**NASA**

**Museum Alliance**

**Cassini**

**May 4, 2004**

**2:30 p.m. CDT**

**Overview:**

Dr. Kevin Grazier, science planning engineer on Cassini who supports the
imaging team, discusses Cassini's orbital tour and the process of
designing it.

Coordinator I'd like to remind all participants this conference is being
recorded. If you have any objections, you may disconnect at this time.
You may begin.

Anita Good morning, everybody. This is Anita. We have Jane Jones, who is
the Saturn Observation Campaign Coordinator for Cassini. We have a guest
speaker this morning, Kevin Grazier; I sent out his bio.

W An awesome bio.

Anita So Kevin is going to give us a rundown of what he's doing on
Cassini, and I think he is prepared to field questions as well. As Jane
alluded to right before we started recording, there is a PDF file that
we just received, and we'll be sending it out to you in the next few
moments. So hopefully most of you will be able to download while we're
talking, because Kevin is going to refer to that quite a bit, I believe.

Kevin Yes. In fact, I highly encourage people to refer to it. Is it sent
out already?

Jane It's sent, but these are big lists. So it's going to take a few
computing moments.

Kevin Okay. Today, I'll be talking about what's called a tour atlas, and
in the context of today's conversation that actually has two meaning.
Today we'll be discussing the series of orbits Cassini will be taking at
Saturn, the different geometries, and what we hope to achieve using
these different geometries, different orbits.

Also, a tour atlas is a physical database. It's something that I
maintain, and it is a monster database of geometric information, ranges,
distances, angles, sizes of planets as seen from the spacecraft. It's
several hundred megabytes worth of information that scientists use to
plan their observations. Again, as I said, the tour atlas is not only a
little map of what we'll be going over, you'll see images of the
different orbits in the PDF I just send out, but it is also a monster
physical database that people use for science observation planning.

Are the PDF files starting to arrive already?

Anita I'm just now sending it to the Muse folks.

Kevin Anybody?

M I haven't got it yet.

Jane It will take a bit. I think you could just start out. In our first
talk, Bob Mitchell actually showed one of those petal plots, so you can
assume that the people have a little bit of an idea of what the first
ones are looking like.

Kevin That's good, because I made those.

Jane They're so cool.

Kevin The petal plots do show the series of orbits we'll be taking, and
they are probably colored, the ones that you saw. The colors correspond
to different parts of the tour, the tour being the sum collection of our
74 orbits during the prime mission. Now understand that as far as the
complexity level, each one of these orbits is roughly equivalent to a
Voyager flyby.

We essentially have to plan four years' worth of Voyager flybys. For the
Voyager mission, we had flybys that were interspersed by two years, then
by five years. There is not a lot of time between Cassini's flybys. We
have orbit after orbit after orbit, and planning these is very
difficult. We've had to do an awful lot of work to get all our science
observations planned. So as I said initially, the tour atlas is
something that we initially generate.

Two tour designers designed 18 different potential tours. When the
spacecraft was first announced, or when the mission was first announced,
NASA announced an opportunity saying what science that we generally hope
to accomplish, and different teams proposed instruments to accomplish
the science objectives at Saturn.

After we knew what the science objectives were, these tour designers
designed 18 different tours that would accommodate the science, and then
they were evaluated for science return. In the end we narrowed it down
to three, then quickly down to two, and then down to the last one. So
this tour was optimized not only for science, but for our ability to
actually do it.

There was one tour that returned a lot more science than this, but if we
had done that I think there would be a new term in American vernacular;
it would be called going Cassini. "Don't go Cassini on me, man," like
instead of going postal. It was virtually unflyable as far as an
operation standpoint. Our people would have just been going nuts.

Anita Wasn't there a recommendation one time that development people
ought to do ops once in awhile, so they see what they created and have
to deal with it?

Kevin Yes, and there are a lot of people moving back and forth between
the worlds. So I'm doing ops right now. I'm on a sequence team. I'm a
sequence lead. A sequence is a series of commands the spacecraft
operates or executes for roughly 40 days. We have 41 sequences during
our primary mission, and these sequences -- first, we go through
integration.

What that means is the scientists from each team look at the tour atlas
and run their own software, and they determine when exactly they want to
make their observations. This yields a highly conflicted timeline,
because it's often the case that if observation is good for one
instrument it's good for several, and we have instruments pointing at
different directions in the spacecraft. Some are pointing at one axis,
some on the other, and as you probably know, the spacecraft is without a
scan platform.

Previous spacecraft like Voyager and Galileo had their optical remote
sensing instruments on the end of an arm that articulates, and that arm,
that articulating joint, is called a scan platform. Well, Cassini does
not have a scan platform, so our optical remote sensing instruments, in
fact, all of our instruments are physically body-mounted, bolted to the
main part of the spacecraft. So in order for us observe a moon, Saturn,
the rings, we have to physically turn the whole spacecraft to point the
instrument at what we're observing. Now this spacecraft is two stories
tall and six tons on Earth's gravity. I'll let you guess how quickly
this spacecraft turns. So that is a level of complexity amongst many
others.

If you've seen the petal plots, then you have an idea of what the orbits
look like. You'll see Saturn in the middle and two rings, the inner ring
being the orbit of Titan -- as you know, that's one of our main science
objectives -- and the outer ring is the orbit of Iapetus, one of our icy
satellites. You often hear the term icy satellites associated with the
non-Titan satellites, because out here at nine and a half times Earths'
distance from the Sun it's cold. In fact, it's so cold ice is hard. It's
as hard as granite out here.

We, planetary scientists, consider ice to be a rock at this distance,
and it is a main component of many of these satellites out here.
Enceladus, for instance, is mostly ice. Others, Tethys, Dione, Rhea,
they're largely ice. The outermost of these fairly large satellites is
called Iapetus. It's the one that looks kind of like yin-yang.

For those of you who are science fiction buffs, it was originally
supposed to be the location of the monolith from *2001*. The reason
being is Iapetus is dark on one side and bright on the other. Before we
ever had seen it up close, we did have what are called light curves. We
actually could see the brightness changing, getting brighter and darker
over one orbit. Where Arthur C. Clarke said, "That's where the monolith
is," that's what we're seeing, the monolith, as Iapetus orbits, but it
turns out Iapetus, like our moon, is tidally locked. In other words, the
same face is presented towards Saturn all the time.

What that means is there is always a leading edge and a trailing edge.
That leading edge is sweeping up material in Iapetus' orbit, and it's
coating it with this dark material. Recent observations indicate that
that material is actually fairly thin, which argues for it being
exogenic, of an extra-Iapetus origin, as opposed to endogenic, something
that has boiled up from underneath. So that outer ring, that outer
dotted white line on these tour petal plots is the orbit of Iapetus, a
particularly interesting moon.

You'll notice, when you get these PDF files, that different colors
correspond to different sequences, and that's how I've split this PDF
file, split this talk, I've split it into different sequences based on
the orbital inclination. That's the tilt above Saturn's equator.
Inclination is usually measured to a reference plane.

In this case, it's the inclination or the tilt of the orbit will be
measured relative to Saturn's ring plane, which tips 27 degrees to the
orbit of Saturn. You'll see in the first two pictures that we actually
come in to the Saturn system at quite an angle relative to the ring
plane, and then we have to wait several orbits to actually crank up our
inclination, so we end up being in a flat orbit with the rings.

Now unlike Galileo, the previous probe to visit the outer solar system,
that spent several years at Jupiter, Cassini is actually going to make
several excursions in inclination. The Galileo tour was essentially
equatorial. That made sense at Jupiter, because at Jupiter all your
satellites are in the plane of the equator. So that made sense at
Jupiter.

It doesn't make as much sense at Saturn, seeing as that we have rings,
big, bright rings, unlike any other planet in the solar system. So
therefore, we want to be able to look down on the rings. We want to look
for moons within the rings. Therefore, it made sense to increase our
inclination over the span of the mission. So what we do is we use the
moon Titan.

Titan, the second-largest moon in the solar system, one of our prime
science objectives, is also used for gravity assists. If you're familiar
with how we got to Saturn, we used the gravity of Venus twice, Earth,
and then Jupiter to slingshot us to the outer solar system. Well, it
turns out that within the Saturnian system, we use Titan as a gravity
assist. We use Titan to change the inclination of our orbit throughout
the tour. So whenever you see the inclination changing, it's usually
from multiple Titan gravity assists within the Saturnian system.

On these petal plots, they are in what's called a rotating frame,
meaning that the Sun is always along the plus x-axis. What this does is
shows the orbit's, essentially what's called the hour angle. The
Saturn-Sun line would be, of course, noon, because if you're standing on
that point of Saturn the Sun would be directly overhead, if you could
actually stand on Saturn, and of course measured around from there 180
degrees would be midnight. Then at 6:00 a.m. and 6 p.m. are dawn and
dusk respectively. So in this rotating frame, the Sun is always to the
right; therefore, you can get the orientation of each petal, and you can
also determine what the phase angle is.

A phase angle, something very important for observations, is the
Sun-target-spacecraft or observer angle. So the reason we print these
petal plots in this rotating frame, where the Sun is always along one
line, is it gives us phase angle information.

The plots are also looking down Saturn's north pole, as opposed to the
orbit north pole. These are the ones in the x/y plane, the ones in the
left in the PDF file. The plots on the right are in the x/z plane. In
other words, it's in Saturn's ring plane. Are there any questions so
far?

On these plots, you'll see there are units along the x and y or x and z
axes. These are in R~S~ or Saturn radii. Also, as an amusement, you'll
see on this it says Tour T18-5TDJ4. Well the tour is T18-5. I mentioned
that initially we had 18 different tours, which we evaluated for science
return. Well, we've done small tweaks on them, and there were five major
revisions, so T18-1, T18-2, up to T18-5, and then there are even smaller
divisions. It got to a point which these were coming out so rapidly we
just called it the Tour de Jour. That's the TDJ. So that's kind of an
"in" Cassini joke there.

The first page shows the entire tour. What I find is you can blow it up
really big on your screen, but for me it looked better as a printout
than it did on my screen. It looks kind of grainy on my screen. It looks
really good on a printout.

The first page shows the entire tour, the whole series of all 74 orbits,
and you'll notice it's color-coded to correspond with inclination
sequences. The color corresponds to essentially a range of science
objectives.

On the next page we have the first few orbits. This is the orbit
insertion and Huygens mission in the first few orbits. What we had done
is initially, one reason why we had variations, is many of you may
realize or have heard that we had some communication problems between
the Huygens probe and Cassini.

The bottom line is that the transponder on Cassini could not hear
Huygens, when there was a Doppler equivalent of greater than about a
kilometer a second, and at Titan, encounter velocities are routinely six
kilometers a second. So what we did is we took one of the initial orbits
and created two resonant orbits, two orbits that take exactly the same
time as the one big one would have taken.

What this does is add a couple of revs. So instead of orbiting our
revolutions one, two, three, four up to 74, it goes zero, A, B, C,
three, four, all the way up to 74. Zero through rev C are those that are
indicated on page three, in the white. You can see we come in on the
right-hand side in the x/z plane, again, out of the ring plane, and then
we spend time cranking up the inclination so it's in the ring plane.

One thing that's interesting is we aren't so much gaining on Saturn as
Saturn is gaining on us. Right now we \[the spacecraft\] are \[is\]
actually out ahead of Saturn in its orbit. Now we let Saturn catch up to
us. That's what's going on right now. We're actually, right now, ahead
of Saturn, almost outside of Saturn's orbit, pretty close. So Saturn is
now gaining on us in its own orbit. So that's what happens in orbit
insertion. We're actually being overtaken by Saturn.

Now you have the first couple of big looping orbits. The right-hand
plot, in the x/z plane, if you look at the very most distant point of
the biggest orbit, which is actually cut off on the left-hand side, on
the outermost part over, you'll see a little discontinuity. It's a TCM,
a trajectory change maneuver. It shows we're firing our engines there.
That is a pretty major course correction, to help us raise the periapsis
or raise the orientation of the orbit. It's a nicely smoothly varying
orbit, and that's because we're firing our engines at that point.

That was numbered page three. The next one actually doesn't have a
number. It's an insert from something else. It says "SOI activities,
Timelines, Small Scale Pacific Time. This actually has a lot of
information on it.

What this shows is the whole series of events that will occur at SOI, or
Saturn orbit insertion. I have to apologize in advance that we tend to
use a lot of TLAs, three-letter acronyms. I mean JPL is a TLA, right? So
if I slip and start using acronyms -- I'll try not to -- but if I do,
and it's really ingrained in us, just stop me and say, "What does PDT
mean?" Pacific Daylight Time, but it also could be pointing design tool.
Anyway, I told you we had a lot of them. I actually literally sat in a
meeting a month ago and said, "If I was not an insider, would I
understand this as being English?" and the answer was no.

So what you see under geometry, in this next page, you'll see the actual
spacecraft trajectory will re-come from underneath or on the southern
hemisphere of Saturn, up and over the rings, and then descend back on
the other side. We actually come up through a gap in the rings, between
what are called the F and G rings. It's the same place that one of the
Voyagers went through. So we come through a clear gap in the rings,
because, of course, ring particles are not spacecraft-friendly, so we
try to avoid ring particles like the plague.

There's also a third dimension, which isn't really shown. We don't
actually just come up and over. The endpoints of this arc are well into
the page. So coming at you, the closest point of approach is right at
the middle of the planet. You see periapsis at 9:03 p.m. That's the
closest point of approach. Then as it's descending through the rings,
it's also receding from us pretty rapidly. Does that make sense?

W Yes.

W That's a great image.

Kevin I can't take credit for this one. This is Dave Seal's. Dave Seal
is not only our mission planning lead, he's also a very accomplished
artist. He's done an awful lot of really good plots. This is a plot.
He's also an artist. He does real Cassini art. Many of the artistic
plots or images you've seen on our Web site are Dave's.

Jane If you go to the multimedia section of the Cassini-Huygens Web site
and go under Images, and then go to Artwork, almost all of those are
done by our own Dave Seal. So that's pretty cool.

Kevin Yes, he's talented. You see our ascending ring plane crossing.
That means that's a point at which we cut through the ring going from
south to north, and then descending later. What we'll be doing, as you
can see under Activities, turn to burn, what we do is we rotate the
spacecraft to orient the engines, so that essentially when we fire our
thrusters we will be slowing down. They're acting like decelerators,
because if we don't slow down, we become the Cassini mission to Neptune.

This is a sequence that has been worked and reworked and reworked. As
far as things that might go wrong, this isn't really a big bother. We
don't think we have a problem with this, knock on wood. So we turn the
spacecraft to the proper orientation. We slow it down. We burn the
engines for roughly an hour and a half.

Slowing the spacecraft allows us to become captured by Saturn's gravity.
As soon as you see max burn end, turn to Earth, close EMI cover. In
other words, there's a clamshell cover that covers the engines. So when
we pass through particles in the ring plane, where we have reached the
density of particles, we point the spacecraft into a ring plane crossing
friendly attitude, so that there's a minimal chance that ring debris
will damage the spacecraft. So we close that clamshell cover on the
engines, and then wait for ring plane crossing, that's the "close EMI
cover" part.

Then we actually rotate the spacecraft, and the closest, highest
resolution imagery we will ever get in this mission of the rings occurs
right after orbit insertion. Right after we fire the engines, we turn
the spacecraft and we image the rings. We also do a lot of particles and
field data, because this is the closest we get to the planet. From this
point forwards, we treat the rings as a collision hazard.

Now there is one fairly large ring, the E ring, that's outside the main
ring system. It's very, very large, but very, very diffuse, made of
micron-sized ice crystals. We'll pass through that routinely, and it's
pretty rare -- it happens -- but it's rare that we'll have to assume a
special attitude and a special spacecraft operational mode to handle
that ring plane crossing. Usually to pass through the E ring is not too
much of a problem.

So as we descend through the ring plane again, we have an SOI data
playback -- you can see that towards the right -- in other words, when
we point to Earth, and that's when we start seeing all the really great
images of the rings. We get back engineering data, which tells us how
the spacecraft performed. Then shortly after that, we have our first
flyby, sort of a distant flyby of Titan.

Now Titan is the second-largest moon in the solar system, the only moon
with an appreciable atmosphere. We have not really ever seen through
that atmosphere. Titan has the largest unmapped solid surface in the
solar system. We think, with the judicious use of filters, we can see
through that atmosphere, but if we can't, that's one of the reasons we
have the radar mapping system onboard Cassini. We know the atmosphere
will be transparent to radar.

Shortly after SOI data playback, we'll have our first opportunity to
image Titan. The distant flyby is 334,000 kilometers, but it's our first
change to potentially see through that atmosphere, and see through to
the surface below. Are there any questions so far? If you ask a
question, tell me who you are and from where you come.

Jane Kevin, this is Jane. You might tell people we're still on the same
slide. You might explain what OWLT is. I'm sure everybody figured it out
already, but just in case.

Kevin OWLT is one-way light time. So it takes about an hour and a half
for these signals sent from the spacecraft to get back to Earth. That's
more or less a constant. It will change by about a factor of plus or
minus 16 minutes over the span of the tour, 16 or 17 minutes. So one-way
light time, for the span of the tour, is about an hour and a half on
average. \[the radio signals travel at the speed of light, ergo light
time\].

If you look at tracking, it says DSS. That tells us which station will
be attempting to listen to Cassini. DSS-14 Goldstone, that's in
California. We have these large dishes that are spaced roughly equal
distances on the planet, 120 degrees apart, so you always have a dish
pointed to your spacecraft. So as Earth turns, Goldstone will hand over
to Canberra, Australia, which will then hand over to Madrid, which you
see along the tracking line. Are there any questions?

W You're doing great so far. Thank you.

Kevin Okay. Go to the next page, which is labeled as page four. This is
part of that previous group of slides. This shows two x/y plots showing
the Huygens release and the probe mission.

On the first one to the left, what you'll see is a petal plot. This goes
from apochron to apochron. You've heard the term apogee, which means the
most distant part of an orbit relative to Earth, or aphelion, the most
distant part of an orbit relative to the Sun. Saturn, in Greek
mythology, was Chronos. So our orbital terminology or nomenclature is
relative to Chronos.

Our orbit's closest point of approach is perichron; the most distant is
apochron. So these are apochron to apochron, and you'll see that because
of engine firings they don't always exactly match up. We've changed the
trajectory by gravity assists and by firing our engines, so it doesn't
always exactly meet up, and these orbits start at the green box and end
at the red box. That's apochron to apochron.

We'll see on the left-hand side orbit, that would be rev B, is the probe
release. The little tick marks you see are at one-day intervals.
Interestingly enough, you'll see they're closely spaced out at perichron
and widely spaced at apochron, thus verifying Kepler's Second Law.

You'll see on the red H, that stands for Huygens. That is the point at
probe release on December 25. Notice it occurs before apochron. What
that means is that Cassini follows Huygens out to apochron and then back
in. Interestingly enough, there is a famous drawing or piece of artwork
that shows Cassini releasing Huygens just above Titan. It's very
dramatic. It kind of gives an idea of what's going on, but I routinely,
when I teach class, give it to my students and say, "Give me five things
wrong with this," but it gets the point across.

Jane That picture is on our Web site. It's called Titan's Surface, if
anyone wants to go through the quiz later. It says Saturn over Titan, is
actually what it says.
\[http://saturn/cgibin/gs2.cgi?path=../multimedia/images/artwork/images/image8.jpg&type=image\]

Kevin A very dramatic picture.

Jane Yes. It shows the planet. It shows the probe. I won't give away all
the boo-boos, but it is pretty.

Kevin It's great. I'm not complaining about its artistic merit. Also,
interestingly enough, this mission has at times been plagued with raging
serendipity. Whenever something goes wrong, it seems to boomerang in our
favor. For example, I mentioned that because of a little issue with
communications between Huygens and Cassini, we ended up taking one orbit
and turning it into two smaller orbits.

It cost us some fuel, but it turns out that in so doing that, the
Cassini spacecraft during its flyby will be much higher over the planet,
over the moon. The flyby time will be much more leisurely, and we
actually have a longer probe mission because of this. We'll get back
more data from Huygens.

Interestingly enough also, we ended up with a second flyby of the moon
Iapetus. Initially we only had one planned. That's the moon I said
previously was considered as the location of the monolith, the yin-yang,
the black/white moon. We actually got a second flyby in the mission, and
it occurs right here, near perichron, in rev DC interface. So we have a
neat Iapetus flyby, better than Voyager resolution, our imaging system.

Then you will see in the right-hand plot, Rev C Probe Mission is the
title of the plot. You will see that there is a whole long period that
is in red. That's what's called a critical sequence. That's at the
point, essentially, that we do nothing but the probe mission. We track
the probe. We listen for telemetry from the probe.

Once we pass Titan on the inbound leg of this orbit, we will go over the
horizon eventually and no longer be able to hear the probe. After
sending back our data, essentially the probe mission is done. By the
time we come back to Titan, the probe will be out of power and will have
been frozen.

Interestingly enough, the bulk of the probe mission is the probe
descending through the atmosphere. The Huygens probe has four science
instruments to take data during descent. It has an instrument that will
sample the cloud droplet composition. It will sample the atmospheric
composition. It will determine wind speed and direction, and it will
even snap images as it is descending, dangling from its parachute. \[the
probe even has landing lights!\]

The spacecraft is to survive to withstand impact on a solid surface, or
if as we think, there are lakes filled with ethane and methane, the
spacecraft will float. There are two more instruments called the surface
science package that will operate once we get on the surface. Again,
that sends the data back to Cassini. Cassini records it on a solid state
recorder to be played back later. Are there any questions there?

Steve This is Steve Fentress in Rochester. Whenever it would be an
appropriate time, I wonder if you could just review once again,
summarize briefly the before and after changes in the whole plan because
of the Huygens adjustment.

Kevin Before, we had a close flyby. The spacecraft was going to fly, at
closest point of approach, 1,300 kilometers above the surface of Titan.
When you fly that close, your tangential and radial velocity are pretty
high. Actually, your radial velocity inbound is pretty high, and then at
closest point of approach your tangential velocity, in other words,
you're flying across the sky pretty quickly, and then you zip out pretty
fast.

We have subsequently changed one orbit into two, made it a resonant
orbit, so two orbits that have the sum total period equal to the
original orbit. It cost us some fuel, but in doing that we have pushed
that flyby altitude out from 1,300 kilometers to 65,000 kilometers. We
can still hear Huygens, but what that means is our tangential velocity
is much slower, relative to the spacecraft. The angle subtends over
time, is much smaller. The radial velocity inbound is much smaller. We
can hear the probe and we're over the horizon much longer.

It turns out the battery state of charge on Huygens is actually doing
far better than originally planned. Therefore, it's going to live longer
and we're going to be able to hear it for the duration of that extended
lifetime. As I said, raging serendipity; a lot of these things that have
looked bad at first have actually totally boomeranged in our favor on
this mission.

Ken This is Ken from North Carolina. When you say live longer, how much
longer?

Kevin A few hours. I don't know exactly how long. I would imagine it's
entirely dependent upon whether it lands on a solid surface or lands in
liquid. Even though it will float, certainly a liquid will draw heat
away from the spacecraft much more rapidly than the surrounding air
would. Therefore, I expect if it were on liquid, it would last not
nearly as long as it would if it landed on a solid surface. Does that
make sense?

Ken Yes. Thank you very much.

Kevin Turning to the next page, it says "Mid Rev 3 to Mid Rev 14
Occultation Sequences." Occultation is when a target, either the Sun or
Earth or a star seems to pass behind the planet or the rings. In other
words, we may be looking at the Sun, and moving in such a way that
Saturn will cut across the face of the Sun.

As you look at the Sun, we can see what wavelength bands drop out. In
other words, we can see what absorption lines appear, and we can
actually identify the species in the atmosphere of Saturn or Titan by
doing solar occultations. We also look at both infrared and ultraviolet
stars to determine composition of the atmosphere, composition and
density.

Further, we also have what are called radio science occultations \[when
an object like a planet, moon or ring passes between the spacecraft and
the Earth or the Sun\]. Radio science is the only experiment that does
not take data on the spacecraft. The spacecraft is a source of a signal.
We have an ultrastable oscillator, meaning we know the wavelengths we
can broadcast to one part in ten to the fifteenth, and we know we have
an extremely precisely well-known frequency of EM radiation, which we
send to Earth. Depending on how that is bent or diffracted we learn
things.

For example, if we're looking at gravity fields, we point our main dish
at Earth point, send a signal, and as the planet passes in between us
\[Cassini and Earth\], \[the spacecraft's signal\] will get bent. Then
we look at Saturn, or Titan, or a moon's gravity field, and then we can
infer information about its interior. Alternately, we can actually send
a signal towards Earth and see how it gets cut off, looking at ring
particle density. So these sequences, the occultation sequences, are all
designed to get both ring and Saturn occultations. So we are looking at
particles, size of distributions, looking at Saturn's atmospheric
composition and density. Does that make sense?

W Yes, pretty much.

Kevin Almost all the tours we designed -- it was 18 -- I think they all
were exactly the same up to this point in the mission. It's after this
point that they diverge.

Going to the next page labeled as six, the revs are in green. It says,
"Mid-Rev 14 to Mid-Rev 26, Magnetotail and Icy Satellites." Now like
Earth, like Jupiter, Saturn has a magnetosphere, a magnetic environment
that stands off the solar wind.

It has what we call a bow shock, a magnetosphere. So in these series of
orbits, you know it's a fairly big orbit. They go out beyond Iapetus;
Iapetus flybys, unfortunately, but you'll see we rotate the petal into
the anti-sunward location. So we're sampling the magnetosphere in
various orientations.

We're looking at what's called the magnetosheath. These are primarily
particles and fields measurements, but also, being in the ring plane, we
have icy satellite flybys. If you look at the right-hand side, the x/z
plane, you'll see that we are definitely in the ring plane. It's pretty
boring, the right-hand plot. That shows you we just stay inside the ring
plane; satellite flybys, color rotation.

Remember what I said about the fact we use Titan for gravity assists? If
you look, if you assume these petals are rotating clockwise, the
orientation of the petals, the long axis of the petals, the major axis
is rotating clockwise; you'll notice the last petal ends where? Right at
the orbit of Titan. What that means is we're about to enter another
inclination sequence, and we're going to use Titan as a gravity assist.
Are there any questions here?

W That's cool.

W Yes, interesting.

Kevin Then no questions at this point so far? The next series is called
a 180 transfer, up and over. We have multiple Titan flybys, because each
time we crank up the inclination we're using Titan to do it. So this is
page labeled seven. The petals are in blue. I believe I duplicated the
same -- yes, I'm sorry. So this doesn't show the x/y, just the x/z
twice. I apologize.

M I thought that was a remarkable coincidence.

Jane Raging serendipity.

Kevin Raging serendipity, that's right. No, this is a raging blunder.
When I teach class, I always make sure I tell students that you'll hear
scientists use the term error, and it's not equated with blunder. Every
scientific measurement has an associated error. You can only make a
measurement to a certain precision. This is a blunder; this isn't that.
So I apologize.

If you go back to the first page, page two, the first page after the
title, you can see what's going on here with the petals. The petals are
rotated a little bit, but essentially we go up and over numerous Titan
flybys, and this is the first really good opportunity to look down on
the rings. So these orbits are dedicated to rings and maps\[?\]. Maps
are our particles and fields instruments.

We have four optical remote sensing instruments. We'll be looking down
the rings, -- we have a mapping spectrometer; it's called VIMS -- in
multi-bands to look at composition.

We will be looking with the imaging science subsystem. That's ISS, not
to be confused with the International Space Station. ISS is the main
visible-light camera. It's the instrument on which I work primarily. ISS
will be looking at rings for ring dynamics, ring/moon interactions,
waves within the rings.

Then CIRS, the composite infrared spectrometer, will be looking at
things like ring particles coming out of shadows, to see how quickly
they cool or warm up, or go into shadows to see how they cool, and that
will tell us about composition of the particles. So it's interesting for
optical remote sensing.

Also, on the spacecraft we have a magnetometer. A lot of our spacecraft
have magnetometers. It's a fairly simple instrument. It determines
magnetic field strength and orientation. So the magnetic field of a
planet is generated interior to the planet. We think that by
understanding the magnetic strength and orientation at multiple
latitudes, orientations, distances, we can eventually infer the nature
of its interior.

Now there was once a scientist who said that there were three major
problems still to be solved in physics, and one of them is determining
how Earth's magnetic field is generated. That scientist was Albert
Einstein. Has anybody heard of him? Magnetic fields befuddle us, how
they're generated. So a magnetometer is one step in a very long process
of understanding how planetary magnetic fields, and for that matter, how
stellar magnetic fields are generated. Are there questions here?

The next page, the yellow sequence, only a couple of revs. This is our
Iapetus flyby preparation and icy satellites. We have a few icy
satellite flybys during this, but essentially we're boosting out our
semi-major axis, our average orbital distance, out to the orbit of
Iapetus, for our close, what we call targeted flybys.

We have different kinds of flybys in the mission. We have ordinary
flybys and we have targeted flybys. Ordinary flyby means during the
course of your mission you just happen to be passing within a reasonably
good range of a satellite, and that's a "Kodak™ moment" or that's an
observation opportunity.

We do have instances where we have flybys that are, on purpose, close to
address a certain scientific goal, so all of our missions of the various
tours pretty much had to have an Iapetus flyby. That was high on our
list of priorities, because we still want to determine the nature of
that light/dark boundary on the moon. So here we're pumping up our
eccentricity, increasing the semi-major axis, the average distance of
the orbit from Saturn.

There's not much to be said about page eight, other than you can see
that it's in the ring plane again, but part of that, the last part of
it, is depicted on page nine, and the interface between that and the
next orbit. You can see very distant, where the green is, where it
starts. As we come in towards Saturn, we have a flyby in close. These
little symbols mean something on the tour atlas. You can click on those
symbols and determine what that event is.

You'll see as we reach perichron, the closest point of approach, as we
recede there's a Titan encounter, a Titan flyby. That's where it changes
to red. If you look at the right-hand plot, you can see -- kind of
interesting -- that once we "hit" Titan the inclination changes. I just
did that to show you that we do indeed use Titan for our gravity assist
and changing inclination. That slingshots us out towards Iapetus, and
that's when we have our Iapetus flyby, our targeted Iapetus flyby. Are
there questions?

The last page, page ten, our high inclination sequences, mid-rev 49 to
end of mission. That's actually kind of a misnomer at this point in
time, which I'll explain. These are high inclination. We crank the
inclination up and up, meaning multiple Titan flybys. Again, since we're
high, looking down on the rings, this series of revolutions is good for
the rings, and it's good for particles and fields. So we have, again,
multiple opportunities to look down on the rings and look at ring
dynamics.

Now I say that end of mission is kind of a misnomer. The reason I say
that is because at the end of a mission, we can propagate the trajectory
out a little ways. We found we didn't have any Titan flybys, meaning the
orientation of the orbit is going to remain the same, and they are small
orbits. They are very, very high frequency or short period, so we've
already actually planned the "extended mission."

We've already planned the next few orbits, after what you see here in
these two images, and we know for the next several orbits what exactly
we're going to be doing already. So that's the quick and dirty version
of 74, if you include extended mission, 78 orbits. Are there any
questions whatsoever?

Jane Kevin, how long did it take to do this, to plan the whole tour?

Kevin Our tour people are two designers, one of whom is on a mission,
John Smith in Mission Planning, and one of whom has gone on to other
things. They worked, interestingly, kind of competitively and kind of
collaboratively. They used similar software to help each other out, but
they were both trying to outdo the other and get the best tour, which
was good, because competition helps breed, I think, excellence. They
both did a great job and we got multiple tours.

The design took a few months. Once you understand this and you get good
at it, they come faster and faster. So it took a few months. I'd say six
to eight months.

At the same time, I and my boss at the time, a scientist named Nicole
Rappaport, she and I were doing these little booklets, doing detailed
analyses of each of the tours that came out for science return. We would
look at return for ring scientists, satellites, flybys and distances,
and things of that nature. So we probably wrote a book about every
single tour for the scientists to pare through all these tours.

We came down to three pretty rapidly. After that, there was a lot of
debate back and forth. There was still kind of the spector that this one
tour was perceived to return so much more science that people really
couldn't let go of it. They couldn't let it go, but it really was
unflyable from an operation standpoint. Our ops people would have just
been going out of their minds. They just couldn't have done it. They
would have been totally stressed out.

So from an operations standpoint, the tour returned more science, but it
was unflyable, but it took awhile to really get people to accept the
fact that we weren't going to do that. After we got down to three, we
rapidly whittled away one, and there was a long debate about the
remaining two.

Then over time, we've had another small tweak to this tour last week. So
we still occasionally have small changes to the tour, but it's been
stable for roughly a year and a half or two years now. Does that answer
your question? I rambled.

Jane Yes

Steve How small is a small tweak? Would that amount to adding a whole
other orbit?

Kevin No. I would say that would be a large tweak. It means in the
latest version of this tour, my orbit has changed such that I'm no
longer flying behind the B ring. I'm actually outside of the rings for
this occultation. I don't get occultation anymore. Let's tweak the orbit
a little bit, so I can get the occultation again. Does that give you an
idea of the scale? Small-scale things.

Steve But it's not enough to seriously change when you're going to get
to one satellite or another?

Kevin No. In fact, that's how we kind of tie the tour down. We have four
space, x, y, z, t, or however you want to look at it. We have to be at
this flyby at this time, and then how we get there between, flyby A and
flyby B is kind of to be determined. So it might take some extra
expenditure of fuel. All we have to do is we have a spot we have to be
at, a time we have to be there, and in between can actually vary a
little bit.

Steve Okay.

Anita Kevin, as you do the tour, are you going to be changing based on
the science observations that need to be done?

Kevin Absolutely not. We actually are well into the tour's
implementation. In other words, we are already compiling the programs
that will run on the spacecraft well into this mission. I'm the sequence
lead right now, the development lead for what is called the S2728
sequence that occurs in 2007.

We have our series of observations. What we do is the spacecraft teams
deliver to us their part of the program. We merge these together, to
make sure they play well with others, and then we put on a show.

Over time, as we know the positions of the satellites and the planets
better, we will tweak them a little bit, move the times a little bit,
but for the most part, this is cast in stone from this point on. We're
not going to change these orbits much, minor, minor tweaks, and minor
timing changes to correspond with satellite uncertainties and things of
that nature.

Anita That sounds different from Voyager and Galileo, in that you won't
be able to respond to new information that might cause you to wish you
did your observations differently?

Kevin Well, we can, because within some of these observations, for
instance with the imaging science subsystem, ISS, on which I work, we
have plans in our timeline called retargs or retargetables. So we have
times where we have yet to describe our pointing, which we will do at a
much later date. That's to accommodate discoveries. So we actually do
put some slack into this schedule to accommodate discoveries, because we
know we're going to discover things, and we don't know what it is yet.

Anita When there are conflicts between what the various types of
instruments want to look at, how are those solved?

Kevin Sometimes it's nice and sometimes it's ugly. I'm kidding. You're
going to like this. We have split this tour into different segments, and
our segments basically correspond to which discipline science is best
achieved at this point in time. There are four of these groups called
target working teams, TWTs, or yes, twits.

We have four TWTs, our Saturn TWT, which is an atmosphere TWT
essentially. We have the ring TWT, the mag TWT, and then what's called
the cross-discipline TWT, which is just pieces of the orbit that don't
really correspond to any of the other three.

Anita So the leaders of those teams are the chief TWTs.

Kevin We have TWT leads and TWT co-leads, and the TWT leads are usually
scientists, and the they actually have co-leads, scientists and somebody
who is a science engineer from JPL, who can get the scientists' bidding
done. So what they do is these TWTs take a highly conflicted timeline
and they meet and the scientists hammer out what series of observations
will occur.

For instance, I'm the ISS representative for the rings TWT. So I sit
there and I argue, sometimes vehemently, for our science and for ring
observations. We make trades. "You can have this timeline if I can have
that part of the time." Sometimes fellow scientists who understand it
will chime in and say, "I really think this person has a better case."
So sometimes you have to understand the science to plead your case, and
usually other people will chime in and 99% of the time they're very
honest with what they're saying as far as, "Yes, I think this person is
better, or that person is better."

It's done by peer review or peer -- I hate to use the word pressure --
but your peers come in and say, "We really think that ISS has a better
case here than UVIS." It can on very, very rare occasions go up to the
project scientists to make a call, make a choice, but that generally
doesn't happen. Usually it's solved within the TWTs.

There are also to other groups called OSTs, orbiter science teams. One
of those works on satellite flybys, that's SOST, and one works with
Titan flybys; that is TOST. So SOST and TOST are just like the TWTs,
only they handle the conflict in timelines that occur plus or minus
three days of a close satellite or close Titan encounter, and they
operate pretty much the same way.

Jane Those will be the subjects of our next two talks, by the way, a
TOST and a SOST.

Kevin I couldn't have led it any better, could I?

Jane No. That's why we planned it this way.

Anita Kevin, wasn't there, in earlier days of Cassini, a sort of
economics professor at Caltech that had these guys essentially playing
poker? Do you remember that?

Kevin That was the professor and a science system engineer on the
mission called Randii Wesson. Randii had developed a resource trading
mechanism, not poker. It's more like stock trading. It's more like I'm
allocated so much in the way of credits, chips, whatever you want to
call it, and I put my value on certain observations, and you go in and
then you trade resources. You can barter with people. You can buy off a
segment. If you really want it, you can just put more of your value on
it.

We ended up not using that, but other people are. Space shuttle uses it
for scheduling payloads, that mechanism. The Southern California Air
Quality Management District uses that technique for budgeting different
businesses, budgeting their missions. We did not end up going with this,
however. Did that answer your question?

Anita Interesting concept, though, for solving some really big issues.
Let them do it themselves.

Kevin Yes. Early on in the mission, I remember somebody saying, "Why
don't we just throw something at the computer and let the computer
schedule it?" and this is what a mathematician or computer scientist
would call an NP-complete problem to do that. NP-complete problems have
the nasty property that they take the fastest computers a sizable
fraction of the age of the universe to finish. That's not an
exaggeration either. That's not an exaggeration at all. This is too
complex for a computer to do a best fit, maybe a first fit, which is
different than a best fit. It's kind of obscure.

April Kevin, this is April \[Whitt\] at the Fernbank Science Center
\[Atlanta\]. Could you tell me the TWT names again? I have ring, mag,
and what were the other two?

Kevin Saturn and cross-discipline.

April Thank you. I have a lecture to do tonight, and I need to have
those right?

Kevin Yes, our TWTs. In fact, a little over a year ago, missions are
pretty supportive of each other. We'll send each other posters or
banners. I came up from the cafeteria and there was a huge Cassini
banner on the front of our building. It said, "Congratulation Cassini on
five years in space. A journey of 1,000 observations begins with a
single TWT." It was a gift from the Mars missions I think.

Anita I saw some e-mail traffic where someone of British extraction
said, "NASA *have* the greatest sense of humor."

Kevin When you work with what we have, you have to.

Anita Kevin, I don't know what your time commitment is here, but do
other people have \...?

Kevin I actually am late for something right now.

Anita Okay, then you need to go.

Kevin I do.

Anita Thank you so much.

Kevin My pleasure.

Anita Is there anything anybody wants to discuss further? We have the
line for another half-hour if we need it.

Michelle Anita, this is Michelle from the Adler. I just have a couple of
logistics questions. Do you know when the high-res versions of the
launch videos might be available?

Anita We are discussing that. Steve, are you on the line?

Steve Yes.

Anita Would you like to send that tape off to Michelle? Do you think
that will work for her?

M Were you asking for Steve Lee or Steve somebody else?

Anita I'm sorry; Steve Lee. We have a beta\[cam\] version that I sent to
Steve Lee \[Denver\]. I'll ask him to send that off to you.

Michelle That would be great. We want to use it in our Secrets of Saturn
show. It opens sometime I think in early June. So we have a little bit
of time. I have one other question. Have the plans for Cassini cleared
the arms traffic or whoever it is committee that needs to look at it?

Anita We actually have a meeting about that tomorrow.

Michelle Beautiful.

Steve: Was this trying to get drawings of the spacecraft?

Anita Right.

Steve I'll tell why I mention it. We have an amateur astronomer in town,
who decided to make a little project of building a detailed scale model
from scratch, and he had a lot of stories about trying to find drawings
that would tell him what he needed to know. He went with it and built a
beautiful little model, which I should send you a picture of. But he
said it was quite an interesting challenge to find some of this.

Anita Cassini was launched in '97, but only in the last few years have
spacecraft been under these regulations. So even though all this stuff
is in the open literature, they are being very cautious.

Steve What's the regulation problem or issue?

Anita There's a whole government process called International Traffic in
Arms Regulations. It's basically to control technology so that it does
not fall into the hands of people we would not like it to be in the
hands of. So anything that we are going to release publicly has to be
cleared before we can do that.

I have to go talk to this lady tomorrow. In the past, like with MER,
actually, I don't think they ever finished the process of clearing the
drawings for general release. Some people, like LEGO, signed a
nondisclosure agreement and a license agreement, and were able to get
sufficient detail to make their models.

Steve How recent is this?

Anita ITAR?

Steve Yes.

Anita It's four or five years old.

Jane We didn't expect to have this little hiccup with Cassini, because
after all it launched in '97, but it uses nuclear energy to generate
electricity to power its systems. \[the same as Voyager and Galileo\]

Steve Okay. I'm just looking for the general background on this. It's an
interesting story.

Jane As you guys probably remember, there was an anti-Cassini launch
group, because of the \[radioisotope thermoelectric generators\]. Are
there other questions? It's been really hard just to get all the people
in the same room, to actually look at some of the models and drawings to
release it to all of you folks.

Anita We're trying. We're really trying.

Jane We actually have a meeting scheduled tomorrow.

Ken Anita, I have two quick questions. First, I know I should have this,
but when is the next press briefing for the MER missions?

M This Thursday at noon.

Anita Thank you.

Ken The second question, I'm having some trouble locating panoramic
slides for some of the panoramic images. I know this is Saturn, but I
have to ask the question anyway. I'm sorry. Who do I talk to about
getting slides of these things, from the images that have come down? I
don't know how to make them myself yet, and of course I would like to
throw them up on the dome.

Anita I would have to ask if any of the partners can help you out. We're
not making very many slides anymore. There's a slide set that just came
out for MER, but it's very much pre-launch. It wasn't made with a
planetarium in mind.

Ken Understood.

April A suggestion, Ken, if you contact Pat McQuillan in Florida, he is
doing all that sort of stuff.

Ken Can you spell his last name?

April M-C-Q-U-I-L-L-A-N.

Anita What facility is he at?

Jane He's in Jacksonville, the Alexander Brest Planetarium.

Ken Thank you so much. Maybe you could e-mail me off-list with his phone
number and all of that stuff.

Steve \[Fentress\] Before you leave, Anita, I know I promised a week ago
before I left town for the Large-Format Cinema Association to send you
some files that we did, sort of a donation to the Museum Alliance. So
those might be helpful, too. What was I going to send? It's either the
Bonneville crater or the Eagle crater with the outcrop. Anyway, I was
about to send it to you and then left town.

Anita You went to that large-format cinema conference?

Steve Right.

Anita That sounds interesting.

Steve It is kind of interesting. One of the people in it, this was an
interesting comment, a producer name Frank Marshall was there giving a
talk. He said he has exclusive rights to the image data from the Mars
landers that he's going to use to make an IMAX movie. I thought,
"Exclusive rights to the data, really."

Anita What was his name again?

Steve Frank Marshall.

Anita There is an IMAX team that's been here a lot, and they've been
shooting their own footage. So they've had access and that's their
footage, because it was shot with their camera.

Steve Right. That I can understand.

Anita Unless they are paying somebody to create IMAX quality or
something, I don't know.

Michelle One additional piece of information is that movie will not come
out until the missions are officially over. So the longer they go, the
more the Mars IMAX movie is going to be doing.

Anita Yes, interesting because I'm hearing rumors that it \[the MER
mission\] could run indefinitely.

Michelle That's what I learned over the weekend, was the solar situation
starts improving after the middle of August. The dust on the panels
hasn't been an issue, so who knows? It depends on how long those
batteries can keep getting charged up and down. I let people know that
yesterday, and people were just floored that the missions could go maybe
September, December, or longer.

Anita You heard Eric saying two weeks ago that posting of images has
slowed down, partially because there are fewer people on the project
now. They've been released to other projects. Those who are left are
working more regular hours, not 24/7. That's partially because all of
that wasn't included in the original budget, so there's a price. Anybody
else?

April Anita, this is also not a Mars question or a Saturn question. This
is a Venus transit of the sun question. Is there a Web site or a
satellite link that NASA has that we can tap into, a broadcast of the
transit going on? On the East Coast of the United States, as the sun
rises for us it's over, the transit is over. So we would like to show
people things like at an overnight event or something.

M There is another group called the Hands-On Universe Project. They have
a group of high school kids in Poland that are going to be doing a
Webcast. So I know of at least one Webcast coming from there. April, I
guess if you talk to me later and we'll do e-mails, and I'll give you
their contact information. You can ask them, if you want to get included
in that.

April Thanks. Actually, I do have that information, but I'm looking for
something from a satellite rather than over the Internet, given the
quality of our computers here.

Anita I see, because I was going to tell you about the Exploratorium's
Webcast.

April That's Internet also, right?

Anita Yes.

Anita Well we can put the question to the Sun-Earth Connection folks who
are working this and see if there is any satellite for you guys.

John This is John Young from the Rueben H Fleet Science Center \[San
Diego\]. I'm looking for a way to record Webcasts. I've been searching
for software to record a Webcast, so that I can reuse it later on. I
haven't had any luck there. If you do any research along those lines,
I'd appreciate sending out that information.

Anita Okay. All of our Webcasts are archived on the JPL Web site or the
Mars Web site. The press conferences were actually archived only on the
CSPAN Web site. If you go to the JPL main page and click on multimedia,
you will get taken to an archive of all of our video products, including
the Webcasts. That includes our lectures, our public lectures.

John Tremendous, thanks.

Anita Jane, do you have anything you want to add?

Jane No, I don't.

Anita Okay. I'm working on a Mars transcript from last week. So you'll
have it this afternoon and we're back to Mars next week. If you have any
questions or requests, ask us.

W Thank you so much. This was fantastic.

W I thought that was a really great talk. It was really interesting.

Anita It's a deep subject, but Kevin does it with a great sense of
humor.

W It's nice to see the whole tour in a nutshell, sort of.

Anita Jane, do you want to talk about the other speakers you have lined
up for the next Cassini telecons?

Jane Yes. The next two speakers we have are other people here at JPL in
our science planning group. These are the people who have been doing
that fighting that Kevin was talking about, to get to maximize the
science on each segment. In two weeks, on the 18^th^ we're going to have
Trina Ray, who is a wonderful public speaker. She'll be talking about
the Titan OST, the TOST.

Then following that is Amanda Hendricks, which will be on June 1^st^,
talking about SOST, or the satellite orbital science team. What they're
going to be talking about is a little more peeling down the onion of
what Kevin talked about, but just about what we're going to do at each
of the icy moons, for example. That will be what Amanda is going to talk
about.

You can get a little flavor of Amanda, if you'd like to, by going to our
Cassini Web site \[http://saturn.jpl.nasa.gov\]. Right on the front page
we have a new feature. It's a spotlight, a Flash animation called, "Why
Go to Saturn?" She's one of the people being interviewed in that new
feature. So it's kind of a cool new thing on our Web site. We're going
to have several of these over the next couple of months, and this is
kind of whetting everybody's appetite, getting everybody all excited
about our mission.

Anita June 1^st^ is potentially a Saturn minus 30 days or so press
conference for Cassini.

Jane It might be on the 3^rd^ and it might be on the 8^th^, according to
our media people. But the cool thing about having Amanda talk right
then, regardless of how close we are to the press conference or the
briefing, is that that's her specialty and we'll be getting really
close, less than ten days from Phoebe, and so she'll be able to,
perhaps, give us a really good bit of information about that.

Anita Perfect.

Jane Send us ideas if you have certain topics you'd like to hear in
these teleconferences, and we'll go find the speakers for you.

W Great.

M Thank you very much for all your help.

Jane You're welcome. These are fun. Thank you, guys. Good bye.