"Dragonfly" Titan explorer drone, NASA funds Johns Hopkins University Applied Physics Laboratory (APL) |
"Dragonfly" Titan explorer drone, NASA funds Johns Hopkins University Applied Physics Laboratory (APL) |
Dec 31 2017, 04:46 PM
Post
#16
|
|
Member Group: Members Posts: 715 Joined: 22-April 05 Member No.: 351 |
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. -------------------- |
|
|
Dec 31 2017, 04:50 PM
Post
#17
|
|
Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
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. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
|
|
|
Dec 31 2017, 05:24 PM
Post
#18
|
|
Member Group: Members Posts: 684 Joined: 24-July 15 Member No.: 7619 |
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... |
|
|
Dec 31 2017, 10:17 PM
Post
#19
|
|
Merciless Robot Group: Admin Posts: 8785 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
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. -------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
|
|
|
Jan 1 2018, 04:39 AM
Post
#20
|
|
Junior Member Group: Members Posts: 40 Joined: 28-July 07 Member No.: 2984 |
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?
|
|
|
Jan 1 2018, 03:30 PM
Post
#21
|
|
Member Group: Members Posts: 715 Joined: 22-April 05 Member No.: 351 |
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. -------------------- |
|
|
Jan 1 2018, 10:44 PM
Post
#22
|
|
Junior Member Group: Members Posts: 40 Joined: 28-July 07 Member No.: 2984 |
|
|
|
Jan 2 2018, 05:51 PM
Post
#23
|
|
Member Group: Members Posts: 120 Joined: 26-May 15 From: Rome - Italy Member No.: 7482 |
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! |
|
|
Jan 2 2018, 06:23 PM
Post
#24
|
|
Member Group: Admin Posts: 976 Joined: 29-September 06 From: Pasadena, CA - USA Member No.: 1200 |
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 -------------------- Disclaimer: all opinions, ideas and information included here are my own,and should not be intended to represent opinion or policy of my employer.
|
|
|
Jan 2 2018, 06:54 PM
Post
#25
|
|
Senior Member Group: Members Posts: 4256 Joined: 17-January 05 Member No.: 152 |
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. |
|
|
Jan 2 2018, 07:56 PM
Post
#26
|
|
Senior Member Group: Members Posts: 2542 Joined: 13-September 05 Member No.: 497 |
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. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
|
|
|
Jan 2 2018, 08:49 PM
Post
#27
|
|
Senior Member Group: Members Posts: 2106 Joined: 13-February 10 From: Ontario Member No.: 5221 |
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 |
|
|
Jan 2 2018, 10:41 PM
Post
#28
|
|
Member Group: Members Posts: 715 Joined: 22-April 05 Member No.: 351 |
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.) -------------------- |
|
|
Jan 3 2018, 06:05 PM
Post
#29
|
|
Member Group: Members Posts: 100 Joined: 30-November 05 From: Antibes, France Member No.: 594 |
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 |
|
|
Jan 3 2018, 06:10 PM
Post
#30
|
|
Member Group: Members Posts: 100 Joined: 30-November 05 From: Antibes, France Member No.: 594 |
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. |
|
|
Lo-Fi Version | Time is now: 23rd September 2024 - 12:01 AM |
RULES AND GUIDELINES Please read the Forum Rules and Guidelines before posting. IMAGE COPYRIGHT |
OPINIONS AND MODERATION Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators. |
SUPPORT THE FORUM Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member. |