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The animation in the announcement article shows landing on a perfectly smooth surface.

That's not what the photo from Huygens shows - a lot of rocks and pebbles. And as anyone who played with drones/quadcopters will attest, landing with one skid on such a rock will result in the drone tipping over, the propellers digging into the ground, and the need to walk up to the drone and set it upright. Except there's nobody on Titan to set Dragonfly upright in such case.

What measures will Dragonfly have to either prevent or recover from such accidents?

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  • $\begingroup$ I suspect it will make extensive use of intelligent navigation systems. Compare to Chang'e 4 which used active lidar and radar to build a 3D surface map and smart autonomous navigation to pick the ideal spot within its landing zone at the last minute. Clearly Dragonfly will have a much smaller mass budget, but I expect we will see a similar thing... $\endgroup$ – Jack Jun 28 at 9:08
  • $\begingroup$ Due to the coaxial octocopter prop arrangement, the drone should still be able to take off/right itself if multiple propellers are obstructed by the ground or other surface features. Additionally, the drone isn't small, it's like 3 meters to a side. This means that for it to tip over, it's navigation computer must've selected a seriously bad landing site. $\endgroup$ – Dragongeek Jun 28 at 10:01
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They plan to use some form of "site evaluation" to prevent tipping over:

However, technology developments in the last two decades, notably the revolution in availability of multi- rotor drones a made possible by modern compact sensors and autopilots as well as the development of sensing and control capabilities for autonomous landing and site evaluation for planetary landers, made a quadcopter or a similar vehicle a much more feasible prospect in 2016.

They plan to survey future landing sites before attempting a landing:

enter image description here

This paper has more detail:

Once safe landing on arrival is achieved, the rotorcraft mobility capabilities can be exercised progressively— for example, first making a brief hop for a few seconds within the immediate vicinity of the landing site where the terrain will be known from panoramic and/or descent imaging. Depending on the heterogeneity of the surface (e.g., patches of sand), a small displacement of a few meters or tens of meters may enable the sampling of different materials.

Then, flights of progressively increasing duration, range, and/or height can be made, returning to the original, known-safe, landing site. These flights can assess the performance of various sensors—for example, an initial hop may be made using inertial guidance alone, whereas later flights use optical navigation only after the quality of in-flight imaging and the abundance of suitable landmarks on Titan have been verified.

And about the sensors used:

The vehicle makes a sortie over this zone using its sensors (lidar for terrain roughness, imaging, etc.)

When using the reconnaissance method from the graph above, the data gathered during flight will be downloaded and analysed by the operations team before a new landing site is chosen.

Analysis on the ground of the sensor data confirms one or more safe sites within zone B

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  • $\begingroup$ So, only prevention by location choice, no recovery measures? $\endgroup$ – SF. Jul 1 at 7:29
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    $\begingroup$ I haven't seen any, but keep in mind the design is far from finished, and the information available now is very general. $\endgroup$ – Hobbes Jul 1 at 9:18

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