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Juno - Jupiter Orbiter
centsworth_II
post Jul 19 2006, 08:34 PM
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QUOTE (AlexBlackwell @ Jul 18 2006, 05:07 PM) *
It'll be interesting to see if a fields and particles mission like Juno can capture the public's attention...


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.
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Guest_Richard Trigaux_*
post Jul 19 2006, 08:43 PM
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QUOTE (centsworth_II @ Jul 19 2006, 08:34 PM) *
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.
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JRehling
post Jul 19 2006, 09:45 PM
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QUOTE (Richard Trigaux @ Jul 19 2006, 01:43 PM) *
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.
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Guest_Richard Trigaux_*
post Jul 20 2006, 06:02 AM
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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.
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JRehling
post Jul 20 2006, 02:27 PM
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QUOTE (Richard Trigaux @ Jul 19 2006, 11:02 PM) *
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.


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.
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Guest_Richard Trigaux_*
post Jul 20 2006, 03:48 PM
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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...
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JRehling
post Jul 20 2006, 07:52 PM
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QUOTE (Richard Trigaux @ Jul 20 2006, 08:48 AM) *
A doppler analysis of a permanent signal will give us only one dimention of a three dimentional problem.


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.
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mcaplinger
post Jul 20 2006, 08:26 PM
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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


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Guest_Richard Trigaux_*
post Jul 21 2006, 06:19 AM
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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.
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mcaplinger
post Jul 21 2006, 02:20 PM
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QUOTE (Richard Trigaux @ Jul 20 2006, 11:19 PM) *
To achieve a better accuracy would require that Juno sense three pulsars with a high accuracy, or three natural masers...
The only practical solution would be to have a kind of GPS positioning around Jupiter.

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.


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Mariner9
post Aug 1 2006, 07:06 PM
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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.
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Lorne Ipsum
post Sep 17 2006, 09:03 PM
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QUOTE (Mariner9 @ Aug 1 2006, 01:06 PM) *
...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


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Roly
post Sep 18 2006, 02:42 AM
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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.
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mcaplinger
post Sep 18 2006, 02:50 PM
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QUOTE (Roly @ Sep 17 2006, 07:42 PM) *
Any further news about JunoCam pictures of the satellites?

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.


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JRehling
post Sep 18 2006, 04:40 PM
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QUOTE (mcaplinger @ Sep 18 2006, 07:50 AM) *
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.


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.
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