Waiting,Patiently . . .

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Sascha KempfSascha Kempf
Cassini Scientist on Cosmic Dust Analyzer

 

Right now we are excited that we collected many mass spectra of fresh dust emerging from Enceladus.  Mass spectra provide information about the composition of the particles.  We obtained about 1,500 spectra during the flyby.

 

We just started the data reduction process which may take some time. Like many of you, we are all eager to know what this data are telling us; however our data require careful analysis and interpretation. 

 

Our mass spectrometer is not like instruments you find in university labs. In space we cannot just catch the particle and prepare it carefully for examination– the particles hit the detector with a speed of about 18 kilometers per second (40,000 miles per hour). Instead, we analyze the composition of the plasma created by the striking particles. The plasma constituents are separated in a strong electric field and accelerated toward a multiplier at the instrument centre. From the ions’ time of flight we get the ion masses and finally the composition of the particle–in theory.  In reality things are much more difficult because within the plasma, the ionized atoms and molecules react with each other and form new compounds. Thus, to interpret an impact ionization mass spectrum correctly we have to understand the chemistry going on in the impact plasma.  In other words, things aren’t always clear cut: a Carbon Monoxide (CO) reading does not necessarily imply that the grain really contains CO. 

 

We are working hard in Heidelberg and as soon as we are certain of our results, we will share it with all of you.  This could take several weeks.  So we wait patiently for the news to unfold on this tiny moon.

 

–Sascha from Heidelberg, Germany

 

Xtreme Navigation,Not for the Faint of Heart

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Shadan ArdalanShadan Ardalan, Cassini Navigator (bio)

Good morning from sunny Southern California.  I have literally been up all night waiting to hear back from the Cassini spacecraft after its closest ever flyby of Enceladus.  It’s nights like this that I feel like a kid again waiting up for Santa on Christmas Eve.

As you know from all the other blog posts, last night we skimmed above the surface of Enceladus at an altitude of 82,000 feet (nearly 16 miles) while traveling at about 40,000 miles per hour…..and as if that wasn’t cool enough, we gave Cassini a “cosmic car wash” by flying the spacecraft through the plumes of the geysers on Enceladus.

Enceladus, from Oct. 9, 2008, flybyThe challenge of navigating a spacecraft with the precision required for such a feat is two-fold.  Not only do my navigation teammates need to determine the orbit of the Cassini spacecraft (i.e., where it is and where it’s going), but there are other members of the navigation team trying to better figure out where Enceladus is (it’s one thing to know where you are….it’s something entirely different to know where your target is).  The experience from the other two Enceladus close encounters earlier this past March and August has improved our knowledge of this moon to such a degree that we feel confident that we can hit this tighter bullseye nearly a billion miles away from Earth.

Fans of extreme sports would especially appreciate what we accomplished.  I’ve bungee-cord dropped before and tonight’s flyby kinda reminded me of that.  This flyby 82,000 feet above the surface and through the plume of water ice is like bungee-cord jumping off a bridge and dipping your head into the river below before getting sprung back up.

As I’m anxiously waiting to receive a signal from the spacecraft, I’ve been spending my time surfing the web to see what the world has to say about us. One of the coolest aspects of working on such a historic mission as Cassini is reading stories on our work in the media.

As I’ve been typing this blog entry (and doing a little more net-surfing), I’ve been monitoring the real-time doppler signal, waiting for a call back home just to tell me everything is all-right.  AND THERE IT IS – YIPPEE!!!!!! and WHEEW!!!!! (wiping sweat off of brow).  This signal tells me in real-time, that Cassini successfully flew by Enceladus.  My friends will process this signal later this morning to tell us how well we hit our target.

And like that kid who just heard Santa land on his rooftop, I best be off to bed because I know when I wake up later this morning, I will have great gifts waiting for me in the form of spectacular images—I can hardly wait!!!!

I have pasted one raw image from the flyby here.To view all the latest images from before closest approach and as the spacecraft sped away from Enceladus, go to:

http://saturn.jpl.nasa.gov/multimedia/images/raw/index.cfm
and click on browse latest images.

–Shadan

 

We Sniffed the Plume!

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Sascha KempfSascha Kempf
Cassini Scientist on Cosmic Dust Analyzer

 

Everything went great for the Cosmic Dust Analyzer (CDA) during this flyby. We got good data during the entire flyby—before, during and after closest approach. We recorded mass spectra even in the deep plume with no data gaps as far as I can see.

The High Rate Data rate count profile shows pronounced peaks at the time we traversed the jets. This data is key for pinning down the structure of the dust jets.

None of it would have been possible without an excellent team overseeing the instrument and the team at JPL for flying us through. Now we are looking ahead to an exciting period of evaluation.

–Sascha, who is heading off to pick up the kids from school.

Where No Hoover Has Gone Before

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Sascha KempfSascha Kempf
Cassini Scientist on Cosmic Dust Analyzer

 

Cassini’s closest flyby so far of Enceladus is rapidly approaching, and we here at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, can’t bear the suspense any longer. Our team has built and operates the Cosmic Dust Analyzer, CDA.

CDA is part of Cassini’s suite of magnetospheric  and plasma science, or MAPS instruments, and is capable of determining the mass, speed, composition, and electrostatic charge of typically micron-sized grains, so called dust, striking the detector with speeds of a few tens of kilometes per second (how many miles is that?). Dust particles can tell us a lot about the Saturnian system, because each grain is a messenger and a participant in the physical processes responsible for forming Saturn’s magnificent rings, structuring the planet’s magnetosphere, and reshaping the surfaces of its moons. Like photons, dust particles carry precious information about their site of origin and about their history.

So what does the CDA team want to achieve during this flyby? Enceladus is the major dust producer of the E ring. Most of the particles are emerging from the plumes in the moon’s unusually warm south pole region. Those particles tell us a lot about the conditions inside the surface fractures, where the particles condense from the water vapor ascending through the cracks. There is, however, a second, although less effective way that Enceladus produces fresh dust: fast impacts by either interplanetary meteoroids or by ring particles onto the moon’s surface
produce many new particles—the surface ejecta. We believe that the composition of these ejecta differs from that of the plume particles, and this is one of the main goals of this flyby. If this turns out be true then we can follow the evolution of plume particles through the E ring until their end of life. This knowledge would also help us to understand whether the plumes’ exhaust is deposited on the surface of Enceladus and if so, how much We need just the right geometry to accomplish this goal since we can observe the surface ejecta only when the spacecraft is very close to the Enceladus surface but outside the south pole region.  That’s because the Enceladus plumes are such a strong dust source.

The upcoming encounter is just right for our needs. Around the closest approach, just 25 kilometers (16 miles) from Enceladus’ surface we hope to scoop particles that come directly from the moon’s surface. Later on, when Cassini traverses the dust plumes, we hope to collect genuine plume particles. This approach worked quite well during the last encounter in August.

We can hardly wait!

Today's the Day!

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Todd BarberTodd Barber
Cassini Lead Propulsion Engineer (bio)

Hello again from Pasadena, California!  As I type these words, our spacecraft is dutifully executing a dynamic encounter with Saturn’s perplexing satellite, Enceladus.  Some of you have expressed an interest in the engineering particulars of our daringly close flyby, with respect to its effects on the spacecraft.  I’m happy to say that even though scientists should gather plenty of material for chemical and physical analysis, the icy plumes of Enceladus are rather tenuous, even with our very close flyby distance of only 25 kilometers (16 miles).  One reason this is true is our dive into the plumes occurs at a much higher altitude than the closest approach, as you can see in the image below.  As such, we don’t expect Cassini to slow down or change course due to impacts.  However, gaseous plume material may place small torques on the spacecraft which will cause our thruster deadbands to be exceeded, a common occurrence while in thruster control.  In that case, our small hydrazine thrusters (0.2 pounds or 0.9 Newtons) will fire to correct the pointing of the spacecraft.  In fact, our attitude control engineers may be able to estimate the density of the Enceladus plume by studying these rocket firings!  

As far as the potential for ice damage to Cassini, fortunately the ejecta from Enceladus consist of very tiny particles only.  This, coupled with our micrometeoroid shielding and relatively high altitude while within the plume, will help keep Cassini safe and sound.  It’s truly the best of both worlds–we’ll be close enough to really ingest the smorgasbord offered up by Enceladus, but we’ll still be comfortably far from the surface and well away from affecting the spacecraft adversely.

A new Cassini video update was recently released, further explaining our busy October plans for twin Enceladus flybys.  You may view the video here

Unfortunately, I won’t be here to report our first signal tomorrow after the flyby, as I am leaving for a leaf-peeping vacation to New England this evening.  Rest assured I’ll be thinking of our intrepid robotic friend and the flood of science data to come.  Go, Cassini, go!

Enceladus,Here We Come!

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

Hi everybody! I’m very excited about today’s Enceladus flyby, which will take us deeper into the plume than we’ve ever been before! Here’s the scoop on the science activities that will take place during the encounter, accompanied by a neat movie provided by Cassini navigator Brent Buffington. Click here to see the movie (30Mb).

We’ve posted these types of movies for previous flybys, but in case you haven’t seen one before, here’s the setup: the left-hand panel shows the spacecraft and its relationship to Enceladus and will indicate the view of the “prime” instrument by showing its viewing frustum in the color corresponding to that instrument. The upper right panel shows the fields-of-view of the remote sensing instruments (i.e. the cameras and the imaging spectrometers), and the lower right panel shows the “active” field-of-view, since at any time, one instrument is “prime” (though other instruments may be simultaneously taking data, while “riding along”). (By the way, you can go to the end of this post for a key to help watch the animation.)

view from Cassini flyby animationNow, this flyby has a similar trajectory to the previous two flybys in March and August: a fast, inclined path coming in over the northern hemisphere and leaving over the southern hemisphere, with closest approach at a low latitude. Recall that summer in the southern hemisphere is winding down, meaning that the active “tiger stripe” region is illuminated by the sun less and less every day. CIRS and RADAR can see in the dark and don’t care too much about solar illumination, but ISS, UVIS and VIMS usually measure solar light reflected from the surface—so opportunities to measure the wild south pole using these methods are dwindling!

OK, so the movie starts while we’re inbound to Enceladus, about eight hours before closest approach, when RADAR makes measurements to get at centimeter-scale roughness and to investigate the energy balance in the upper layers of the surface – so you can see the green circle doing repeated scans over Enceladus. The scans are accomplished by slewing the entire spacecraft.

Then the spacecraft turns 90 degrees so that the remote sensing instruments can point at Enceladus. First CIRS is prime and does a series of stares and scans. CIRS measures the temperature of the surface. Fellow blogger John Spencer will probably tell you later more about CIRS measurements, which are super important and interesting at Enceladus.

After CIRS, we’re about two hours from closest approach, and UVIS is prime, starting from several radii away from the body and slowing scanning onto Enceladus, to map out any neutral gases, such as oxygen or hydrogen, that are present in the vicinity.

When UVIS is finished with the slow scan, the spacecraft executes a big turn to put the fields-and-particles instruments (especially CDA and INMS) into position to “scoop up” dust particles and gas species during closest approach and while in the plume. Such a close approach and relatively deep plume passage are going to provide really interesting and key results on plume composition and also the composition of material sputtered from the surface away from the plume. (Note that during the closest approach period, the remote sensing instrument boresights are actually on the planet – see the upper right panel – though they’re not taking data.)

Closest approach goes by quickly (we whiz by at nearly 40,000 mph!), and about 15 minutes after closest approach, the spacecraft turns so that the remote sensing instruments can check out the south pole. ISS is prime first, for about 30 minutes, to image the active tiger stripes while Enceladus is in sunlight. Then CIRS takes over, and at around 19:52, Enceladus will enter eclipse, and will be in eclipse for about 2.5 hours, so CIRS will be able to map south polar surface temperatures without the influence of solar input.

Finally the Enceladus sequence ends with a distant view of the body with UVIS as prime instrument!  That’s the instrument I work on.

I’ll report again on progress, from the DPS science meeting in Ithaca, NY.

It’s going to be great! Thanks for coming along with us as we fly by this crazy moon.

Amanda

Here’s the key to help watch the animation:
UVIS = magenta long skinny rectangles
CIRS = red circle and red small parallel rectangles
WAC = large white box
NAC = smaller white box
VIMS = red box
RADAR/HGA = green circle

Strapping in for the Ride

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Geraint JonesGeraint Jones
Scientist on the Cassini Plasma Spectrometer (bio)

Cassini’s next white-knuckle Enceladus flyby is quickly approaching, and the excitement is building for those of us working on the Cassini Plasma Spectrometer, CAPS. This instrument team is headed by Dave Young at the Southwest Research Institute, San Antonio, but the team members work in several countries. This includes the UK, where several of us on CAPS work at the Mullard Space Science Laboratory—part of University College London that’s located in the countryside to the south of the city.

CAPS is part of Cassini’s suite of magnetospheric and plasma science, or MAPS experiments. With these, the spacecraft can sense its immediate environment: the gases, plasma, electromagnetic fields, and dust that can tell us a huge amount about the Saturn system.

artist concept of Enceladus flybyThe results from each of this year’s Enceladus flybys has a different flavor. The main reason for this is that not all instruments can be pointed in their respective “best” directions at once, and the flybys are so brief that there’s no time to turn Cassini, so every instrument gets a good look or samples the particles they want to… it’s a bit like deciding who gets the window and aisle seats! Luckily, because we’ve got several flybys, the teams can take it in turns to get the best data out of their respective experiments… this time, as it was back on March 12th, the MAPS instrument teams are in their favorite seats.

So what are the CAPS team going to be looking at during this daring dive? Enceladus is sitting in a flow of plasma—a mix of ions and electrons that’s trapped around Saturn by the planet’s magnetic field.  We expect Cassini to briefly enter a wake where this magnetospheric plasma can’t penetrate, a “shadowed” region where CAPS should sense a big drop in the density of the plasma. Once past closest approach, only 25 kilometers, or 15.5 miles, from Enceladus’ surface, Cassini will spend a few minutes actually inside the plume of gas and ice particles being thrown out by the moon.

CAPS will be pointed in the right direction to scoop up this material at almost 18 kilometers. or 11 miles a second. as we whiz through the plume.  Some of the gases released in the plume are electrically-charged by the time they reach Cassini; CAPS can measure the energies of these and how many are present. From this, we should be able to learn a lot about the plume: how dense it is, its composition, and how this plume affects the plasma flowing past it. This approach worked really well during the March encounter, so we’re hoping to repeat that success, but taking a different “cut” through the plume because Cassini will fly past Enceladus from a different direction.

We’re strapped in, noses against the window, and can’t wait for the ride!

Cassini Is 'GO' for Enceladus-5

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Todd BarberTodd Barber
Cassini Lead Propulsion Engineer (bio)

Hello again from the realm of Cassini engineering, just 48 hours before another wonderful date with destiny!  It is a distinct pleasure to kick off yet another Enceladus flyby blog, particularly one about a flyby so thrilling and daring.  I’m happy to report the spacecraft is right on target for this historic encounter with Saturn’s icy and active companion.  As an engineer, I think I’m most floored by the closest approach distance of 25 kilometers, roughly 16 miles.  Cassini hasn’t been this close to any solid body since our ascent in a pre-dawn October sky in Florida in 1997!  To further put this flyby in perspective, one can convert the minimum altitude into feet–yes, we’ll actually be that close!  In this system of units, we will buzz this active water-geyser surface at only 82,000 feet, which puts Cassini closer to Enceladus (900 million miles from Earth, mind you) than an SR71 Blackbird can fly above the ground on the third rock!  Wow!

flyby trajectoriesGiven this truly up-close-and-personal flyby, the primary scientific focus will be “sniffing” the tenuous atmosphere of Enceladus, a rarefied collection of gas and dust spewed forth from a surprisingly active surface.  As such, E5 will concentrate less on imaging results, but E6 will tip the scales towards imaging yet again, all before the end of the month.  Truly, Cassini is embarking on a busy October for the ages!

From the spacecraft engineering and navigation teams, I’m happy to report our final E5 flyby approach maneuver, OTM-166, was executed successfully yesterday afternoon.  It was a mere 15 millimeters per second (0.033 mph) speed change to our essentially on-target spacecraft.  However, even traveling thousands and thousands of miles per hour, such corrections are necessary in the intricate billiard game that is celestial mechanics.  We also monitored the spacecraft very carefully after OTM-166, looking for any rocket thruster leakage after their usage during the maneuver.  Even though any such leakage would be exceedingly unlikely, it could have theoretically put Cassini on an Enceladus impact trajectory, and that might be, well, career-limiting for the scientists and engineers on the project. 🙂  I’m happy to report the maneuver went well, there is no sign of thruster leakage, and we are ready to hand over the spacecraft to our eager scientists.  May you take a big whiff of whatever Enceladus has to offer, and may it offer the sweet scent of scientific promise and discovery!

Jackpot!

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Carolyn PorcoCarolyn Porco

Cassini Imaging Team Leader

 

As you can imagine, we Cassini imaging scientists have been bee-busy trying to understand what our recent images from this week’s Enceladus flyby are telling us about the nature of the moon’s south polar surface and sub-surface environments.

 

I can now report that, so far, we have successfully located the surface sources of the jets for which Enceladus has become renowned.

 

source of jets on EnceladusThere is still much more to do to see if we can glean any information at all about the eruptive process itself from the geological characteristics we see on the surface.  But this, you have to admit, is a very good start!

 

Click here for our latest release.

 

Image left: Surface sources of some jets on Enceladus. Full image and caption

 

And click here for a similar image.

 

We Nailed It!

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John SpencerJohn Spencer

Cassini Scientist on the Composite Infrared Spectrometer (bio)

 

Click here to browse Cassini raw images site for Enceladus images

 

All sorts of emotions over the last couple of days.  Yesterday morning began with the great (but not surprising) news that our trusty spacecraft had successfully negotiated its latest and deepest- yet passage through the Enceladus plume, successfully executed its observations, and was starting to ship its cargo of data home.  There wouldn’t be any calibrated data to look at for hours, so I focused for a while on something much more down-to-Earth: my wife Jane and I put in an hour harvesting produce at a local vegetable garden.   Searching through the luxuriant, dripping-wet foliage for green beans and tomatoes, Jane remarked, “Isn’t it amazing what can happen on a planet that has water on it”?  That of course, is part of the reason why we’re so excited to be exploring Enceladus–the geysers breaking through that intensely cold surface harbor heat, lots of it, maybe enough to melt the ice below the surface and, just maybe, enough to give Enceladus its own chance for life.  Maybe our new Composite Infrared Spectrometer (CIRS) observations of Enceladus’ internal heat, now on their way home, could give us new clues about whether liquid water really does lurk beneath the surface.

 

close-up view of Enceladus

Image left: This image shows our initial discovery, back in 2005,  that the south polar tiger stripe fractures were warm. Larger view

 

The rest of the day was an exercise in patience as we waited for the CIRS data to be calibrated at CIRS’s home at NASA’s Goddard Spaceflight Center in Greenbelt, Md., a complicated and time-consuming process.  By late afternoon, right before I had to leave for the evening, we got a nibble–a short sequence of data from the few minutes right after closest approach.  The processed data ended, tantalizingly, just before our planned stare at the active fracture Damascus Sulcus, which we hoped, if targeting was perfect, would give us perhaps our best-yet determination of the temperatures of the tiger stripe fractures.  But something bothered me–CIRS was operating in a mode that I didn’t expect.  Had something gone wrong with the instrument commanding?  It was too late in the day to check with the folks in Maryland.  That worry preyed on my mind all evening, so this morning I pounced on the data as soon as I could, to run some more checks.  To my great relief, everything was fine–I had forgotten that we had planned to use that unfamiliar instrument mode for this unusual close-up observation.  Still, the rest of our data were still not calibrated, and I had to wait a bit longer.

 

In the meantime, there were the close-up ISS camera images to look at.  Like the other bloggers here, I was blown away by both the quality of the images, which were taken under very difficult 
circumstances, and by the bizarre landscape that they revealed.  Utterly stunning.  Hats off to the imaging team, particularly (as Bonnie and Carolyn also mentioned) to Paul Helfenstein, who sweated for months on the details of planning that sequence.

 

Then, finally, it was our turn–the Goddard team completed the CIRS calibration this morning, and I downloaded the data.  More nervousness, until the plots started coming up on the screen and showed a beautiful spike in the signal strength, right when we expected to be staring at Damascus.  It was obvious that we were pointing right at the warm fracture, just as planned.  We nailed it!  Not that CIRS gets credit for this bit of precision targeting–the camera team was driving and we were along for the ride.  Credit goes once more to Paul Helfenstein and rest of the ISS team, and also the navigation team who put the spacecraft exactly where it was supposed to be.  Now we have to delve deeper to find out what that beautiful observation of Damascus is telling us.


 

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