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Posted by: Myran Oct 27 2006, 11:09 PM

The weather of Uranus gets more interesting when Uranus turns the northen hemisphere towards the Sun.

There was some suggestions that Uranus was in a calm phase when Voyager 2 flew by. Even though the contrast have been enhanced, the image from Hubble suggest that it might very well have been the case.

http://hubblesite.org/newscenter/archive/releases/2006/47/

Posted by: RichardLeis Oct 28 2006, 08:29 AM

So little we still do not know about the other planets. Is the dark spot a clearing in the atmosphere or an upwelling of material?

Posted by: SigurRosFan Oct 28 2006, 02:56 PM

There's another thread:

- http://www.unmannedspaceflight.com/index.php?showtopic=3261

Posted by: um3k Oct 28 2006, 04:30 PM

When will Uranus realize that as long as it keeps pulling stunts like this it will never stop being the butt of crude, immature jokes?

Posted by: nprev Oct 28 2006, 05:16 PM

Well, it's a mature planet; I'm sure that it's put all this foolishness behind it...

Still, it sure is interesting how the atmospheric transparency seems to be increasing. We REALLY need a long-lived orbiter there with multispectral optics and a radar "sounder" to monitor these changes. Beginning to wonder what kind of organic chemistry might be going on; the other gas giants do not experience such dynamic, global alterations in atmospheric properties, at least not since we've been able to make detailed observations.

Posted by: tasp Oct 28 2006, 05:24 PM

Alex Blackwell posted a while back that he saw a paper that shows a Galileo style orbital tour of the Uranian system is possible.

A long lived orbiter would certainly seem justified for such an interesting planet and family of moons. Imagine zipping past Umbriel at less than 100km altitude . . . .

Posted by: David Oct 29 2006, 12:12 AM

Hurrah, at least I'm not the only person who thinks that. Just one of a very few, alas...

Posted by: nprev Oct 29 2006, 01:53 AM

Yeah, David, I don't really get why Uranus & Neptune don't get a bit more buzz as far as future missions. They are both unquestionably fascinating places with a lot to tell us about the history of the Solar System, especially given the oddities each possesses (Uranus' axial tilt & Miranda, Triton, etc.)

Anybody have a good reason why U&N are off the radar screen all the time? Is it just the fact that they're quite remote, or could it also be that they are thought of as "twins"?

Posted by: karolp Oct 29 2006, 12:21 PM

Being so remote, they will probably be considered when it comes to demonstrating some kind of new propulsion, like nuclear-powered ion engine known from the cancelled project Prometheus. Announcing a "mission to planet Uranus" would make most senators giggle and reaching the planet after a decade is still a major turnoff especially that it already HAS been visited unlike the object formerly known as planet Pluto :-) So I guess a Galileo-like mission is too much of a "re-run" to be considered for funding.

As for the reasons to go there - a few years ago I read a book "Moons of the Outer Planets". The authors were trying to show what could be discovered in the years to come based on the questions raised by Voyager data. They thought Enceladus could prove to be active based on its geomorphology - there you have it. They also considered present geologic activity on ARIEL. So if Ariel is a kind of a larger version of Enceladus, then it is certainly worth going there. But on the other hand many icy bodies seem quite similar to one another and nowadays geysers and underground oceans are even supposed to exitst on Pluto...

Posted by: nprev Oct 29 2006, 04:20 PM

Yeah, those all sound plausible, karolp. Still, I'm sure that there are Jupiter-assisted trajectory opportunities at least every 12 years or so, which should make conventional propulsion still a feasible option.

But, selling the mission on its scientific merits indeed might be a challenge. Aside from all the stupid Uranus jokes (okay, I like them, too! ), it's true that some in Congress would view it as a rerun because of Voyager 2. It's been done before, though; witness Galileo & Cassini.

Hmm...Maybe, just maybe it could be sold as part of an integrated, progressive outer system exploration strategy, because there are clear precedents. Fly-bys followed by orbiters followed by landers has been the core US UMSF methodology since the beginning. Every universally recognized major planet (I'm not Pluto-hatin', here, just stating a fact) has had at least one fly-by; every planet from Mercury to Saturn has had (or is about to have) at least one orbiter mission. Therefore, it's time to send orbiters to Uranus and Neptune.

Heck, they even have ready-made names: Herschel & LeVerrier, and we can call the Triton lander Lassell. All we need now is a couple of billion bucks... Seriously, though, maybe Emily can help out. Any chance that TPS would be interested in lobbying for U&N missions?

Posted by: TritonAntares Oct 29 2006, 06:12 PM

Hi,
I once read an article about a possible New Horizons II mission to Uranus (launch in 2008/09),
here 2 illustrations I downloaded from it:

Don't know exactly what happened to this idea?
It has probably been turned down due to funding reasons or the lack of RTGs as propellant material.

I remember Jupiter to be in a useful swing-by-position for Uranus or Neptun only until 2010.
There was an alternative chance to reach Triton in 2023 and a larger KBO in 2029 with a launch in 2012,
without passing Jupiter of course.

Who knows more?

Bye.

Posted by: nprev Oct 29 2006, 06:43 PM

Neat...wish it would've happened. Way too late now...

Still not an orbiter, though, and I really think it's time to add U&N orbiters (with a Triton lander for the latter) as Flagship missions in the NASA planning queue. Looks like the next favorable launch windows won't open until the 2020s, so now is the time to get things rolling!

One nice selling point is that Herschel & LeVerrier could be almost identical, save for the lander support infrastructure on the latter...although if Herschel carried a lander for Ariel or Miranda then they'd be identical all the way. Also, I would be surprised if ESA couldn't be persuaded to participate al a Cassini/Huygens; after all, U&N were European discoveries.

One other quick note: Recommend that the lander(s) utilize a variant of the Pathfinder/MER EDL system sans parachutes; this has been well established as an effective way to safely reach rough terrain, and we have no idea at all how bad the surfaces of U&N's target moons might be...

Posted by: TritonAntares Oct 29 2006, 10:51 PM

Some additional informations should be in this thread:
http://www.unmannedspaceflight.com/index.php?showtopic=715

Here a presentation:
http://www.boulder.swri.edu/pkb/NH2_community_info.ppt

I must read this now...

Posted by: nprev Oct 30 2006, 01:15 AM

Thanks, TA...well done...I was unaware of this previous thread.

I understand the political undercurrents that ultimately undercut NH2 now. Alan Stern's comment that he was amazed at how many of his colleagues wanted "the ultimate mission" or nothing was revealing...okay, then...Herschel & LeVerrier need to be "ultimate missions"!

Let's build a wish list. Please flesh out the payload instrumentation based on the following root platforms:

1. Orbiters with multispectral imaging/sounding capabilities (X-band radar through UV).
2. Landers for one each selected moon per planet utilizing a variant of the Pathfinder/MER EDL system.

Posted by: tasp Oct 30 2006, 02:55 AM

Perhaps a lander carried on a Uranian orbiter for one of the moons wouldn't have a firm target till after a few close flybys had been made.

Titania, Ariel or Miranda might warrant a close look before commiting the lander to a specific target.

Posted by: JRehling Oct 30 2006, 05:52 AM

The ideal time to arrive at Uranus would be near equinox. One is happening about now, and it's obviously too late for that. The next one is in 42 years. Put some pennies in the piggybank for a 2035ish launch.

A next-best arrival time might be when the anti-Voyager 2 hemispheres are in the light (to "finish" the coverage)... the next such solstice is in 20 some years (with lots of leeway for off-goal-but-OK illumination conditions). That's not going to happen (with NH2 being a dead possibility), and the next one after that is in 66 or so years.

For the satellites, obviously nothing short of close-up observations will do much justice to them. Uranus itself, though, is a decent target for Hubble and its successors.

This spot is a cyclone or anticyclone -- whichever it is would determine something about why the spot is dark, but that would seem to be a mystery for now. It has to be one of the two

Posted by: TritonAntares Oct 30 2006, 09:39 AM

Hi again!

That'll be probably the reason why we won't see a launch of a Uranus-orbiter-mission in say the next 40 to 45 years.
New inventions in propulsion systems will hopefully offer us a variety of capabilities to send and maintain an orbiter at Uranus then.
Maybe there could be 5 landers for the large moons on a platform or 2 corresponding missions -
one with such landers and another with a long surviving (21 years) orbiter.

Neptune and of course Triton for me seem to be the more rational targets.
There's no illumination problem like in the Uranian system - I'm still aware of Triton's 'chaotic' retrograde orbit!
But Neptun could be reached roughly every 12 years by a Jupiter swing-by with a launch window of 1-2 years.

Mission goals are clearly fixed - observation of Neptune itself and full cartography/remote sensing of Triton over years -
maybe for 1-3 decades, depending on the RTGs.
'Neptuneshine' should help on imaging Triton's dark hemisphere.
A Triton lander should be on board if manageable at this cold temperatures!
The rest few percent of the mission should aim at 340 km small Nereide (maybe like Phoebe at the begin of the mission)
and the other small satellites, most interesting here is 440×416×404 km large Proteus.

Bye.

Posted by: edstrick Oct 30 2006, 11:34 AM

A Cassini class Uranus orbiter, even if it arrived at the solstice, would be able to image about 3/4 of each moon, using Uranus-shine on the solstice-night "quartisphere" that faces the planet.

I'm almost inclined to think it's simply not worth the effort to go back to Uranus, except on a probe-carrying "new frontiers" class mission, unless we fly a nuclear electric vehicle that can rendezvous and polar orbit each of the 5 major moons. Lidar from polar orbit would be able to image the entire surfaces as was done for Mars with Global Surveyor's lidar. A Multi-beam lidar and a radar scatterometer would be able to do a bang-up job on the moons, even the in-dark areas. We don't have to composition image the entire surface, though it would be nice.

Posted by: JRehling Oct 30 2006, 03:59 PM

Sooner or later, Uranus will be lined up for an opportunistic flyby mission en route to some KBO or other. There seemed to be a possible Jupiter-Uranus-Sedna trajectory according to my imprecise eyeballing of things. At some point, I think, we'll want to launch a fast flyby mission of some outer KBO and the added science of a Uranus flyby could be the tiebreaker in choosing which KBO is the target. I think the Uranus flyby could also accelerate the craft a bit more than the Jupiter flyby alone, as an added bonus.

Posted by: Rob Pinnegar Oct 31 2006, 03:40 PM

Wouldn't the solstice be the worst time?

Away from the solstices, each moon's rotation allows us to see more than half of its surface. At a solstice, we get the minimum -- half, and always the same half. (For the purpose of this argument I'm simplifying things by assuming Uranus' inclination is 90 degrees to a first approximation.) There's probably a 1/2(1+cos 2 theta) term in the math here, but I won't dwell on that.

Basically the worst time to launch a Uranus orbiter would be the date that gets the orbiter to Uranus a year or two before a solstice (i.e. right about now). Assuming a Cassini-like tour, after four years, you'd have seen the same parts of the moons over and over again (plus whatever could be gotten from Uranus-shine, as has been pointed out above). At least if you arrived right at the solstice, after four years you'd be able to see down to about 20 degrees latitude in the unseen hemisphere by the end. That's a lot of territory.

Even halfway between a solstice and an equinox, you can still see about 85% of each moon's surface. That's not too bad at all, and it's not even a particularly good scenario.

Posted by: ngunn Oct 31 2006, 04:10 PM

I've already advocated (some will say ad nauseam) a modest but very long-lived Titan orbiter to monitor seasonal and other secular changes on that world over decadal timescales. It strikes me that the Uranian system is another place where a similar approach might be appropriate. I'm thinking of a fully automatic imaging system that just goes on faithfully recording data for a century or so and which can be interrogated from time to time by more powerful fly-by craft on their way to the KB or beyond - a sort of long term weather-watch for the planet with the most extreme seasons. Of course this doesn't fit in with our current concept of a 'space mission' started and finished (usually) by the same team of scientists. It also has no category in space agency budget allocation, and no viable power source to date. All the same perhaps it's worth thinking about how it could be done.

Posted by: JRehling Oct 31 2006, 07:00 PM

I should have been clearer.

A solstice (the correct, ie, anti-Voyager 2 solstice) would be the best time for a flyby: Voyager 2 saw one hemisphere of each moon. A flyby at the other solstice would see the other hemisphere. An equinox flyby would only show us half of each unseen half -- at closest approach, anyway.

A little before equinox would be best for an orbiter.

Posted by: alan Oct 31 2006, 10:40 PM

Would it be possible to do a mission at Uranus similar to Cassini or Galileo? I believe the moons are too small, less than 3% of the mass of Titan, to be used to significantly alter a spacecraft's orbit.

Posted by: Myran Nov 1 2006, 12:56 AM

With smaller moons it might still be possible if the flyby of each sattellite were correspondedly closer, in this case extremely close, but it certainly would be a cosmic billiard of a kind that havnt been attempted before. So I share your pessimism alan for that solution, less risky to simply let the orbiter carry more fuel.

Posted by: nprev Nov 1 2006, 05:24 AM

Oh yeah, no question about that: we'd want to design in as much flexibility as possible if for no other reason than that reflying the mission would not be a realistic option!

One big concern, though, would be availability of favorable intrauranian system trajectories to eject & safely deposit (& communicate with!) a lander. Seems like the constraints would be very significant, unless a HUGE amount of fuel is available to cope with late-breaking discoveries.

[EDIT] Here's a thought: Would an ion propulsion system like Deep Space 1 or a xenon/Hall Effect thruster system (both strictly intended for use in Uranian orbit) be desirable? Although such systems surely would increase the time required to do maneuvers, they conserve reaction mass quite well...

Posted by: edstrick Nov 2 2006, 10:21 AM

I've thought that one way to do certain types of missions, like a Uranus/KB fkyby or a Contour type mission is to build your entire spacecraft around a HiRise type camera and have all major instruments with pickoffs at the focal plane, like Hubble. You might have one "wide" angle, maybe 5 deg or something camera for close encounter observations when the motion blur is too great and you briefly get a range of phase and viewing angles you can't get from approach of flyout trajectories.

What would HiRise have gotten in terms of resolution at Uranus, if Voyager had had such a camera?

Posted by: ugordan Nov 2 2006, 11:52 AM

If I have my calculations right, here is a comparison of pixel sizes of Miranda the two cameras would have had on Jan 24, 1986 00:00 UTC:

http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=705&vbody=-32&month=1&day=24&year=1986&hour=00&minute=00&fovmul=1&rfov=0.42&bfov=30&porbs=0&showsc=1 --- http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=705&vbody=-32&month=1&day=24&year=1986&hour=00&minute=00&fovmul=1&rfov=0.04585&bfov=30&porbs=1&showsc=1

HiRISE has an IFOV about 9 times narrower than ISS NA. What I did was use the IFOVs of both cameras and multiplied it with 800 to get the window the Solar System Simulator uses. In case of ISS NA, the width of the window would be the same as the camera FOV, whereas in case of HiRISE it would comprise only a tiny fragment of the instrument FOV. Coupled with the fact CCDs are used nowadays, which have a far superior S/N ratio compared to vidicons, a HiRISE-type camera would bring a more than decent resolution increase.

Here's a not very illustrative closest approach comparison (around 30 000 km, assuming the ephemeris is correct):
http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=705&vbody=-32&month=1&day=24&year=1986&hour=17&minute=00&fovmul=1&rfov=0.42&bfov=30&porbs=0&showsc=1 --- http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=705&vbody=-32&month=1&day=24&year=1986&hour=17&minute=00&fovmul=1&rfov=0.04585&bfov=30&porbs=1&showsc=1

The HiRISE swath width would probably cover the majority of the visible disc at C/A, eliminating the need for a dedicated wide-angle camera. This, of course, is due to the fact it's a push-broom camera instead of a framing one and has a very large CCD array. I'm not sure how useful it would be in case you're not in a circular orbit around the target so complex slews would need to be done.

Posted by: edstrick Nov 2 2006, 12:12 PM

A HiRise type detector system would probably be a bad idea that far out at those low light levels. You probably want a framing camera with a mechanical shutter and filter wheel. Something like a small version of one of Hubble's cameras, in effect.

But the basic point is that you can get detailed global mapping and real mineralogical mapping during late far-encounter observations where a Voyager or a Stardust class camera system could only get gross morphology. And get that good quality data on ALL of the main moons and inner moons, unlike the "just barely see general geology" quality of imaging of Oberon and Umbriel from the best possible flyby trajectory they could get.

Posted by: tasp Nov 2 2006, 02:06 PM

Alex Blackwell a while back posted an abstract from a report that shows a Cassini or Galileo style orbital tour of Uranus is possible. The Uranus system is almost a perfectly scaled down version of the Jupiter system.

4 of the moons are sufficiently massive (Ariel, Umbriel, Titania, and Oberon) to alter a spacecraft trajectory sufficiently to encounter a different moon on the next orbit. Some of the flyby altitudes are under 50 kilometers!

IIRC, about the only major hassle was that the plane of the initial orbit for the craft won't be correct for the majority of the time for Uranus. The inclination of the orbiter can be changed, but it takes time.

The out of plane portion of the mission would be advantageous for studies of the Uranian magnetsphere, however.

Posted by: ugordan Nov 2 2006, 02:22 PM

That looks like a nontrivial issue given how far Uranus is and navigation uncertainties involved. While navigators these days are clearly able to fly a space probe through a keyhole, Uranus is quite far away and <50 km flybys are a bit on the low side. I still get the chills remembering Cassini will zoom some 30 km (?) above Enceladus.
I don't have access to the full http://www.unmannedspaceflight.com/index.php?s=&showtopic=1662&view=findpost&p=26445 to find out what the predicted 3-sigma delivery errors would be. I guess something on the order of 10 km wouldn't be unreasonable.

Posted by: tasp Nov 2 2006, 03:59 PM

Alex sent me a copy of the whole report. Fascinating (at least the parts I understood). I would forward it to you, but I printed it off, and then I have had 2 hard drive replacements since, so it is not in my PC anymore.

If Alex would be so kind as to send you one too . . . .


I found the orbital tour so elegant and compelling, it would certainly be a shame not to fly the mission.