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From an interview with Tim Canham, Mars Helicopter Operations Lead at JPL in the article How NASA Designed a Helicopter That Could Fly Autonomously on Mars:

It has a sequencing engine on board, and we write a set of sequences, a series of commands, and we upload that file to the helicopter and it executes those commands. We plan the guidance part of the flights on the ground in simulation as a series of waypoints, and those waypoints are the sequence of commands that we send to the guidance software. When we want the helicopter to fly, we tell it to go, and the guidance software takes over and executes taking off, traversing to the different waypoints, and then landing.

But in this case Ingenuity doesn't need waypoints, just direction and distance !

We use a cellphone-grade IMU, a laser altimeter (from SparkFun), and a downward-pointing VGA camera for monocular feature tracking. A few dozen features are compared frame to frame to track relative position to figure out direction and speed, which is how the helicopter navigates. It's all done by estimates of position, as opposed to memorizing features or creating a map.

(Emphasis by me)

So Ingenuity doesn't need (and has not) a terrain database and thus will not need the processing power to consistently match images with that !

From Guidance and Control for a Mars Helicopter:

The camera is used together with the laser rangefinder to determine the height above ground and the translational velocity; this information is fused with the IMU solution to limit drift over time. Details of the navigation design will be published in a future paper.

Fig.6 in that article shows us the sequence of Mode Commander states and transitions, and that in the Idle state command from ground station is awaited.
Could not somehow in the last file upload the exit of the command signal from the ground station be replaced by the exit of an internal signal, for instance from a temperature control unit or from a unit that monitors the battery voltage ?
Or the exit from a signal from an internal timer so that the flight could take place at a certain time each (other) day ?

Looking at Possible Path for Perseverance Rover and MARS 2020 ROVER Depot Caching Strategy, the sample cache depot might be at the entrance of Neretva Vallis, about 10 km away from the current position of Ingenuity. So if the helicopter could fly in that direction a hundred meters every other day, it would arrive at the depot location in 200 days, well before Perseverance could show up there.

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    $\begingroup$ Even if theoretically possible, it would be of dubious wisdom. The sample caches are the primary scientific objective of at least two different spacecraft. The helicopter was an "extra". You are going to trust the helicopter to avoid crashing into your expensive primary objective? $\endgroup$
    – DrSheldon
    Apr 25 at 15:21
  • $\begingroup$ @DrSheldon The helicopter could be programmed to fly no longer than a year for instance, so if it would arrive there within that time, it could be planned to be before the arrival of Perseverance. $\endgroup$
    – Cornelis
    Apr 25 at 16:15
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    $\begingroup$ I'm still not clear on the why. What does getting the helicopter to the depot accomplish? There's no particular reason to bring it back, and given its size (much larger than the sample vials), it would be quite difficult to do. $\endgroup$
    – Harabeck
    Apr 26 at 17:28
  • $\begingroup$ @Harabeck No, not to bring it back to Earth, but when Perseverance would show up there too, radio contact could be resumed and Ingenuity' s condition could be examined, even over a period of several years. $\endgroup$
    – Cornelis
    Apr 26 at 17:46
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Mars has a standard lat/long coordinate system, so the waypoints are indeed fixed points on the surface. But Mars doesn't have a flock of satellites providing a location service like GPS.

So Ingenuity can navigate only optically (albeit with help from its sensor-fusion IMU, per this question's edit).

It could conceivably travel for some time without help from Perseverance (and thus from anything at all), but it may lack the processing power to consistently match its nav cam's images and laser altimeter's distances to an onboard terrain database (if it even had one).

So a multi-day journey to a destination at some bearing and distance could be embarked on after Perseverance's departure, but without a map obstacle avoidance would be tricky. During a flight, if its sensors show that it's climbing a steep hill that might lack a spot to land on, or traversing optically featureless sand, or some other hazard, should it return to its last launch point and tomorrow try to feel out an alternate route? Should it make a rudimentary map each morning by pirouetting while nonlevel, so the camera and altimeter sweep out more territory? Can it stitch such data together? Can NASA write and upload that much new software in just a few days? These questions are too ambitious for Ingenuity, but might well be attempted by its successors. Right now, such a trip would end up like that famous DARPA one.

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    $\begingroup$ From the first article, "A few dozen features are compared frame to frame to track relative position to figure out direction and speed, which is how the helicopter navigates. It's all done by estimates of position, as opposed to memorizing features or creating a map." Are you sure that Ingenuity has a terrain database ? It doesn't need one ! $\endgroup$
    – Cornelis
    Apr 25 at 17:08
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    $\begingroup$ I don't think Ingenuity has a terrain db, because that's not needed for its intended short hops. But even if NASA sent it one, for it to navigate autonomously for days on end after Perseverance trundles off, its computer might not be adequate to use it. $\endgroup$ Apr 25 at 19:57
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    $\begingroup$ It's only hope for going any place specifically is to stay with the rover. How long could the Mars helicopter Ingenuity keep up with the Perseverance rover if it wanted to? $\endgroup$
    – uhoh
    Apr 26 at 12:25
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    $\begingroup$ @uhoh and Camille. I've made an edit with a sentence from the linked article that says that information from the camera and the rangefinder is fused with the IMU solution to limit drift over time. Couldn't that prevent increasing drift ? $\endgroup$
    – Cornelis
    Apr 26 at 17:03
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    $\begingroup$ @Cornelis cool video illustrating how optical flow (or similar) is used in the helicopter youtu.be/Sr9yk5eBL1M $\endgroup$
    – uhoh
    May 1 at 13:36

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