I thought that it was time to start a new thread devoted to the JUNO Jupiter
Orbiter mission. This New Frontiers Mission #2 seems to be a "stealth" project
with little information available on the Web. In fact, the official NASA JUNO
web site is quite pitiful. It contains the minimal amount of information on what
seems to be an intriguing mission, in terms of both science and engineering.

Does the UMSF community have information on this mission that has not
been widely seen before?

Another Phil

Up to now we've been using the "Nasa Picks "juno" As Next New Frontiers Mission" thread. But I guess we're well past the 'picking' so a new thread is in order.

Bruce posted a link to a good pdf on the mission: http://trs-new.jpl.nasa.gov/dspace/bitstre...4/1/05-2760.pdf (at the time only visible in the US, but I had no problems here in Oz just now...) for a nice bit of background.

James

Will this probe make any attempt to image Jupiter's moons?

Couldn't access it here, (UK)

Try this.

Analyst

Still nothing, page just times out eventually.....maybe it's a problem my end.

I think the link got munged in the quote. Correct address is:

http://trs-new.jpl.nasa.gov/dspace/bitstre...4/1/05-2760.pdf

Copy and paste the link if it still doesn't work.

Same thing

Keep on trying! This pdf doc is a good read. I got it from http://trs-new.jpl.nasa.gov/dspace/ and typed 05-2760 in the search window.

Success,
Peter

Or just turn to that address for the overall JPL Technical Papers site and type in "juno" in the search window. (This same technique works for lots of other interesting JPL papers, too.)

I have a few crumbs more information about this mission besides those in the article, which I'll reprint here as soon as I get over this damn headache. One thing we had better purge purselves of, though, is the hope that it will do any significant studies of the Galilean moons. It's designed to study Jupiter -- period -- and its orbit and mission duration make it almost impossible for it to study anything else (except for long-range studies of Io's ionosphere and torus).

OK, here are those crumbs. The JPL description is pretty good, but there are a few things missing from it:

(1) The 2002 Solar System Decadal Survey noted that the five main goals for the next Jupiter mission are: (A) Determine if Jupiter has a central core to constrain models of its formation; ( B ) determine the planetary water abundance; ( C ) determine if the winds persist into Jupiter's interior or are confined to the weather layer; (D) assess the structure of Jupiter's magnetic field to learn how the internal dynamo works; and (E) measure the polar magnetosphere to understand its rotation and relation to the aurora. Juno will do a nice job on all five - and while, the Survey's original desire for at least one and preferably 2 or 3 deep entry probes (down to 100 bars) would have further improved the data on ( B ) and ( C ), the added expense was so great that a deep Jovian Multiprobe Flyby mission by itself is now ranked pretty low on the list of desired New Horizons missions -- shallow Galileo-type entry probes of the other giant planets are higher-ranked. Moreover, the data from Juno will allow us to better plan the targeting of those deep Jupiter entry probes when we finally DO fly them. (Note also that -- if they absolutely have to descope Juno -- they could toss off every single instrument except the microwave radiometer and magnetometer, and lose only goal (E) in the process.)

(2) Currently we know Jupiter's gravity-field harmonics down to level 6 -- Juno will take it down to level 12 to 14. Not only can it nail down the size of any hevy-element core -- which is crucial to decide which of the two rival theories of giant-planet formation is true -- but it can measure that core's rotation rate, and even obtain profiles of the density of the planet's middle layers sensitive enough to determine how deep its convective wind cycles really run, all the way down 1/5 of the way to the core!

(3) Our current knowledge of Jupiter's magnetic-field harmonics is level 4. Juno will take it all the way down to level 20 -- much BETTER than we can ever obtain for Earth itself, where we're forever limited to level 14 due to interference from crustal fields! Thus Juno is likely to provide radical new information not only on the generative processes of Jupiter's magnetic field (including the dynamo radius and changes with time), but of Earth's field as well.

(4) Knowledge of the total oxygen content of Jupiter's atmosphere is crucial -- and the Galileo entry proe didn't get it because of its bad-luck fall (9-1 odds against) into a hot spot where a downdraft removed the local water vapor. The probe DID find not only that the concentration of the other heavier elements -- Ar, Kr, Xe, C, N and S -- was somewhat lower than expected, but that they were very consistent in being enriched about threefold relative to the Sun, whereas much bigger element-to-element differences had been expected in that ratio. This was a shock. The logical conclusion is that the icy planetesimals that formed Jupiter were actually made of much colder ice than that which existed at the planet's current distance from the Sun (150 K) -- those other elements were imprisoned either in regular ice at only 20-30 deg K or clathrates at >38 K, so either the planet itself formed much farther from the Sun and migrated a great distance inwards, or the planetesimals that formed it themselves came from much farther out and migrated inwards before accreting to form Jupiter at something like its present distance from the Sun. (The entry probe found further confirmation of this in the nitrogen isotopic ratios, which indicates that Jupiter's nitrogen was originally delivered as molecular N rather than as ammonia -- which in turn provides an odd clash that I've mentioned elsewhere with the indications from Huygens that Titan's nitrogen DID arrive as ammonia in relatively warm ice.)

Since water ice was the carrier of all these other heavier elements, we need to know the ratio of water ice to them -- for which we must know Jupiter's current oxygen content. If the planet's oxygen is enriched to only about the same degree relative to the Sun as all the other heavier elements measured by the Galileo entry probe, then they must have been carried into the planet in very cold water ice, from the Kuiper Belt or beyond -- and Jupiter itself may have originally accreted at that distance and then spiralled a great distance inwards. But if oxygen turns out to be enriched more relative to its solar abundance than those other elements -- say, about 9 times solar abundance -- then those other elements were trapped by water ice, and carried into the forming Jupiter, in a more diluted form as clathrate ices, which could have formed somewhat closer to the Sun.

The microwave radiometer (whose viewfield is 1 degree at the equator and 4 degrees at the poles) should allow water abundance measurements down to about 100 bars -- plus better ammonia data (which is a bit fuzzier from the Galileo probe than we would like), thus nailing down both Jupiter's overall oxygen content, and further sharpen our data on its nitrogen content. It will also get more data on the temperature and cloud depth profiles in different parts of the planet, which in turn should help tell us more about just how deep the convective and wind patterns that create the belt-zone structures really run. But it can only do all this reliably because the Galileo entry probe measured the other trace components of Jupiter's atmosphere -- some of which, like PH3, have a significant effect on the planet's microwave spectrum.

(5) Juno's mission is scheduled to run 32 orbits of 11 days each -- and any extended mission will be only a month or so, because they want to make sure that they can crash it into Jupiter, and thus avoid any chance of contaminating Europa, before they lose control of it from radiation damage. In fact, they may end the mission ahead of time -- most of its science will come from its first 16 orbits, and its periapsis latitudes are designed to give it only 5% of its total radiation dosage during that period. (As the JPL paper says, 5 of its first 7 orbits are directed toward microwave radiometry, with all the rest of its orbits being devoted to precision tracking for gravity-field data.)

(6) Juno spins at 3 rpm. Its "JunoCam" -- the most dispensable of all its instruments, whose data will be processed by students at JPL -- should send back 5-10 images per orbit. Juno is focused entirely on the planet itself -- any data it does get on the moons will be pure gravy. For instance, it's very unlikely that they will be able to arrange for it to fly through Io's flux tube.

Try a proxy server. This is how I could get this document from Germany.

Using solar power for JUNO has always intrigued me. Starting with Pioneer 10 and onward all of our outerplante probes (including the ESA Ulysses) have been nuclear powered. The stated reason is that the available sunlight gets too low much beyond the orbit of Mars or the mid-asteroid belt.

Yet here is JUNO using solar. The panels in the diagram don't look all that much bigger big to me in relation to the craft than say the Viking orbiters or MRO, yet the solar power at Jupiter must be less than 1/4 what it is at Mars.

What am I missing? Are they using amazingly compact and low powered instruments? Is a large percentage of the power being used to charge batteries much of the time, then the batteries are used for peak power usage?

I was rooting around on the ADS server, looking for papers related to Juno, and I found this one.

http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1564.pdf

It describes an instrument for Juno, but it's not one that's mentioned in the mission overview linked above. Is it a recent addition, a pipe dream, or something in between?

Bart

The panels actually ARE somewhat bigger than those for the Mars missions. Solar panels actually are feasible to power Jupiter craft, IF you stay out of the intense radiation regions (which took a lot of careful orbital planning for Juno), which will quickly fry them -- and if you're willing to accept their weight. All three of the Discovery proposals which were Juno's ancestors (two of which were orbiters, and one of which was a finalist twice) used lightweight solar arrays -- and, in fact, the suggestion was made to put FOUR such solar panels on a copy of one of those craft and use it as the flyby carrier for a Saturn entry probe! http://www.lpi.usra.edu/meetings/outerplan...01/pdf/4113.pdf

By the way, ESA's Rosetta comet craft, which has big solar panels, has an aphelion all the way out at Jupiter's orbit -- but it will be in a state of near-hibernation during those periods.



I'm about to look into this. Apparently it may be added to the payload, but I haven't heard anything from any other source about it. If they can squeeze it on (maybe as a replacement for the JunoCam), it could be very useful.

At the risk of becoming permanantly tagged as "that Solar Power nut" I'd also add that Solar cell technology has progressed enormously since Viking days. I don't have the efficiency of the Viking orbiter arrays at hand but I'd be surprised if they were any better than 15% and were probably closer to 10%.
Similar improvements have been made in the remaining power management and distribution technologies (regulation and storage) so on a similar mass budget you can now generate 3-5x as much power using solar panels as was possible 30 years ago. Even within the time frame of the Cassini mission that increase is close to 2-3x.

One thing's for sure... the increase in solar cell efficiency had better top out at 100% or a trace less..... or the free-energy psycho-ceramics will win!

It's sort of like Moore's law... unless you can start engineering with nuclear-matter, we're gonna bottom out with atom sized machinery components.

"It describes an instrument for Juno..."

It looks to me like they're trying to persuade NASA to squeeze it on the mission. It would be much the same way the X-ray fluroescence instrument was added to the Viking's biology dominated payload after formal instrument selection was done, but Mariner 9 discovered an unexpectedly complicated and active geology. The instrument ended up with some significant compromizes from being squeezed onboard, but did a fine job anyway.

I really hope we do have good data from Junocam and / or that this proposed instrument flies. I've wanted to see more and better of the polar regions "boiling porridge" (as I call it) that we saw in Pioneer 11 data and get some good info on it's motions right up to the poles (impossible from equatorial missions).

Slight historical correction: NASA decided to add an element analyzer to the Viking landers BEFORE Mariner 9's discoveries -- in summer 1971, when the science payload was being seriously shaken up anyway by cost and weight overruns, and scientists were complaining about the shortage of nonbiological experiments. There was a hasty competition between the XRS and Turkevich's Surveyor alpha-scatter spectrometer, which the XRS won.

That's not what I recall.... but given "NASA-Speak" .... I would not be at all surprised if that was after-the-fact PR spin.

But again, my memory may be wrong... or it may have been prompted in part by the observations of "featureless terrain" and "chaotic terrain" in the Mariner 69 data instead.

There was a very detailed "Science News" article in late spring 1971 on the overall changes in Viking's payload. At that time, the choice between the two element anal,yzers had not yet been made, but was called imminent. By early 1972, when Icarus did a whole special issue on the Viking science payload, it had been made.

(Not that this is exactly an earthshaking point -- but they definitely had an element analyzer of some type planned before Mariner 9's results. The official Viking history, "On Mars", can probably tell us more -- I have a copy.)

I have an original copy of that Icarus special issue, but dragging them out of bookshelves 200 feet from here after I step over several boxes of books without breaking my legs.... inhibits a quick "lemme take a look"

Again, I apologize for reviving a dormant thread; however, has anyone noticed this particular Juno website?

I crave good dormant-thread awakenings.

That site is incomplete, but apparently because they're putting very careful work into each section. In fact, it was the fact that the completed sections went so far over my head that I looked for explanations in the glossary section (which is incomplete).

The whole business with the gravitational mapping of Jupiter's interior is going to expand my math education before the mission's over.

I was thinking the same thing - the topic of gravitional field mapping has come up here previously and it's one of those things that I'm intrigued by but I'm a bit concerned that the mathematics will be way too much for me.

I had a chance to talk to one of the engineers on the project at the JPL open house in May. It was fascinating stuff, particulalry the plan to use the radiometers to help determine if Jupiter's belt zones above and below the equator are linked to matching internal structures inside Jupiter.

It was so off the wall, I don't fully remember the specifics, and not even sure how to describe it properly. Essentially, there is a hypothosis that for each major atmospheric belt, there is a corresponding belt opposite the equator that is powered by the same internal dynamics. AKA ... if there is a belt at +33 degrees lattitude, then the belt at -33 degrees is part of the same structure. The belt at +42 degrees is connected to the belt at -42 degrees and so on. (I'm making up the numbers just for the example).

I was also able to confirm my suspicion that not every orbit will be devoted to gravity mapping. I asked the guy and he confirmed that the high gain antenna has to be pointed directly at Earth during the Periapsis pass of the orbit, and when that is being done the vehicle rotation axis will be such that the Junocam and radiometers are not pointing at Jupiter. So there are dedicated orbits for the gravity mapping, and other orbits for the radiometry.

He also said that just a single orbit would give them the data they need for the Radiometry experiment, but naturally they plan on at least 4-5 just to be sure their data is confirmed.

Juno is a fascinating mission.... but I'm not entirely sure how to explain it to the general public. Even my eyes partially glaze over when you start talking about exploration of the polar magnetosphere, and I at least have some idea what that means.

It'll be interesting to see if a fields and particles mission like Juno can capture the public's attention, but I agree that it's a fascinating mission. I'm sure that JunoCam will help in the PR department, assuming it stays on the payload.

I think it's fortunate that a mission of this type can be attempted through New Frontiers. If the Jupiter science required a Europa Orbiter level of expenditure this mission might be sitting on the back burner.

Juno still has to be confirmed for flight (i.e., pass its CDR). I guess we'll know then whether a Jupiter orbiter (even one sans probes) can be done on a New Frontiers budget, or at least whether such a mission isn't deemed not-doable prior to launch.

I remember that Dawn, too, looked pretty nice prior to the descopes/cancellation/re-start.

If I match your description with what I have already read, I think the question is between two alternative hypotheses:

1) The belts are "surface" phenomena only, not penetrating very deeply into the atmosphere. The northern and southern hemispheres have similar patterns because they are similar structurally: two different examples of dynamics with similar parameters.

2) The belts are where deep concentric "cylinders" happen to intersect the surface. The belt at +33 is the ring where a north-south oriented internal cylinder slices into the upper clouds in the northern hemisphere; most of the cylinder is buried very deeply; the southern intersection of the cylinder and the "surface" is at -33.

I guess there's some complex integration of the gravitational data that can help settle the question. I can't picture that analysis, but there's plenty of time to read up on it before/if the data comes back.

I think that what is most likely to capture the public is the prospect of getting a description of what sits beneath the thick layers of gas and clouds. Solid? What size? Sharp transition from gas to solid? Is there a liquid layer? How deep?

I hope these sorts of questions can be answered. They are the most interesting to me, and I think the public at large.

How this could be answered? By radar? or by sismology? Is it possible to make sismology on Jupiter, from an orbiter, with enough sensitivity? I don't expect sound waves like on the sun, but perhaps tidal waves, produced mainly by Io. To detect them would require a very accurate position measurement of the orbiter.

Measuring tidal bulges is sure to be a key part of the science: Amalthea and the Galileans will induce tidal bulges. When Juno passes over them, it will speed up relative to other perijoves.

What happens when two bulges coincide? Note that it will happen on opposite sides of Jupiter simultaneously. I imagine this tells us about the upper reaches of Jupiter but not the depths. This will happen often, and every perijove, Juno will slice along a meridian located somewhere with respect to those five bulge-pairs. It'll get some interesting data every time.

Will the effect of these bulges be detectable by analysing Juno's position?

Analysing this position alone will be a great chalenge, as, if Juno changes speed and trajectory relative to the bulges, the moons too will do this. So assessing the trajectory alone will already be very complex, especially if the only reference is the set of jovian moons. With my opinion, we need some other stable references:
-ultra stable radio uplink from Earth
-using pulsars or other stable galactic source
-measuring star position.



Once the movement known, analysing tidal effects will too be complicated. Tides are basically waves, which want to propagate at their own speed, independently of the astronomical cause. On Earth such waves can resonate into large oceans, giving a different tide regime for the atlantic ocean and the pacific ocean. On Jupiter, we can think that we shall have resonances along the equator, or more likely different spherical vibration modes. Some will be directly excited by one of the moons, some will on the countrary opose to the excitation by one of the moons.

In a first approximation, we shall have linear waves, or more accurately a spectrum of discreet vibration modes. This will already allow us to sense the depth of the atmosphere and obtain a pressure profile. (if the waves go deep enough. This is not sure, and in heliosysmology there is still a lack of modes involving the core).

In a second step, discrepancies to the linear models will allow us to search for non linear effects, such as damping, elliptic shape of the layers, movements, layers of helium or layers of hydrogen, etc.

The dream would be, like as in heliosysmology which is now able to sense the presence of spots on the opposite side, to see inner Jupiter features like large storms, solid surface features, or convection patterns. After a computer model which was made several years ago, Jupiter would contain a set of several vortexes, paralel to its rotation axis, but avoiding the solid core.


What will be ultimately possible to see will depend on the accuracy of trajectory measurement, I think. This is worth adding some weight, like a telescope (to sense stars) or a set of large antennas.

I think the key will be to measure the doppler shift of a continuous Juno-to-Earth radio signal to determine Juno's velocity and compare that to the no-bulge expectations of velocity. That's how mascons were discovered on the Moon (and Ganymede). Actually, since merely detecting the bulges is not the point, I think the analysis will be to construct models of how the ten tidal bulges alter Jupiter's shape, make predictions of what Juno's velocity should be, and refine the model based on the data. The bulges will not be moving "hills of atmosphere", though -- they should have manifestations at depth as well, which makes the models more complex, but also more informative. That will help us, in a roundabout way, understand Jupiter's interior.

Using a Juno flyby to calculate the planet's moment of inertia is also/instead a way to go about this. And with that, I find the need to read up on more mathematics.

A doppler analysis of a permanent signal will give us only one dimention of a three dimentional problem. Maybe it would be fine to also have a pulsar or something as a second doppler source in a perpendicular direction. But this implies a large dish...

True, but considering velocity to be a measure of the mass in the chord between Juno and the center of Jupiter, there's for the most part only one dimension that's unknown in Jupiter's shape. To address that qualitatively, it's not that Jupiter will suddenly be shaped like a dog-bone or a torus... that would be tough to find out from gravity data! But with a slightly warped elliptical spheroid, we can assume we know the side-to-side characteristics of the trajectory and just measure how much it accelerates due to Jupiter's gravity in the downward direction. I think knowing that one dimension will serve us pretty well.

I think you guys are at least a few orders of magnitude off concerning what's possible with radio tracking of Juno. They are using conventional X-band radiometric tracking only, and all they are looking for is the first three even spherical harmonic terms to get information about the core of Jupiter. I find it extremely unlikely that the atmosphere can even be sensed by this.

See
http://trs-new.jpl.nasa.gov/dspace/bitstre...4/1/05-2760.pdf

JRehling, I think that sensing several bulges moving around Jupiter is actually a three dimentional problem (or at least two, if we assume a symmetry regarding the equatorial plane).



mcaplinger, in fact you reply my previous question: "is Juno position measurement accurate enough to sense high ranking harmonics and detect tidal effects?". After your reply, it is not, and by several order of magnitude.


detecting only the first three harmonics will only allow to sense the inner spherical layer structure, and even not very accurately. No hope to detect vortexes or other exotic things.

To achieve a better accuracy would require that Juno sense three pulsars with a high accuracy, or three natural masers. But I am afraid that this would involve very large antennas, much too large for a ship like Juno.


The only practical solution would be to have a kind of GPS positioning around Jupiter.

I already said several times in this forum that a GPS positioning and radio relay (with large data storage) would be one of the first things to do for seriously exploring any planet. Such small satellites would be designed to last for tens of years, for further missions.

On Jupiter, this is especially difficult, with the radiation belts. But could be a ship like Juno be left in orbit, once it exhausted its fuel, and be used as such a relay? This would just require some tens of kilos of additional mass, and be very useful for further missions.

I don't think either of these solutions would work to solve the problem you're describing. You can't determine your location by observing pulsars from a single point with any kind of accuracy. You may be thinking of VLBI, which is used for geodesy on the Earth, but this requires simultaneuous observations from several locations and high bandwidth communications between them.

As to GPS, one of the components of such a system is knowledge of the transmitting satellites' positions. So without a fixed location from which to track them, I think there may be a chicken-and-egg problem if you are trying to get very high positional precision (even on Earth, GPS can't do better than a half meter or so even using DGPS.)

There may be some sort of multiple-satellite, multiple-transmitter solution to this problem, but that would require a very large investment to build.

The bottom line is that I just don't think it's practical to study this problem using gravity sensing with our current level of technology. Fortunately there are other ways; see the Juno reference I mentioned earlier.

http://www.aip.org/fyi/2006/093.html

I just found an article on the Senate Appropriations commitee, dated July 17th. It has an interesting note on JUNO:

"The Committee has provided the budget request of $120,000,000 for the Juno-Jupiter Polar Orbiter mission and fully expects NASA to maintain this mission and its out-year budget profile to accommodate a 2010 launch as originally envisioned."


I know that the budgets shift back and forth until the fall, but if this is still in the final version, it looks like we might be back to a 2010 launch.

I talked to one of the JPL engineers about JUNO at the open house in May, and he said they could launch much earlier than even 2010, but it was entirely about budget cycles at this point.

Sorry, not a chance of this happening. Once upon a time, the program was happily lined up for a 2010 launch. After the slip, contracts were changed, and the whole program replanned from top to bottom. If Juno had *originally* been slated for a launch before 2010, and the funding had held, it would have been doable.

At this point, though, it'd be horrendously expensive to launch in any year BUT 2011. An awful lot of analysis would have to be re-done, at the very least. Meanwhile, some number of long-lead items probably wouldn't be ready in time.

Lorne

Any further news about JunoCam pictures of the satellites? I know this is absolutely outside the mission, but there was some speculation I believe (assuming it ends up being fitted to the spacecraft) that there may be some possibility. I seem to remember that there might be a chance at Io.

JunoCam is a wide-field-of-view instrument, so a satellite approach would have to be pretty close to yield anything better than what we have already. And I suspect that Juno will be deliberately kept away from the satellites to keep the orbit perturbations to a minimum. But it's a long time until this mission flies, so I wouldn't count anything out yet.

And on the topic of gravity measurements, I ran across an abstract, "Gravity Inversion Considerations for Radio Doppler Data from the JUNO Jupiter Polar Orbiter" ( http://www.aas.org/publications/baas/v36n4/dps2004/158.htm ) that describes some possibilities, though I haven't seen the full paper.

Since Io has a time-varying phenomenon or two, occasional medium-range pictures could be informative. Earth-based observations have been proven capable of spotting the big ones, but some more frames of what we could consider to be a "movie" with many gaps (mainly gaps) on the ongoing record of post-1979 flareups on Io couldn't hurt.

The Anderson, et al, abstract on gravity science is interesting. They do mention observing the tides raised by the Galileans and Amalthea (which is much, much closer to the cloudtops, thus having a serious tidal effect despite its small size and low density). I might as well start learning the math behind the rest of the content of that abstract now.

I find the current 'tussle' on the forum about this missions lack of Jupiter moon photography some what ironic, Pioneer 10/11 were essentially focused almost entirely on Jupiter to the exclusion of the satellites.

The same thing almost happened to Voyager, if the BBC documentary series 'The Planets', was accurate in its description of the 'one man' fight to have the moons included as imaging targets for Voyager.

Supposedly until the Io pictures came in the mission team was entirely composed of Atmospheric and Astrophysics specialists ready to unravel the mysteries of the Jovian atmosphere...

So in that sense this mission is a return to basics, a focus on the 'main show' namely Jupiter itself rather than what orbits around it.

Very early in the planning stage (about 1972/73) MJS 77 got cameras with Mariner 10 heritage. This has not been easy (budget etc.) and I guess this is the "dramatic fight" in The Planets. The moons have been a primary science target at least since then. JPL studied many trajectories and could only get close encounters with three moons at Jupiter. At Saturn, Titan has been a so high priority, Voyager 2 could be sent to it again if Voyager 1 failed.

As for Juno: Its not about images first, not even second. It's not a sexy mission imo, but we will learn at lot.

Analyst

I know the images are not a priority, but there are two things I am hoping for from JunoCam. First, any serendipitous shot it can get of the four inner moons, since coverage from Galileo and Voyager is so limited and most of the moon oriented missions likely to be selected any time soon are not likely to get close to them. Secondly, a few decent Io images for temporal coverage with better resolution than we have from earth. Plus, especially if the cloud tops are in the background, these images would be great for PR.

I've watched the relevant episode again ('Terra Firma') and it's definitely implied that the argument was not about having cameras on Voyager, but about where they were going to be pointed when Voyager reached Jupiter.



You're absolutely right there, this is the sort of 'basic science' mission that needs to be carried out so that we can plan properly for the next major mission without any more incidents like dropping the atmosphere probe into the wrong region as happened with the Galileo's mission.

And its been a long time in coming, this sort of mission was first proposed by the designers of Pioneer 10/11, even before the first flyby of Jupiter. In that case they planned to use an 'up-rated' version of Pioneer 10/11 to carry out long term (2 yr) observations of Jupiter (or Saturn) during the late 70's/early 80's. In these craft as with Juno, particles and fields studies would have been the main objective while imaging would have taken the back seat, despite the replacement of the Imaging Photopolarimeter with a 'line scanning' imager which would have presumably produced better images.

I recall reading about that proposed orbiter. I vaguely remember Dr James Van Allen being one of the proponents of it.

Basically Galileo was a hybrid space vehicle in order to do both spining (which is better for the particles and fields instruments) and a stable (better for imaging) platform.

And after all the suffering involved in engineering it, a lot of those involved swore they would never try another dual-spin spacecraft again.

Cassini was supposed to be the "cheaper' vehicle... although it seems to me that at 3 billion dollars it ended up more expensive. Difficult to be sure, since Cassini was developed later and hence with inflated dollars compared to Galileo. Also, the antenna failure on Galileo introduced a lot of extra operations expenses, on a program that already was delayed several times, and redesigned a few times. I don't think I've ever seen a final tally on Galileo's costs, but I'm pretty sure it ultimately went over 2 Billion.