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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 Saturn’s 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 Titan’s 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 Titan’s 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 Titan’s equator are both scientifically attractive and favorable in terms of terrain characteristics for landing safety—indeed, 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. Can’t 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. Can’t 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 23º 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 I’ll 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 – H2O and CO2 – 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"..

Posted by: Explorer1 Nov 22 2019, 04:19 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?

Posted by: Jaro_in_Montreal Nov 22 2019, 07:18 AM

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 ?

Posted by: volcanopele Nov 22 2019, 04:27 PM

Maybe that's referring to the possibility that Hotei Regio and Tui Regio are dry lake beds? There are no extant lakes there...

Posted by: Explorer1 Nov 22 2019, 10:24 PM

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.

Posted by: centsworth_II Nov 22 2019, 11:06 PM

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).

Posted by: Juramike Dec 1 2019, 03:59 PM

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".)

Posted by: JRehling Dec 1 2019, 06:59 PM

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.

Posted by: rlorenz Dec 5 2019, 04:07 AM

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).




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'....

Posted by: Steve5304 Dec 6 2019, 02:17 AM

QUOTE (rlorenz @ Dec 5 2019, 05:07 AM) *
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).




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'....




I really enjoyed your post. Very informational. Thanks for this

Posted by: ngunn Dec 6 2019, 04:40 PM

I too am glad to see this topic revisited here. I remember we had a discussion along similar lines a number of years ago that many current members and visitors may have missed. There is so much potential on Titan for active processes that don't fit within familiar terrestrial categories and timescales. That's one reason why it will be a fascinating place to explore further. It would be a tremendous aid to understanding if we had a way of establishing even the relative chronology of surface features large and small. Absolute dating of any kind would be even better, of course. Meanwhile those Iranian salt extrusions are great to think about. They don't need internal heat to drive them for a start.

Posted by: kymani76 Dec 10 2019, 08:48 PM

Slightly off topic, but still relevant...here is my take at 3d view of Dragonfly's landing area using SAR data, combined with DTM from dr. Lorenz....the view is towards northwest...Selk crater is on the right...in front of it to the south sand dunes can be seen...as I understand, Dragonfly will touch down somewhere among those dunes in 2034.



Jake

Posted by: Daniele_bianchino_Italy Jul 8 2020, 11:12 AM

I hope this mission will show us magnificent things. We are all a little bitter for not seeing the seas of ethane-methane. Maybe it's everyone's dream. I hope there are many hidden things unknown to us between Shangri-La and the selK crater. I would not like to see a colder copy of Mars (dunes, dunes and more dunes) after many years of waiting :-) I also trust in the extension of the mission for objectives not yet thought out (I hope wet objectives). We inhabitants of planet Earth cannot miss this opportunity!

Posted by: centsworth_II Jul 8 2020, 03:06 PM

Huygens was designed to land in liquid, but did not. I don't think Dragonfly's landing in even a deep puddle would end well. sad.gif

Posted by: Decepticon Jul 9 2020, 02:25 PM

QUOTE (centsworth_II @ Jul 8 2020, 10:06 AM) *
Huygens was designed to land in liquid, but did not. I don't think Dragonfly's landing in even a deep puddle would end well. sad.gif



I thought dragonfly starts its flight right away. After decent and deployment.

Posted by: mcaplinger Jul 9 2020, 03:44 PM

QUOTE (Decepticon @ Jul 9 2020, 06:25 AM) *
I thought dragonfly starts its flight right away. After decent and deployment.

And then it descends under power and lands after a fairly limited flight.

I think we should define a rule banning complaining about not going to lakes.

Posted by: Decepticon Jul 9 2020, 06:11 PM

QUOTE (mcaplinger @ Jul 9 2020, 10:44 AM) *
And then it descends under power and lands after a fairly limited flight.

I think we should define a rule banning complaining about not going to lakes.



Huh? I didn't complain! blink.gif

Posted by: mcaplinger Jul 9 2020, 06:40 PM

QUOTE (Decepticon @ Jul 9 2020, 10:11 AM) *
Huh? I didn't complain! blink.gif

Read the past few messages. I wasn't sure what point you were trying to make in that context. Certainly there has been some complaining in this thread.

Posted by: nprev Jul 10 2020, 10:40 AM

Alright, no more complaining about lakes, which includes complaining about people complaining. This is making me complain & so we're now perilously close to an infinite meta-loop or something...

Posted by: JRehling Jul 11 2020, 10:17 PM

I'm sorry that Titan is so marvelously diverse that we can't see all of its variety in one mission. Maybe we should explore Rhea instead, to avoid this conundrum! Rhea Orbiter and Multiple Landers or bust.

Posted by: volcanopele Jul 12 2020, 12:23 AM

Exactly, and I'm sure that in the next round of Discovery proposals, particularly if two are selected this time around for the 2026 and 2028 windows, there will be at least one TiME-like mission to Titan's northern lakes. Maybe? Assuming Discovery maintains its every two year cadence, that puts the next launch window around 2030? Northern equinox is in 2039 I think... Given Titan's diverse geology, I'm sure that Dragonfly won't be the only lander in the near to medium future to Titan.

And I 100% endorse a mission to Rhea. But it really is sample return or bust from that tremendously exciting world.

Posted by: vjkane Jul 12 2020, 01:19 AM

QUOTE (JRehling @ Jul 11 2020, 03:17 PM) *
I'm sorry that Titan is so marvelously diverse that we can't see all of its variety in one mission. Maybe we should explore Rhea instead, to avoid this conundrum! Rhea Orbiter and Multiple Landers or bust.

Your point on Titan is exactly that of this draft Decadal white paper: https://drive.google.com/file/d/1d3lGh3_lQcyFTJxwsWO3SQdyAyRc0qPF/view?usp=sharing


A mission such as this one, https://www.youtube.com/watch?v=NAM8SWw14vs&list=PLQ7WzZtg-qMBtrVb1OumD53X8UG597sks&index=9&t=0s, would need to use many gravity assists from the moons inside Titan's orbit, including Rhea, to match orbits with Enceladus. So not quite a Rhea orbiter/multiple landers/sample return mission, but a multi-Rhea-Dione-Tethys flyby bonus mission.

Posted by: Steve G Jul 30 2020, 03:50 AM

What's the interaction of the RTG's heat going to be in the local environment and atmosphere? That's a lot of heat interacting with a lot of cold.

Posted by: Explorer1 Jul 30 2020, 12:22 PM

There will probably be some condensation (even Huygens saw a droplet fall across the camera, I recall?). I'm sure they will do plenty of testing in a Titan simulation chamber once assembled, if that hasn't already been done for the individual components. We will know it is real when we see it flying in a chamber...

Posted by: rlorenz Aug 3 2020, 03:33 AM

QUOTE (Explorer1 @ Jul 30 2020, 07:22 AM) *
There will probably be some condensation (even Huygens saw a droplet fall across the camera, I recall?). I'm sure they will do plenty of testing in a Titan simulation chamber once assembled, if that hasn't already been done for the individual components. We will know it is real when we see it flying in a chamber...


Is Curiosity real? Did you see the descent stage doing a skycrane manoeuvre in a chamber? No. And yet it is real.

And MSL was a flagship project, not a cost-constrained New Frontiers mission.

Validation and Verification on planetary missions relies, of physical and fiscal necessity, on much analysis as well as testing, because the testing can never completely replicate the planetary environment anyway (put a Titan chamber in the Vomit Comet to replicate gravity.....? Something close was done once - at the wheel level, not the rover level, to test wheel/soil interaction for the Apollo LRV. But never since.) Typically one tests some key aspects, and uses models to bridge that data to the planetary setting. There will be aerodynamic tests at relevant Reynolds numbers and densities (e.g. TDT and/or NTF wind tunnels at Langley) and we are building a Titan chamber at APL for thermal balance tests etc, but earth gravity is earth gravity.... so like other planetary projects we use a lot of analytic and computer models. (But unlike most, can fly a scaled-down and/or lightweighted vehicle)

The possible droplet detected in a Huygens image was likely the result of surface heating by a lamp, dumping 20 W of heat on a small patch of ground (20cm across)
That's actually a pretty strong degree of heating.

Dragonfly needs the heat from a radioisotope power source to stay warm (just as MSL) and (like MSL) uses a pumped fluid loop to pull the heat inside. (It of course is ultimately rejected to the environment through the insulation all over the lander body, but at a low power density.) The meteorological measurements need to take this into account and are being designed accordingly

See my papers

Lorenz, R. D., 2016. Heat Rejection in the Titan Surface Environment : Impact on Science Investigations, AIAA Journal of Thermophysics and Heat Transfer, 30, 257-265

R D Lorenz, Thermal Interaction of the Huygens Probe with the Titan Environment : Surface Windspeed Constraint, Icarus, 182, 559-566, 2006

R. D. Lorenz, H. Niemann, D. Harpold, J. Zarnecki, Titan’s Damp Ground : Constraints on Titan Surface Thermal Properties from the Temperature Evolution of the Huygens GCMS inlet, Meteoritics and Planetary Science. 41, 1405-1414, 2006.

Lorenz, R. D. and K. S. Sotzen, Buoyant Thermal Plumes from Planetary Landers : Application to the Height of Meteorology Masts, Planetary and Space Science, 90, 81-89, 2014

Lorenz, R. D. 2018. Atmospheric Test Environments for Planetary In-Situ Missions: never quite "Test as you fly", Advances in Space Research, 62, 1884-1894


Posted by: Explorer1 Aug 3 2020, 04:50 AM

Thank you for the very detailed response; I could have phrased the last sentence better. (I should have said I will know it's real when I see it!) My reply to Steve G was made with the Insight mole's troubles in mind (unusual physical properties in the environment impossible to predict ahead of time). Titan's surface is complex in an entirely different way, so I'm glad to hear of the lower power density. The next six years will be exciting no matter what....

Posted by: rlorenz Feb 8 2021, 02:42 PM

A paper describing the factors in site selection for Dragonfly, and the datasets describing the target area, is now online

https://iopscience.iop.org/article/10.3847/PSJ/abd08f

Posted by: vjkane Feb 9 2021, 02:25 AM

QUOTE (rlorenz @ Feb 8 2021, 06:42 AM) *
A paper describing the factors in site selection for Dragonfly, and the datasets describing the target area, is now online

https://iopscience.iop.org/article/10.3847/PSJ/abd08f

In the paper, there's a figure of the trajectory to Titan with the original launch date of 2025, which has now been delayed to 2027 per NASA's directive (as I understand, to spread out spending).

In the paper for the caption of the figure, there's a statement that states, "Phase A interplanetary trajectory with launch in 2025 and Titan arrival in 2034. The launch date has been prescribed to be 2027, although the arrival date and conditions remain the same."

I see two interpretations of this: 1) despite a two year delay in launch, Dragonfly still arrives at Titan in 2034; 2) the arrival date refers to local time on Titan relative to its orbit around Saturn but is a later Earth calendar year.

Posted by: rlorenz Feb 9 2021, 03:30 AM

QUOTE (vjkane @ Feb 8 2021, 09:25 PM) *
In the paper, there's a figure of the trajectory to Titan with the original launch date of 2025, which has now been delayed to 2027 per NASA's directive (as I understand, to spread out spending).
In the paper for the caption of the figure, there's a statement that states, "Phase A interplanetary trajectory with launch in 2025 and Titan arrival in 2034. The launch date has been prescribed to be 2027, although the arrival date and conditions remain the same."
I see two interpretations of this: 1) despite a two year delay in launch, Dragonfly still arrives at Titan in 2034; 2) the arrival date refers to local time on Titan relative to its orbit around Saturn but is a later Earth calendar year.


Yes, that wasnt quite clear. The arrival date will depend on the launch vehicle class that NASA assigns but will in any case be in the mid-2030s, and as you say the local time will be the same as shown.

Posted by: vjkane Feb 9 2021, 03:42 PM

QUOTE (rlorenz @ Feb 8 2021, 07:30 PM) *
Yes, that wasnt quite clear. The arrival date will depend on the launch vehicle class that NASA assigns but will in any case be in the mid-2030s, and as you say the local time will be the same as shown.

I know you can't speak to this, Ralph, since launch vehicle selections are confidential. But here's hoping for a selection that limits the travel time, both so we are all younger when Dragonfly arrives and so there's a longer life for the MMRTG once on Titan.

Posted by: mcaplinger Feb 9 2021, 04:49 PM

QUOTE (vjkane @ Feb 9 2021, 07:42 AM) *
But here's hoping for a selection that limits the travel time...

See https://trs.jpl.nasa.gov/handle/2014/48626 for trajectory details.

The LV selection is obviously a tradeoff between LV cost and mission ops costs. Since the former is a lump sum up front and the latter is spread out over time, the latter tends to be favored by budgeteers, but we'll see.

Posted by: JRehling Feb 9 2021, 08:48 PM

This is a fascinating read, Ralph. As a starting point, it's enlightening to understand that operational constraints and the basic dynamics of Titan's orbit and rotation favor a certain range of longitudes. This is also true, though the details are different, for Venus, which meant that seven Venera landers ended up in a fairly small fraction of the planet's surface. So, not only were Dragonfly landing sites relatively constrained, but future landing sites will either respect the same constraints or have to make some tradeoffs to go beyond them.

Posted by: vjkane Feb 10 2021, 01:51 AM

QUOTE (rlorenz @ Feb 8 2021, 06:42 AM) *
A paper describing the factors in site selection for Dragonfly, and the datasets describing the target area, is now online

https://iopscience.iop.org/article/10.3847/PSJ/abd08f

I believe that the landing site is on the anti Saturn hemisphere, so no images of Saturn in the sky

Posted by: rlorenz Feb 10 2021, 04:53 AM

QUOTE (vjkane @ Feb 9 2021, 08:51 PM) *
I believe that the landing site is on the anti Saturn hemisphere, so no images of Saturn in the sky


Sadly true. I guess maybe Iapetus might be in the night sky at some point, havent looked into whether it would be detectable.

When we were working on the Titan Mare Explorer, IIRC even though Ligeia is on the anti-Saturn hemisphere, I think it was far enough north that Saturn would have been visible from the early part of descent..... but Selk is far too close to the anti-Saturn point.

Posted by: rlorenz Feb 10 2021, 04:59 AM

QUOTE (mcaplinger @ Feb 9 2021, 11:49 AM) *
See https://trs.jpl.nasa.gov/handle/2014/48626 for trajectory details.


That paper goes into the orbit design very nicely, but was written and presented at a stage during the New Frontiers competition when we werent comfortable disclosing the actual science target landing site..... hence no maps.

Posted by: rlorenz Feb 10 2021, 05:07 AM

QUOTE (JRehling @ Feb 9 2021, 03:48 PM) *
This is a fascinating read, Ralph. As a starting point, it's enlightening to understand that operational constraints and the basic dynamics of Titan's orbit and rotation favor a certain range of longitudes. This is also true, though the details are different, for Venus, which meant that seven Venera landers ended up in a fairly small fraction of the planet's surface. So, not only were Dragonfly landing sites relatively constrained, but future landing sites will either respect the same constraints or have to make some tradeoffs to go beyond them.


I guess the best example of the astrodynamics-->landing site mapping is the Soviet sample return missions, where there was basically just a point on the Moon where if you launch straight upwards and keep going, you get back to Soviet territory....

As for future Titan missions, the large atmospheric scale height means the aerothermodynamic constraints on entry angle allow the torus of locations for a given incoming asymptote to be quite broad. So the situation may be less constrained than at Venus. Furthermore, while the longitude of the asymptote on Venus is restricted for a given launch date, on Titan it sweeps around every 16 days, so for a given cruise trajectory you can just nudge the arrival back or forth by a week to get to a different longitude (although at the penalty of increasing your entry speed. Whether that matters or not depends on how fast the interplanetary trajectory is, and how close or otherwise you are to some heatshield material limit.)

It's a fascinating multidisciplinary problem.

Posted by: charborob Feb 10 2021, 11:53 AM

QUOTE (vjkane @ Feb 9 2021, 08:51 PM) *
I believe that the landing site is on the anti Saturn hemisphere, so no images of Saturn in the sky


Would Saturn actually be visible through the atmospheric haze? A quick Google search couldn't give me a definitive answer.

Posted by: Steve G Feb 10 2021, 03:06 PM

Landing on the Saturn-side would be more than just for pretty pictures. It would offer some light during the eight-day-long nights.

Posted by: vjkane Feb 10 2021, 03:51 PM

QUOTE (charborob @ Feb 10 2021, 03:53 AM) *
Would Saturn actually be visible through the atmospheric haze? A quick Google search couldn't give me a definitive answer.

One of the Titan spectral windows falls in the near infrared range that is commonly covered by visible-to-near-infrared imaging chips used for spacecraft instruments. I forget the specific band.

Posted by: mcaplinger Feb 10 2021, 04:21 PM

QUOTE (vjkane @ Feb 10 2021, 07:51 AM) *
One of the Titan spectral windows falls in the near infrared range that is commonly covered by visible-to-near-infrared imaging chips used for spacecraft instruments. I forget the specific band.

938 nm, and depending on the sensor, "covered" is overstating it a little. For one sensor we commonly use, the sensitivity at 938 nm is about a factor of 6 lower at 938 nm than it is at say 600 nm. Still, you have to work with what you've got.

Posted by: JRehling Feb 10 2021, 11:03 PM

QUOTE (charborob @ Feb 10 2021, 04:53 AM) *
Would Saturn actually be visible through the atmospheric haze? A quick Google search couldn't give me a definitive answer.


Nor, likely, would a casual analysis. There are a lot of variables here rather than an absolute categorical answer. Think about trying to see the Earth's Moon (or the Sun) through various degrees of cloud cover on Earth. This can depend on the altitude of the object above the horizon, the wavelength, whether we are talking about the human eye vs. the result of extensive processing. The Milky Way is by no means visible to the human eye from my urban location, but if I work at it, I can bring it out in long exposures.

Certainly if Saturn were the main source of light in a titanian night sky, it would provide detectible illumination. How sharp the image of Saturn would be would depend on the variables I mentioned and more.

Remember that Voyager managed to capture surface detail on Titan in visible wavelengths. The signal to noise ratio is not zero, but it is low.

Posted by: rlorenz Feb 11 2021, 12:07 AM

QUOTE (JRehling @ Feb 10 2021, 06:03 PM) *
Certainly if Saturn were the main source of light in a titanian night sky, it would provide detectible illumination.
How sharp the image of Saturn would be would depend on the variables I mentioned and more.

Remember that Voyager managed to capture surface detail on Titan in visible wavelengths. The signal to noise ratio is not zero, but it is low.


Yes, exactly right. The sharpness will depend very much on wavelength - the optical depth decreases by a few between visible red and 938nm.

Note also that the haze is strongly forward-scattering, so some directional information is retained in each scattering event.

There are a few journal papers on the haze scattering function and its effects, this one (open access) looks at twilight
https://iopscience.iop.org/article/10.3847/1538-3881/aae519/meta

There's also this simulation project which is pretty solid
https://www.cadfem.net/fileadmin/user_upload/05-cadfem-informs/resource-library/Revealing_the_True_Face_of_Titan_With_Physical_Simulation.pdf

I'm not aware of any simulations of the night sky generally, nor of Saturn specifically

Ralph

Posted by: Explorer1 Feb 11 2021, 12:51 AM

Not to make this even more of an academic discussion, but Dragonfly's cameras don't even face the sky anyway, right? They seem to be pointed mostly down and at an angle in all the concept illustrations I've seen.

Posted by: scalbers Feb 11 2021, 12:57 AM

Fyi - my rules of thumb for seeing the sun through clouds (at least on Earth) are that an optical depth of <10 along the line of sight allows one to see sharp (albeit low contrast) edges (through cloud droplets). If there are crystalline clouds (like ice on Earth), the sun can be seen up to an optical depth of 25, though it is more of a frosted appearance without any sharp edges. Cloud ice on Earth though probably has a sharper forward scattering peak than the Titan haze and cloud liquid has a somewhat wider peak.

I've read that the optical depth in green light at the zenith on Titan is about 8, so by this analogy Saturn should be dimly visible at night if it's reasonably high in the sky. However the light from Saturn is more diluted than the sun case, since the angular diameter of Saturn seen from Titan is about 10 times that of the Sun from Earth. This lowers the surface brightness of Saturn relative to the overall scattered light illumination. The associated requirement would change to an optical depth <5 to be needed. This is just barely achieved in red light, so perhaps Saturn's disk as a sharp outline would only be seen visually with difficulty near the zenith, if one uses a red filter.

Conversely the Sun seen from Titan is a much smaller angular diameter and this would translate into being easier to see from Titan, compared with the same type of cloud/haze from Earth. The view in this landing video from a while back shows an interesting representation of the Sun at the 4:22 time mark: https://www.youtube.com/watch?v=9L471ct7YDo.

Posted by: vjkane Feb 11 2021, 01:18 AM

QUOTE (Explorer1 @ Feb 10 2021, 04:51 PM) *
Not to make this even more of an academic discussion, but Dragonfly's cameras don't even face the sky anyway, right? They seem to be pointed mostly down and at an angle in all the concept illustrations I've seen.

If I remember correctly, there are two cameras on the main antenna, which is used to point the cameras and in that mode will function much like the turret on Curiosity. So we will get views across the landscape and presumably they could be pointed to image the sky. (Perhaps images of the sun will be taken to estimate optical depth as on Curiosity.)

Posted by: Fox Feb 11 2021, 03:07 PM

QUOTE (JRehling @ Feb 10 2021, 05:03 PM) *
Remember that Voyager managed to capture surface detail on Titan in visible wavelengths. The signal to noise ratio is not zero, but it is low.


Interesting, I've never heard that. Always read that the surface was "completely obscured" or things like that.

Posted by: dtolman Feb 11 2021, 03:15 PM

Is there a map available on the public internet showing what the Saturn facing hemisphere and anti-Saturn "far side" hemisphere are of Titan? Its hard to visualize just how far over the horizon (or under its feet!) Saturn will be from the landing site of Dragonfly.

Posted by: vjkane Feb 11 2021, 03:45 PM

QUOTE (dtolman @ Feb 11 2021, 07:15 AM) *
Is there a map available on the public internet showing what the Saturn facing hemisphere and anti-Saturn "far side" hemisphere are of Titan? Its hard to visualize just how far over the horizon (or under its feet!) Saturn will be from the landing site of Dragonfly.

I believe that 0 degrees longitude is the sub-Saturn point and 180 degrees is the anti-Saturn point.

Posted by: scalbers Feb 11 2021, 05:01 PM

QUOTE (Fox @ Feb 11 2021, 03:07 PM) *
Interesting, I've never heard that. Always read that the surface was "completely obscured" or things like that.

Yes it makes sense that at least large scale variations in surface albedo could be seen from space, since some diffused light passes through the clouds, then is either reflected back by the surface or it isn't. I suspect this wouldn't necessarily translate into seeing Saturn from the ground however.

Dtolman - this map has 0 degree longitude at the edges and would be the longitude best facing Saturn: https://solarsystem.nasa.gov/resources/16252/titan-global-map-june-2015/

Posted by: rlorenz Feb 12 2021, 03:40 AM

QUOTE (Fox @ Feb 11 2021, 10:07 AM) *
Interesting, I've never heard that. Always read that the surface was "completely obscured" or things like that.


I talk about this in my book "Titan Unveiled". When (during my postdoc at U. Arizona) we published the first maps of Titan based on the 1994 Hubble observations, there was some limited longitude coverage at visible red wavelengths (673nm) that seemed to show (albeit more faintly, maybe 2% contrast) the same surface features we saw in the near-IR at 940nm (~10% contrast)

Some years later, a grad student (Jim Richardson) worked with myself and Alfred McEwen on a project to see if we could pull out the same features (basically the western edge of Xanadu, where it has good contrast against the Shangri-La sand sea) in the Voyager orange filter images (~640nm). Indeed, there it was. You probably wouldnt be sure it was there if the Voyager data was all you had, but the exercise showed there was still a bit of signal leaking through the haze even at that wavelength. Jim's work was published in Icarus http://www.jerichardsonjr.info/Papers/jerichardson_ICAR2004.pdf

Posted by: rlorenz Feb 12 2021, 03:53 AM

QUOTE (vjkane @ Feb 11 2021, 10:45 AM) *
I believe that 0 degrees longitude is the sub-Saturn point and 180 degrees is the anti-Saturn point.


Correct. (I think the formal IAU definition refers it to the subsaturn point at a particular epoch). Because Titan's orbit around Saturn is eccentric (0.029), there is a 'libration' such that Saturn oscillates back and forth by about 3 degrees in longitude about that zero (and grows and shrinks by 3%)

Fun trivia (as I note in my 'Saturn's Moon Titan: Owners Workshop Manual" - the 14 looks at Titan that we got in 1994 with HST were selected to have 7 somewhat closely-spaced looks (somewhat over Xanadu), to measure possible cloud dynamics, and the rest to fill out the longitude range. The way things panned out with HST scheduling, there was one longer interval between images than the others, which meant there was a bit of a coverage gap, as it happens close to the sub-saturn longitude.

Because putting this in the middle of the maps would be rather unsightly, we centered our maps on 180 longitude, rather than zero. Then because much Cassini planning (especially radar, in which I was involved) relied on those HST maps, the radar maps used the same longitude convention. Similarly, the Cassini camera ISS looked at the same wavelengths as HST, so it was natural for their maps to also put 180 in the middle for comparison. This convention puts Xanadu to the right.

The VIMS team published most of their maps with 0 in the middle, so Xanadu appears to the left.

Posted by: Webscientist Feb 12 2021, 09:17 PM

QUOTE (rlorenz @ Feb 12 2021, 04:53 AM) *
Correct. (I think the formal IAU definition refers it to the subsaturn point at a particular epoch). Because Titan's orbit around Saturn is eccentric (0.029), there is a 'libration' such that Saturn oscillates back and forth by about 3 degrees in longitude about that zero (and grows and shrinks by 3%)


Thanks Ralph for the details. Tidally locked but significantly oscillating. If we could discern the glow, Saturn would be living in the sky to a certain extent during the 16 days of revolution around Saturn. A few days ago, I saw the Sun with a remarkably uniform appearance (a very nice white) without burning my eyes through a layer of clouds (or maybe a layer of fog I don't know...) in the sky. During a fraction of a second, I was wondering whether it was the Moon or the Sun.
Sometimes some physical phenomena can be really surprising!
Perhaps, there are some oasis or mirage effects with the disk of Saturn in the sky! laugh.gif

Posted by: volcanopele Feb 13 2021, 01:30 AM

QUOTE (rlorenz @ Feb 11 2021, 08:40 PM) *
Jim's work was published in Icarus http://www.jerichardsonjr.info/Papers/jerichardson_ICAR2004.pdf

It has been a while since I've read that paper and I have to say, looking at figure 4, the comparison with the Cassini ISS map, with the margin of Xanadu, Adiri, and Dilmun is actually quite close. Like you said, if you didn't have a better data set to compare it to it would be hard to believe it, but still.

Posted by: JRehling Feb 13 2021, 03:11 AM

FWIW, another change that Saturn would display in the titanian sky would be phases. For something under half of Titan's diurnal cycle, Saturn would be above the horizon without daylight interfering, and there would be some changes in phase.

Per Voyager, we also would have had no idea at the time if variations in albedo were largely due to surface variations or variations in a cloud deck. A significant source of misconception in the early mapping of Mercury from Earth around 1880-1950 was the mistaken notion that clouds were moving around. This led observers to dismiss basically accurate visual observations that should have rejected the notion that Mercury was tidally locked.

Because Voyager only flew by Titan once (twice if you count the more distant Voyager 2) we had no way to check if the observable details stayed locked in place over time.

Posted by: rlorenz Feb 28 2021, 03:33 AM

A new post on the Dragonfly website about sampling system testing in APL's new Titan simulation chamber

https://dragonfly.jhuapl.edu/News-and-Resources/From-the-Flight-Line/

Posted by: vjkane May 21 2021, 01:00 AM

The latest annual GAO (Government Accounting Office) report on NASA missions provides an update on Dragonfly (there's some more detail on potential technical issues (the focus of the report is on risks to missions; these seem normal for a mission so early in its development).

https://www.gao.gov/assets/gao-21-306.pdf


PROJECT SUMMARY

NASA has not yet approved a preliminary cost and schedule estimate for Dragonfly. In September 2020, NASA directed Dragonfly to start planning for a launch readiness date in 2027 because NASA said it was not possible to fund the project's plan for an earlier launch date due to competing budget priorities. This will require replanning development efforts. Dragonfly is continuing to finalize the designs of its science payload and develop its critical technologies before its preliminary design review. The project is tracking a risk that it may experience delays acquiring Domestic Phenolic-Impregnated Carbon Ablator (PICA-D) material used for its spacecraft thermal protection system. Further, the delayed launch readiness date now means the project may benefit from a heavy-lift class launch vehicle that would allow it to arrive at Titan sooner than the medium-class launch vehicle included in the original design proposal. Such a change would affect the design, and the project is currently evaluating its launch vehicle options.
Launch

Uncertainty surrounding the project's launch vehicle could affect the project's design. According to NASA officials, the project could benefit from using a heavy-lift class launch vehicle as it would allow Dragonfly to arrive at Titan almost 3 years earlier, even with a delayed launch. However, in accordance with its original proposal, the project is baselining its design to a medium-lift vehicle, which would allow Dragonfly to arrive at Titan in 2036. In addition, the launch vehicle will need to be nuclear-certified because Dragonfly will use a Multi-Mission Radioisotope Thermoelectric Generator for power. However, of the five candidate launch vehicles, only one is nuclear certified as of August 2020. The project would prefer to have the vehicle selected early in case changes are needed to the design based on the selection. Currently, the project is evaluating its launch vehicle options, which will inform NASA's selection.

Posted by: charborob May 21 2021, 11:24 AM

According to https://spaceflightnow.com/2016/07/25/nasa-books-nuclear-certified-atlas-5-rocket-for-mars-2020-rover-launch/, as of August 2020, the Atlas 5 was the only nuclear-certified launch vehicle.

Posted by: Hungry4info Jun 14 2021, 10:35 PM

Apparently Dragonfly might get to Titan three years early thanks to an approved decision to place it on a different, more capable launch vehicle. This is more important than getting the science earlier, it extends the amount of the lifetime of the RTG that's spent on Titan, and reduces how much of the RTG decays meaninglessly en route to the destination.
https://twitter.com/ThePlanetaryGuy/status/1404547710372311042

QUOTE
This is information from Lori Glaze, during today's NASA PAC meeting.

Posted by: dtolman Jun 15 2021, 08:24 PM

For context, assuming the 2027 launch date is the same, then the arrival date will now be 2033! That slashes the cruise phase from 9 years to 6 years.

I can't find anything on the expected useful lifespan of the RTG for powering flight - https://www.nasa.gov/dragonfly/dragonfly-overview/index.html. Does that imply with the reduced cruise phase that we should expect the RTG to be able to power flight for almost 6 years now?

Posted by: mcaplinger Jun 15 2021, 08:47 PM

QUOTE (dtolman @ Jun 15 2021, 12:24 PM) *
I can't find anything on the expected useful lifespan of the RTG for powering flight...

The RTG charges batteries, which then power flight. Reduced electrical output from the RTG means it will take longer for the batteries to charge, which only affects flight cadence, not the ability to fly, up to the point that the batteries simply can't be charged up enough to keep the vehicle alive at all.

Minor nit: RTG useful lifetime for electrical generation is set by thermocouple degradation, not by Pu decay.

Posted by: vjkane Jun 15 2021, 10:33 PM

QUOTE (mcaplinger @ Jun 15 2021, 12:47 PM) *
The RTG charges batteries, which then power flight. Reduced electrical output from the RTG means it will take longer for the batteries to charge, which only affects flight cadence, not the ability to fly, up to the point that the batteries simply can't be charged up enough to keep the vehicle alive at all.

Minor nit: RTG useful lifetime for electrical generation is set by thermocouple degradation, not by Pu decay.

RTG lifetimes are usually quoted, if I remember correctly, as ~14 years. With the original flight time to Saturn of ~7 years and a nominal ~3 year prime mission, this would have left ~4 years for an extended mission.

However, as mcaplinger notes, the power drop off from the RTG is gradual. As long as the battery can still recharge, then the mission could go on for many years, but perhaps with a reduced flight frequency and/or time per flight. Other parts of Dragonfly such as the rotors may go first.

Curiosity works much the same way - the RTG powers a battery that powers travel and high-powered instrument use. There has been talk about the need for reduced levels of activity for Curiosity starting in a couple of so years. One goal has been to get well in into the sulfate-bearing layers before this becomes a hindrance.

Posted by: mcaplinger Jun 15 2021, 10:57 PM

QUOTE (vjkane @ Jun 15 2021, 03:33 PM) *
Curiosity works much the same way - the RTG powers a battery that powers travel and high-powered instrument use.

It should also be observed that while waste heat from the RTG -- which doesn't tail off very quickly -- is used to keep the internals of MSL warm, the actuators and external instruments use electrical heaters, and that can be a substantial use of energy, especially in the winter.

How Dragonfly compares as far as thermal design I don't know. But at -180C typical temperatures, Titan makes Mars look downright balmy.

Posted by: vjkane Jun 17 2021, 02:11 PM

QUOTE (mcaplinger @ Jun 15 2021, 03:57 PM) *
It should also be observed that while waste heat from the RTG -- which doesn't tail off very quickly -- is used to keep the internals of MSL warm, the actuators and external instruments use electrical heaters, and that can be a substantial use of energy, especially in the winter.

I once read a paper or conference abstract on what it would take to enable a rover on Mars to travel hundreds of kilometers during its mission. The key was low temperature lubricants for the wheels. Apparently, a substantial amount of the battery's output goes to warming the lubricant in the wheels.

Posted by: Brian Swift Jun 17 2021, 09:10 PM

QUOTE (vjkane @ Jun 17 2021, 06:11 AM) *
I once read a paper or conference abstract on what it would take to enable a rover on Mars to travel hundreds of kilometers during its mission. The key was low temperature lubricants for the wheels. Apparently, a substantial amount of the battery's output goes to warming the lubricant in the wheels.

In this podcast interview with JPL material scientist Dr. Douglas Hofmann, I believe he mentioned a goal of developing materials that would allow creation of gears and bearings that could operate without lubricant in off-earth environments. http://omegataupodcast.net/247-bulk-metallic-glass/

Posted by: mcaplinger Jun 17 2021, 10:58 PM

Some may recall that a substantial part of the reason for the launch slip of MSL was the failure to get dry lubricants to work. https://www.thespacereview.com/article/1319/1 And as far as I know, they aren't used on M2020 either.

Posted by: vjkane Jul 24 2021, 02:29 PM

The Dragonfly science team has just published a paper on the science goals for the Dragonfly mission n The Planetary Science Journal:

https://iopscience.iop.org/article/10.3847/PSJ/abfdcf/pdf

It is an open access paper. I learned quite a bit from it.

Posted by: vjkane Jul 28 2021, 06:30 PM

At today's meeting of the Decadal Survey, the chief of the Planetary Science Division, Lori Glaze, provided an overview of the budget and several missions. I captured this screenshot of the Dragonfly slide, which confirms the switch to a heavy lift launcher and the earlier arrival date.

In the QA, she was asked if this switch meant the Falcon Heavy. She said that the actual vehicle would be selected through NASA's launch procurement process which has not started, but that the procurement would be for this class of launcher.

 

Posted by: JRehling Jul 29 2021, 03:07 PM

As a topic that's more general than any one mission: It seems like there could be a lot of missions returning data during the same timeframe in the early 2030s. If most of Dragonfly, Veritas, EnVision, JUICE, Europa Clipper, and Lucy are all in their prime missions at the same time, that would be a busy time for the data downlink assets.

Posted by: Fox Dec 31 2021, 05:34 PM

Many missions like these receive extensions and the spacecraft last far longer than their original timelines. In light of that, I wonder if there is any chance that Dragonfly could eventually reach the Huygens probe landing site, and photograph Huygens?

Posted by: Explorer1 Dec 31 2021, 07:06 PM

QUOTE (Fox @ Dec 31 2021, 01:34 PM) *
Many missions like these receive extensions and the spacecraft last far longer than their original timelines. In light of that, I wonder if there is any chance that Dragonfly could eventually reach the Huygens probe landing site, and photograph Huygens?


Someone asked that question here of the P.I., Dr. Elizabeth Turtle: https://youtu.be/9ls9fV8U_wg?t=1487


Posted by: vjkane Dec 31 2021, 08:13 PM

QUOTE (Fox @ Dec 31 2021, 09:34 AM) *
Many missions like these receive extensions and the spacecraft last far longer than their original timelines. In light of that, I wonder if there is any chance that Dragonfly could eventually reach the Huygens probe landing site, and photograph Huygens?

Assuming no other system failures, the limiting factor for the mission should be electrical power. This is, as I understand it, primarily limited by the decay/failure of thermocouples, not the decay of the plutonium; so it is electrical power, not "waste" heat to keep Dragonfly warm, that should limit the mission. Curiosity's managers are already thinking about the coming limitations on operations as it takes the battery (which really runs the rover and instruments) longer and longer to recharge. The same will eventually occur for Dragonfly. Flights eventually will become fewer per terrestrial year as the battery takes longer than a single Titanian day to recharge.

That said, by my reckoning, Dragonfly should have 4-6 years of normal operation on the surface (the thermocouples also will be decaying while in flight to Titan). Figure that the primary and and extended mission around Selk Crater might take 3-4 years. That would leave 2-3 years for an extended extended mission.

The illustrations of Dragonfly's flights tend to show it moving in hops of ~8 km per Titan day, and there are just under 23 Titan days per Earth year. So that would suggest (ignoring Titan days where the craft remains in the same landing area for more intensive studies) that Dragonfly might travel 200 km per terrestrial year. In an extended mission with lots of operational experience, perhaps the operators would go for longer flights. Your guess as to how long that might be. 300-400 km/terrestrial year?

I did a simple little map with an approximate scale bar that shows distances around the Selk crater. You can make your own estimates.

However, I suspect that simply traveling a long distance to see a long frozen probe might not be a priority for the mission scientists. If I had my fantasy destination for an extended mission, it would be Menerva Crater where the impactor probably broke through the crust to the ocean below, allowing its frozen contents to now be examined on the surface. Unfortunately, it is many, many thousands of kilometers away.

[I'm always hesitant to post speculations about Dragonfly knowing that Ralph L. will read them. smile.gif I hope I haven't gone too astray.

 

Posted by: vjkane Dec 31 2021, 09:33 PM

Sorry for the duplicate post. Not seeing the delete post button

Posted by: JRehling Jan 1 2022, 03:19 AM

Given the combination of mobility, the complexity of Titan, and the extraordinary degree to which Titan is as-yet unknown, it seems that this mission has tremendous potential for opportunistic changes in direction once we learn more as the mission itself is in progress. And so, comparatively less ability for us to make a determined plan for an extended mission and feel sure that we can already commit to it before we see what Dragonfly discovers during the main mission.

Titan has probably the most diverse surface of any world in the solar system, the most complex chemistry, geology involving materials not seen at all on Earth, and we have thus far seen only one fairly homogeneous (though very interesting!) patch of it close-up. I'd lay a bet that before Dragonfly gets far into the main mission, we're going to see things that merit investigation and won't even have been anticipated until we see them.

Posted by: rlorenz Jan 1 2022, 03:32 AM

QUOTE (vjkane @ Dec 31 2021, 03:13 PM) *
it is electrical power, not "waste" heat to keep Dragonfly warm, that should limit the mission.
....

I did a simple little map with an approximate scale bar that shows distances around the Selk crater. You can make your own estimates.
....
I hope I haven't gone too astray.


Van

Your reasoning is basically sound, and your graphic sums the situation up well. Dragonfly has unprecedented mobility compared with wheeled rovers, but it is still regional, not global, mobility. I talk about some of all this in my book "Planetary Exploration with Ingenuity and Dragonfly : Rotary-Wing Flight on Mars and Titan" to be published by AIAA next year....

The electrical power is limiting, yes, if by limit you mean range or science activity. As you say, declining power just means it takes longer to charge the battery. But "Limiting" as in "ending operations altogether" might well be a thermal limit rather than an electrical one.

The basic plan is to fly once every other Titan day, to allow full investigation of (and downlink of the data from) each site. There's also a commissioning phase of many months before full-length 'traverse' flights begin to be routinely performed. And conjunctions also knock out an opportunity per year. So the practical/useful range is maybe only of the order of 200 km in the 3-and-a-bit year mission. The design is still evolving so the flight actual performance is not yet known (and in practical terms is limited by quasi-arbitrary margin policies like battery discharge levels), and I could believe we would not typically fly as far as the battery would let us anyway insofar as it may be difficult scientifically to identify the best future landing sites at shallow slant ranges of more than a few km. Obviously we do want at least need the ability to fly from one interdune area to the next, though (typically a 3-4km spacing, although you want not to have to fly orthogonal to the dunes, so that means a 5-6km distance capability). Note that the net progress per flight is only a third of the actual flight range, as we do a two-steps-forward-one-step-back aerial reconnaissance of the candidate future landing sites.

So, a lot of details are still in work. But from a global perspective we're exploring the Selk crater, not anywhere else. Even if you play games like 'forget 50% depth of discharge rules, fly until the battery melts', and 'forget doing science and downlinking any data, fly every Tsol', and 'forget scouting future landing sites, just fly as far as you can and hope for the best' (after all, the first landing is made 'in the blind' using the on-board hazard detection and what we know from Cassini, without any in-situ scouting), but it still wouldnt get you to Menrva.

No reason you couldnt send a build-to-print Dragonfly to Menrva, though ;-). (Aeroshell design might need looking at, though, as Menrva's on the leading face of Titan, so entry velocity would be higher).

The original question of visiting Huygens recalls the artist's impression I had James Garry do for my first book "Lifting Titan's Veil", which shows a faintly War-of-the-Worlds gangly coaxial-rotor helicopter shining a searchlight on the heroic corpse of the Huygens probe..... ;-)



Posted by: rlorenz Jan 13 2022, 08:09 PM

Video of Dragonfly navigation systems being tested on a half-scale drone at Imperial Dunes

https://www.youtube.com/watch?v=naDSycxZqEM



Before the actual Dragonfly soars over the organic dunes of Titan, the team developing the NASA rotorcraft lander at the Johns Hopkins Applied Physics Laboratory is testing the concept by sending instrumented models over the sands of Earth’s deserts.

This is what sent nine APL engineers to Imperial Dunes, California, in September 2021. Over three days the team flew a “testbed” over the dunes to collect images and sensor data they’ll need to develop optical navigation algorithms for the real Dragonfly, set to embark for Saturn’s largest moon in 2027.

Working from sunrise to sunset, the team collected data from numerous flights in a variety of lighting conditions – and captured data critical to developing and testing the navigation algorithms. The natural dunes serve as an analog to the terrain that Dragonfly will encounter on Titan, and the environment is ideal for testing the navigation algorithms that will use camera images to sense the rotorcraft’s position and motion.

The Dragonfly team has built two identical, half-scale “Integrated Technology Platform” drones (called ITPs) with hardware and software similar to what will fly on the real thing – including eight independent rotor assemblies, a flight computer and digital image processor, a navigation camera, an inertial measurement unit with comparable gyroscopes and accelerometers, and initial versions of the image processing and flight control algorithms.

The ITPs are undergoing a graduated series of flight tests to evaluate their performance. In the past year, the drones have logged over 100 flights at multiple test sites and under varying wind conditions as their configurations have matured in complexity.

Learn more about Dragonfly at http://dragonfly.jhuapl.edu

Posted by: nprev Jan 14 2022, 01:53 AM

Thanks, Ralph! Very cool, as of course is the entire mission. smile.gif

Quick question about Titanian surface mechanical properties: I assume that Huygens is the main reference point for assumptions about what kind of surfaces Dragon may land upon, but will there be any provisions in the event that, say, it encounters a place with sticky organic goo? Will there be any sensors on the landing skids to measure gross soil properties (or indirect ways to infer that)?

For most unfavorable scenarios I imagine that even a very minor amount of heat applied would quickly remove unwanted material & free the vehicle.

Posted by: rlorenz Jan 14 2022, 02:40 AM

QUOTE (nprev @ Jan 13 2022, 08:53 PM) *
Quick question about Titanian surface mechanical properties: I assume that Huygens is the main reference point for assumptions about what kind of surfaces Dragon may land upon, but will there be any provisions in the event that, say, it encounters a place with sticky organic goo? Will there be any sensors on the landing skids to measure gross soil properties (or indirect ways to infer that)?
For most unfavorable scenarios I imagine that even a very minor amount of heat applied would quickly remove unwanted material & free the vehicle.


The Huygens landing site is not a great analog actually, in that it was a damp cobblestrewn streambed. The most likely initial landing sites will be dune plinths or interdune plains, so (dry) sand and gravel. But of course Huygens-like areas cannot be excluded.

The surface force model assumptions being used in Dragonfly design are currently undergoing peer review. But there is indeed an allocation in our takeoff thrust requirements for surface adhesion.

There are sensors on the skids to assess wetness (via thermal response) and we have a whole strategy laid out for diagnosing surface properties prior to committing to ingesting surface material in the sampling system.

Heating the skids is absolutely not done. Too energetically demanding, and more likely to cause harm than good. The skids attain ambient temperature during EDL, and stay Titan-cold forever.

Posted by: nprev Jan 14 2022, 03:13 AM

Thank you! Vastly informative as per your usual. smile.gif

Posted by: Fox Jan 16 2022, 01:58 AM

Yes, this is such an interesting subject! I'm really looking forward to watching the development of this mission.

Posted by: Decepticon Jan 16 2022, 05:41 AM

Do the cameras compensate for the low light levels?


Posted by: mcaplinger Jan 16 2022, 06:29 PM

QUOTE (Decepticon @ Jan 15 2022, 09:41 PM) *
Do the cameras compensate for the low light levels?

Mostly by making the exposure time longer, like visible cameras nearly always do. For example, https://atmos.nmsu.edu/PDS/data/hpdisr_0001/BROWSE/PNG/PNGIMG_0698_08671_S_0910_M.PNG had an exposure time of 50 msec, and the DISR SLI had 23x17 micron pixels and a bandpass of 660 to 1100 nm, f/2.5. So it's dim, but not exactly dark.

Posted by: StargazeInWonder Jan 24 2022, 02:02 AM

Here is a composite of three images from Ralph, et al's 2021 paper, "Selection and Characteristics of the Dragonfly Landing Site near Selk Crater, Titan." This uses the brightness of ISS, color from VIMS, and a sample landing ellipse found in a third image.

The distance from a landing site in the ellipse to inside Selk varies from a best case of 55 km to a worst case of 120 km. With a primary mission traverse of 200 km, that will allow exploration inside the crater after taking a beeline there, or some lateral exploration on the way there. In the better cases, Dragonfly would be able to enter Selk, then leave it after some exploration inside, taking a different path out than it took in. In an ideal case, it might be possible to reach Dilmun, the bright area seen just barely in the upper right, but I don't know if there's any realistic scenario where the decisions enabling that could or would be made as the mission unfolds.

Hopefully, this helps people visualize how the mission will really be focused on Selk and its immediate vicinity, as already noted by the people who would know best!

 

Posted by: vjkane Jan 24 2022, 10:06 PM

QUOTE (StargazeInWonder @ Jan 23 2022, 06:02 PM) *
Here is a composite of three images from Ralph, et al's 2021 paper, "Selection and Characteristics of the Dragonfly Landing Site near Selk Crater, Titan." This uses the brightness of ISS, color from VIMS, and a sample landing ellipse found in a third image.

Much appreciated!

Posted by: rlorenz Jan 25 2022, 02:49 AM

QUOTE (StargazeInWonder @ Jan 23 2022, 09:02 PM) *
Hopefully, this helps people visualize how the mission will really be focused on Selk and its immediate vicinity, as already noted by the people who would know best!


The scale bar looks slightly long in this graphic (tho it may be a bit long in fig. 6 of the paper too.) Selk itself has an 84km rim diameter..

But your takeaway message is quite right

Posted by: Tom Tamlyn Oct 27 2022, 01:35 PM

Interesting article in Aerospace America:

QUOTE
Designing Dragonfly, NASA’s Titan Explorer

A planetary lander that can fly to new sampling sites will be able to do far more surface science than a slow, trundling rover. Easy flight in the super-dense atmosphere and ultra-low gravity of Saturn’s cryogenic moon, Titan, makes it the perfect celestial body on which to test the idea. Paul Marks spoke to the team behind NASA’s Dragonfly.


https://aerospaceamerica.aiaa.org/features/designing-dragonfly-nasas-titan-explorer/

Posted by: Bill Harris Oct 28 2022, 07:06 PM

Indeed interesting. And Ralph's book on the Ingenuity and Dragonfly planetary exploration helicopters is an excellent primer to understanding these, uh, "Helirovers".

--Bill

Posted by: climber Apr 3 2023, 07:24 AM

About recent Dragonfly PDR : https://scitechdaily.com/saturns-moon-titan-beckons-as-nasas-dragonfly-mission-achieves-critical-milestone/

Posted by: vikingmars Apr 4 2023, 09:38 AM

QUOTE (climber @ Apr 3 2023, 09:24 AM) *
About recent Dragonfly PDR : https://scitechdaily.com/saturns-moon-titan-beckons-as-nasas-dragonfly-mission-achieves-critical-milestone/

Thanks a lot Climber for this useful link smile.gif

Posted by: StargazeInWonder Apr 4 2023, 02:51 PM

Great work by the Dragonfly team.

The article refers to the rotorcraft approach as "game-changing." Of course, there is basically one other world where long distance travel by rotorcraft would be new, so I hope we see that particular game be changed sometime this century with a Venus rotorcraft.

The next Titan northern solstice after Dragonfly's will be about 45 years from now, so I think waiting for such a mission to the northern seas, anyway, will fall upon posterity.

Posted by: climber Nov 29 2023, 08:38 PM

Good news for la libellule !
https://www.jhuapl.edu/news/news-releases/231128-dragonfly-mission-development

Posted by: vjkane Nov 30 2023, 05:39 AM

QUOTE (StargazeInWonder @ Apr 4 2023, 06:51 AM) *
The next Titan northern solstice after Dragonfly's will be about 45 years from now, so I think waiting for such a mission to the northern seas, anyway, will fall upon posterity.

Solstice, with it's tilt toward the sun and Earth, is only necessary if the probe is doing direct to Earth communications (and if you want to do some imaging). There have been proposals for lake landers that are short-lived and relay their data back through their carrier craft. They can land and carry out their measurements in darkness.

Posted by: rlorenz Dec 1 2023, 03:07 AM

QUOTE (StargazeInWonder @ Apr 4 2023, 09:51 AM) *
The article refers to the rotorcraft approach as "game-changing." Of course, there is basically one other world where long distance travel by rotorcraft would be new, so I hope we see that particular game be changed sometime this century with a Venus rotorcraft.

The next Titan northern solstice after Dragonfly's will be about 45 years from now, so I think waiting for such a mission to the northern seas, anyway, will fall upon posterity.


Fixed-wing (or lighter-than-air) probably makes more sense for Venus. Rotorcraft only come into their own when accessing a planetary surface, which is challenging at Venus owing to the temperatures....

And Titan northern summer solstice is in 2046, which is only 23 years from now, not 45 years.. (recall Titan's year is only 29.5 Earth years long) But I agree that is a dismayingly distant epoch...

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