**NASA**

**December 28, 2004**

**1:00 p.m. CST**

Coordinator This is the coordinator. I would like to inform parties,
today\'s conference is being recorded. I you have any objections, you
may disconnect at this time. Ma\'am, you may begin.

Trina Hi, everybody. Welcome to today\'s CHARM telecon. We hope you
really enjoyed the... today. We have, as you can imagine, the whole
project has been just in a flurry of activity in the last week for the
Huygens probe release in the upcoming Huygens mission. And so today, we
have Shaun Standley who is the system engineer for the mission on with
us. Shaun, you have two hours. Although typically with one person, we go
about an hour, but if you want to run over, it would be perfectly okay.

> Just as a word of warning to everybody online, there are several
> movies on the Web site that you should probably start downloading
> those now because they\'re going to take sometime especially when
> everybody starts hitting the server at the same time. Thank you very
> much, Shaun, for doing this today.

Shaun It\'s pleasure. Thanks, Trina. My name is Shaun Standley. I\'m the
systems engineer for the European Space Agency Huygens Probe. It\'s my
pleasure today to give you guys some information about what\'s happening
recently in the mission, what we\'re up to, so that you can pass it on.

> In about 17 days on the 14^th^ of January 2005, the Huygens probe will
> slam into the atmosphere of Titan, and a few hours later, it will
> become the first spacecraft to land on a moon in the outer solar
> system. So today, I\'m going to give you some background on what\'s
> going on now.

So on page two to start off with, we'll have probe facts and a bit of
mission background and a short segment on why study Titan. I\'m not a
scientist., but I\'ll give you the engineering reasons why we\'re
interested in it, the probe mission objective and the science mission
overview.

Moving on to page three, Cassini-Huygens is a joint effort between NASA,
the European Space Agency and also Italian Space Agency to explore the
Saturnian system and in particular, Titan. It's comprises of the
Cassini-Saturn orbiter, which will do the tour and the Huygens probe,
which will parachute into Titan\'s atmosphere and take direct
measurements.

On page four, a couple of teaser photographs of Huygens, so you get an
idea of its shape and size and where it\'s attached on the orbiter or at
least where it was attached on the orbiter; it\'s not there anymore.
It\'s about three meters across. You can see the multilayer installation
blankets on the outside being attached there on the right-hand
photograph.

On page five, I\'m not going to read over this, but I wanted to give you
an idea of how difficult it can be to start off an international
collaborative mission or any mission this size. The joint ESA/NASA study
started in 1984 and there are a lot of discussions before that before
getting underway with the mission in its current form. In 2000, we
discovered a problem with the Huygens receiver on board the orbiter, the
part of the probe system that stays on Cassini to receive the radio
signals and a revised mission has been worked between 2001 and today to
correct that receiver problem. So we\'re all set-up for the mission now.

On next page, I\'m afraid this is animated, but just a few facts about
the mission and the probe system weight, the front shield, the back
cover and control subsystem and on page seven, more facts about the
subsystems on Huygens platform.

The next page, Huygens' exploded view to give you an idea of how the
things is put together. It's put together in kind of like a clamshell.
The front shield protects the probe instruments during the entry. The
outside of the front shield heats up to about 1,900 Celsius, and the
plume during entry is of the temperature of the gasses, about a
temperature of 8,000 degree Celsius. So the heat shield is exposed to
that for about three minutes. Then you have fore dome, which protects
the instruments during the descent after the heat shield is detached
with the cut-throughs for the instrument sensor heads to poke through;
the external platform, which also contains part of the housekeeping
subsystems, top platform aft cone and then the back cover which will be
pulled off by the first parachute that's deployed during the descent.

There are some more photos during integration and testing. On the top
left, you can see the heat shield being lowered down on the fore dome,
probe is upside down; below that, a picture of the probe during
separation testing where they were testing separation to heat shield
pulling it upwards off the separation mechanism. You can see that kind
of tripod device holding the probe off the floor, which is part of the
separation mechanism. In the middle, you see the spin vanes on the
probe. These are usually covered up by the heat shield, so I thought I
put this one in. These are the little vanes that give the Huygens probe
a little of spin on the way down as it moves through the atmosphere, so
it can get a good panorama with its imaging subsystem around horizon.

On bottom right, this is final part of integration. Interesting thing
you can see here, if you look on the right where the back cover of the
probe is off and you can see some of the items exposed on the top of the
platform, at about 11 o'clock on there, you can see the CD that we put
on including people signatures, good wishes, some of the music that was
composed for the Huygens mission, there's a very far outreach item
included there.

And also, right in the middle, you can see the parachute mortar. That\'s
what where the first parachute will be fired through the cutout on the
back cover to deploy the first parachute that will pull the back cover
off.

Next page, payload location, I won't talk much over this. You can see
where the little booms deploy on the Huygens atmospheric structure
instrument, where the parachute is located, and spin vanes and other
instrument cutaways. There\'s also on page 11, showing you a rough
layout of the equipment and the batteries.

So onto the mission, Cassini-Huygens was launched in October 1997. We
took the long way around. It, first of all, went in to the inner solar
system to pick up some Delta-V from a Venus swing-by in 1998. There was
a further Venus swing-by in 1999, followed by an earth swing-by in
August 1999. This centers on our trajectory to the outer solar system.

On this diagram, ICOs are instrument checkouts where they checked out
the orbiter instruments and PCs are probe checkouts, where we turned on
the probe for about six hours to check the descent sequence of the
probe, calibrate the instruments and make sure the engineering
subsystems were still okay. I have to go on to Jupiter swing-by in
December 2000, where the orbiter did some major science.

The next page, page 13, shows you the trajectory on the approach to
Saturn. It starts out in the top right-hand corner, June 2004, this is
just after the Phoebe flyby. We come into SOI on the 1^st^ of July and
immediately swing out in a very long trajectory, taking us back out deep
into the Saturnian system for the Periapsis Raise Maneuver on August
23^rd^. This is the maneuver that took us outside the rings of Saturn,
where we have a thread through those with the SOI maneuver and set us up
for the initial orbits of the tour. Where the trajectory goes green, you
see a notation for Periapsis Raise Maneuver cleanup that corrected
statistical error on the first maneuver, that wasn\'t actually done, the
Periapsis Raise was so perfect. We swing back in on the green trajectory
for Titan A encounter on the 26^th^ of October---I\'m sorry. I misread
that. We swing back in on the green trajectory for Titan encounter on
the 26^th^ of October and then a cleanup maneuver after that a few days
later. This brings us around to Titan apoapsis and now we\'re setting up
the trajectory for the probe mission.

We did a Titan B encounter on the 13^th^ of December, a probe-targeting
maneuver, which puts the Cassini orbiter and Huygens onto a collision
course with Titan on the 17^th^. We were on that collision course for
quite sometime until probe release finally on December 25^th^. We have
just done early this morning an orbit-deflexion maneuver. Now, that the
probe is going, we\'ve taken Cassini off that collision course with
Titan, and you\'ll be happy to know that the orbiter is not only off the
collision course, but setup properly to collect the probe data on the
14^th^ of January.

So key events that have happened recently, of course, SOI, this is on
the next page, SOI on the 1^st^ of July. October 26, we did the Titan-A
flyby. This is very important to, not only as a science event for
Cassini, but to gather engineering data on the atmosphere of Titan. We
have the probe battery depassivation on the December 5^th^. This was
turning on the batteries on the probe and applying a current to them to
each battery for a few minutes to remove the chemical passivation layer
that builds up on the electrodes over the years that the batteries have
been traveling out to Saturn.

The probe doesn\'t take any power from Cassini. It's completely reliant
on its batteries. We can switch on orbiter power to check the probe out
during its tour, but what we cannot do at all is charge the batteries.
So these batteries have been, more or less, in storage on the probe for
the past seven years.

The first time we had a look at them was in September 2004 and the final
de-passivation was to make sure the chemical deposition on the
electrodes is removed and the probe batteries were ready to power the
probe during its descent. We went on to have a Titan-B flyby on December
13^th^ to gather more data on Titan\'s atmosphere; that was very
important for us. Then probe-targeting maneuver on December 17^th^. That
set us up the impact, it was a perfect targeting. We\'re going to hit
the probe-landing site perfectly. On December 25^th^, after confirmation
that we were on the right course, we had probe separation. And during
this, Cassini set us up for exactly the right separation attitude so we
have the right angle of attack during the entry. And as I said, just had
orbiter deflexion maneuver and we\'re looking forward to probe arrival
at Titan on January 14^th^.

Next slide, page 15. This is a close-up of the separation mechanism
during integration. You\'re looking at the back of the Huygens probe.
There are three attachment points like the one you see in the
photograph. Separation mechanism consists of some preloaded springs,
three of them, that are in a tube and they're sitting there for seven
years until a pyro fires, a bolt fires to release the spring. The spring
expands and pushes Huygens outward and there are some rails there with
little rollers that gives the probe a spin. So when the probe detached
from Cassini, it's spun up to about 7.4 rpm to give it some stability
during its 20-day cruise and also to make sure it\'s stable for the
initial stages of the atmospheric entry, so 7.4 rpm when we departed
from the orbiter with a relative velocity of about 0.34 meters per
second.

The next two slides, I\'m going to run a short part of this movie
showing the Huygens separation. If you weren\'t able to load the Codec,
the driver for the first slide, the second one is an MPEG of exactly the
same sequence. I\'m going to run the one with the Codec here, but you're
welcome to run the MPEG if that\'s easier for you. So I\'m going to
start it now. You see the Cassini move to the separation attitude; it
loses contact with Earth at this point. It charges the capacity banks,
waits awhile in the attitude for the fuel slosh and boom oscillation to
die down. And then bang, we separate, spin the probe up.

Cassini tumbles out of control for a while. We have to disable attitude
control. You can stop the movie when it darkens out there. We have to
disable attitude control for a while because, of course, if Cassini try
to recover its attitude while the probe were separating, it may hit the
probe with the boom. The MAG boom is around 11 meters long and if
Cassini was trying to de-tumble, there was a risk of impact. So attitude
control was suspended for about five minutes after separation to make
sure everything was okay. We reacquired the Earth about half an hour
later and we were pleased, after holding our breaths for about an hour,
that the separation was absolutely perfect. From everything we could see
from the orbiter at that time, because the orbiter recorded over
kinematics during the separation, it was absolutely perfect.

Next page down is entitled example probe imaging mosaic. On Christmas
day, as a special Christmas present to us, we attempted to, with the
navigation team and AACS team, we attempted to image the probe. We
weren\'t sure exactly where it is because there is some transverse
velocity when you separate so they designed a 5x5 wide-angle camera
mosaic. This isn't the real background that would be on that mosaic with
real plants and stars, it's just in an arbitrary direction. But the
probe was supposed to appear in the very center of that mosaic although,
clearly, we weren\'t sure that so we did a 5x5.

You can see just above the center image, I put a white dot there, and
that\'s where we obtained first wide-angle camera image of the probe.
It\'s in the overlap between the mosaic tiles, so we actually obtained
two images, which was a great confirmation. This is just perfect. It\'s
exactly where we expected it to be. We\'re very pleased about that.

The next day, with the probe being similarly far away, this time it was
about 53 kilometers away, we did a narrow-angle camera view of the
thing, which gave us a bigger image. It was about ten pixels across.
Probe range was 53 kilometers and it was, again, perfect right where we
expected it to be, very nice indeed.

Next page, page 19. You can see the---I put the wide-angle camera image,
the center mosaic one in there. This is only about three to four pixels
across. It wasn\'t very exciting to look at but it was exciting for us.
It just looks like a bright star.

Trina Is it the smudge in the middle or the star at the upper...?

Shaun It\'s the star at the top. It\'s a bright star on the top right.
It\'s not a star, the bright image on the top right. You can see that
these images are completely raw. They haven\'t been enhanced at all, so
you can see cosmic ray streaks on them and the two-hertz interference,
which is the banding across the image. I\'ve never seen a prettier one
myself get this confirmation.

Next image down is the narrow-angle camera. This, once again, hasn\'t
been enhanced. You can actually see a disc and some shading on the
enhanced one, but this has only taken place in the past few days over
the weekend, so we didn\'t really get time to put that one in. But once
again, it's beautiful, it confirms the separation was perfect and we\'ve
setup with exactly the right entry conditions for Huygens entry on the
14^th^ of January.

So, now, I want to do a short piece, I\'m not a scientist, but I want to
do a short piece on why study Titan and particularly tell you why it\'s
important for the probe to study Titan. The first two pages are just
what I\'m going to say so we can skip over those and go straight to page
24 where the first guy, we\'re going to give some credit to the first
guy, who was credited with discovering Titan, Christian Huygens. He made
measurements of its period of revolution and he also after his death,
some of his more speculative prose on Titan and the outer planets was
published. He actually speculated on the existence of animals and trees.

Here then, we have found in those new world warmed by the kindly heat of
the sun with nothing, but creeping shrubs and bushes and will send them
some noble and loftier plants like trees or somewhat like them. So in
his posthumous book that was published, Huygens really speculated on
some fanciful things in the outer planets on Titan in particular. I
can't imagine trees there, but he certainly was keen on that idea.

Moving on to the real world, Jose Comas Sola is credited with early
observations of Titan to observe darkened edges, two round white patches
that he thought he saw on the central disc. He argues that this was
evidence that Titan had a dense atmosphere and it was Kuiper that first
discovered the presence of methane on Titan. Methane is very, very
important in the atmosphere of Titan to the probe because the proportion
of methane is what dictates most of the heating during entry. So we are
very interested coming in, to try and get a good estimate of what the
methane content of the atmosphere was.

When you design something like Huygens, you\'re designing it to go and
discover an unknown environment; but of course, the engineers have some
sort of atmosphere model to design the entry, descent on landing systems
for this probe. So we were very keen to see if our atmosphere model, the
new atmosphere, match the model that we designed the probe to.

Next page is Voyager observations. I guess the important thing here is
that we couldn\'t see down to the surface with Voyager. It\'s a fussy
ball. Some banding was observed in the atmosphere, some haze layers were
observed and really we couldn't see any of the surface, though, and it
really created a big mystery and even more first to know what Titan was
all about.

Trina The discovery of nitrogen, though, happened with Voyager. That\'s
when they discovered the nitrogen atmosphere, which is 98% of the
atmosphere.

Shaun Yes. Ground-based observations, we got some great ground-based
observations or Earth-based observations, I should say, in the early
'90s. Hobble images that showed this bright spot, Xanadu Regio, and also
some European observatory images, adaptive optic images, which are
fantastic and really gave us some good detail of the surface. People
started to name regions of the surface of the fanciful objects, which
you may or may not be able to see, depending on what combination of
substances you\'ve been doing a night before. The dragon's head, the
dog, the boar, and lying "H" were the names given for those off the
adaptive optic images.

> T0 flyby, this is when we really started to---want to get some
> information about methane content, the first time we could really see
> down to the surface. The first image on the top left is full color.
> These were taken by the Visible Infrared Mapping Spectrometer, and you
> can see darker regions---well, the left image in red, the darker
> regions are suggestive of maybe some water ice and brighter regions
> possibly simple hydrocarbons. And the center image on there is a
> combination of three, it's a rather beautiful image of Titan's
> surface.

Also at T0, we saw some cloud patterns and learned a little bit more
about the atmosphere, but not in the detail we needed for the methane
content. Looking at the at the Titan-A info, you can see at top right,
we have this patch haze layer. This is the haze layer Huygens will
sample directly as it descends, which we\'ll talk about a little later.

> Ion and Neutral Mass Spectrometer spectrum that we put in the center
> at the bottom, this is very important because this is where we really
> sample the atmosphere at high altitude, and there were surprisingly
> some pretty complex hydrocarbons present, benzene and di-acetylene,
> and it was during Titan A that we got a good indication that the
> methane content wasn\'t above 2%. In fact, I think the amount agreed
> upon after Titan-A was 1.8% and this is very good news for the heat
> shield, if we had gone above 3% content, that would have started to
> give the probe some problems and we were very concerned about that.

Okay. Also, I wanted to talk briefly about the radar swath that you see
in the center. I am not going to try and interpret this. In fact, I
remember one of the team leads, science team lead's comments during the
press conference after Titan-A, and I couldn\'t put it better myself,
"Oh my God, this is fantastic, but I don\'t know what we\'re looking
at." So who am I to interpret this data? But one of the interesting
things about the radar image was one of the things that came out of that
is the altitude difference in the train was banded by about 50 meters.
So we were looking at a fairly flat surface of the region that\'s
measured.

The reason this is important to us is because if Huygens lands---if it
lands tilted away from the orbiter, we won't get such good radio
performance. But if it lands flat or tilted toward the orbiter, better
performance. So clearly, a lot of chasms and deep train wouldn\'t be too
good for the surface data.

(Background noise on unmuted line)

Something else that Titan-A gave us on page 30 were the best state
images of the probe landing site. You can see on the right image, it\'s
picked out there and expanded on the left. We still don\'t know what
these dark and light images mean but we have a good view of where we\'ll
be landing.

Going on to the Titan B\...

Trina Who has got an open mic and they\'re playing music? The background
has an open mic. There you go. Thank you very much.

Shaun We're going to try and correct that problem to the operator.
...the TV on, will you please mute your microphone? Thank you.

Okay. Moving on to the Titan B images on page 31. In fact, these aren't
all Titan-B, the first one on the bottom left, was taken by the Visual
Infrared Mapping Spectrometer during the Titan-A flyby. The second one
was taken during Titan-B at a similar range and you can see evidence of
cloud formation in the temperate zone and from these clouds we can get
wind estimates. This is something else very interesting to the probe
because the parachute deployment loads are very dependent on local
winds. So this was of great interest to us. And, of course, I couldn\'t
resist on the top right, another depiction of the haze layers that we'll
measure the composition of on the way down.

Okay. So that\'s it for background material for you. I know you probably
seen those images before, but I couldn\'t resist. Let\'s move on to
mission objective for Huygens. Direct sampling of Titan's atmospheric
composition to look at the energy sources for atmospheric chemistry
including electrical activity on the atmosphere. This directly studies
the aerosol compositions and the cloud physics to measure winds and
global temperatures, determine the properties of the surface and from
that infer the internal structure and investigate, of course, the upper
atmosphere and ionosphere.

On page 34, it\'s a chance to make an in situ study of Titan\'s
atmosphere. There\'s only so much you can do with this wonderful remote
sensing package that Cassini has but this is all about in situ
measurements. All the instruments will be on a 165 kilometers altitude
and they\'ll have direct access to the atmosphere for measurements. So
atmospheric structure, composition dynamics, we also have a camera on
board which will take panoramas all the way from the initial instruments
turn on 165 kilometers all the way down to the surface.

The descent about 135 minutes plus/minus 50 minutes depending on
atmospheric conditions, it will land on the surface. I don\'t like it
would impact, but land at about five to six meter per second which is
the impact you'd feel if you jump off a desk. It wasn\'t designed to
absolutely survive for landing but we expect it to whether it lands on
liquid, slush or some sort of hard material, it has very good chances to
survive and there\'s a surface science package that will make surface
measurements at the landing site.

The next page is just to show you the variety of atmospheric conditions
Huygens will be encountering. At the toluene haze layer---toluene is a
polymer made from methane and nitrogen under the influence of
ultraviolet light. The aerosol collector and paralyzer on Huygens will
pump in some of this haze layer and the condensed states, pyrolyze them
and pass the products off to the gas chromatograph for analysis. And
then you\'ll see clouds, there\'s also another sampling opportunity of
ACP down at the cloud layer and, of course, the gas chromatograph will
be sampling, as well as taking the paralyzed condensed state products
that will also be sampling the atmosphere directly all the way down. We
also have the capability to detect liquid if we land on a lake or some
sort of liquid surface and infer the structure of the liquid from
defraction measurements and direct sampling.

So moving on to 37, just to give you the dates and times. Huygens will
wake up, it\'s currently depowered in cruise, and the only thing on the
probe is a timer powered by battery counting down to the time when it\'s
going to wake up. The time that will expire at 04:42:22 UTC if we did
our thumbs right, spacecraft even time on the 14^th^ of January. And at
that time, it will be switch on the probe and start pre-heating it for
about four hours to warm the transmitters up to temperature, where it
will operate optimally for the receiver on both Cassini to get the radio
signal. It will reach the interface altitude, the so called interface
altitude at 1,270 kilometers above the surface of Titan at 9:06:56 on
the 14^th^ and the first parachute will parachute will be deployed by
mortar at 9:10:28 approximately.

The parachute deployment isn\'t done by timer alone, it\'s done by the
deceleration detection after the heat shield hits the atmosphere. So
looking for that deceleration pulse leading edge, wait for the trailing
edge and then pops up the parachute. So as another instance of this
separation entry video here which I want to start now, we'll go to the
separation again but most of this movie is the EDL. So I\'ve just
started it. You should be able to see the separation again. \... Pyros
fire, Huygens pops off and that\'s the beginning of its 20-day cruise to
Titan.

During this time, as I said, you can see the spin on it there, 7.4 rpm.
We just confirmed that by direct observations being 7.5, so we were
right on the money during separation. The time is counting down over 20
days and 32-second increments ready to wake up. When the probe does wake
up four hours before interface, that's just to preheat the platform, to
preheat the transmitters, so that when they come on their frequency,
we\'ll be close to optimal for the radio receivers on Cassini. When the
probe enters, we separate it for perfect zero degree angle of attacks.
The actual measured angle of attack was less than one degree so we, once
again, right on the money during separation. Huygens slams into the
atmosphere. The deceleration pulses between this---whoever has the TV
on, please mute it. It\'s really distracting. Thank you.

Moving on with the movie. Thermal blanket is burned up pretty quickly.
The temperature is 1900 degrees Celsius. It\'s 8,000 Celsius in the gas
plum. Deceleration will last about three minutes. Deceleration peak is
between ten and 18 Gs, follow the descent sequence is fired off from
when we detect the trailing edge of deceleration pulse. So the Huygens
accelerometers and G switch is waiting for the Gs after the peak to go
down to an acceptable level to deploy the parachutes. The parachute
mortar fires and deploys a small parachute, which pulls off the back
cover. The back cover pulls off and pulls out the main parachute on a
strap. You can't see the strap in the movie, but the main parachute is
about 8.3 meters across and it does a supersonic deceleration of the
probe down to about 400 meters per second and about 15 minutes of the
early descent is done under the main parachute, the 8.3-meter parachute.

Next slide is page 39 is a schematic of descent event, the entry T0 is
what we call the trailing X detection where the parachute mortar fires;
a few seconds later, the parachute is fully inflated. It pulls off the
back cover, which is also separated by pyros and this in turn pulls out
the main parachute on it. Parachute inflation is within about five
seconds. After the main parachute has done its job, the heat shield is
cutaway and then, the transmitters turn on and we start data
transmission to Cassini.

Of course, we won't know anything on Earth at this time. Cassini is
pointed away from the Earth and at Titan to collect the data, so we have
a very long baseline interferometry program on the Earth, VLBI program,
where a lot of radio telescopes will be looking at Titan trying to
detect Huygens carrier. We won\'t be able to see any dates or get any
dates right of the signal because it\'s so faint. We\'re talking about
20 watts of transmission power over a billion miles here, but we should
be able to see the carrier. So there are lot of happy people when that
lonely spike comes up on Spectrum Analyzer in the VLBI stations.

After 15 minutes of main shoots released and the stabilizing drone comes
out, it's a smaller parachute because Titan\'s atmosphere is so thick
and thickens up so quickly during descent that we would never reach the
surface in time with the battery power that we have if we stay them to
the main shoot. So this is a small one to make sure we hit the surface,
while we still have some battery power.

It's probably worth mentioning at the stage as well when we did battery
depassivation; all the batteries were in perfect health. Before
September, depassivation one, we haven\'t really looked at the batteries
and we didn\'t know if we had possible contingencies of one or two
batteries having failed after that long storage period, but they were
absolutely perfect. So now we have enough battery power to survive
possibly long after Cassini goes over the horizon on Titan, we may be
transmitting data for two hours on the surface. So that\'s very good
news and far beyond the expectations we had, which was three minutes on
the surface and possibly an extended mission of 15 minutes.

So page 40 is a little MPEG of how the aerosol collector and pyrolizer
works. I want to tell you a little bit more about the instruments now.
If you stop the movie, you will see ACP when we come into the
atmosphere, it\'s covered, it\'s blown off. The gate valve pulls back, a
filter is pushed into the aperture and a pump starts which pumps the
aerosol laden atmosphere through the filter and the filter collects the
aerosol and condensates that pull back into the oven, the gate valve
closes, the oven turns on, pyrolizes the contents of the filter and then
it's flushed with nitrogen; a valve is open and it goes off to the gas
chromatograph mass spectrometer and the gas chromatograph mass
spectrometer analyzes the constituents of the aerosol in between doing
its own job of directly analyzing the atmosphere without any pyralisis.

Okay, 41 just tells you about DCMS.

On page 42, the descent image or inspect for radiometer. There\'s a
little over photograph over there. You can see on the right-hand side,
three sensor heads; one pointing to pieces of black cylinders, one
pointing directly down, pointing at a 45 degrees and one pointing out to
the horizon and this will take the three constituents of the DISR image
at those three angles. The upward pointing cylinder pointing out within
about 45 degrees is the sun sensor, which gives Huygens a sun pulse
during its rotation because it\'s rotating on the way down. And you\'re
getting this all the way around the horizon panorama and that sun pulse
gives a reference on how to reconstruct the images and the timing of the
image-taking as the instrument rotates.

There\'s a large lamp on the bottom left and this will be turned on
about 200 to 300 meters above the surface, so that some surface spectra
can be taken. This isn\'t just an imaging instrument. It also takes
spectra, so we\'ll be able to infer some surface composition from the
spectra that are taken.

On the next page, 43, I\'ve given you three DISR triplets, which are
composed from the direct downward looking the 45-degree down looking
camera and the one out to the side and you can see how the circle
triplets are matched up. These images, of course, not Titan, I think
this was taken during a flight test over Arizona. DISR is managed out of
the Lunar & Planetary lab at University of Arizona and these are from a
flight test. So you can imagine what sort of wonderful images we\'re
going to get of Titan with test images like this.

Also, the atmospheric structure instruments directly measures the
physical and electrical properties of Titan\'s atmosphere. There\'s an
accelerometer, so we can tell when the acceleration and parachutes
swing, pressure and temperature senses and electrical properties
measurements. The little booms you see at the side of Huygens are the
\[HASI\].booms to measure the electrical properties.

The Doppler wind experiment is half on the probe and half on Cassini
that uses the properties of the carrier radio signals from the probe
received by an ultra-stable oscillator as part of the probe package that
remains on Cassini and from the Doppler, there's going to be significant
Doppler from the wind on the way down and from the Doppler they can
infer what the winds look like. That\'s very important.

There\'s another movie there of Huygens descent. I\'m not going to play
that one right now. I just wanted you guys to have it as presentation
material.

Surface impact: On page 46, you can see some images that were taken
during the Earth bound test of the probe descent. This particular set
were done in Karoon or in Sweden up in the north and it was a full test
of the probe from the balloon drop to see what does the descent sequence
looks like and, of course, what the landing looks like. You can see
Huygens very much as we hope it will look on the surface of Titans, a
slight tilt there. I hope that tilt is towards Cassini not away from it,
so our radio signal is good. We also did a lot of balloon drop test in
Sicily and in Brazil. It's tough to get clear airspace to do this kind
of thing because Huygens is plummeting down fairly quickly, but there
are extensive flight tests done that are a lot of fun and very exciting.

(Audio interference)

Let\'s talk about the Surface Science... Thank you. That\'s good.
Surface Science Package, yes. Surface Science Package is the primary
instrument to understanding the nature of the landing site. It\'s also
operational on the way down through the atmosphere and has a tiltmeter
that can measure parachute swing and speed assigned to different
altitudes, acoustic sounder to infer the condensation of methane
droplets and the bumpiness of terrain on approach and possibly the
depths of any liquid and also capability to measure the index of
refraction and density of liquid. So, a short carbon fiber sticking out
the bottom of the probe will be the first part of Huygens to strike the
surface and this will detect the force of impact and the surface
properties whether it\'s crunchy, solid, gooey, liquid, whatever it is.

Trina Is that where the microphone is?

Shaun No. The microphone is on HASI, the Huygens Atmospheric Structure
Instrument, and although there\'s a lot of collaboration between the two
instruments, it doesn\'t have any connection with SSP. As Trina was
saying, HASI has a microphone on board which will record the sounds of
Titan as we descend. And as a special program with The Planetary
Society, we\'re trying to get the sounds on the way down processed and
released very, very early, so that people can hear the sounds of Titan
just after descent. That\'s being coordinated by The Planetary Society
and that\'s going to be a pretty interesting outreach opportunity.

Page 48, look at the sensors inside SSP, force transfuser for the impact
signature, acoustic sonar, parallel play capacity test the permittivity
and conductivity of the surface and refractometer and temperature probe
and, of course, the tilt-meter, so we\'ll know more about parachute
swing and the dynamics of the probe under the parachute during the
descent and also what angle we land at.

The tiltmeter, this is slide number 49 entitled wave dynamics and we
start this up. We can also see how the tilt-meter will be used if we
land on a liquid. You can see the probe bobbing around there and you can
learn a lot about the properties of the liquid from looking at the wave
dynamics. So that will be an exciting opportunity, and of course, we all
hope that we land on liquid, but we\'re ready for other properties as
well.

Next slide, other landing scenarios. Well, one is, the first one that we
may land on liquid and you see Huygens washing up on a beach there. The
second one is that we\'ll land on something gooey, some kind of
hydrocarbon sludge. We don\'t know what, but it will be a softer
landing. And the third one is, of course, landing on a harder surface,
which as I said, Huygens isn\'t absolutely designed to be able to
survive, but there\'s a very good chance that it will.

But, I\'ve left out one of the landing scenarios. Christian Huygens told
us that there maybe trees on Titan. If you go to the next slide, number
51, this is my favorite. You can see Huygens hung up in one of Christian
Huygen\'s trees with the DSIR lamp just shining down there on the
surface from a distance of one meter. So that\'s another one that we may
hope for.

I want to tell you about the timing of the playback data on the 14^th^.
The orbiter is completely out of contact with the Earth during the
descent. It listens to Huygens, listens for Huygens until it goes over
the horizon and then turns back to Earth. Then when the orbiter turns
back, we\'ll get a short piece of engineering telemetry telling that the
orbiter is okay but immediately we\'ll get the playback data back with
all the recorded Huygens data.

So, I want to emphasize that apart from VLBI measurements that we\'re
getting to from Earth bound to the carrier and some real-time optical
observations from Earth that are looking for the flash as Huygens
enters, we don\'t get any real-time data from Huygens. And I want to
explain to you guys how the playback works.

The descent time is, as I said, 135 plus/minus 15 minutes more or less.
The data is relayed to orbiter on two channels over four hours and 26
minutes, the orbiter listens for two hours before this, though. We
wanted to make sure that we point on Titan in time to collect the data
clearly. So we\'re looking two hours beforehand, so there\'s going to be
two hours of nothing recorded and then up to four hours and 26 minutes
of probe data before the probe goes over the horizon.

The orbiter points to the predicted landing site, it records everything,
all the other RF on the orbiter is turned off to make sure that we get
the data without interference. At 13:44:17 UTC spacecraft event time,
the orbiter will stop collecting probe data and begin its turn back to
Earth. So, seconds after begins its turn, it will lose the link with the
probe, but it would anyway because it's going over the horizon.

The first playback data will be received at 15:21 Earth receive time.
This is ground time UTC on the 14^th^ of January minutes after the
Orbiter turns back, so that is the beginning of the playback. So what
will be played back first is the first part of the orbiter listening
period which is zero. It\'s looking at the probe landing site, waiting
for the probe to be there.

The probe at that point still on its way to Titan, so there will be
about two hours of no data until the probe starts entering. So, the
first data from the probe will appear in the playback at about 16:15
Earth receive time, that\'s not on here, but that\'s our estimate of
when we\'ll see the first probe data in the playback.

The first absolutely complete data set will be ready for off-line query
in our data system at 20:11 Earth receive time. If there are no playback
problems due to weather or other playback problems or gaps in the data.
So, this is the very best we can expect playing the data back at the
very highest rate we can sustain during that period. And of course,
after that, the scientists who will be sitting at the European Space
Operation Center in Darmstadt will be furiously pouring over the data
trying to analyze it. So we\'re not able to do a real-time thing here
with this data. We won\'t be able to see the images played back as they
were to some of the Titan encounters.

Let me tell you about image data availability. While we\'re playing
back, we\'re not just going to play it back once, of course, we\'re
going to be playing this data back multiple times over two days. So with
any luck, you\'ll be able to get results from the first part of the
playback, the very early playback, but if there\'s a thunder storm in
Madrid and we can't get the data down from the Madrid DSN station.
We\'ll pick it up over Goldstern or Canberra, so multiple playbacks to
avoid problems in the system.

Individual raw images will be available immediately the scientists get
the playback, so that immediately means within about one hour. And then,
these images are kind of postage stamp size DISR images of the nature
that you saw in that slide entitled "DISR Triplets." The individual
sharpened images will be available after several hours and sharpened
triplets, which of the three cameras put together will be available
after several plus two hours. This is how the instrument team put it to
me, so this is the best estimate we have.

Panoramas are when the triplets all stitched together, so that you see a
complete cycle of Huygens spin for a given altitude and this takes a
long time to do because you imagine, Huygens is spinning and swaying
under the parachute, and although the triplets are matched up with the
\[sun poles?\] to stick the panoramas together is a lot more difficult.
So these preliminary panoramas will be available after about one day.

Refined solutions after two days and the final panoramas won\'t be
allowable into after about six months, but we will have a lot to see the
day of Huygens descent.

Okay. Well, that\'s the end of my talk. I didn\'t take up anywhere near
as much time as I thought I would, but I\'ll be very happy to try and
answer any questions you may have.

Steve I\'ve got one. This is Steve Lee in Denver. Will the descent
imager, if Huygens survives to the surface, will it be able to take
images while it\'s on the surface?

Shaun It will. I\'m not sure of the DISR work cycle. I know they\'re
taking more spectra near the surfaces they descend, but I don\'t exactly
know if they are going to be taking images around that time because,
obviously, the downward looking and 45-degree looking cameras won\'t be
much good. So I can get back to you with exactly what the work cycle is
but I\'ll have to do it off-line**. \[DISR Work cycle\]**

Steve Okay. Thanks.

Bob Shaun, you mentioned 20 watts of signal power between Huygens and
Cassini. Do you happen to know what the signal strength is between
Cassini and Earth?

Shaun No. \[Signal strength between Cassini and Earth\]

Trina I should know that, but I don\'t have it off the top of my head.

Bob I assume it's going to be a whole lot more powerful than 20 watts.

Shaun I can't tell you that. We can answer that question, we\'ll have to
do that on off-line as well, but initial playback rate to Cassini when
it points to Earth over a 70-meter station 66 kilobits, and when we get
to a better elevation station, Madrid or Goldstone, we\'re playing back
at 144k. So that implies a pretty good signal strength, but I\'ll have
to answer your question off-line. What was your name please?

Bob It\'s Bob. Last name is Polcyn, P as in Peter; O-L-C-Y-N as in
Nancy.

Trina And you know what we\'ll do, Bob, is we\'ll just send anything
like this. We\'ll just send it out to the whole group the same as the
invitation that went out.

Bob Great. Yes. Thank you.

Trina And the power of high-gain antenna should actually be a lot less
because the most important quality is distance and the distance between
the Cassini orbiter and the Huygens probe when the link is happening is
only about 70,000 kilometers. The distance between the Cassini
spacecraft and the Earth, of course, is 10 AU, so it\'s one AU is about
93 million, so it\'s a billion kilometers. So it\'s actually quite a bit
less than the strength between the probe and the Orbiter.

Shaun Quite apart from the direct transmit power, Cassini also have this
wonderful high-gain antenna. But, of course, Huygens has these two
dipoles. So, Cassini is in a big advantage, no matter what the transmit
power with its huge high-gain antenna.

Greg This is Greg Donahue, Solar System Ambassador from Seattle. A
couple of questions about the atmosphere. I think I recently heard that
the atmosphere extended out a little bit farther than we thought. Is
that going to have any effect on Huygens in terms of its descent time or
anything at all?

Shaun Well, yes. We did take a look at that. Of course, the beginning of
the EDL sequence won\'t be affected because we turn on so far out and
there\'s considerable slop in that. So it won\'t affect EDL, but it will
conceivably effect the descent time. We said 135 minutes plus/minus 15,
depending on which of my slides you look at here, but I\'ve seen
estimates as long as 156. So, we\'ll have to see. We\'re going there to
find out. So it won\'t really have any negative effect on the Huygens
mission, 156 is a lot longer that we had anticipated, but we\'re well
able to operate with that.

Greg Okay. And then one terminology you\'ve got to know is the SCET for
time. What does that mean?

Shaun SCET means Space Craft Events Time, and here we\'re trying to
distinguish between the time you see the time and event occurs on the
spacecraft and the time you would see information from that event on the
ground. It takes a signal of the time of the Huygens mission; it takes a
radio signal one hour and seven minutes to get from Cassini to Earth. So
if something happens at 12:00 spacecraft event time on Cassini, you
don\'t see it on the ground until 1:07 Earth Receive Time. And the other
acronym I\'ve used in there is ERT, Earth Receive Time and that is the
hour and seven minutes later when we see it on the ground.

Greg Okay. Thank you very much.

Shaun Sure.

Trina And when Shaun says Earth Receive Time, he is using the time zone
of England, Greenwich time.

Greg UTC, okay.

Shaun It\'s not because I\'m English; it\'s because we do all of our
calculations in UTC. There\'s just huge potential for confusion. So
nothing you hear me say is ever in any local time; it's always in UTC
and I will specify spacecraft event time, Earth Receive Time or
sometimes more rarely Earth transmission time if we're sending something
up to Cassini.

Ken Okay. This is Ken in North Carolina. I\'ve got a couple of questions
about the link between Cassini and Huygens. Our first question is
approximately what percent of the data is going to be uplink to Cassini
before the probe lands?

Shaun Nearly all of it. I can\'t give you a percentage, but I can tell
you time probably. Huygens is an atmospheric sounder. It\'s not really a
lander. It will land and we hope to do some measurements, and very
important measurements they are, but most of the Huygens mission takes
place between entry and landing.

> So if I used one of my estimates here of 135 minutes descent time, the
> nominal time on the surface, so you\'ve got a 135 minutes of in-flight
> atmospheric data. The nominal is three minutes on the surface and the
> maximum we anticipated in mission design is 15 minutes on the surface.
> Now, we think we\'ll be able to do up to two hours because the
> batteries work so well if Huygens last that long. But I can\'t do
> those percentages for you, but it\'s less than---it's very significant
> science, but it\'s a very small proportion of it if you look at the
> time.

Ken And the follow-on, are there any plans for the radio telescopes that
are Earth-based to do any interferometry to try and pull in Huygens
signal, even though it's very weak.

Shaun Yes, absolutely. There\'s a Very Long Baseline Interferometry
program, VLBI, being managed by the joint institute for VLBI in Europe,
that's in the Netherlands and they\'re using parks. I can possibly reel
off all the antennas they\'re using, but they're using parks in Green
Bank. They\'re also using a lot of Chinese Antenna \<break in audio\> a
very big program. If you look at the geometry of it, the probe is kind
of entering over Hawaii and then the landing takes place over Indonesia,
if you think of the earth rotation. So, there is a huge collection of
the huge collaborative effort, the joint institute for VLBI has
organized and it will be a pretty exciting result.

Ken Thank you.

Trina Probably to be clear, Shaun, you don\'t expect to be able to get
any data from that. You\'re just looking for the carriers.

Shaun That\'s right. It will take all those telescopes, just to look at
the carrier. We absolutely will not get any date out of that signal.

Trina Sort of a follow-on to that also this flash as it enters the
atmosphere. Are there several telescopes, including Hawaii and local
here to southern California that are going to be looking for the flash?

Shaun Yes. Huygens experiences a megawatt per square meter during entry,
and there will be a huge amount of energy over that short three-minute
period. A lot of it expanded at the peak, so there should be some scope
for optical observations and, certainly, some are planned, although
Trina probably knows more about the details of those than I do.

Trina Yes. There\'s a couple of groups that are taking a look at it and
they\'re just going to be recording the whole time to see if they can
see it. And that will be a nice sort of, well, the probe definitely went
in, and actually, we\'ll get that several hours before we get any data
for the probe because that\'s just literally a one in a lifetime from
the top of the entry. That\'s when all the heat is released in the
Huygens decent. So, you would get that and then you\'ll have the full
several hours of recording the probe and then spacecraft is going to
turn, and then like you said for a long time. So that will be hours
before we get any data but it will be a nice, warm fuzzy, maybe burning
hot fuzzy.

Greg This is Greg Donahue again. Just the descent time again we\'re
talking a couple of hours, plus or more. It just seems like a long time
to me to descent to the atmosphere. Is this the result of the increased
density of the atmosphere and do you have like an extra large chute, so
that this thing is drifting very slowly down or why such a long descent?

Shaun Huygens atmosphere is ends a long---are you comparing the descent
now to ...

Greg I'm just thinking of something like when Genesis came back or a
spacecraft, used capsule used to come back, it seemed like it would
20-30 minutes or something in the Earth\'s atmosphere and it just seems
like this is such a long descent time.

Shaun Yes. We\'re descending from a 165 kilometers into an atmosphere
that is thicker than Earth's, and the descent time was tuned to maximize
the science not to be fast. So, really, what you\'re looking at is, I
mean those parachutes, the main shoot have to be sized for the
supersonic deceleration but the drove shoot was sized to get us down to
the surface to exploit exactly the amount of battery power we thought we
would have.

Greg Okay.

Shaun Yes. And also, I should point out that the geometry of Huygens
mission has changed significantly over the past four years since the
radio receiver anomaly was discovered in 2000. We actually redesigned
the geometry between the probe and orbiter. So we\'re actually getting a
little bit more observation time from Cassini now, which is good.

> If we\'d known we\'d have this observation time originally, we may not
> have done it that way; but certainly in the original mission, Cassini
> was plowing in to tighten the very, very small closest approach
> outset. I think it was about 1,500 kilometers instead of 60,000, so
> the observation time is a lot less. Now we're 60,000 kilometers away,
> it\'s a relatively slow relative motion, so there\'s a lot more of the
> time.

Greg Thank you.

Lori This is Lori Danley, a question from New York. On your last slide,
you say the images are available one hour, two hours, so forth. I take
that means available on the ESA Web site. Is that right?

Shaun Yes.

Lori And on the press conference that happens at 11:00, I think it\'s
11:00 central European time I thought I saw, which is I think 5:00 a.m.
New York time. Are there going to be new results released at that time
that will not have been available on the Web site and can you say a few
words about that press conference what you expect to cover in that?

Shaun Well, I mean I can't answer that precisely. It really does depend
very much on how the data analysis goes. If everything goes normally,
then yes, then sure they\'ll have new results to talk about but it\'s
difficult for them to guarantee a timing on data release during a press
conference because it\'s so dependent on the data flow. So that\'s not a
very good answer to your question, but I can say of everything goes
normal, yes, they should have some new stuff to release. It also depends
on what the principal investigators want to say. I mean these guys very
much---they\'re in control of the data and they decide in near real-time
what it is they need to release.

Lori Thank you.

Trina I guess I had a question, Shaun. You mentioned that in the Science
Surface Package, there is a little device that sticks out that\'s going
to be the first thing that hits the surface of Titan, the first manmade
object to impact the moon in the Solar System. I thought I have seen in
previous things that the HASI instrument had things that stick out from
the spacecraft.

Shaun They do stick---HASI has two booms which are used for the
electrical properties measurements, but they stick out horizontally.
They don\'t stick down. And then some schematic of Huygens, there\'s a
schematic going around not like mine; but another one, a more colorful
one at the descent sequence and you see little legs sticking out of
Huygens like it has a little undercarriage. There are no legs sticking
out of Huygens. It just have the spin vanes, the fore dome and the
measurement cutouts in the fore dome.

Jim This is Jim Todd in Portland, Oregon. I\'ve got a question regarding
the slide 47 through 50. How will we know what kind of surface the
Huygen had actually landed on? I mean what can we tell if it's actually
water, liquid or hard surface? How can we really tell, based on the
landing.? What data are we looking for?

Shaun Okay. Well, starting just before we hit, we\'ll take surface
spectra, so that will give us some idea of the composition, and of
course, we\'ll have visual images. But when we actually hit, first of
all, you\'ll have the accelerometer, the little probe sticking out the
bottom of the Surface Science Package which will give you a force
against time measurement of that. So if you get a very short high-pulse,
you\'ll know it\'s something rocky or something solid. If you get no
pulse at all or a very small one, it will be liquid, and if you get a
sort of extended moderate force against time plot, you\'ll know that you
landed on something crunchy or slushy, so that\'s one way you\'ll know
the surface properties.

> Also, there are sensors to measure the refractive index of the liquid
> if you land on liquid or any translucent material if you land on that
> there is in the Surface Science Package. So, we\'ll know something
> about the transparency and optical properties of the surface, and
> clearly once a gain, if you land on rock or something sandy or opaque
> hydrocarbon material, you\'ll know that.
>
> Also, the tiltmeter, if you see a time history from the tiltmeter
> during landing of the probe moving around, you\'ll know you\'re on
> liquid. Whereas if it lands at a constant angle, you\'ll have to infer
> a slush or a solid surface. So it\'s a quite of complex array of
> instruments but they can put from measurements it makes, they can put
> together a pretty good image of what the surface properties are.

Jim Thank you.

Kevin Yes. This is Kevin in California. I had a question about the
descent imager. It seems looking at the, I guess you\'re slide 39, your
instruments started at T0 plus 10 seconds, and I assume that descent
image is part of that package. And then later, you\'re going to release
the front shield and the main shoots.

> I guess a two-part question is, one is can you give us an analogy as
> to how sensitive this camera. It seems to me that this must be
> incredibly low light conditions and how do you plan to deal with that.
> And then second is, do you think you will be able to see the shield or
> the shoot come off and gain any information from that?

Shaun The first part of your question the low light. The camera has
plenty of light to make the measurements it needs to because it was
designed with that sensitivity, so there are really no concerns about
that. The image that I showed you in the DISR Package on page 43, this
is what you see in representative Earth-like, but I\'ve also seen images
taken in dim rooms, giving testing and things like, so it really was
designed for the illumination conditions on Titan, no concerns there.

> The lamp on DISR that\'s activated in the surface, this isn\'t a flash
> because DISR needs extra light to make images near the surface. It\'s
> just to take spectra from this insulation from the surface materials.
> So, I hope that answers you first question. The second one about the
> shoot deployment, I don\'t know.

Trina If you gave that, it would just be very cool.

Shaun Yes. Once again, I have to apologize. I don\'t remember the work
cycles of these instruments. The work cycle all the way down from
instruments switch on has been very carefully worked out to optimize the
overall science, and DISR and all the instruments get different
priorities at different times; and I think the upper atmosphere, it\'s
probably a lower priority for DISR than some of the atmospheric sampling
instruments, so I\'m not absolutely sure about that but I can check for
you. \[Imaging of shoot deployment\]

Kevin Thanks.

Shaun So I have three off-line questions I need to answer so far: the
work cycle in the surface for Steve Lee.

Steve That\'s correct.

Shaun From Bob, the signal power from Cassini and something about the
link properties, and the possibility of imaging the heat shield or
shoot. Okay? Anymore questions?

Mike Yes. This is Mike Lucas in North Carolina. I have a question for
you---actually, two. As far as meaningful data is concerning the
atmospheric content structure and dynamics, will we have something
meaningful on the evening of the 14^th^ do you think?

Shaun I think so. It\'s so difficult for me to predict how the PI team
in Darmstadt are going to be able to handle their data and the timing of
the release. I doubt that they would even be able to predict it.

Mike Yes. This will be forthcoming for weeks even more.

Shaun Yes, exactly. I mean the Huygens PR would be analyzing the data
for years and it \'s always and issue for them for the science teams to
decide whether to release something immediately when they haven\'t had
time to properly analyze the data or if they wait for a few days and,
perhaps, be more accurate, but to lose the timing of it. We realize
it\'s a very timely event and people want data in real time, but it\'s a
judgment call on the part of the science teams how they choose to
release it.

Mike Okay. And the second question was I think you said originally, you
were expecting somewhere between three and 15 minutes of surface data
transmission provided that it provides the contact, and now, do I
understand you to say there could be as long as two hours of
transmission?

Shaun Yes, I did say that. The three minutes and the 15 minutes are the
original design time on the surface, that\'s in three minutes and the
possible extended mission time. There are two things going on that lead
me to suggest that they may be up to two hours, which is now the
official estimate. First of all, the batteries performed so well. The
batteries were manufactured put on board, they may never look at them
again until September, but we did have some flight spare batteries that
were stored on the non-optimal conditions at a warehouse in the European
Space Technology Center. And when we discharged the batteries, we got
fantastic performance, in fact, a little better than I have been
designed to. So the battery testing we\'ve done and state of the
batteries just we see them on the probe during de-passivation activities
in September and on the 5^th^ of December that lead us to believe the
battery life is going to be more than we originally thought. That\'s the
first thing.

> The second thing is that Cassini is going to look at Huygens until
> Huygens disappears over the horizon. It\'s not going to give up and
> turn the way just because the original mission estimate was 15 minutes
> past landing. It\'s going to look for a heck of a long time. It\'s
> going to look for four hours and 26 minutes past entry. So certainly,
> if the batteries are healthy, Huygens will try and transmit data if
> they have been frozen by then because it\'s very cold on Titan. And if
> it's transmitting data, Cassini will be listening to pick it up. So
> we\'re very optimistic about this extended surface period.

Mike Well, very good. Thank you. Keep up the great work. This is really
exciting stuff.

Shaun Thank you.

Jim This is Jim Taw from Portland, Oregon, again I have another
question. Is there such thing as a safe mode where the Cassini is not
able to make contact with the Huygens probe, I don\'t recall there\'s
another Titan flyby for Cassini in a later date. They will try to
retrieve the date again from Huygen or is there such a thing at the
backup plan for this probe?

Shaun Since Huygens is a one-shot deal and it will only transmit data
for this period. So even if there was another Titan flyby, we\'ll never
be able to pick up the data, Huygens would be completely dead. There
will be other Titan flybys when we fly over, but we certainly won\'t be
listening to the Huygens signal. So your question is a very good one,
and we thought about it a lot in designing the Tc flyby.

> Certainly, Cassini does have safe modes to respond to a variety of
> failures on board and these result in a wide variety of responses,
> depending on the failure, and some of them can result in some pointing
> to try and reacquire attitude, some of them can result in Earth
> pointing and some of them can result in de-pointing for quite a long
> time. But during the probe mission, since it such an important one
> off, the Cassini is in a special mode called the critical sequence,
> and the sequence of commands will be executed with special regard to
> full protection and special regard to the attitude of the spacecraft.
>
> For instance, Cassini as it undergoes default during the period of
> probe mission, will never sun-point or Earth-point. It will always
> point with critical attitude, which is the landing site of the probe.
> So in the presence of any fault on Cassini, it will never the
> de-point. I won\'t run you through the rest of the full protection
> arrangements made during this period, but the critical sequence does
> ensure that just like the Saturn orbit insertion with the critical
> sequence that had to ensure that the Saturn orbit insertion maneuver
> went off. The probe relay critical sequence does ensure that Cassini
> does everything it can do to ensure the data is picked up.
>
> And this thing has been tested to death. I spent a good part of my
> life over the past three years verifying that it works under any
> anticipated fault conditions, and we\'re very confident that any fault
> Cassini sees in the probe relay period will still result in data
> acquisition from the probe.

Jim And second question, the optical picture they're standing back,
they\'re black and white, correct?

Shaun Yes.

Jim Okay. Thank you.

Anne This is Anne... in Abington, Pennsylvania.

Shaun Hello, Anne.

Anne Hello. I have a question about, if you are able to detect the
Huygens signal directly with the VLBI, these sorts of events---will NASA
TV be picking up any---or giving a press conference to relay to us as
this is happening or how can we know?

Shaun I don\'t know how real-time that will be. There are several
stations listening for a very, very faint signal, and they have to pick
the signal out of noise, it's so faint. So I don\'t know if they\'re
going to see a spike on a spectrum analyzer or if they\'re going to have
to send their data to the institute for analysis, and we\'ll able the
spike later after a month of analysis. It may be somewhere between the
two.

> So I\'m not sure how this information will be conveyed in real-time,
> but all of the data on Huygens is going to be produced out of
> Darmstadt from the Huygens probe operation center and the ESA Web
> site, so those will be the two places to tune in to. And certainly
> NASA TV will be echoing---will be getting the feed from ESOC. So I
> should think you\'ll see everything you will see either on one of
> those resources.

Anne Thank you.

Bill Hello. This is Bill in Wisconsin. Is there any consideration of
observing life or shrubs and trees in the mission?

Shaun No. That was just a joke.

Bill Yes. I know it was\...

Shaun There\'s no expectation to find any life on Titan. There\'s a lot
of expectation to find in very interesting organic chemistry on Titan,
but none of these is expected to be biological, and there\'s certainly
no special observations for that purpose. When I say organic chemistry,
I mean chemistry based on carbon compounds not necessarily associated
with life in any way.

Bill And there was some methane, too, that wouldn\'t have anything to do
with it either?

Shaun I\'m sorry, can you repeat your question?

Bill There\'s methane in the atmosphere, too?

Shaun Yes.

Bill But that is not an organic---that doesn\'t come from anything
organic?

Shaun It\'s an organic molecule because it contains carbon---organic
just means that it contains carbon, but this can be explained from
a---it\'s certainly not from biological sources.

Trina We don\'t actually know what the source of the methane is yet.
That\'s one of the key question that we\'re trying to answer. There
could be out gassing, sort of vulcanizism sort of kind of mechanism for
it, but no expectation that it\'s biological.

Bill Thanks very much.

Trina It's very cold on Titan.

Bill All right.

Trina Although, if it was not biological, that would be the front page
in the *New York Times*.

Bill Do you know whether the Cassini has reoriented its flight path, so
that it is no longer on collision course with Titan itself?

Shaun Yes, we do. The orbit of deflexion maneuver took place early this
morning and not only did it successfully take itself off a collision
course with Titan, so it\'s no longer going to hit the Titan. It is
setup perfectly for the right trajectory to collect the probe data. This
is a 60,000 km flyby. So yes, the orbiter is definitely safe.

Bill Thank you.

Trina Any other questions?

Ken Yes. This is Ken in North Carolina. Is Cassini planning on making
any observations of Titan while it's flying by this time?

Shaun No. All of the instruments are off as is most to the RF
during---all of the RF on Cassini during the flyby because we want to
obviate any interference from any source during probe data reception.
The only exceptions to that is that the magnetometer will be on in---it
will be on and muted, and the Visual Infrared Mapping Spectrometer will
be on in sleep mode and muted for engineering reasons, but there will be
no observations.

Trina Will the magnetometer be able to tell you whether or not Titan was
inside of that magnetosphere or not?

Shaun It\'s in snapshot mode, but I don\'t know what implications that
has on its science data collection. It certainly is of a lot of
interest, but I don\'t know what snapshot mode implies.

Trina Yes. The two-time of flybys we had so far, TA and TB, we've
transitioned just between being inside the solar wind and being inside
the magnetosphere of Saturn just within hours or days of the Titan
flyby, so it really could go either way.

Shaun It's worth pointing out that the probe sends back a tremendous
amount of data and we\'re not feeling up Cassini\'s solid state
recorders with the data, but that\'s not that much space left over for
other science data collection. So, no, certainly the plans are not to do
anything.

Trina Any other questions? Okay. This is great. Shaun, thank you very
much. We really appreciate you\'re taking the time today. We know
you\'re pretty busy and probably pretty tired after the last week, and
we really appreciate it.

Shaun It\'s a pleasure. I\'m very happy to help and I'll get these three
questions that I couldn\'t answer on line off to you as soon as I can.

M Thank you.

Shaun Thanks very much.

Trina Thank you.

M Thanks a lot.