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Europa Orbiter, Speculation, updates and discussion
Jeff7
post Sep 18 2005, 02:38 AM
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Someone mentioned an impactor - how about using a small stream of impactors to blast successive craters, and at the end of the stream would be the instrument-laden lander itself? It might still need to drill, but not nearly as much.
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Guest_BruceMoomaw_*
post Sep 18 2005, 07:56 AM
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Uh-uh -- you'd need a huge weight in impactors to blast a hole of any significant depth, whereas you could achieve much greater penetration for tremendously less weight just by making the probe a melt probe (or giving the surface lander a longer drill). To say nothing of the gargantuan targeting difficulties...
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ljk4-1
post Sep 18 2005, 02:35 PM
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Back in 1998 I initiated a discussion list for landing a probe on Europa to explore its subsurface global ocean. Named Icepick, the discussion lasted until just a few months ago.

http://www.klx.com/europa/

You can read the discussions here. I think we hit on many if not most of the scenarios for making this mission plan a reality.

http://www.mail-archive.com/europa%40klx.com/

If someone wants to revive the Icepick list and get discussions going again, I would be most grateful. Jeff Foust ran the intial list and Web site.


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I see that such intercourse long continued would make one thoroughly prosaic, hard,
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not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

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Guest_BruceMoomaw_*
post Sep 18 2005, 09:46 PM
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Yep, that's the site where I got my start as a space commentator -- and where Simon first ran into me. Sad to see that it's finally disappeared. Maybe I should have hung around there, but I've been juggling several plates at one time for the last few years and just never got around to dropping back in. It starts to look as though the discussion site for Europa exploration may migrate over here.
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Redstone
post Sep 19 2005, 02:47 AM
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Apologies if this has already been discussed, but on the OPAG site, there's a fascinating report on Europa Surface Science options. It runs to 86 pages and covers radiation issues as well as landing methods. It was based on the JIMO as the mothership, but much of the discussion is still relevant, I think. I haven't had the chance to go through it in detail, but one point caught my eye: for 375 kg, you can soft land 167 kg on the surface using powered descent. For comparison, the Huygens probe had a mass of 320 kg.
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Jeff7
post Sep 19 2005, 03:25 AM
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QUOTE (BruceMoomaw @ Sep 18 2005, 02:56 AM)
Uh-uh -- you'd need a huge weight in impactors to blast a hole of any significant depth, whereas you could achieve much greater penetration for tremendously less weight just by making the probe a melt probe (or giving the surface lander a longer drill).  To say nothing of the gargantuan targeting difficulties...
*


Ok, a melt probe. RTG powered I assume? Just did a quick search.....one page says this of Cassini's RTG's:
"The alpha particles naturally heat the pellets to 572 degrees Fahrenheit (300 degrees Celsius)."
Not too bad at all, more than I expected actually. That'd definitely make a hole....though I'm just thinking now, it'd encase itself beneath the ice. The water above would likely refreeze fairly quickly, even with a toasty robot beneath it. So the little meltbot would be sealed under the ice rather quicly. What would it use for communication? A fiber optic line would be risky (might get tangled), and would add weight. And I don't know how well radio waves penetrate ice.
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hendric
post Sep 19 2005, 04:39 AM
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QUOTE (Jeff7 @ Sep 18 2005, 09:25 PM)
So the little meltbot would be sealed under the ice rather quicly. What would it use for communication? A fiber optic line would be risky (might get tangled), and would add weight. And I don't know how well radio waves penetrate ice.
*


A fiber optic cable is probably the best bet, using a floating transmitter/receiver at the end of the line to keep it above the meltwater until it refreezes. Radio would require repeaters to go through the ice, which is possible, but you'd have to power them somehow, and keep them from melting down (or up!) when they activate.


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Guest_BruceMoomaw_*
post Sep 19 2005, 09:04 AM
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Jeff: I saw that OPAG report -- and the two more recent papers att the OPAG site that I mentioned previously elaborate on it somewhat.

Hendric: The idea of a fiber-optic line for communications -- originally the favored idea -- got the boot several years ago, both because of weight problems and becuase the slow but steady ductile sliding of Europa's ice layers would almost certainly snap it. The current plan is to have the probe carry a stack of tiny disk-shaped radio repeater packages powered by tiny RTGs, and release one every kilometer or so that it descends -- so that they're close enough to pick up each other's radio signals through the ice and thus chain-link the signal from the melt probe all the way to its surface carrier.
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Guest_BruceMoomaw_*
post Sep 19 2005, 09:05 AM
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I should add that the heat from the extremely tiny RTG that each such package would require would not be nearly enough to melt the surounding ice and make it sink deeper.
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deglr6328
post Sep 19 2005, 09:14 PM
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Wouldn't it? Let's say you want a 10W transmitter. You will need at least, I don't know, ~15W total for electronics and losses and such..? The abysmal efficiency of RTGs meas you will need at least a ~100W heat source to power the thing......ice is a very good insulator.....

I would very much like to see a plot of EM wave attenuation vs frequency for ice so that any "windows" could be identified and the necessary transmitter power could be constrained with higher confidence.

Hmm this looks interesting... huh.gif
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Guest_BruceMoomaw_*
post Sep 20 2005, 04:45 PM
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There are two relevant JPL Technical Reports on this design. Unfortunately, JPL's technical-report server seems to be offline for now, so I've attached both reports.

Actually, each transceiver would use a mere 0.12 W power source, hooked up to a capacitor to allow periodic bursts of 1.3 W transmission power. So that's why there's no RTG ice-melting problem.
Attached File(s)
Attached File  CDAR____Europa____JPL_TR_01_2122____Bryant.pdf ( 477.38K ) Number of downloads: 959
 
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Guest_BruceMoomaw_*
post Sep 20 2005, 04:48 PM
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And here's the other JPL report.
Attached File(s)
Attached File  CDAR____Europa____JPL_TR_99_2051____Zimmerman.pdf ( 832.18K ) Number of downloads: 201
 
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deglr6328
post Sep 24 2005, 09:00 PM
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smile.gif hmmm! very interesting thank you!
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Roly
post Oct 23 2005, 04:49 AM
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Was anyone at the recent (October) OPAG meeting where the new Europa Orbiter was due to be discussed?

The October report and documents aren't up yet, but surely it can't be too long now. Wonder how the talks with ESA went? Hope there was some more support for the 2013 opportunity, given the extra dry mass that could be delivered (probably enough for the soft lander studied by Balint, Nov. 2004).

Roly
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Guest_BruceMoomaw_*
post Oct 24 2005, 05:00 AM
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I wasn't able to make it to OPAG, and have been monitoring their site for news on the presentations and final report from the October meeting. They haven't turned up yet, but I expect them soon.


http://www.lpi.usra.edu/opag/meetings.html
http://www.lpi.usra.edu/opag/reports.html
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