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Enceladus-3 (March 12, 2008)
tty
post Mar 10 2006, 07:24 PM
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Isn’t landing on Enceladus an unnecessarily complicated way to investigate the possible existance of life there? Here we have a watery planet that is obliging enough to blow its water and whatever is in it off into space and thereby preserving it at cryogenic temperatures where you can get at it without having to get down into the gravity well.
What is needed is a probe that gets into an orbit that is nearly, but not quite co-orbital with the E-ring and deploys a scoop to collect ice/water for analysis. It takes quite a lot of energy to heat ice from -200 and melt it, so you can use a fairly high relative speed (certainly a couple of hundred meters per second) and so sweep a fairly large volume in a short time.

You might also “trawl” the plumes themselves for fresher material but it would be difficult to stay in the plumes for any length of time without having to go into orbit around Enceladus.

tty
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Guest_BruceMoomaw_*
post Mar 10 2006, 07:24 PM
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QUOTE (AlexBlackwell @ Mar 10 2006, 03:52 PM) *
Looks like you missed my sarcasm. A better description would be "blindlingly obvious."


Oh, I got it. My whole point was that Spilker's group didn't seem to realize that this provided another good reason to orient the piggyback lander on EO toward engineering rather than scientific measurements until Karla Clark and I mentioned it. It hadn't been "blindingly obvious" to them -- or rather the political implications of a last-second EAL failure hadn't been blindingly obvious to them.
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volcanopele
post Mar 10 2006, 07:36 PM
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a few notes:

E3 Imaging: Don't expect super high res images. Cassini will be approaching Enceladus while the moon is in high phase and closest approach will occur over the night side. A good amount of the blur in the high res images from July were because we were tracking gamma Orionis, not a point on the surface. If we were targeting the surface and had 5 ms exposures, it's possible the smear would be less, though as Bruce mentioned, you also have to keep the spacecraft point so that the HGA is in the RAM direction to protect the spacecraft from E-ring particles. Unfortunately, to see anything in saturn-shine, as would be possible at closest approach, we would need significantly more than 5 ms exposures to see anything. And that's assuming we had prime pointing. Which as of right now, we don't (INMS does I think). Then, three minutes after C/A, Enceladus goes into eclipse. Plenty of time for CIRS to look for even higher temps, but not good for ISS imaging.

Composition of reservoir: INMS observations of the plume suggest that it isn't pure H2O. Their composition measurements suggest 91% H2O, 3% CO2, 3.3% N2 (though CO is possible), and 1.6% CH4.


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Guest_Richard Trigaux_*
post Mar 10 2006, 07:41 PM
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QUOTE (tty @ Mar 10 2006, 08:24 PM) *
Isn’t landing on Enceladus an unnecessarily complicated way to investigate the possible existance of life there? Here we have a watery planet that is obliging enough to blow its water and whatever is in it off into space and thereby preserving it at cryogenic temperatures where you can get at it without having to get down into the gravity well.
What is needed is a probe that gets into an orbit that is nearly, but not quite co-orbital with the E-ring and deploys a scoop to collect ice/water for analysis. It takes quite a lot of energy to heat ice from -200 and melt it, so you can use a fairly high relative speed (certainly a couple of hundred meters per second) and so sweep a fairly large volume in a short time.

You might also “trawl” the plumes themselves for fresher material but it would be difficult to stay in the plumes for any length of time without having to go into orbit around Enceladus.

tty


No, plumes are better than the E ring. Whatever material there is, it will qhickly burn with UVs, so that only the plume at low altitude is interesting. Anyway only one passge in the plume may collect more matter than scooping the E ring.
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Guest_AlexBlackwell_*
post Mar 10 2006, 07:44 PM
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QUOTE (BruceMoomaw @ Mar 10 2006, 07:24 PM) *
Oh, I got it. My whole point was that Spilker's group didn't seem to realize that this provided another good reason to orient the piggyback lander on EO toward engineering rather than scientific measurements until Karla Clark and I mentioned it. It hadn't been "blindingly obvious" to them -- or rather the political implications of a last-second EAL failure hadn't been blindingly obvious to them.

OK, Bruce, let me suggest this. Take a magic marker and write on your palm "EAL landing failure = bad; EAL landing success = good." biggrin.gif

Hey, maybe it's me, but if the "political implications of a last-second EAL failure [isn't] blindingly obvious to them," then "the[y]" have been living in a cave if "they" do not realize the ramifications in a failure of a multi-billion dollar Flagship-class mission.

This post has been edited by AlexBlackwell: Mar 10 2006, 08:18 PM
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JRehling
post Mar 10 2006, 08:12 PM
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QUOTE (AlexBlackwell @ Mar 10 2006, 11:44 AM) *
OK, Bruce, let me suggest this. Take a magic marker and write on your palm "EAL landing failure = bad; EAL landing success = good." biggrin.gif

Hey, maybe it's me, but if the "political implications of a last-second EAL failure [isn't] blindingly obvious to them," then "the[y]" have been living in a cave if "they" do not realize the ramifications of a failure a multi-billion dollar Flagship-class mission.


I've noticed that sometimes (ideally, in fact) people don't say blindingly obvious things; that doesn't mean that they don't recognize them. It also doesn't mean that they didn't recognize it if they don't tell a stranger that the stranger just said something obvious.</2000 LB weight>
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Guest_BruceMoomaw_*
post Mar 10 2006, 09:16 PM
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OK. All I can report is what I saw: before Ms. Clark and I mentioned that, they'd been talking primarily about the scientific uses of an early Europa lander, and whether they were adequate to justify flying one. SHE certainly thought it was a worthwhile point for me to bring up. Since the cost-benefit lever for this whole squabble is beginning to resemble that of the arguments on Laputa, it might be wise for me to drop it at this point (acompanied by jeers about how I'm Admitting Defeat, which in this case I'm not).
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Guest_AlexBlackwell_*
post Mar 10 2006, 09:34 PM
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QUOTE (volcanopele @ Mar 10 2006, 07:36 PM) *
...you also have to keep the spacecraft point so that the HGA is in the RAM direction to protect the spacecraft from E-ring particles.

Doesn't RADAR have a scatterometry sequence during this flyby that at some point precludes HGA shading from SC_RAM? (i.e., POS_Z to Sun, NEG_Z to Enceladus, NEG_X to North_Pole_Dir.).

If I remember correctly, after the hand off from ISS NAC, RADAR has control of both primary and secondary axes to obtain correct polarization.
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Guest_AlexBlackwell_*
post Mar 10 2006, 10:15 PM
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QUOTE (BruceMoomaw @ Mar 10 2006, 09:16 PM) *
...about how I'm Admitting Defeat, which in this case I'm not).

"Admi[t] [d]efeat"? I would never expect that from the Tireless Rebutter. tongue.gif

Actually, Bruce, you're manufacturing a dispute. I was merely amazed that someone involved in architecting a Flagship-class mission, and no, I don't mean you, would have to state something as obvious as "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." Moreover, I was amazed that you found that such an important point. I guess I would have just said, "You think?" biggrin.gif
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Guest_RGClark_*
post Mar 10 2006, 10:48 PM
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QUOTE (volcanopele @ Mar 10 2006, 07:36 PM) *
...

Composition of reservoir: INMS observations of the plume suggest that it isn't pure H2O. Their composition measurements suggest 91% H2O, 3% CO2, 3.3% N2 (though CO is possible), and 1.6% CH4.


Wow that 1.65% methane figure itself has interesting astrobiological implications.
It could be due to hydrothermal activity or active microbes. Even if hydrothermal in origin it still raises the possibility of biology.


- Bob Clark
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Guest_BruceMoomaw_*
post Mar 10 2006, 11:20 PM
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QUOTE (AlexBlackwell @ Mar 10 2006, 10:15 PM) *
Actually, Bruce, you're manufacturing a dispute. I was merely amazed that someone involved in architecting a Flagship-class mission, and no, I don't mean you, would have to state something as obvious as "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." Moreover, I was amazed that you found that such an important point. I guess I would have just said, "You think?" biggrin.gif


*sigh* The significance of my putting "NOT" in capitals, for special emphasis was something that YOU didn't catch. Of course everyone knew damn well that we don't want EAL to fail during landing. What struck me (to repeat what I've been saying from the start) was that until Clark and I opened our yaps, virtually all the discussion in the little group had been about whether a small Europa lander was justifiable on purely scientific grounds or not. There didn't seem to be much thought about the fact that minimizing the chances of an EAL landing failure was so important that it might well justify the small earlier lander even if it WASN'T justifiable on scientific grounds. Clark noted the same thing, and got downright shrill about it when she started talking.

Actually, I have the whole thing on tape, since I tape-recorded all the subgroup's deliberations (with their permission). At some point in the near future I'll review it -- and if it doesn't match up with my memories of what happened, I will not only admit it here; I will kill myself in the most disgusting manner conceivable. Now, back to Enceladus (I hope).
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Guest_AlexBlackwell_*
post Mar 10 2006, 11:51 PM
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QUOTE (BruceMoomaw @ Mar 10 2006, 11:20 PM) *
Actually, I have the whole thing on tape, since I tape-recorded all the subgroup's deliberations (with their permission). At some point in the near future I'll review it -- and if it doesn't match up with my memories of what happened, I will not only admit it here; I will kill myself in the most disgusting manner conceivable.

Bruce, you really crack me up. That's what I meant about manufacturing a dispute. I'm not questioning your veracity. Jeeez. I accepted what you said at face value. I was only amazed that something so obvious had to be stated. That's all.

Now, I'll await your inevitable (1,000 word?) response to this.

Actually, I'm beginning to feel like a sadist poking a stick at a caged tiger biggrin.gif
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helvick
post Mar 11 2006, 01:54 AM
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QUOTE (AlexBlackwell @ Mar 10 2006, 11:51 PM) *
Actually, I'm beginning to feel like a sadist poking a stick at a caged tiger biggrin.gif

Bruce\Alex.
I'm not in a position to comment on history here but....

I value both of your perspectives on these issues and would like you both to keep to the topic. It's not my call so feel free to ignore this but far too much of this debate has been personalised.

You are both extremely well informed on the issues and can do better than this in a forum such as this. If you want to have a personal scrap I think you should do that elsewhere.

All of the above is clearly in the "ad hominem" space - I really hate feeling that I'm doing such a thing but I really would like you both to step back and think about what you post on this topic before hittting the post button.

[Doug: I'd be happy to see this post deleted but please do so in conjunction with a broad brush]
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Guest_AlexBlackwell_*
post Mar 11 2006, 02:00 AM
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QUOTE (helvick @ Mar 11 2006, 01:54 AM) *
I'm not in a position to comment on history here but....

No, you're absolutely correct, helvick. Point taken.
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Guest_BruceMoomaw_*
post Mar 11 2006, 02:50 AM
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Fine -- especially since the whole damn thing was a diversion from what this thread is supposed to be about anyway. (Admittedly I launched it, but I had no idea it was going to drag on THIS long.) Now back to Enceladus.
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