A reworked hypothesis about #Ingenuity's last #Flight72 explained with an animation. It is based on a number of assumptions, most of which come out of #NASA's statements.
Animation explained in alt text.
Processed, cropped MCZ_RIGHT, FL: 110mm
looking NW (320°) from RMC 50.1534
Sol 1067, LMST: 10:27:39
@65dBnoise
If the blades failed unexpectedly then presumably it is imperative to know why with sample return helicopters in future based on it. Thus I would think it should be a very high priority target for Perseverance to get as many images as possible from different angles to help them understand - unless of course they already do. I don't recall blades falling off in mid-air being an expected mission end failure mode.
@Undertow
This is all speculation of course. We know that the heli was designed only for a few flights, 5 at most. Not for 72. We don't know how the carbon fiber blades would fair under constant UV radiation. Maybe NASA do know. We don't know what mechanical fatigue of 72 flights, probably half of which flew at high rotor rpm, could cause to them.
If the sequence of events could be established it would be a good point to start. Telemetry before the event could probably give some answers.
@65dBnoise
Probably also worth noting that Ingenuity wasn't designed for 5 flights - that was just all they were given and that only after some/(most?) of the Perseverance senior teams were dragged kicking and screaming (in public!) into allowing a minimal technology demonstration by higher ups. Still 72 flights is to be celebrated whatever the case.
@Undertow
Right, wrong word "designed", Ingenuity was indeed not self destructible. "Expected to operate" should be more accurate. Thanks for pointing that out.
@Undertow
Expectations are mental constructs that project an outcome into the future, forming internal beliefs. Feedback from reality forms a loop with them that we call experience. Our feedback from Ingenuity's reality is limited at present, so theories, whether built on the expected or the unexpected, fill in for missing facts until more of them come to light, if ever, and prove or falsify such theories. Sarcasm indicates (dis)belief, but is poor proof in falsifying a theory, isn't it?
Facts and/or assumptions:
• The #MarsHelicopter flew to an altitude of 12m
• At that altitude of 12m, it hovered for a while, sending telemetry
• It started looking for a clear spot to land
• After selecting the best spot for landing, it started its descent as usual
• During the descent, communication with #Perseverance was lost.
Other (almost) facts:
• Whatever was that caused the failure (mechanical, electrical or electronic), all rotor blades had their tips sheared while one of them
detached from the assembly and flew 13-14m to the SW, bouncing once before it stopped.
• The elevation difference between the location of the helicopter and the broken off blade appears to be less than 0.5m, from the #USGS 1m DTM.
• It takes 0.37s for a body to drop 0.5m under the 3.72m/s² of Martian gravity. The initial velocity for a projectile to travel 13m in 0.37s would be ~35.5 m/s, without taking into consideration friction in the thin Martian air. If friction is to be considered for
a very lightweight object with large surface, like the broken off part of #Ingenuity's blade, then the initial velocity should be significantly higher to cover the same distance.
• If however the blade broke off at a, let's say, 3m altitude, then the initial velocity would be ~14.5 m/s, which is much more logical, considering that a significant amount of kinetic energy would have been consumed by the tip of the blades being sheared before flying away, either by hitting the ground or by
disintegrating in mid air. From a 12m altitude, which was the planned altitude for #Flight72, the initial velocity would need to be only 7.23 m/s.
• The fact that the ejected blade appears to have bounced only once and came to a stop a short distance away from the point of impact suggests that its velocity when it bounced was not high.
All the above appear to suggest that the failure occurred at a higher altitude rather than on the ground. The fact that NASA knows it
@65dBnoise so essentially like what happens to a piece of cheap plastic when one leaves it in the garden on the sun for a year? It had to happen at some point and it happened mid-flight, helped by the kinetic energy? That makes the well known fact that radiation is huge in Mars much more... tangible
lost communications before touchdown, as well as that there are no visible marks on the regolith, other than those probably made by the copter's feet (see https://mastodon.social/@65dBnoise/111992357079999905), seems to support this hypothesis. Is it the only possible explanation? Probably not. But it appears to me to be the most plausible one.
@65dBnoise
The loss of communication is a puzzle, unless the sudden imbalance of the rotors triggered an emergency power shutdown.
If the rotors were still under power at that point, surely the loss of one blade would have caused the heli to spin, having lost the counter-rotation effect. But the footprints of where it bounced don't appear to show rotation.
@tom30519
True. They don't show marks of blades on the regolith either.
The broken blade's trajectory needs an explanation in both cases. A piece of thin blade thrown 13m away from the ground after hitting loose regolith needs some special conditions to happen. The impact would have absorbed most of the kinetic energy of the lightweight blade. Unless the grounding shock broke off its connection to the other blade and it flew off without hitting the ground. But we don't see it in one piece.
@tom30519@65dBnoise
In one of the early press conferences after the incident it was said that one theory was that whatever happened to the blades caused a power demand surge in the motor which caused a "brown-out" and a system reboot. Another theory they said was that battery voltage dropped too low for other reasons triggering a shutdown/reboot during the flight.
@Undertow@65dBnoise
Oh, right. I'd forgotten about that brown-out having been mentioned.
I suppose that, if the severed blade had twisted to present a much greater resistance before breaking off, that would indeed cause a sudden spike in the motor's load.
@65dBnoise During flight, the blade tips are moving at 150 meters per second (40 revolutions per second * 2 * pi * 0.6 meter length of a blade). The middle of the blade would be going half that fast. So they could have enough velocity left, after breaking off on the ground. And if the helicopter was not level when they hit, they could have left with a bit of vertical velocity, to get more distance.
@johnlamping
The tilt of the heli after it landed supports the argument that the broken blade could gain some flight time due to a non zero departure angle. That's a good point.
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