Cassini Engineering Is Ready for Enceladus!

Todd BarberTodd Barber

Cassini Lead Propulsion Engineer (bio)


Greetings from the engineering side of the Cassini mission to Saturn on this auspicious date, 8/8/08!  As most folks on the third rock from the Sun turn their attention toward China and the Summer Olympics, Cassini scientists and engineers at JPL are turning their gaze skyward for some Winter Olympics of our own at Enceladus.  As Amanda so eloquently posted in her blog entry, this is truly an exciting time for the mission.  We are a mere three days away from a daring pass near Enceldaus’ tumultuous south pole, peppered with fractures called “tiger stripes” and active ice volcanism!  Though we’ve been to Enceladus a few times before, every encounter is a new adventure, allowing each science instrument its time to shine.


E3 is March flyby and E4 is August flyby.

Image left: E3 is March flyby and E4 is August flyby. 


Before any science results may be achieved, though, we have to make sure the spacecraft is on course for a truly close approach to Enceladus.  Next Monday, Cassini will zip over this icy orb within 50 kilometers (30 miles), a close shave indeed considering Enceladus is roughly 1.5 billion kilometers (900 million miles) from Earth.  From the spacecraft engineering and navigation teams, I’m happy to report our final E4 flyby approach maneuver, OTM-163, was canceled yesterday afternoon.  These cancellation-decision meetings are always very interesting, representing a wonderful example of the collaborative efforts required of our scientists and engineers.  It turns out we could have performed OTM-163 today (i.e., it was large enough to execute), and we know where the spacecraft is very precisely.  The “tall tent pole” in the process turned out to be our uncertainties in the position of Enceladus itself, rendering the tiny maneuver superfluous!  Naturally, our understanding of Enceladus’ position will improve after Monday’s close flyby, but I thought it was quite interesting that we know where our (relatively) small spacecraft is better than we know the position of this moon of Saturn.  Among countless scientific reasons, this is another incentive for close flybys of moons like icy Enceladus.


Perhaps I could have predicted this maneuver would get canceled, given its cushy positioning on a regular working Friday, during prime shift.  Why aren’t the off-shift, holiday, and weekend maneuvers afforded the same cancellation probability, statistically?   I’m sure this perception of mine is incorrect, but no matter, because the important point is we’re on course for Enceladus.  Our engineering and navigation teams are happy and excited, and scientists are about to enjoy another thrilling encounter with this most perplexing of Saturn’s moons.





Prepare to be Amazed!

Carolyn PorcoCarolyn Porco

Cassini Imaging Team Leader


So here we are, getting ready to bear down … again … on one of the most remarkable places in the solar system. Only this time, our encounter with Enceladus could be the best of them all for us imaging scientists, who are hoping to peer deep into the fractures at the surface sources of Enceladus’ spectacular jets. (see image below and read more about it here.)


In fact, there have only been a few times during this whole mission when I was more anxious and sleepless with anticipation than I am now:  on approach to Saturn and waiting for the first sighting of landforms on the surface of Titan, anticipating the Saturn Orbit Insertion imaging sequence and wondering what the finest looks we would have of the rings might show us, and waiting for the first close-up high-phase image of the Enceladus jets around Thanksgiving 2005 … the image that has been seared into the minds of all of us.


This upcoming flyby holds that kind of fascination for me, because we have the chance of seeing those very special locales on the tiger stripe fractures that we now know are active, warm eruption vents and because of the daring targeting technique of `skeet shooting’ that has been employed to make it happen.  Estimates of the tidal stresses across the south polar region indicate that over the course of an Enceladus’ orbit, the vents could open by as much as 1/2 meter (about 2 feet). We won’t see such openings even in our highest resolution images, but maybe … just maybe … we might see other evidence of eruption, either something geologically unusual or banks of snow where icy particles in the jets fall back to the ground. Whatever we see, this will definitely be a first and very unusual event. We all are so very privileged to be here, alive, now, and living the dream of so many who came before us   …. to fly, to explore, to learn.


sout pole of Enceladus, stars indicate vent locationsI will say what I said four years ago as we were first entering the Saturn system and about to begin our explorations of this mysterious and far-away place … a time that now seems like a lifetime ago:  Prepare to be amazed!


Image left: Heat radiating from the entire length of 150 kilometer (95 mile)-long fractures is seen in this best-yet heat map of the active south polar region of Saturn’s ice moon Enceladus. The stars indicate the location of vents. More about the image 

Enceladus News Conference – Wednesday,March 26

Carolina MartinezCarolina Martinez, JPL News Team


There will be an Enceladus news conference at NASA headquarters in Washington at 11 a.m. PDT (2 p.m. EDT), Wednesday, March 26.  New results from the March 12 flyby will be presented.


For live streaming of NASA TV, visit:


Participants in the news conference will be:

Hunter Waite

– Hunter Waite, Southwest Research Institute, San Antonio–principal investigator,

  Ion and Neutral Mass Spectrometer

John Spencer

– John Spencer, Southwest Research Institute, Boulder, Colo.–co-investigator,

  Composite Infrared Spectrometer

Larry Esposito

– Larry Esposito, University of Colorado, Boulder, Colo.–principal investigator,

  Ultraviolet Imaging Spectrograph



Spilling the Beans

John SpencerJohn Spencer, Cassini Scientist on the Composite Infrared Spectrometer (bio)

Well, now it can be told!  It’s frustrating for me to sit on exciting
new results – when we’ve found something cool in our data I want to
tell everyone all about it right away.  But it’s important to present
mission results in a coherent and coordinated way, and of course we
have to take the time to be sure we have our facts straight.  So
we’ve waited till today, Wednesday 26th March, 2 weeks after the
close Enceladus flyby, to spill the beans.

The days after the Wednesday March 12th Enceladus flyby were a blur
of frenzied activity for me as I worked to find the goodies in the
tens of megabytes of data that Cassini’s Composite Infrared
Spectrometer (CIRS) instrument had gathered during the flyby.  My
first peek at the uncalibrated data the next day, on Thursday
afternoon, was already thrilling – the glow of the tiger stripes was
visible not just at the usual 9 – 16 micron wavelength range where
we’d seen them before, but at wavelengths as short as 7 microns.  
Shorter wavelengths mean hotter temperatures (in the same way that
white-hot is hotter than red-hot), so it looked like the fractures
might be warmer than we had thought.  By the time I got all the files
I needed for the full analysis, from CIRS’s home at the Goddard
Spaceflight Center, it was time for dinner.  Precious ones and zeros
that had been flying through the Saturn system onboard Cassini 24
hours earlier, and squirted overnight across the solar system at the
speed of light, made the final leg of their journey to analysis by
bicycle, as I cycled home with my laptop.

After dinner I got comfortable on the sofa and dived in.  By bedtime
I had a preliminary map of the heat radiation from the south pole, at
four times the resolution of our previous best map.  Each of the four
tiger stripe fractures, clearly resolved in the thermal infrared for
the first time, lit up with the bright glow of internal heat.  A
couple of other fractures, not previously suspected to be active,
were warm too.  By Friday afternoon I also had preliminary
temperature estimates for the fractures- yes, they were pretty warm,
at least 180 Kelvin!  That’s -135 Fahrenheit, which isn’t exactly
toasty until you consider that the surrounding terrain is at around
65 Kelvin or -342 Fahrenheit.  The highest temperatures we’d seen on
the previous flyby in July 2005 were much lower, around 145 Kelvin
(-198 Fahrenheit)- not because Enceladus’s fractures were cooler
then, but because the older, more distant, scans were less
sensitive.  If it’s 180 K on the surface it must be even warmer down
below, perhaps approaching the magic number of 273 Kelvin or +32
Fahrenheit, where Enceladus’ ubiquitous ice can melt to form the holy
grail of astrobiology, liquid water.

Since that initial frenzy I’ve been checking calibration and refining
details, preparing graphics for today’s press briefing, and hearing
by e-mail and telecons about all the great data that was gathered by
the rest of Cassini’s arsenal of science instruments during the
flyby, some of which will be revealed by Hunter Waite at today’s
telecon.  We’ve also been modifying plans for upcoming flybys based
on the new data- we now know the hottest and most interesting parts
of the south polar region and can zero in on them next time.  Already
the theoretically-inclined members of the Cassini science team are
honing their models of the south polar plumes based on the new
findings, and the rest of the planetary science community will soon
be following suit.  And this is just the beginning- there are seven
more Enceladus flybys to come in the next two years.

I’ll end this blog with a big thank you to the rest of the CIRS
team.  I’ve been doing the fun job of analyzing these data, but there
would be no CIRS data to analyze without the tireless efforts of the
many folks at Goddard Spaceflight Center who designed and built CIRS
back in the 1990s, keep it running, design the observations, and
calibrate the data.  Special thanks are due to my CIRS colleagues
John Pearl and Marcia Segura, and CIRS Principal Investigator Mike

Culling Through It All!

Linda SpilkerLinda Spilker, Cassini Deputy Project Scientist
It’s been a whirlwind here at JPL as the data from the Enceladus flyby comes pouring in, and we scientists have been doing our thing . . . culling through it all! Sometimes there’s so much to choose from that I feel like a kid in a candy story.  There is much excited email chatter among the many Cassini teams, all suggesting awesome findings.  These first-looks are being matured by the team members, and we have begun to share and compare results. 

You may have already seen the press release from JPL explaining that the
Cosmic Dust Analyzer (CDA) had an unfortunate software hiccup at closest approach to Enceladus and their data was not recorded. The CDA instrument measures the composition of small particles that hit the instrument, which is an important thing to do at Enceladus to understand its geyser-like jets.  But like all small bumps on the road to discovery, we will find out what happened, fix it and get on with our business about the Saturn system.  And what an amazing system it is. 
On the very bright side, all of the other fields and particles instruments and remote sensing instruments, worked perfectly at Enceladus.  They are returning fantastic data and providing an incredible look around and inside the plume, and of the surface.  The fields and particles instruments are complementary to CDA and provide information on particle composition and characteristics, among other things.   
As soon as possible in the week or two ahead, we will be able to announce the preliminary results to the world.  Until then, I’m waiting like the rest of you are for these data sets to be analyzed, since the first-looks are looking so great!  Stay tuned for some Earth-shaking — I mean moon-shaking — results!

A First Peek at the Data

John SpencerJohn Spencer, Cassini Scientist on the Composite Infrared Spectrometer (bio

Yesterday was a long day of waiting for our Composite Infrared
Spectrometer (CIRS) data from Wednesday’s Enceladus flyby.  CIRS’s
most important job on this encounter was to map the temperatures in
the active south polar region, to learn more about what warms the
“tiger stripe” fractures and measure the total amount of heat that
Enceladus is generating (the current estimate, based on earlier CIRS
data, is a whopping 6 GigaWatts).  Before I and others could do much
with the new data, they had to be calibrated, and calibration of CIRS
data, which is done by the CIRS team at Goddard Spaceflight Center in
Maryland, is pretty complicated.  It turned out there were some
hiccups in the calibration process, and though the team was working
as fast as they could, everything took longer than expected.

So all through the morning I was reading excited e-mails from members
of other instrument teams, enthusiastically describing their first
look at their data, without being able to contribute any news from
CIRS.  I *did* copy over some files early in the day, but when I
learned that they were only partially calibrated, I decided to wait
for the good stuff – I concentrated on getting my software ready instead.

Marcia Segura at Goddard, who did the detailed designs for these
observations, kept me posted on the progress of the work at Goddard,
and by mid-afternoon it looked like the final calibration was still a
couple of hours away.   So I broke down and took a quick-and-dirty
look at the preliminary files I’d downloaded in the morning.  And
they showed …  well, I can’t tell you, because we still need to
properly calibrate and check everything, and make sure we don’t
announce any results that turn out to be wrong on closer inspection.
But I’m pretty happy with what I saw, and we (and the other
instrument teams) hope to have some cool findings to release in the
next few weeks.

Greetings From Houston

Amanda HendrixAmanda Hendrix, Cassini Scientist on the Ultraviolet Imaging Spectrograph

So here I am in Houston at the Lunar and Planetary Science Conference (aka LPSC). It’s Tuesday morning and yesterday was an interesting day, filled mainly with results from the first MESSENGER flyby of Mercury. Thursday afternoon there’s a session dedicated to Enceladus with talks on topics such as the possibility of a near-surface ocean, frictional heating, and crater chains. So I’ll be yawning my way through that session — not that it won’t be interesting, but I’m planning to stay up most of Wednesday night to watch my science data come in from tomorrow’s exciting Enceladus flyby! I’m super excited about it, and crossing my fingers that everything goes as planned.  Also, tomorrow at noon, Alan Stern (Associate Administrator of the Science Mission Directorate at NASA HQ) will give a talk — I’m hoping he’ll mention the Enceladus flyby!

More soon from LPSC …


Waiting for Hidden Treasures

Linda SpilkerLinda Spilker, Cassini Deputy Project Scientist

I just got the good news that the playback has ended.  Now for the fun part!   I am eagerly waiting to see what new discoveries are buried in the bits streaming back from Cassini.

All sorts of questions are running through my head.  I wonder if the Ion and Neutral Mass Spectrometer (INMS) will find more exotic hydrocarbons in the gases it samples deeper in Enceladus’ geysers.  Will the magnetometer find an induced magnetic field that points to an ocean just under Enceladus’ crust?  If there is a water ocean, what are the chances that life might exist in it?

As a Composite Infrared Spectrometer (CIRS) co-investigator, I am especially interested in the new thermal maps of the south polar region.  I am eager to find out if any of the hot spots that our instrument saw back in July 2005 disappeared or if any new hot spots appeared, indicating that the geysers might change locations.  Given the golden opportunity to observe Enceladus up close during an eclipse, I wonder how quickly the surface of Enceladus warms up once sunlight hits it again.  With Enceladus’ fluffy surface, will it warm up faster than any other moon circling Saturn?
You’d think that being a veteran of icy satellite flybys this would be old hat for me by now, but each flyby is just as exciting as the one before it!


Amanda HendrixAmanda Hendrix, Cassini Scientist on the Ultraviolet Imaging Spectrograph (bio)

Well everyone, this is both exciting and a relief! — the flyby is over and we couldn’t have hoped for a smoother ride! I got word last night (during dinner!) that we had a signal from Cassini, which initially meant that the spacecraft hadn’t safed (always a good thing), and then the data started coming in.  Now, the downlink pass is over, the images are down, and they look wonderful!  I’m busy downloading and having a first look at the Ultraviolet Imaging Spectrograph data (thanks to Alain and crew for getting them into the database so quickly!).
Thanks so much to everyone out there for your support and great questions. We have more Enceladus flybys planned for later this year — here’s hoping they all go as nicely as this one. There’s a lot more to come!!
Amanda from Houston

A Great Day for Engineering

Todd BarberTodd Barber, Cassini Lead Propulsion Engineer (bio)

Hello again from the other side of Enceladus!  I’m happy to report that the engineering teams are very pleased this morning with this historic Enceladus flyby.  I attended a 9 am weekly meeting regarding engineering subsystem status, and all engineers reported a very nice flyby.  The team includes attitude control, command and data subsystem, power, propulsion, thermal, fault protection, and telecommunications engineers.  Our telecom guy brought in some nice pastries from his favorite European bakery to help celebrate another successful Cassini encounter.  Just before the meeting, I did manage to find five minutes to look at the latest Enceladus images from the flyby–they’re breathtaking!  Makes all of the hard work seem more than worthwhile.

We’d love to celebrate this engineering success, but as I mentioned in a prior blog, the show must go on.  We did open the main-engine cover successfully last night, which is vital for today’s main-engine maneuver.  Around 5:30 pm PDT, as seen on the third rock from the sun, Cassini will fire its main engine for about seventeen seconds.  So, as our science teams digest a treasure trove of new data, the engineering teams are looking forward to a thrilling Titan low-altitude flyby in a few weeks.  This friendly give-and-take between science and engineering isn’t always easy, but it’s truly wonderful how the teams support each other and pull off things that seem impossible.  I’m honored to be a part of this world-class team, and I thank you for your continued support of Cassini!