Jupiter Balloon Options

[nprev]

Just out of curiosity, has anyone ever done a study on putting a balloon in Jupiter's atmosphere? I think it would be fascinating and potentially quite scientifically valuable to have such a vehicle drift around the planet at the 1-bar level or so, acquiring meteorological data and even imagery, perhaps also equipped with a radar sounder to glean some data about what's going on far deeper.

(And, yes, I'm channeling Clarke's Meeting with Medusa... )

[ugordan]

IIRC, someone once brought up the fact Jupiter's atmosphere is mainly hydrogen, the lightest gas there is. It wouldn't be trivial to produce a balloon with enough buoyancy to sustain an instrument package. Probably heated "air" balloons would be the only way to go. The question is how hot does the hydrogen have to get for a modest size balloon volume?

[nprev]

Good point. Gonna take a WAG here, but if you're looking at an isothermal air column then the deeper you go, the denser it gets, and therefore the less heat is needed. Of course, Jupiter's atmosphere is NOT isothermal and generally the deeper you go the warmer it gets, which would increase the amount of heat needed for the balloon to maintain buoyancy. There might be some favorable transitional temperature areas near, say, the tropopause, but have no idea what the ambient pressure is there.

Really silly idea follows that may well get me laughed right off the forum: What about a "hard" balloon? What I'm thinking of here is something like a carbon-fiber composite 'buoy' pressurized appropriately with hydrogen during the descent (at something like 0.5 bars), completely enclosed, with an internal heater to vary the container's ambient internal density for altitude control. Maybe maritime-analog systems like this are worth considering.

Okay, you may laugh now...

[ElkGroveDan]

I know what you are doing Nick. You are sitting around bored silly because of the pounding rain, and now that you've read all the recent posts you are coming up with wild ideas to pass the time.

Meanwhile the storm has given me enough work to do.

[nprev]

Busted... , and, holy crap, Dan!!! Hope this was the only damage you sustained; sure as hell is more then enough!

The rain's pretty much over down here. Actually, I'm sitting around waiting for the cable guy; my box decided that it was a good day to die back on Wednesday.

[JRehling]

It's an interest exercise in material science to determine if a "vacuum balloon" could work for any material and any radius. My hunch says no.

About as silly: sustain a gas of monoatomic hydrogen (which is unstable) and fill the balloon with that, achieving half the density of diatomic molecular hydrogen.

Even with hot "air", you still have very little buoyancy, since the molecular weight is so low. In fact, even with a vacuum "in" the balloon, you would have a lot less buoyancy on Jupiter than you would with, say, a neon balloon on Earth.

I think a light glider might be a better way to go, and see if you can get a mission to last some tens of hours. My guess is that the turbulence would spoil any dreams of a nice long smooth scientific cruise.

Note that things are even worse on Saturn (with more hydrogen) but somewhat better for Uranus and Neptune, where the helium abundances are higher, and there's some methane to boot. The easiest place to float a balloon in a gas giant would actually be Uranus.

[nprev]

I think it would work, but it might not be at the desired atmospheric density depending on the container weight/materials used. Could be that the lightest, strongest vacuum balloon we could build would only achieve static buoyancy at, say, 200 bars ambient, which in turn still might crush the container to say nothing of completely screwing up instruments, bus hardware, etc.

Definitely agree that it's an interesting problem in material science. Hopefully someone with some knowledge in this field will chime in. (As a side note, also interesting that apparently many applications traditionally reserved for marine engineering seem to surface when talking about exploring the Jovian system...)

EDIT: Just as a visualization aid, a submarine or, better yet, a diving bell is a direct analog of a "vacuum balloon"...the external ambient pressure is many times the internal.

[JRehling]

EDIT: Just as a visualization aid, a submarine or, better yet, a diving bell is a direct analog of a "vacuum balloon"...the external ambient pressure is many times the internal.

Oh, constructing a vacuum shell that doesn't crumple would be easy. Making it buoyant in hydrogen is the trick. Hydrogen gas is about 5600 times lighter than water. This sounds like making a submarine so light that the crew could carry it on a hiking trail.

[vjkane]

I remember reading some NASA studies in the early 80s on this topic. They concluded that hot air balloons were the only solution because lift is hard to achieve in an H2 atmosphere. Even then, I remember that the balloons had weight problems (large balloons needed) and couldn't reach too far above the lower cloud decks.

In theory, a paraglider would give a long descent life time, but managing the data relay would get really tricky

All this is moot now, though. NASA has lost the expertise and facilities for a Jovian entry probe. I believe they've dropped consideration of any more entry probes for Jupiter after they realized the cost of recreating the expertise and facilities.

[nprev]

I was thinking in terms of external pressure resistance vs. weight savings (the thinner the shell, the better), but I see your point exactly, JR; this may require an unreasonably strong material.

[Greg Hullender]

Why so pessimistic? I took Wikipedia's figures for a "normal" hot air balloon

http://en.wikipedia.org/wiki/Hot_air_ballo...ry_of_operation

Which is 113 kg for a balloon with 2800 cubic meters of volume, plus their recomended max operating temperature of 120 C (393 K).

Then I took their figures for Jovian temperature at 1 bar (100k Pa) of 165 K http://en.wikipedia.org/wiki/Jupiter

Finally, using the ideal gas law, I figure the envelope to hold 7,290,000 moles of H2 at 165K and 3,060,000 at 393 K, meaning it displaces about 240 kg of H2. Since the mass of the balloon is less than half that, it leaves over 100kg for payload.

Mass of the balloon vs. volume enclosed goes up as the 2/3 power, so a large balloon (100,000 m^3) could carry an amazing 8 tons!

As usual, I may have a math error somewhere, but my first cut at this suggests it doesn't look bad at all.

--Greg

[vjkane]

Why so pessimistic? ... i t leaves over 100kg for payload.

Mass of the balloon vs. volume enclosed goes up as the 2/3 power, so a large balloon (100,000 m^3) could carry an amazing 8 tons!
--Greg

As I recall, the payload was about 100kg for a balloon in the water clouds (where you calculated). It shrank rapidly as desired elevation increased.

My pessimism comes from the expertise to build and the facilities to test the heat shield. That is the technology that has been lost. I'm sure that if we paid to rebuild it, we could do the balloon.

[J.J.]

I had no idea that the obstacles to a Jovian balloon were so high, though they make sense, in retrospect. I remember reading about the Soviets once having interest in a Jupiter balloon probe (only natural the originators of Vega), but of course that fell through.

Me, I'd just be happy with a kamikaze multiprobe mission that could sample various latitudes...

[vjkane]

Me, I'd just be happy with a kamikaze multiprobe mission that could sample various latitudes...

I was really intrigued by the idea of a balloon that would study the Jovian atmosphere for months. I'd be even more intrigued now that we know that Jovian and super Jovian planets are common. I still think that it scientifically would be a great mission. All the reasons for doing a balloon at Venus apply at Jupiter. It would be a difficult mission to fit within a budget, though.

I really liked the idea of the multiprobes -- a great compliment to Juno. I was bummed out to hear that we no longer had the capacity to recreate the entry technology. That is one of the reasons that the idea of a Saturn multiprobe has gained such favor. We do have the entry technology for every other planet in the solar system. The current idea with a Saturn probe is that it would carry two entry vehicles that have microwave radiometers bolted to the back of the entry capsules (the radiometers would detach before entry). The radiometers would get deep atmosphere soundings prior to entry, and the probes would get get in situ measurements down to a few bar.

[nprev]

I was bummed out to hear that we no longer had the capacity to recreate the entry technology.

Can you elaborate a bit on that, VJ? I'm assuming that one or more facilities or other critical infrastructure components were closed and/or reconfigured.