Uranus

Swampcat · Aug 21, 2007

"I think it's QUasi Autonomous Non-Governmental Organisation..." This is getting way off topic, but... If you read the wikipedia article I posted it gives several possibilities for the acronym. I didn't want to write all of them out...being lazy <img src="/images/icons/blush.gif" />. <div class="Discussion_UserSignature"> ------------------------------------------------------------------- "I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."Thomas Jefferson </div>

3488 · Aug 21, 2007

Our government is spending a fortune on these, tottaled up probably much more than the cost of a dedicated Uranus system mission (Orbiter, Atmospheric entry probe & perhaps a lander or two for the moons). Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

h2ouniverse · Aug 21, 2007

Thanks. Now I get it. Being a citizen of a country that provides for almost 10% of the World public money, where one people out of two is waged directly or indirectly with public money, and so three families out of 4 depend on public spending, I have nothing to say. It is just that on this side of the Channel we are so accustomed that nobody would even bother trying to hide it... There would not be any quango row [SORRY].

h2ouniverse · Aug 21, 2007

I hope we can have a Uranus mission for less than Â£170bn !!! By ESA standards I would say â‚¬1.5bn for an orbiter plus for $150Mn for US RTGs(*). Double that for an orbiter + an Oberon lander (two separate launches needed probably given huge delta-v). Regards. (*) and $10,000 of soporific gases for environmentalist protesters on launch day

jaxtraw · Aug 21, 2007

My practical rocketry knowledge is poor. I'm sitting here wondering what, with currently available technologies (i.e. no inventing nuclear boosters etc <img src="/images/icons/smile.gif" /> ) would be a practical configuration for such a mission. Considering one would want (a) a reasonable (i.e. fast) transfer to Uranus, and then (b) to stop there instead of flying past, requiring a significant delta-v at the Uranus end. Which means lots of fuel, so a big payload to send from this end at high speed. None of this waltzing around 25 other bodies to get there. <img src="/images/icons/smile.gif" /> Suppose we had say a billion pounds*- two billion dollars- floating around to pay for an orbiter and two smallish landers. Do-able? *that's about Â£17 per person in the UK, certainly less than Â£30 per taxpayer, hardly a king's ransom we're talking about here, a fraction of what we're squandering on the Olympic bunfest.

MeteorWayne · Aug 21, 2007

LOL, you hit on the tradeoff with interplanetary craft. Scenario 1 You want fast? OK sure, you cut your spacecraft weight by 75% and we can do it. Won't get much science, but you'll still have a job when the results come in. Scenario 2. You want WHAT weight spacecraft??? Man that science will be incredible, but the only way to do that is to use the billiard table of the solar system's masses to get there, i.e. long time. Is your kid interested in science? My $2.32 worth <img src="/images/icons/wink.gif" /> MW <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

Mee_n_Mac · Aug 21, 2007

An idea just occured to me, having read MW's post above, that seems like a possible solution (though no doubt would appear silly if I gave it more than a moments thought). Since we're having fun here why not use the EOR/LOR concepts but applied to interplantary vehicles. Send up a science package with it's booster and fuel to get it quickly to planet X. Do the same for a slowdown booster module and fuel module if you have to. Have them self assemble enroute to plantet X. Expensive ... sure. Difficult ... sure. Risky ... oh yeah. But I think do-able if we really, really wanted to get there fast. <div class="Discussion_UserSignature"> -----------------------------------------------------Ask not what your Forum Software can do do on you,Ask it to, please for the love of all that's Holy, STOP ! </div>

jaxtraw · Aug 21, 2007

Well, there's no need to be rude. I wasn't asking "most efficient within the budget allotted to this mission" kind of thing. Sorry. We got a decent sized spacecraft, and lander, in a reasonable amount of time, to Saturn, and stopped it when we got there. I'm just wondering how much bigger the rockets need to be to do the same at Uranus, sort of back-of-a-***-packet kind of a way, not costed down to the last nut and bolt.

MeteorWayne · Aug 21, 2007

"Well, there's no need to be rude" What??? Hey jaxtraw, you're interpretation that I was being rude is way off base! I was saying that you hit on the tradeoff that every mission has to ask. Craft mass vs. launch velocity. Every mission is a thousand tradeoffs. You give up this, you get that. You insist on this, you give up that in return. Speed, mass, power, cooling/heating.... Repeat and rinse, a thousand times. In the end, a mission hopefully is a good compromise between the tradeoffs, using the available money to the best benefit. Time vs science when you get there. You can have bigger rockets to slow down. But then, your spacecraft has to weigh 12 kilograms. Not 120. What is the best cost benefit ratio for the mission? <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

jaxtraw · Aug 21, 2007

Sorry for taking offense slightly, I misconstrued your LOL as laughing "at" rather than "with" <img src="/images/icons/smile.gif" />

MeteorWayne · Aug 22, 2007

Glad we cleared that up <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

3488 · Aug 24, 2007

A nice image of Uranus in May 2007, taken by the Hubble Space Telescope. This has been posted on the Uranus Ring Plane crossing thread, but have put this image here also as it is a recent view of the 7th planet. The oblateness of Uranus is clearly visible here, due to its rapid rotation of 17 hours & 54 minutes & its low density of 1.32 G/CM3. The atmosphere is approx: 83% Hydrogen, 15% Helium, & 2% Methane (in the lower troposphere), not to mention that it is the Methane that gives Uranus & Neptune their blue hues (absorbs red light, reflecting the blue). The 'fans' are not real as they are image artifacts, but the thin spikes are, they are the rings almost edge on. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

robnissen · Aug 25, 2007

We got a decent sized spacecraft, and lander, in a reasonable amount of time, to Saturn, and stopped it when we got there. The problem is that the mass of Uranus is only 1/8 of the mass of Saturn, so we either go 1/8 as fast or we have 8 times the engine once we get to Uranus. Uranus is about twice as far as Saturn, so if we go 1/8 as fast, for twice as far, and Cassini took 7 years to get to Saturn, then we are talking a mere 112 YEARS to Uranus (this may be a bit of an overstatement because Cassini took a circuitous couse to take advantage of gravity assits). Therefore, the only hope is to have a much larger rocket to use to slow the craft when we get to Uranus but those cost more and add more weight, so no matter how you slice it, an orbital mission to Uranus is very problematic.

3488 · Aug 25, 2007

I agree RobNissen. it is very problematic, but I think with lighter composites & more efficient electronics & smarter computers, a Uranus Orbiter may not be out of the question for too much longer. Cassini used 1990s technology, hence the large size & mass. A Uranus Orbiter could be a New Horizons type craft, much smaller & low mass, so using a powerful retrorocket & perhaps using Titania or Oberon could brake into orbit, after a trip that maybe would not have to last too long. A Neptune Orbiter would also be very desirable. However, I do think for these two, flybys are still more likely for the forseeable, although perhaps at a lower speed than Voyager 2 did. It was such a pity that New Horizons 2 was cancelled. A Uranus encounter in 2014 would have been a superb opportunity. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

jaxtraw · Aug 25, 2007

Can't we aerobrake in the upper atmosphere with a big f*&$-off ablative shield, or something?

3488 · Aug 25, 2007

That did occur to me. The only problem is to get a detailed denisty profile of the atmosphere of Uranus. Mind you, I think we got good data from Voyager 2 with the occultation experiment, showing it is very deep. Below diagram of density & temperature profile of the atmosphere of Uranus. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

Aetius · Aug 25, 2007

If the craft was designed to make many aerobraking passes, like the Mars orbiters are, I wonder if the onboard science package could provide enough meteorological data.

3488 · Aug 25, 2007

Hi aetius. Cannot see why not!!! This would present an opportunity to get some real science from the earliest stages. Perhaps several atmospheric probes could be dropped off???? Mutispectral imagers to image what is going on beneath that haze & magnetometers listening out for whistler waves from lightning. Great idea. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

Kalstang · Aug 26, 2007

I have a suggestion. Why not just aim a probe directly at the heart of Uranus? Like we did with the comet? <div class="Discussion_UserSignature"> I have an answer for everything...you may not like the answer or it may not satisfy your curiosity..but it will still be an answer. "Imagination is more important then Knowledge" ~Albert Einstien~ Guns dont kill people. People kill people.Solar System </div>

h2ouniverse · Aug 26, 2007

"Why not just aim a probe directly at the heart of Uranus" -------------- Some planetologists would love doing that. But they want to probe Saturn first (Kronos mission, 2 twin probes to be dropped by a mothership either flying by or orbiting). Jupiter has been probed by Galilieo (not very successfully, as the probe fell into a "hole" in the atmosphere, decreasing the learnings). By combining data they hope to get the composition of the primordial protostellar cloud that formed the Solar System. Uranus and Neptune would be interesting but less urgently for that particular objective. Doing that on Uranus would be easier than on Jupiter or Saturn since Uranus's gravity well is less steep, so the energy dissipated during aerocapture is lower. Note that although it would be within our current technological ability to have an entry probe, aerobraking to be captured into Uranus orbit is another kettle of fish. Indeed in the first case you "just" have to deploy parachutes when your speed is low enough and you are not very sensitive to the actual thickness of the upper atm layers. In the other you have to fully master the altitudes and densities of the atmosphere otherwise you will either escape out of Uranus grav well (underbraking) or plunge into Uranus (overbraking). To me a major objective would be the supercritical ocean of water of Uranus, but unfortunately it is very deep, very hot, very high pressure... For now we envisage probes withstanding about 20 bars max... With Uranus though, the 20 bars area is supposed to be quite close to ambient temperatures. Interesting if there are droplets of water. Best regards.

h2ouniverse · Aug 26, 2007

Aetiut, In reply to: "If the craft was designed to make many aerobraking passes" ---------------- mmm. I wonder whether that would work on Uranus. I think the idea of detaching microprobes from the mothership to get data is quite good. Another possibility would be to have an on-board commanded variable shield section. Easier said than done given the huge thermal load and the need to have a contiguous shield.

3488 · Aug 26, 2007

Hi Joel, Do you think that Uranus & Neptune have H20 rain clouds??? Yes the Supercritical water layer will be very deep down & under enourmous pressure of at least 19,000 Bars (19,000 times Earth's atmospheric pressure), both Uranus & Neptune. Under those pressures, the water would remain frozen at very high temperatures. IMO we cannot build an atmospheric entry craft that can survive that now. What what be interesting would be to parachute a craft into Uranus's atmosphere, parachute deploy in the stratosphere, to sample the very cold Hydrogen, Helium mix (about minus 220 Celsius / 53 Kelvin), than descend into Uranus's troposphere at the 100 millibar level, sample the methane haze, measure winds, rising temperatures & densities. Descend to the one bar level, where temperatures have risen to minus 195 Celsius / 78 Kelvin. By this point should be within the methane clouds. Two bar level, temperatures have risen to minus 175 Celsius / 98 Kelvin, three bar level, minus 158 Celsius / 115 Kelvin. At about the 15 bar level, temperatures will be about 0 Celsius / 273 Kelvin. Uranus is clearly much colder at these levels than Jupiter!!!!!!! It would be an interesting journey!!!! Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

Aetius · Aug 26, 2007

Could you describe a "variable shield section", and how it might be integrated into the bus of the spacecraft? The weather satellite microprobes seem like a great idea, by the way. I'd think that they would free up the primary imaging equipment on the mother ship, for the moon and ring science teams. I totally eat this stuff up. <img src="/images/icons/cool.gif" />

h2ouniverse · Aug 26, 2007

Hi Andrew, There might be rain clouds indeed in the 10-20bars layer IF the density of water is large enough. The point is that nobody knows because you just need small amounts to form clouds (on Earth few percents). It seems that the only thing we know about Uranus atm composition at that altitudes is that it is mainly H2. But that does not preclude H2O, especially if there are currents. (otherwise gravity will concentrate H2O more in depth). I think probing these "warm" layers of Uranus is doable with today's technology. With two big reservations however: * the transmission might require relays, for the cumulated attenuation from upper atm to 15 bars will be far larger than on Saturn (and it is already an issue for Saturn) * the winds velocities may be tremendous: until recently Uranus was thought far calmer than Neptune but apparently this vision is changing Best regards.

h2ouniverse · Aug 26, 2007

I would think of the microprobes as small items released from the mothership few weeks before the aerobraking (as posted by another poster on this thread), so that they enter the atm few days / hours before the aerobraking, giving time for a final boost on the mothership to adjust trajectory. As for the variable-section shield., unfortunately that is very difficult to achieve. What I meant was a "magical" shield, the section of which can be increased/decreased by command. In a concrete way, that would probably require flaps. But the hinges of those flaps would undergo such an aerthermal flux that they would probably be destroyed [with current technological status]. You might achieve that without mechanisms just by having a static but asymmetrical shell shape and by playing on the incidence in order to offer more or less cross section to the drag. Easier said than done since your profile will become aerodynamically unstable (sigh!)

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