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.

[edstrick]

(Without reading the voluminous material on the opag site...)

Would a JSO mission have a higher angular resolution camera than Cassini's narrow angle cam?...
Would it be a multi-megapixel camera, 4-megapixel camera on Rosetta, or even higher pixel-count-format?
Would it be able to take images every few seconds, rather than about one per minute?...
Would it have many times more data storage than Cassini, and be able to dump it all to Earth during apoapsis, as it heads in for the next encounter?

As Meriner 10 approached and receeded from Mercury, it "fireshosed" the illuminated disk with continuous mosaicing until the field of view and frame rate became too small and slow to get contiguous coverage.

Voyager was somewhat able to do the same at Jupiter with the flyby-targeted moons.
Galileo was a salvage job.. very successful, but still a salvage job.

A current technology mission should be able to saturate-cover the illuminated disc with multi-spectral images down to maybe 1/4 kilometer with higher camera resolution from long range, a faster frame rate, and more data storage and transmission capability. Maybe even UV/VIS/NIR color coverage at that resolution. During near-encounter, they should be able to do "quadrangle-maps" of target regions with several strips of contiguouis images down to something like 50 meters, much the way Viking Orbiters mapped landing sites with the twin rapid-fire framing cameras and it's scan platform.

I'm not going to vote on Europa vs Jovian System, but we damn near better be able to do as much better at Jupiter than Cassini does at Saturn, as Cassini did over poor Galileo.

Beyond that... Near Infrared imaging is vastly advanced over Cassini's technology level.. A megapixel 1 to 5 <maybe> micrometer framing camera with a good set of wide and narrow band filters should be state-of-the-art and extend multispectal mapping at good resolution to longer, more diagnostic wavelengths.

[tedstryk]

Voyager was somewhat able to do the same at Jupiter with the flyby-targeted moons.
Galileo was a salvage job.. very successful, but still a salvage job.

Yes, Galileo was a salvage job, but it did have some encounters that did not fall into this category, namely its earth-moon flybys, which give one an idea of what SSI was really capable. Also, when one looks at the ultra-high resolution mosaics from its high-speed flybys of the Galileans, the short integration led to images that are neatly nested, especially compared to Cassini mosaics. I would love to see a JSO or EE with a Rosetta-sized (at least) camera with a fast integration time. In fact, it could do more than Mariner 10 if it had reaction wheels, because the coverage could be neatly nested, as opposed to Mariner 10, which appeared to bounce all over the place.

[nprev]

I would love to see a JSO or EE with a Rosetta-sized (at least) camera with a fast integration time.

I completely agree, and this seems technically feasible, of course. In fact that's the strongest argument yet for merging these mission proposals. Completing a full Jovian system survey should be the primary objective, and after this task is complete the spacecraft should be capable of orbiting Europa or Ganymede, with target selection determined by the survey findings.

Building in adaptability seems like the best way to resolve this conflict. The main idea here is to acquire enough information about the Galileans to make an informed choice when the time comes (though I suspect that the meetings will be real roof-raisers; heck, look how much discussion there's been on this thread alone!)

[ugordan]

Building in adaptability seems like the best way to resolve this conflict.

Adaptability will inevitably imply sub-optimality for either Europa or Ganymede. You want to optimize your payload (science instruments, rad shielding, fuel) for a specific target, there's no margin like that to accomodate free choice once you get there. It's not a case of choosing the landing site a-la Viking from orbital survey first. You'd inevitably have an impact on science capability to allow for those margins. Once again, it boils down to "do you really want to sacrifice X in order to be able to do Y?". Just as EE sacrifices coverage of the entire system and JSO would leave certain questions open if you went into Europan orbit.

[djellison]

You want to optimize your payload ... for a specific target

Should that target be a specific body, or a specifc set of scientific goals?

Doug

[ugordan]

Should that target be a specific body, or a specifc set of scientific goals?

Probably scientific goals. Some goals can be pretty constraining though, suggesting you end up with a target body again. We're back at that point: would we like a little bit of everything (possibly best bang per buck), or do we want a quantum leap in knowledge about a single object?