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Europa Orbiter, Speculation, updates and discussion
Guest_Richard Trigaux_*
post Oct 24 2005, 09:54 AM
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QUOTE (BruceMoomaw @ Sep 19 2005, 09:04 AM)
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.
*


Why not ultrasonic communication? Sounds transmit well and far in solid mediums, and there would be no need of lines, repeaters and the like. I see well the penetrator having an array of piezoelectric crystals on its top, it would even be directive. On the countrary a radio link could not work if there is a fault or ice layer at 0°C soaked with salty water.
After, if the penetrator has a density between water and ice, it would float at the bottom of the ice and collect many molecules with a filter.

And with no added cost this sonar (call it by its name) would be a wonderfull mean to probe the ice crust, faults and galeries, and above all to probe the ocean itself, its depth, eventually layers and currents, floating objects, and the ocean floor...

fascinating: an ultrasonic "image" of volcanoes from the rocky core of Europa... "black smokers" (thermal vents) would be already fine.

More and more: the penetrator abandons its floater, and sinks to the rocky floor itself, and takes photos of it, eventually showing weeds and living forms...

Wow!



And on the surface?
A repeater left on the surface could send enough power (like Huygens did) to be picked from Earth (with a slow bit rate. Of course if there is an orbiter to relay data it would be better). If the repeater is buried in ice, just its radio antenna out, it could work for months and years, much compensating for the slow bit rate.
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Guest_BruceMoomaw_*
post Oct 24 2005, 09:01 PM
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The presentations from the third OPAG meeting have just arrived: http://www.lpi.usra.edu/opag/oct_05_meeting/agenda.html . (The final report from the meeting isn't available yet, though.)
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ljk4-1
post Oct 25 2005, 04:27 PM
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Though this may sound terribly obvious, any Europa landers/ocean explorers had better be designed to last a long time if their main goal is going to be the search for life on that Jovian moon.

Unless the ice crust is encrusted with dead microbes or such similar creatures and their alien jellyfish counterparts are saturating Europa's ocean, I do not want to end up with the same situation as the Viking landers, who were stuck on two tiny spots on Mars and had scientists and the media declaring the Red Planet a dead world (again) when a few scoopfuls of dirt revealed no native microbes. Europa will require a long exploration.

To add: The global ocean on Europa is estimated to be *60 miles* deep. Thankfully in one sense the moon's much smaller mass makes the bottom water pressure on Europa no "worse" than that found in the deepest parts of the Pacific Ocean (7 miles down), but if there are black smokers and alien versions of red tubes worms and giant crabs living around them, can we design a probe that could make it all the way to the bottom of the Europan Ocean and return the data to Earth?

Another question: Life may be able to survive on Europa in its present state, but based on what we know, could it ever have gotten off to a start in the first place?


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
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."

- Henry David Thoreau, November 15, 1853

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Guest_BruceMoomaw_*
post Oct 25 2005, 10:35 PM
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The reply to the second question is simply: we don't know. We don't know whether life could have evolved out of prebiotic molecules on Earth had the water been as acid and/or saline as Europa's appears to be; there has been at least one abstract I've read expressing doubt, but given our stupefying continuing level of ignorance about how the chemical process occurred on Earth itself, we just don't know.

As for the first question: even if we don't get all the way down to isolated "smokers" on the floor of Europa's ocean, we should be able to detect microbes (or their remnants) from such locations spread uniformly through the ocean water -- after all, that's how life on Earth gets transferred from one isolated smoker to another and so survives after the first smoker finally goes out. And if the alternative theory is true that Europan microbes may derive their nourishment instead from chemicals manufactured by radiation in Europa's upper ice layer and then gradually transferred down to the ocen by geological processes in that ice layer, the principle is even more true -- in fact, in that case the life would probably be concentrated at the TOP of the liquid-water layer.

This also leaves the question of whether we can find evidence of microbes in Europa's liquid ocean without even having to bore down through the ice layer to the ocean, by instead analyzing the surface ice itself to look for such remains transported up to the surface by those same slow geological processes in the ice layer. The consensus seems to be that this is a real possibility -- but, since there's a thin layer of brittle supercold "nonconvective" ice 1-3 km thick on top of the warmer main ice layer which slowly convects (and which even perhaps carries pockets of still-liquid brine upwards), we are going to have to be careful to choose landing sites that look likely to have had buried material erupted all the way up to the surface. (There are several types of Europan surface features that show promise of this, which is another reason why we do need a Europa orbiter first to pick out good landing sites.)
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Guest_Richard Trigaux_*
post Oct 26 2005, 09:02 AM
Post #50





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QUOTE (BruceMoomaw @ Oct 25 2005, 10:35 PM)
This also leaves the question of whether we can find evidence of microbes in Europa's liquid ocean without even having to bore down through the ice layer to the ocean, by instead analyzing the surface ice itself to look for such remains transported up to the surface by those same slow geological processes in the ice layer.  The consensus seems to be that this is a real possibility -- but, since there's a thin layer of brittle supercold "nonconvective" ice 1-3 km thick on top of the warmer main ice layer which slowly convects (and which even perhaps carries pockets of still-liquid brine upwards), we are going to have to be careful to choose landing sites that look likely to have had buried material erupted all the way up to the surface.  (There are several types of Europan surface features that show promise of this, which is another reason why we do need a Europa orbiter first to pick out good landing sites.)
*


Yes, good approach in a first time, before trying to reach the bottom of the ocean (what I think possible but more complicated). But the very upper layer of ice (about 1m) is exposed to strong radiations, and thus sterilized, and anyway not representative of the global ice chemistry. So we need to drill from the very first landing, even if only 1-2m. For this reason penetrators were proposed (sticking themselves in ice like an arrow, which solves the problem of soft landing) or using a more classical drill, or a heat source able to melt ice. (RTGs were proposed, but RTGs are weak, a chemical source would perform better for this very purpose). A tip would be to place all the electronics into the drill, so that it is protected from radiations and it can last for much longer, very useful if it carries a seismometre.


Also a RTG was proposed to melt the ice down the ocean. But are RTGs powerfull enough for this? I would rather see a bot with a screw-shaped nose and a body with fins, like in sci-fi novels, running with a high gear rate, it would be much more power-efficient and faster than just melting ice. We have plenty of places on Earth to test this, in the Antarctic ice shelds. If there are interesting results from a surface examination, there will be a strong support for the idea of looking at the botton of the ocean.
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Ames
post Oct 26 2005, 02:03 PM
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The beauty of an RTG is that it creates a LOT of "waste" heat that can be put to use here for "free".
Also the electricity generation efficiency can be increased if there is an effective cold sink.

So an RTG probe is Perfect - as long as you don't hit a buried rock/meteorite.

Nick
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Guest_BruceMoomaw_*
post Oct 27 2005, 01:05 AM
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If they do add a small lander to the first Europa orbiter -- and that is a very big "if" -- I've been a fan for some time of making it a penetrator rather than a surface lander, for a whole swarm of reasons:

(1) Such a penetrator can punch down a meter or two into the ice just by impact, giving it a good chance of getting below the radation-modified upper layer. (As far as I'm concerned, no lander that doesn't drill down that far is worth sending.)

(2) It could couple a seismometer -- the second most important instrument for a Europa lander, according to the science working group -- to the crust far more firmly than a surace lander.

(3) It would bury itself in the ice deeply enough to be shielded from Jupiter's radiation -- a very serious problem for an exposed surface lander.

(4) It could land on virtually any kind of terrain, no matter how rugged.

As far as I can tell, its ONLY disadvantage is that it would have more trouble getting post-landing surface photos -- but it could carry a descent camera and memory buffer to record and later play back the last few images before impact to get imaging data almost as good.

Sure enough, Paul G. Lucey -- the Univ. of Hawaii scientist who has proposed the "Polar Night" Discovery-class penetrators to look for lunar ice (they would weigh only 65 kg, penetrate 1-2 meters into the surface, and carry mass spectrometers which have already survived impact tests at four times the planned landing speed) -- is now proposing "Thunderbolt", a mission to look for Europan surface organics. He hasn't yet described it -- and I'm still waiting to hear any details from him -- but it is surely another penetrator mission.

However, there's another problem, as Chris Chyba pointed out in "Europa As An Abode of Life": the probe may have to process one hell of a lot of meltwater to filter out enough organics for study -- quite possibly 100 times more than any pentrator or small surface lander could possibly collect. We may have instead to fall back on a larger and later surface lander with an attached heated melt probe capable of melting down at least 100-200 meters, and filtering all the large amount of meltwater which it produces in the process. And while the waste heat from an RTG would do just fine to generate the melting heat -- that's been the plan from the start -- if Europa's ice is as highly saline as many think, a salt crust would build up ahead of any simple melt probe. It may need both a melting head AND a rotating drill head to chew through the accumulated salt. In any case, I don't see any way to put either of these on a penetrator.
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ljk4-1
post Nov 10 2005, 05:25 PM
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Here's a use for an Europa Ocean Probe - as a neutrino detector!


Paper: astro-ph/0511243

Date: Wed, 9 Nov 2005 17:14:51 GMT (304kb)

Title: Development of Acoustic Sensors for the ANTARES Experiment

Authors: Christopher Lindsay Naumann, Gisela Anton, Kay Graf, Juergen Hoessl,
Alexander Kappes, Timo Karg, Uli Katz, Robert Lahmann and Karsten Salomon

Comments: 5 pages, 3 figures. Proceedings of the ARENA 2005 Workshop
\\
In order to study the possibility of acoustic detection of ultra-high energy
neutrinos in water, our group is planning to deploy and operate an array of
acoustic sensors using the ANTARES Neutrino telescope in the Mediterranean Sea.
Therefore, acoustic sensor hardware has to be developed which is both capable
of operation under the hostile conditions of the deep sea and at the same time
provides the high sensitivity necessary to detect the weak pressure signals
resulting from the neutrino's interaction in water. In this paper, two
different approaches to building such sensors, as well as performance studies
in the laboratory and in situ, are presented.

\\ ( http://arXiv.org/abs/astro-ph/0511243 , 304kb)


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
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."

- Henry David Thoreau, November 15, 1853

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ljk4-1
post Nov 11 2005, 05:39 PM
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Anyone know if clay minerals exist on Europa, or could exist?

http://www.spaceref.com/news/viewpr.html?pid=18272


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
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."

- Henry David Thoreau, November 15, 1853

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Roly
post Nov 16 2005, 04:11 PM
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I know this has come up before but is it possible to do a Europa fly-by within a Discovery cost-cap?

Given that the Europa Orbiter is going to be 2012 at the earliest, surely there is scope for someone to propose something for Europa at the next Discovery AO.

I don't know that much about the design of orbiters, and this may
demonstrate (and probably does) some fundamental misconceptions, but I was
curious about a return to fly-by missions instead of orbiters like Galileo,
Cassini, EO etc. From what I have gathered, for many missions, the largest
problem is the energy required to brake into science orbit, particularly
where there is no potential for aerobraking, meaning a huge percentage of
the mass budget must be spent on a powerful engine and the requisite
propellant. I was under the impression that these problems were vastly
reduced in fly-by trajectories (?) With VEEGA trajectory perhaps this would be possible on a very economical LV (though it seems everything going forward is flying on Delta IV and Atlas now, not Delta II?) Okay so not a Taurus but there must be something in between Taurus and Delta/Atlas EELVs.

So instead of spending mass on an large engine with enough fuel to get into
a science orbit, couldn't the spacecraft instead focus on acquiring a huge
amount of data over a very short period of time in a low-altitude fly-by?
It would then sample a small area of the target at high-resolution.

It could carry (and I'm only guessing, the exposure/integration
times/pointing accuracy might make it truly impossible) stereo cameras and a
high
resolution imaging spectrometer on a motion compensation
scan-platform. All would operate
simultaneously, with power from advanced Solar arrays (Rosetta heritage?) lithium-ion batteries,
which would be charged during the cruise phase by the array to make up for any
power deficit during the very short and high-demand encounter phase. They could even be augmented with lithium primary batteries if required. The
spacecraft would be equipped with extremely wide and fast data busses,
caching the acquired data to memory and writing it out to solid-state disks
for later playback. No-RPS, easier admin. burden, compatibility with Discovery AO.

It would record this to high-capacity solid-state data recorders (multi-100s
GB), and then replay it once it had left its target, potentially over a
period of months or even years, depending on how much power was available,
local limits on the downlink and so on. This eases DSN management perhaps? Offline compression would be helpful, especially given that there might be issues with heavy compression in the Jovian environment (I'm suprised ICT did so amazingly well).

As an added bonus some of the
radiation hardening requirements would be reduced, as the spacecraft would
not be remaining in the most dangerous areas for a prolonged period,
repartitioning mass away from shielding and to the science payload. Lithium polymer batteries might be decent for providing some incidental shielding in any case.

I suspect I am heavily overestimating the ability of the scan platform to
provide adequate motion compensation, and the amount of time needed for the
instruments to acquire data - but I was curious about the idea because it
leverages some of the things that have become much better and cheaper over
time, like bus bandwidth, memory, disk write performance, processing power,
detector resolution/sensitivity - to replace things that have not, like
putting large amounts of propellant and engine mass into orbit.

I read a bit about Firebird recently, which seemed to utilize a similar approach. Perhaps there is geometry which would make possible a "Fire and Ice bird" (like the old JPL 'Fire and Ice' theme) ?

I've wondered out loud about this on other forums but no-one ever seems to have any ideas (other than Orbiters are better, which of course they are...)

Roly
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dvandorn
post Nov 16 2005, 05:00 PM
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It's not just that orbiters are better (though that rather goes without saying, in many ways).

First, there is the issue of time-and-change-dependent observations. If one of your goals at Europa is finding places where the ice crust is thin enough to provide some form of access to the ocean below, you need to observe Europa over a matter of weeks and months and track the movements of the crust.

Second, there is the issue of coverage. No matter how you design your approach trajectory, you're going to be able to observe only a tiny fraction of the surface during a fast fly-by. And there will only be one side sunlit during that snapshot. So no matter how capable a fly-by probe might be, its choice of what it can view is severely limited.

Lastly, there is the politics of funding. We are *barely* to a point where we can think about getting Congress to fund a Europa Orbiter mission -- a mission that we really need, in order to answer fundamental questions and set up a possible landing mission (and, more ambitiously, a mission to explore the subsurface ocean). Because of the points I raised above, a fly-by mission is far less likely to provide those answers, no matter how much data it returns about a very small portion of Europa. And now, *in addition* to funding an orbiter for a billion or more dollars, we're going to ask them to fund an interim fly-by mission for another half a billion dollars? If we were to do that, we'd end up with either the less-useful fly-by and NO orbiter, or (more likely) just getting laughed off the Hill for trying to get them to fund *two* different missions to the same chunk of ice millions and millions of miles away -- a chunk of ice most of them think is worthless in the first place.

Is that a little better answer than a simple "orbiters are better" statement?

-the other Doug


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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JRehling
post Nov 16 2005, 08:13 PM
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QUOTE (dvandorn @ Nov 16 2005, 10:00 AM)
Second, there is the issue of coverage.  No matter how you design your approach trajectory, you're going to be able to observe only a tiny fraction of the surface during a fast fly-by.  And there will only be one side sunlit during that snapshot.  So no matter how capable a fly-by probe might be, its choice of what it can view is severely limited.-the other Doug
*


Something that the continued Cassini imaging of Saturn's many moons has made me aware of is the value of terminator observations, which are even more severely limited than observations intended merely to map albedo. A single flyby will show a world in 50% illumination, but only a small fraction of the surface in the low sun angles near the terminator. When Cassini's mission is done, we will be able to generate low-resolution DEMs for all of Saturn's inner icy moons, which would be very hard to achieve by performing direct measurements of altimetry for so many worlds (JIMO comes to mind).

Amateur astronomers know how dull an object the full Moon is, and Mariner maps of Mercury show how much more detail is seen at the terminator than mid-disk. An orbiter (even a Jupiter-orbiting craft) would provide not just twice the imaging of Europa -- in terms of terminator observations, it would provide perhaps 100 times as much imaging.

Any flyby of Europa better be a sample return.
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Guest_Richard Trigaux_*
post Nov 16 2005, 08:16 PM
Post #58





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QUOTE (ljk4-1 @ Nov 11 2005, 05:39 PM)
Anyone know if clay minerals exist on Europa, or could exist?

http://www.spaceref.com/news/viewpr.html?pid=18272
*


At rough guess, it is possible, if there are basaltic rocks at the bottom of the ocean. clay is the usual result of slow chemical attack of such rocks by water. But perhaps the chemistry of Europa water is very different of Earth rainwater, so the result may be different. And if Europa has a carbon layer around its rocky core, clay becomes unlikely.

That this clay may arrive at the surface is another question. Europa shows strong evidences of the ice layer being broken is small icebergs and turned upside down, from some catastrophic events. So things in the ocean can reach the surface. That some clay from the bottom of the ocean could reach the surface needs a double transfer, first into the ocean, second into the ice layer. Maybe the catastrophic events can achieve both in the same time.

So a lander could search for such particles in the molten ice. From them it could give clues about the core of Europa
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Guest_Richard Trigaux_*
post Nov 16 2005, 08:23 PM
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QUOTE (Roly @ Nov 16 2005, 04:11 PM)
I don't know that much about the design of orbiters, ... the largest
problem is the energy required to brake into science orbit, particularly
where there is no potential for aerobraking, meaning a huge percentage of
the mass budget must be spent on a powerful engine and the requisite
propellant.
*



Would not an economic trajectory achieved with a ship in orbit around Jupiter, using the moons as a gravitational assistance, until getting a nearby circular orbit at the level of Europa, which provides the most economic way to brake and land?

The only inconvenience of this is that it would require some months, and also staying into radiation belts for a long time. So what is gained in fuel may be lost in hardening the electronics.
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Guest_BruceMoomaw_*
post Nov 17 2005, 02:06 AM
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That is exactly the plan that has ALWAYS been written for Europa Orbiter -- it will make, first, about 6 flybys of Ganymede and about 3 of Callisto, and then (in the so-called "Tour Endgame") as many as a dozen close flybys of Europa itself to almost match orbits with that moon before orbital insertion. (For a drawing of a typical such tour, see page 10 of http://www.lpi.usra.edu/opag/jun_05_meetin...ssion_Study.pdf .) The whole process will take roughly 18 months, during which EO will soak up about 900 kilorads of radiation -- equal to the dose it will get during its 1 month in orbit around Europa itself.

As for aerocapture for EO, it's been considered, but -- besides the fact that aerocapture technology won't even nearly be ready for an EO launch by 2014 -- I was told at the COMPLEX meeting that studies indicate that aerocapture doesn't provide much of an advantage for this particular mission. (The plan, by the way, is also to use a flyby of Ganymede to help brake the craft into orbit around Jupiter initially, as Galileo used a flyby of Io for that purpose.) But -- even with all this gravity-assist -- half of EO's weight must be propellant. This is simply a difficult mission.
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