Enceladus-3 (March 12, 2008) |
Enceladus-3 (March 12, 2008) |
Guest_AlexBlackwell_* |
Feb 24 2006, 09:12 PM
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Excerpt from Cassini Significant Events for 02/16/06 - 02/22/06:
"As mentioned in previous weeks, the project has been working on adopting a new reference trajectory in order to raise the minimum Titan flyby altitude for various encounters. Today the project reached a decision to proceed with the 'optocc2' trajectory. Additional work is still to be performed before delivery of the final files. This will include minor tweaks that have been analyzed in other trajectories, adjusting orbit 68 timing, and capture of an Enceladus plume occultation on orbit 28." For the record, the new reference trajectory will result in an even more spectacular Enceladus-3 flyby [61EN (t) E3] on March 12, 2008. |
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Guest_BruceMoomaw_* |
Mar 9 2006, 09:36 PM
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TWENTY-FIVE KM?!! You guys are really taking this place seriously, aren't you? I hope the navigation is better than that on MCO...
In that connection, one catastrophe that has yet to strike the US space program is the failure of an long, expensive outer Solar System mission just before its arrival. What will the public and Congressional reaction be when that finally happens? It looked as though it might happen with Galileo, but JPL succeeded (to their unquestionable credit) in pulling enough chestnuts out of the fire to remove that impression in that case. At the risk of setting off the dog (aka Alex) again: I mentioned this point to Spilker's subgroup on Europa lander design at the Europa Focus Group Workshop, and got an enthusiastic response from JPL's Karla Clark -- we do NOT want something as expensive and long-term as a Europa Astrobiology Lander to fail at the very moment it's trying to land on Europa, and for that reason the best role for a little piggyback lander attached to Europa Orbiter may well be to check out the engineering characteristics of Europa's surface rather than carrying out any specifically scientific studies. |
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Guest_AlexBlackwell_* |
Mar 9 2006, 09:47 PM
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...JPL's Karla Clark -- we do NOT want something as expensive and long-term as a Europa Astrobiology Lander to fail at the very moment it's trying to land on Europa... Now that's a visionary statement. I'm wondering about this figure as well, I noticed volcanopele edited it out of his post. Does that figure really hold in the new updated trajectory? "Officially," the new reference trajectory is still in review at the Project/Program level; a decision should be forthcoming very shortly. I won't speak for Jason, but unofficially, the 25 km figure is the new Enceladus-3 flyby C/A altitude under all options that were being considered. What exactly is the scientific justification of such a dangerously close pass? More on that later; however, sooner than 2008 |
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Mar 9 2006, 10:12 PM
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#4
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Senior Member Group: Moderator Posts: 3242 Joined: 11-February 04 From: Tucson, AZ Member No.: 23 |
Technically, that number is official (well, it isn't going to change). As the Sig. events report suggest, a few additional tweaks are planned, but nothing that will effect Enceladus-3.
-------------------- &@^^!% Jim! I'm a geologist, not a physicist!
The Gish Bar Times - A Blog all about Jupiter's Moon Io |
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Mar 10 2006, 04:43 AM
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#5
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Junior Member Group: Members Posts: 39 Joined: 29-September 05 Member No.: 518 |
Technically, that number is official (well, it isn't going to change). As the Sig. events report suggest, a few additional tweaks are planned, but nothing that will effect Enceladus-3. what I heard is that the altitude is not set in stone, but could change with another new trajectory... I'm guessing is that there will be more studies made to make sure it is safe. At that low altitude, I just hope they model Enceladus as an ellipsoid rather than as a sphere... the radius differs at the pole and the equator by something like 10 km, right? ...actually, I wonder how well they really know the radius anyway. |
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Guest_AlexBlackwell_* |
Mar 10 2006, 04:26 PM
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#6
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what I heard is that the altitude is not set in stone, but could change with another new trajectory... That's a good point: any trajectory is subject to change, and I wouldn't be surprised if 61EN (t) C/A ends up being tweaked upwards slightly. Still, unless the new reference trajectory resulting from optocc2 (or even those that would have resulted from 28EN_occ3, 28EN_opt3b, or Option 3b) changes dramatically, Enceladus-3 is going to a barnstorming flyby, regardless. And there is an important non-targeted encounter coming up later this year, September 9, 21EN (nt), which will allow for occultation data on Enceladus' plumes. P.S. The significant events report I started out with in this thread referred to "optocc2." Is this different from optocc3? I've seen the latter referred to extensively by MP during this latest trajectory re-design but not the former. I assume both are in the same "class" but have different tweaks. |
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Mar 10 2006, 05:32 PM
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#7
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
Various notes:
However we might wring our hands over missing out on 30cm/pixel images, note that we did obtain only slightly blurred 4m/pixel images which are certainly sharp when desampled to 8m/pix. The question is how many such images Cassini could snap in E3, and if an imaging strategy could guarantee a supercloseup of a Tiger Stripe near or at a vent. Dangerwise, I start to imagine the possible endgame of the mission, setting a trajectory that points straight ahead and gets some low-blur images of the vents without the use of a shield on a flyby where we no longer care if Cassini is destroyed. This would have to be combined with a free trajectory into its destruction somewhere besides Enceladus or Titan, and my top candidate would be the B ring. Maybe a low-inclination orbit that slices into the B ring could return some "downlooking" shots of the rings at incredible resolution before sure death when the orbit hits the ringplane. (If light doesn't go through them, neither will Cassini.) Thus, two high-value images could be obtained on the final death orbit, whenever that would be. Astrobiologically speaking, I wonder if one of the problems for the Enceladan reservoirs might be if the water is too pure. Undoubtedly, there's no way to get life out of 100% H2O if there were no other compounds there. Nature seems to abhor purity in most cases, so hopefully that will be the case with Enceladan H2O as well. Explorationwise, I fear we might have a reservoir under pressure with no way to get into it. Imagine trying to stick your digital camera into an open fire hydrant. There's a reason why those jets are spraying so far up, even in that super-light gravity. Even if we drill our own hole, that might just uncap a new vent. Sarcasmwise, Alex, Bruce isn't going to get your putdowns unless you do the rhetorical equivalent of hitting him on the head with an anvil that says "2000 LBS" on the side. He's too hyped up to come down. |
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Guest_RGClark_* |
Mar 10 2006, 06:26 PM
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#8
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... Astrobiologically speaking, I wonder if one of the problems for the Enceladan reservoirs might be if the water is too pure. Undoubtedly, there's no way to get life out of 100% H2O if there were no other compounds there. Nature seems to abhor purity in most cases, so hopefully that will be the case with Enceladan H2O as well. ... True but I wonder what would be the percentage of H2O of a sample from a fresh water lake? - Bob Clark |
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