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Mars Rover Perseverance Discussion Thread


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35 minutes ago, cubinator said:

And the scientist who unveiled it was speaking into an identical microphone to demonstrate that it records natural sound.

Indeed, if you tried to listen to it on Mars with your bare ears you would mostly just feel pain in your ears, but you might hear and feel a little whoosh against your spacesuit if you were wearing proper Martian attire.

Or maybe not. You see, microphones are a lot more sensitive to wind-generated turbulence because the turbulence is self-generated by the microphone. This is why there are windscreens for microphones. The turbulence around a fuzzy ball of foam is different (and less) than the turbulence around the edges of a mic, which tend to have some fairly sharp, clean lines and arcs. The noise you would hear from the wind inside a helmet would depend very greatly on the aerodynamics of the helmet. Is it smooth? Does it have sharp edges? Are there any antennas sticking out? Etc.

My previous career as a noise control engineer is kind of resurfacing lately.

Edited by mikegarrison
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1 minute ago, JoeSchmuckatelli said:

Anyone ever tried or had any success in noise cancellation of jets via negative waves?

This is known as active noise control, and it really only works in certain circumstances. The problem is that phase matters.

Mostly this is used for headphones, because the distance between the headphone and the eardrum is very controlled.

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1 hour ago, mikegarrison said:

This is known as active noise control, and it really only works in certain circumstances. The problem is that phase matters.

Mostly this is used for headphones, because the distance between the headphone and the eardrum is very controlled.

I recall that Bombardier tried active noise cancellation in the cabin of the Dash-8 Q400 aircraft, but it struck me more as a gimmick... and we're getting off topic.

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24 minutes ago, PakledHostage said:

I recall that Bombardier tried active noise cancellation in the cabin of the Dash-8 Q400 aircraft, but it struck me more as a gimmick... and we're getting off topic.

Yes, that came to mind for me too.

We (airplane manufacturers) have all looked at it, because passive noise control tends to be heavy. There are two ways to block noise -- mass and damping. Mass is pretty obvious, but also obviously heavy. It tends to work on low frequencies. Damping works on high frequencies, and tends to be expensive. Some things act as both mass and damping, like fiberglass insulation. This is a nearly universal noise and temperature insulation material for airplane cabins.

Active noise control has the potential to be lighter and possibly cheaper, but it has limitations. It's terrible at treating random noise sources like turbulence. And phase matters, so either you have to treat it at the source or at the receiver. Treating it at some intermediate point just tends to result in a few nodes where the cancellation happens, but a lot of other places where you actually made things worse.

With the Q400, they had a very discrete frequency they wanted to treat (the blade-passing frequency of the propellers), which gave them an opportunity to try to make use of active noise control. I don't know much more about the specific details than that, however.

Edited by mikegarrison
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My understanding is there is concern the mic wont even last that long, and end up non-functional before a number of different activities occur during the mission. I assume its because they are more "off the shelf" and not a priority part of the mission?

Would really be a bummer not to hear Perseverance take her first "steps", let alone hear Ingenuity take to the skies, or the drill doing its job, or just "listening" to the world.

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As I personally have seen together with others that milk-white UFO triangle passing right above our site with absolutely no sound, yes, active sound suppression works and THEY use it.

(It's a pity in mid-90x there were no smartphones always at hands).

Edited by kerbiloid
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12 hours ago, JoeSchmuckatelli said:

Nerds

Speaking of nerds... I went back and refined my estimate of Perseverance's entry trajectory.  I initially went with the simplifying assumption that the path between data points was linear (rather than hyperbolic) and that the speed over that distance was just the average of the speeds at the two data points. Unfortunately, the solution is quite sensitive to the angular distance between the data points used in the system of equations, so the small error introduced with that assumption turns out to be significant. That assumption did provide a good seed value for a couple of rounds of iterations, however.

To make a long story short, I refined the solution by computing the actual distance along the hyperbolic curve between the two data points, and computing the actual average speed over that distance. I then adjusted the angular distance between the two points iteratively, so that the distance traveled was correct for the speed and elapsed time between the points. The solution converged quickly. It only took two iterations to settle onto a result that was consistent, all around. I also used the most widely spaced values from the mission control video that were still consistent with the vis-viva equation, in order to minimize the error that results from not knowing the exact elapsed time between the data points. (I used the video's elapsed time at each data point as my time measurement, so I was probably only accurate to +- a second or so.)

Anyhow, the new estimate was that:

The periapsis point of the hyperbolic trajectory was about 76 km below the Martian surface
The hyperbolic eccentricity "e" was about 1.327
The velocity at periapsis (in the absence of pesky atmosphere and rocks) would have been about 5.473 km/sec
The entry interface angle (at the  entry interface time cited during the landing) was -14.6 degrees

And just for completeness, I plotted it.  The heavy read line represents the Martian surface, the dotted red line the Martian atmosphere, and the blue solid line is the entry trajectory. The two pluses show the computed locations of the data points that I used for the estimate.

 

MQYhFJfL_o.png

 

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5 hours ago, sevenperforce said:

Someone on Facebook made an edit of one of the 360 images from Perseverance's navcam to include the sky. This is not the actual sky as seen from the surface of Mars but it is really cool nonetheless.

https://www.facebook.com/360creator/posts/751879702136518

I saw that somewhere else. Apparently you can see Mars in that sky?

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13 hours ago, cubinator said:

The uplook camera should be able to capture some REAL Martian skies sometime...

I wonder if the uplook camera has enough dynamic range to set a low long exposure and really get a good skyview as well a surface lit by starlight....

Edited by sevenperforce
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