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Neptune Orbiter, Another proposed mission
Rob Pinnegar
post Nov 16 2005, 06:25 AM
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QUOTE (tedstryk @ Nov 15 2005, 05:59 PM)
It is interesting to see how irregular Proteus is, despite the fact that it is a bit larger than relatively-round Mimas.  Perhaps it is because it is the re-assembled lumps of old Neptunian moons.  Perhaps some other reason.  Either way, I find it most interesting.

Could be that it's just really beat up from impacts -- which makes one wonder about whether Triton had anything to do with that. I don't have much trouble imagining that satellite-satellite collisions would have been epidemic in the Neptune system right after Triton came barrelling onto the scene.

If Neptune's early system was similar to Uranus' (with Proteus as the "Miranda" perhaps) the chaos would have been pretty incredible there for a while.
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hendric
post Nov 16 2005, 08:22 AM
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QUOTE (elakdawalla @ Nov 10 2005, 12:20 PM)
However I'm not sure when there would be a launch opportunity that would permit such a repeat of Voyager 2's flyby "grand tour" -- that would be my first question.
--Emily
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According to Wiki, about every 176 years

http://en.wikipedia.org/wiki/Planetary_Grand_Tour

But...We've learned alot about gravitational assists since Voyager, and I wouldn't be surprised if it is now possible to do a repeat tour or tours.


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Rob Pinnegar
post Nov 16 2005, 02:02 PM
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QUOTE (hendric @ Nov 16 2005, 02:22 AM)
According to Wiki, about every 176 years

Yup. Uranus has now overtaken Neptune in its orbit, which means that we can't have a Grand Tour now. We have to wait for Uranus to catch up to Neptune again.

Since Uranus and Neptune are almost in a 2:1 orbital resonance, 176 years sounds about right. (That assumes Jupiter and Saturn will be well placed, of course.)
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tedstryk
post Nov 16 2005, 02:28 PM
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It is no doubt battered, but so is Mimas. A possibility is that it is positioned to receive very little tidal energy, so it never even partially melted down. If it does turn out to be a collection of fragments from an ancient Neptunian system, this could be good, as it would give us much more insight into what it once was than, say, Miranda.


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Rob Pinnegar
post Nov 16 2005, 05:09 PM
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QUOTE (tedstryk @ Nov 16 2005, 08:28 AM)
A possibility is that it is positioned to receive very little tidal energy, so it never even partially melted down.

In a way, that's a shame -- if Proteus had shown any evidence of long-term (but long-lost) tidal heating, this might have given some evidence that other large moons used to be nearby.

Of course, had such activity been found, Triton could also have been the culprit. I guess there's not much point musing about the might-have-beens.
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tasp
post Nov 16 2005, 06:31 PM
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And even Miranda is somewhat oblongish.

Would I be presumptuous to request a mosaic of Proteus, Hyperion, Miranda, etc. (all the satellites around the transition zone from irregular to sphereical) ?

The moons to scale mosaics are fascinating, if my computer skills were better, I might try to put one together, but I defer to those who are skillful in such things.

Thanx for the consideration.
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David
post Nov 17 2005, 03:11 AM
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QUOTE (tasp @ Nov 16 2005, 06:31 PM)
And even Miranda is somewhat oblongish.

Would I be presumptuous to request a mosaic of Proteus, Hyperion, Miranda, etc.  (all the satellites around the transition zone from irregular to spherical) ?
*


By way of reminder, those moons are Enceladus, Miranda, Proteus, Mimas, Hyperion, and Nereid; then there's a large gap in size before we get down to Amalthea and Phoebe, which I would say are no longer "transitional" -- that is, they might be vaguely roundish (as Phoebe is) but there's no particular reason for them to be so, other than chance. I would go so far as to say that Hyperion and Nereid are probably outside the "transition zone".

The Main Belt asteroids which are also in that "transition zone" are Pallas, Vesta, Hygiea (and - smaller than Hyperion - Interamnia and Davida); unfortunately none of them other than Vesta and Davida have images that show their shape.

The "transition zone" appears to be the 400km-600km diameter range. Below Mimas everything is pretty irregular. I don't know where the cutoff would be above 600km, since Vesta is itself rather irregular, and there's a big gap between it and Ceres.

If you count Iapetus as irregular, then there's a much larger transition zone, including Charon, Umbriel, Ariel, Dione, and Tethys, but Iapetus is really the odd one out there.
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tasp
post Nov 17 2005, 04:46 AM
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I suspect the 'lumpiness' of Iapetus is a result of a 'leisurely' formation period, time to radiate impact and radio-nuclide heat, too distant to have been warmed significantly from Saturnian formation heat, and also a very slow tidal braking effect from the the distant Saturn.

All these effects would allow for maximum thickness and strength of its crustal materials via cryogenic rigidity.
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Bob Shaw
post Nov 17 2005, 08:01 PM
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QUOTE (tasp @ Nov 17 2005, 05:46 AM)
I suspect the 'lumpiness' of Iapetus is a result of a 'leisurely' formation period, time to radiate impact and radio-nuclide heat,  too distant to have been warmed significantly from Saturnian formation heat, and  also a very slow tidal braking effect from the the distant Saturn.

All these effects would allow for maximum thickness and strength of its crustal materials via cryogenic rigidity.
*



I agree - it's not just a simple x-axis/y-axis graph, but a series of interconnecting variables, but with similar processes leading to similar outcomes...

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tasp
post Nov 26 2005, 02:55 PM
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With a greater understanding or how orbital tours work (thanx to the Heaton and Longuski paper on a possible Uranian mission) it seems a very interesting orbital mission at Neptune is possible.

The favorable mass ratio of Neptune/Triton would allow for considerable flexiblity for an orbital tour.

Which ever is easier at Neptune orbit insertion, a prograde or retrograde path, doesn't seem so critical now, as it seems repeated flybys of Triton could be used to change either orbit into the other. A detailed examination of Neptunes magnetic field at virtually all orientations would be possible. Neptune might be the key to understanding the diverse magnetic fields of all gas giant planets.

While Neptune seems 'short changed' in the satellite department, the satellites that are present were revealed by Voyager 2 to be interesting objects nevertheless.
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Decepticon
post Nov 26 2005, 03:41 PM
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A simple Google search reveled this!?

What Probe concept was this?

http://www.astro.univie.ac.at/~wuchterl/Ku...er_probe_02.jpg
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Guest_BruceMoomaw_*
post Nov 27 2005, 02:43 AM
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That's the nuclear-electric version of Neptune Orbiter, back when Sean O'Keefe's nuclear behemoth was still among NASA's official plans. It will, I think, be a long time before we see it -- not just because of the huge cost and environmental problems, but also because it turns out to significantly PROLONG the travel times of many spacecraft into the outer System, although it does allow a huge amount of cruising around from one moon to the next after you get there.

But the concepts for the Neptune entry probes and the possible Triton lander do still look just the way they're shown in that picture. As for the new "aerocaptured" Neptune Orbiter concept -- the one which is now overwhelmingly most likely to fly first -- you can see it still folded up behind its aerocapture heat shield on page 9 of http://www.lpi.usra.edu/opag/jun_05_meetin...eptune_API1.pdf . I can't find a picture of the Orbiter after it's been released from that shield and unfolded in Neptune orbit, but clearly it will look radically different from Galileo and Cassini -- and clearly it requires an unfolding high-gain dish. (Note how much it initially looks like the classic SF magazine-cover spaceship!)
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Decepticon
post Nov 27 2005, 12:31 PM
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I hate anything that Unfurls. mad.gif

When Galileo's Antenna failed to open I was Beyond upset.

I even read a article in Astronomy magazine where the person being interviewed (Forgot who) One of his fears was Galileo's antenna failing to open.
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Guest_BruceMoomaw_*
post Nov 27 2005, 01:32 PM
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Just keep in mind that Galileo's antenna was exactly the same design used on the TDRS satellites, each of which carried four of them. Out of (I believe) a total of 28 on them, not one has ever shown any trouble unfolding -- which is why the Galileo failure caught virtually everyone by shock. No one had ever anticipated truck vibrations as a cause. Now they do. And so, while I distrust moving parts in space as much as anyone, I see no reason to flee screaming from the idea of an unfolding antenna. It only requires making sure that the deployment springs have enough of a margin this time.
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Guest_vjkane2000_*
post Nov 28 2005, 03:38 AM
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QUOTE (BruceMoomaw @ Nov 27 2005, 06:32 AM)
Just keep in mind that Galileo's antenna was exactly the same design used on the TDRS satellites, each of which carried four of them.  Out of (I believe) a total of 28 on them, not one has ever shown any trouble unfolding -- which is why the Galileo failure caught virtually everyone by shock.  No one had ever anticipated truck vibrations as a cause.  Now they do.  And so, while I distrust moving parts in space as much as anyone, I see no reason to flee screaming from the idea of an unfolding antenna.  It only requires making sure that the deployment springs have enough of a margin this time.
*


Or make sure that reverse on the deployment motor is enabled. The cut the wires for reverse on Galileo before launch to make sure that the motor would never refold the antenna. From what I understand, the problem would have been simple to solve if they could have simply removed the tension from the pins.
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