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]

Again, the problem is that the EE has nothing to with any possible jellyfish in Europa's ocean. EE is caught in a catch-22 where the whole push to go to Europa is to look for life, but EE won't have anything to do with that question, but we may need the orbiter to look for good places to land to answer that question. I think it might be useful, as vjkane has suggested, merge JSO and EE to get the best of both worlds: get the added science that the pre-EOI (or pre-GOI) orbital mission would provide at Io, Jupiter, and the other moons, then get the orbital mission at Europa. This would add to the cost of EE, but it might be worth it.

The only problem right now with the Europa "vision" at NASA are the timescales involved. The Mars people are complaining about a possible gap in Mars mission in the next decade to pay for MSR; at Europa, we would have EE in the 2017-2027 time frame, and the lander in the decade after that...

[ugordan]

The only problem right now with the Europa "vision" at NASA are the timescales involved. The Mars people are complaining about a possible gap in Mars mission in the next decade to pay for MSR; at Europa, we would have EE in the 2017-2027 time frame, and the lander in the decade after that...

That's assuming the orbiter would find anything interesting enough to merit a landing... I see your point about funding and prioritizing, though.

We'd all like to have JIMO back so everyone'd be happy, but this is not an ideal world. To be frank I'll be happy to see the day any flagship Jupiter-bound mission gets off the ground. If it turns out to be focussing on Europa, all the better.

[vjkane]

Just to add more fun to this debate, a long time ago when a Europa orbiter was a new idea I read an AIAA paper on possible implementation architectures. The majority of the paper talked about implementing an orbiter. However, as a backup option, an arbitrarily large number (I think this paper discussed a dozen or two) flybys of Europa could be done. Using gravity assist, the encounter point with Europa in its orbit could be changed. In this way, you can have the closest flyby occur at any number of longitudes at Europa. Apparently it was harder to vary latitudes.

Fast forward to the $1B Enceladus flyby study. It had a number of flybys of that moon that walked around latitudes and then modified the Saturn orbit to approach Enceladus from the other side. This way, both hemispheres would be observed.

Now look ahead to a Jovian orbiter. It's mission could be tweaked to make a large number of flybys of one moon and then orbit another. The primary costs would be mission operations, fuel, and radiation exposure (especially if the moon with lots of flybys is Europa).

So get on your wishing caps. You almost can have two intensive moon studies (plus remote studies of Jupiter and Io and maybe some Io flybys). Imagine what the JSO instrument set could do with 24 flybys of Ganymede or Europa spaced 15 degrees around the equator. If the flybys are close enough, you can get snippets of coverage with the radar system.