http://www.nasa.gov/topics/solarsystem/features/20090218.html
There will be some happy people, and some disappointed people. Both systems have plenty to offer, so no one should be too upset.
I'm not upset (or surprised). I always wanted both, and with luck we'll get both. There is no law that says there has to be a ten year gap between them. Returning to Saturn and Titan at a season complementary to Cassini's visit is a good argument for not waiting that long.
Now I'm wondering how this will play out on the European side. It always struck me as awkward that ESA should have a stake in the overall decision two years before it fully commits to participating. Also, supposing that Nasa did go ahead with both in (relatively) quick succession it's highly doubtful that ESA would be able to contribute to both.
Of course anything is possible if the will is there. I await an ESA statement with great interest.
For those, as I, who were looking forward for a TSSM selection here are some words that just arrived my e-mail from Athena Coustenis, TandEM project leader:
"It seems we may have to wait a little longer to see this mission launched, to plunge through Enceladus' plumes, to hover over dune fields and to land in a Titan lake. No matter. The first aim of this community is to have the need for a future space mission to the outer planets recognized and transformed into reality. We may be heading for Jupiter first, but as said in the text, and as it has been well demonstrated by the reactions within this community, the public and the press, we shall need to go even further in the future.
I take this opportunity to say that during the past 15 months I have had the immense pleasure and honor to work, exchange ideas and argue with you all over the most fascinating subject ever: a future mission to return to the Saturnian system and hunt down information on fascinating aspects like Titan's atmosphere and surface, Enceladus geysers and Saturn's magnetosphere. For some of us, the adventure had even started earlier, when we were preparing the proposal for Tandem within the framework of ESA's Cosmic Vision 2015-2025 or the study of the 2007 Flagship Titan Explorer mission.
I want to thank you and tell my appreciation, in particular to my friends and colleagues of the JSDT and the ESA and NASA study teams, who have managed to create a complete science and mission architecture case out of nothing within such a short time. They have done this with help from all of you. AND WE ARE READY TO GO ON."
Sometimes you win sometimes you lose, the important now is that we're going somewhere...Onward Europa Jupiter System Mission!
Although I was a "Titan Now" kind of person, my first reaction is more of excitement than disappointment. Two orbiters? Not too shabby. It will be great to see the Jupiter system get the complete Cassini treatment... times two!
Just curious. Does anyone think that there may be plume activity on Europa similar to that on Enceladus?
Plume activity on Europa can't be ruled out, though it's perhaps not very likely. Europan plumes would be much smaller than those on Enceladus (more like Prometheus-sized), due to the higher gravity, and might have been missed by Galileo, which of course had very limited ability to do extensive monitoring. And remember that on average, Europa's surface is much younger than that of Enceladus...
John.
Sorry for the ignorant mode here but I don't know the mission architecture...does the future mission count "only" the two orbiters or are there plans tu include extra goodies, an impactor or something similar towards Europa?
EDITED: ngunn, that wasn't an exclusive e-mail...
Regarding spacEurope, I've made campaign for TandEM...don't tell me you didn't http://spaceurope.blogspot.com/2007/10/in-meeting-held-on-17-and-18-october.html?! I even had some graphics of mine and that beautiful logo (it was...it was...) included in the http://www.lesia.obspm.fr/cosmicvision/tandem/concept.php...
Interviews are not predicted so soon I'm afraid...in March/April we'll talk about it...
Well, I was hoping for Titan, but Ganymede & Europa will be fine too!
It'll be great to finally have a torrent of data streaming down from the Jovian satellite system after the painful trickle that was Galileo's tour.
Rui - I always keep an eye on spacEurope - even when it's quiet. I have lots of questions now, such as: Will CNES proceed with development of a Titan montgolfiere? How soon could ESA scramble a TITAN LAKE EXPRESS outside of the flagship framework? In time to arrive before Cassini dies??? I'm counting on you to find out!
Oh yes, and will Ganymede beat the astronomy missions in 2011?
I originally preferred TSSM but eventually became fairly neutral so overall I'm happy. Actually I kinda expected this result - comparing the kind of coverage Cassini has given at Saturn to what Galileo did at Jupiter is one obvious justification. Lots of atmospheric movies of Saturn at several wavelengths compared to very limited movies of Jupiter (actually the best ones are from Cassini), extensive ~1 km/pixel multispectral imaging of Saturn's satellites compared to Galileo's limited color coverage, to name a few. And significantly better instruments on Cassini. Also the Cassini mission isn't over yet while the Galileo mission ended several years ago.
EJSM is going to be a spectacular mission, a 'Galileo 2 on steroids' - and with a functional HGA. The only problem is that ESA hasn't commited to flying the Ganymede orbiter yet.
Am I the only one here who preferred EJSM? TSSM is surely a great mission concept too, it was just my 2nd choice
I also preffered TSSM, based mostly on the idea that Jupiter could be explored with more limited missions (such as the Io Volcanic Observer) but that Saturn/Titan really needed something more in the flagship range. I also thought that the TSSM was mature enough of a mission canidate to compete with the EJSM .
But, it seems that the reviewers felt that the Saturn elements needed more technical study. That changes my mind. If there is a technical readiness difference, definately go with the Jupiter mission.
I hope that the Europeans actually do the Ganymede mission, but in any case we now know that the Europa mission is a go.
One last thing: at least the cruise time to Jupiter is much shorter than the Saturn system. We'll be seeing great pictures by 2026, instead of having to wait until 2030. As an aging baby-boomer, I'm all in favor of that.
mps, don't worry, you are not the only one As I have done so much work on Titan and that is my second favorite celestial body, I would have been fine with TSSM. But the Jupiter system really needed the kind of treatment Cassini has given Saturn, and more. EJSM does that. And of course it studies Europa and Ganymede quite extensively too.
Well this is indeed a fascinating news, like long way to go but still something to look forward to. For last 10 years, just following the Cassini mission has been nothing short of a blessing, and hopefully getting an opportunity to live for another Outer planet Flagship mission is just too captivating.
EJSM or TSSM , both are amazing missions and will keep all of us busy to cherish this fascinating world of planetary exploration ! Good luck to NASA & ESA
Great great news! I was also at first a bit pro-titan but now i feel fine with this decision, actually quite positive, because both missions have been recognized important ones and are moving forward. As mentioned here before I also believe "Cassini's goodness" was one reason why Jupiter is now getting its shot. And to be honest, we really need a Europa orbiter, finally. Science moves on small steps and this way we will eventually have Europa lander/driller/diver sooner in the still distant future. This also levels nicely the scientific returns on two giants, Jupiter after all is still the most important planet in our system in many aspects.
One thing here is also, that if Titan mission would have been given priority, pretty likely there would have been then more of these less capable discovery-class stuff going to Jupiter anyway, so this would have been effectively eliminating other interesting discovery options like Venus balloon/lander. Titan anyway needs to be flagship-way and letting technology mature a bit especially with balloons we improve chances of success there in the future.
What a great time to be anyway. I am just impatiently waiting for first pictures from Ceres, Pluto/Charon, around Mercury and of course the first light of Kepler...
Selection of the Jupiter mission would mean that the late-10s Jupiter-Saturn slingshot opportunity will probably be lost. The next will be more than one decade later. too bad!
2026 arrival?
Ralph, I figure the JS assist opportunities out to recur every 20 years, because 1/(1/12 - 1/29.5) = 20.2. That doesn't say how long the launch window stays open, though, but is it as much as three years?
--Greg
In my perfect world, the Jupiter flagship is earmarked and slated for launch first, but money and effort is also poured into the technological development of the TSSM mission. Such that the TSSM launches within months after the Jupiter flagship.
'Course in that same perfect world, my investments have gone through the roof and I've already retired and am sitting on a beach with a fuzzy drink...
Jim Green posted a message on the OPF website: http://opfm.jpl.nasa.gov/community/decisionontheouterplanetflagshipmission/
I just put up a post on my blog about the next steps for EJSM: http://gishbar.blogspot.com/2009/02/whats-next-for-europa-jupiter-system.html
I really anticipated that EJSM/JGO would be the choice. Poor GALILEO could only send a dribble of data homeward. It is time to go back to Jupiter system with a mission that can recoup what was not possible with GALILEO due to it's stuck high gain antenna. It is the Europa / Jupiter research communities turn.
Who can guess what new wonders EJSM/JGO will reveal?
Titan's dunes and lakes and strange highlands will get their turn. As will the plumes of Enceladus.
The 2020's is some time ahead.... we can hope that newer technologies will mature enough to fling smaller, more capable tech at the worlds out there so far from the Sun..... (just hope here - since I want the ice giant research community to get it's turn at Uranus/Neptune as well....
So much to discover and these little mayfly lives we lead are so short. But I really cannot complain. We know SO much more than when I was born.... watching the universe unveil continues to be a source of solace in a human world that sometimes seems all too crazy.
Craig
Since the probe that will be flying by Io has been approved, can I have champagne and dancing girls anyway?
It sure seems to me that ESA has made up its mind.
http://www.esa.int/esaCP/SEMPHGWX3RF_index_0.html
How did it happen that there was such a gap between Cassini and this mission? Was this is a result of the Battlestar Galactica JIMO fiasco?
Was MSL explicitly funded instead of an outer planets mission or did it just kinda work out that way in the end?
Caveat: I'm trying to avoid a political discussion. Just answering his question with history as I remember it.
I don't think the term 'flagship' came into common use until around the time of the Decadal Survey in 2003. The survey concentrated mostly on non-Mars missions, so if I recall correctly in the Survey the term was used mostly to refer to the large outer planets missions like Galileo and Cassini. I never recall MSL reffered to as a flagship until around 2007-2008 when Michael Griffin called it one.
The reccomendation was that in every decade NASA try to fly one flagship, a New Frontiers mission every 3 years, and a Discovery mission every 18 months. (notice the nice multiples of 3 here..... 1 Flagship, 3 New Frontiers, 6 Discovery) .
The survey also recommended that if the missions could not be flown that often, that the ratio remain somewhat the same. In other words, do not attempt to fly 3 New Frontiers and 6 Discoveries in a decade, and then just keep putting off the Flagship. I read this as a deliberate attempt to get away from nearly a decade of all new mission starts essentially being Discovery class.
More or less NASA seems to be attempting to follow this recommendation. Over the last few years the rate of New Frontiers Announcements of Opportunity comes along every 5-6 years, Discovery every 3 years or so. Six years after the Decadal Survey we now have (hopefully) a commitment to an outer planets flagship.
Cassini - 1997, MSL - 2009 (goal), and EJSM - 2020, roughly speaking we are getting a flagship every decade or so.
Again, this is just the events as I recall them. Not trying to start a funding debate.
Something that I can't figure out is how large the solar panels would be for the ESA JGO. JGO is much heavier on the imaging and spectroscopy than say Juno, and no one has tried to perform a "flagship" class mission this far from the Sun. (Sure there is Rosetta, but its primary mission sweeps back toward the Sun after the comet rendez-vous.) Can ESA pull off a large solar powered mission so far from the sun without having prohibitively large (and heavy) solar panels?
I think the term was coined during the early Goldin era unless it predates it. I remember him referring to Cassini as such.
You mean when Goldin wasn't calling Cassini "Battlestar Galactica" ?
As I recall he hated that mission, thought it was much too large and unwieldy.
At the risk of offending Titan-lovers here, I have to be honest and say that I'm glad Jupiter got the nod for this flagship mission, Don’t get me wrong; I love the Saturn system, and I love Titan too. What’s not to love about a planet-sized satellite that has its own atmosphere, coastlines, lakes and maybe ice volcanoes, too? And the proposed Titan mission sounds thrilling - who wouldn’t be thrilled to the point of blacking-out by the prospect of seeing pictures from a probe that has just splash-landed in one of Titan’s methane lakes, or from a balloon that is drifting over Titan’s plains - but that sounds like a very, very tough challenge to me. It will happen one day, I’m sure, but maybe not for another three decades… and I can’t wait that long! Jeez, I'm going to be 61 - sixty frakking one! - when the new Europa images start coming back. That's quite a depressing thought.
But I'm still excited at the prospect of seeing Europa again. It's one of my favourite worlds in the solar system. It’s captivated and fascinated me ever since I saw those first fuzzy Voyager images of it back in the days of Charlie’s Angels. (Oops, showing my age now!) and, spookily, I just finished reading John Varley's "Rolling Thunder" novel, a huge chunk of which is set on Europa. Reading it reminded me why I love its icebergs and ice cliffs; grooves and channels; crevices and crevasses. Voyager and Galileo showed us features on its mottled, fractured, colour-spattered surface that still make me shake my head in wonder. And those images, which are pretty good, were taken with old technology, cameras nowhere near as good as the kit we have today! Just imagine the stunning images we’ll see when EJSM starts taking pictures… we’ll zoom in on those jagged edged icebergs… see right into the fractures and pits and grooves… catch sunlight glinting off the vast ice plains… see Jupiter looming over Europa’s horizon, just as it’s been shown in space art for all these years…
Of course, these pictures are all a long, long way ahead, and I can't help wondering what kind of world we’ll all be living in then. As I said, I’ll be 61 in 2026... how badly will Earth and mankind have been affected by global warming and economic hardship by then? Will China already have beaten the US to the Moon, and be in the process of training astronauts for a manned expedition to Mars? Will we have the first picture of an Earth-like extrasolar planet? Will we have detected a signal from another civilisation from deep space? It could literally be a New World by then, in so many ways. I don't know whether to be excited or frightened by that thought.
But it's good to know we're planning the Next Great Mission.
Well said Stu! I had the same thrill from Voyager and Galileo. And on top of that there is Ganymede and Callisto... forgive me folks, but there is something very intriguing to me about the sublimating seltzer surface of Callisto, and the tectonics on Ganymede...... and how the freak does Callisto have an ocean when it formed too cold to differentiate.?
We stand to learn do much...
Craig ... 72 in 2025
"sublimating seltzer surface of Callisto"
Gold star for effective alliteration, sir!
Stu
Coming from our resident poet, I am quite flattered...
Thanks really
Who does not find these Callisto 'knobs' begging for better resolution..... sublimating seltzer.
http://photojournal.jpl.nasa.gov/jpeg/PIA03455.jpg
Of course, it will take the ESA contribution... JGO, to open up this world.
Craig
Artist's impression Callisto's Spires...
http://www.arcadiastreet.com/cgvistas/jupiter_130.htm
I agree. With four planet-sized moons, the surface area to explore is tremendous, and Galileo, while it was a noble salvage mission, barely could scratch the surface. I strongly favored this mission, although much of my bias comes from the fact that the Titan mission strikes me as more technically difficult (in the sense that it depends on more new technology), and is therefore more likely to be delayed.
The selection makes sense to me. After all, we've had many years to wring every last little bit of interpretation we can manage from the Galileo data, and even longer to analyze the Voyager and Pioneer data from Jupiter.
Cassini is still going strong at Saturn, and may find even more new things that could, conceivably, impact the kinds of sensors we might want to load onto the next Saturn probe. But there is almost nothing new waiting in the wings that will affect what you'd want to put onto a Jupiter mission.
So, from a mission design and planning point of view, I think this was the best decision. I truly think there are wondrous things yet to behold in Jupiter space. And I'd hate to be bending tin for a Saturn/Titan probe when I found out that there's a truly interesting phenomenon to be studied that our design is ill-equipped to look at.
-the other Doug
True enough, but sometimes it's just nice to turn a blind eye to such a thing and praise artistic effort and intent, you know?
Your quite right Stu. I take no pleasure in being pedantic, and should not have picked on anyone in particular. The trouble is that these altruistic ices are proliferating everywhere, even in places that normally command respect.
Think you meant "You're quite right..."
I know what you mean though; standards are slipping in everyday life, but I think that when you're amongst friends, as we are here on UMSF, some leeway is allowed. Personally, when it comes to writing about space, I'll take infectious enthusiasm and passion over 1000% correct grammar any day.
The topic has veered a bit from the discussion of the Jupiter Flagship so I moved everyone's complaints about being old (j/k) to http://www.unmannedspaceflight.com/index.php?showtopic=5835 in the Chit Chat sub-forum
I really look forward to the large color images that the Galileo mission generally lacked. Fragments like this tease us with what might have been taken (This is the only fragment of an I27 global mosaic of Io that was transmitted).
i have been traveling recently and been waiting to see how people felt about the selection. I am really quite pleased to see the level of support shown for the Jupiter selection. It was an extraordinarily difficult choice from the science side, and the disappointment must be great on the other side. NASA has reaffirmed the high importance of Titan/Encleadus so that all is not lost. it will just take a bit longer. In the man time, Cassini can operate for maybe another decade, perhaps more. That is a rich mission and Titan folks will have their hands full for a verrrry long time. Both systems are truly planetary systems in miniature with an incredible diversity of features, bodies, processes and phenomenon. I study the icy satellites and regard them all as fun places to study. so id have been happy with either choice.
I can echo sentiments made by others. We still have many unanswered questions, especially about Europa and Io. Is Europa active??? Seems plausible if not likely but Galileo could not address this issue, period. Period. We dont know. The antenna failure was catastrophic on so many levels, including this one. It is my firm belief that the gains to be made by a return to Jupiter are simply too large and too important. Ive been mapping the satellites for more than 20 years (most of which will be published before the end of the year) and every day i work on these bodies I am reminded that we missed out on so much when Galileo "failed" that i am sometimes driven to tears. the This is certainly true, but it is the amazing diversity of the system and its importance in understanding volcanic and habitable worlds that are the best reason to return.
I am less familiar in detail with the technical issues, but will say that both face significant issues in the short term that we must be sure to address wisely and prudently. The chief of these is the radiation environment of course which can and did upset the Galileo spacecraft on numerous occasions. but it did work and succeed! We just need to start the job and get it done.....
paul
**POOF**
**POOF**
From the release "Based on these and other studies as well as stringent independent assessment reviews, NASA and ESA agreed that the Europa Jupiter System Mission, called Laplace in Europe, was the most technically feasible to do first." I certainly agree that a Titan mission is a high priority and doable. What I am arguing is that people who consider the Europa mission more technically feasible are not doing so to insult the Titan mission as you seem to suggest. I am not saying that you are necessarily wrong in saying that Titan might be just as feasible with current technology - my point is that those who disagree are not doing so simply to insult the Titan mission.
Not to fan flames, but it also might be wise to consider some of the possible implications of Juramike's http://www.unmannedspaceflight.com/index.php?showtopic=5854.
I'm not totally convinced that we understand Titan well enough yet to make conclusive choices with respect to surface exploration methodologies.
**POOF**
Well, even if both were equally technologically feasible, the mission profile with less failure points would be more technically feasible.
Are you suggesting that they need to handle a landing in french onion soup?
That would be tame compared to actually landing on one of the lakes. besides we don't even know if they're lakes, they could be huge masses of chunky and gooey hydrocarbon goop.
**POOF**
**POOF**
**POOF**
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If anything I thought the press release didn't go far enough to explain the reasoning behind decision to go with Europa first, then Titan later. But to say that it didn't make it clear that both are needed, or that it is putting an albatross on the Titan mission, I don't think is fair. I think the fairer thing to say is that NASA and ESA acknowledged that there has been more technological development in preparation for a Europa mission over the last decade, particularly in rad-hard electronics, than the Titan mission, where Cassini follow-ons have only been considered in earnest for the last two or three years.
It is clear from the press release that this isn't an end for development of a Titan mission. Like the Europa mission, it could use more marinating, in other words, now that we have an idea of what a Titan mission might look like, we can work over the next decade to get those technologies up to the level where Europa is now, so that when the next Flagship mission is chosen, Titan will be ready-for-primetime. The press release makes this clear when it mentions that Titan mission will continue to be developed in conjunction with the upcoming decadal survey.
I agree. The press release seems to leave Titan quite clearly next in line, and not neccessarily a decade behind. It even proclaims "everybody wins". I don't think they'd have said that if Titan was to be very much deferred, or in doubt altogether.
Titan easier than Mars? Well I have to say I agree with that too. I think that's one of the new insights we have, thanks to Ralph Lorenz and friends. It's easy to fly, and it's easy to splash down and sail. Most importantly, it's easy to slow down when you arrive there at high speed through the vacuum of space. That lovely deep, cool and chemically benign air and gentle gravity do the whole job. There is nowhere else so welcoming or with so much to offer the (robotic) explorer.
If it won't fit in the tube just ask it to walk up the ladder.
**POOF**
I was certainly not mocking anybody there, nor weighing in with a particular point of view. My post was entirely and solely whimsical and surreal. I do that occasionally - maybe it's not such a good idea. My sincere apologies for any annoyance caused.
Well now, and I took it to mean I'd missed some well-known reason liquid sampling's harder than solids. ("Is there some exotic surface-tension or electrostatic effect I haven't heard about which makes sample "walk" up a "ladder"? I pondered. I was about to hit start googling... I suspect we're all in violent agreement here, actually. ( Group hug? [1] )
My last comment on this is that although Titan isn't capital-aitch Hard, it's something we've only done once, compared to, what, almost a dozen attempted Mars landings. As is clear from Mike's awesome heptane experiment, the surface properties are not well understood right now - certainly nothing like as well as Mars, and we saw with Phoenix that there are unknown unknowns there, too. The distance to Titan means there'll always be a substantial lead-time between receiving data from one mission, doing our best to grok it, and designing, building and flying the next. NASA's decision to fly Europa first whilst continuing work on Titan strikes me as a clever (and presumably difficult) cutting of the Gordian knot.
[1] wildly O/T sidenote: an American friend left my employer recently; after seeing him give two successive people massive bear hugs as he left, I couldn't resist taking a step backwards and extend my hand for a polite shake... "Jolly good luck, old chap!" :>
Re remote examination of cryogenic-temp liquids: After some thought, this seems like a non-trivial problem. Gross compositional measurements via a GCMS seem quite feasible, but what of the more volatile fractions? (Thinking complex organics of unfamiliar structure, here). Detailed chemical analysis seems necessary, and I frankly don't even know where to begin there.
All this stuff, whatever it might be, is at thermal equilibrium with its environment. I may be wrong here, but to my knowledge we really don't have much experience designing complex electronics & associated small-scale mechanical systems that work in hypercold environments like Titan for prolonged periods of time--and they'd HAVE to in order to avoid destroying a liquid sample before it could be analyzed.
Point being, this particular aspect is just one small but crucial component of the overall technological readiness needed to really tackle Titan at a Flagship scale. It's wise to remember as well that future missions to Saturn need to be very capable indeed scientifically if for no other reason than that it's a real ordeal just to get there. Launch opportunities to Jupiter are more frequent, and the transit time is much less than that to Saturn. Therefore (IMHO), EJSM seems like the right mission at this time.
I'm going to draw a line under the 'technical readiness' debate. People can read the various proposals and figure it out for themselves.
I'm going to assume you didn't see the message above whilst adding your reply. Post culled - Admin
I'm a bit concerned about this statement by Louis Friedman I read over on the Planetary Society blog:
While the previous FY 09 budget request included new initiatives including a Mars Sample Return mission, an Outer Planets Flagship mission, and a Joint Dark Energy mission, among others, that could not realistically be accommodated within the FY 09 budget proposal, the FY 10 budget plan for space science no longer includes these or other major new initiatives. For example, NASA selected the Europa Jupiter System target as the focus of an Outer Planets Flagship mission, but elected to proceed with technology development, further definition, and discussions on a potential partnership with the European Space Agency (ESA) on a potential future mission. The FY 10 budget plan for planetary sciences does not include a Mars Sample Return mission. NASA officials have indicated their interest in working more closely with ESA on potential Mars missions for the 2016 and 2018 launch opportunities.
Interesting language in the House markup:
Interesting wording. I wonder what is 'inconsistent' in the budget profile? My first guess would be that it is a mystery where NASA intends to find 3 billion dollars over the next decade to fund the the mission. But then congress requests an alternative timeline that is 2 years earlier... which seems counterintuitive if the problem is not enough money being available.
Still, I must say I like hearing launch dates that are two years earlier rather than two years later. Anyone remember just a year or two back when the projected launch period was 2016-2017? Then 2018, then 2020.
Yep.... I like hearing the date move earlier for a change.
Seems to mean "Wow it's expensive.....but hey we are feeling lucky how much more expensive will it be 2 years sooner......
My reading of the budget plan as presented by the President for the out years doesn't allow funding of the outer planets flagship. Either Mars has to lose most of its planned funding or the Discovery and New Frontiers programs have to be gutted. I hope my reading is wrong, but no one has challenged this reading on my blog (futureplanets.blogspot.com).
So, this request makes a lot of sense.
What does a 2018 launch opportunity provide that a 2020 launch wouldn't? In other words, are there technical reasons beyond the obvious 2 year gap to prefer one versus the other?
Up until now the only reasons I have read for extending the launch to 2020 were funding and political.
If ESA approves the Ganymede orbiter mission then it would not be ready until 2020, so one of the reasons for delaying the Europa mission was to launch at the same time and get semi-coordinated science observations of the Jovian system.
The other reason for the delay was to allow more money to get the mission up to a roughly 3 billion dollar "sweet spot".
There may be technical issues favoring one launch date over the other, but I've never seen any mentioned.
Bob Pappalardo has a http://news.bbc.co.uk/2/hi/science/nature/8537992.stm on the Europa mission.
TTT
today on arXiv: Title: http://arxiv.org/abs/1005.0991
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