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Perseverance Rover lands on Mars [video]

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Re: Perseverance Rover lands on Mars [video]

#271

Post by Koshkin »

ddingus wrote: post #233
kharak wrote: post #203

Earlier quoted context omitted.

Thank you for the explanation. That was highly interesting. Does anyone else know if the human eye does perceive color directly? Is this at all technically possible? And if yes, why aren't we doing it with cameras?

I believe in purple. After you get done exploring how we perceive colors associated with different wave lengths of light, and how nobody really knows whether these are common somehow, or unique to each of us, that sentence should bring you both a chuckle and some wonder about perception.

From the physiological standpoint human individuals are far, far from being unique. The electrochemical reaction of a neuron in the cortex which indicates the perception of ‘red’ is pretty much the same in any human (and not only).

Re: Perseverance Rover lands on Mars [video]

#272

Post by minitoar »

unanswered wrote: post #223
johncolanduoni wrote: post #215

Earlier quoted context omitted.

Now is the part where someone brings up even with the low relative velocity, you haven’t accounted for the simultaneity issues we’d have if the earth collided with a black hole while the rover landing was happening.

Or the fact that mars is not as deep in the gravity well of the Sun! I wonder if they have to account for that one when programming, like, antenna aiming or something.

IIRC gps suffers about 1hz of blueshift due to descending into earths gravity. I think the velocity (Doppler) shift of the spacecraft is a way bigger factor than the gravitational shifting.

Re: Perseverance Rover lands on Mars [video]

#273

Post by buzzerbetrayed »

fckthisguy wrote: post #264
Daho0n wrote: post #222

Earlier quoted context omitted.

S/he already did. We just don't know yet.

You can just say "they". (Not trying to be judgy. People just seem to forget about the gender neutral use of "they".)

There are like 500 other ways you could have said what you just said as well. Doesn’t mean the way you said it is invalid.

Re: Perseverance Rover lands on Mars [video]

#274

Post by ddingus »

Koshkin wrote: post #271
ddingus wrote: post #233

Earlier quoted context omitted.

I believe in purple. After you get done exploring how we perceive colors associated with different wave lengths of light, and how nobody really knows whether these are common somehow, or unique to each of us, that sentence should bring you both a chuckle and some wonder about perception.

From the physiological standpoint human individuals are far, far from being unique. The electrochemical reaction of a neuron in the cortex which indicates the perception of ‘red’ is pretty much the same in any human (and not only).

Whether that subjective perception is the same remains unknown. We have no solid way to communicate any of that yet.

I am inclined to believe it is, but we do not really know.

Re: Perseverance Rover lands on Mars [video]

#275

Post by boilerupnc »

spaetzleesser wrote: post #236
tectonic wrote: post #14

You can also watch an EDL visualization in your browser: https://eyes.nasa.gov/apps/mars2020/#/home And read about how it will use Terrain Relative Navigation to find a safe landing spot: https://www.jpl.nasa.gov/news/a-neil-armstrong-for-mars-land... Perseverance is phenomenally complex, its Sample Caching System alone contains 3,000+ parts and two robotic arms. So exited for all the sciencing this nuclear-powered,…

They should make km the default unit and not miles....

NASA has experience in unit foul-ups. Mars Climate Orbiter is the $125M poster project reminding everyone of the importance in having consistency in units.

"At 09:00:46 UT Sept. 23, 1999, the orbiter began its Mars orbit insertion burn as planned. The spacecraft was scheduled to re-establish contact after passing behind Mars, but, unfortunately, no signals were received from the spacecraft.

An investigation indicated that the failure resulted from a navigational error due to commands from Earth being sent in English units (in this case, pound-seconds) without being converted into the metric standard (Newton-seconds).

The error caused the orbiter to miss its intended orbit (87 to 93 miles or 140 to 50 kilometers) and to fall into the Martian atmosphere at approximately 35 miles (57 kilometers) in altitude and to disintegrate due to atmospheric stresses."[0]

[0] https://solarsystem.nasa.gov/missions/mars-climate-orbiter/i...

Re: Perseverance Rover lands on Mars [video]

#276

Post by dylan604 »

m4rtink wrote: post #150
jxcl wrote: post #127

Earlier quoted context omitted.

> My guess is that using color sensors would have either increased the 3D mapping precision or added weight/power/bandwidth requirements, or otherwise been less robust in that environment. I think you meant to say decreased? In which case I think you would be correct! Camera pixels are made up of these things called photosites which don't by themselves record color, only brightness. In order to record color informati…

That's why "real" space cameras usually have color filters on a carousel before the sensor - they take 3 pictures each with different filter and BAM, color! That way you get high regulation as well as color. You can also have some special (infrared, ultraviolet, etc.) Filters on the carousel, not just RGB.

>and BAM, color!

and BAM, false color! FTFY

Re: Perseverance Rover lands on Mars [video]

#278

Post by vietjtnguyen »

ggreer wrote: post #225
nelsonmandela wrote: post #117

Apparently the copter was made with off-the-shelf parts. I wonder if I can cop a replica somewhere, and how it would fly considering it is built for martian air

If it was made with off-the-shelf parts then it's a testament to how wasteful NASA has become. Building that helicopter took them 6 years and $80 million.[1] 1. See page 20 of the launch press kit: https://www.jpl.nasa.gov/news/press_kits/mars_2020/download/...

They can't exactly procure a bunch of parts and then call it a day. Lots of the cost is tied to the verification and validation. Then there's the system design, requirements engineering, trade studies, system integration, engineering models, simulation, software, environmental testing, launch costs, ground command and data systems, interfacing with the rover, etc. Paying engineers to do all that is what makes it so expensive.

Re: Perseverance Rover lands on Mars [video]

#279

Post by natosaichek »

Koshkin wrote: post #262
natosaichek wrote: post #217

Earlier quoted context omitted.

What do you mean by "directly"? Color is a human abstraction over the reception intensity of certain wavelengths of light.

What do you mean “abstraction”? The colors that I am seeing look very concrete to me. (Also, the “wavelength theory” of color perception does not explain why TV screens work.)

The human retina is composed of cells that are responsive to different wavelengths of light. Color is the word that we use to describe the subjective sensations associated with certain patterns of stimulation of those cells. There is no "yellowness" in a bananna. We cannot construct an instrument capable of measuring "yellow" as such. What we can measure are the intensities of wavelengths of light.

We can notice that when people say they perceive "yellow" that the spectral intensity graph has certain patterns. This is the physical phenomenon that produces the sensation of "yellow."

Humans are not good at judging reality introspectively. We experience everything heavily filtered through a variety of lenses. Our feeling that color is "concrete" is not predictive or explanatory... we cannot build mechanisms based on it. The idea that our perception of color is a result of interactions between certain wavelengths of light and certain photosensitive tissues in our eyes is both predictive and explanatory. We can design systems that have similar types of wavelength intensity sensitivity components and measure the physical response of those systems. That's how cameras work.

We can reverse the process and take those measured wavelength intensities and re-emit them from variable-wavelength light sources and produce images. That's how you're reading what I've typed right now - the images produced by the display you're looking at were generated in this fashion.

I'm not sure what you mean by the “wavelength theory” of color perception.

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