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Onwards to Uranus and Neptune!
SFJCody
post Jan 12 2008, 09:40 PM
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As soon as MESSENGER gets to Mercury, the most poorly explored planets in the solar system will be Uranus and Neptune. Could this lead to a revival of interest in the ice giants and their retinue, in the same way that the existence of New Horizons is perhaps partly due to the Pluto stamp*?







*via Pluto Fast Flyby and later Pluto Kuiper Express
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tedstryk
post Jan 12 2008, 10:01 PM
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QUOTE (SFJCody @ Jan 12 2008, 09:40 PM) *
As soon as MESSENGER gets to Mercury, the most poorly explored planets in the solar system will be Uranus and Neptune. Could this lead to a revival of interest in the ice giants and their retinue, in the same way that the existence of New Horizons is perhaps partly due to the Pluto stamp*?
*via Pluto Fast Flyby and later Pluto Kuiper Express


Here is what makes it difficult. Due to the expense and the long time commitment, it takes a lot more of a push to explore Uranus and Neptune than it does Mars, Venus, or even Jupiter. Also, the fact that Voyager-2 has been there. I am not saying Voyager is the be all and end all of exploration. What I am saying is that Pluto had the benefit of the "There is only one of the nine planets we haven't explored, and this flyby mission would get us there." I should add that this has nothing to do with the "is Pluto a planet" debate - the fact of the matter is that it was officially recognized as one at the time. In fact the questions about its status gave the mission media attention as well - as if New Horizons could somehow carry a Multispectral Mapping Planetometer (yes, I made that up, so don't ask me how it would work biggrin.gif ) to answer this
"question." This gave the mission publicity and enough clout to lead congress to override its omission from the budget.

Selling another flyby of Uranus and Neptune requires much more explanation. And anything beyond a flyby would be a huge flagship. With active Triton and the exciting Voyager images of Neptune's clouds, I think it fares a better chance at another visit. Unless there is some probe going to explore the heliopause (in other words, something coincidental) and Uranus is a target of opportunity, I don't think we will be visiting it for a long time to come. Perhaps it could be sold as a chance to see the northern hemisphere of Uranus and its moons. I would really like to see a mission like this happen, but I am not holding my breath.


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vjkane
post Jan 13 2008, 12:12 AM
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There is the opportunity, brought up in another thread, for a Jupiter > Saturn > Neptune tour with launch opportunities 2016-1018. It could then go on to visit one or more KBOs. A presentation on this opportunity as a New Frontiers candidate was made to a group reviewing the program in November, I think.

An ideal mission would drop a probe into the Saturn atmosphere as well as Neptune. It would also do a close fly-by of Triton. Don't know if the orbital mechanics will allow this and still do the probe relay.


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tasp
post Jan 13 2008, 12:31 AM
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"Economics engineering' seemed to be the key to Mariner 10 visiting Mercury (for the then bargain price of 98 mil). And was also a key factor in New Horizons and Messenger.


It might be a concatenation of ion drive, Sterling Cycle generators, follow on design revisons of existing hardware, some clever gravity assists, and the continued progression of Moore's Law that will bring a capable and affordable probe to either/both planets.
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Greg Hullender
post Jan 13 2008, 02:32 AM
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Does anyone have a link to any of the JSN proposals? I searched several different ways, but always kept getting Voyager material.

I suppose even ion drive doesn't make an orbiter all that much better a proposition. That is, assuming you use conventional means to launch the thing to Jupiter, only depending on the ion drive (and maybe some aerobraking) to slow it down at the end. Even so, it probably still busts the budget for a New Frontiers mission.

Trouble is, I agree it's hard to justify another Neptune flyby.

--Greg
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climber
post Jan 13 2008, 06:00 AM
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Do you think this: http://planetary.org/blog/article/00001285/ could help or even be a reason to go ?


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mchan
post Jan 13 2008, 09:53 AM
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Re: JSNK mission. Front this more as a Saturn probe mission with Neptune and KBO flybys as extras. IIRC, the Decadal survey has a Saturn atmosphere probe higher up on the priority list. Make it international with ESA supplying the probe and better yet most of the spacecraft instruments similar to Dawn. Don't see ion propulsion being required. Use Earth flybys to get to Jupiter so a low end EELV like Atlas 401 can be used. Use NH experience with hibernation during cruise to reduce operations costs until the Jupiter flyby. We have enough images from other Earth flybys, so don't even turn on any instruments (except for bring up tests) until Jupiter if that will save a million dollars or more.
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J.J.
post Jan 13 2008, 02:52 PM
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QUOTE (tedstryk @ Jan 12 2008, 04:01 PM) *
"There is only one of the nine planets we haven't explored, and this flyby mission would get us there."


I think that was definitely a factor--the whole "let's get this notch in our belt!" syndrome. Even I subscribed to it. wink.gif

I'd *love* to see another Uranus or Neptune flyby with a NH-style suite, with instruments optimized for studying them (like Voyager 2's weren't), but I agree it would be a tough sell. Let's not forget that even NH came within an ace of getting cancelled...

P.S.--Unfortunately, I also think Neptune would win out over Uranus in the bid-war. Though I find Neptune fascinating, I think Uranus's unique axial tilt and larger retinue of major moons just edge it out over Triton's volcanoes and its primary's more active atmosphere.


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vjkane
post Jan 13 2008, 06:16 PM
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QUOTE (mchan @ Jan 13 2008, 09:53 AM) *
Re: JSNK mission. Front this more as a Saturn probe mission with Neptune and KBO flybys as extras.

Without more information on the trajectory through the Saturn system, it's not known if the Saturn portion allows a probe relay or probe entry with reasonable parameters. One hopes so.

The current Saturn probe proposal involves an equatorial and a polar probe, which requires the relay craft to traverse the Saturn system at high latitudes. The probably would not be possible for a gravity assist to Neptune.

If Neptune is a requirement of the mission, then the Saturn trajectory is fixed. One hopes that it allows a reasonably close pass to Enceladus (see if the geysers are sill operating) and a probe relay.

Then at Neptune, there may be a trade off between a close Triton flyby and probe relay.

In my opinion, getting the elemental compositions of a gas giant and an ice giant would be the primary goals. Then I'd do the best possible at Triton with the understanding that coming close will probably put the spacecraft well out of the elliptic, which may may KBOs harder (I'm not sure what percentage of inner KBOs fall well out of the elliptic).


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Greg Hullender
post Jan 13 2008, 06:18 PM
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How much of the cost of one of these missions is the launch vehicle? Is it possible that the Falcon 9 Heavy could be enough to put a Neptune (or Uranus) orbiter under the New Frontiers ceiling?

--Greg
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JRehling
post Jan 13 2008, 10:40 PM
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[...]
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djellison
post Jan 13 2008, 10:55 PM
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I would consider aerocapture an enabling technology for both Uranus and Neptune orbiters. Get that sorted, and you don't have to trade fuel vs flight time quite so much.

Doug
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CAP-Team
post Jan 13 2008, 11:11 PM
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I think they should build two spacecraft, and send them both to JS and then one to Uranus and one to Neptune.
Building the spacecraft simultaneously will keep the building and development cost low.

Then the time it takes to get to Uranus and Neptune, if breaking is much a problem, then the speed to get there should be lower, at least much slower than New Horizons gets to Pluto.
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ugordan
post Jan 13 2008, 11:18 PM
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QUOTE (CAP-Team @ Jan 14 2008, 12:11 AM) *
I think they should build two spacecraft, and send them both to JS and then one to Uranus and one to Neptune.
Building the spacecraft simultaneously will keep the building and development cost low.

It will not keep the costs low. It will only enable you to get a second, identical spacecraft for less than 2x the cost of one. We're talking flagships here. You don't get two expensive launch vehicles at less than 2x of one to launch them, either.

QUOTE (CAP-Team @ Jan 14 2008, 12:11 AM) *
Then the time it takes to get to Uranus and Neptune, if breaking is much a problem, then the speed to get there should be lower, at least much slower than New Horizons gets to Pluto.

And you come back to what JRehling is saying that by the time the orbiter gets there, all the scientists will be retired. A minimum energy Hohmann transfer to Uranus/Neptune takes decades and is simply not worth it. What do you do for power? Even RTGs degrade over such long periods and you really want to get a capable and power-hungry instrument suite to orbit (since you're going through all this trouble already). The sad state of affairs is chemical propulsion is just not feasibly up to the task. We need new concepts, there are some feasible ones out there, but they need development. For serious delta-V in outer solar system you simply have to go nuclear (either reactor-based or RTG-electric).


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nprev
post Jan 13 2008, 11:40 PM
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You know if anyone's done a serious study on a NERVA-style mission to deliver an orbiter to either Uranus or Neptune, Gordan? Interested in what the passage time would be.


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