"Dr David Rothery, the lead scientist on Bepi's Mercury Imaging X-ray Spectrometer (MIXS), said the science case for another Mercury mission was exceptional.
'The best way I heard it expressed, very kindly by a member of the Messenger team, was that Messenger is providing the 'hors d'oeuvre' and BepiColombo will be the 'feast'.
'BepiColombo has more instruments and more capable instruments than Messenger does."
I have also reposted the blog entry on why a comet sample return mission is so hard. I normally clip the images from presentation on my workstation, but that machine has been tied down doing multi-day data analyses. For the original post, I clipped the images on my netbook. Lesson learned, clip from a big screen.
Bruce Moomaw has also been digging into the history of presentations on this topic and has some corrections and extensions to my post:
I had written: "The small body science community has ranked a comet sample return as its top priority for the last decade or so. This mission was included (optimistically, for reasons explained below) in the first set of mission candidates for the New Frontiers (~$650M) missions and remains on that list."
Bruce corrects my poor memory: "Actually, the comet sample return included in the first set of NF mission candidates (as listed in the previous Decadal Survey) was the less ambitious warmer Comet Surface Sample Return, rather than the Comet Cryogenic Sample Return, which was recognized in the first Survey as a mission sufficiently difficult that it was Flagship class. And it's the Comet Surface Sample Return that was listed among the acceptable candidates in the first New Frontiers solicitation. The considerably greater difficulty of the CCSR has been clearly recognized from the start."
"Note also the very next page in the CNSR (aka CCSR) presentation that you quote: "If you can’t maintain cold enough temperatures to preserve the ice sample during return, then at least collect the evolved gases. Must also store them in a way that prevents chemical changes (e.g., using special getters, different chambers filled at different temperatures)." The Small Body scientific community seems to regard this as a clearly justifiable mission, although of course they'd prefer a cryogenic return if there was the money for it.
" I do note from Hal Weaver's and Michael A'Hearn's Nov. 2007 advance report that CSSR would use "flasks" (in the plural) to collect those gases, which presumably is the same thing Weaver mentioned in his new CNSR presentation. Note also from the 2007 mission presentation (pg. 17) that only one out of 11 SDT members thought volatile preservation in flasks was an absolute necessity for the mission, although the others considered it "highly desirable" and it is baselined."
I still think that this is a very complicated mission given the sampling challenges and the necessity to preserve the evolved gases. I hope that the community comes up with good solutions to the problem. I want to see this mission fly.
I really appreciate corrections. Planetary exploration is a huge field, and I follow it part time as a hobby while (supposedly) writing my dissertation in an unrelated field. Please point out my errors and omissions!