OPAG Reports, Formal proposals/evaluations of future outer SS missions Options

[JRehling]

http://www.lpi.usra.edu/opag/announcements.html

That's one little URL with a lifetime's worth of reading material.

Three detailed studies are available in PDF format. The missing body is Titan, which will be the subject of a forthcoming report.

The three focus missions are:
Europa Explorer: Fairly detailed description of a mission that is pretty much what Europa Orbiter would have been.

Jupiter System Observer: Basically, Galileo 2 (without the antenna mishap!). The craft would start with a 3-year tour of all the Galileans, then spend 1 year in an elliptical Ganymede orbit, then the rest of the mission in a tight, polar Ganymede orbit (like MGS at Mars). That would map the heck out of Ganymede, but also be close enough to the rest of the system to make long-range observations for years. Note that Ganymede would thereby provide a lot of radiation shielding.

Enceladus: where three profiles are examined in depth: Enceladus Orbiter only; Enceladus Orbiter with soft lander; Saturn orbiter with Enceladus soft lander.

There's more to chew on here than I have had (or may ever have) time for, but I'll throw in my two cents' worth:

Seems like a Europa-only mission would only benefit from coming after a JSO. EE would explore Europa much better than JSO would; why even have JSO observations at Europa if EE came first? In many ways, these two missions are competitive. EE would have the big payoff, but JSO seems like basic recon that would prime EE, especially giving specs on radar performance. But if we waited til JSO was 4 years into its mission before completing design of EE, then put EE sometime mid-century.

If an Enceladus mission included a Saturn orbiter, then maybe the same orbiter could provide data relay for separate Titan elements. However, a lot of the Enceladus science goals would require an Enceladus orbiter, so I don't think a Saturn orbiter for Enceladus/Titan will win out.

Note that Enceladus orbital velocity is low enough that the craft could manage to take lots of hits from ice pellets and survive. Put a bulletproof vest on the craft and let it soar through the plumes endlessly.

[volcanopele]

Sweet! Obviously, the two that I favor are JSO and the Titan Explorer. Of the two, I am pulling for JSO, but I wish both could be selected. JSO seems to be the best mission WRT science/dollar. Yes, it seems a lot like Galileo 2, but I don't think that should be considered a bad thing. We don't stop sending orbiters or landers to Mars, for example, simply because it was done before. With each mission, we understand what questions to ask and what instruments best answer our new questions. JSO will end up doing quite a bit of Europa science that will answer the most pressing question about that world (that an orbiter can answer): what is the thickness of the ice shell? My only problem with this mission is that it could make it more difficult to justify a dedicated Io New Frontiers mission, but barring an opening up of the mission selection process for NF, JSO maybe the Iophiles best hope for the next couple of decades.

The Titan Explorer is probably a close second for me, mostly because it is a mission dedicated to only one object, so I think the science/dollar is a bit lower, but considering the diverse geology and atmospheric science that could be obtained from this mission, it would still be a spectacular mission. Still want to see what the baseline mission looks like. An arrival date in the mid-2020s would be ideal to hit around equinox.

The Europa Explorer and the Enceladus mission, I think, are tied for third. I think a choice between those two missions would have to wait till the end of the Cassini mission. By then, hopefully the question of the source of the plume will be resolved. If the source is in fact a liquid water reservoir, as Porco et al. suggest, I think this mission just way ahead of Europa, given that samples from such a reservoir could be much more easily obtained, in a single mission, than Europa. If the source is much more mundane, as Kieffer et al. suggest, then a mission to Enceladus becomes a much lower priority. For Europa, while the orbiter mission is quite interesting, its focus on Europa pre-EOI and the fact that it will not answer the most pressing question about Europa (the presence of life), I think makes its science/dollar much lower than JSO.