Tag: spacecraft

Linda 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!
 
–Linda
 

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

Today’s Enceladus flyby is a bit more adventurous than most satellite flybys by Cassini. 
We are dipping into the jet of water vapor and ice spewing from Enceladus’ south pole, because by doing so we can take full advantage of the amazing opportunity to study
fresh samples from inside this strange world.  The mass spectrometer, dust, and plasma
instruments will be running flat-out, gathering priceless information on the composition
of the gases and the ice particles for the sixty seconds or so that Cassini will be in
the dense part of the plume.

Plume particles are wonderful things to study, but it’s possible to have too much of a
good thing – at the speed that Cassini is going, particles as small as a millimeter in
size could cause serious damage to the spacecraft if we ran into one.  So the decision to
enter the plume was not taken lightly.  The project convened an “Enceladus plume working group”, led by fellow-blogger Amanda Hendrix, which held a series of meetings to determine whether there was any hazard to the spacecraft from flying as close as we plan to go.  Though we fly 50 kilometers (30 miles) above Enceladus’ surface, this happens near the equator and away from the plumes–the closest approach to the source of the plumes is more like 200 kilometers (120 miles)–see the graphic on the left by David Seal (E3 is the official name of today’s Enceladus flyby).

We know from the Cassini images, and from observations from the dust detector during the July 2005 flyby, that there are many ice particles a few microns (a few 1000ths of a
millimeter) in diameter in the parts of the plume we’ll be traversing, and these provide
juicy samples without posing any hazard.  But was there any way that much bigger
particles could be lofted into Cassini’s path?  We reviewed the observational evidence,
and theories about how the plumes might work (for instance, figuring out how much gas it would take to accelerate an ice grain of a dangerous size to a speed high enough to reach the spacecraft) and we decided that the danger was very small.  Still, it will be good to hear from the spacecraft when it turns its antenna back to Earth and sends home word that the flyby was safely negotiated.  That will be at 7:05 p.m. Pacific time this evening, not that I’m counting…

Future flyby plans could probe even deeper into the plume, coming as close as 100 kilometers (62 miles) from the source on November 2, 2009 (though this depends on official approval of the proposed extended mission).  But we’ll review the results from this flyby before committing to anything that close.  If Cassini reports “come on in, the water’s fine!”, as we expect, we’ll dip our toes in a little further next time.

 

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

Well our flyby sequence has officially started!! Last night we began our observations of Enceladus! We are very distant, but getting closer all the time, over the northern hemisphere.  The first observation was a long stare at Enceladus, which is still pretty far away and small, but this is a nice opportunity to do compositional measurements. As of 9 a.m. Pacific, radar observation of Enceladus began, which will give us an idea of the roughness of this side of Enceladus, at centimeter scales.  The closest approach is around 1 p.m. Pacific today.

The entire flyby sequence is on-board the spacecraft, and there’s really no opportunity to change it at this point. We’re in it for good. However, the sequence gets thoroughly tested prior to uplink, so we are confident that things will go smoothly. The next time we hear from Cassini will be tonight after the flyby at around 7 p.m. Pacific.  We are being fairly cautious, though: even though Cassini will come about 30 miles of the surface, while flying through the plume we will be 120 miles from the surface. So we’re “dipping our toes” in the plume a little more than we’ve done before!

Cheers from Houston,
Amanda