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Unmanned Spaceflight.com _ Uranus and Neptune _ Onwards to Uranus and Neptune!

Posted by: 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

Posted by: tedstryk Jan 12 2008, 10:01 PM

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.

Posted by: vjkane Jan 13 2008, 12:12 AM

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.

Posted by: tasp Jan 13 2008, 12:31 AM

"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.

Posted by: Greg Hullender Jan 13 2008, 02:32 AM

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

Posted by: climber Jan 13 2008, 06:00 AM

Do you think this: http://planetary.org/blog/article/00001285/ could help or even be a reason to go ?

Posted by: 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. 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.

Posted by: J.J. Jan 13 2008, 02:52 PM

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.

Posted by: vjkane Jan 13 2008, 06:16 PM

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).

Posted by: Greg Hullender Jan 13 2008, 06:18 PM

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

Posted by: JRehling Jan 13 2008, 10:40 PM

[...]

Posted by: djellison Jan 13 2008, 10:55 PM

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

Posted by: CAP-Team Jan 13 2008, 11:11 PM

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.

Posted by: ugordan Jan 13 2008, 11:18 PM

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).

Posted by: nprev Jan 13 2008, 11:40 PM

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.

Posted by: Planet X Jan 14 2008, 03:08 PM

QUOTE (JRehling @ Jan 13 2008, 04:40 PM) *
One tradeoff with orbiter missions is how long we can tolerate the cruise phase to be. With a flyby, it's not such an issue, but with an orbiter, the faster you get there, the more fuel (or heatshield) that you need to slam on the brakes at the end of the cruise. A minimum-energy trajectory to Neptune is prohibitive unless we expect the people running the mission at the onset to be retired (or dead) by the time the science mission begins. The more we shave off of that cruise, the more mass problems intrude. That's one big factor in Uranus's favor -- it's 11 AU closer.


Personally, I see Uranus as the better target. Though Neptune may have more to offer, it's just too distant for an orbiter mission, barring some miracle advancement in technology. For instance, the Hohmann transfer time to Neptune is 40 years, while the time to Uranus is 16 years. I see no problem with designing a probe to last a couple decades (16 year trip time + 4 year length of primary mission) for a Uranus mission. Besides, there's always the possibility of a mission profile similar to that of Cassini, involving Venus, Earth, and Jupiter that could shorten the trip time somewhat. Later!

J P

Posted by: vjkane Jan 14 2008, 04:35 PM

Neptune has been ranked as a higher priority as ranked by the scientific community for a follow on mission because of the interest in Triton.

I looked at Titon's orbit relative to Neptune in the mid-2020's on the Solar System Simulator. As viewed from the sun (which I presume is the direction of arrival for a flyby mission), Triton's orbit remains well away from Neptune for this time frame. However, Triton's distance from Neptune is less than the distance of Io from Jupiter. A mission that targets a Triton close encounter still comes reasonably close to Neptune, and probably close enough to act as a relay for a Neptune probe. (However, the ammonia in Neptune's atmosphere will weaken the probe's signal; I don't know how this would effect this scenario.) In fact, a more distant flyby of Neptune than was done by Voyager might be required to give adequate viewing time for the probe relay.

Posted by: Greg Hullender Jan 14 2008, 05:48 PM

I get 16 years for the Hohmann to Uranus, but just 30 2/3 to Neptune -- not 40. Calculating as follows:
1) Since the Hohmann is at 1 AU at perihelion and at the target planet at aphelion, the SMA of the Hohmann is (1+a)/2, where a is the SMA of the planet. 10.1147 AU for Uranus and 15.5518 for Neptune.
2) Kepler's third law says period is SMA to the 3/2 power, but we only want HALF the period (since we're done when we reach the target). That gives me 16.08422 years to Uranus and 30.6650 to Neptune.

As a cross check, using these numbers I calculate an 84-year period for Uranus and 165 years for Neptune, so I do think I have it right this time. :-)

Even so, 30 years is a long time to wait. So's 16. Add to that the fact that currently we can't even swing the delta-V for a Hohmann to JUPITER for a large probe -- much less one to Uranus or Neptune. That's why Cassini and Galileo had to make all those swings by Venus and Earth first.

Aerobraking, ion propulsion, and cheaper boosters all seem needed to get a reasonable-sized package to either destination in a reasonable time. On the other hand, all three look like they might be just over the horizon.

--Greg

Posted by: Del Palmer Jan 14 2008, 07:12 PM

QUOTE (Greg Hullender @ Jan 14 2008, 05:48 PM) *
Add to that the fact that currently we can't even swing the delta-V for a Hohmann to JUPITER for a large probe -- much less one to Uranus or Neptune. That's why Cassini and Galileo had to make all those swings by Venus and Earth first.


Galileo could have reached Jupiter directly, had it been allowed to use its original liquid-hydrogen-fueled Centaur IUS instead of that pansy solid-fuel IUS...

Posted by: Jyril Jan 14 2008, 10:40 PM

But it would have missed Ida and Gaspra, and the cool photos of Earth and Venus.

On the other hand, the main antenna might have worked, and the probe would have followed the SL9 impacts from orbit...

Posted by: ugordan Jan 14 2008, 10:54 PM

QUOTE (Jyril @ Jan 14 2008, 11:40 PM) *
and the probe would have followed the SL9 impacts from orbit...

It would have been on the wrong side of the planet at the time.

Posted by: Jyril Jan 14 2008, 11:04 PM

QUOTE (ugordan @ Jan 15 2008, 12:54 AM) *
It would have been on the wrong side of the planet at the time.


How do you know that? Wouldn't the Jupiter tour have been different, if it had traveled directly to the planet? It would have been there already for years.

And even if wouldn't have seen the impacts, it would have had much better view of the impact effects than any observatory at Earth.

Posted by: ugordan Jan 14 2008, 11:06 PM

QUOTE (Jyril @ Jan 15 2008, 12:04 AM) *
How do you know that?

Murphy's law.

Posted by: tedstryk Jan 15 2008, 12:54 AM

Yes, but during the post-Challenger delay and replanning, they also discovered that the rocket motors were defective. Galileo would have gone the way of CONTOUR had it launched in 1986 or 87. In other words, things could have been a whole lot better, but they could have been a thousand times worse.

Posted by: tasp Jan 15 2008, 06:08 AM

IIRC, the Galileo Jupiter trajectory provided by the Centaur stage would have included a nice flyby of Amphitrite, an otherwise obscure, largish main belt asteroid. Had that occured, it would have been the largest asteroid flown by till Dawn reaches Vesta in several years.

Posted by: Toma B Jan 15 2008, 09:02 AM

QUOTE (Jyril @ Jan 15 2008, 01:40 AM) *
On the other hand, the main antenna might have worked,...

It would have worked.
If I remember correctly it was plan to open HGA while still near shuttle so that if any problem occurred it could be fixed right away... <spacewalk>
Also that heat shield for HGA would not be there.....
I am not sure about this just remembering..... sad.gif

Posted by: Greg Hullender Jan 15 2008, 02:32 PM

Uh, I hope they didn't plan to open the main antenna before firing the Centaur upper stage. :-)

Anyway, I've heard the switch away from the Centaur blamed for the antenna problems. (e.g. Carting the probe around for so long led the lubrication to dry out so the pins didn't release.) But I've heard other explanations too.

Biggest problem with the upper stage (based on reading "Taming Liquid Hydrogen: The Centaur Upper Stage Rocket 1958–2002") was that the shuttle couldn't actually lift the Centaur-G-Prime because the shuttle never achieved its originally planned lift capability. They were talking about throttling up to 109% instead of 104% for the Galileo and Ulysses launches. The astronaut crews were already calling Centaur "the Death Star" before Challenger exploded.

After Challenger, safety changes made the shuttle heavier, and any changes to the Centaur would have made it heavier too. If it was marginal before that, it was hopeless afterwards.

Anyway, the real problem wasn't failing to use the Centaur upper stage; it was using the Shuttle in the first place. Galileo should have been a Titan-Centaur launch, and I don't think there's much dispute over that now. Depending on the shuttle for launching unmanned probes turned out to be a huge mistake. It may have put us as much as 15 years behind where we'd otherwise have been.

But this is old news, long hashed over here. However, if you haven't read it, do have a look at "Taming Hydrogen." It's a great read.

--Greg

Posted by: Toma B Jan 16 2008, 07:49 AM

QUOTE (Greg Hullender @ Jan 15 2008, 05:32 PM) *
Uh, I hope they didn't plan to open the main antenna before firing the Centaur upper stage.
--Greg

Why not?
Actually that's what I thought they were planing.....I really don't know... huh.gif

Posted by: Greg Hullender Jan 16 2008, 04:29 PM

Actually, I think you're right. The only reason they folded the antenna up in the first place was to hide it behind a sun screen, and the only reason they had to do that was to protect it during the Venus flyby. Obviously they wouldn't have done a Venus flyby if they could have launched with Centaur.

Sorry about that. :-)

--Greg

Posted by: Mariner9 Jan 16 2008, 09:51 PM

Some years ago at a JPL open house I spoke with one of the engineers on Cassini. I asked about the reasoning behind using the Titan 4 vs. using the shuttle. It turns out it would have been cheaper to launch on the shuttle, but only by the way NASA does accounting. The price charged to the Cassini project would have been the processing fees and upper stage, and not the actual shuttle flight itself.

And it wasn't payload capacity or safety that were the main drivers either. It was schedule. The Cassini team figured they would rather rely on the Titan to get a launch accomplished during a planetary launch window. The shuttle, with it's frequent delays and down times was just too unreliable.

Not exactly on topic for this thread, but since everyone was discussing launch issues with the shuttle......

Posted by: Gladstoner Jan 19 2008, 08:54 AM

.

Posted by: nprev Jan 19 2008, 09:05 AM

Uh...say what?! We haven't launched a Galileo follow-up, which would be easy compared to Uranus/Neptune recon mission(s) (to say nothing of orbiters, the technical hurdles of which have been extensively discussed). We are extremely lucky that Voyager 2 did succeed, else I suspect that none of us now living would have ever seen these planets up close in any respect.

Think I know what you mean, but frankly it seems that you're overestimating the impetus for doing such missions. Remember that there was actually a serious proposal floated to turn off Voyager 2 while it was enroute to Uranus as a cost-cutting measure; thank God it didn't happen.

Posted by: JRehling Jan 19 2008, 09:14 AM

[...]

Posted by: Gladstoner Jan 19 2008, 09:34 AM

.

Posted by: nprev Jan 19 2008, 10:18 AM

QUOTE (Gladstoner @ Jan 19 2008, 01:34 AM) *
And the bean counter who considered switching off Voyager 2 before Uranus..... I hope he is now wrapping burrito supremes at Taco Bell.


No argument there! laugh.gif Still, the fact of the matter is that Uranus & Neptune are really off the radar screen right now, and have been for a considerable period of time. I don't like it either, but it is what it is. NH took advantage of an excellent launch opportunity to get to Pluto within a reasonable time to complete the initial recon of the major objects in the Solar System (Note: NO planet/ain't a planet comments welcomed!!! mad.gif I'm serious! Uh, would be remiss without mentioning Dawn as part of this effort as well), and I think that the vibe is to wait on Uranus & Neptune until a viable means to undertake a Cassini-style mission to each of them becomes available.

Posted by: Jyril Jan 19 2008, 10:26 AM

Voyager 2 was only able to visit Uranus and Neptune because of the rare alignment of the planets which made the "Grant Tour" possible. No mission that could visit both ice giants is currently possible.

Posted by: Gladstoner Jan 19 2008, 11:00 AM

.

Posted by: Jyril Jan 19 2008, 02:22 PM

One thing should be remembered when discussing about Uranus and Neptune systems: all the moons, including Triton have their axes almost coplanar to ecliptic meaning that parts of the moons are hidden from view for decades or more. The southern polar regions of Uranian satellites are now disappearing from view. If we sent a probe to Uranus today, it wouldn't see the same regions that Voyager 2 saw. On the other hand, having a probe there right now would have been perfect: currently the surfaces of the moons are fully visible because of the equinox. It'll take 40 years until the next time this is possible.

Posted by: mps Jan 19 2008, 02:50 PM

QUOTE (Gladstoner @ Jan 19 2008, 01:00 PM) *
Instead, we currently have inferior vidicom images to play with, and probably will for the rest of our lives.

So, Gladstoner, would you cancel the next flagship mission, so that our grandchildren could see a little bit better quality images of Galilean moons or Titan? tongue.gif

Posted by: centsworth_II Jan 19 2008, 03:46 PM

QUOTE (Gladstoner @ Jan 19 2008, 04:34 AM) *
Considering that New Horizons is on its way to Pluto, I would surely think that recon
missions to Uranus and Neptune would have at least as high a priority.

New Horizons just barely made it as a priority:

"The Bush Administration canceled it twice, NASA claimed its budget couldn't cover it
and Congress earmarked funds to be cut in mid-development; yet the trail-blazing
New Horizons Pluto-Kuiper Belt mission has survived....

It is a successor to a long line of planned Pluto missions, none of which ever left the
drawing board. New Horizons' immediate predecessor, the Pluto Express, got farther
than most, but in the summer of 2000 NASA canceled mission."

http://www.planetary.org/programs/projects/pluto/

Not exactly an example of the easy time a Uranus or Neptune mission would
have getting approved and flown, even if those planets had not yet been visited.

Posted by: nprev Jan 19 2008, 04:18 PM

Come to that, Voyager itself was a scoped-down version of the Grand Tour, which IIRC would have also included Pluto had it been launched earlier.

There are many variables in UMSF, but none are so capricious (or, arguably, as influential) as budget environments. Still think that we were EXTREMELY lucky that the Voyagers flew at all.

Posted by: dvandorn Jan 19 2008, 04:57 PM

You know, Nick, unlike a lot of the people here, you and I can recall when NASA and JPL were pushing hard to get the Grand Tour mission approved. I remember when it was first proposed in the late '60s, I remember when it was canceled, and I remember how elated I felt when its poor second cousin, a simple Jupiter/Saturn flyby, was "tweaked" into something approximating the original GT mission.

Also, IIRC, Voyager 2 could have been targeted for a Pluto flyby, thus completing the original GT mission plan -- but it would have lost its close flyby of Triton. The Pluto option was still possible after the Uranus encounter (though close to the limits of the remaining delta-V in the vehicle), but the craft was deteriorating (scan platform issues, among other things) to the extent that the decision -- and I think the right one -- was made to maximize science during the Neptune encounter.

When it came to deciding between doing as complete a recon of the Neptune system as possible with the healthiest spacecraft you could manage, or giving up Triton on the hope you'd still be operating well (or at all) when you got to Pluto, I think they did make the right decision.

-the other Doug

Posted by: nprev Jan 19 2008, 05:41 PM

QUOTE (dvandorn @ Jan 19 2008, 08:57 AM) *
When it came to deciding between doing as complete a recon of the Neptune system as possible with the healthiest spacecraft you could manage, or giving up Triton on the hope you'd still be operating well (or at all) when you got to Pluto, I think they did make the right decision.

-the other Doug


smile.gif ...approaching geezerhood does have its advantages! I agree, oDoug, but IIRC (fading memory, not sure it's accurate), a Pluto flyby was off the table for both Voyagers after Saturn. V1 would have had to give up its close Titan encounter, and V2 would have had to have made some kind of ungodly close approach to Neptune, perhaps even within its atmosphere...in any case, not feasible.

Must confess that in my heart of hearts I'll always think of them as Mariners 11 and 12...the proud cumulation of an historic series of spacecraft that gave us the initial recon of the Solar System. (When you get to be a geezer, you get sentimental easily.. rolleyes.gif )

Posted by: Greg Hullender Jan 19 2008, 06:54 PM

Nice account of the history of the Grand Tour project here:

http://history.nasa.gov/SP-4219/Chapter11.html

"Who killed Grand Tour? The demise of Grand Tour was less a simple case of its expensive price tag than its competition with other high-cost new starts (the shuttle and the space telescope) and Viking in a shrinking Federal and NASA budget. The smaller the budget became, and the more that costly programs competed for those shrinking funds, the more expensive each program appeared."

--Greg

Posted by: Gladstoner Jan 19 2008, 08:30 PM

.

Posted by: nprev Jan 19 2008, 09:54 PM

Well, don't we all, though? smile.gif Sad fact of the matter is that planetary exploration budgets are very limited, launch opportunities to the outer Solar System are severely constrained, and harmonizing these two major domains of influence is anything but easy. We live in the real world, not the ideal one.

(Dammit; I am a geezer; now I'm lecturing!!! Gonna go drink beer till I reboot....)

Posted by: JRehling Jan 20 2008, 07:15 AM

[...]

Posted by: Gladstoner Jan 20 2008, 07:38 AM

.

Posted by: edstrick Jan 21 2008, 10:19 AM

"...I'll always think of them as Mariners 11 and 12......"
My briefcase carries a VERY battered decal of "Mariner Jupiter Saturn". I'll have to take a photo of it and post it.

Posted by: nprev Jan 21 2008, 06:22 PM

Dou you think that Alan will hate me if I privately refer to NH as "Mariner 13"...? tongue.gif

Posted by: tedstryk Jan 21 2008, 07:06 PM

While imaging systems have certainly improved, Voyager's vidicon imaging was quite good. Much of the "inferior" quality comes from the use of old 1970s and 80s style processing and copying of the images. Also, many of the images are blown up to rather insane levels. The problem for Voyager with the Uranian moons was that when the planet is near solstice, approaching it from a flyby trajectory is like hitting a dartboard - you pass through the plane in which the moons orbit all at once, so you can only have one close encounter (and one more semi-decent one, such as Voyager-2 at Ariel), and all the encounters happen at about the same time. Since Voyager could only hold ~30 frames on its tape recorder and was limited by distance in what it could send in real time, the number of images that could be taken of the Urianian moons was limited. It was correct to say that Miranda would not have been picked for a dedicated Uranus mission - the Voyager team was quite frustrated by this, but it was the only moon that could receive a close flyby and still allow a trajectory that would send the spacecraft on to Neptune. Due to its small size, they were expecting it to be another Mimas, but by luck it turned out to be one of the most interesting worlds Voyager encountered. In fact, during the approach phase, when Voyager was bearing down on the Uranian system but not yet at closest approach, the lions share of the images were spent on Titania, which would likely have received the close encounter had they had the choice.

Voyager-2 at Triton was another spectacular encounter. It seem to me that the coverage seems in many classes cleaner than the coverage of the Galileans. While the increased speed, lower data rate, and lower light levels were an issue, when one looks at Voyager's early encounters, there is a lot of over and under exposure, partial (and total) misses of the target (a lot of close images of the Galileans were off the limb or on the dark side of the terminator), as well as smear from moving the spacecraft in the middle of exposures. While conditions at Neptune were more severe, by this time the Voyager controllers were veteran experts at operating the spacecraft and knew all its idiosyncrasies, rendering it almost like a new mission.

Posted by: JRehling Jan 21 2008, 07:56 PM

[...]

Posted by: dvandorn Jan 22 2008, 06:11 AM

QUOTE (nprev @ Jan 21 2008, 12:22 PM) *
Dou you think that Alan will hate me if I privately refer to NH as "Mariner 13"...? tongue.gif

I'd argue that Galileo was Mariner 13 and Cassini is Mariner 14.

And here they thought they'd get around any possible numerological issues by renaming these programs before they got to a Mariner 13...!

rolleyes.gif

-the other Doug

Posted by: edstrick Jan 22 2008, 10:19 AM

"I'd argue that Galileo was Mariner 13 and Cassini is Mariner 14."

You left two out: Magellan was Mariner 14 and Galileo was Mariner 15.
There are also two "Honerable Mention Mariners": the two Viking Orbiters.

I have a rather technical but straightforward technical point that this is based on.

ALL, repeat, ALL, the Mariner and Mariner like spacecraft up to Galileo used a polygonal ring shaped set of electronics and equipment bays as the "core" of the spacecraft. EVERYTHING else, damn near, was attached to the ring. On Mariner 4 (as the classiest example of the layout) solar panels were mounted on 4 of the 8 sides of the octagon (number of bays varied from design to design), antenna and magnetometer boom on the sunside, scan platform on the anti-solar-side. Mariner 9 mounted a bit set of fuel tanks and a rocket engine on the sunside, scan platform on the cold side, solar panels as usual. Viking orbiters added the attached bioshield and lander on the cold side, scan platform on the side of the enlarged polygon. Voyagers had no solar panels, RTG booms and scan platform on the sides instead, mounted the big antenna on the solar side. Magellan stuck a monstrously large radar electronics box between the (Voyager derived) antenna and the (I think Voyager derived) electronics bay ring. Galileo was the last to carry the electronics bay ring, despun scan platform on the cold side, the @#$#@ antenna on the sun side. It's spinning attitude control didn't change the fact that it was essentially a Mariner.

Cassini is the first "Mariner" that uses the modern "brick" shaped rectangular box for the main spacecraft body.

Posted by: MarcF Feb 6 2008, 09:37 PM

After the proposal of a New Horizons-like mission to Uranus and KBOs (NH 2), a new mission to Neptune is now proposed (NH 3 ?) :

http://www.lpi.usra.edu/meetings/lpsc2008/pdf/1117.pdf

Will surely have the same fate as NH 2, even if the mission is interesting.
Marc.

Posted by: Big_Gazza Feb 7 2008, 10:33 AM

Oh Great Maker, let it be so.... biggrin.gif

(for the record, I'm a staunch atheist, but if prayer has one part in a trillion chance of success... laugh.gif
)

Posted by: ugordan Feb 7 2008, 11:00 AM

To me, any new mission to Neptune that isn't an orbiter will be a tough concept to sell. Spending considerable time and money on an essentially Yet Another Flyby mission. An orbital mission would be significantly costlier, but the increased science return would most likely far outweigh the cost increase.

Posted by: Doc Feb 7 2008, 11:24 AM

QUOTE (ugordan @ Feb 7 2008, 02:00 PM) *
To me, any new mission to Neptune that isn't an orbiter will be a tough concept to sell. Spending considerable time and money on an essentially Yet Another Flyby mission. An orbital mission would be significantly costlier, but the increased science return would most likely far outweigh the cost increase.


I totally agree. But try and tell that to the bean counters. They'll never take their eyes off the $numbers.

Posted by: vjkane Feb 7 2008, 03:45 PM

QUOTE (ugordan @ Feb 7 2008, 12:00 PM) *
An orbital mission would be significantly costlier, but the increased science return would most likely far outweigh the cost increase.

From various outer planet mission studies, we can safely say that a Neptune or Uranus orbiter will likely cost in the $2-3B range (one Flagship mission to outer planets every 10-20 years). (The last outer planets new start was Cassini in 1990.) This proposed flyby is in the ~$850M range (one New Frontiers mission every 3-5 years). We'll pick either Jupiter or Titan for the next Flagship mission, and then presumably will pick the other one 10-20 years later. That pushes an ice giant mission out to the 2040-2050s or so by the time it arrives. So if we want to learn anything about ice giants from a spacecraft mission in the working lifetime of the present cadre of scientists (and for many of us, in our lifetime at all), it will have to be a mission like this. My only complaint about the proposal is that it doesn't have an atmospheric probe, which could be very minimal and provided by an international partner. Understanding the elemental composition of ice giants is key to understanding the formation of the solar system.

Posted by: nprev Feb 7 2008, 04:18 PM

QUOTE (JRehling @ Jan 21 2008, 11:56 AM) *
I have a sort of Moore's Law optimism for far-future missions that the ability to perform operations rapidly and store everything will increase so that the very crowded encounter sequence can be managed. It would definitely be a challenge with a slower spacecraft.


I do too, but am convinced that it will have to come in the form of both increased data-handling capability and major advances in propulsion technology. The whole IT revolution experience makes the idea of sustaining (or re-developing & procuring) the necessary systems to interpret data received decades after launch seems like a significant added consideration.

Posted by: JRehling Feb 8 2008, 07:55 PM

[...]

Posted by: vjkane Feb 8 2008, 08:37 PM

QUOTE (JRehling @ Feb 8 2008, 08:55 PM) *
It's unsatisfactory to have a small set of programs for mission selection, and to thereby allow targets of moderate interest to attract zero attention for decades on end. Much better if a broad long-term plan included contingencies for Uranus/Neptune (including, if the priorities weight out that way, to ignore them) than to see them perpetually bridesmaids because of the dynamics of one-upping.

Extremely well stated, John. For the foreseeable future, Mars (e.g., MSL, sample return), Jupiter, and Titan are going to take all the flagship spots. Discovery missions are severely limited in their scope and range, especially with the new rules to constrain develop cost risks. That leaves New Frontiers as the only mechanism to explore the solar system from the surface of Venus, Mercury (can't top MESSENGER and Bepi-Colombo on a Discovery budget), to the solar system beyond Jupiter. (You can throw the surface of Mars in this list, too. A Mars network mission has been recommended for New Frontiers). If our knowledge of these places is going to increase in any systematic way, then we need a list of prioritized missions. Otherwise, it's a crap shoot of which proposal looks best each time.

Right now, the New Frontiers queue includes (this is from memory, so I may miss something):

Lunar sample return
Venus lander and/or balloon
Comet sample return

A Saturn dual-probe mission has been strongly recommended (and if it launches ~2016-2018, it can also fly by Neptune; perhaps it could even carry a third probe for Neptune)

At 2-3 New Frontiers missions a decade, this list of (in my opinion) superb missions will take 1-2 decades to complete.

A number of missions have been suggested to augment this list or even to throw each announcement of opportunity wide open.

I don't favor the latter approach. I think the science community needs to set priorities so that this funding mechanism can ensure a systematic approach to studying all the places that Discovery can't reach and Flagship missions won't reach. This also allows the engineering community to focus on finding solutions for a constrained set of options. I do favor reviewing the list every time a mission is selected from it. For example, the discovery by Stardust that at least one comet's dust is composed of highly reworked, solar origin material may greatly lower the attractiveness of a comet sample return. Similarly, another nation may decide to fly a mission equivalent to one of the candidates.

By the way, I've heard that the next New Frontiers mission will not be allowed to use nuclear power (to save costs or a dwindling supply of nuclear material or both?). All the missions on the current list can be flown with solar power, although that would constrain any Saturn mission to just Saturn.

By the way, my favorite sequence of the next selections would be the Venus lander (which also likely would include atmospheric composition) followed by a combo Saturn-Neptune mission. But like I said, there's not a dud in the bunch.

Posted by: tedstryk Feb 8 2008, 10:10 PM

I think that Uranus has a bigger problem. The bland appearance of Voyager photos doesn't help. Also, it lacks a big moon, like Triton. Both planets could be combined with Kuiper Belt flybys, but with Neptune, you get a large (if melted down) KBO right off the bat. Plus, Triton is active, meaning that looking for changes since Voyager is a selling point for a flyby sooner rather than an orbiter later. I am not saying that Neptune out-merits Uranus, I am saying that I think a Neptune flyby mission has more of a chance of happening, perhaps tied to a New Horizons followup.

Posted by: mchan Feb 9 2008, 06:36 AM

Unfortunately, any mission with Uranus as primary objective will be cheap joke fodder on the late night TV shows and elsewhere in the US. It would be difficult to garner support for such a mission if it is being so ridiculed.

Posted by: tedstryk Feb 9 2008, 06:20 PM

Neptune also has the advantage of being the most distant official major planet (This was also true in the Voyager days, since Pluto was inside Neptune's orbit at the time). To the bean counters and to the novice "only the second visit to the most distant planet" has a ring to it that Uranus would have difficulty competing with.

Posted by: JRehling Feb 11 2008, 06:40 PM

[...]

Posted by: nprev Feb 11 2008, 09:21 PM

Heh, heh...I see that some of our more distinguished members are tuning into marketing, however reluctantly and/or facetiously... cool.gif

I see it as another 'gapfiller' initiative, much like Messenger. Uranus & Neptune are midway between the terrestrial planets and Jupiter/Saturn in terms of mass. Oddly enough, they have surface gravities not much greater then that of Earth, making surface exploration (if there is one on either of them) a tantalizing far-future possibility...we need to learn more, to say nothing of the satellites of each, Triton being one of only 5 known volcanically active bodies in the Solar System.

(It's all about framing the issue, guys.)

Posted by: kwp Feb 11 2008, 11:08 PM

QUOTE (nprev @ Feb 11 2008, 02:21 PM) *
Triton being one of only 5 known volcanically active bodies in the Solar System.


Five?

-Kevin

Posted by: tedstryk Feb 11 2008, 11:13 PM

QUOTE (kwp @ Feb 11 2008, 11:08 PM) *
Five?

-Kevin


Earth, Io, Enceladus, and Triton. Titan and Venus likely fit in that group, and some data suggests the same is true for Dione and even Mars.

Posted by: nprev Feb 12 2008, 04:32 AM

I was counting Titan; the atmosphere is extremely powerful circumstancial evidence.

Posted by: Greg Hullender Feb 12 2008, 04:47 AM

I still wish I could see a breakdown of costs. I keep wanting to believe that two identical orbiters (one for Uranus and one for Neptune) wouldn't cost twice as much as a single one, and that if one could time them right, the Neptune one would arrive just as the Uranus one reached the end of its life, so you could just keep more or less the same team. Even if the Neptune probe took 20 years to get there, it would just be the second act.

--Greg

Posted by: nprev Feb 14 2008, 04:20 AM

Again, this is why I wish that there was a 'library' of outer-planet launch opportunities. Seems like trajectory calcs only happen when there is a viable mission proposal like NH in the pipeline; might have the cause & effect relationship backwards here.

If we knew that there were favorable launch opportunities for Uranus & Neptune (even with inner-system gravitational assists) in, say, the late 2020s, then draft mission proposals could start development now. With that much lead time, it's even conceivable that Frontier-class missions would be feasible given assumed technology advances.

Posted by: mchan Feb 14 2008, 05:27 AM

[removed in-line quote]

There may or may not be such a library, but there are usually a couple or more papers each year at the AIAA/AAS Astrodynamics conference that discuss trajectories for future missions to places all over the solar system. Probably >95% of these come to naught but some folks are having fun cranking out the plots.

Not sure what is gained by a stretched development cycle. There is the risk that product of earlier development efforts be obsolete or difficult to support when launch date comes around.

Posted by: ugordan Feb 14 2008, 09:28 AM

There really is no need for a launch opportunity library for the outer solar system if you want to go from A to C via B. As long as B and C are on the "same side" of the solar system there'll probably be an extended gravity assist trajectory with a varying efficiency over a couple of years. Jupiter would typically be your B body and from then on tweaking the launch date is a piece of cake if you have constraints on launch energy, launch date and/or arrival velocity. These sorts of calculations can be done on demand in a matter of minutes I figure.

More complex slingshot trajectories (involving say Jupiter AND Saturn) to get to Uranus or Neptune will occur rare enough that it's probably no use predicting them that far into the future. Furthermore, they usually impose bigger trajectory constraints which then constrain the slingshot gains. It might prove more efficient to use just an aggressive Jupiter flyby to catapult yourself outward than trying to fly by both J and S for what can turn out to be a weaker boost in the end.

Posted by: kwp Feb 14 2008, 05:02 PM

QUOTE (ugordan @ Feb 14 2008, 01:28 AM) *
As long as B and C are on the "same side" of the solar system there'll probably be an extended gravity assist trajectory with a varying efficiency over a couple of years. Jupiter would typically be your B body and from then on tweaking the launch date is a piece of cake if you have constraints on launch energy, launch date and/or arrival velocity. These sorts of calculations can be done on demand in a matter of minutes I figure.


Since this is a three body problem (spacecraft, Jupiter, Sun), I believe there is no closed, analytical solution to the problem of finding the best trajectory. I have thus assumed that it is done via Monte Carlo simulations. Alternatively, while there is no analytical solution, there might be good approximations. I'm hoping one of our resident experts will weight in and tell me how slingshot trajectories are calculated, and how computationally intensive the process is.

-Kevin

Posted by: ugordan Feb 14 2008, 05:25 PM

I believe trajectory search and optimization software nowadays uses Keplerian orbits and http://en.wikipedia.org/wiki/Patched_Conics to find plausible/optimum trajectories (and things like impact parameter or miss distance during flybys) and then when a "conceptual" trajectory is selected, it's precisely worked out by numerical integration and taking into accounts other factors such as solar light pressure, etc. That last part might be iterative and computationally more expensive, but it's all within reach of modern computers.

Posted by: JRehling Feb 14 2008, 08:17 PM

[...]

Posted by: simonbp Feb 17 2008, 08:17 PM

This has got me thinking about if you could pull off a Uranus/Neptune Orbiter for less than $850 million...

Aerocapture is obviously the way to go, and the Titan Explorer orbiter seems a good place to start. It masses ~1800 kg wet, while the cruise stage ~1500 kg, mainly fuel. If we drop the balloon and lander, we cut out roughly 2/3 the mass of the cruise stage, giving a payload mass of ~2300 kg. That's about half the mass of TE. The option then is either to use a low-end EELV (Atlas 401, Delta IV sans SRBs, or Falcon 9) for a single launch (more likely), or launch two spacecraft (one Neptune, one Uranus) on an Atlas 551 (much more cost effective, but less likely).

The point is, I don't think it's a given that a ice giant orbiter has to a ridiculously expensive Battlestar Galactica style mission like Cassini. It's just like Mars Sample Return; if you're willing to use new technology (aerocapture and ASTG in this case) and make compromises, you can turn a perpetually paper mission into reality...

Simon wink.gif

Posted by: cawest Feb 18 2008, 04:35 AM

QUOTE (vjkane @ Jan 13 2008, 01:12 AM) *
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.


This had me thinking... why can we not have three droppers, one at each? This would make an orbit of Neptune cheaper. How do you ask.. if you drop of a probe into Jupiter, Saturn, and before you make Neptune orbit you have less mass to slow down. what do you all think?

Posted by: ugordan Feb 18 2008, 08:55 AM

QUOTE (cawest @ Feb 18 2008, 05:35 AM) *
you have less mass to slow down.

What about mass you actually need to launch? Does it go down as well?

Posted by: tasp Feb 18 2008, 02:55 PM

QUOTE (simonbp @ Feb 17 2008, 02:17 PM) *
This has got me thinking about if you could pull off a Uranus/Neptune Orbiter for less than $850 million...

Simon wink.gif



Not to put you off of working through cost savings for interesting mission concepts, but my ideas for a 'cheap' Neptune orbiter were pretty thoroughly discredited and chewed up here a while back . . .





Posted by: Greg Hullender Feb 18 2008, 05:08 PM

I think the problem with launching a Neptune and Uranus probe in the same rocket is that the next obvious launch window for that is about 80 years away.

Of course, gravitational assists are complicated beasts; there could well be some complicated sequence that managed to split them up at the right point and get them both to the right places, but it'd be a wonder to behold.

--Greg

Posted by: JRehling Feb 18 2008, 07:15 PM

[...]

Posted by: Greg Hullender Feb 19 2008, 03:03 AM

I thought about that, but I think the trouble is that one of the two is going to get a pretty lousy gravitational assist, and given the distances involved, that seemed like a loser -- and maybe not even enough delta-V to get both to their targets.

And, as you say, every year it gets worse.

--Greg

Posted by: cawest Feb 19 2008, 04:45 AM

QUOTE (ugordan @ Feb 18 2008, 09:55 AM) *
What about mass you actually need to launch? Does it go down as well?


it would be less fuel mass to launch than a reguler orbiter.

Posted by: Greg Hullender Feb 19 2008, 04:26 PM

How does that follow? You'd clearly have less mass to launch if you didn't drop anything at the earlier planets.

--Greg

Posted by: simonbp Feb 20 2008, 06:26 AM

Well then drop the second vehicle and fly the one with a faster trajectory. Point is, I still think it's possible to build a very capable New Frontiers-class Neptune Orbiter...

Simon wink.gif

Posted by: Greg Hullender Feb 21 2008, 12:42 AM

I hear you. I'd love to see a serious proposal. Say, starting with $90 M for a Falcon 9 Heavy to put 12 tons in GTO. What can you do with 12 tons in GTO with about $800M to spend on it? And, assuming no other never-before-flown technology.

--Greg

Posted by: Big_Gazza Feb 21 2008, 01:14 PM

QUOTE (Greg Hullender @ Feb 21 2008, 11:42 AM) *
$90 M for a Falcon 9 Heavy to put 12 tons in GTO.


Sorry, but i'll believe it only when I see it fly. And even if it ever does, it'll cost way more than 90M.

Posted by: Greg Hullender Feb 21 2008, 04:27 PM

QUOTE (Big_Gazza @ Feb 21 2008, 05:14 AM) *
Sorry, but i'll believe it only when I see it fly. And even if it ever does, it'll cost way more than 90M.

Good points, but my question is "taking Falcon 9 Heavy on faith -- but nothing else, does that change the picture? That is, is the launch vehicle cost the only thing that keeps us from having a New Horizons-class Uranus or Neptune orbiter?"

--Greg

Posted by: Mark6 Feb 25 2008, 02:00 AM

QUOTE (nprev @ Jan 19 2008, 11:18 AM) *
No argument there! laugh.gif Still, the fact of the matter is that Uranus & Neptune are really off the radar screen right now, and have been for a considerable period of time. I don't like it either, but it is what it is. NH took advantage of an excellent launch opportunity to get to Pluto within a reasonable time to complete the initial recon of the major objects in the Solar System (Note: NO planet/ain't a planet comments welcomed!!! mad.gif I'm serious! Uh, would be remiss without mentioning Dawn as part of this effort as well

By that logic a flyby of Eris & Dysnomia should take priority over Uranus or Neptune. After Dawn and New Horizon reach their targets, Eris is the only "major object" left unexamined.

Posted by: JRehling Feb 25 2008, 04:34 AM

[...]

Posted by: edstrick Feb 25 2008, 06:12 AM

"Sedna would be a somewhat more appealing target."

After the Synoptic Survey Telescope's nearly whole sky survey's been going for a year and they've had time to chew on data to spot slow moving 24'th magnitude objects over the whole sky. we're going to have a LOT more Sedna's and other very interesting objects, including some that will blow our mind. There remains the possibility of a considerably larger object way-the-<bleep>-out-there that's one of the possibilities being invoked for explaining the dynamic structure of the KB.

We can keep updating our personal lists of our "KB and Beyond objects we'd like to explore", but till around 2015, when results will be coming in from the SST, etc., all these discussions will be based on a tiny sample of what's in the KB

Posted by: Mark6 Feb 25 2008, 01:25 PM

QUOTE (JRehling @ Feb 25 2008, 05:34 AM) *
Eris would be a good target, but loses out big-time in terms of the cruise time needed to get there. What's more, I bet you a soda-pop that before the craft got there, Eris will be down the list of largest remaining unexplored objects.

I would not take this bet. My previous post was only semi-serious.

Posted by: JRehling Feb 25 2008, 06:16 PM

[...]

Posted by: nprev Feb 25 2008, 06:57 PM

Yeah, the LSST will undoubtedly provide a LOT of surprises; gonna be interesting, to say nothing of paradigm-shifting (such investigations nearly always are, of course)... wink.gif

Getting back to Uranus & Neptune, I'm beginning to think that NH evolutes for flybys might be the way to go given the current state of the art for propulsion & on-board power. As has been pointed out on this thread, any given portion of any of the Uranian moons is illuminated for a few decades or so over an 84 year period, so a flyby really is as good as an orbiter there. Hopefully some innovative proposals might be forthcoming from the community...?

Posted by: laurele Feb 26 2008, 07:00 AM

"So we should find any Sednas (now the 5th largest KBO) out to about 200 AU."

I thought Sedna is in the Oort Cloud rather than the Kuiper Belt. Is that incorrect?

Posted by: edstrick Feb 26 2008, 08:37 AM

Sedna is between what were supposed to be KB orbits and Oort orbits.

That "supposed" theory has been rattled more than a bit by our expanding understanding of KB dynamics, but it's still got a perihelion way beyond the classical KB.

"You can't get there from here" ... "Tiz a Puzzlement".



Posted by: Greg Hullender Feb 26 2008, 06:44 PM

Mike Brown has sometimes called Sedna an "Inner Oort Cloud object," speculating that it's one of a number of bodies between the Kuiper Belt and the Oort Cloud. I just can't WAIT for the LSST to show us what's really out there!

--Greg


Posted by: nprev Feb 26 2008, 07:57 PM

I just had a probably very silly idea, and would like to bounce it off of our orbital dynamicists: What about using a cometary heliocentric orbit to reach Uranus or Neptune?

Suspect that the required delta-V might be prohibitively large, but here goes anyhow. What I have in mind is basically using the Sun for a gravity assist by doing a close flyby & throwing an orbiter into a cometary trajectory with its apogee tangental to the orbit of either planet; if the planet just happens to be there at the time, then presumably minimal deceleration would be required to enter orbit.

Very simplistic, and probably not practical (thinking you might need as much as a 50 km/sec maneuver to swing by the Sun close enough)..but thought I'd throw it out there anyhow.


Posted by: ngunn Feb 26 2008, 08:04 PM

You could try it this way:
http://www.physics.uci.edu/faculty/STAEF2002Desorp.html

Posted by: JRehling Feb 26 2008, 09:36 PM

"Gravity assist" by definition involves a second large body in addition to the Sun. You don't get anything by flying by the Sun in terms of digging out of the Sun's gravity well. In fact, you suffer a net loss. Basically, if the Sun is the only body whose pull is significant (until the craft gets to Uranus/Neptune), then the orbit is going to be a conic section. And the minimum energy involves never being closer to the Sun than necessary (ie, Earth, for launch).

The down side of a minimum-energy orbit is that it will take a long time to get there. But it would only be worse if you tried dipping inside the Earth's orbit. Anything you gained by falling sunwards you'll lose, exactly, on the way out.

Posted by: Mark6 Feb 26 2008, 09:57 PM

QUOTE (JRehling @ Feb 26 2008, 09:36 PM) *
"Gravity assist" by definition involves a second large body in addition to the Sun. You don't get anything by flying by the Sun in terms of digging out of the Sun's gravity well. In fact, you suffer a net loss.


Actually, there is a way to do it: http://books.google.com/books?id=tIfJM8Nu8iYC&pg=PA48&lpg=PA48&dq=sun+%22gravity+assist%22+perihelion&source=web&ots=_OrS-d0UUG&sig=pEb8akM4W92P3wK_tIP1i_7Jq4c#PPA47,M1

Posted by: ilbasso Feb 26 2008, 10:13 PM

Also, as Star Trek IV showed us, is that by going close to the Sun for a gravity assist, you will go forward several hundred years in time. We could load the craft with nearly extinct animals so that it could repopulate the Earth on the way back out to a KBO. Oh, but then the craft will be several hundred years behind us and we won't get the benefit of its data. Hmm, back to the drawing board...

Posted by: ngunn Feb 26 2008, 11:03 PM

The Sun Diver idea is not a 'gravity assist'. It is using solar power (heat) to change the trajectory at perihelion by shedding mass with the right direction and speed. Have another look. It works. So does the idea of a solar sail edge on to the sun on approach and fully presented for illumination after perihelion. Going close to the sun pays off both ways.

Posted by: dvandorn Feb 27 2008, 04:05 AM

My understanding has always been that gravity assists work by robbing a body of a bit of its rotational velocity by flying along with its rotating gravity field. The Sun rotates -- why ought this process not work with the Sun?

-the other Doug

Posted by: ermar Feb 27 2008, 05:18 AM

Actually, this is not how gravity assists work - rather, they take advantage of an orbiting body's orbital motion relative to background space. Say a planet is orbiting with a speed V relative to the sun and a spacecraft approaches it (from the planet's point of view) from one side with a speed v. From the planet's perspective, the spacecraft ought to have the same relative magnitude of speed leaving it as approaching it, so the spacecraft leaves with speed v too. From, say, the Sun's point of view, though, the spacecraft approached the planet (which was moving at speed V) with some other speed z; by the time the spacecraft has left the vicinity of the planet, the planet has "dragged it along," and some significant fraction of the planet's orbital speed V is added to the original spacecraft velocity. (This can also be used to decelerate the spacecraft, too, by setting up the initial encounter differently.) The bottom line is that gravity assists depend on the mass and orbital velocity of the "assisting" body alone (robbing it of orbital, not rotational momentum), and have nothing to do with its rotation rate.

Posted by: JRehling Feb 27 2008, 06:57 AM

Little physics tidbit: Imagine a spacecraft orbiting the Sun in an elliptical orbit, and imagine that it (for the time being) will not pass closely enough to any planet for them to have a significant pull on it.

The sum of the gravitational potential energy of the craft and its kinetic energy is utterly constant. (This is true of circular, parabolic, and hyperbolic trajectories as well.) What it loses in kinetic energy from perihelion to aphelion (or at any other time) is exactly equal to what it gains in gravitational potential energy. And this will be true forever.

So imagine a spacecraft that has left Earth, and that proceeds in to some closer distance to the Sun, then passes on the other side back to (and then past) the orbit of the Earth. (Again, assume that Venus and Mercury don't get in the way.) Between launch (once it gets sufficiently outside the Earth's sphere of influence) and perihelion, what it gains in kinetic energy will be lost, exactly, in gravitational potential energy. Between perihelion and crossing, again, the Earth's orbit, what it lost in kinetic energy will be gained, exactly, in gravitational potential energy. And moreover, because gravitational potential energy is determined by the distance from the Sun, the kinetic energy of the craft when it crosses the Earth's orbit on the way out will be EXACTLY what it was when it left the Earth in the first place. You gain a net sum of nothing. You may as well have just launched in the outward direction in the first place (at some different launch window).

Posted by: Juramike Feb 27 2008, 07:18 AM

OK.

Just to be nitpicky, wouldn't some miniscule amount of energy be imparted on the spacecraft due to the sun's rotation during a "solar dive"?

I would assume this would be similar to tidal effect. In theory, there should be a (teensy) tidal bulge raised on the Sun due to the spacecraft's gravity, and the friction of this bulge on the Sun's surface relative to the rotating surface material should fling the spacecraft forward a teensy bit. [Assuming the spacecraft's approach velocity is smaller than the rotational velocity].
This is similar to the process that is making the Earth slowly fling the Moon to a higher orbit, while the Moon is slowing down Earth's rotation.

(Any math whizzes out there able to calculate the amount of (de/ac)celeration of a typical sized spacecraft from the Sun's rotation field due to tidal effects?)

-Mike

Posted by: JRehling Feb 27 2008, 09:35 PM

Tidal effects are harder to model than your typical sophomore calculus class lets you do. I know that in some instances, natural satellites spiral in due to tidal effects and in other cases they spiral out. I guess it's a question of whether the sub-satellite point is tracking on the surface faster or slower than the rotating surface or the speed of a wave through the surface. Something passing at a few tenths of an AU from the Sun would be moving slower, so the tidal bulge could track it fairly well, whereas something speeding over Jupiter's cloudtops would outpace the bulge.

But as for integrating over the density of various layers through the depth of the Sun... sounds like a major research problem.

Posted by: Greg Hullender Feb 28 2008, 03:22 AM

Or are you expecting to get a boost from the relativistic frame-dragging effect? That'd be tiny, but compared to the tidal effect caused by the spacecraft on the Sun, . . .

--Greg

Posted by: nprev Feb 28 2008, 03:34 AM

Well, clearly, JR answered the question in its fundamental form: there ain't no such thing as a free lunch. We can game planetary orbital motion & rotation only so far; sure looks like genuinely revolutionary propulsion systems are needed (very badly) for outer-system exploration.

Posted by: rlorenz Feb 29 2008, 02:59 PM

QUOTE (nprev @ Feb 27 2008, 10:34 PM) *
Well, clearly, JR answered the question in its fundamental form: there ain't no such thing as a free lunch.


I think there has been some confusion here. 2 very different things

1. gravity assist, as people have mentioned, relates to robbing the planets of their angular
momentum (=orbital velocity, since tides are small and the rotational angular momentum of the
planets is tiny anyway)

The way to visualize this is that the planets are big billiard balls, and you can bounce off them (their
gravity fields can be considered the same as an elastic collision). If you bounce off them the right
way, you can get a speed boost at their expense, but it relies on them moving fast.

2. more efficient propulsive manoeuvres deep in the gravity well. If your speed relative to the sun
is A, and your engine gives you a velocity increment B, the energy increment is (ignoring factors
of 2 etc( (A+cool.gif^2 - A^2, or roughly 2AB. So the bigger A is (i.e. the faster you are going
relative to the sun, which is to say, the closer you are to the sun when you make the burn)
the more energy increment your fixed B gives you.

Not a free lunch, but a way of making your lunch more satisfying.

Posted by: nprev Feb 29 2008, 04:28 PM

I get it now; thanks very much for that clarification, Ralph! smile.gif

Still sounds like Sun-diving with conventional propulsion systems isn't quite worth it. You'd have to expend a massive amount of fuel just to get into a close solar approach trajectory anyhow, then execute another major maneuver to take advantage of the C/A dynamic.

I don't know; could doing a few pump-down gravity assists with the inner planets make this more feasible? Seems to me that if you can save the maximum amount of thrust for solar C/A you still might be able to make some money here. Not sure if conservation of angular momentum for the entire Solar System wouldn't turn around & bite you in the butt, though.

Posted by: punkboi Nov 8 2008, 02:56 AM

Emily posted an interesting blog on Planetary.org regarding a proposed flyby of Neptune that could be done by 2027 if it launched by 2020. Called Argo, it would be the fourth New Frontiers mission if approved it in the next selection process, which is to take place in 2013.

http://www.planetary.org/blog/article/00001729/


The original proposal page:

http://www.lpi.usra.edu/opag/march_08_meeting/presentations/hammel.pdf

Posted by: elakdawalla Nov 8 2008, 03:56 AM

Thanks for pointing to that entry -- but Argo's being discussed actively in http://www.unmannedspaceflight.com/index.php?showtopic=5413.

--Emily

Posted by: Zvezdichko Jan 7 2009, 10:45 AM

Emily,

You have mentioned that New Horizons may try to photograph Uranus and Neptune. Do you have any information about whether pictures have been taken?

Posted by: tedstryk Jan 7 2009, 10:52 AM

http://www.unmannedspaceflight.com/index.php?showtopic=675&pid=133721&st=1185&#entry133721

Alan Stern has stated that they have indeed been taken.

Posted by: Zvezdichko Jan 7 2009, 11:25 AM

Thanks, Ted.

Posted by: briv1016 Aug 14 2009, 10:21 PM

I've been following the Review of U.S. Human Space Flight Plans Committee meetings the past few weeks and one of the presentations had a relevant chart regarding the lift capability of the Ares V in regards to unmanned planetary missions. Without going into the taboo discussion of human spaceflight or the likelihood of the Ares V being built in this configuration [or at all], I thought that it would be interesting to include the chart.


 

Posted by: briv1016 Aug 15 2009, 12:20 AM

Here's the entire slide for context and volume considerations.

 

Posted by: imipak Aug 15 2009, 04:36 PM

50 mT to Mars! _wow_. That would open up a whole new vista for the fun game of Fantasy UMSF.

Posted by: ugordan Aug 15 2009, 06:16 PM

Yes, except for two inconvenient facts:

1) should the "classic" Ares V ever materialize, it will be expensive as hell
2) Spacecraft are usually many times more expensive than the launch vehicle. It's not a problem of launching a largish spacecraft into space, it's a problem of funding it in the first place. See JWST.

I would put my hand in the fire that no unmanned spacecraft would ever be launched on a dedicated Ares V launch.

Posted by: nprev Aug 15 2009, 10:19 PM

Sad but true. The Saturn V was never used for UMSF for the same reason, even though the original Voyager Mars concept (which evolved into Viking) did envision two Saturn launches.

Posted by: Greg Hullender Aug 16 2009, 12:12 AM

QUOTE (ugordan @ Aug 15 2009, 11:16 AM) *
Spacecraft are usually many times more expensive than the launch vehicle.

Then why is it so much more expensive to have a Neptune orbiter than a Jupiter orbiter? This is a poinit that puzzles me a lot. If SpaceX really succeeds in reducing launch costs by a factor of 10, does that suddenly enable lots of interesting outer planet missions or not?

--Greg

Posted by: dvandorn Aug 16 2009, 02:13 AM

I think a 5-fold to 10-fold reduction in launch costs would result in more twin-probe or multi-probe missions. It costs maybe half-again more to produce two new probes than a single probe (if you take the MER project as an example). A third probe adds quite a bit less to your costs, as does a fourth, etc.

So -- if you can design four probes that are nearly identical (with perhaps some variation in their scientific payloads) and launch them to the same destination for the same cost as what you'd pay today for a single flagship mission, you can get a potential for a lot more bang for your buck. I can envision flying a really solid NetLander mission to Mars this way, or sending a flotilla of four to six Jupiter-system probes, each with its own unique program to execute, and each perhaps half as capable as a flagship probe.

You're still talking flagship mission funding, of course, and so only looking at seeing such multi-probe missions once a decade or so. Even so, in the meantime, you'd at least be able to spend a little more on Discovery-class mission spacecraft and a little less on their launch costs. In other words, reduction in launch costs is always a good thing, but I think it'll have more of an impact on flagship-class planning than on intermediate-class missions.

-the other Doug

Posted by: ugordan Aug 16 2009, 10:33 AM

QUOTE (Greg Hullender @ Aug 16 2009, 02:12 AM) *
If SpaceX really succeeds in reducing launch costs by a factor of 10, does that suddenly enable lots of interesting outer planet missions or not?

There are two schools of thought to this. One would be that scientists would still want to build expensive spacecraft, but launch them more cheaply, but it's not a really high net saving. Let's take Cassini: $3 billion + $400 million Titan IV launcher. If the launcher was switched to a 2 or 3 times cheaper one, you see that's still very expensive in total program cost.

Another school of thought says that if you suddenly have cheap launchers that can launch a lot of mass to space, you can build spacecraft that are more massive and rugged, while maintaining the same science capability as before. Essentially less science per kg, but you can ease up on expensive structural and environment testing and just beef up systems to make them more rugged. This would be an enabler for cheaper missions, but there is always the siren call of putting as much as we can on it and it ends up expensive again.

Posted by: imipak Aug 16 2009, 10:33 AM

QUOTE (ugordan @ Aug 15 2009, 07:16 PM) *
Yes, except for two inconvenient facts:
[...]
I would put my hand in the fire that no unmanned spacecraft would ever be launched on a dedicated Ares V launch.


I'm sure you're right, but that's why it's _fantasy_ UMSF! smile.gif My daydreams were of a multi-vehicle MSR project, for instance. An MSL-scale sample-collection rover, with a separate lander carrying nothing but an ascent stage to receive the samples, with sufficient mass still in orbit for the return leg to earth, with the remaining orbiting infrastructure left in place for communications and data relay. Using a hand-waving assumption that cost scales with mass, roughly ten times the mass of Cassini-Huygens would cost well over $30B, so I shan't be holding my breath for an announcement any time soon, though.

Posted by: tasp Aug 16 2009, 02:39 PM

A little levity this Sunday morning as we enjoy our coffee and doughnuts:


the mighty Saturn V did manage on 2 occasions to loft craft appropriate for discussion here. PFS-1 and PFS-2 were used to study fields and particles from lunar orbit back in the seventies. Each were under 40 kilograms and probably set the record for the largest launcher used on the smallest spacecraft.



laugh.gif








Posted by: Enceladus75 Aug 16 2009, 07:55 PM

QUOTE (Greg Hullender @ Aug 16 2009, 01:12 AM) *
Then why is it so much more expensive to have a Neptune orbiter than a Jupiter orbiter? This is a poinit that puzzles me a lot. If SpaceX really succeeds in reducing launch costs by a factor of 10, does that suddenly enable lots of interesting outer planet missions or not?

--Greg


I think part of the difficulty in a Uranus or Neptune orbiter is not the mass or the design of the spacecraft, but getting the spacecraft into orbit around these planets in the first place. With conventional rockets, the fuel tank required for the fuel to brake into orbit would be prohibitely expensive. I think some type of aerobraking/aerocapture would be required with all the related dangers that this approach would involve.

Posted by: Greg Hullender Aug 17 2009, 01:39 PM

QUOTE (Enceladus75 @ Aug 16 2009, 11:55 AM) *
With conventional rockets, the fuel tank required for the fuel to brake into orbit would be prohibitely expensive.

By that logic, both Gallileo and Cassini were impossible, so that can't be it. Although I'm a big fan of aerobraking, it's clearly not required. As far as I can tell, everything flows from the exponential in the rocket equation. For a given weight of payload, the fuel cost goes up exponentially with the delta-V divided by exhaust velocity. Since chemical rockets have exhaust velocity of about 3 kps, this means an extra factor of e (multiplied!) for every 3 kps of delta-V. Outer planet missions need more delta-V, so they have higher fuel costs.

I think a Neptune mission using a Jupiter gravity assist COULD be no more expensive than a regular Jupiter mission, since the chemical rocket only needs to get the probe as far as Jupiter, and it only has to slow it down for Neptune -- easier than slowing it down for Jupiter. I think the extra delta-V requirement comes from us wanting to get the probe there in a decade or so -- not wait 20 or 30 years. That makes sense to me, but (again) it suggests that the lion's share of the cost of a Neptune or Uranus probe should be fuel, and so a 10x reduction in cost-to-LEO should result in a 10x cost reduction (almost) of the Uranus/Neptune mission itself.

There's probably a hole in this logic somewhere, but I'm not seeing it -- I've even considered whether the main cost might be salaries (which would be more on a long mission) but based on how small the incremental costs of running the MERs has been, I find that hard to credit.

So I remain convinced that sharply lower launch costs should be a HUGE enabler for Uranus/Neptune missions, but I'd love it if one of the real rocket scientists could give me a clear answer; even if only to show me where I'm wrong. :-)

--Greg

Posted by: Holder of the Two Leashes Aug 17 2009, 02:47 PM

QUOTE (Greg Hullender @ Aug 17 2009, 07:39 AM) *
... it only has to slow it down for Neptune -- easier than slowing it down for Jupiter.


Not necessarily, depends on what you mean. The deeper the gravity well, the more effect you have firing off a rocket at the bottom of that well after falling into it. It can be a lot easier getting into orbit around Jupiter than an asteroid. The excess velocity the spacecraft carries with it on appoach, say a few miles a second, will end up being just a fraction of that speed above orbital velocity at close approach, making only a small burn necessary to achieve an elongated orbit. For an asteroid target at the same distance as Jupiter, and with an identical trajectory, you have to cancel out all of the relative speed. The asteroid's gravity doesn't offer much help.

But, if you're talking about rocketing directly into a close circular orbit around Neptune, as opposed to Jupiter, well then yeah, Neptune will be a lot easier. Except that with current technology both would be impossible.

Posted by: ugordan Aug 17 2009, 04:25 PM

QUOTE (Holder of the Two Leashes @ Aug 17 2009, 04:47 PM) *
The deeper the gravity well, the more effect you have firing off a rocket at the bottom of that well after falling into it.

Right, and this is also known as the http://en.wikipedia.org/wiki/Oberth_effect.

Posted by: nprev Aug 17 2009, 05:44 PM

The other thing to remember is that a putative Neptune orbiter would be approaching the planet with a great deal of excess velocity to shed (assuming that it's to make a reasonable transit time, say 15 years from launch to beginning of mission).

So, unless aerobraking or some other exotic deceleration method is used, you're looking at sending a good-sized engine + lots of fuel along in addition to the spacecraft, sort of like keeping the Apollo CSM + LM attached to the S-IVB all the way to lunar orbit (bad analogy, but you hopefully see what I mean.) Bottom line is that the total throw weight (and cost) would go way, way up, which would constrain the actual payload considerably.

Posted by: stevesliva Aug 17 2009, 05:50 PM

That is his point, though, is it not? If huge launchers get 10x cheaper, you design the Neptune Orbiter you want and can also afford the huge detachable propulsion module for NOI for the same launcher price... maybe. And you get there in 10 years rather than 30. Or whatever.

(Isn't aerobraking useless for orbital insertion, anyways? It's for circularization, right?)

Posted by: tedstryk Aug 17 2009, 06:05 PM

It is useful for both. The difficulty with aerocapture comes from the fact that, a) it will take a great heat shield to hit the atmosphere that fast and be slowed down enough to go into orbit, and b ) the parameters of the atmosphere of Neptune are poorly known. If it goes to a depth where the atmospheric thickness is too great, it could end up being an entry probe, might end up being permanently disabled/rendered inoperable, or might be put in such a short orbit that it decays before the periapsis can be raised to a safe distance. If it doesn't go far enough into the atmosphere, it could end up flying by the planet never to return or in some five year orbit that lasts longer than the probe's designed lifetime.

Posted by: stevesliva Aug 17 2009, 06:26 PM

QUOTE (nprev @ Aug 15 2009, 06:19 PM) *
Sad but true. The Saturn V was never used for UMSF for the same reason, even though the original Voyager Mars concept (which evolved into Viking) did envision two Saturn launches.


And was envisioned for some brutishly huge MSR missions. If you have two separate huge landers-- an MSL-class rover and a large direct-to-earth ascent module-- is there any benefit to one Ares V rather than two Titans? Or two Ariane Vs... or whatever. Is it more economical to launch two things going the same place in one big launcher?

Posted by: Juramike Aug 17 2009, 09:11 PM

Here's a timely little tidbit about an inflatable (=potentially cheaper) heat shield in this space.com http://www.space.com/missionlaunches/090817-inflatable-heat-shield.html.

But low cost still won't mitigate the risk of unknown atmospheric characteristics (like at Neptune or Uranus).

Posted by: nprev Aug 17 2009, 11:14 PM

QUOTE (stevesliva @ Aug 17 2009, 10:26 AM) *
Is it more economical to launch two things going the same place in one big launcher?


Yeah, generally, although there is a risk tradeoff to consider...'all the eggs in one basket'.

If you recall, most of the missions from Voyager on back were pairs but on independent boosters, and at least part of the rationale for that strategy was ensure that the whole project wouldn't be sunk by a booster failure. I'm sure that applied to the MERs as well. This was wise, considering that Mariners 1, 3, and 8 all splashed.

Posted by: dvandorn Aug 18 2009, 12:56 AM

Also, dual-probe missions have increased the science return from their given opportunities. Primarily, we've been able to target the two probes on dual-probe missions somewhat differently, using the same instrument suite to look at different locations. That was actually done on Mariners 6 and 7, Vikings 1 and 2, Pioneers 10 and 11, and Voyagers 1 and 2. There were also, of course, plans for the Mariner 3/4 and 8/9 missions to use the same instrument suites to look at different locations.

Dual- and multi-probe missions, though, also give you the opportunity to send probes with different instrument suites to the same location. I can imagine this kind of approach would work very, very well for outer planets missions, where your orbiters all have shots of their own at observing the primary planet and each of its moons. Once you finish your pre-planned primary mission, you use the results of one instrument suite to define how the rest of the instrument suites are used on each extended mission.

I'd think you'd have more flexibility, as well -- imagine if you had 4 mini-Cassini's at Saturn now, one with SAR and general imaging, one with high-resolution multi-spectral imaging, one fields-and-particles vehicle, and one with VIMS and additional spectroscopic analyzers to look at the chemistry of the planet, rings and moons.

Now, each of these guys would be on their own mission orbits, with the SAR probe staying out near Titan a lot. One suite would follow up the results from the other suites. Perhaps the vehicle with all the spectroscopic analyzers could be designed a little mechanically tougher than the others, so you could dive it through plumes and the vaporous edges of rings.

Figure that each of these spacecraft could share designs (and manufacturing, etc.) for a common physical bus, common attitude control and propulsion systems, common data handling and communications systems... You'd be developing maybe 20% more sensor systems for the various instrument suites, but your designs, fabrications, engineering, etc., can actually get into savings-of-volume. If you can spend maybe 50% more on your multiple spacecraft than you would on a single Flagship mission, but spend only 60% of what you'd currently spend on launch costs, then it tends to even out. You get more science, a more flexible mission, and the ability to follow up on discoveries by some instruments with detailed analyses by others, without hauling all of the rest of your instruments along on your detailed analyses.

Does that kind of mission architecture sound exciting to you? 'Cause it sure does to me! biggrin.gif

-the other Doug

Posted by: stevesliva Aug 18 2009, 01:12 AM

QUOTE (nprev @ Aug 17 2009, 07:14 PM) *
Yeah, generally, although there is a risk tradeoff to consider...'all the eggs in one basket'.


It's funny, though, when you think of the complicated MSR profiles, one basket might be best, rather than risking the whole thing with extra launches. If we wanted a rover to put samples in an MSR ascent vehicle, no point not having half the eggs. wink.gif

Posted by: tedstryk Aug 18 2009, 02:16 AM

With missions like MSL and Europa Orbiter, failure is a really scary thing. Remember when the quasi-flagship Mars Observer failed and Galileo's antenna didn't open? Then again, with those failures (in Galileo's case I mean antenna failure, not mission failure), lightning might have struck twice...I am especially thinking of Galileo. If they didn't lubricate one antenna, having a second spacecraft to deal with wouldn't have changed much. I would be interested in knowing how much it would cost to have a backup vehicle that could, if necessary, be made flight-worthy in the event the initial mission failed. You would at least save the second rocket cost of the first mission succeeded.

Posted by: vjkane Aug 18 2009, 04:26 AM

QUOTE (tedstryk @ Aug 18 2009, 03:16 AM) *
If they didn't lubricate one antenna, having a second spacecraft to deal with wouldn't have changed much.

As I recall, the failure for Galileo is that the repeated trips across the U.S. by road allowed the dry lubricant to fall out. Ironically, if they'd flown the spacecraft back and forth (an option rejected for cost reasons), I read that the lubricant would have still been there. I also seem to recall that if they had been able to back up the antenna screw mechanism (a capability eliminated by cutting a wire so it would never be done in space and collapse the antenna), they could have worked around the problem.

Fundamentally, the problem was that they didn't retest the antenna mechanisms after several years of storage and thousands of miles of road travel. It's those little things that in hindsight seem so obvious that get you. Like the solid rocket booster plume on CONTOUR.

This is so hard that I am always amazed that so many missions work so incredibly well.

Posted by: vjkane Aug 18 2009, 04:29 AM

QUOTE (stevesliva @ Aug 18 2009, 02:12 AM) *
It's funny, though, when you think of the complicated MSR profiles, one basket might be best, rather than risking the whole thing with extra launches. If we wanted a rover to put samples in an MSR ascent vehicle, no point not having half the eggs. wink.gif

I've always thought that the risk in this mission is in the landing and launch. I'd put two sample collection craft down on the surface and then send one orbiter to collect the samples. If the orbiter fails, you can fly another one in a few years. The samples will still be in orbit.

Posted by: tedstryk Aug 18 2009, 04:50 AM

Well yes, you are correct. What I am referring to is that despite a decade and the truck rides, no one checked on the condition of the lubricant before launch. My point is that had there been a pair, it is unlikely that this error could have been recognized and corrected for the second spacecraft since it would have likely been already in space when the problem was discovered.

Posted by: Greg Hullender Aug 19 2009, 10:02 AM

QUOTE (stevesliva @ Aug 17 2009, 10:50 AM) *
That is his point, though, is it not? If huge launchers get 10x cheaper, you design the Neptune Orbiter you want and can also afford the huge detachable propulsion module for NOI for the same launcher price... maybe. And you get there in 10 years rather than 30. Or whatever.

(Isn't aerobraking useless for orbital insertion, anyways? It's for circularization, right?)

Yeah, it's always a clue that people didn't read your whole post when they offer supporting arguments as evidence to the contrary. :-) It does leave one hopeful that if SpaceX really does prove itself, we might see a slew of new Outer-planet mission proposals. (Of course, there's still that power-supply problem.)

An additional obvious problem with Aerobraking is that (by itself) it only lowers the apapsis, leaving you with a periapsis inside the planet's atmosphere, so you still have to burn fuel (when you do reach apapsis) to raise that high enough to avoid things like atmosphere, rings, radiation belts, etc. Supposedly that's why it's not attractive for planets like Jupiter -- you burn more fuel raising the periapsis than you gained from the aerobraking in the first place. (I haven't worked this out myself though.) In the case of Neptune, in addition to the uncertainty about the atmosphere, I suspect there might also be doubts as to just how high we'd need to raise the orbit in order to be safe.

--Greg

Posted by: ugordan Aug 19 2009, 12:55 PM

QUOTE (Greg Hullender @ Aug 19 2009, 12:02 PM) *
An additional obvious problem with Aerobraking is that (by itself) it only lowers the apapsis, leaving you with a periapsis inside the planet's atmosphere, so you still have to burn fuel (when you do reach apapsis) to raise that high enough to avoid things like atmosphere, rings, radiation belts, etc.

I think the difference between aerocapture and aerobraking should be clarified. What you're describing is aerocapture, while all recent Mars probes for example used aerobraking to condition the orbit. Aerocapture gets you from the initial hyperbolic trajectory to a capture orbit (though with periapsis inside the atmosphere as you say), aerobraking typically bleeds off your capture orbit's eccentricity.

Posted by: tedstryk Aug 19 2009, 01:08 PM

In the case of Jupiter, the radiation environment is also a factor.

Posted by: dmuller Aug 20 2009, 01:14 AM

I think the only more or less realistic (partial) aerocapture scenario at the outer planets would be using Titan to assist a Saturn orbit insertion. I read that the Titan atmosphere is "quite good" for that - dense atmospere & low gravity, and known to quite a degree. It will still require orbit trims and possibly a retro-burn to "finish up" the orbit insertion, but still use much less fuel than without the slowdown at Titan (hopefully the fuel savings vastly outstrip the weight of the heatshield+related equipment). The day-or-so it will take the spacecraft from the Titan atmosphere encounter to periapse should give enough time to calculate the additional burn needed.

No such option exists at Uranus or Neptune AFAIK.

Even if you have a strong rocket, budget constraints will still force missions to go as low-weight and low-cost launch as possible.

Posted by: dvandorn Aug 20 2009, 02:37 AM

The real problem is that, with outer planet missions, you play transit time against approach velocity. To get out to Uranus or Neptune in 10 to 15 years, you have to be traveling pretty fast relative to your destination by the time you arrive. You can design a trajectory that results in a much lower approach velocity, but such a trajectory will take 30 or more years to get out to the farther reaches of the System.

So, unless you want to launch a probe that will be managed by multiple generations of PIs, flight support personnel, etc., you have to deal with taking out a pretty hefty amount of velocity upon arrival. This will be the case right up until we can design a constant-acceleration propulsion system and we can accelerate for half of the outbound trip and decelerate the other half. When we eventually develop such a propulsion system, we'll be able to travel to Mars in weeks and the outer planets in months.

Until then, though -- you gotta slow down when you arrive, so you need to carry enough fuel and/or aerobraking equipment to do so. And, the film 2010's fictional flight planning aside, you gotta have enough fuel to raise your periapsis out of the atmosphere after a primary approach aerobrake, and the amount of fuel plus the mass of the aerobraking equipment required for the aerobrake vs. the amount of fuel you need to do a rocket-only insertion generally comes out in favor of the rocket-only option.

-the other Doug

Posted by: Holder of the Two Leashes Aug 20 2009, 01:52 PM

Don't forget one other possiblility, aerocapture followed by a satellite swingby to raise the periapsis. In Neptune's case you might be able to use Triton. For Uranus, well... probably not.

Posted by: tedstryk Aug 20 2009, 02:06 PM

QUOTE (Holder of the Two Leashes @ Aug 20 2009, 02:52 PM) *
Don't forget one other possiblility, aerocapture followed by a satellite swingby to raise the periapsis. In Neptune's case you might be able to use Triton. For Uranus, well... probably not.


A problem with that is that the uncertainties concerning Neptune's atmosphere translate to a very uncertain trajectory. It would be very hard to pass close enough to Triton to get the desired effect without risking lithobreaking.

Posted by: Holder of the Two Leashes Aug 20 2009, 04:29 PM

There are various ways to address that problem. Observations of stellar occultations of Uranus and Neptune can help refine the models of their upper atmospheres. This is especially true of space based observations where you can observe a broader range of the spectrum, plus less noise in the signal.

Then there is the heatshield. The manned Gemini and Apollo capsules had off-center shields that allowed for some adjustment and piloting of the trajectory during entry. The same principle can be applied to aerocapture. With a sensitive enough inertial guidence system and enough built-in intelligence, the craft could fly its way through the upper atmosphere to the proper outcome for orbital speed and direction (within a reasonable initial approach, of course).

Finally, the craft doesn't have to immediately aim for Triton on the way out. The orbit would be a long loop outward that could have a period of maybe half a year. Such an orbit would be very sensitive at apoapsis to small adjustments leading to large changes in targeting later on, putting Triton well within range. On the way back to Neptune you make a close pass to the moon and ... there you go. It might be possible to "flatten out" the orbit, lowering apoapsis and raising the periapsis at the same time.

Plus, I don't think it really would take all that much fuel at apoapsis to raise the orbit out of the atmosphere, so a satellite flyby might not be all that necessary to save the spacecraft (highly desirable, though, to reduce the period).

Posted by: tasp Aug 20 2009, 06:14 PM

There is a thread here somewhere (sorry don't have time to check right now) about aerobraking at Triton. As I recall, the scale height of that atmosphere is useful for the technique, and having an orbit about Neptune with your low point at the height of Triton's orbit might be handy.



Posted by: Juramike Aug 20 2009, 06:47 PM

QUOTE (tasp @ Aug 20 2009, 01:14 PM) *
There is a thread here somewhere (sorry don't have time to check right now) about aerobraking at Triton. As I recall, the scale height of that atmosphere is useful for the technique, and having an orbit about Neptune with your low point at the height of Triton's orbit might be handy.


Uhhh, wait a minute, are you recommending to use Triton's atmosphere for aerobraking?

Posted by: Floyd Aug 20 2009, 09:08 PM

tsp my be confused. Two earlier post were talking about Neptune aerocapture and swingby of Triton to raise periapsis--while avoiding lithobreaking. wink.gif




Posted by: tasp Aug 20 2009, 09:59 PM

http://www.unmannedspaceflight.com/index.php?showtopic=3768&st=15&start=15

Posted by: Gsnorgathon Aug 24 2009, 12:21 AM

Would it be possible to use an atmosphere probe to get enough info to mitigate the risks of aerocapture? It seems you'd want to have an atmosphere probe along for the ride anyway.

(And btw - isn't it lithobraking, rather than breaking? Though I guess both ultimately amount to the same thing... (and in Triton's case, wouldn't it be cryobraking? (And if you cried when your probe cryobraked and cryobroke, would anyone be so cruel as to call you a cryobaby?)))

Posted by: Greg Hullender Aug 24 2009, 10:17 PM

I always assumed that "lithobreaking" was a deliberate joke. I prefer to call it "impact." :-)

--Greg

Posted by: tedstryk Aug 25 2009, 01:11 AM

QUOTE (Greg Hullender @ Aug 24 2009, 11:17 PM) *
I always assumed that "lithobreaking" was a deliberate joke. I prefer to call it "impact." :-)

--Greg



Yes, you assumed correctly. The "break" instead of "brak" was a tongue-in-cheek reference to what happens when one hits the lithosphere.

Posted by: Juramike Aug 25 2009, 01:46 AM

QUOTE (Gsnorgathon @ Aug 23 2009, 07:21 PM) *
Would it be possible to use an atmosphere probe to get enough info to mitigate the risks of aerocapture? It seems you'd want to have an atmosphere probe along for the ride anyway.


You'd want the atmospheric probe to return data well before trying an aerocapture. You'd need the parameters well in advance to plan and design for how much fuel to carry for the retro-burn, the ballute design, etc..

Atmospheric probes might make the next Neptune mission aerocapture possible, but not the first one.


Posted by: briv1016 Nov 5 2009, 12:15 PM

In conjunction with the Decadal Survey, the "Giant Planets Panel" had a study performed in regards to a Neptune Orbiter/Flyby/Probe.

http://www.spacepolicyonline.com/pages/images/stories/PSDS%20GP2%20Spilker%20NeptuneRMA.pdf

Posted by: Drkskywxlt Nov 5 2009, 06:16 PM

QUOTE (briv1016 @ Nov 5 2009, 06:15 AM) *
In conjunction with the Decadal Survey, the "Giant Planets Panel" had a study performed in regards to a Neptune Orbiter/Flyby/Probe.

http://www.spacepolicyonline.com/pages/images/stories/PSDS%20GP2%20Spilker%20NeptuneRMA.pdf


Unless something changed, this study also had a recommendation and co-sponsorship from the Satellites Panel due to the likely high emphasis on Triton science.

Posted by: vjkane Nov 5 2009, 07:19 PM

QUOTE (Drkskywxlt @ Nov 5 2009, 07:16 PM) *
Unless something changed, this study also had a recommendation and co-sponsorship from the Satellites Panel due to the likely high emphasis on Triton science.

This assessment was commissioned as part of the first wave of mission assessments selected prior to the science community input. (See http://futureplanets.blogspot.com/2009/11/first-decadal-mission-assessments.html). My understanding is that there will be several tens (low tens?) of rapid mission assessments and around a dozen full mission architectures and costings.

What I found interesting in this Neptune/Triton assessment was that the cheapest orbiter mission is probably about $1.5-2B, while the more capable missions are in the $3+B range. (Scaling from a New Frontiers flyby cost factor.) This suggests that there is an intermediate class of missions possible between flybys and full Flagship missions.

Fitting an intermediate mission into a $12B decadal budget with a moderate Mars program and JEO, however, would be difficult.

Posted by: Greg Hullender Nov 8 2009, 01:56 AM

I'm just absorbing the fact that a 14-year mission launched in 2035 (the latest date mentioned) would enter its extended mission just after I turn 90.

--Greg

Posted by: vjkane Nov 8 2009, 06:59 AM

QUOTE (Greg Hullender @ Nov 8 2009, 01:56 AM) *
I'm just absorbing the fact that a 14-year mission launched in 2035 (the latest date mentioned) would enter its extended mission just after I turn 90.

Youngster.

Posted by: infocat13 Mar 29 2010, 12:36 PM

recent updates and white papers on proposed Uranus and Neptune missions

http://www.spacepolicyonline.com/pages/images/stories/PSDS%20GP1%20Hofstadter_Uranus%20Orbiter.pdf


http://www.spacepolicyonline.com/pages/images/stories/PSDS%20GP1%20Hansen_Argo_Neptune%20Mission%20Concept.pdf
this one is the Argos mission in its latest version, it might make it as a new frontiers mission.competition for the ASRG's for the Argos mission would come from a sample return flyby through the geysers of Enceladus mission being proposed!

Posted by: Greg Hullender Mar 29 2010, 08:31 PM

I've been curious whether a Falcon 9 or Falcon 9 Heavy could improve the Argos mission, but this was the first time I actually saw an estimate for the cost of the launcher spelled out in the proposal. I notice that they don't mention either as a possiblity, but I figure a Falcon 9 could save $165M and a Falcon 9 Heavy could save $110M and increase the payload into the bargain.

To arrive at this, I started with their report. On page 58, they talk about mission concepts using the "smallest" Atlas V, a "mid-sized" one and the "largest" with a Star-48 upper stage. For each, they give a mass that could be delivered to a particular C3 (hyperbolic excess velocity squared). Figuring the smallest to be the 401 the medium to be the 541, and the largest to be the 551, and using the Atlas V numbers from Wikipedia, I figure one can convert from mass-to-GTO into mass-to-C3 if you multiply by 5 and divide by the desired C3.

Taking the Falcon 9 numbers from Wikipedia, the Falcon 9 could deliver slightly less payload than the Atlas V 401 (making it viable for the C3=25 scenario) while the Falcon 9 Heavy could deliver over 600 kg for the C3=162 scenario -- a big increase over the 478 kg scenario in the paper.

On page 63, they give a $200M estimate for the 551 with Star-48, $190M for 541, with $10M being the cost of the Star-48. Falcon 9 is only $35M and Falcon 9 Heavy is quoted at just $90M.

Of course, the Falcon 9 Heavy hasn't launched yet, so I could see not wanting to risk anything on it. Also, it seems they're currently not required to include the launch vehicle cost to get under the New Frontiers spending cap. Still, I'm surprised they included so many other options but left this one out.

Maybe once a Falcon 9 actually launches we'll see some proposals start to include it.

--Greg

Posted by: nprev Mar 30 2010, 01:58 AM

I don't think anyone would ever submit a mission proposal with total cost estimates based on the manufacturer-projected price of an as-yet unproven booster, Greg. That would really be doubling down on assumed risk; NASA probably wouldn't even bother to finish reading the proposal once they saw that.

Posted by: Greg Hullender Mar 30 2010, 04:56 AM

I wouldn't expect it to be the main proposal, but I'm still a bit surprised not to see it mentioned at all -- if only to show that the stated cost is conservative.

To turn it around, I'll be curious to see at what point we DO start seeing Falcons in the proposals.

--Greg

Posted by: machi Mar 30 2010, 10:55 AM

What is really interesting is accessibility of Eris in Argo mission.

Posted by: ngunn Mar 30 2010, 11:45 AM

But no mention of how long it would take to get there? Just 'date of KBO arrival depends on which KBO is chosen.' Mmm . .

Posted by: machi Mar 30 2010, 01:08 PM

I think around another ~20 years (29 years after start). I suppose, that it's technically possible after some closer KBO flyby like mission of opportunity (or more precisely mission of survive).

Posted by: Greg Hullender Mar 30 2010, 03:42 PM

I can't find a figure for Argos' expected final speed, but if we take Voyager 2's average speed from Earth to Neptune (19 km/sec) and divide that into the difference between Neptune (30.1 AU) and Eris (96.7 AU) I come up with 16.7 years. That's very crude, of course (Neptune and Eris aren't aligned THAT well and the speed PAST Neptune must be a good bit slower than the speed before it) but I'd say that's got to be a lower bound. Even 20 years seems optimistic.

Eris is just too far.

--Greg

http://voyager.jpl.nasa.gov/science/neptune.html is my reference for 19 km/sec.

Posted by: elakdawalla Mar 30 2010, 05:06 PM

QUOTE (machi @ Mar 30 2010, 06:08 AM) *
"mission of survive"
I like that terminology! But don't think it's one NASA will be adopting any time soon smile.gif

Posted by: punkboi Mar 30 2010, 07:52 PM

QUOTE (Greg Hullender @ Mar 29 2010, 09:56 PM) *
I wouldn't expect it to be the main proposal, but I'm still a bit surprised not to see it mentioned at all -- if only to show that the stated cost is conservative.

To turn it around, I'll be curious to see at what point we DO start seeing Falcons in the proposals.

--Greg


I assume it won't be till after 2011...when Falcon proves its mettle in safely delivering cargo (and/or crew) to the ISS.

Posted by: ugordan Mar 30 2010, 08:27 PM

QUOTE (punkboi @ Mar 30 2010, 09:52 PM) *
I assume it won't be till after 2011...when Falcon proves its mettle in safely delivering cargo (and/or crew) to the ISS.

There's more to it than just the price of a launch vehicle, some payloads for example impose requirements like vertical integration (F9 is integrated horizontally), access to payload at all times before launch campaign without needing to say destack the vehicle, ground support equipment requirements, etc.

SpaceX was awarded a http://www.spacex.com/press.php?page=41 two years ago and they're still yet to win a launch contract. Atlas V still wins payloads even though it is overpowered for some of the spacecraft (with Delta II being phased out and becoming too expensive), F9 is still too risky and unproven. Keep in mind F9 price down the road also needs to stabilize once the vehicle becomes operational and true costs become clear.

Posted by: qraal Jun 27 2010, 10:37 AM

QUOTE (ugordan @ Mar 31 2010, 07:27 AM) *
There's more to it than just the price of a launch vehicle, some payloads for example impose requirements like vertical integration (F9 is integrated horizontally), access to payload at all times before launch campaign without needing to say destack the vehicle, ground support equipment requirements, etc.

SpaceX was awarded a http://www.spacex.com/press.php?page=41 two years ago and they're still yet to win a launch contract. Atlas V still wins payloads even though it is overpowered for some of the spacecraft (with Delta II being phased out and becoming too expensive), F9 is still too risky and unproven. Keep in mind F9 price down the road also needs to stabilize once the vehicle becomes operational and true costs become clear.


Nice to see Musk's bird finally took wing and they've won the Iridium upgrade contract. Of course there's no such thing as statistics based on one example, thus the next few launches will be watched very carefully indeed.

Need I say it? Go ARGOS!

Posted by: antipode Jun 28 2010, 11:01 PM

The F9 is going to need an EDS - what are they thinking of? One of the Star solids?
Even then I cant see the F9 being up to an outer planets mission unless the trajectory is a LOOONG one

P

Posted by: ugordan Jun 29 2010, 07:59 AM

F9 doesn't inherently need an "EDS" any more than Atlas V needs one. The upper stage has performance for an escape trajectory. The problem as you say is it lacks performance required for outer planet missions. In terms of C3 energy capability, F9 is somewhere between a Delta II and a vanilla Atlas V 401. For comparison, New Horizons used 5 solids on the boosters and an additional solid kick stage and JUNO will use 4 solids IIRC.

Theoretically, a F9 Heavy could do it, but with 27 engines and being very much a paper rocket, it's only a theoretical what-if.
I can see F9 winning Discovery class missions in the future, New Frontiers missions will still be ruled by Atlas.

Posted by: punkboi Sep 15 2010, 10:56 PM

Any new development on the Argo mission proposal? Just wondering.

Posted by: ZLD Jan 4 2011, 06:09 AM

Hadn't seen any mention of this proposal yet.

http://www.mssl.ucl.ac.uk/planetary/missions/uranus/

Here is a short write-up about the proposal as well: http://skymania.com/wp/2010/12/mission-planned-to-probe-uranus.html

Posted by: tedstryk Jan 4 2011, 06:09 PM

I hope it never flies under that name, because I can't read it and keep a straight face. It reminds me of my days as a planetarium intern, where I would have real trouble during live shows explaining to people how to "find Uranus" without cracking up. rolleyes.gif

Posted by: ZLD Jan 4 2011, 06:28 PM

Better than the National Geographic headline: http://blogs.nationalgeographic.com/blogs/news/breakingorbit/2011/01/europe-asks-to-probe-uranus.html rolleyes.gif

But yeah, I entirely agree the name of the proposal probably shouldn't stick but likely wasn't unintentional.

Posted by: elakdawalla Jan 4 2011, 06:33 PM

I've learned to embrace Uranus jokes (there, I did it again). About 75% of space-related conversations between me and my husband (of which there aren't very many, admittedly) involve Uranus jokes. Don't view it as a handicap, view it as a way to warm up the audience!

Posted by: tedstryk Jan 4 2011, 06:40 PM

My problem was that I was running slides on timed sequences from a reel to reel tape (we had a more modern-for-the-time system, but it died and forced us back to the old one), so by the time I finished laughing the slides were visualizations of the Kuiper Belt. And yes, my wife and I make plenty of jokes...the last name Stryk (pronounced "Strike" for those who don't know) doesn't help.

Posted by: tasp Jan 4 2011, 07:00 PM

Thanks for that, ZLD.

Couple of good Hubble shots I don't recall seeing before too.

Article didn't say if the craft was a flyby or orbiter, but at my age, this is probably my last chance for a Uranus mission.

If the craft is an orbiter, I hope they can utilize the Longuski/Heaton plan to visit the satellites. There is a thread here somewhere on that . . .



Posted by: tasp Jan 4 2011, 07:08 PM

LOL.

It was the obscurely titled 'Uranus Orbiter' thread.

I bumped it to the top of the pile.

The Longuski/Heaton trajectory is modeled after the Galileo Jupiter orbital tour. Turns out Uranus system is scaled appropriately from Jupiter system to make an analogous tour possible.

Amazing idea they had. Also, they note that at mission end, a (IIRC) 1000 km/hour decel would park the craft in orbit around Ariel.


This is sounding pretty sophisticated for a $400 million mission . . . .

Posted by: ZLD Jan 4 2011, 08:48 PM

Just curious (I don't have access to AIAA during break), how does the orbital insertion work for Uranus in such a trajectory? I hadn't even really thought about how that would work with Uranus being basically on its side.

Posted by: Hungry4info Jan 4 2011, 10:53 PM

Same as at any other planet, as long as you arrive during Uranus' equinox, the initial orbit around the planet won't be too inclined relative to its moon system.

Posted by: vjkane Jan 4 2011, 10:57 PM

This will be an interesting mission competition. In addition to Uranus Pathfinder (something to look forward to after age 50 rolleyes.gif ) there is also the http://futureplanets.blogspot.com/2010/11/titan-on-budget.html concept. If the latter can figure out a decent data relay (the http://futureplanets.blogspot.com/2010/12/jet-journey-to-enceladus-and-titan.html proposal?), then my money is on that mission.

I'm sure there are more planetary proposals that were submitted along with many astronomy and astrophysics proposals.

As I understand it, the proposals are competing for 2-3 slots for Phase A funding from which the final mission will be selected. Flight time early 2020s.

Posted by: Paolo Feb 25 2011, 05:36 PM

Uranus Pathfinder has not been selected for the initial Assessment Phase
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=48467
the good new is that Marco Polo-R is one of the four finalist mission (and EChO looks great as well!)

Posted by: briv1016 Apr 15 2011, 06:53 AM

Since no one has mentioned this yet, I guess I will. The NRC Planetary Decadal Survey for 2013-2022 mentions a Uranus Orbiter and Probe. A link to the report is available through Emily's Blog.

http://www.planetary.org/blog/article/00002945/


More info including Steve Squyres' Presentation, slides and a copy of the original mission concept study are available at the PDS site.

http://sites.nationalacademies.org/SSB/CurrentProjects/ssb_052412



Keep in mind that this is a report from National Academy of Science, not NASA. And that NASA's budget is highly volatile.

Posted by: mchan Apr 15 2011, 10:53 PM

http://www.unmannedspaceflight.com/index.php?showtopic=6922

vjkane has excellent blog on future missions, see http://www.unmannedspaceflight.com/index.php?showtopic=5565

Posted by: Paolo May 18 2011, 05:11 AM

I didn't know it until yesterday, but the ESA medium class mission proposal included a Neptune and Kuiper Belt flyby and General Relativity mission.
see this prez http://moriond.in2p3.fr/J11/transparents/christophe.ppt

Posted by: Decepticon May 18 2011, 07:43 AM

QUOTE (Paolo @ May 18 2011, 12:11 AM) *
I didn't know it until yesterday, but the ESA medium class mission proposal included a Neptune and Kuiper Belt flyby and General Relativity mission.
see this prez http://moriond.in2p3.fr/J11/transparents/christophe.ppt



I would of loved a Neptune and Eris flyby. Wishful thinking blink.gif .

Posted by: infocat13 May 22 2011, 12:23 AM

QUOTE (briv1016 @ Apr 15 2011, 02:53 AM) *
Since no one has mentioned this yet, I guess I will. The NRC Planetary Decadal Survey for 2013-2022 mentions a Uranus Orbiter and Probe. A link to the report is available through Emily's Blog.

http://www.planetary.org/blog/article/00002945/


More info including Steve Squyres' Presentation, slides and a copy of the original mission concept study are available at the PDS site.

http://sites.nationalacademies.org/SSB/CurrentProjects/ssb_052412



Keep in mind that this is a report from National Academy of Science, not NASA. And that NASA's budget is highly volatile.



Its interesting to note that the decadal survey now states that duo to the budget, the Jupiter mission is now to expensive and if the Exomars can not be descoped then Uranus and a mix of discovery missions becomes the default plan.

Posted by: machi May 25 2011, 09:24 PM

Document about Uranus Pathfinder: http://www.google.cz/url?sa=t&source=web&cd=3&ved=0CDsQFjAC&url=http%3A%2F%2Fwww.mssl.ucl.ac.uk%2Fplanetary%2Fmissions%2Furanus%2Fdownloads%2Fup_expastron_submitted.pdf&ei=fnDdTfKxAdHusgbDq6jEBQ&usg=AFQjCNEE-gj956WeKBnbjKT_mpSVg3FrRg

This mission wasn't selected, but still it's interesting pdf.

Posted by: Paolo May 25 2011, 09:54 PM

QUOTE (machi @ May 25 2011, 11:24 PM) *
Document about Uranus Pathfinder


thanks for sharing. I guess it is the paper on UPF due for publication on Experimental Astronomy. A paper on the Neptune OSS mission has also been submitted

Posted by: stevesliva Sep 5 2012, 04:07 AM

Interesting mention that the Decadal Survey recommended a Uranus mission:
http://www.planetary.org/blogs/guest-blogs/20120904-hammel-uranus-dark-spot.html

... not that Decadal Survey, but the Solar Physics decadal survey. However it's not exactly binding and would mostly fund a magnetometer. But cool, nonetheless.

Posted by: Paolo Jan 25 2013, 06:10 AM

just out on the arXiv: http://arxiv.org/abs/1301.5781
I am posting it here because the determination of the D/H ratio was one of the objectives of the decadal survey Uranus mission

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