Uranus Orbiter, The other proposed ice-giant mission Options

[Guest_BruceMoomaw_*]

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 .

[tasp]

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 . . . .

[vexgizmo]

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

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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.

[JRehling]

Weird it may be easier to land on Pluto than Mercury . . . .

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!

[PhilHorzempa]

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

[Cugel]

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.

[PhilHorzempa]

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

[Cugel]

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.

[Greg Hullender]

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

[JRehling]

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

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.

[dvandorn]

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

[JRehling]

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.
-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.

[hendric]

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.

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.

[Rob Pinnegar]

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.

[jsheff]

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.