Since the Neptune Orbiter thread has started to veer into talking about a Uranus orbiter as well, it seemed like a good idea to start a topic for Uranus.

Thanx. It is ok to move the Uranus orbiter post here if possible.

{I am imagining an era of NASA/JPL funding that results in the site being flooded with orbiter threads }

I admit a keen interest in Uranus. The mass ratios of the larger satellites to Uranus are not all that different from the Galilean satellites to Jupiter. Having two systems so grossly similar , yet with such huge differences, such as the axial tilt and the strength of the magnetic field, are so intriuging.

Would Hubble (or some of the larger ground based installations) be put to good use checking for co-orbital lagrangian moons of the larger satellites? I recall Voyager doing a thorough search closer in to the planet, but could small dark co-orbitals at Titania and Oberon have been missed?

That Jupiter seems to not have them, and Saturn having a few, it makes me all the more curious for a good inspection of Uranus to see where it stands regarding Lagrangian objects.

Finding some at Uranus might bump up the level of scrutiny Cassini is giving them at Dione and Tethys.

The four big Uranian moons are at about the same distance from Uranus as Tethys, Dione and Rhea are from Saturn. They also have similar masses. That being the case, you'd think that there would be at least one Lagrangian satellite somewhere in the Uranian system.

I wonder if the lack of co-orbital satellites for Ariel, Umbriel, Titania and Oberon has to do with Uranus itself, rather than the major moons? Uranus only has about 15% of Saturn's mass. Could this cause Lagrangian orbits to be less stable at Uranus?

Interestingly, a stronger comparison exists between Uranus and Jupiter, namely that both planets have similar planet/satellite mass ratios. In fact, in 2003 Andy Heaton and Jim Longuski published a paper showing that a Galileo-style tour is, unlike at Saturn and Neptune, possible at Uranus:

Feasibility of a Galileo-Style Tour of the Uranian Satellites
Andrew F. Heaton and James M. Longuski
J. Spacecraft Rockets 40, 591-596 (2003).
First page

I'll be darned! How 'bout that. I was aware of the mass ratio and distance scaling between Uranus and Jupiter, but I assumed there was an inverse square {or cube} law that prevents a 'quick' style tour of the Uranian moons. I thought I was really 'pushing' things suggesting a tour of the system lasting upwards of 20 years. {btw, a 20 year mission duration at Uranus is desirable for other reasons}

The lack of a strong resonance of three (or more) members of the Uranian system doesn't hurt the mission either. The lower radiation environment at Uranus would certainly be a relief after the ordeal Galileo experienced.

Appreciate the post!

Yeah, thanks Alex -- that link was a good read. Very interesting.

I wish I could post the entire paper, which is fairly interesting, but AIAA is, like many organizations, very fastidious regarding copyrights, and Doug's forum is fairly visible.

The most important thing for a "Galileo-like" tour is the availability of multiple satellites to utilize gravity assists, which adds flexibility to the tour design process. Cassini, on the other hand, can only use Titan and, consequently, must always return to Titan for a gravity assist to continue a given tour. This makes designing a "Cassini-like" tour very difficult, especially when multiple targets (e.g., Saturns icy satellites) are desired and the mission has severe operational constraints. Just ask the Cassini mission planners what they went though during the design process for the "T9-X" and "T18-X"-class tours.


I assume you're referring to monitoring Uranus' atmosphere and/or changing solar illumination?


Agreed.


My pleasure.

Trivia: For those who do happen to read the full paper by Heaton and Longuski, one might note that I get a brief mention in the acknowledgements section. I provided a couple of Uranus scientific references to Andy Heaton between the time he presented the paper at an AAS/AIAA conference and when he submitted the final for publication in J. Spacecraft Rockets.

Without incurring copyright snags, of course, could I field a question about the ideas in the paper?

The portion available through the link ends with an intriguiging acknowledgement that the vehicle could enter orbit about Ariel after ~40 loops around Uranus.

Is this characteristic of the orbit tour similar (at least broadly) to the clever trajectory Messenger is utilizing to eventually end up in orbit about Mercury?

I realize the mass ratios of Sun - Mercury - Venus - Earth are quite different, but is there a correlation between the flight plans?

Amazing article, regardless!

Darn, wouldn't you know that I don't have a copy of the paper available on my system at the moment

That said, I'll review it when I get home but from what I recall, the main concept behind the end-of-tour plan to insert into orbit at Ariel is based on orbital pumping and cranking, which not only changes inclination from the initial Uranian insertion, but reduces relative velocity so that the deterministic delta-V for insertion at Ariel can be handled by the orbiter's propulsion system. I can't remember whether the scheme also utilizes any "third-body" effects from Uranus or "fuzzy boundaries" but these might possible as was planned for the original Europa Orbiter insertion in europan orbit.

Whether this resembles, even in a broad sense, the MESSENGER trajectory through the inner solar system, is, I guess, in the eye of the beholder.

{In re the 20 year mission life at Uranus}

I realize with Jupiters small axial tilt, we didn't see too many (any) seasonal effects with Galileo.

With Cassini, if we are lucky and have 7 years of probe life, we get to travel with Saturn roughly 90 degrees around the sun. We can see the rings from nearly full open to the sun to edge on. Assuming the rings look pretty much the same top and bottom (north and south?) we get to see the 'whole show' or at least be able to extrapolate it form a 7 year exploration of Saturn.

At Uranus, same thing. How does the ring look through forward scattering at edge on and full on to the sun? (I'm hoping for some phase effects, perhaps some of the Uranian ring particles are elongated and align radially to Uranus)

Additionally, if a probe arrived at Uranus with Uranian rings 45 degrees short of edge on to the sun (not that orbit for a probe would be easier to achieve in this orientation) and the probe could watch the rings go edge on then to 45 degrees further (in ~20 years), we could also get near 100% coverage in sunlight of all the surfaces of the main satellites.

A probe arrival with the rings full on to the sun, would also be desirable for other reasons.

{granted a probe with an even longer life would be great, but a factor of 2 or 3 increase from Cassini would seem technically possible}

Orbiting Ariel would be a remarkable ending to this mission -- especially given the assumptions I've been making until this month about the helplessness of a Uranus Orbiter. (I might as well say that Spilker told me that his own navigator for the Neptune Orbiter mission design took just a few days to reach a similar conclusion that a moon tour is perfectly feasible with a Uranus Orbiter; the only thing needed is experience with navigating a craft through a rapid-fire series of moon flybys, which Cassini has now given us. He didn't say anything about a finish-up at Ariel, though.)

A long time ago (the early 1970s!), I suggested that there might be all sorts of odd effects around Uranus as a result of it's axial tilt - specifically, that at certain times of the Uranian year the relative velocities of both incoming spacecraft and meteorites, comets etc could be very much slower than expected (not so much a matter of traditional orbital dynamics as simply the summing of vectors). The end result might be a natural cache - as in Antarctica - of almost Kuiper Belt material, available for access in crater/canyon walls or by drilling on some of the icy moons. Or even interstellar material...

Bob Shaw

For $450, Amazon claims it can deliver a copy of the proceedings:

http://www.amazings.com/sbb/reviews/review0494.html
http://www.amazon.com/exec/obidos/ASIN/087...8920362-6213764

Well, shucks, how can anybody not jump at a bargain like that? However, they receive that journal at U.C.-Davis, which is within my driving range, so I'll photocopy it next time I'm down there. (That may be a while, though -- the advent of the Internet has tremendously reduced my need to go traipsing regularly to various university libraries for my astronautical information needs.)

That's nuts.

I could post a scanned version of the Heaton and Longuski paper here (temporarily) but I'll let Doug decide since it's his forum. Of course, I'm assuming he's reading this thread.

I confess a burning desire to see the whole paper.

An amazing finding I hope is employed in future exploration plans of Uranus.

Comparing the Uranian staellites close up to all the other moons would synergistically expand our knowledge of all the objects.

I dropped a line to Doug but I don't think he saw he it before his sojourn to Spain. I don't want to post it here without his permission. I guess I could email it to interested parties; however, maybe we should wait on Doug's return, especially since I don't know what the potential demand is.

EDIT (11/23/05): Anyone (as long as the number remains reasonable) who wants a scanned PDF version can drop me an email via this board and I'll send it via my own personal email account. A few members already have taken this route.

Have reviewed the Heaton/Longuski paper (Thanx!) now and have some comments.

The 'clever bit' of the Messenger trajectory, gravitational interaction with the target object to facilitate orbital insertion, isn't employed at Ariel. This technique is not addressed in the paper, but since utilizing it would take quite a while (if it were even possible at Ariel) and the paper was assuming 2 year long orbital missions the omission is not surprising. Also, the 1km/sec 'burn off' at Ariel doesn't seem excessive anyhow, so the utility of the technique at Ariel is less appparent. That the technique works at Mercury may be due more to Mercury's high density alowing the craft to approach closer to the planets center of mass to 'realize the math' than may be possible with an icy body like Ariel. It is not clear (to me) how the mass ratios and distances scale for this technique from sun/Mercury to Uranus/Ariel.

I am also amazed with the Heaton/Longuski trajectory in that in 2 years, 40 (!) encounters with Oberon, Titania, Umbriel, and Ariel are possible. A significant truth revealed in the paper is that since the Uranian system is 'scaled' smaller than the Galilean satelllites, useful distant flybys of Uranian moons also occur more frequently than they did for the Galileo spacecraft.

Inferring to Cassini, it seems the mass ratio of Saturn/Titan being so different from that of Jupiter or Uranus does allow Cassini much more flexibility in changing it's inclination around Saturn. I had wondered why this was not done with Galileo at Jupiter, and it seems many more satellite flybys would be required for a given inclination change than for Cassini at Saturn.

It does seem that an interesting mission could be orbited at Neptune following the Cassini style tour.

Also, granted the enormous delta vee needed to effect orbit insertion around Pluto, once that is achieved, an interesting mission at Pluto is possible utilizing Charons gravity for orbit shaping. Close observations of Pluto and Charon at a variety of inclinations seems quite feasible, and arbitrarily close approaches to the 2 new satellites seems 'easy' now. The big problem remains though, the difficulty in achieving orbit around Pluto due to the high approach speed of any reasonable spacecraft.

The best way to orbit -- or land on -- either Pluto or Triton seems to be Angus McRonald's suggestion for a big, heat-resistant ballute dragged behind the spacecraft on a cable to serve as an aerobrake in their extremely faint atmospheres. His preliminary studies show this to be quite workable. There was a little bit of discussion on it at COMPLEX, but as they said it will require quite a bit of technological work as compared to simple heat-shield aerocapture, which is almost ready to go right now. McRonald himself has become a victim of Ames Research Center's rather unselective layoffs, but some groups at Knoxville and Purdue U. are studying the question further.

As for a Neptune orbital tour, the plan already worked up for Tom Spilker's JPL design team involves a lot of orbital flexibility, but no actual switch from retrograde to prograde orbit at any point in the tour. (By the way, a lightweight but scientifically useful Triton lander that does most of its braking by ballute is seriously considered for addition to the Neptune Orbiter mission, if NASA hits the really big money.)

Wow, imagine watching the ballute go overhead while standing on the surface of Triton!

Would it radiate enough heat to flash the surface frost to vapor as it goes by?

Interesting to watch the surface after that if it did.

I assume that an accelerometer on the main body of the craft would cut the cable to the ballute when the craft slowed enough to enter orbit, but if the ballute didn't get deep enough into the thin atmosphere, the system wouldn't decel enough. Sounds stress provoking for the mission team at JPL.

Amazing concept, hope to live long enough to see one fly.

McRonald's best paper on the subject seems to be at http://trs-new.jpl.nasa.gov/dspace/bitstre...6/1/99-0422.pdf .

Doesn't look like it will burn off too much Tritonian frost.

But what an amazing technique for getting to interesting places in the solar system!

Not sure a human payload will ever try this technique (shades of 2010), at least not at Pluto.

It is quite hard to imagine decel at up to 40 gees from such a thin atmosphere at hundreds of km above Pluto's surface. Still, the technique has great potential for orbiters and landers at a variety of objects.

Just keep in mind that -- because Pluto's gravity is so weak -- its atmosphere, thin though it is, towers up and up and up above the surface, with a huge scale height. In fact, there is speculation that some of it may get exchanged with Charon through tidal forces! High-altitude aerocapture in this situation is quite practical, if you have a moderately-sized ballute. (Ditto for Triton.)

I noted with interest in the referenced paper on the ballutes the one with a lens shape.

If this is not an original idea with me, my apologies; could such a near disk shaped ballute be angled during decel ? That advantage might be that a craft could manuever during the deceleration phase. The force applied by the ballute to the craft would not have to pass through the center of mass of the craft. The effect would be usable lift. The decel phase could be prolonged at a higher altitude while the craft arced further around the target object. Regions that perhaps would not be accessable from the 'standard' ballute might be reachable with a steerable one.

Should Pluto (or whatever) not be favorably aligned at arrival, this technique might still get you were you want to go.

Perhaps the decel could start over the far side (as seen from earth) and wind up on the fore side for the actual landing phase.

Another application might be (again using Pluto as an example) to enter the deceleration phase where convenient from the arrival trajectory, and manuver during decel and then exit the atmosphere on a path that leads to Charon (at a low enough speed that perhaps you could orbit or land there).

An application at Triton might be to decel in its' atmosphere, but not so much as to be captured by it, and wind up in an orbit favorably inclined about Neptune.

Aerocapture into Saturn orbit via ballute passage through Titan's atmosphere seems doable. Perhaps the manuvering technique would put the craft into an equatorial orbit about Saturn (for example) from a greater variety of incoming trajectory angles than any other technique?

The biggest problem with using steerable aerocapture / landing trajectories is that you need to have a *very* good model of the atmosphere you're using to slow down with.

It's bad enough to have only a vague idea of the temperature/pressure profile of an atmosphere you're using to do straight-line drag braking. If you're designing into your spacecraft and trajectory a need for predictable changes in direction based on lift, *any* significant variation in the atmosphere's pressure, density and temperature profile from your model will result in completely different results.

They're talking about needing a Mars orbiter for day-to-day monitoring of the upper atmosphere in order to successfully land future probes -- apparently, Mars' upper atmosphere was so much thinner and extended than predicted during Spirit's EDL that she was very nearly dashed against the surface a la Beagle II. Cassini is seeing that Titan's upper atmosphere also seems highly variable in pressure/altitude. So, in order to successfully use Titan aerobraking for a Saturn orbiter, you'd almost need to already have a working Saturn orbiter there to tell you the detail you need about Titan's atmosphere at that moment...

Like many other elegant ideas, this one tends to fall apart when you look at it in greater detail.

-the other Doug

{grasping at straws}

Can the craft itself scan ahead with a lidar device (or whatever would work) and adjust path 'on the fly' ?

Do we expect the Titanian weather reports to repeat precisely every Saturnian year?

Are Pluto and Triton far enough out that their atmospheres will model out quite stable in the the relavent altitudes?

Would a more 'structured' decel device be worth while? Maybe an RCC wing with some movable aerodynamic surfaces on the trailing edge. (I'm thinking of a shuttle type re-entry with hypersonic manuevuering capability, the craft flies to the appropriate density/altitude, executes the manuvuer wherever that layer happens to be).

I'm thinking the amount of gas over a particular surface area will be constant, but its' distribution vertically will vary. Set up something that tolerates the vertical gas distribution range expected and GO!

What about a small,simple atmospheric probe that would fly ahead, similar to the way Huygens arrived at Titan before Cassini?

You don't need to grasp at straws -- Tasp's fears about the unusability of aerocapture due to uncertainties about the planet's atmospheric structure are, according to Jeffrey Hall of JPL, very seriously overstated. Hall's team has run almost 2000 simulated aerocapture entries into the atmospheres of both Titan and (more difficult) Neptune, inserting random changes in atmospheric structure to see if the written autopilot programs can cope with them -- without a single failure. (I can give you the URL for this actual report, once I track it down again in my records.)

He said flatly at COMPLEX that -- once a single New Millennium mission (maybe ST-9 in 2010) is flown to confirm the overall validity of the aerocapture autopilot programs -- the technology will be ready for use immediately at the smaller worlds (for instance, MEPAG was wrong in saying that an engineering test of aerocapture will be necessary at Mars) And he also went so far as to say that -- while aerocapture at the giant planets requires a radically different kind of boat-shaped heat shield, to provide the higher lift/drag ratio that will allow the autopilot to make corrective maneuvers faster, we won't even need another flight test for those aerocaptures; just some more ground work. Indeed, his cheerleading for this technology was one of the major pieces of news at the COMPLEX meeting, and seemed to effectively change the minds of the assembled members.

The document for simulation tests for a Neptune orbiter -- of which there were 2000 -- is at http://library-dspace.larc.nasa.gov/dspace...a-2004-4955.pdf . That for tests for the easier Titan orbit aerocapture is at http://www.inspacepropulsion.com/tech/pubs...Performance.pdf .

Amazing findings. Seems 'banking' the craft during the decel is the preferred technique. I thought perhaps pitch manuvers (or a combination of both) would be used. The banking technique seems (roughly) analogous to the hypersonic manuveurs the shuttle employs during earth atmosphere re-entry.

The banking technique would have obvious utility in expanding the cross range deflection for a lander type mission (at Titan, Triton, or Pluto).

Appreciate very much the information, it sure whets the appetite for future missions. Weird it may be easier to land on Pluto than Mercury . . . .

An excuse to post in the oh-so-obscure Uranus Orbiter thread!

----------

Uranus Pre-Equinox Workshop - First Announcement

2-3 May 2006, Pasadena, CA

Purpose: To ensure a comprehensive collection of Uranus System
Equinoctial observations, by gathering the community of Uranus system
observers, modelers, theorists, and lab experimentalists prior to
the 2007 equinox to coordinate both observations and analyses.

Who Should Attend: Those scientists planning either to make observations
of the Uranus system at equinox (including the atmosphere, rings,
and satellites), or to conduct theoretical and/or laboratory work
specifically pertinent to the Uranus system at equinox.

Date and Location: The meeting's timing and venue, 2-3 May 2006
in Pasadena CA, were selected to dovetail with the OPAG meeting on
the following two days, in order to minimize extra travel.

Next step if interested: Send email confirming your interest to
Heidi B. Hammel (...) with "uranus workshop" in the
subject line, and please indicate in the body of the message
the particular aspect(s) of the Uranus system you plan to study.
A second notice (and preliminary agenda) will be distributed in
late February.

Note: the primary purpose of THIS workshop is coordination and
facilitation of equinox observations and analyses, not review of
current science results. Some of us are considering hosting a
pre-DPS workshop to focus specifically on current atmospheric studies,
and similar workshops could be envisioned for other sub-fields.

It certainly is -- far easier. In fact, it takes considerably less delta-v to get a direct flight to Pluto than a direct flight to Mercury. It would take less delta-v to get a powered descent to Pluto's surface, and it just may be desirable to use that thin atmosphere to help more.

Dismissing the Sun, Mercury is the hardest place to fly to in terms of delta-v, and it has no atmosphere to help with a landing, so in two out of three categories, it is the hardest place to land. Among solid bodies, it ranks in escape velocity only behind the other three terrestrial planets, and so only Mars rivals it in terms of difficulty.

Not only is Pluto easier than Mercury -- they're near opposite ends of the spectrum!

Time to re-start this thread. Thanks to Cassini, we now have a better idea
of the diversity of all of the non-Titan moons of Saturn. This makes me feel that
an Uranus Orbiter should be flown before a Neptune Orbiter. Uranus is "only"
2 billion miles away, instead of Neptune's 3 billion. No matter which method one takes
to get there, the travel time will always be shorter to Uranus.

Also, for the meteorologists, the atmospheres of Uranus and Neptune are very
similar, except that Uranus is easier to get to.

Triton has always been thrown in as an extra Neptune bonus. It is a fascinating moon, I
must admit. However, as mentioned above, Cassini has shown us that even the smaller
icy moons of Saturn show complexity, perhaps even including zones of liquid water, e.g.,
Enceladus.

Uranus has 5 mid-size icy moons, with interesting possibilities for several of them.
We all know of Miranda's strange surface (Miranda is about the size of Enceladus)
The other 4 moons are in the size range of Dione and Rhea, which Cassini has shown are
more complex than Voyager led us to believe.
In fact, take a look at an image of Ariel and you will be reminded of recent views of
Dione's cracked and fractured surface.


My vote is for an Uranus Orbiter first.

Another Phil

Let's not forget that at Neptune Triton would also be used for orbital plane changes. For Uranus, lacking a big moon, that would take a lot of fuel.

I refer you to some of the earlier posts in this thread, particularly #5, in which a paper,
entitled, "Feasibility of a Galileo-Style Tour of the Uranian Satellites," is referenced.
Because of the similarities in the planet/satelite ratios in the Jupiter and Uranus systems,
a spacecraft could execute quite the tour of Uranus' moons. In fact, the paper proposes
a 2-year mission that involves 40 flybys (!), ending with insertion into an orbit about
the moon Ariel.


Here is a link to a good view of Ariel. Doesn't it call to mind Dione and Enceladus?
Is Ariel hiding an ocean, or perhaps a lake, of liquid water?


http://www.solarviews.com/raw/uranus/ariel3.jpg


Another Phil

I stand corrected. I just wasn't following this thread 18 months ago....
Bruce's articles on SpaceBlogger.com kind of renewed my interest in outer planets exploration and I have the bad habit of catching up with threads starting with the last post.

Apparently the big reason to prefer Neptune to Uranus, given that you could only do one in a ten (or twenty) year period was that by the time you got to Uranus, it'd be tilted on the side just as it had been for Voyager, ~40 years before. (Although, technically, it'd be the OTHER side.) Accordingly, they'd rather wait an extra 20 years and try to visit it at the next Uranian equinox. Maybe by my 100th birthday in 2058.

Pity is, if Alan could have sent NH2 there, it'd have got there at the Equinox -- more or less.

--Greg

They're made of the same stuff, and their gross dynamics are similar, but Neptune shows those huge cyclones which Uranus never has.

http://lasp.colorado.edu/~bagenal/3720/CLA...ntPlanets3.html

I agree that Uranus's larger satellites are made more interesting by forming a class with Saturn's midsize satellites. It would be interesting to see them upclose and from all angles.

Triton, though, is an understated "star". It has geysers being blown in the wind. Only Venus and Titan might match that doubly-impressive dynamism.

I don't think the gravity assist factor is all that important. Seeing what impressive results came from the single Voyager 2 trajectory, which was constrained by the need to get to Neptune, I think even a random orbit through the small Uranian system would produce some pretty good imaging of all of the satellites in time. The early tour could accomplish the satellite flybys, then a propulsive manuever at apoapsis could tilt the orbit to get some looks at the rings and the Uranian poles.

The other attraction of Triton is, of course, that it is almost definitely a captured KBO. A Neptune orbiter would give you both a good look into the satellite system of an ice giant *and* an opportunity to study what may well be a prototypical KBO.

For my money, though, I think we need to wait for the next major breakthrough in propulsion technology. Then we may be able to launch an unmanned probe to *both* Uranus and Neptune -- and even have a chance of letting all of us see the data in our lifetimes!

-the other Doug

I think in bulk composition, perhaps, Triton is a prototypical KBO, but its got a history (and present) of tides that only one character in the neighborhood can churn up, and that character is Neptune. It's almost a thousand times the mass of anything else out there.

It may be that massive impacts or tight coorbital situations (like Pluto-Charon) may have melted the odd KBO or two, but Triton's probably pretty damned irregular by now, however it may have begun.

Pluto may be pretty irregular itself, being a tidally-locked world with a curiously patchy surface. And of course Triton and Pluto are both on the larger end of KBOs. Charon may be more like a typical KBO than either of them. Really, the post-Pluto encounter(s) by NH will be most important for a chance of truly seeing an ordinary KBO.

Actually, there was a recent update in Science about a presentation at the LPSC:

http://www.sciencemag.org/cgi/content/summ...ourcetype=HWCIT

Basically, someone sat down and did all the calculations for a large KBO, 1200 km, and found that with differentiation and a little ammonia anti-freeze that the KBO would retain a deep liquid ocean below the crust until present day. This could explain why some KBOs are bright, since any cracking would release water to the surface.

A couple of random thoughts in favour of Neptune over Uranus (some already stated):

(1) Triton is a wickedly bizarre object worth a mission on its own.
(2) More atmospheric activity on Neptune.
(3) Nereid: captured, or scattered by Triton? If it's scattered, that's *very* interesting.
(4) Is Proteus primordial, or debris that assembled after Triton spoiled the fun?

And in favour of Uranus over Neptune:

(1) More large moons to study. Even Oberon may turn out interesting
(2) Miranda: a currently-dormant Enceladus?
(3) Small inner satellites: how stable are their orbits? Do they hit each other from time to time as has been hypothesized?
(4) Is Ariel still active, even at a "Dione level"?

In favour of both: How the heck did those magnetic dipole fields get tilted over at such crazy angles and displaced from the planets' centres? Something *weird* is going on inside those ice giants, and from a science perspective, at Uranus this could be the single most interesting thing to find out.

But of course, it's going to be Neptune, not Uranus, because no politician is ever going to publicly support a mission that is going to get laughed at on the Tonight Show. If we want that to change, then we'd better think of a different name for Uranus. They shoulda named it Minerva or Apollo or something.

Don't forget that both of them have ring systems - radically different from each other and from those of Saturn. Either one would teach us a lot.

And don't forget Neptune's second largest moon Proteus. It is larger than Mimas but still more or less irregular. Has it always been so?

We know so little about both of the planets so any mission to them would be scientifically very useful.

Just the huge number of fast-moving inner satellites means that a close-in orbiter is always going to have something to look at.



No American politican, I guess you mean. Happily, there are other countries which don't base policy on stupid puns (in somebody else's language).



They did name it something different. "Georgium Sidus"...

What about building two identical probes and launching one to Uranus and the second to Neptune? It will certainly lower the cost of the missions. And if we launch them at appropriate times, we can have the same team working on both projects - first on Uranus Orbiter and later on Neptune Orbiter.

Sounds great! You paying?

Seriously - that'd be an ideal way to do it - but if they can't find money to do one of them, they're not going to be able to find the money to do both.

Doug

A mothership with a bunch of micro-landers would be great. I wish Cassini had a few. Imagine dropping one into an Enceledan geyser!