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OPAG Reports, Formal proposals/evaluations of future outer SS missions
JRehling
post Nov 9 2007, 08:28 PM
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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.
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Mariner9
post Nov 12 2007, 08:19 PM
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Drats. Everytime I try to download the Europa report I only seem to get four pages. I wonder if my Adobe Reader needs to be upgraded. The other reports come down fine.

As I recall the whole idea for a JSO / Ganymede orbiter mission came along a couple years back. The proposal was made to fly a very high resolution imaging package and eventually park it in orbit around Ganymede. The idea was to keep it alive a lot longer by keeping it out of the heavier radiation it would encounter in Europa orbit.

My impression was that it was beleived that it would be cheaper to develope the JSO because it wouldn't need all the radiation hardening you would have on a Europa orbiter. I scanned through the JSO report, and saw budgetary numbers in the 3 billion range.

If NASA headquarters was hoping that these studies would provide them with a cheaper alternative then one of two possibilities comes to mind. Either (a) those hopes were in vain and you just can't save that much by this route, or (cool.gif someone didn't get the memo and the JSO engineers decided to go whole hog with a full fledged (and radiation hardened) Flagship study and go for the gold. Gold in this case being 'plated'.

A third more cynical possibility would be that people really want the Europa orbiter and so purposely made the JSO come out just as expensive and therefore no more appealing from a budget standpoint.

Please note that I'm NOT advocating that third option... just saving someone else from suggesting it. I'm leaning more towards option (a) as an explanation.
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JRehling
post Nov 12 2007, 08:42 PM
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QUOTE (Mariner9 @ Nov 12 2007, 12:19 PM) *
Drats. Everytime I try to download the Europa report I only seem to get four pages.
[...]
As I recall the whole idea for a JSO / Ganymede orbiter mission came along a couple years back. The proposal was made to fly a very high resolution imaging package and eventually park it in orbit around Ganymede. The idea was to keep it alive a lot longer by keeping it out of the heavier radiation it would encounter in Europa orbit. [...] I scanned through the JSO report, and saw budgetary numbers in the 3 billion range.


I think the Europa report is only four pages. That's all I see.

JSO would certainly average lower radiation per day than EE (dose at Ganymede about 5% the dose at Europa), the plan is for a very much longer mission, so it will take a high lifetime dose. A short JSO mission would take very little radiation dose, but also have not much point.

JSO sounds like a good mission to me, on the Galileo/Cassini level. But its competition with EE puts it in strange turf. I don't see it taking root.
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vjkane
post Nov 12 2007, 08:57 PM
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QUOTE (Mariner9 @ Nov 12 2007, 08:19 PM) *
Drats. Everytime I try to download the Europa report I only seem to get four pages. ...

My impression was that it was beleived that it would be cheaper to develope the JSO because it wouldn't need all the radiation hardening you would have on a Europa orbiter. I scanned through the JSO report, and saw budgetary numbers in the 3 billion range.


It's not your Acrobat reader -- I get just four pages, too.

As for JSO, I spent some time going through the budget figures. There's really two missions described. One uses up all the potential flagship budget (~$3B) and the other reduces the amount of Ganymede science through some instrument descope and an elliptical rather than circular orbit. The descoped mission appears to be about 2/3 the cost of the proposed mission (there are more expensive versions, for example with an atmospheric probe). See figure 3-4 on page 3-5. The report also says that no attempt was made to define a minimal acceptable mission, although some descope options are presented that suggest ideas.

My take is that once you get to this class of mission, you are in $2-3B range, and the choice of moons doesn't matter that much.

It is a shame the Europa report isn't up. I'd like to compare the science packages. From the JSO report, it appears that two instruments weighing about 100 kg are needed to enable long distance observations (a combined camera/NIR spectrometer and and an IR spectrometer). I think it would be criminal to return to Jupiter with a 3-axis stabilized craft and not include these instruments plus along with flybys of Io and a long orbital tour to observe satellites not to be orbited plus Jupiter.


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vjkane
post Nov 13 2007, 05:14 PM
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Some more details comparing the Europa explorer and JSO options.

There's a very good detailed description of Europa Explorer's strawman instruments and the way they would be used -- as of last May -- at http://www.lpi.usra.edu/opag/may_07_meetin...gship_study.pdf . You'll notice that they are very similar to those in the JSO Flagship final report, with the following differences:

(1) The final version of JSO calls for a half-meter aperture telescope with the Narrow-Angle Camera and Vis-NIR Spectrometer hooked up to it, for a resolution of 0.4 meters/pixel from 200 km range for the Camera. (This is actully a change from the design of JSO's strawman payload last May, which called for separate optics for the camer and spectrometer -- the result being that they both had considerably lower resolution while weighing only 5 kg less total than the new setup.) Europa Explorer as of last may called, by contrast, for a Narrow-Angle Camera with a resolution 5 times poorer, but weighing only 15 kg -- plus a separate Vis-NIR spectrometer weighing 30 kg. I rather expect to see a similar combined-optics system now adopted for Europa Explorer (whether it features a comparably big telescope or not).

(2) JSO contains a big hulking Thermal-IR Spectrometer weighing fully 43 kg -- whose separate IR optics, in fact, are as huge (0.5 meters) as those for JSO's NAC-VNIS combination! (This is also a new change; last May, the TIR Spectrometer was to weigh only 20 kg but was to be accompanied by a separate 15-kg Thermal Imager.) Clearly good high-res thermal-IR spectra are considered very important on this mission, in order to study Jupiter's atmosphere and Io. Europa Explorer, as of my latest info, carried only an 8-kg Thermal Imager. So presumably a full-fledged Thermal-IR spectrometer is the most likely instrument to be listed for JSO but rejected from Europa Explorer -- since the latter is supposed to focus more on Europa, with general Jupiter-system science being a lower priority than it is for JSO.

(3) The Medium-Res Stereo Camera on JSO, again, has a resolution 5 times better than the stereo camera on Europa Explorer (plus a pixel swath twice as wide) -- but weighs twice as much. (Europa Explorer would also carry a 3-kg Wide-Angle Camera.)

(4) The Plasma and Energetic Particle Spectrometer on JSO weighs twice as much as the 12-kg one on the Europa Explorer (although it uses only a little more power) -- but Europa Explorer would also carry a separate 15-kg Ion & Neutral Mass Spectrometer, which is not on JSO, to analyze substance sputtered off Europa's surface by Jupiter's radiation. (This is the lowest-priority instrument on Europa Explorer.) I don't know what to make of this difference -- since the Europa Explorer plasma instrument, unless it's descoped, would also have ability to make time-of-flight analyses of the composition of plasma. Presumably the JSO version is more sophisticated in its sensitivity or resolution.

So, really, the instrument payloads for the two missions are strikingly similar. The main differences seem to be higher optical resolution for the cameras and near-IR spectrometer on JSO, and the absence of a thermal-IR spectrometer on Europa Explorer. All of which is to some extent changeable; the final version of Euripa explorer might easily end up carrying a thermal-IR spectrometer and combined optics for its cameras and spectrometers, although I imagine these would all be lighter-weight and lower-capability than their equivalents on JSO.

One more important note: it was stated at the Icy Moons Workshop that JSO would carry just as much radiation shielding as Europa Explorer, in order both to allow those Io flybys (reduced from four to three in JSO's latest version) and to prolong its lifetime in the Jupiter system for as long as possible. The overall features of the final version of the JSO spacecraft and that of May's version of Europa Explorer are very similar:
Europa Explorer: 7225 kg total mass, 2608 m/sec delta-V
JSO: 7262 kg; 2705 m/sec

The main differences are that JSO would carry a lot more total instrument mass (310 versus 212 kg), an 8th MMRTG to power the craft, and of course more area of radiation shielding to cover the extra instruments (although, since JSO would only be designed to endure 1.8 Mrad versus Europa Explorer's 2.3 Mrad, the shielding would be thinner and so its total mass would be virtually identical -- 165 versus 162 kg). The buses for the May version of Europa Explorer and that of the current JSO -- minus their science instruments and radiation shielding -- have almost the same mass: 1889 kg versus 1934. But the new JSO has not only more science instrument mass (310 vs. 212 kg), but considerably more radiation shielding (243 kg vs. 165) -- so that its total dry mass is 220 kg higher than that of Europa Explorer.

Also, JSO carries more propellant for the additional 97 meters/sec of delta-V it required for its mission. All this is apparently possible because the 2017 launch opportunity listed for JSO is a good deal better than the 2015 window listed for Europa Explorer: 7810 kg capability versus 7225 (using a Delta IV-heavy and a VEEGA trajectory in both cases). So: delay Europa Explorer by a couple of years, and you could put a lot more on it, too.

One other difference: JSO's final version allows mission data rates of fully 600-1600 kbps, whereas the May version of Europa Explorer provided only 200-300 kbps -- but this seems due to the fact that JSO would have a 50-watt Ka-band transmitter with a low-powered X-band backup, whereas the May version of Explorer used a 50-watt X-band transmitter and only a 3.5-watt Ka-band one. The power requirement of JSO's version is only modestly higher, and its mass is actually slightly less than for Explorer's version -- so I imagine the final version of Explorer will be changed to the JSO setup.

We seem to be looking at only minor differences between Europa Explorer and JSO: the latter would trade off somewhat thinner radiation shielding to allow more instruments an 8th MMRTG, and maybe a somewhat higher com rate. And, even then, the only significant instrument differences are (as mentioned above) just smaller optics for the cameras and VNIR spectrometer (which Europa Explorer would partially compensate for by lowering itself into a 100-kg attitude Europa orbit, versus JSO's 200-km Ganymede orbit), and the lack of a full-fledged thermal-IR spectrometer.


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Guest_PhilCo126_*
post Nov 13 2007, 06:08 PM
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Again this points out we live in exciting times, with upcoming missions near Mercury (Messenger 2011), cometary & asteroid flyby (Rosetta 2011 + 2014) and the flyby of the best-known KBO Pluto (New Horizons 2015). Exciting times indeed!
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JRehling
post Nov 13 2007, 07:39 PM
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QUOTE (vjkane @ Nov 13 2007, 09:14 AM) *
Some more details comparing the Europa explorer and JSO options.
[...]
We seem to be looking at only minor differences between Europa Explorer and JSO: the latter would trade off somewhat thinner radiation shielding to allow more instruments
[...]
And, even then, the only significant instrument differences are (as mentioned above) just smaller optics for the cameras and VNIR spectrometer (which Europa Explorer would partially compensate for by lowering itself into a 100-kg attitude Europa orbit, versus JSO's 200-km Ganymede orbit), and the lack of a full-fledged thermal-IR spectrometer.


Thanks for breaking it down.

Another aspect to the better optics for JSO is that the studies of Io and Jupiter from long range will benefit directly from the improvement in spatial resolution. Ganymede itself doesn't warrant such a commitment in hardware, and it basically "lucks out", becoming one of the best-mapped bodies in the solar system because this mission architecture doesn't really sacrifice anything by providing that capability.

Added note on the JSO report: Its discussion of radiation exposure assumes no shielding from Ganymede, even though it is expected that close proximity to Ganymede will provide net shielding. A priori, I would have guessed that it would block almost 50% of the charged particle flux. I know that Ganymede's own magnetic field makes that somewhat unpredictable, but I still figure that about half the time, Ganymede would stand in between JSO and the "radiant" of charged particle flux from Jupiter's field.

I guess the way this will end up shaking out is that EE will fly soon-ish, and JSO will fly way later. It would be nice to tailor their durations so that more or less continuous coverage of Io and Jupiter's temporally-varying phenomena could be provided, or even to have both of them operating initially simultaneously to provide excellent studies of the particles and fields sorts of things, but that would entail a lot of billions being spent at Jupiter while Saturn's retinue waits for a follow-up.

So I think EE will be the next Outer SS flagship mission and the following slot will probably go to Titan. JSO may be able to outshine Enceladus for the next spot, and then perhaps tailor its tour to provide more unique closeups of Io and Callisto while ignoring Europa and Ganymede which will be otherwise covered thoroughly.

Other Outer SS priorities worth considering include Neptune orbiter and yet other Europa/Titan follow-ons. It's not a question of whether or not something interesting will be ignored, but how many interesting things will be ignored (for the next 40-60 years or so).
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JRehling
post Nov 13 2007, 10:38 PM
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The full Europa Explorer report is now up. More reading (282 pp) material for your bedside stand.

Baseline mission is a jovian system tour of about 2 years followed by a 92-day primary mission in Europa orbit, with high expectations that the craft would survive considerably longer. Presumably, other targets in the jovian system would get minimal attention once Europa orbit was achieved, since more Europa coverage will always be desirable. (Eg, stereo/laser topographical map will get denser and denser with more observations.)

14 Ganymede flybys and 4 Callisto flybys before Europa orbit. Ganymede is highly useful for gravity assists, but the scientific value of Ganymede flybys would be severely lessened if a JSO mission were ever to fly.

JSO thus becomes a mission where Io is a major consideration, although Ganymede would be better observed. Deep in the radiation belts, Io doesn't fare well as a flyby target according to the real estate rule of Location, location, location.
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volcanopele
post Nov 14 2007, 07:38 PM
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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.


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vjkane
post Nov 14 2007, 08:01 PM
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QUOTE (volcanopele @ Nov 14 2007, 07:38 PM) *
I am pulling for JSO, but I wish both could be selected. JSO seems to be the best mission WRT science/dollar.


would you vote the same way if the JSO long distance remote sensing instruments (big camera/NIR spectrometer and IR spectrometer) were on the Europa orbiter? Assume that the two missions (JSO and Europa Explorer) were combined, both did Io flybys, both flew by which ever moon wasn't orbited a lot of times, and the only difference was which moon was orbited at the end of the mission.


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volcanopele
post Nov 14 2007, 08:07 PM
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Yes, if the only difference were which moon was orbited, then yes, I would change my vote to the Europa Explorer. However, keep in mind that another thing that makes JSO interesting is that it can orbit Ganymede for a much longer period than EE could due to the greater radiation exposure at Europa. This provides a much longer opportunity to observe Io and Jupiter which maybe more important than the resolution gained by being at Europa (plus, with a much shorter mission at Europa, more than likely there were would be few if any observations of the rest of the system while in Europa orbit).


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vjkane
post Nov 16 2007, 12:39 AM
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I've taken a look through the JSO and Europa Explorer proposals. My take on the choice for the next Flagship mission is that there are two classes of missions being proposed. The first class is to a single moon: Europa, Titan, or Enceladus. (While the Europa Explorer will do some Jovian system science, it's instruments are not optimized for that purpose.) The JSO mission would be a true Jovian system mission with a Ganymede mission in addition. It appears to this arm chair engineer that JSO could be flown to either Europa or Ganymede with fairly few changes.

In my opinion, if the next mission is a focused moon mission, Titan is the most interesting of these three options, and the proposed Titan mission with an orbiter, lander(s), and possibly a balloon (I read somewhere that this may be dropped from the proposal, but am not sure) seems very capable. However, if given a choice between a Jovian system mission that ends orbiting either Europa or Ganymede, I think this is the most science for the buck.


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JRehling
post Nov 18 2007, 10:14 PM
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QUOTE (vjkane @ Nov 15 2007, 04:39 PM) *
I've taken a look through the JSO and Europa Explorer proposals. My take on the choice for the next Flagship mission is that there are two classes of missions being proposed. The first class is to a single moon: Europa, Titan, or Enceladus. (While the Europa Explorer will do some Jovian system science, it's instruments are not optimized for that purpose.) The JSO mission would be a true Jovian system mission with a Ganymede mission in addition. It appears to this arm chair engineer that JSO could be flown to either Europa or Ganymede with fairly few changes.


As described, here are the difference in outcomes:

Jupiter: Long-range reconnaisance more frequently and for a much longer time with JSO.
Io: Long-range reconnaisance more frequently and for a much longer time with JSO. About four well-distributed close flybys with JSO. No close flybys with EE (several nontargeted flybys about 400K km in distance all with similar geometry).
Europa: "Total" mapping with EE. About 7 close flybys with JSO.
Ganymede: "Total" mapping with JSO. About 14 close flybys with EE.
Callisto: Roughly the same outcome in either mission. (Slightly better with JSO.)

Here's my question: How much of the Io long-term observations CAN'T be done from Earth for a ton less money? AFAIK, Io sports about ten major eruptions at any given time, and those are observable from Earth with adaptive optics. For a fraction the cost of JSO, build about 5 tropical observatories dedicated to Io, such that two or three of them can view Io at any time. And, hey, observe Jupiter, Uranus, Neptune, etc., every few hours as well.

If you run a program like that, then JSO looks like a distant poor stepchild to EE in science value. Sure, it would provide some nice close-ups of Io, but Galileo didn't totally skimp on those. And the value of those would be more than made up for by the fact that EE would provide "total" mapping of a world of primary interest (Europa) instead of a world of secondary interest (Ganymede).

The key with Europa is that a survey with selected, partial coverage at top resolution might miss a landing site of unique value, eg, over a hot spot where the ice shell is thinner/softer. None of the other moons have any potential payoff of that kind, and JSO would only provide a chance at finding such a place if it exists.

I'd say that EE is the better mission by far if we do what we should and track Io (and all the gas giants) consistently from here a few AU away. I'd add that I see a lot more value to a few Io flybys than the 14 Ganymede flybys if the EE plan could be tweaked like that. Plan JSO for the distant future, and EE could plan on skipping all Ganymede science except where programmatically convenient (gravity assists).

My lone-wolf conjecture on Europa vs. Enceladus is that Europa's ocean is likely more interesting than Enceladus's because it's "dirty". Even if water is key to life, we can also say that 100% pure water is inherently incompatible with life. From what we've seen so far, Enceladus's water is not quite 100% pure, but doesn't feature many complex compounds. I could see it being a reservoir of window-washing fluid of no astrobiological potential. Meanwhile, we can *see* that Europa's innards have some interesting goop in them; otherwise, the triple bands would be white, not tan.

Titan deserves a heck of a mission, too, but I think it'll merit waiting for Cassini finishing its reconnaisance before completing that design. Europa had its last close-up about a decade ago; it's due.
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rlorenz
post Nov 19 2007, 01:37 AM
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QUOTE (JRehling @ Nov 18 2007, 05:14 PM) *
>Here's my question: How much of the Io long-term observations CAN'T be done from Earth for a ton less money? AFAIK, Io sports about ten major eruptions at any given time, and those are observable from Earth with adaptive optics. For a fraction the cost of JSO, build about 5 tropical observatories dedicated to Io, such that two or three of them can view Io at any time. And, hey, observe Jupiter, Uranus, Neptune, etc., every few hours as well.
.....


Interesting question. I think there is a lot of great science to be had from planetary monitoring
(20 mins per target per night would do fine in most cases) of io's eruptions and clouds on
Titan, Uranus and Neptune, plus Venus nightside, and Jupiter/Saturn by an observatory system
like you suggest . But to do a good job these need to be 10m-class facilities with AO...not cheap
and NASA is in the business of building spacecraft rather than infrastructure.

A lot of that science could be had by more creative scheduling of existing facilities (e.g. allowing 1/20
of a night allocations for months on end..)

(A retort question - how much more science would you get by beefing up (or even restoring to
higher reliability) the DSN - allowing you to downlink more (and/or lose less) data from existing missions.
I bet in terms of science/$ it is a good expenditure, but infrastructure is never a sexy item to
sell)

As for Io - you can see eruptions are there from the Earth, identifying the location, measuring the total
heat flux in a number of bands (allowing area/temperature estimates) but that doesnt give you any
of the geomorphology, plume dynamics etc that a JSO would give you.
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tedstryk
post Nov 19 2007, 11:37 AM
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I tend to favor JSO due to the better Io coverage, not to mention the Ganymede coverage. However, while I find Europa interesting, I have never been on the Europa bandwagon. To put it another way, I find it one member of the Callisto-Ganymede-Europa-Io series, and to understand these worlds, obsessively focusing on just one of them (at this point, at least) seems a poor choice.


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