Cassini Calls Home!

Todd BarberTodd Barber

Cassini Lead Propulsion Engineer (bio)


Hello from the “flip” side of Enceladus!  I’m happy to report via this blog that the Deep Space Network in Canberra, Australia, locked onto Cassini’s radio signal around 9:03 p.m. PDT on Monday, Aug. 11. 


We’ve executed yet another successful flyby of Saturn’s ice-geyser moon!  Playback data has just begun streaming to our breathless scientists and engineers at JPL, and it will continue throughout the evening and into tomorrow morning.  With the rest of you, I’m pumped up for the raw (unprocessed) images that will be posted Tuesday morning, Pacific Time.  For the latest raw images, check here:


Cassini engineering may pay my bills, but Cassini science sparks my passions.


A few engineers are still here, working away this evening, making sure the spacecraft came through its scientific marathon unscathed.  I can’t speak for all these engineers, but I can tell you the propulsion subsystem is healthy and is ready for yet another Reaction Wheel Assembly (RWA) bias after midnight PDT.  Thankfully, this activity is fairly commonplace, so long before then I plan to be celebrating another engineering success with some Olympics viewing, perhaps an appropriate beverage, and an indefatigable smile.  It’s been a long day but oh so tremendous!  Now let the flood of Enceladus science data commence! 



Seeing The Images For The Very First Time

Bonnie BurattiBonnie J. Buratti  (bio)

Cassini Scientist on the Visual and Infrared Mapping Spectrometer 


What a way to start Cassini’s extended mission! On Tuesday afternoon (Aug. 12, 2008) about 50 scientists sat in the Spaceflight Operations Facility at JPL to view the images as they came down. 


I was as dumbfounded as anyone, but rapt in awe to be among a privileged group of humans to see another part of nature for the first time.  How fantastic that the public can share in this excitement through the raw image gallery .  Those few sublime moments were worth the many months of drudgery that went into planning these observations. Some of the views were of old familiar terrains, roads that we traveled many times. But many of the features revealed were new, and seeing them evoked the same level of astonishment I experienced at my first sight of the Grand Canyon or Niagara Falls. 



Image left: That’s me to the lower left of the image screen. My colleagues and I gathered to look at these raw images from Enceladus.


Inspiring as that first peek at new data was, I am now confronted with Thomas Edison’s cogent remark about the nature of discovery: it’s one percent inspiration and 90 percent perspiration. Much of the most important discoveries to come from this flyby will be squeezed out of the data over the coming days and weeks: teams of scientists poring over the measurements, analyzing, massaging, modeling, thinking, going up blind alleys – that is just the nature of research. It is also very much a team approach, with each member contributing from an area in which they are expert.


Jerry Jones, who heads the Cassini Navigation Team, told the assembled scientists yesterday that we came within one kilometer of our planned trajectory. Instead of a close approach of 50 km (30 miles), we came within 49 km of the surface of Enceladus. That Navigation Team is awesome! Imaging scientist Paul Helfenstein built a clever sequence at closest approach that was designed to place observations right on the hot tiger stripes, and which he nicknamed the “skeet shoot” (explained in Amanda’s first post).  The skeet shoot that was successfully executed on August 11 was equivalent to the clay pigeon being thrown into the air in New York, and the bullet being fired from Pasadena.  Good going, Paul.


How fortunate we are to have the spacecraft alive and well, with all systems and scientific instruments operating. What we saw at Enceladus represents just a small part of what we will learn over the coming years. There are six more targeted flybys of Enceladus coming up over the two years of the extended mission. There is still so much to learn about the ringed planet and its family of moons.  


The Perspective From an Airplane

Amanda HendrixAmanda Hendrix (bio)

Cassini scientist on the Ultraviolet Imaging Spectrograph


Well as luck would have it, much of my day yesterday was spent on an airplane flying to Baltimore for a non-Cassini-related meeting Wednesday and Thursday. I knew the data would be coming in while I was in the air and was excited to check it all out once I landed.  For most flybys, I am in front of my computer, watching the data come in real-time.  So I’m on the flight, and I’m working on some UVIS (Ultraviolet Imaging Spectrograph) Enceladus data from a past flyby that I think will be interesting to compare with the data from Monday’s flyby, and I’m gearing up for the new UVIS data, listening to my iPod (Sigur Ros, which is always nice n’ mellow for a flight) and I hear my name being shouted (above the music) and I look up and it’s Bob Pappalardo, who is sitting one row up across the aisle. He’s the Cassini Project Scientist for the Extended Mission and has been a colleague and good friend of mine for several years. I take out my ear buds and Bob is shouting at me that, just prior to taking off, he received an email from Carolyn Porco (Imaging Team Lead and fellow blogger) that she’d seen the first of the closest-approach images and her reaction was (an informal version of) “Golly!” That got me all excited and I took my laptop over to his row of seats and we checked out the playback table again to review which images were hitting the ground when. I told Bob, “The second we land you must fire up your remote internet access thing so we can get at those images!!”


close-up, raw image of Enceladus

Image left: Here’s an example of a raw image from Enceladus. Click here for the full image


Went back to my seat, experiencing the first waves of absolute thrill that I always get during these flybys, and happiness because I am so lucky to do this for a living! What fun.  I switched to something more upbeat than Sigur Ros … I’m thinking old school Oingo Boingo or maybe some MGMT. I’m excited to see these data!


And now it’s Wednesday morning and we’ve all seen the fabulous images. All the excitement was well-founded. Golly, indeed! I’m having fun digging through the UVIS data and we’ll see what they reveal about the south polar region. What an interesting, fascinating little world. What a surprising bit of insight into solar system processes! Thanks to Paul Helfenstein and the Imaging Team for their hard work on the closest-approach “skeet shoot” and mosaic, and to the entire Cassini spacecraft team for their diligence in making this flyby work so incredibly well!


Cheers from Baltimore,


How Hot Is Hot?

Bonnie BurattiBonnie J. Buratti (bio)

Cassini Scientist on the Visual and Infrared Mapping Spectrometer


Figure 1. The best Voyager 2 image of Enceladus, showing the heavily cratered terrain of the northern hemisphere. This image was obtained on Aug. 25, 1981, at a distance of 112,000 km (69, 500 miles).

When I was a graduate student at Cornell University, studying Enceladus with Voyager images, I had this sneaking suspicion that the little moon had active geysers, spewing fresh material into outer space. Why? Because Enceladus is so bright – this gleaming object reflects light as if it were covered in fresh, bright snow. No other body in the Solar System looks quite like it. Voyager never saw the plumes because it flew over the northern hemisphere of Enceladus (Figure 1). The plumes are on the south pole.

So you can imagine how exciting it is to be here at JPL, 27 years later, studying the intriguing surface of Enceladus and its plumes. This moon has literally been a life-long passion of mine. Every time Cassini encounters Enceladus, I feel as if I were right there, in my own personal observatory whizzing by the moon. This time, we are coming within 50 kilometers (30 miles) of the surface, and “all eyes” (cameras and spectrometers) onboard will be peering intently as the moon gets closer and closer.

Figure 2. The Visual Infrared Mapping Spectrometer under construction in a laboratory at JPL (it’s now orbiting Saturn!). The mass of VIMS is 37 kg (82 lbs) and its longest dimension is 78 cm (31 inches). It uses only 22 Watts of power.

I am a member of the Visual Infrared Mapping Spectrometer (VIMS, seen in Figure 2) team, led by Dr. Robert Brown of the University of Arizona. During the flyby, VIMS will be taking images of Enceladus in 356 wavelengths (colors) in the visible and infrared part of the spectrum. When we think of the infrared, we think of heat. One thing Cassini scientists don’t know yet is how hot the hottest parts of the tiger stripes are. If we could detect temperatures at or near the melting point of water, we would know for sure that there is liquid water – maybe even an ocean – under the surface of the moon. The Cassini Composite Infrared Mapping Spectrometer (CIRS) has detected and mapped the thermal energy around the tiger stripes.  During the past three targeted flybys, VIMS, which is only sensitive to much hotter temperatures than CIRS, didn’t detect any thermal energy. But the question now is: are we looking at a tiny area that is very hot, or at a larger area that is not so hot? With the much better spatial resolution attained during today’s flyby, VIMS may be able to observe small hot spots.

Another “hot” topic that interests our team is the presence of organic materials on Enceladus. The moon is almost pure water ice, but we think we found some light organics during our previous flybys. “Organics” are materials composed of hydrogen, carbon, oxygen, and nitrogen, the building blocks of life. With liquid water and the presence of organic material, the conditions on Enceladus may be similar to those in the oceans where life arose on the young Earth.

I am sure that Nature will have more surprises for us in the days ahead.

Waiting and Wondering …

Carolyn PorcoCarolyn Porco

Cassini Imaging Team Leader

I woke up unusually early this morning, on pins and needles, and looked
out my bedroom window from my house on a narrow ridge in northern
Boulder Colorado, onto the foothills of the Rocky Mountains and the
town below, and wondered how the day would unfold.  I paused to let my
gaze fly, in my mind, beyond the horizon and around and over the Earth,
pulling back in `powers of ten’ fashion, imagining our planet suspended
in space.  And I thought about how remarkable the inhabitants of that
small blue world truly are, and how extraordinary their achievements
over these past 4 years have been.

Those years of intensive examination of an alien planetary system have
brought us humans to this juncture, right now, awaiting news from clear
across the solar system of the outcome of our latest bold experiment in
interplanetary maneuvering, focused on one of the most fascinating
places in our solar system… a place we never even knew existed before
we set out on this adventure.

In this painstaking work, we proceed, step by step, to lay bare those
things which hold the greatest promise of comprehension, the greatest
significance for piecing together the story of the origins of the
bodies in our solar system, our Earth, and indeed ourselves.

The images we await now are just a few of those steps.  I wonder: What
will they show?


Video From Mission Control

Carolina MartinezCarolina Martinez 

JPL News Team

This is a video clip of the Cassini mission control area and Grant Eller, on console, confirming with the Deep Space Station in Canberra, Australia, that data has begun transmitting from Cassini to Earth.  Play clip 

Here is a high-resolution, broadcast quality clip of the same event: High-resolution clip

And here’s an interview clip with Todd Barber, Cassini lead propulsion engineer:  Play clip

You can get a high-resolution, broadcast quality clip of Todd here: High-resolution clip

Tomorrow we will have more postings from our scientists and engineers and their comments on the images. 

Raw images may begin to appear in the pre-dawn hours (PDT) with some of the best raw views arriving in the late afternoon.  For the latest raw images see:

Today,Monday August 11th,Is the Day!

John SpencerJohn Spencer

Cassini Scientist on the Composite Infrared Spectrometer (bio)

Our next Enceladus encounter is very soon, at 21:06 Universal Time or 14:06pm Pacific time. This promises to be a spectacular encounter, giving our first high-resolution sunlit view of the south polar region since the discovery of activity there three years ago (the most recent encounter, in March 2008, observed the south pole only in the darkness of Saturn’s shadow). Our instrument, the Composite Infrared Spectrometer (CIRS), will be mapping the heat radiation from the warm tiger stripes as we did in last March’s flyby, but on that flyby our best views were from a range of 14,000 km (8,500 miles), allowing us to see details of the heat radiation on scales as small as 4 km (2.5 miles). This time we’ll start our observations from a range as close as 900 km (560 miles), showing us Enceladus in fabulous close-up, with CIRS mapping details as small as 270 meters (0.17 miles). As we scan the south pole we’re screaming away from Enceladus at nearly 18 kilometers/second (40,000 mph) so we have to work fast to make the most of this high-resolution opportunity.

heat radiation from tiger stripesImage left: Heat radiation from tiger stripes. Full caption

I’m most excited about the observation we’ll be attempting at about 21:11 UT, when we will try to put the CIRS short-wavelength detector right along one of the most active tiger stripes, called Damascus Sulcus, from a distance of only 4,500 km (2,800 miles). On our last flyby we saw temperatures as high as at least 180 Kelvin (-135 Fahrenheit) on this part of Damascus, from 15,000 km (9,000 mile) range, and from three times closer we might see even higher temperatures because the warm material, which we think occupies a strip just tens or hundreds of meters wide along the fractures, will fill more of our detector and give us a more accurate reading. However, this is a challenging observation because our detector consists of a linear array of ten pixels, which will be aligned parallel to the fracture. Pointing may not be perfect this close to the moon, so we may get all ten detectors, or none of them, on Damascus. You might ask why we didn’t align the detector across the fracture rather than parallel to it, to be sure that at least some of our pixels would fall on the warm material. But we needed to align the spacecraft in the direction that allows it to rotate as fast as possible to keep up with Enceladus as we zoom past, and we didn’t have the luxury of also optimizing the orientation of the detector.

The animation to the right depicts Cassini flying close to Enceladus.

So tomorrow morning, when we hope the data will be processed and ready for us to look at, we’ll be both nervous and excited to see if this particular gamble paid off. But even if we are unlucky in this case, we’ll get lots of other spectacular data. Here’s a blow-by-blow account of the planned CIRS observations of the south pole, with times given in Universal Time (UT):
21:07-21:11 UT Very high resolution scan of the tiger stripes, riding along with the ISS camera “skeet shoot” observation that Amanda described in her previous blog entry, and ending with that view of Damascus Sulcus that I discussed above.

21:11-21:34 UT Ride along with the ISS camera mosaic of the south pole- more very valuable high-resolution views of selected locations on and near the tiger stripes.

21:36-21:50 UT A long-wavelength map of the entire southern hemisphere, which will allow us to measure total heat flow from the active south polar region. Enceladus enters Saturn’s shadow during this period, at 21:41.

21:52-22:09 UT A single scan of the south pole using our short-wavelength detectors, which will pick up the small part of the tiger stripes, along Alexandria Sulcus, that we missed in our March 2008 scan.

22:10-22:56 UT A global 7-16 micron map of the southern hemisphere with our short wavelength detectors, including the south pole, to look for changes in thermal emission since previous observations.

22:57-23:37 UT A stare at Damascus Sulcus with each of our two short-wavelength detectors, to give other instruments a chance to watch Enceladus in eclipse.

23:37-23:55 UT A maneuver to change the spacecraft orientation.

23:55-00:24 UT Watch the warming of Enceladus as it emerges from Saturn’s shadow at 00:07 UT, with the our long-wavelength detector.

00:25-00:42 UT ISS camera and VIMS compositional maps of the now-sunlit south pole.

00:42-01:04 UT Complete the CIRS long-wavelength observation of the post-eclipse warming.
It’s going to be one heck of a ride- I’ll report back once we’ve had a look at our data.

Flyby Underway!

Todd BarberTodd Barber,
Cassini Lead Propulsion Engineer (bio)


Best wishes from Pasadena, California on this fine day!  As I write
the highly anticipated Enceladus flyby is underway.

I was in the office this weekend trying to get caught up a bit (a
weekend tradition), allowing me to hit the ground running on another
busy work week.  This week holds exciting promise and scientific
anticipation, though, in addition to my typical engineering duties.
Over the weekend, we did two Reaction Wheel Assembly (RWA) biases to
optimize the rotational speeds of these objects.  Through angular
momentum changes, these wheels can turn and point the spacecraft,
allowing incredible precision.  One of my tasks is to calculate how
much propellant these biases use, so that’s one thing I’m working on

arist concept of Enceladus flybySpeaking of propellant usage, there have been some questions about how
much propellant we will use in the maneuvers around Enceladus and for
the flyby itself.  As I mentioned in my prior blog entry, we were
actually able to cancel our approach maneuver, OTM-163.  In addition,
the next propulsive maneuver (OTM-164) is nearly two weeks off,
setting up Cassini for solar conjunction and yet another Enceladus
encounter (E5) in October.  OTM-164 will be rather large, however,
using roughly 10 kg of bipropellant, about 6 kg of nitrogen tetroxide
(oxidizer) and 4 kg of monomethylhydrazine (fuel).  For the E4
encounter itself, I don’t have a propellant-usage prediction handy,
but I can tell you it will be at most a few tens of grams of hydrazine
(the monopropellant fuel), for yet another RWA bias.

The bottom line is that we have plenty of propellant for our two-year
extended mission and beyond.  Thanks for that great question, and
we’ll see all of you on the other side of Enceladus!


Enceladus August Flyby Preview

Amanda Hendrix

Cassini Scientist on the Ultraviolet Imaging Spectrograph (bio)

Hi everybody,

Well, after the successful and exciting Enceladus flyby in March … we’re doing it again!!  Cassini is executing a close pass by the little active moon, on Monday, August 11. Woo hoo!


This is the 5th close Enceladus flyby we’ve done. The first was in February 2005 (that one was not an official “targeted” flyby), the 2nd was in March 2005, the 3rd was July 2005 and the 4th was in March 2008. This is the 4th targeted flyby, so it’s sometimes referred to as E4.


It’s super exciting, because we’ll pass just about 50 kilometers (30 miles) from the surface, and fly into the plume at the south pole. This is similar flyby geometry to the pass we did in March 2008 — but this time, the focus is on the imaging instruments.  (Recall in the March flyby – E3 – the spacecraft was oriented to optimize measurements by the fields and particles instruments, especially the INMS-Ion and Neutral Mass Spectrometer–so they could “taste” the plume as we flew through.) This time, the spacecraft will be oriented to optimize imaging of the south polar region – to get the highest possible resolution images of those tiger stripes, the primary sources of the jets that feed the plume.


Here’s a little overview of what’s going to happen during the flyby, focusing on the remote sensing measurements. Have a look at the accompanying cool movie (put together by navigator extraordinaire and all around heckuva guy Brent Buffington). Some of it goes by pretty fast, so you might want to go through it a few times to absorb what’s happening. I’ll talk you through it.


At the beginning of the Enceladus segment, Enceladus is still pretty far away and small. We start with a long (6.5 hr) observation where ISS (the Imaging Subsystem – the movie shows the Narrow Angle Camera, or NAC, as a white box) is the “prime” instrument (but all the other cameras — ultraviolet, infrared, long-wave infrared – are taking data too). So ISS scans around, to sort of map out the environment of Enceladus and probe into any visible plume material around Enceladus. We then turn to Earth for a short (3 hr) downlink. We want the solid-state recorders (SSRs, where the data are stored until downlink) to be as empty as possible before we get closer to Enceladus and want to really fill them up with a lot of bits of good data. After the short downlink, we turn back to Enceladus and this time VIMS (the Visual and Infrared Mapping Spectrometer – with the field-of-view indicated by the red box) is the “prime” instrument. Enceladus is still small so we’re just staring and building up signal as we get closer and closer, to get good signal-to-noise spectra to understand the composition of Enceladus. By the end of the VIMS observation, Enceladus is just about fills the NAC. By the way, we’re coming in over the northern hemisphere of Enceladus; this is a relatively old part of the moon, which is apparent from the amount of craters present. Still not nearly as many craters as the Earth’s moon or Rhea, but it’s pretty heavily cratered for Enceladus. (The south polar region has *no* craters – since all that geologic activity wipes them out.) But I digress! So after VIMS, we switch to UVIS (the Ultraviolet Imaging Spectrograph) as “prime” instrument. This is the long, skinny pink/magenta field-of-view that you see in the movie. UVIS does a slow scan of the space near Enceladus by orienting the slit several radii off the body and slowly scanning onto the bright limb. If there are neutral gases such as hydrogen or oxygen in the vicinity of Enceladus (and we expect there to be, since we know there’s H2O vapor in the plumes), this is a possible way to detect those species and map them out. So after UVIS, ISS is prime again. And now we get into the really cool part.


ISS starts off with a two-panel mosaic of the northern hemisphere. Since the trajectory is pretty similar to the E3 trajectory, these images will be pretty similar to the ones obtained back in March – but still neat. Then the spacecraft does a large turn to get ready and oriented for closest approach. The flyby is so close and fast that it isn’t possible to make observations throughout the pass – we simply can’t keep up. The plan since the beginning was to orient the spacecraft, just prior to closest approach, so that the cameras will observe the active south pole region at the highest resolution possible. Notice in the movie that the spacecraft does the big turn, and then the boresights are actually pointed away from Enceladus for just a little while — so that as we zip by the moon, we’ll capture the south pole. So the imaging team (and I think Paul Helfenstein was primarily responsible) came up with this “skeet shoot” plan to execute 7 NAC frames across the tiger stripes, with resolutions between just 7 and 28 meters per pixel! Such high resolution images, combined with context frames, will really help in understanding the cracks and jets, and will provide clues to the origin of the plume. So the 7 frames are taken in under 3.5 min, and then 7 more are taken at resolutions up to 140 meters per pixel over the next 20 minutes or so. (The other instruments are “riding along” to get compositional and temperature information.) Note that the south pole is partly in darkness, and we’re moving fast, so the images and exposure times are carefully planned to balance light and smear. Images close to the terminator will really bring out the topography of the region, so they should be pretty spectacular.


After ISS is finished, CIRS takes over. CIRS is the Composite Infrared Mapping Spectrometer – the instrument that can “see in the dark” and map surface temperatures. CIRS becomes “prime” and does a few scans with their FP1 slit (the red circle) and their FP3 slits (the two little red rectangles). These observations will complement the *great* measurements made by CIRS on the last flyby in March (E3). Note that at about 21:41, Enceladus goes into Saturn eclipse – so there’ll be very little reflected solar light off Enceladus, which creates ideal conditions for measuring heat coming from within Enceladus. Enceladus comes out of eclipse at ~00:07. At ~01:06, or 4 hours after closest approach, VIMS is prime again for 1 hour, to get more compositional information on the south pole. We then turn to Earth for a 5 hour downlink. Then we turn back to Enceladus for a final stare with UVIS as prime instrument.


Recall that equinox is coming up in a year — Aug. 11, 2009 – and as we approach equinox (and solstice after that) the south pole is dominated more and more by darkness. So it’s really important that we get as many good looks at this wild south pole while we can! Of course, CIRS can do a lot of science even if the pole is in complete darkness – and later in the mission those will be important measurements to make, in case there is any seasonal input to the plume activity.


Whew! I’ve written a lot and hopefully haven’t bored you all completely to tears … I’m obviously very excited about this flyby and hope that you are too! Thanks for reading and coming along with us to explore Enceladus.