NASA and ESA have decided to pursue the Europa Jupiter and Ganymede Jupiter missions for the late 2010's Flagship mission. Per the announcement, the Titan Saturn mission had "several technical challenges requiring significant study and technology development," whereas the Jovian system missions were judged ready to fly.
Summary of Announcement
Here are several key paragraphs from the announcement that summarize the decision:
"At a meeting in Washington last week, National Aeronautics and Space Administration and European Space Agency officials decided to continue pursuing studies of a mission to Jupiter and its four largest moons, and to plan for another potential mission to visit Saturn's largest moon Titan and Enceladus.
"NASA and ESA engineers and scientists carefully studied both potential missions in preparation for last week's meeting. 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. However, ESA's Solar System Working Group concluded the scientific merits of this mission and a Titan Saturn System Mission could not be separated. The group recommended, and NASA agreed, that both missions should move forward for further study and implementation.
"The decision means a win, win situation for all parties involved," said Ed Weiler, associate administrator for NASA's Science Mission Directorate in Washington. "Although the Jupiter system mission has been chosen to proceed to an earlier flight opportunity, a Saturn system mission clearly remains a high priority for the science community."
"The Europa Jupiter System Mission would use two robotic orbiters to conduct unprecedentedly detailed studies of the giant gaseous planet Jupiter and its moons Io, Europa, Ganymede and Callisto. NASA would build one orbiter, initially named Jupiter Europa. ESA would build the other orbiter, initially named Jupiter Ganymede. The probes would launch in 2020 on two separate launch vehicles from different launch sites. The orbiters would reach the Jupiter system in 2026 and spend at least three years conducting research.
"The Titan Saturn System Mission would consist of a NASA orbiter and an ESA lander and research balloon. The complex mission faces several technical challenges requiring significant study and technology development. NASA will continue studying and developing those technologies. Future work also will provide important input into the next Planetary Science Decadal Survey by the National Research Council of the U.S. National Academy of Sciences, which will serve as a roadmap for new NASA planetary missions to begin after 2013. On the European side, the interested community of scientists will have to re-submit the Titan mission at the next opportunity for mission proposals in the Cosmic Vision programme in the years to come."
I am not surprised by this decision. A Europa mission has been intensely studied and technology to handle the radiation has been developed for over a decade now. Technically and programmatically, the Jovian system mission has been ready for a number of years. The Titan proposal has just a couple of years worth of analysis and technology study.
If I understand the process, this announcement puts the Europa Jupiter orbiter firmly on NASA's roadmap (subject as always to future Congressional appropriations of money). The ESA craft, though, is in competition with other good missions for a slot in the next Cosmic Visions selection in 2011 and may not be selected.
A future Titan mission, if it is a flagship class (>$3B) would presumably be in competition for a 2020's new start. It will need to compete against a Mars flagship mission (such as a sophisticated rover or a sample return) and a Venus mission. Other strong mission concepts may appear in the next decade, too.
A study done a couple of years ago found that the lowest cost for a meaningful return mission to Titan would be $1.5-2B (FY 2007 dollars, I believe) for a craft that would be multi-flyby Saturn orbiter. For around the same amount, a balloon that would directly communicate with Earth could be done (with much less data returned than would have been done with the Flagship mission). I would like to see the space agencies challenge its engineers to see what they could do to reduce this cost.
I am currently in my young 50s. When the Jovian mission(s) arrive, I will be in my young 70s. I very much would like to see a return to Saturn in my lifetime.