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"Dragonfly" Titan explorer drone, NASA funds Johns Hopkins University Applied Physics Laboratory (APL)
HSchirmer
post Sep 7 2019, 10:51 AM
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QUOTE (mcaplinger @ Sep 6 2019, 07:11 PM) *
I suspect that there is very little about the design that is finalized at this point, and many things will be evaluated during development and may end up different.

Discussion about what might change could be interesting, or not.


There's a certain, er, elegance, to copying the evolutionary anatomy or behavior of animals into space probes.
My inspiration for Dragonfly dropping rocks to break them open was seagulls. They lack the physical strength to break the shells of clams, mussels, or snails; so they developed a behavior of grabbing mollusks off the ground and dropping them from high up to break them open. After a bit more calculation, air-drop won't work for breaking up Titan rocks, but what about other natural adaptations for breaking things?

Well, we still have Mantis shrimp (hulk smash) and Pistol shrimp (cavitation cannon).

Copying the Mantis shrimp is an interesting option.
QUOTE
It is reported to have a "punch" of over 50 miles per hour (80 km/h). This is the fastest recorded punch of any living animal. The acceleration is similar to that in a .22 caliber handgun, with 340 pounds-force (1,500 N)[4] per strike.
Hmm, the comparison with a .22 rifle reminds me of an air-powered rifle that Lewis and Clark carried, it was a 1790 design, a hand-pumped 800 psi, 40 shot rifle that was .46 cal. with a 20 round magazine made by Girandoni. Perhaps Dragonfly might carry a pneumatic rock breaking gun.

Lewis and Clark's air gun didn't need powder, but did need bullets, but what if you could just use the air around you as the projectile? What if you could use VACUUM as the projectile? Well, given that Titan has an atmosphere 4x denser than earth, perhaps copy the Pistol shrimp
QUOTE
The animal snaps a specialized claw shut to create a cavitation bubble that generates acoustic pressures of up to 80 kPa at a distance of 4 cm from the claw. As it extends out from the claw, the bubble reaches speeds of 100 km/h (62 mph) and releases a sound reaching 218 decibels.[10] The pressure is strong enough to kill small fish.

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tanjent
post Sep 7 2019, 03:28 PM
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Centsworth2 and JRehling's point a few posts back has me hoping that the existence of dunes offers some reassurance that the surface is not terribly sticky. But this does seem like something the designers would want to be very sure of. Tholins may be airborne and are often likened to tars. It would be quite a threat to the mission if the helicopter blades, skids, and body quickly became covered with goo. (In my kitchen anyway, even the teflon-coated utensils often require a bit of scrubbing.)
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rlorenz
post Sep 9 2019, 05:19 PM
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I'm not going to wade into a big unstructured discussion on environmental risks and preceptions thereof but let me note the following

- a wide range of surface constitutions are being considered (dry, granular, damp, solid, fine-grained, etc.) this is one reason for using wide skids.
- the skids stay cold
- the drill motors have to be heated for operation, but the drill bit and sample-facing surfaces (like the pneumatic hose for conveying sample) stay cold
- the drills can operate rotary-only or rotary-percussive
- the sampling system has been tested in a wide range of room temperature Titan simulants and on several materials at cryogenic temperatures

There is a presentation on the sampling system (70MB, contains movie) at the IPPW website
https://pub-lib.jpl.nasa.gov/docushare/dswe...ials_LORENZ.pdf
(there were several other Dragonfly presentations at the same meeting)
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mrpotatomoto
post Sep 10 2019, 02:31 PM
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QUOTE (rlorenz @ Sep 9 2019, 05:19 PM) *
I'm not going to wade into a big unstructured discussion on environmental risks and preceptions thereof but let me note the following

- a wide range of surface constitutions are being considered (dry, granular, damp, solid, fine-grained, etc.) this is one reason for using wide skids.
- the skids stay cold
- the drill motors have to be heated for operation, but the drill bit and sample-facing surfaces (like the pneumatic hose for conveying sample) stay cold
- the drills can operate rotary-only or rotary-percussive
- the sampling system has been tested in a wide range of room temperature Titan simulants and on several materials at cryogenic temperatures

There is a presentation on the sampling system (70MB, contains movie) at the IPPW website
https://pub-lib.jpl.nasa.gov/docushare/dswe...ials_LORENZ.pdf
(there were several other Dragonfly presentations at the same meeting)


Very informative! Thank you for your reply.
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HSchirmer
post Sep 11 2019, 11:29 PM
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QUOTE (mrpotatomoto @ Sep 10 2019, 03:31 PM) *
Very informative! Thank you for your reply.



Interesting idea for skid anti-seize-

Some boffins created a water-glider powered by a reaction-

QUOTE (https://www.popularmechanics.com/technology/robots/a29003643/glider-robot-chemical-reaction/)
The small aerial-aquatic glider, which can fit in the palm of your hands, uses a chemical reaction to propel itself out of the water.


Hmm, perhaps catalytic skid coatings?
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JRehling
post Sep 13 2019, 03:04 AM
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It seems safe to say that Titan's surface composition is varied and far from thoroughly understood, although there are some useful constraints. One work (with an interesting abstract) is here:

https://link.springer.com/chapter/10.1007/9...1-4020-9215-2_6

A more recent work (with a less specific abstract) is here:

https://www.sciencedirect.com/science/artic...01910351400462X
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HSchirmer
post Sep 13 2019, 11:48 AM
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QUOTE (JRehling @ Sep 13 2019, 03:04 AM) *
It seems safe to say that Titan's surface composition is varied and far from thoroughly understood, although there are some useful constraints. One work (with an interesting abstract) is here:

https://link.springer.com/chapter/10.1007/9...1-4020-9215-2_6

A more recent work (with a less specific abstract) is here:

https://www.sciencedirect.com/science/artic...01910351400462X


Thanks! Very helpful for channeling those interested in this towards good information.

Tangentially, since Titan sounds more and more like the fire-swamp from Princess Bride (lightning sands, fire spurts, ROUS?)
I suggest "Buttercup" as the name for the lander.
I guess that makes the poor backshell "Wesley"..
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Explorer1
post Nov 22 2019, 04:19 AM
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I haven't seen this new geological map mentioned yet:

https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA23174

I was really surprised to see that there is a region of low-latitude lakes (just east of Xanadu)! There are a couple of impact craters (albeit not as large as Selk) nearby.
Is the landing site selection for Dragonfly completely locked down? Is there any scientific value to considering them?
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Jaro_in_Montreal
post Nov 22 2019, 07:18 AM
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QUOTE (Explorer1 @ Nov 22 2019, 05:19 AM) *
I haven't seen this new geological map mentioned yet:

https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA23174

I was really surprised to see that there is a region of low-latitude lakes (just east of Xanadu)! There are a couple of impact craters (albeit not as large as Selk) nearby.
Is the landing site selection for Dragonfly completely locked down? Is there any scientific value to considering them?

Very good point !
And even a few smaller ones, S-W of Xanadu.
But no crater, like the eastern ones.
Maybe those are all considered to be transitory ?
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volcanopele
post Nov 22 2019, 04:27 PM
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Maybe that's referring to the possibility that Hotei Regio and Tui Regio are dry lake beds? There are no extant lakes there...


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Explorer1
post Nov 22 2019, 10:24 PM
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In that case, the map's legend could be a bit more clear! I would think the discovery of extant equatorial lakes would be a significant story.
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centsworth_II
post Nov 22 2019, 11:06 PM
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In the text they do say "...now or previously filled with liquid methane or ethane...".
QUOTE
...and lakes (regions now or previously filled with liquid methane or ethane).
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Juramike
post Dec 1 2019, 03:59 PM
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QUOTE (volcanopele @ Nov 22 2019, 11:27 AM) *
Maybe that's referring to the possibility that Hotei Regio and Tui Regio are dry lake beds? There are no extant lakes there...


"So...what do we call this stuff? I mean, it looks like an empty lake basin. There's a alluvial fan structure over there. Local drainages seem to be pointing into to it. It has those weird-o shaped margins and radar backscatter margin characteristics like some of the polar lakes. Topo shows depression. DEM, too. If this were anywhere near the poles we would say 'Yah sure, that's another empty lake basin' right? So why not here? We'll just call it like we see it."

"OK"

"Sure. Seems fine. Fits observations."

"OK, let's put it in the 'Lakes and Basin' meta-unit and we'll put it in one of the empty lake terrain units. We can flag it at the feature level as a "possible cryovolcanic region" just to keep this on everyone's radar and also link for past literature. (Get it? We're mapping with SAR! Haha!)"


(and that's pretty much how it went down when we were looking at this. We saved mapping the Xanadu region for last because we knew it would be extra-weird. And in the end, it all gets down to "report what you observe, then interpret".)


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JRehling
post Dec 1 2019, 06:59 PM
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Seriously, thanks for the account, Juramike!

On a meta-level, I think the issue here (not necessarily one to be fixed) is that we use terrestrial terminology that means very specific things to us while discussing a world where things may correspond only roughly. On Earth, weather and geology generally don't mix, at least not on human timescales. On Titan, something may very well be a perfect blend between a lake and a volcanic structure, and the rain and the lava and the "aquifer" may be intermixed whereas on Earth, basalt and water seem categorically distinct in our minds.

Though, note, a phreatic eruption on Earth is what happens when lava meets an aquifer, but we don't all stroll past phreatic craters on a daily basis.
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rlorenz
post Dec 5 2019, 04:07 AM
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QUOTE (JRehling @ Dec 1 2019, 01:59 PM) *
On a meta-level, I think the issue here (not necessarily one to be fixed) is that we use terrestrial terminology that means very specific things to us while discussing a world where things may correspond only roughly. On Earth, weather and geology generally don't mix, at least not on human timescales. On Titan, something may very well be a perfect blend between a lake and a volcanic structure, and the rain and the lava and the "aquifer" may be intermixed whereas on Earth, basalt and water seem categorically distinct in our minds.


In this context (and in the 'Titan: Dead or Alive?' debate I had with Jeff Moore some years back) I've liked to show the attached as something of an analog : the salt glaciers in Iran. Salt layers emplaced when the Sea of Tethys (!) dried up are buoyant compared with their superposed sediments, and halite is a soft enough rock to flow somewhat (especially when mobilized by moisture). In a few places, the salt diapirs pierce the surface, and flow at ~1m year, spreading out in a blob (I guess ultimately material is lost at the edges by dissolution in occasional rainfall - certainly the surface is dissected).

Attached Image


So, it's functionally solid material, it has exuded from underground: perhaps if we saw it on Titan we'd call it a cryovolcanic flow. But it isnt what we'd call on Earth a volcano. On the other hand, it wasnt emplaced meteorologically, like an ice glacier. It's something in between, and Titan may have a lot of 'in between'. Arthur C. Clarke's 'Imperial Earth' has a nice word - 'waxworms'....
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