Makes sense; thanks for the clarification, Paolo!

One thing that excites me about the HIRES imager on JSO is what it can do for Ganymede orbit. At is closest to Io, it will obtain 1.3 km/pixel - 3km/pixel images of Io. For scale, Galileo's famous C21 mosaic, its best, has a resolution of 1.3 km/pixel. This still isn't really fair, because Galileo's camera obtained this resolution in only one wavelength (The other colors used 2x2 binning), it is only 8-bit data, and very lossy compression was used. The maximum resolution for Europa is 798 m/pixel from Europa. By contrast, the highest resolution Galileo mosaic (the one used here) has a resolution of about 2/km pixel (and again, is also compressed, with at most two filters cover and with gaps and with some color data brought in form other orbits, as well as lossy compression, so a nice, clean JSO view at the same "resolution" would be much better). This is of course ignoring views that would be obtained earlier in the mission, which would be even better.

Color imaging was one of the main casualties of Galileo's hain gain antenna failure. Helping to fill in that gap was one of the reasons that the Cassini and New Horizons Jupiter encounters were so valuable.

So I agree that JSO would help out a lot in the global color imaging of Io and Europa even while in it's final parking orbit at Ganymede.

But one thing to remember is that the resonances of the three inner Galilean moons means that closest approach between them always brings the same hemisphere into view. So those great global shots are always of the same area. And that doesn't even give you 50% coverage, because the areas close to the horizon are essentially out of view, so you are maybe getting 35-40%.

In any case, while I'm more of a fan of the Europa Orbiter, JSO wuold be one hell of a great mission and I won't complain (much) if it gets chosen.

FWIW, the same face of Callisto would also be seen at every closest approach. It's not the resonance of the satellites themselves but the fact that each is tidally locked in rotation that leads to that consequence.

The factor by which viewing the other satellites besides at closest approach would be somewhat lesser for Io. In any event, both Io and Europa will over time show almost 100% of the surfaces to Ganymede while in the half of their orbit closest to Ganymede (ie, within Ganymede-Jupiter distance of Ganymede).

By and large, the imaging from Ganymede orbit would be about monitoring Jupiter's weather and Io's volcanism over time. There would be some use to the global mapping done from a distance, but that would be outclassed by the close-up observations. Otherwise, I think the main value would be to look for lighting effects near the terminator to derive topographical data. The problem being that Europa and Callisto are incredibly smooth anyway, so this wouldn't work incredibly well. (In contrast, there's a lot of good Cassini data of that kind with respect to Iapetus, which is not very smooth.)

Overall, the close-approach breakdown for the two missions goes about like this:

Io: JSO 4, EE 0
Europa, JSO 6, EE infinity
Ganymede: JSO infinity, EE 14
Callisto: JSO 4, EE 4

I'd lay a bet that EE wins out. If it's the option of delaying by two years, which would improve mass margins and allow an Io flyby or two, then JSO has no chance. Ganymede just ranks infinitely far below Europa as a priority. Heck, the US has only flown five missions to Venus, ever, and Ganymede has less interesting geology, no atmosphere, and is much farther away. And would receive 14 close flybys from EE.

Over the summer I read that the two teams were going to discuss combining the JSO remote science campaign with EE. I presume that this would include looking at Io flybys, remote Jupiter studies, and optimizing studies of moons other than Europa.

Now that would be cool.

Mariner9, at closest approach you are correct, but as for the areas near the limb at that point, keep in mind that they could be seen at lower resolution farther away. Also, I don't have the numbers handy for Europa, but for the opposite side of Io, the resolution would be about 3km/pixel at worst, which isn't bad. Europa would be somewhat worse (my back of the envelope is 5km/pixel), although assuming these areas were covered earlier in the mission, Io is a very different target due to the need for global-scale change monitoring. Also, at closest approach from Ganymede orbit, while the side would stay the same, the illumination angle wouldn't, offering many different perspectives.

FULL INLINE QUOTE REMOVED - how come the old hands of UMSF still do this? - DOUG

Yes, and Io and Europa show pretty strong effects of phase angle.

Also, the main phenomenon of interest at Io can actually be observed regardless of the illumination.

It would be interesting to see what (if anything) that post-Europa EOM science operations can provide (assuming the spacecraft is not left to orbit Europa at EOM).

Where would you send it? Once it entered Europan orbit, basically the only way out is down.

If I recall correctly from the mission description of the cancelled "Fire and Ice" Europa Orbiter, the approach to Europa orbit insertion was a series of Europa resonant orbits, e.g., 3:4, 4:5, 5:6, etc. with Europa flyby at perijove to reduce the apojove and a delta-V near apojove to setup for the next Europa flyby. The delta-V's burned a significant amount of the propellant load, around the same order as the JOI burn as I recall. The Europa orbit insertion did not require anything on the order of the JOI burn with some description about EO being "nudged" into Europa orbit.

For quarantine, it seems to me the orbiter would "nudge" itself back into Jupiter orbit. At this point, I don't know how EO can prevent future impact with Europa if there is no propellant to adjust Jupiter orbit to an eventual Galileo exit. But if there is sufficient residual propellant to do the Galileo exit, then could some incremental fuel load combined with Europa flybys move the apojove back out to lower radiation dose orbit by running the approach scheme in reverse? An eventual Galileo exit will be required, but can some time be bought before then?

The maneuvers in actual Europa orbit have best and worst case with regards to propellant usage. If the propellant load allows for the worst case, but the actual maneuvers took something closer to best case, then there could be some load left at end of primary mission. The extended mission could stay for additional science in Europa orbit, or if the fuel load is great enough, get back out to a Jupiter orbit out of the higher radiation zone (at least at apojove) and do Jupiter orbit science.

The devil is in the calculations of accumulated dose at EOM, how much the incremental dose can be decreased with residual propellant, and the expected remaining life given the accumulated dose and the decreased incremental dose. It could just be impractical. I just haven't seen this aspect discussed, and I don't have the background to readily run the sims to find this out.

The mission summary clearly states "The flight system eventually impacts Europa". I think that's unfortunate. It would be nice if the first human artifact to touch Europa were at least to attempt some kind of biological audit of the status quo ante.

I don't think you can "nudge" yourself into a stable mapping orbit around Europa. What those resonant flybys do is lower the hyperbolic excess velocity w/respect Europa to a minimum so the orbit insertion burn costs the least amount of fuel. You still need to get rid of that excess Vinf to go into orbit and just as well you'd need to provide the same delta-V to again escape Europa.

The thought of moving EO out of Europa's orbit at EOM seems similar to me as ideas of ejecting Cassini out of the Saturnian system. Nice concepts, but not gonna happen IMHO.

To me EE as described in the OPAG reports does not win out. JSO's instruments are superior and the Io flybys are a big plus. Less radiation and the longer time in Ganymede orbit (and therefore more time to monitor Io and Jupiter) is also a big plus.

If the missions are somehow combined with EE carrying JSO's instruments and flying by Io the situation could change. This is not completely clear though. An orbiter can be put in orbit around Ganymede that is stable for several decades. This is not possible for Europa and the radiation is much less severe at Ganymede. So in this case EE probably wins out but things are not completely clear. Longer time in orbit is always a big plus - there are lots of things at Jupiter where long-term monitoring is useful.

Or could he mean Italian Giuseppe ("Bepi") Colombo, who was behind the calculations of first ever gravity assist by a spacecraft with Mariner 10 to Mercury...?

I wish I have the paper handy. I think the "nudge" comes from putting EO from the last n:(n+1) resonant orbit into a 1:1 resonant Jupiter orbit with Europa nearby. The transition from the 1:1 Jupiter orbit to a low Europa circular orbit is gradual thru an initial high and unstable Europa orbit and takes some number Jupiter / Europa orbits to accomplish. Instead of a single big Europa insertion burn, there are a bunch of smaller burns which total up to less than the one big burn. The resonance with Io and Ganymede may play a part.

Agree about it being unlikely, but I have read more about Cassini EOM options than EO (or EE) EOM options and am just looking for additional info on EE.