PDA

View Full Version : Newbie Q about Jupiter



NoXion
2004-May-14, 11:28 AM
Would it be possible to build floating structures above the clouds of Jupiter? (Or any other gas giant for that matter)

PS I've heard of something called a Roche Limit, within which moons get crushed into itty bitty bits of rock, but on the other hand, a probe whose name I can't remember right now didn't get crushed until it was sometime below the clouds...

Wally
2004-May-14, 12:00 PM
You mean place something in orbit? Sure! It'd have to withstand a tremendous amount of radiation, etc.

And the Roche limit only applies to massive bodies, such as moons, etc. It doesn't come into play with small things, like man-made satellites.

NoXion
2004-May-14, 12:18 PM
You mean place something in orbit? Sure! It'd have to withstand a tremendous amount of radiation, etc.

No, I mean actually above the clouds of Jupiter, like an airplane is above the clouds of earth, to collect gasses from the planet.


And the Roche limit only applies to massive bodies, such as moons, etc. It doesn't come into play with small things, like man-made satellites.

How big does an object have to be before it experience the effects of the Roche Limit?

Wally
2004-May-14, 12:24 PM
Oh. My mistake on the first question. I'll defer to someone with more knowledge on the matter. . .

as for the second, there's probably some formula out there to figure it out, but what it comes down to is if the body in question is large enough, then the tidal forces on the side nearer to the planet differ so much from those on the far side, that the body is literally ripped apart. If an object is small enough, the tidal forces will not differ enough to do the ripping apart thing.

Moose
2004-May-14, 12:38 PM
You mean place something in orbit? Sure! It'd have to withstand a tremendous amount of radiation, etc.

No, I mean actually above the clouds of Jupiter, like an airplane is above the clouds of earth, to collect gasses from the planet.


There was a book in one of the more "recent" (around 1995, IIRC) TSR Buck Rogers series that suggested such an arrangement, a hydrogen collection station on Jupiter.

The comment about the radiation holds. You'll need to deal with it somehow.

As far as floating a city is concerned, you first need enough structural strength to withstand the violent winds and gravity. You need to maintain breathable atmosphere at a comfortable pressure, and withstand the differences in pressure outside from inside.

The city will maintain altitude under two conditions: either you propell it against the atmosphere to produce lift (like an airplane), or you make the station light enough to weigh less than the atmosphere it displaces (like a submarine or a helium balloon.)

I'm not sure the second is possible. What's less dense than hydrogen? Vacuum? You'd have to build huge (and I mean HUGE) rigid vacuum containers in order to displace enough hydrogen to offset the weight of the station (including lifting structures), residents, visitors, and all goods attached to the station.

Kaptain K
2004-May-14, 12:47 PM
What's less dense than hydrogen?
Hot hydrogen! 8)

Moose
2004-May-14, 01:09 PM
What's less dense than hydrogen?
Hot hydrogen! 8)

How hot (http://www.otr.com/hindenburg.html) did you want it? :o :P

[Edit: My first reaction was: "very small rocks?"]

ngc3314
2004-May-14, 06:27 PM
You mean place something in orbit? Sure! It'd have to withstand a tremendous amount of radiation, etc.

No, I mean actually above the clouds of Jupiter, like an airplane is above the clouds of earth, to collect gasses from the planet.


And the Roche limit only applies to massive bodies, such as moons, etc. It doesn't come into play with small things, like man-made satellites.

How big does an object have to be before it experience the effects of the Roche Limit?

It's not a size limit, but whether the object in question is held together only by gravity - in which case the Roche limit applies - or by additional forces. For spacecraft, these would include welds and bolts; for small moons, chemical forces - they have to be essentially single rocks (obviously formed somewhere else than their current environments.

No rubble-pile satellites allowed inside the Roche limit - we call the result of such a thing "rings".

Kaptain K
2004-May-14, 09:04 PM
What's less dense than hydrogen?
Hot hydrogen! 8)

How hot (http://www.otr.com/hindenburg.html) did you want it? :o :P

[Edit: My first reaction was: "very small rocks?"]
Yeah, but... That was hot hydrogen plus oxygen! A hot "air" balloon would be viable in the atmosphere of Jupiter, where the is no pesky oxygen around.

Bob
2004-May-14, 09:37 PM
"A Meeting with Medusa" by Arthur C. Clarke is an excellent novella describing a balloon-like probe exploring Jupiter's upper atmosphere with a human pilot aboard. Vintage Clarke.

Moose
2004-May-15, 03:00 PM
What's less dense than hydrogen?
Hot hydrogen! 8)

How hot (http://www.otr.com/hindenburg.html) did you want it? :o :P

[Edit: My first reaction was: "very small rocks?"]
Yeah, but... That was hot hydrogen plus oxygen! A hot "air" balloon would be viable in the atmosphere of Jupiter, where the is no pesky oxygen around.

The residents are breathing what again? :P

(Yes, I know, the inside of the station != the inside of the lifting chambers. It might be easier to deal with change-of-pressure hazards inherent in the alternative atmosphere: nitrogen. (like deep-sea divers).)

In any case, leaks and pressure-lock integrity (plus trimming for the weight changes of docking spacecraft) would be another significant challenge in creating such a station.

Mr. Milton Banana
2004-May-15, 08:23 PM
You mean place something in orbit? Sure! It'd have to withstand a tremendous amount of radiation, etc.

No, I mean actually above the clouds of Jupiter, like an airplane is above the clouds of earth, to collect gasses from the planet.


There was a book in one of the more "recent" (around 1995, IIRC) TSR Buck Rogers series that suggested such an arrangement, a hydrogen collection station on Jupiter.

The comment about the radiation holds. You'll need to deal with it somehow.

As far as floating a city is concerned, you first need enough structural strength to withstand the violent winds and gravity. You need to maintain breathable atmosphere at a comfortable pressure, and withstand the differences in pressure outside from inside.

The city will maintain altitude under two conditions: either you propell it against the atmosphere to produce lift (like an airplane), or you make the station light enough to weigh less than the atmosphere it displaces (like a submarine or a helium balloon.)

I'm not sure the second is possible. What's less dense than hydrogen? Vacuum? You'd have to build huge (and I mean HUGE) rigid vacuum containers in order to displace enough hydrogen to offset the weight of the station (including lifting structures), residents, visitors, and all goods attached to the station.

Moose, you forgot one BIG problem...

Thunderstorms.

As I've said before in past posts, Jupiter's thunderstorms can grow to 50 miles in height, and can reach 2,500 miles in diameter. Jupiter's lightning is 1,000 times more powerful than Earth's.

I'd imagine such violent thunderstorms-the most violent in the the solar system, with the exception of Saturn and probably Neptune-could develop quite rapidly. And let's not even get into the subject of how vicious tornadic activity could be in such storms. If you can't maneuver your floating station away from these violent storms, you're in for a heap of trouble.

[-X

NoXion
2004-May-17, 10:57 AM
Moose, you forgot one BIG problem...

Thunderstorms.

As I've said before in past posts, Jupiter's thunderstorms can grow to 50 miles in height, and can reach 2,500 miles in diameter. Jupiter's lightning is 1,000 times more powerful than Earth's.

I don't think lightning striking such a structure should matter any more than lightning striking an aircraft on earth.
(Something to do with not being earthed?...)

Crazieman
2004-May-17, 11:45 AM
You still have to address the biggest issue - radiation that would fry anyone in a literal instant.

Kaptain K
2004-May-17, 12:28 PM
You still have to address the biggest issue - radiation that would fry anyone in a literal instant.
In orbit around Jupiter (at least in certain orbits) - Yes!

In Jupiter's atmosphere - No!

Moose
2004-May-17, 01:20 PM
Moose, you forgot one BIG problem...

Thunderstorms.

As I've said before in past posts, Jupiter's thunderstorms can grow to 50 miles in height, and can reach 2,500 miles in diameter. Jupiter's lightning is 1,000 times more powerful than Earth's.

I don't think lightning striking such a structure should matter any more than lightning striking an aircraft on earth.
(Something to do with not being earthed?...)

The way I understand it, the outer (aluminium) fuselage of an aircraft passes the full current from a lightning strike in a way that it doesn't affect the aircraft's electronics, fuel, or passengers. I was once told you'll apparently see some scoring where the lightning arcs into and out of the metal.

It turned out to be an issue in the Apollo 12 launch, where the first stage of the Saturn V was damaged by a pair of lightning strikes.

I don't know what this means in terms of Jupiter's more intense storms. It could well be a showstopper. Maybe a station could be build so as to safely pass such a charge. I really couldn't say. The physics of electricity never was very intuitive for me.

Amadeus
2004-May-17, 01:25 PM
If you mean something like "Cloud City" in "Empire Strikes Back" Then I would recomend you have very long tubes going done into the atmosphere and park in orbit.

As for the radiation well enough shielding will sort that. Could you not use the radiation as a power source? It is energy after all.

The biggest question is it worth the money spent to set it up?

milli360
2004-May-17, 05:15 PM
PS I've heard of something called a Roche Limit, within which moons get crushed into itty bitty bits of rock, but on the other hand, a probe whose name I can't remember right now didn't get crushed until it was sometime below the clouds...
Yeah, it's the other way around--the Roche limit tears things apart by the tidal effect. It's not a function of the atmospheric pressure.

mike alexander
2004-May-17, 10:51 PM
Since density is a function of altitude you could use a rigid container and let it sink into the atmosphere until the increasing density provides neutral bouyancy.

See "Brake" by Poul Anderson.

eburacum45
2004-May-17, 11:56 PM
http://www.orionsarm.com/worlds/Ozymandias.jpg

The cloud cities of Ozymandias are supported by hot hydrogen or vacuum microspheres; each one perches at the top of an upwelling current, anchored by an adjustable sky-anchor on a long tether- the laminar flow of the atmosphere is surprisingly smooth most of the time, and the cities are quite comfortable.
All Ozymandians have radiodurans type chomosomes, proof against radiation- although they retire to the outermost moons to breed true.

Gullible Jones
2004-May-18, 12:16 AM
"A Meeting with Medusa" by Arthur C. Clarke is an excellent novella describing a balloon-like probe exploring Jupiter's upper atmosphere with a human pilot aboard. Vintage Clarke.

Yeah, that was a cool story. Though I really don't think that using a fusion ramjet in atmosphere is such a hot idea...

oynaz
2004-May-18, 10:04 AM
Here is a little thought-experiment.

If there was any reason to place a floating city in Jupiter's atmosphere, it could be done.

The only reason for placing anything big in Jupiter's atmosphere is for collecting hydrogen, and the only reason to collect hydrogen is to use it as fuel.
Following this logic, the city has virtually unlimited power at it's disposal.
The city would be held up by some kind of engines. Radiation could be shielded against, as weight is not an issue.

Or is my logic flawed?

Moose
2004-May-18, 01:34 PM
Following this logic, the city has virtually unlimited power at it's disposal.
The city would be held up by some kind of engines. Radiation could be shielded against, as weight is not an issue.

Or is my logic flawed?

Possibly. The real question is: can enough energy be produced from hydrogen to indefinitely hold aloft the weight* of the station and the weight of the equipment required to produce that energy?

(* "weight" is deliberately used here)

The answer will require maths beyond my ability to produce.

Another issue is maintainance. This is always-on must-never-ever-fail engineering. How much redundancy is necessary so as not to potentially lose the station to maintainance issues?