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"Dragonfly" Titan explorer drone, NASA funds Johns Hopkins University Applied Physics Laboratory (APL)
vjkane
post Dec 31 2017, 04:46 PM
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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.




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mcaplinger
post Dec 31 2017, 04:50 PM
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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.


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HSchirmer
post Dec 31 2017, 05:24 PM
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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...p;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...
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nprev
post Dec 31 2017, 10:17 PM
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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.


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Y Bar Ranch
post Jan 1 2018, 04:39 AM
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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?
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vjkane
post Jan 1 2018, 03:30 PM
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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.


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Y Bar Ranch
post Jan 1 2018, 10:44 PM
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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.
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Daniele_bianchin...
post Jan 2 2018, 05:51 PM
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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!
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RoverDriver
post Jan 2 2018, 06:23 PM
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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


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fredk
post Jan 2 2018, 06:54 PM
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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.
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mcaplinger
post Jan 2 2018, 07:56 PM
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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.


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Explorer1
post Jan 2 2018, 08:49 PM
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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 not yet confirmed
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vjkane
post Jan 2 2018, 10:41 PM
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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 not yet confirmed

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.)


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Webscientist
post Jan 3 2018, 06:05 PM
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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



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Webscientist
post Jan 3 2018, 06:10 PM
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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.

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