'re right.

The picture 24, is just - I like that picture. You know, engineers
always like pictures of what it really looks like. This is the actual,
this is a probe engineering model that was used in the drop test in
Norway, to actually, you know drop the probe out of a plane flying way
out, in order to see the parachutes deploy.

You can see the parachute lines there. And that is probably not unlike
what the probe looks like on Titan right now, sitting there. It is
probably a little bit darker from the methane than it is in this
picture. But it looks pretty close to probably what it would really look
like if we could get a good picture of it on Titan.

I won\'t go into the details of - I\'m sure if you had a talk of the
probe, plus one year, a month ago, you\'ve been hearing about the probe.
So I\'m not going to go into any details on that.

The next picture\...

Man: Excuse me, I have a probe question.

Julie Webster: Sure.

Man: The problem that was experienced with the Doppler, with that, it
was identified after the launch, obviously. And you took steps to
correct it.

In retrospect, and in analysis, was this a very, very serious problem?
Or moderately serious?

Were you being overly cautious or was it an absolute deal killer for
getting that data out?

Julie Webster: It was an absolute deal killer. The problem was, it was,
like having your FM radio and where it couldn\'t suddenly shift. Like
your FM radio, and you\'re driving along and you\'re going up and down
over the hills and your radio constantly adjusts for the signal levels
so that you don\'t get blasted out when it\'s a really good signal and
you don\'t get really quiet when it goes away or it\'s a bad signal.

And it actually couldn\'t, it was designed to vary with the Doppler, but
it didn\'t - the tracking loop just was about less than half of what it
was supposed to be.

So the signal would have gotten to the spacecraft, the S-band receiver
would have been there, the carrier would have been there, but the data
tracking loop just failed to perform over the frequency change of the
Doppler rates. So it was a deal killer.

We discovered it, one of the things that engineers like to do, of
course, is always the end to end test. And back in March of 2000 when we
finally went on high gain on a permanent manner, the probe guys - and we
certainly agreed, because we haven\'t seen a full end to end maneuver -
asked us for a special test.

They asked us to make the Deep Space Network act like a probe receiver,
act like the spacecraft probe receiver and receive the probe data in
exactly the manner that it was going to, that the Cassini spacecraft was
going to receive the probe data coming from the probe.

So we set up a special test. And there is a radio engineer that works
for the European Space Agency that I can\'t speak highly enough for it.
It was (Boris Smeds) who designed this test. And we all said, oh, we
don\'t need the data, we can - we don\'t use the data. And he kept
saying, I can do the data. And of course by adding the data, and
finishing this true end to end test, he found the flaw.

And we wouldn\'t have found it if he hadn\'t have run this test. So you
can\'t do enough testing on the ground.

Man: So you\'re saying that this was, in fact, missed by many, many
teams, of engineers? And that this problem was, it really didn\'t come
to a point error, it was just by so\...

Julie Webster: Right. They just hadn\'t done the - doing Doppler
adjustments on the ground is hard because you, you know, you have to
switch, you have to change frequencies and you have to put in a phase
delay system. And so it\' a little - so it\'s harder on the ground.

We always try to do it, to make sure that we can - all, most radios do
this but this was just one of those things that they thought didn\'t
need to do on the ground.

Man: The part of it that has really never been explained is really,
exactly how the problem was uncovered and how the problem originated
with so many people thinking about it.

Julie Webster: Yeah. We discovered the problem in 2000, when we did a
probe test, and we did a complete end to end data link test. So we sent
the probe signal back through the high gain from Cassini and then the
Deep Space Network actually out here at Goldstone, we used one of the 34
meter sites to act like a probe receiver. And then we recorded the data.
And we spent many, many months trying to figure out why we didn\'t get
all the data we thought we got.

Man: So this is more of the systems engineering success than a systems
engineering error, in that the system found it and fixed it?

Julie Webster: It was, actually. I like to think of it that way.

You never - again, and I\'m an old (ATLO) test conductor, and you never
can run enough tests. You keep hoping that you trap all the big items
but that\'s why during the whole seven years - and even this year after
the Saturn orbit insertion, where you think we were pretty quiescent -
we have done nothing but keep a test lab up and running testing future
sequences, testing future designs, and testing future flight software
even, to make sure that we haven\'t missed something that is going to
bite us later..

Man: Thank you very much.

Julie Webster: So what - the next picture is this fancy 76 orbit tour
that goes all around Saturn and what they call the (petal plot). And so
what the engineers are doing during this time, for each of those orbits
that goes around Saturn, or actually around Titan, and then out to
(apoapsis) and then back in, that each of those orbits to maintain the
orbit exactly as designed, takes three trim maneuvers.

We do one act Titan - three days before we approach Titan, we call it
the approach maneuver. We do a maneuver at Titan plus three days, we
clean up any effects that the Titan gravity or the Titan atmosphere even
might have given us that we didn\'t understand in advance.

And then out at the furthest point, out at each one of those loops, from
Saturn, we do an (apoapsis) maneuver and that\'s used to start to target
the next Titan, and/or to change the orbit size and angle as it moves
around.

We are also responsible for, of course the more we fly, and the more we
go by things, the better position of knowledge we have. And since we had
to design sequence years, sequences years ago, we now have better
knowledge of where the moons, or where Saturn is that the scientists
want to take pictures of. So we update vectors in real-time, what we
call live update.

We also have to do periodic engineering maintenance. Especially we have
to exercise the moving parts, like the engine gimble assemblies that
move those main engine thruster around, to make sure that they stay
lubricated. And if we encounter the E-ring dust hazards, we also have to
articulate and close this engine cover.

And then sometimes if the dust hazard is deemed serious enough by the
people that know what \"serious enough\" means, we turn the high gain to
the ram direction so that we fly through the dust, high gain first and
let it take the brunt of the force.

And then, one of the things that\'s interesting, once a year, the
spacecraft and the Earth are on opposite sides of the sun. And trying to
send radio signals through the sun doesn\'t work very well. So we have,
we plan for about a 10 day quiet period, because the telecommunications
up, and the telecommunications down, are fairly severely disrupted
during that time.

And that\'s what we\'re doing for our days, to occupy our days now that
we\'re in tour.

Man: For those three maneuvers, that you have to make each orbit, what -
is the thrusters used? Or the main engine? Or the, are the reaction
wheels used?

Julie Webster: It depends, on what we\'re trying to do. Usually the
approach maneuver, the Titan minus three days, and the Titan plus three
days, those tend to be thruster maneuvers.

And actually, the navigators have done so well in this design that we
frequently cancel those. We look at them and look at them, and look at
them as we get better navigation signals through there. But it just
depends on what we\'re trying to do.

Now, when we are trying to change that (petal plot), when we\'re trying
to move in a different - Trina, help me out here - what angle?

Trina Ray: Inclination angle?

Julie Webster: Inclination angle, thank you. We tend to have, those are
more main engine maneuvers, what they call deterministic maneuvers.

But we have used - in fact, we just did a main engine maneuver this past
week. It was the first one we have done since November. And it was not a
very big one. It was actually about a 2.7 second burn, which isn\'t very
long on these main engines.

Man: And I have a follow-up question.

So when these thruster maneuvers are going on for the Titan minus and
Titan plus, are they automatically calculated by the spacecraft and you
just kind of okay them down on the ground? Or do you actually, you know,
calculate them and send them up?

Julie Webster: We calculate them and send them up. We don\'t have - we
don\'t do auto-navigation and we don\'t do automatic course correction.
We send up - we build them on the ground based on the navigation, what
the navigators say you needed to turn to this angle and we want so much
a delta velocity, Delta V, what we call. So they\'ll want anything from
a few millimeters per second, to meters per second of burn.

If it\'s over half a meter per second, it has to be main engine. Under
half a meter per second, it usually is the thruster burn. So we use
these to do one, to 300 mm per second course correction.

(Ken Kramer): Can you give a range of the propellant used and how much
did you use for this main engine maneuver, please?

Julie Webster: Oh, sure. The 2.7, you know what, let me see if I have
that in front of me.

And of course, I don\'t. It was on the order of, it was - no, I\'m not
going to guess.

For example the - well let me give you an example of a big one, like the
Saturn orbit insertion was a 96 minute burn. And it used about 530
kilograms of oxidizer, the nitrogen tetroxide, and about 320 kilograms
of the (monomethyl) hydrazine.

And it scales down pretty close to that.

(Ken Kramer): All right. So what would be typical for these approach or
cleanup maneuvers?

Julie Webster: They are on the order of tenths of kilograms, let me see
if I can try and\...

(Ken Kramer): Yeah, that\'s what I\'m trying to get at.

Julie Webster: Yeah, tenths of kilograms.

Let me see - if you can hold on a second, I\'ll look up in my email - if
you are willing to hold for just a second and let me look this up.

(Unintelligible) well, this is going to take a minute, so\...

(Ken Kramer): It\'s okay to find it later.

Julie Webster: Okay.

(Ken Kramer): Or email it.

Julie Webster: Yeah, I\'d be glad to do that.

(Ken Kramer): Sure. And can you just give us your email, please?

Julie Webster: Julie.l.webster\...

(Ken Kramer): Julie.l.webster

Julie Webster: \...@jpl.nasa.gov.

(Ken Kramer): That will take care of it. Thank you.

Julie Webster: And I\'d be glad to answer any other, you know,
engineering questions that I didn\'t go over in this presentation or
anything else like that, that you\'d be interested in.

(Ken Kramer): Great.

Man: I\'m sorry, I got cut off and just came back here. Are we through?

Julie Webster: Almost. I\'m at page 28. So, you know, for more
information, there\'s the Saturn Website. And also, if you haven\'t gone
out - if you are Solar System Ambassadors, you may already have seen
this, but (Dave Doody) has a wonderful basics of space flight that is
out on the JPL public Website. And it is a great description of what we
have to do to fly spacecraft, basically, not just Cassini.

Man: (Unintelligible)?

Julie Webster: It\'s on the JPL Web site.

(Ken Kramer): Yeah, where?

Julie Webster: I\'m not real sure. You can just - usually is from the
main page, you can go in and search for \"Basics of Space Flight,\" is
what it\'s called.

(Ken Kramer): Okay, thank you.

Julie Webster: Okay.

Man: Do the reaction wheels - are they completely automated in terms of
their use?

Julie Webster: No. What we do it is we - they are automated in terms of
they know how to calculate how much electronic signal or force to put
into make a torque, to make a change. So we tell the spacecraft to
target Titan, for example, and that we want to continue to target Titan
as we fly by it. And so the reaction wheels get a torque input that
keeps the spacecraft turning in the correct direction all the time.

They - we bias the wheels to a certain speed. Most spacecraft do what,
we used to call them desaturations, where you spin up the wheels and
eventually the wheels will spin fast and you stop and you go on
thrusters and have the wheels spin down.

We actually, bias the wheels. And we tend to bias them every trajectory
correction since we go on thrusters for either roll control on the main
engine or we use the thrusters to do the small corrections. And then we
let the wheels spin down to zero.

And then we rebias them to a certain speed to keep them out of this real
slow rpm regions, where we think we have more problems with lubricant,
and then not above. So that the ideal reaction wheel speeds that we
want, at any given time, is between 3 and 1800 rpm, revolutions per
minute.

Man: Thank you.

Man: Julie, were there any things - this is a little far out, but I am
one of the ambassadors and one of the areas that I\'m trying to promote
are the medical advances made through NASA technology - can you think of
anything in this mission that might contribute to a technology transfer
or whatever, towards the medical field, or at least medical science, in
other words?

Julie Webster: Well, I - in this specific area, no. But I believe that a
lot of the spacecraft - of course, you know, a lot of the ways that we
get signals, the way that we pick-up signals that we, with telemetry
things, like thermocouples for temperature and, you know, pick up
signals of electronics, very small electronic impulses - I think that
probably that is one of our greatest contributors is how to pick up,
amplify, receive signals, vary signals, use it against a microprocessor
to tell you if it\'s going high or low.

You know, you can check into the hospital today without being hooked up
to a monitor.

Man: Right.

Julie Webster: And that is nothing but a sophisticated telemetry system
that was really - you know, it probably started in the auto industry but
really exploded in the field of NASA spacecraft in general.

Man: (Unintelligible) at NASA or JPL that actually has you know, a link
to, you know, like is there a section on just these advances or\...

Julie Webster: You know, there is. And I don\'t know the Website exactly
but there are people that are working on very specialized techniques for
like amputees to get the electrical signals back to their arms and legs,
the prosthetic devices.

Man: Do you know where, I mean, which Website JPL\...

Julie Webster: Boy, Trina, do you? Or (Jane)?

Trina Ray: Maybe (Jane).

I know we had a technology transfer Web site. The two that - for the
Cassini, the one that I always use is that it is very direct to Cassini,
Cassini in its very, very early R&D spend a ton of money working on the
CCDs for the cameras, to bring them down in weight, needs for power, and
how fast they read out.

And basically, that technology went straight into your hand-held digital
video recorder. You know, these little handheld\...

Julie Webster: And also, in the cameras that you swallow and that go
through your system these days.

Trina Ray: Yeah, that too.

Julie Webster: That\'s definitely a good example.

Trina Ray: For overall JPL, I know we\'ve got a lot of stuff with MRI
technology. We have a lot of stuff with the Global positioning networks.
But you know, there is a website somewhere. I will find it. It\'s called
technology transfer. And I\'ll send that out with some of the other
answers to the questions that we\'ve had today.

Julie Webster: There is another, besides the information technology, and
they just did a blurb on a guy that was doing - (Barcohen), (Josef
Barcohen), Trina - who is doing work with the arms. So\...

Man: Yeah, because particularly rehabilitation is one of the interests
that I\'d take back to D.C. and promote.

And I don\'t want to take up all this time up for everyone else, away
from everybody else who is on the conference call, but do you have my
email address?

Or do you know who to send it to? Or how are you going to do it?

Trina Ray: What I\'ll do is after something like this where we had a few
pieces of information to send out, we send it out to an email that goes
through the full distribution so that everyone will get it.

As long as you have the original email from CHARM leads inviting you to
this, you\'ll get the follow-ups.

Man: All right. Great, thank you.

Trina Ray: And if anybody is not getting those emails, just let
charm_leads@cdsa.jpl.nasa.gov let them know and we\'ll add you to the
distribution.

Man: Okay.

Julie Webster: By the way, serendipitously, the person that asked for
the oxidizer and fuel for this last burn, it just popped up in my email
from my propulsion engineer. So for a 2.7 second burn, we used .3
kilograms of oxidizer, and .2 kilograms of fuel. And that is about the
right mixture ratio.

And we used 117 grams of the hydrazine for roll control. We fire the Z
thrusters to keep us from rolling too much during a main engine burn.

(Ken Kramer): Thank you.

Julie Webster: Okay?

(Ken Kramer): Kind of a related question, actually about the Saturn
orbit insertion maneuver, if you can go to your slide 26.

Julie Webster: Okay.

(Ken Kramer): I\'ve always wondered about the angle, the approach angle
here in this diagram on the right. It seems a bit exaggerated to me,
when I compare it to some other views that I\'ve seen.

Is this accurately represented, you know, the one on the right
approaching from the bottom?

Julie Webster: The trick is on the scale of the way you see Saturn in
there. It\'s hard to tell. The best approach pictures I\'ve ever seen
were the ones that we did for a very specific Saturn orbit insertion
talks where we showed how we shot through between the F and G rings.

(Ken Kramer): Yeah.

Julie Webster: And went over the top of Saturn\...

(Ken Kramer): Right.

Julie Webster: \...And then came back out.

(Ken Kramer): Right.

Julie Webster: And that is probably a much better representative angle
than this is.

(Ken Kramer): Yeah, I believe I recall them from an earlier seminar and
they were, I don\'t know, maybe 10 to 20 degrees, or something like
that.

Julie Webster: That is probably about right.

(Ken Kramer): See, because this gives the impression of 45 degrees.

Julie Webster: No, no. We were not\...

(Ken Kramer): And that just doesn\'t seem right to me.

Julie Webster: \...not anywhere near.

(Ken Kramer): Not anywhere near, exactly. That\'s why I didn\'t - this
is a great picture, I believe, except for that one line.

Julie Webster: Yeah. And I would use - and if it\'s not out on the
Website, I\'ll attach it to Trina\'s, so you can see it - the one where
we actually showed what we had to do when we fired the engines and when
we shot through the rings.

And do you remember during Saturn orbit insertion, we actually had to
turn the high gain into the ram direction because of course, the rings
are a dust hazard on both sides?

(Ken Kramer): Yeah. Great. I like this. It\'s very high resolution too.
It\'s much better than what\'s on the public Website.

Julie Webster: Oh, it could.

(Ken Kramer): And, yeah, that\'s nice what\'s on the Website but not
this clear. And also the fact that you added the Titan orbit and the
Iapetus orbit. That\'s very good for perspective.

Julie Webster: I didn\'t do that. I got these from the mission planners
so\...

(Ken Kramer): (Unintelligible).

Julie Webster: But it is, you know, and I tell you even as an engineer
it took me a long time to kind of understand this picture. But once I
did, it was like oh, okay.

(Ken Kramer): Yeah. Yeah. Well, the one on the left really shows the
petals.

Man: Julie, a question about the orbital tour. In the future - and this
probably might lap into the next telecon we have about what future
extended missions might do - but just from a Delta V available after the
primary mission, can you give us some ideas for what some possibilities
would be with Delta V?

Not necessarily what\'s being planned but how - I mean, how much could
you do? Could you go (do a blow) by the rings? Could you get into
something closer to orbiting Titan?

Julie Webster: Yes.

Man: What it is possible?

Julie Webster: Yes. We have about, we\'re going to hopefully - if
everything goes right over the next year and a half, almost two years -
we are going to have about 250 meters per second Delta V left.

And don\'t quote me on that because it can be anywhere from 250-300,
depending on how we do and what our measurements are and how we\'ve
repressurize. But we are going to have - that is quite a bit of Delta V
just to fly the trajectory.

And I have seen the navigators offer the scientist anywhere from walking
all the way back down from these high inclination orbits and then coming
back into an equatorial plane again. I\'ve seen them walk up, walk down
very quickly, come back around the other side.

I think, and this will be up to the scientist to decide, not us, we just
tell them what they\'ve got available to them. But there is quite a push
to be more conservative in the use over the next few years and get us
out into the - tell me Trina, we are Saturn winter and we want to go to
Saturn spring or (unintelligible) Saturn spring?

Trina Ray: Yeah, basically the start of the mission was roughly some
time \"in the middle of January,\" and we\'re only going to end the
mission sometime in I think, the equivalent of February. And they would
love to get out to spring, which would be, I think, 2010. I could look
that up but\...

Julie Webster: Yeah, remember the 29 year orbit. They would like us to
last longer as we go around the sun. So stay tuned. That will be decided
in the next six months.

(Ken Kramer): I thought I read that you may even have enough fuel to go
another four years beyond the first four.

Julie Webster: It depends on how they use it.

(Ken Kramer): Right.

Julie Webster: We\'ve - we\'ve certainly put tours out there that can
use it all up. And be done in 2010. And we can put out orbit
trajectories, Titan - flying by Titan\'s - very low - costs\...

(Ken Kramer): Right.

Julie Webster: \...a lot of thrusters. It costs a lot of bi-prop to
maintain getting back into the Titan orbits.

And so if you want to do a lot of Titans, and get lots of pictures,
those are going to be more costly then flying kind of in a more
leisurely or where we can, you might want to take other icy - oh,
getting to the icy satellites for close-ups, again, Enceladus is of
course, now a critical objectives. That is going to cost.

(Ken Kramer): That is going to cost?

Julie Webster: Because to target a moon, that specifically costs a lot
more.

(Ken Kramer): Well, that\'s worth it.

Julie Webster: I think you\'d have a lot of people agree with you on
that.

(Ken Kramer): I\'m an organic chemist so I\'m very excited about that.

Julie Webster: I started out my life as an organic chemist.

(Ken Kramer): Yeah, Enceladus and Titan are both interesting. But
you\'re saying both of them are kind of like fuel hogs, huh?

Julie Webster: They are more costly, if you want to target - for
example, we did the majority of our icy satellite fly by\'s in this past
year. And those costs a lot more in terms of larger burns, larger
things, the OTM.

There are two or three in here that were like in the order of two minute
burns, three minute burns, four minute burns. Those were almost all to
target specialized icy satellites.

(Ken Kramer): This is really interesting. I hadn\'t known that this part
before.

Julie Webster: Yeah, it\'s a little more costly.

Man: Julie, one last question from me.

Julie Webster: Sure.

Man: It\'s to what do you owe your success with this piece of equipment
in orbit there?

Do you think it\'s the solid state power management, or temperature
control, or what is it that makes everything (last)?

It\'s just been remarkable.

Julie Webster: Well now I have a - I\'m very, very biased on this
subject.

Man: Good. That\'s what I really want to hear.

Julie Webster: I think it\'s the design. The overall design. You know,
if you think about space, for us, we\'ve only really been working space
for the last 40/50 years. And this spacecraft, the designers on the
spacecraft, typically had 30 to 40 years of experience as they were
designing this spacecraft.

We had several major, major subsystem retirees right after we launched
Cassini. So there was an incredible amount of experience that was added
to, and added to, and added to, that went into the Cassini design.

They took a lot of the mistakes of a Magellan - Magellan had some issues
with heat problems. And Galileo was - didn\'t have heat problems - but
they had a really hard thermal management system. And they took that
experience and put it into this spacecraft. So we just had - it was the
people. We had an amazing amount of knowledge.

And my team, my team which was about - were about 90 people at launch
and were down to about 45 now - the spacecraft engineers themselves,
well over a third of my team has been here since pre-launch. They find
this a very interesting spacecraft to fly. They find it, you know, one
that really works remarkably well.

But I think it was the utter experience that went into this design, in
general.

Man: If you put your finger though, on a physical factor, do you think
it would be thermal control or power management or solid state circuits?

Julie Webster: The power management - the solid state circuits make our
lives considerably easier, by having to go into this operational modes
and not worry about those relays all the time is good.

I think the fact that - I just don\'t - you know, of the things that
keep me up at night, I never ever think about, and I haven\'t since
launch, thought about thermal, thought much about power states and
things like that, just because they\'re so reliable. They are reliable
mechanically.

The things that keep me up at night are reaction wheels.

Woman: They keep me up at night too.

Man: Well, congratulations.

Julie Webster: Thank you.

(Ken Kramer): Great mission. Thank you. Great talk.

Trina Ray: Do we have any of their questions for Julie?

Man: I have a question.

Trina Ray: Okay, go ahead.

Man: How do you deal with the advance in technology from the time you
first start designing the spaceship until its launched?

And then, you know, understanding that Cassini has been in cruise now
for 7/8 years, technology has advanced, how do you deal with those
issues?

Julie Webster: You don\'t. You basically, by the time you launch a
spacecraft - now remember, this isn\'t really true of the newer era
because they are getting to build, test and launch much quicker than a
Cassini. But for example, a Galileo was built on 1970s technology even
though it didn\'t launch until 1989.

Cassini, Cassini was really designed in the late \'80s/early 90\'s. And
you just - some things you can take advantage of, some of the later
microprocessors may be a little bit faster and newer. But you design
your mission around what you have at the time.

We\'ll never be able to - mostly because of the (length) at Saturn, and
the size of that antenna - but we would never be able to do what the
Mars reconnaissance orbiter is doing today. We\'d never be able to
down-link almost terabytes of data in a few days.

And you - but you basically take your technology, design your mission
around what you have at the time, and go.

Man: Okay. Thank you.

Man: One more question.

Trina Ray: Go ahead.

Julie Webster: Sure.

Man: (Unintelligible) (the underside) of the micro circuitry? Solar wind
can damage micro circuitry. How do you factor that into the design?

Julie Webster: I don\'t know about solar wind so much as like radiation
and galactic cosmic rays. We have - we have actually been affected by
that in two different regions.

One, the solid state power switches that occasionally trip off, it\'s
because they didn\'t really put in enough capacitor in a flip-flop
circuit. And so galactic cosmic rays are usually the ones that hit us
and cause the solid state power switches to flip off. And that happens
at the rate of about two per year.

So when we found this out, discovered it, realized it, and understood
that this was going to be an issue, we wrote flight software to look at
the telemetry and see if this happened then react to it.

So the answer to - if the guy that asked me about the technology is
still on the line - that is the real answer is you make as much of your
ability to be reprogrammed in flight, and flight software.

Again, we did three really major reprograms. And each time, we took
advantage of the things that were giving us fits.

So the galactic cosmic rays and solar winds - we are very, very
radiation hardened. It is something that most Mars missions, and Venus
missions don\'t do. So we just don\'t get hit with a lot of the single
event upsets that a lot of other missions do. And then we just write
flight software to work around an SEU.

And we have some flight software that is written around SEUs but mostly
we are pretty radiation hardened.

Man: And is that shielding primarily?

Julie Webster: Shielding. Yes.

You - they\'re special, like in the bays, that really need to be
protected from cosmic rays and another radiation particles - we actually
have brass hardware. And, you know, the structure itself is aluminum.
But we put some brass in certain places, around the cables, so that we
don\'t get hit with - well this is actually more not radiation, it\'s
more micrometeors - but we actually braid fairly heavy, thick braided
shields around the exposed wiring and cables.

The thermal blankets are designed to take a certain thing. The tanks -
the thermal blanket actually stand off from all those hydrazine and mono
prop tanks by what we call whoopedy-whoops. They are little metal loops
that actually cause the blankets to stand off so if you got, if you took
a hit, a micrometeor hit on a blanket, for example, if it wouldn\'t get
to the tank.

So we do a fair amount of both dust and also the radiation. And we
reprogram in flight. We have written some fault protection type things,
programs, to take care of what we\'ve seen in fight.

Okay?

Trina Ray: Okay. Do we have any other questions?

Well Julie, I would like to thank you very much. We really appreciate
you taking time out of your schedule to talk to folks today.

It was a very, very interesting talk, and kicks off sort of a year of
tutorials we are going to have, which are basic tutorials on the
spacecraft, and the rings, and the magnetosphere that people can really
use as background material.

So this is the first of our tutorials. And you did a great job we really
appreciate it. Thanks.

Julie Webster: Well, thank you.

Trina Ray: And next month, we\'ll have Dr. (Josh Caldwell) he\'s with
the UVIS team. He\'ll be doing a rings tutorial about the basic
structure of the Cassini ring. And then he will also talk about the
ultraviolet star occultations that he\'s involved in. And sort of the
recent results that have been coming from his UVIS star occultations.

So join us at the same time next month. And everybody have a great
month.

Man: Think you.

Julie Webster: Thank you, Trina.

Trina Ray: You\'re welcome.

(Jane): Thank you.

Man: Thanks, Trina.

END