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Unmanned Spaceflight.com _ Saturn _ "Dragonfly" Titan explorer drone

Posted by: Jaro_in_Montreal Dec 20 2017, 09:04 PM

Is there a specific website for this Johns Hopkins University Applied Physics Laboratory (APL) concept for a Titan explorer drone?
Looks to be an RTG powered machine, somewhat reminiscent of MSL Curiosity (RTG sticking out the tail end).
But no camera mast, ChemCam, or sampling arm visible in the concept illustration.

QUOTE
Dec. 20, 2017
RELEASE 17-101
NASA Invests in Concept Development for Missions to Comet, Saturn Moon Titan
Dragonfly
Dragonfly is a drone-like rotorcraft that would explore the prebiotic chemistry and habitability of dozens of sites on Saturnís moon Titan, an ocean world in our solar system.
Elizabeth Turtle from the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, is the lead investigator, with APL providing project management.


https://www.nasa.gov/press-release/nasa-invests-in-concept-development-for-missions-to-comet-saturn-moon-titan



Posted by: elakdawalla Dec 20 2017, 09:33 PM

http://dragonfly.jhuapl.edu

Posted by: rlorenz Dec 22 2017, 01:22 AM

QUOTE (elakdawalla @ Dec 20 2017, 04:33 PM) *
http://dragonfly.jhuapl.edu


Note especially the quite detailed article that went online there this morning.(jump/scroll to resources)

Posted by: Julius Dec 22 2017, 03:55 PM

This mission should easily top the list. Titan here we come! cool.gif

Posted by: Y Bar Ranch Dec 29 2017, 10:45 PM

I use Titan as a case study for an aero class I teach, and am super-psyched at the idea of such a probe. Low gravity and high density are a rotorcraft's best friends.

Already drooling over the detailed 3D photogrammetry extracted from aerial images.

Posted by: vjkane Dec 30 2017, 05:39 AM

QUOTE (Julius @ Dec 22 2017, 07:55 AM) *
This mission should easily top the list. Titan here we come! cool.gif

The science for a comet sample return is very compelling (as is the science for Dragonfly; it comes down to do you prefer a great apple or a great banana?).

And I'd never bet on an easy competition with any proposal lead by Squyres, and he's devoted much of his time the last three years putting his comet sample return proposal together.

Posted by: Julius Dec 30 2017, 12:23 PM

QUOTE (vjkane @ Dec 30 2017, 06:39 AM) *
The science for a comet sample return is very compelling (as is the science for Dragonfly; it comes down to do you prefer a great apple or a great banana?).

And I'd never bet on an easy competition with any proposal lead by Squyres, and he's devoted much of his time the last three years putting his comet sample return proposal together.
. No disrespect to Squyres, but I can already imagine drone flying over titan lakes and magic Island plus extra miles of vistas to image and investigate. This is too good to let go and yes to me is definitely more compelling than the comet sampling mission.

Posted by: mcaplinger Dec 30 2017, 04:52 PM

I share everyone's excitement, but we are unlikely to get a lot more public information about either of these missions before the downselect, and the decision isn't made based on popularity. You can go back historically and look at which missions were competing and which were selected, but even if there are clear patterns there, that's not a great indication of future decisions.

Posted by: Jaro_in_Montreal Dec 30 2017, 05:30 PM

QUOTE (Julius @ Dec 30 2017, 12:23 PM) *
I can already imagine drone flying over titan lakes and magic Island plus extra miles of vistas to image and investigate.


From the description of Dragonfly in http://dragonfly.jhuapl.edu/docs/DragonflyTechDigestAPL.pdf it would not be able to go anywhere near the polar lakes region, landing instead in the equatorial dune fields.

QUOTE
Although the exploration of Titanís seas had previously been considered, notably by the APL-led Titan Mare Explorer (TiME) Discovery concept, the timing mandated by the announcement of opportunity precluded such a mission.
Specifically, with launch specified prior to the end of 2025, Titan arrival would be in the mid-2030s, during northern winter.
This means the seas, near Titanís north pole, are in darkness and direct-to-Earth (DTE) communication is impossible.


Like TIME, Dragonfly also proposes direct-to-Earth (DTE) communication.

Maybe a south-polar visit might be feasible ? ....Ontario Lacus ??



Posted by: mcaplinger Dec 30 2017, 06:03 PM

QUOTE (Jaro_in_Montreal @ Dec 30 2017, 09:30 AM) *
Maybe a south-polar visit might be feasible ? ....Ontario Lacus ??

From the article:
QUOTE
Arrival at Titan in the mid-2030s with DTE communication suggests a low-latitude landing site. This
requirement means a similar location and season to the Huygens descent in 2005, so the wind profile and
turbulence characteristics measured by the Huygens probe are directly relevant. Furthermore, the sand
seas that girdle Titanís equator are both scientifically attractive and favorable in terms of terrain characteristics for landing safetyóindeed, it was for these reasons that the 2007 Flagship Study identified these dune fields as the preferred initial target landing area.


And it's unlikely that the vehicle will have enough range to fly from equator to pole.

Posted by: vjkane Dec 31 2017, 02:12 AM

QUOTE (mcaplinger @ Dec 30 2017, 10:03 AM) *
And it's unlikely that the vehicle will have enough range to fly from equator to pole.

I'm not so sure. Assume that Dragonfly lands exactly at the equator. The north pole (and the lake region begins before this) is 4044 km away. Assume that Dragonfly has had a great prime mission and the team is willing to just push it to go the distance. At 40 km per hop once every Titan day (~16 Earth days), the north pole is 4.4 years away.

Given that Titan is pretty benign, once you've solved the problem of how to stay warm (always take your warm MMRTG with you when you visit), the limiting factor on the mission may well be how long the the MMRTG power lasts given radioactive decay.

This map in this conference abstract suggests targets that might be in the range of a primary or a first extended mission.

https://www.dropbox.com/s/yt1wx28aoi4iufz/Dragonfly%20LPSC%201958.pdf?dl=0


Posted by: Explorer1 Dec 31 2017, 02:55 AM

Opportunity certainly went beyond its designed range, I wouldn't be surprised that a flying vehicle could go so much farther.
I would be more worried that perhaps the environment isn't so benign; Oppy dealt with dust storms, but what about possible flash floods (as the Huygens landing site showed)? Without weather observations from orbit, that would be a nasty surprise outside the equatorial dune seas! Or the rotors' reaction to giant raindrops in-flight....

Posted by: nprev Dec 31 2017, 09:31 AM

I wonder how effectively it could navigate over long distances. We don't have nearly good enough surface maps for AI terrain recognition, there's no significant magnetic field, so all that's left is inertial. Maintaining a good heading alignment over long periods may be problematic since IMUs do have inherent drift, and though periodic realignment is the usual method to correct that Titan's outer shell rotation seems to vary significantly in comparison to the rest of the moon's mass (not sure if that's a fixed offset or variable), and measuring rate & direction of rotation after vertical alignment is the usual method of finding true north (and latitude).

This could possibly be augmented by RDFing the vehicle's downlink to Earth, but not sure how much position precision could be achieved...tens/hundreds of km? Then again, maybe the position of the Sun could be used as well, foggy though it's gonna be. Dunno if Saturn would be detectable, but the Sun's definitely gonna be the only possible reference star.

Posted by: HSchirmer Dec 31 2017, 02:36 PM

QUOTE (nprev @ Dec 31 2017, 09:31 AM) *
We don't have nearly good enough surface maps for AI terrain recognition, there's no significant magnetic field, so all that's left is inertial.


Not necessarily, just old-school triangulation: "1800s mountain peak GPS", using trigonometry to track where the mountain peaks are on the horizon.

Ala "the Englishman who went up a hill, but came down a mountain" you build up a triangular grid of the highest points by surveying.
That lets you triangulate your map location, and calculate your height, based where they are on the horizon.

Posted by: RoverDriver Dec 31 2017, 04:25 PM

QUOTE (nprev @ Dec 31 2017, 01:31 AM) *
...
but the Sun's definitely gonna be the only possible reference star.


The nadir vector can be detected by the accelerometers. The Mars rovers we use: clock, Sun position, and nadir vector. As an alternative gyro compassing might be quite more difficult but not impossible.

Paolo

Posted by: vjkane Dec 31 2017, 04:46 PM

QUOTE (nprev @ Dec 31 2017, 01:31 AM) *
I wonder how effectively it could navigate over long distances. We don't have nearly good enough surface maps for AI terrain recognition, there's no significant magnetic field, so all that's left is inertial. Maintaining a good heading alignment over long periods may be problematic since IMUs do have inherent drift, and though periodic realignment is the usual method to correct that Titan's outer shell rotation seems to vary significantly in comparison to the rest of the moon's mass (not sure if that's a fixed offset or variable), and measuring rate & direction of rotation after vertical alignment is the usual method of finding true north (and latitude).

This could possibly be augmented by RDFing the vehicle's downlink to Earth, but not sure how much position precision could be achieved...tens/hundreds of km? Then again, maybe the position of the Sun could be used as well, foggy though it's gonna be. Dunno if Saturn would be detectable, but the Sun's definitely gonna be the only possible reference star.

From Ralph et al.'s paper, Dragonfly would do 40 km hops with 16 days between. I presume the quadcopter would have its position updated during the between days.

The paper hints that longer flights are likely possible and 40 km is the safe planning distance. One factor that would shorten traverses is the plan to use each flight to locate a more distant future landing site and then fly back to a previously scouted nearer landing site. With experience, the mission team might gain the confidence to not do the fly back and allow the quadcopter to chose its own safe landing site. With lidar or structure from motion (building 3D maps from stereo images), Dragonfly could continuously search for safe landing sites below its flight path and know of safe landing sites.



Posted by: mcaplinger Dec 31 2017, 04:50 PM

QUOTE (RoverDriver @ Dec 31 2017, 08:25 AM) *
The Mars rovers we use: clock, Sun position, and nadir vector.

That gives you rover orientation for antenna pointing, but AFAIK, not absolute location to any kind of accuracy.

For Titan, I would expect Earth-based radiometric positioning to be accurate to at least 100s of meters, easily good enough for vehicle navigation.

Posted by: HSchirmer Dec 31 2017, 05:24 PM

QUOTE (vjkane @ Dec 31 2017, 04:46 PM) *
From Ralph et al.'s paper, Dragonfly would do 40 km hops with 16 days between. I presume the quadcopter would have its position updated during the between days.

The paper hints that longer flights are likely possible and 40 km is the safe planning distance. One factor that would shorten traverses is the plan to use each flight to locate a more distant future landing site and then fly back to a previously scouted nearer landing site. With experience, the mission team might gain the confidence to not do the fly back and allow the quadcopter to chose its own safe landing site. With lidar or structure from motion (building 3D maps from stereo images), Dragonfly could continuously search for safe landing sites below its flight path and know of safe landing sites.


Well, when it comes to auto-navigation, you really have to check out U-Penn's GRASP program, and the Kumar lab's drones...
https://www.grasp.upenn.edu/research-groups/kumar-lab
They've done some really neat work, check "Journal of Field Robotics"...
And their youtube channel

https://www.youtube.com/watch?time_continue=1&v=rJfQncmWpCo

IIRC, somebody had the brilliant idea to modulate the prop speed among the 4 blades to generates a beat tone
for sonar range finding. The drone "listens" for the echo to measure distance to large objects.

Nice coincidence that Earth and Titan have nitrogen atmospheres, acoustics shouldn't be that different...

Posted by: nprev Dec 31 2017, 10:17 PM

QUOTE (vjkane @ Dec 31 2017, 08:46 AM) *
With experience, the mission team might gain the confidence to not do the fly back and allow the quadcopter to chose its own safe landing site. With lidar or structure from motion (building 3D maps from stereo images), Dragonfly could continuously search for safe landing sites below its flight path and know of safe landing sites.


Interesting, and thanks for the responses, all. Didn't know that terrestrial-based radiometry was accurate at sub-km resolution, Mike, so that solves the main problem: navigating to targets like lakes and cryovolcano candidates that may be extremely distant from the original landing site. Periodic position fixes combined with the local-scale 'hop & look' nav methods described should solve that with a high degree of precision and operational safety.

Posted by: Y Bar Ranch Jan 1 2018, 04:39 AM

Wonder what kinds of information can be gathered by just going into a low hover or running the rotors on the ground to generate some airflow. Properties of surface particles? Etc?

Posted by: vjkane Jan 1 2018, 03:30 PM

QUOTE (Y Bar Ranch @ Dec 31 2017, 08:39 PM) *
Wonder what kinds of information can be gathered by just going into a low hover or running the rotors on the ground to generate some airflow. Properties of surface particles? Etc?

That is specifically mentioned in the paper Ralph gave the link to a few posts up.

Posted by: Y Bar Ranch Jan 1 2018, 10:44 PM

QUOTE (vjkane @ Jan 1 2018, 10:30 AM) *
That is specifically mentioned in the paper Ralph gave the link to a few posts up.

Ahhh, missed it on the first read.

Posted by: Daniele_bianchino_Italy Jan 2 2018, 05:51 PM

I certainly hope for this mission. but ... if one of the most extraordinary things in the solar system are the Titan lakes and seas, why spend it on a mission for dry Titan areas ?
I do not really understand, 99% of us are hoping to see lakes closely. Why after many years of waiting do a mission on Titan in area without lakes? ... bha!

Posted by: RoverDriver Jan 2 2018, 06:23 PM

QUOTE (mcaplinger @ Dec 31 2017, 08:50 AM) *
That gives you rover orientation for antenna pointing, but AFAIK, not absolute location to any kind of accuracy.
...


True, although maybe you can get latitude, definitely not longitude. Likely dead reckoning would be quite difficult unless some kind of visual odometry or SLAM is employed.

Paolo

Posted by: fredk Jan 2 2018, 06:54 PM

QUOTE (RoverDriver @ Jan 2 2018, 07:23 PM) *
definitely not longitude

Knowing the time, couldn't you also get the longitude? We'd need the sun's elevation (I guess from imaging in some IR band, if possible) relative to the nadir (from accelerometers) for a few observations. Of course the precision won't be good - one degree relative precision of the sun's position translates to about 45 km position accuracy on the surface, so it sounds like the radio approach would be more precise.

Posted by: mcaplinger Jan 2 2018, 07:56 PM

QUOTE (fredk @ Jan 2 2018, 10:54 AM) *
Knowing the time, couldn't you also get the longitude?

Certainly (see https://en.wikipedia.org/wiki/Longitude_(book) ) but as I noted this is not to any accuracy and AFAIK has never been used for Mars rover positioning as there are better ways to do it.

I'm not sure you can position the sun very accurately with imaging on Titan, but my point is, you don't have to.

Posted by: Explorer1 Jan 2 2018, 08:49 PM

QUOTE (Daniele_bianchino_Italy @ Jan 2 2018, 12:51 PM) *
I certainly hope for this mission. but ... if one of the most extraordinary things in the solar system are the Titan lakes and seas, why spend it on a mission for dry Titan areas ?
I do not really understand, 99% of us are hoping to see lakes closely. Why after many years of waiting do a mission on Titan in area without lakes? ... bha!

I believe the issue is the seasons; Saturn (and Titan) will enter northern winter by the time the mission arrives, which not only means it is dark, which makes it tougher to run a mission without extra lights, but there is also no direct line to communicate with Earth (without a relay satellite, which would be quite expensive). The last chance this Saturnian year was Titan Mare Explorer, but it was obviously not selected in the last round of Discovery proposals, so it will be a wait until the northern lakes are illuminated again.

Ontario Lacus is in the southern hemisphere, but it is much smaller and shallower than its northern counterparts. Other more equatorial lakes have been theorized but http://www.sciencedirect.com/science/article/pii/S0019103515002110

Posted by: vjkane Jan 2 2018, 10:41 PM

QUOTE (Explorer1 @ Jan 2 2018, 12:49 PM) *
I believe the issue is the seasons; Saturn (and Titan) will enter northern winter by the time the mission arrives, which not only means it is dark, which makes it tougher to run a mission without extra lights, but there is also no direct line to communicate with Earth (without a relay satellite, which would be quite expensive). The last chance this Saturnian year was Titan Mare Explorer, but it was obviously not selected in the last round of Discovery proposals, so it will be a wait until the northern lakes are illuminated again.

Ontario Lacus is in the southern hemisphere, but it is much smaller and shallower than its northern counterparts. Other more equatorial lakes have been theorized but http://www.sciencedirect.com/science/article/pii/S0019103515002110

How far south does the most southern northern lake go? Would that be outside the polar night? (Sorry, don't have time to go look at a map and compare to the axial tilt.)

Posted by: Webscientist Jan 3 2018, 06:05 PM

QUOTE (vjkane @ Jan 2 2018, 11:41 PM) *
How far south does the most southern northern lake go? Would that be outside the polar night? (Sorry, don't have time to go look at a map and compare to the axial tilt.)


I had the same question in mind.

I've taken a look at a map of 2016.
It seems that Kraken Mare has extensions at about 60 degrees north latitude, roughly the equivalent to the top of Scotland (Ralph must know).
But the axial tilt of Titan is a bit higher than that of the Earth (27 degrees versus 23.4 degrees).
So wha




Posted by: Webscientist Jan 3 2018, 06:10 PM

QUOTE (Webscientist @ Jan 3 2018, 07:05 PM) *
I had the same question in mind.

I've taken a look at a map of 2016.
It seems that Kraken Mare has extensions at about 60 degrees north latitude, roughly the equivalent to the top of Scotland (Ralph must know).
But the axial tilt of Titan is a bit higher than that of the Earth (27 degrees versus 23.4 degrees).
So for the next good exploration window, maybe in the 40s.
But if there is the will...
2017-2024 was the perfect time I guess.


Posted by: Daniele_bianchino_Italy Jan 3 2018, 07:07 PM

iL kraken sea extends to 56 north. I think small lakes can be on 50 north.

Posted by: scalbers Jan 3 2018, 11:25 PM

How about some twilight lake watching?

https://www.space.com/36609-twilight-outshines-daylight-saturn-moon-titan.html

Although the paper mentioned in this article is mainly referring to the total disk brightness as seen from space, it is a reminder that a reasonable amount of scattered light is available at the surface during twilight (e.g. in near-polar winter).

Posted by: Habukaz Jan 4 2018, 04:20 PM

QUOTE (Explorer1 @ Jan 2 2018, 09:49 PM) *
Ontario Lacus is in the southern hemisphere, but it is much smaller and shallower than its northern counterparts. Other more equatorial lakes have been theorized but http://www.sciencedirect.com/science/article/pii/S0019103515002110


https://www.google.com/maps/space/titan/@-38.938954,84.0304017,1433599m/data=!3m1!1e3

This mission seems like an excellent opportunity to test the lake hypotheses for these two features. wink.gif

Also of note:

QUOTE
However, Stofan et al. (2007) and Tan et al. (2013) state that liquid methane is thermodynamically stable anywhere on the surface of Titan.


So, maybe there could be smaller pools of liquid, or even smaller lakes too small to have been resolved yet, even closer to the equator.




Posted by: JRehling Jan 6 2018, 08:15 AM

From half of Titan's surface, Saturn will be visible almost all the time. That seems like it'd be very useful for navigation, even more so than the Sun, because the Sun will vanish for ~192 hours at a time.

Going a lot farther down the magnitude scale, a really interesting possibility would be if you could see Betelgeuse, Antares, Aldebaran, and possibly some other stars like Arcturus. The former are red giants that are bright in infrared, which, as we know, penetrates Titan's haze pretty well. You'd never see them in the daytime sky, but at night they'd be brighter in the IR band than they are in visible light from Earth. Seems like navigating by the stars could cover your nights on Titan and the combination of the Sun and Saturn would handle the daytime. And an IR sensor could be pretty sensitive operating at 94K.

In addition, the radio link with Earth would give you greater precision longitude checks twice per sol.

Posted by: vjkane Jan 6 2018, 06:26 PM

QUOTE (JRehling @ Jan 6 2018, 12:15 AM) *
Going a lot farther down the magnitude scale, a really interesting possibility would be if you could see Betelgeuse, Antares, Aldebaran, and possibly some other stars like Arcturus. The former are red giants that are bright in infrared, which, as we know, penetrates Titan's haze pretty well. You'd never see them in the daytime sky, but at night they'd be brighter in the IR band than they are in visible light from Earth. Seems like navigating by the stars could cover your nights on Titan and the combination of the Sun and Saturn would handle the daytime. And an IR sensor could be pretty sensitive operating at 94K.

The descriptions so far don't mention an IR sensor, although it could be considered an engineering instrument. The highest frequency atmospheric window is 0.93 microns. The Mastcam Z cameras goes to 0.88 microns. I don't know if the sensor itself goes to 0.93 microns and the Mastcam Z limit is based on the scientific value of that band and not the sensor.

Posted by: vjkane Jan 7 2018, 03:31 AM

QUOTE (vjkane @ Jan 6 2018, 10:26 AM) *
The descriptions so far don't mention an IR sensor, although it could be considered an engineering instrument. The highest frequency atmospheric window is 0.93 microns. The Mastcam Z cameras goes to 0.88 microns. I don't know if the sensor itself goes to 0.93 microns and the Mastcam Z limit is based on the scientific value of that band and not the sensor.

I'll correct my last post after finding a better paper. The MastCam Z sensor goes out to a full micron, so if Dragonfly uses a similar sensor, it could image through the 0.93 band. If nothing else, it could take great tourist pictures of the surface with Saturn in the sky (although it would be a monochrome image).

Posted by: scalbers Jan 7 2018, 10:28 PM

At around 0.93 microns these images would be interesting, though still a bit hazy since the aerosol optical depth at this wavelength is about 3 at the zenith. Thus looking at Saturn and stars would be a bit like the view through medium-thin cirrus clouds on Earth. Some details are in figure 12.18 from this paper: http://ciclops.org/media/sp/2010/6514_15623_0.pdf. Saturn may look best during twilight and it should be high in the sky. A wide angle lens (or a mosaic) would help with showing the terrain at the same time.

Posted by: rlorenz Dec 14 2018, 09:51 PM

QUOTE (elakdawalla @ Dec 20 2017, 04:33 PM) *
http://dragonfly.jhuapl.edu


The website has been updated with some new images and animations

Posted by: Explorer1 Jan 17 2019, 12:22 AM

A nice video overview from the PI: https://www.youtube.com/watch?v=G-OgzT5KO9o

And a Planetary Radio interview: http://www.planetary.org/multimedia/planetary-radio/show/2019/0116-2019-elizabeth-turtle-dragonfly-clipper.html

Posted by: propguy Jun 27 2019, 08:12 PM

Announcement is out. Dragonfly is the next New Frontiers Program! Cheers to all involved.

Posted by: charborob Jun 27 2019, 08:55 PM

According to https://www.jhuapl.edu/PressRelease/190627b, launch in 2026 and arrival at Titan in 2034. (Which means I will be 80 years old then! I just hope I still have some brains left to enjoy the mission.)

Posted by: Steve G Jun 27 2019, 09:23 PM

QUOTE (charborob @ Jun 27 2019, 12:55 PM) *
According to https://www.jhuapl.edu/PressRelease/190627b, launch in 2026 and arrival at Titan in 2034. (Which means I will be 80 years old then! I just hope I still have some brains left to enjoy the mission.)


Yeah, I did the age calculator thing on myself. We're the same age! It's life expectancy will likely outlive mine.

Posted by: pioneer Jun 27 2019, 09:31 PM

Interesting mission. I wonder how it will avoid landing in a lake of liquid ethane or sinking in anything resembling quicksand.

Posted by: nprev Jun 27 2019, 10:01 PM

Congrats to all involved! Should be a VERY exciting mission, and hopefully the nice people at the nursing home will let me watch it! laugh.gif

Speaking of that, be interesting to see what trajectories, assumptions, and trade-offs are in play for the launch. There may be some interesting booster options available by the middle of the next decade.

Posted by: JRehling Jun 27 2019, 10:26 PM

This is super exciting.

Posted by: Explorer1 Jun 27 2019, 11:31 PM

Huygens was one of the highlights of my youth, and to see another landing (hopefully followed by many more!) will be wonderful. Just a coincidence it will be exactly one Saturn year later? (2005-2034).

And oh, wow, to see Huygens itself again, that would be something (if it's not covered in organic rain or washed downstream...)

Posted by: MahFL Jun 28 2019, 12:09 AM

QUOTE (pioneer @ Jun 27 2019, 10:31 PM) *
Interesting mission. I wonder how it will avoid landing in a lake of liquid ethane or sinking in anything resembling quicksand.


It does a recon before landing.

Posted by: Hungry4info Jun 28 2019, 12:53 AM

QUOTE (pioneer @ Jun 27 2019, 04:31 PM) *
I wonder how it will avoid landing in a lake of liquid ethane.


It will be landing near the equator and heading to Selk crater. It will therefore likely be much too far from any liquid bodies of ethane to worry about that.

Posted by: volcanopele Jun 28 2019, 12:58 AM

Cassini RADAR mosaic of Selk and the surrounding environs: https://pirlwww.lpl.arizona.edu/~perry/RADAR/RADAR_Selk.png

Posted by: MahFL Jun 28 2019, 02:28 AM

QUOTE (Hungry4info @ Jun 28 2019, 01:53 AM) *
It will be landing near the equator and heading to Selk crater. It will therefore likely be much too far from any liquid bodies of ethane to worry about that.



Good point, it's landing in sand dunes.

Posted by: Explorer1 Jun 28 2019, 02:52 AM

Well, one thing that is guaranteed is Dragonfly finding many, many surprises. Could there be very small liquid bodies below the resolution of Cassini's radar?

Posted by: vjkane Jun 28 2019, 03:52 PM

Ralph L: recovered from the celebration yet? laugh.gif

Posted by: vjkane Jun 28 2019, 03:58 PM

A year or so ago, the Cassini VIMS team released a surface color map of Titan. Does anyone have a link to the final product? I'd like to see what it looks like around Shangri-La and Selk.

https://www.space.com/41217-saturn-moon-titan-cassini-infrared-photos.html

Posted by: JRehling Jun 28 2019, 08:30 PM

Here is a zoom to the region of Selk (upper center) and the Huygens landing site (lower center). This is from an 8MB jpg at:

It looks like by crossing from the dunes outside Selk across its rim into into its center at least three distinct terrain units would be reachable with a fairly short traverse, and maybe much, much higher diversity that the spatial and spectral resolution here cannot convey.

https://data.caltech.edu/records/1173

 

Posted by: rlorenz Jun 29 2019, 03:01 AM

QUOTE (Explorer1 @ Jun 27 2019, 10:52 PM) *
Well, one thing that is guaranteed is Dragonfly finding many, many surprises. Could there be very small liquid bodies below the resolution of Cassini's radar?


Nothing is impossible. But this is relatively unlikely - 2034 is a season that is dry and will have been dry for some years before at this latitude (slightly north of the equator),
in an area with sand dunes (note that Huygens landed in a streambed, slightly south of the equator)

Posted by: lilmac Jun 29 2019, 04:37 PM

Exciting news. I find Titan to be the most fascinating body in the solar system. I was a bit disappointed by the Huygens imagery. Good to see we will get a second crack at viewing the surface, close-up, beneath the haze. Glad NASA is fully behind the mission (instrumentation, fabrication, design, engineering) and leveraging our first rate expertise. Canít wait for 2034!

Posted by: dolphin Jun 29 2019, 04:39 PM

QUOTE (lilmac @ Jun 29 2019, 05:37 PM) *
Exciting news. I find Titan to be the most fascinating body in the solar system. I was a bit disappointed by the Huygens imagery. Good to see we will get a second crack at viewing the surface, close-up, beneath the haze. Glad NASA is fully behind the mission (instrumentation, fabrication, design, engineering) and leveraging our first rate expertise. Canít wait for 2034!



Agreed. Good post.

I do wish the site selected had potential liquid deposits vs sand dunes

Posted by: Superstring Jun 29 2019, 10:32 PM

Really excited about this! Question to anyone who knows: What will be the resolution of the images from the surface (as compared to Huygens), and will we get any sort of global imagery/mapping?

Posted by: mcaplinger Jun 29 2019, 11:11 PM

QUOTE (Superstring @ Jun 29 2019, 02:32 PM) *
What will be the resolution of the images from the surface (as compared to Huygens), and will we get any sort of global imagery/mapping?

I'll refer everyone to http://dragonfly.jhuapl.edu/News-and-Resources/docs/34_03-Lorenz.pdf -- I'm not sure how many of the details of the imaging system design I'm free to disclose, and of course these are early days. From that document:

QUOTE
DragonCam—Dragonfly Camera Suite (Malin Space Science Systems). A set of cameras, driven by a common electronics unit, provides for forward and downward imaging (landed and in flight), and a microscopic imager can examine surface material down to sand-grain scale. Panoramic cameras can survey sites in detail after landing...


I think it's safe to say that the imagery quality will be many orders of magnitude improved over Huygens.

As for "global coverage" -- Titan is larger than Mercury, so one vehicle will only see a tiny fraction of the surface. But we'll see pretty much all there is to see from one vehicle's vantage point.

Posted by: MahFL Jun 30 2019, 02:41 AM

Most of the time DragonFly will be GroundFly...

Posted by: Decepticon Jun 30 2019, 04:34 AM

I was a little upset that we may not see any close observations of the lakes but we do know channels are known to be there from Huygens images. Landing and sampling the liquid that carved these features will be a science and visual bonanza.

Posted by: JRehling Jun 30 2019, 07:50 PM

Titan has extraordinary diversity of surface units, so the value of the mission will not be in covering a large fraction of the total surface but in taking a path that samples a wide variety of those surface unit types. I don't know what sort of total traverse distance is possible, and we'll all be hoping for an Opportunity-like success beyond the nominal lifespan, but it seems likely that one, nominal ground track could visit many of the major surface unit types, and a fairly long one could visit most of them.

Unfortunately, there is some latitude-based regularity in Titan's geography, so a mission landing at the equator will likely miss what is at the poles, and the converse would also be true.

I think we can guess that Titan might have a few unique areas scattered around its surface and of course we can't visit them all, but this one mission to Titan might encounter more diversity of surface units than all our missions to Mars, Venus, and the Moon have, combined.

Posted by: Webscientist Jun 30 2019, 08:41 PM

Great news!
A major technological and scientific challenge! blink.gif
Potential rainfall events from time to time in the equatorial or tropical area. So why not puddles (if the surface is not too porous or absorbent).
Many questions regarding the nature and the physical characteristics of Titan's dunes.
Are those dunes related to an ancient ocean or sea of methane or to the repetitive action of rainfall events (erosion, evaporation...) for instance ?
What kind of chemistry of course?

Posted by: JRehling Jun 30 2019, 09:01 PM

Most locations in Titan's low latitudes did not receive rainfall during Cassini's mission and a mean time between rainfall events is almost certainly in the range of decades if not centuries.

We don't know what we don't know about Titan, and so we explore it, but I wouldn't bet on finding puddles that have lasted decades.

Posted by: kymani76 Jun 30 2019, 09:08 PM

QUOTE (vjkane @ Jun 28 2019, 04:58 PM) *
A year or so ago, the Cassini VIMS team released a surface color map of Titan. Does anyone have a link to the final product? I'd like to see what it looks like around Shangri-La and Selk.


The VIMS basemap is available to download using https://trek.nasa.gov/titan.

On hearing about Dragonsfly's selection I also made this quick orthogonal map showing the illuminated portion of Titan as it will appear in 2034, with solar subpoint at latitude 23ļ south. The view is centered at Dragonfly's landing area around Selk crater, which is about 3500 kilometers from the nearest lakes at the southern pole.


Posted by: Webscientist Jul 1 2019, 08:06 AM

For a presentation upon the Cassini-Huygens mission in my astronomy club, I recently made this view of Titan compared to the other moons of Saturn at scale.




 

Posted by: Webscientist Jul 1 2019, 08:09 AM

For the perspective, another one revealing the worlds containing liquid surfaces:


 

Posted by: ngunn Jul 1 2019, 06:02 PM

I like that liquid surfaces one. Just maybe you will be able to add Venus to it at some point.

I have another perspective for anyone not wishing to wait until 2034 for great views over Titan. This is a painting I finally got finished recently after many delays. It's called Weathered Shore: Titan

(Mods or admins - I tried unsuccessfully to post this on another thread. If you are seeing those efforts please delete/ignore them.)


 

Posted by: titanicrivers Jul 1 2019, 07:12 PM

What a superb creation ngunn! I really like the weathered and porous looking lower foreground. The white band in the center ... ? evaporite terrain?, waves crashing? (sorry if way off on the interpretation!).

Posted by: ngunn Jul 1 2019, 07:36 PM

I was thinking banks of icy shingle strewn here and there over the dark plains by intermittent floods, but hey - see whatever you like. smile.gif Not everything in the picture is meant to be immediately comprehensible, as I figure that's how it would be if you were standing there.

Posted by: HSchirmer Jul 1 2019, 07:37 PM

QUOTE (ngunn @ Jul 1 2019, 07:02 PM) *
I like that liquid surfaces one. Just maybe you will be able to add Venus to it at some point.
(snip)


Would melted components of the Venera probes count as liquid on the surface?

Amazing when you have to revise the ides of gasses here being liquids and solids on Titan.

Posted by: Webscientist Jul 1 2019, 08:54 PM

[quote name='ngunn' date='Jul 1 2019, 08:02 PM' post='245157']
I like that liquid surfaces one. Just maybe you will be able to add Venus to it at some point.

I have another perspective for anyone not wishing to wait until 2034 for great views over Titan. This is a painting I finally got finished recently after many delays. It's called Weathered Shore: Titan

Thanks ngunn and congratulation for your true artwork. The color of the sea is a big question mark. We'll see in the 40's or before if you were close to reality! rolleyes.gif

Posted by: JRehling Jul 1 2019, 09:15 PM

Beautiful painting, ngunn! First I was struck by the beauty, then wished I could stand there and take in the view (with a very warm coat).

Posted by: vjkane Jul 2 2019, 02:49 PM

I've added a 200 km scale bar and a 200 km radius circle to a VIMS color image of the Selk crater area. The mission plans to land ~180 km away from Selk (although I don't know if this is rim or center of the crater). The mission may also spend time exploring the bright region to the southeast of the crater.

The mission will take approximately 2.5 years to go from the landing to the crater (again, don't know if this is rim or center and whether that includes time exploring the crater). Assuming it spends another 2.5 years exploring the crater and perhaps the southeastern bright area, then that leaves around three more years for further exploration of another region before power becomes a problem.

Selk sits in a sea of sand dunes. Assuming these were previously well explored, the craft might motor across them to reach another area. If it can do ~15 km per Titan day, then it might do ~360 km in a year. That might put the bright area Dilmun in reach. (I could not find any information on the nature of this area in a Google search.) The mountainous Adiri region would seem to be out of reach.


Posted by: mcaplinger Jul 2 2019, 03:40 PM

QUOTE (vjkane @ Jul 2 2019, 06:49 AM) *
The mountainous Adiri region would seem to be out of reach.

Back in 2017 you were still speculating that it would be possible to fly from equator to pole. What changed? wink.gif

I think it's a little early yet to know what the baseline mission profile will look like, though conservatism is not an unreasonable assumption.

Posted by: vjkane Jul 2 2019, 04:14 PM

QUOTE (mcaplinger @ Jul 2 2019, 08:40 AM) *
Back in 2017 you were still speculating that it would be possible to fly from equator to pole. What changed? wink.gif

I think it's a little early yet to know what the baseline mission profile will look like, though conservatism is not an unreasonable assumption.

In the NASA Live discussions following the announcement, someone said that Dragonfly would land 180 km from the crater and take 2.5 years to get there. Also, it was either there or something I've read since that said Dragonfly would advance 10 km per flight. Assuming one flight per Titan day (which other documents suggest), that limits how far it can go in a year. My back of the envelope imagining suggested 15 km per Titan day if the goal was just to get to somewhere, similar to Opportunity's traverse from Victoria to Endeavour crater.

My earlier post was based on the craft doing little more than putting as many km on the odometer as possible. Once I did the research for my blog post on the mission, I realized that a better way to think of the mission is as a regional explorer that will explore 200 to perhaps 400 km.

It is a shame that Selk crater isn't closer to Adiri. There appears to be lots of interesting terrain and surface materials there.

Posted by: atomoid Jul 2 2019, 10:49 PM

...Dragonfly would advance 10 km per flight. Assuming one flight per Titan day ...

looks like that average 10km value already has baked into it having to operate largely within limited communication windows when Selk crater isn't occluded from comm link with Earth, which seems like it would consist of on/off 8-earth-day sessions as the 'Titan day' of activity, since despite autonomous abilities I suspect 'daily' uplinks are still going to be the basis of operation (and someone might do Celestia simulations to enlighten us on communications windows) so apparently no red-eye flights to increase that 10km, but in an extended mission scenario who knows, RTG power allowing.. seems the plan is to send Dragonfly purely on its own, no assistive communications relay or independent sister orbiter with its own suite of experiments, no MarCO analog with jumbo solar array.. but such are hopes and wishes and unlimited budgets...

Posted by: vjkane Jul 3 2019, 03:02 PM

QUOTE (atomoid @ Jul 2 2019, 02:49 PM) *
...Dragonfly would advance 10 km per flight. Assuming one flight per Titan day ...

looks like that average 10km value already has baked into it having to operate largely within limited communication windows when Selk crater isn't occluded from comm link with Earth, which seems like it would consist of on/off 8-earth-day sessions as the 'Titan day' of activity, since despite autonomous abilities I suspect 'daily' uplinks are still going to be the basis of operation (and someone might do Celestia simulations to enlighten us on communications windows) so apparently no red-eye flights to increase that 10km, but in an extended mission scenario who knows, RTG power allowing.. seems the plan is to send Dragonfly purely on its own, no assistive communications relay or independent sister orbiter with its own suite of experiments, no MarCO analog with jumbo solar array.. but such are hopes and wishes and unlimited budgets...

One of the technical articles on Dragonfly showed an example power budget over a Titan day. Between the one flight, science, and communications to Earth, the battery was drawn down to about 30%. The craft then went into low power mode for the night with just occasional science activities to recharge the battery.

Another reason for no nighttime flights is that the navigation depends on assessing images taken in flight, which requires daylight.

QUOTE (atomoid @ Jul 2 2019, 02:49 PM) *
...Dragonfly would advance 10 km per flight. Assuming one flight per Titan day ...

looks like that average 10km value already has baked into it having to operate largely within limited communication windows when Selk crater isn't occluded from comm link with Earth, which seems like it would consist of on/off 8-earth-day sessions as the 'Titan day' of activity, since despite autonomous abilities I suspect 'daily' uplinks are still going to be the basis of operation (and someone might do Celestia simulations to enlighten us on communications windows) so apparently no red-eye flights to increase that 10km, but in an extended mission scenario who knows, RTG power allowing.. seems the plan is to send Dragonfly purely on its own, no assistive communications relay or independent sister orbiter with its own suite of experiments, no MarCO analog with jumbo solar array.. but such are hopes and wishes and unlimited budgets...

One of the technical articles on Dragonfly showed an example power budget over a Titan day. Between the one flight, science, and communications to Earth, the battery was drawn down to about 30%. The craft then went into low power mode for the night with just occasional science activities to recharge the battery.

Another reason for no nighttime flights is that the navigation depends on assessing images taken in flight, which requires daylight.

Posted by: JRehling Jul 3 2019, 08:47 PM

This is probably already in everyone's consciousness but day/night cycles and radio contact with Earth are almost equivalent, except for superior conjunction when the Sun will block radio contact.

A lander/flyer/floater at high latitudes, however, could spend several terrestrial years in continuous daylight and continuous radio contact with Earth. An equatorial landing site would mean almost uniform periods of day/night.

Terrain types on Titan correlate very strongly with latitude. The polar stuff and the equatorial stuff are almost literally two different worlds.

Posted by: climber Jul 3 2019, 10:27 PM

Did you notice that launch will be 29 years after Cassini which means exactely 1 Saturn orbit?
Add another 29 years and Iíll be exactely 100 years old rolleyes.gif
Interesting coincidences

Posted by: elakdawalla Jul 25 2019, 05:06 PM

The launch being 1 Saturn year after Huygens is sort of a coincidence but also a selling point and a helpful risk reduction factor. It means that Huygens descent data will be relevant for Dragonfly's EDL.

Posted by: Decepticon Jul 26 2019, 07:40 AM

What is the minimum number of propellers needed to fly on titan?

I'm worried about damage or motor failures.

Posted by: rlorenz Jul 26 2019, 11:22 AM

QUOTE (Decepticon @ Jul 26 2019, 03:40 AM) *
What is the minimum number of propellers needed to fly on titan?

I'm worried about damage or motor failures.

Dragonfly is an octocopter (quad layout of coax pairs) to provide resilience to failure. It can still fly fine with as many as three rotors out

Posted by: Jaro_in_Montreal Aug 19 2019, 01:46 PM

With the high atmospheric density and low gravity on Titan, I'm thinking that Dragonfly might be able to "autogyro" unpowered to the ground, following reentry.
Has anyone looked at what the lading speed would be, unpowered ?
Could the quadcopter control system maintain level flight in such a case?
In the affirmative, maybe Dragonfly could dispense with the EDL parachute, saving mass for more science instruments or bigger battery?

Posted by: mcaplinger Aug 19 2019, 03:07 PM

QUOTE (Jaro_in_Montreal @ Aug 19 2019, 05:46 AM) *
With the high atmospheric density and low gravity on Titan, I'm thinking that Dragonfly might be able to "autogyro" unpowered to the ground, following reentry.

I haven't worked out what the terminal velocity of the aeroshell would be before chute deploy, have you? The vehicle has to be slowed enough for the deployment/unfolding sequence to work in the first place.

That said, as a rule, autogyros require forward motion to generate lift. You may be thinking of what's called an autorotation in a helicopter. To do an autorotation, you need blade pitch control to reduce your descent rate from the fairly high rate needed to keep the blades turning to a rate low enough for landing, and of course you have very little choice about where you land (you have to commit to a landing spot pretty high up). Dragonfly has no blade pitch control and the small diameter props of a quad don't have enough momentum to do autorotations, on Earth anyway.

The battery is charged at the start of EDL so there's no particular advantage to landing unpowered anyway. The mission profile calls for a long flight traverse before the first landing to find the best landing site.

Posted by: djellison Aug 19 2019, 07:41 PM

QUOTE (Jaro_in_Montreal @ Aug 19 2019, 06:46 AM) *
Could the quadcopter control system maintain level flight in such a case?
In the affirmative, maybe Dragonfly could dispense with the EDL parachute, saving mass for more science instruments or bigger battery?


Quadcopters maintain level flight by adjusting the RPM of all 4 ( or in the case of Dragonfly... all 8 ) rotors.

Also - without a parachute....how do you successfully separate the heatshield?

Posted by: vjkane Aug 20 2019, 06:23 AM

QUOTE (djellison @ Aug 19 2019, 12:41 PM) *
Quadcopters maintain level flight by adjusting the RPM of all 4 ( or in the case of Dragonfly... all 8 ) rotors.

Also - without a parachute....how do you successfully separate the heatshield?

Dragonfly has both a drogue and main parachute. It descends on the drogue from about 6 minutes into the entry until about 88 minutes and then is on the main chute until about 105 minutes. As the presentations says, "Plenty of time to stage heatshield separation, activate radar & lidar, deploy landing legs."

Presentation doesn't say how long after the lander release the actual landing would be, likely because the lander can search for a suitable location and that time is non deterministic.

Posted by: djellison Aug 20 2019, 03:47 PM

The great thing about Titan EDL...you've got PLENTY of time under your parachute.

Posted by: rlorenz Aug 21 2019, 01:49 AM

QUOTE (djellison @ Aug 20 2019, 11:47 AM) *
The great thing about Titan EDL...you've got PLENTY of time under your parachute.


The talent on this forum is impressive. Mike, Doug and Van's responses are all correct (and well-reasoned,
I don't think all those details - like rotors being fixed-pitch - have been presented/published, but are obvious
when you start to think about them)

The EDL sequence as presently conceived (which can be adjusted, as Doug notes, we have oodles of time) is to
drop from the backshell and make the transition to powered flight about 1km off the ground to set up for
landing site search. More than a couple of minutes of flight, but less than a couple of tens of minutes..

Right at the very beginning of developing Dragonfly I had imagined we might land on a chute, and then do the
fancy new rotorcraft stuff after an initial landed mission, but then you are exposed to terrain risks (probably small,
but not controllable) for that first landing. And when you consider all the bits you need (hazard sensing, rotors etc.)
for flight, you might as well land with them from the get-go. Unlike a rocket-powered skycrane, you can test all
that stuff very effectively on Earth.

Posted by: mrpotatomoto Sep 4 2019, 10:01 PM

Is there any risk that Dragonfly's landing skids could become frozen stuck to Titan's surface, given the cryogenic temperatures?

Posted by: centsworth_II Sep 4 2019, 10:37 PM

I imagine that the skids, not being heated, would never melt any of the surface and so not be refozen to it.

Posted by: HSchirmer Sep 4 2019, 11:03 PM

Two quick questions-

First - Sonar?
Some quadcopters use a sonar location system, and IIRC, U-Penn's drone lab experimented with
sound pulses by running 1 rotor slightly slower to create an acoustic beat at a different frequency from the rotors.
Is there any interest in using echolocation for mapping?

Second - Mini "rods from god"
Any possibility of grabbing a rock and dropping it from 4km up to create your own fresh crater to study?

Posted by: mrpotatomoto Sep 4 2019, 11:08 PM

QUOTE (centsworth_II @ Sep 4 2019, 11:37 PM) *
I imagine that the skids, not being heated, would never melt any of the surface and so not be refozen to it.


Thanks for your reply. Don't the skids have some sampling devices (drills) on them? Can they operate at ambient temperatures?

Posted by: Explorer1 Sep 5 2019, 12:37 AM

QUOTE (HSchirmer @ Sep 4 2019, 06:03 PM) *
Second - Mini "rods from god"
Any possibility of grabbing a rock and dropping it from 4km up to create your own fresh crater to study?


You would first need to add an arm on the probe, and then be able to lift off with the rock (of water-ice, I'm assuming), and then release it mid-air.
And then presumably have a way to speed up the terminal velocity so that it actually falls fast enough to leave a crater! Titan's combination of low gravity and thick atmosphere makes it much easier to just find a natural crater, as the mission's long term goal already is.
Note how there are no craters on Earth's ocean floors from falling shipwrecks...

Posted by: centsworth_II Sep 5 2019, 01:53 AM

QUOTE (mrpotatomoto @ Sep 4 2019, 07:08 PM) *
Thanks for your reply. Don't the skids have some sampling devices (drills) on them? Can they operate at ambient temperatures?


Posted by: nprev Sep 5 2019, 02:00 AM

Gonna guess here that additional moving parts besides the rotors themselves will be greatly minimized for reliability/mission assurance purposes, plus of course Dragonfly likely will not be a very large spacecraft with a great deal of surplus mass budget for extra experiments by virtue of the facts that a- it's a helicopter and b- it's gotta get clear out to Saturn over some reasonable timeframe.

Posted by: HSchirmer Sep 5 2019, 02:21 AM

QUOTE (Explorer1 @ Sep 5 2019, 01:37 AM) *
You would first need to add an arm on the probe, and then be able to lift off with the rock (of water-ice, I'm assuming), and then release it mid-air.

And then presumably have a way to speed up the terminal velocity so that it actually falls fast enough to leave a crater! Titan's combination of low gravity and thick atmosphere makes it much easier to just find a natural crater, as the mission's long term goal already is.
Note how there are no craters on Earth's ocean floors from falling shipwrecks...


Well, I was already thinking about gravity and atmospheric density, so yes I knew there's a terminal velocity issue.
So, quick estimate, terminal velocity scales according to the square root of gravity dived by atmosphere density,
that's .138g divided by density at 1.45 bar, so ballpark guess is that's about 25% the terminal velocity of an object on Earth.
Now, the estimated terminal velocity of a 144mm hailstone on Earth was ~100 mph, giving around 25 mph on Titan,
That roughly equal to dropping it from 20 feet high on Earth. Not enough to make a crater, but perhaps break a rock.

-edit-
better number, Titan atmospheric density at the surface is almost 4x Earth's, (not 1.45) so that's a terminal velocity around 9 mph for a grapefruit-sized water ice rock. So, that's not going to do anything...


Actually, I was thinking more along the lines of using an electromagnet to grab the first iron meteorite they come across, making this the first probe to make its own tools from local resources (Yikes, our machines have reached the stone age...)


Followup question - what is the parachute diameter and material?
I like to think that some future Montgolfier-balloon probe would benefit from having several yards of material from Huygens and Dragonfly available for patching holes...
https://www.lpl.arizona.edu/~rlorenz/balloonjbis.pdf

Posted by: mcaplinger Sep 5 2019, 06:33 AM

From https://dragonfly.jhuapl.edu/News-and-Resources/docs/34_03-Lorenz.pdf (which answers a lot of questions):

QUOTE
a sampling arm like those used on Viking, Phoenix, or the Mars Science Laboratory, was considered, but it would be expensive and heavy and presented a single-point failure. Instead, two sample acquisition drills, one on each landing skid, with simple 1-degree-of-freedom actuators were selected... the material is sucked up through a hose and is extracted in a cyclone separator (much like in a Dyson vacuum cleaner) for delivery to the mass spectrometer instrument.


Posted by: HSchirmer Sep 5 2019, 01:04 PM

QUOTE (mcaplinger @ Sep 5 2019, 06:33 AM) *
From https://dragonfly.jhuapl.edu/News-and-Resources/docs/34_03-Lorenz.pdf (which answers a lot of questions):
QUOTE
Instead, two sample acquisition drills, one on each landing skid, with simple 1-degree-of-freedom actuators were selected...


Yes, that's a great resource to get information. However, the idea of drills mounted to the skids and sampling near the triple point of methane rock is what prompted me to imagine "hammer sampling" instead...

So, if the drill bit generates friction and pressure, and the bulk material is close to phase change temperature:
http://research.bpcrc.osu.edu/LARISSA/2010/02/the-stuck-ice-drill-saga-the-team-completes-drilling hint ... kid-tongue-flagpole

Posted by: JRehling Sep 6 2019, 03:59 AM

The precise composition of Titan's surface is still unknown; there are several substances that we know could or should be there, but there is also extremely complex chemistry taking place and this is not completely understood. It remains possible that the surface material, in many places, would have melting points far above anything that Dragonfly would generate. Just because Titan is very cold, that doesn't mean that solids on its surface melt at low temperatures. There certainly are substances making up part of Titan that would melt at low temperatures, but we don't know that those are at the surface. Some simple molecules that could exist as solids on Titan Ė H2O and CO2 Ė would not melt readily in the first case and would sublimate rather than melt in the second.

I'm not sure how one would assess the risk of stickiness when the surface composition is so subject to doubt, but I think one key is that by the time Dragonfly gets to the surface, its skids will be close to ambient temperatures.

Posted by: nprev Sep 6 2019, 05:17 AM

<shrug> Many, many years ago one of our mods suggested that the surface could have significant amounts of azides, which might detonate on contact. Huygens apparently only landed once, so that's probably not a significant risk. Huygens also didn't ooze downward into the cryogenic equivalent of quicksand, so the surface material did not experience a phase change from the impact.

At least all that's true of where Huygens landed. Might be completely different 100m away. Titan's geochemistry may well be more complex than that of Earth for all we know.

We don't know. That's why we're exploring. This will involve risk.

The Dragonfly team is without question composed of the most qualified people in the world for this job, and nobody here is qualified to second-guess their design choices.

Posted by: centsworth_II Sep 6 2019, 09:11 AM

QUOTE (centsworth_II @ Sep 4 2019, 09:53 PM) *
I suppose I should add my thoughts rolleyes.gif .
My first thought: 'no worries of Dragonfly skids sticking to the surface' were based on the oversimplified view of a surface of water ice (hard as rock). Posts since then have pointed out the presence of other ices with much higher lower melting points as well as exotic organic materials with who-knows-what properties. So maybe there should be a concern of surface materials sticking to Dragonfly. Could some kind of no-stick coating be applied?

Posted by: mrpotatomoto Sep 6 2019, 04:48 PM

QUOTE (nprev @ Sep 6 2019, 06:17 AM) *
The Dragonfly team is without question composed of the most qualified people in the world for this job, and nobody here is qualified to second-guess their design choices.


I apologize if it seemed as if I was second-guessing the team with my question.

I'm just trying to understand *why* this issue is considered low-risk, and thought some discussion on that would be interesting.

Posted by: HSchirmer Sep 6 2019, 05:30 PM

QUOTE (nprev @ Sep 6 2019, 05:17 AM) *
The Dragonfly team is without question composed of the most qualified people in the world for this job, and nobody here is qualified to second-guess their design choices.


Oh, not second-guessing, just very curious how the highly qualified people analyzed that issue and how they came to their designs.

I figured this is somewhat similar to the scientists drilling cores from the Antartic ice sheet; they found that their drills can freeze in place in a few seconds if the drill stops turning, so they added heated drillbits and eco-friendly antifreeze to deal with that.

Sometimes, the dumb questions highlight something you wouldn't have thought about...
I always imagine the lowest ranking intern on the Venera 14 design project asking "Sir, should the lens cap have a tether?"

Posted by: mcaplinger Sep 6 2019, 07:11 PM

QUOTE (mrpotatomoto @ Sep 6 2019, 08:48 AM) *
I'm just trying to understand *why* this issue is considered low-risk, and thought some discussion on that would be interesting.

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.

Posted by: HSchirmer Sep 7 2019, 10:51 AM

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 https://en.wikipedia.org/wiki/Odontodactylus_scyllarus 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 https://www.youtube.com/watch?v=-pqFyKh-rUI. 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 https://en.wikipedia.org/wiki/Alpheidae
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.


Posted by: tanjent Sep 7 2019, 03:28 PM

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.)

Posted by: 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/dsweb/Get/Document-7061/08_Drilling%20and%20Pneumatic%20Transfer%20of%20Titan%20Surface%20Materials_LORENZ.pdf
(there were several other Dragonfly presentations at the same meeting)

Posted by: mrpotatomoto Sep 10 2019, 02:31 PM

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/dsweb/Get/Document-7061/08_Drilling%20and%20Pneumatic%20Transfer%20of%20Titan%20Surface%20Materials_LORENZ.pdf
(there were several other Dragonfly presentations at the same meeting)


Very informative! Thank you for your reply.

Posted by: HSchirmer Sep 11 2019, 11:29 PM

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?

Posted by: 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/10.1007/978-1-4020-9215-2_6

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

https://www.sciencedirect.com/science/article/abs/pii/S001910351400462X

Posted by: HSchirmer Sep 13 2019, 11:48 AM

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/10.1007/978-1-4020-9215-2_6

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

https://www.sciencedirect.com/science/article/abs/pii/S001910351400462X


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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