Uranus Orbiter, The other proposed ice-giant mission Options

[Rob Pinnegar]

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.

[tasp]

The Galileo style tour of the Uranian system is quite exciting. With the 'scale' being smaller, the mission generates very close encounters of Ariel, Miranda, Titania and Oberon in fairly a fairly short time interval.

Additionally, with even Oberon being less than (IIRC) 600,000 miles out from Uranus, you are having virtually continuous (well, not quite) reasonably close encounters with non-targeted moons on each orbit.

With the (IMO) near certainty of ongoing geological process on Ariel, and a good chance perhaps for Titania, too, a Uranus orbiter is looking like a pretty useful mission.

Our understanding of these smaller bodies grows synergistically with each one we study.

To learn more about the 'Enceladus phenomena', study Ariel.

And possibily, to learn more about Cassini Regio, study Umbriel.


A Uranus orbiter mission is a lot of bang for the buck.

[JRehling]

I think one difficulty owing to the no-big-moon situation would be lifting the orbit out of the equatorial plane to get a good look at the rings. If the whole mission were spent in the equatorial plane, the rings would be very hard to study. Whereas if the mission were spent in an inclined orbit, satellite flybys would be severely limited. Either some fuel or a Titania boost would be needed to get the UO out of the equatorial plane on one pass, beginning a period of ring observations, and then back down there afterwards.

We could start a pool on which will happen first: a Uranus Orbiter mission or D.C. statehood.

[JRehling]

Another consideration, a happy one, is that for the biggest target in the uranian system, namely Uranus, there is a considerable and growing ability to monitor it telescopically from Earth at almost all times. Percentagewise, its distance from Earth is almost invariant. Excepting brief blackouts at solar conjunction, it is technically feasible to snap a multispectral image of Uranus practically *hourly* for years at a time.

Some images released in the press just a month back:

http://www.berkeley.edu/news/media/release...gcrossing.shtml

And from 2004:

http://www.newscientist.com/data/images/ns...n6657-1_370.jpg

The rings can also receive some useful studies from Earth. Obviously, the satellites cannot be resolved in any interesting way, so the scientific value of a UO mission depends most crucially on them. Since Miranda was wonderfully imaged (though only partially) by Voyager 2, the focus narrows even more.

In my mind, one of the key elements of interest in the uranian system is for us to have the contrast between many worlds of similar size that have nonetheless evolved differently. In the size range of 300 km to 1600 km, the Saturn and Uranus systems combine to give us 13 examples, all with approximately similar bulk composition and similarly low temperatures. Whereas the obvious view of exploration is that the unique places (like Io, Mars) deserve the most attention, you actually learn key things about the dynamics of planetary evolution by finding places that seem to have had similar initial conditions, but diverged. A good look at the uranian satellites would give us a pretty dense sample(s) of similar-sized worlds. At the top end of that group, there is a quartet: Rhea, Iapetus, Titania, and Oberon of almost identical size, and yet none of them look alike. There's really no opportunity in the solar system, except in the Kuiper Belt or among much smaller and less evolved worlds, to see a contrasting set of four worlds the same size and same bulk composition. (Since Mercury isn't made of the same stuff as Ganymede, Callisto, and Titan.)

None of this changes the fact that we'll have to wait a long time to get that next look at them. The main question is which multiple of 42 years we'll have to wait. (Alternate, worse possibility -- a flyby at an anti-Voyager solstice.)