[X] My Assistant

[ngunn]

Thinking about all that methane rain descending on Titan's south pole, draining out into Mezzoramia and then - who knows where? - set me wondering . .

IF it seeps through a porous material it could possibly warm up at depth and re-emerge gradually at the surface as methane gas. This could be a peaceful process, like the emission of methane from a terrestrial marsh (or rubbish tip) rather than anything sudden or localised. Now suppose a large sheet of impermeable material is simply laid over the ground in such a place it might begin to trap methane underneath and become buoyant. Something like this is maybe what starts mid-latitude convection cells. Could it be possible to harness the phenomenon to lift balloons? Relatively cool balloons, smaller heat loss problems, very low power requirements. With a nitrogen atmosphere and methane both readily available on Earth the technology could be tested here.

[ngunn]

I agree absolutely this is not a serious suggestion for something to try soon! Purely a flight of fancy on my part. For a start you'd have to know when and where warm methane gas was seeping out of the ground. But unlike water vapour on Earth you'd only have to keep the methane a relatively small amount warmer than ambient temperature for it to remain gaseous.

Whilst trying to think of how to get a suitable fabric to stretch itself out neatly on the surface of Titan I realised that another of your specialities could come into play - the frisbee! Attach the payload in the form of a lot of small elements around the perimeter of a circular membrane and somehow arrange for it to spin as it descends. Speeding up the spinning just prior to landing would stretch it out nice and flat.

Anyhow, back to reality . . .

That was interesting about the use of coal gas in early balloons. I didn't know that.

And a question about the Titan hot air balloon (a thrilling proposal). How warm will the air inside be when it's flying? Will it be above the boiling point of methane?

[rlorenz]

And a question about the Titan hot air balloon (a thrilling proposal). How warm will the air inside be when it's flying? Will it be above the boiling point of methane?

About 10K above ambient - http://www.lpl.arizona.edu/~rlorenz/balloonjbis.pdf

Boiling temp depends on altitude; I dont think this is above boiling, but well above the dewpoint

[ngunn]

About 10K above ambient -

Many thanks. I'll read that thoroughly when time permits.

That temperature difference is a lot less than I'd have guessed, but is makes sense with heat loss being a major factor in such a dense atmosphere. Another 10 degrees or so would see methane boil, I think. (111K at 1 bar, but I don't know the figure for 1.5bar.) The reason I asked was that it occurred to me you could then envisage a hybrid design with a methane balloon inside the hot air one. Volume for volume that would provide a lot more lift. Again though, probably too complicated for the first go.

Good luck with the Titan project. Everything we are learning about the place tells me that - barring a total failure of civilisation - we are in at the beginning of a very long story.

[JRehling]

Keep in mind that 10K above normal means about 10% higher temperature in terms of absolute zero. That would provide the same lift as heating a balloon on Earth by 32K above normal, so if you picture a hot air balloon on Earth where the balloon is hot enough to sting your hand if you touched it... that's the performance we'd be talking about. Of course, touching the Titan balloon would have a different effect on your hand.