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Perseverance Rover lands on Mars [video]

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Re: Perseverance Rover lands on Mars [video]

#381

Post by unanswered »

jtsiskin wrote: post #339
unanswered wrote: post #196

Earlier quoted context omitted.

Yes, yes, you have shown you know what relativity is. But the relative velocity of earth and mars — which I can't convince Wolfram Alpha to tell me, but it's got to be on the order of their orbital velocity so let's say 5x10^4 mph — is a tiny tiny fraction of c so their inertial reference frames are essentially identical. So sitting in our reference frame, we can make inferences about what's happening "now" on mars,s…

No, I don’t think you’re quiet understanding what they are saying. They aren’t talking about the different speeds of earth or Mars. Simultaneity is not “perfectly well defined in a single intertidal reference frame”. That is just a convention. If the RTT of earth to Mars is 20 minutes, then we can say that it takes us 20 minutes for our message to reach the rover, and the rover’s message arrives instantly, and that’s…

Except that an observer located in the (hypothetical/approximate) common reference frame, but situated halfway to Mars, will report observations inconsistent with this definition (NB of course we receive their report at a time consistent with the definition, but the contents of the report are not consistent). So yes, you can play games with your definition of simultaneity, but you will win stupid prizes like observers in the same reference frame no longer agreeing about simultaneity when such a result is worse than what relativity requires.

Your link points this out. You can play these games; I don't dispute it. But it's a separate matter entirely from anything to do with relativity, as your link points out, which is itself separate from the classical problem I originally posed. So we are now two steps removed from anything relevant to the Mars rover; I guess we get a sense of pride and accomplishment?

Re: Perseverance Rover lands on Mars [video]

#382

Post by acomjean »

jaegerpicker wrote: post #84
BurningFrog wrote: post #71

Earlier quoted context omitted.

Is part of the joy that they now have secure jobs for years to come?

Maybe but for me I think it would the joy of completing such a massive task so well. They literally just achieved something that no one else in history has.

It is the fifth rover... But still super impressive feat, with years of detailed planning. I boogles my mind thinking about all the bits of engineering put together to make this happen.

I can’t wait to see what it sends back. Always celebrate your successes.

Re: Perseverance Rover lands on Mars [video]

#383

Post by mr_toad »

alkonaut wrote: post #195
andbberger wrote: post #59

Earlier quoted context omitted.

no. hohmann transfer, not a straight line. also there are no absolute reference frames.

> also there are no absolute reference frames. "Well, officer, perhaps to you it seemed like I was speeding there..."

Just, remember that you're standing on a planet that's evolving And revolving at nine hundred miles an hour That's orbiting at nineteen miles a second, so it's reckoned A sun that is the source of all our power The sun, and you and me, and all the stars that we can see Are moving at a million miles a day In an outer spiral arm at forty thousand miles an hour Of the galaxy we call the Milky Way

- Monty Python.

Re: Perseverance Rover lands on Mars [video]

#384

Post by nwallin »

whuffman wrote: post #189
nwallin wrote: post #177

Earlier quoted context omitted.

Other posters have pointed out that it's the hazard avoidance camera, but they haven't said why the hazard avoidance camera is black and white. When you do computer vision, the first step you do is convert your color image into a black and white image, and run your CV algorithms on the black and white image. This is because when you're looking at objects and shapes and stuff, it's contrast that tells you where the bo…

Just as a heads up, the HazCams on Perseverance are in fact in color (Source: https://link.springer.com/article/10.1007/s11214-020-00765-9 - "The Mars 2020 Navcams and Hazcams offer three primary improvements over MER and MSL. The first improvement is an upgrade to a detector with 3-channel, red/green/blue (RGB) color capability that will enable better contextual imaging capabilities than the previous engineering cam…

Huh, I guess so. Looking over the study it looks like they had issues by looking at dirt in scoops and being unable to tell whether it's Martian dirt or a shadow.

I have a feeling I'd be the angry guy in the meeting who wouldn't accept the consensus. "but what about latency! what about the descend and landing!" shakes fist

Re: Perseverance Rover lands on Mars [video]

#385

Post by lmm »

mulmen wrote: post #359
lmm wrote: post #350

Earlier quoted context omitted.

> If I am traveling toward Mars at 47 meters per second it doesn’t help me to know that is also .047km per second. Yes it does. It means you can immediately sanity-check your numbers even if you don't have a good sense of what meters and kilometers are, because you have that base/kilo relationship. > My bike ride is six miles, I’m never going to express that in feet. You can eyeball how fast you're going in feet per…

I’m not sure how that sanity check works, can you explain? Do you mean checking conversion between meters and kilometers? Because sure, that’s easier but you could just do everything in meters instead and not run the risk of crashing a spacecraft because of unnecessary conversions or bad assumptions. I estimate my bike ride progress in landmarks and time. Not feet per second. Did I get to the boat ramp in 20minutes?…

> Do you mean checking conversion between meters and kilometers? Because sure, that’s easier but you could just do everything in meters instead and not run the risk of crashing a spacecraft because of unnecessary conversions or bad assumptions.

But you'll have small distances and large distances and pieces from external sources who use measurements on a scale that makes sense to them. You can make your external sources do conversions themselves, but that's just moving the problem around. There will usually end up being a point, or probably several points, where you have to relate a small distance to a large distance, and wherever that happens, a human sanity check is a help.

> I estimate my bike ride progress in landmarks and time. Not feet per second. Did I get to the boat ramp in 20minutes? Better speed up and get to the park by 30.

Precisely - you have no sense of the relation between your speed and how far you can go, because you're using a terrible measurement system, and you don't even notice the how that's robbing you of the ability to develop useful intuitions.

Re: Perseverance Rover lands on Mars [video]

#386

Post by shazmosushi »

notum wrote: post #124
joe_91 wrote: post #53

Earlier quoted context omitted.

NASA also requires 10-100x more money & time to do so. Both just have very different ways of working. Both work and there are pro's and con's to either way!

I'll just leave Thunderf00t's latest video here: https://www.youtube.com/watch?v=4TxkE_oYrjU Let's not diminish ether's breakthroughs, but financial isn't one of SpaceX's.

That video was incorrect on so many levels that I have made a rebuttal: https://www.youtube.com/watch?v=36o4UrS9OS4

Re: Perseverance Rover lands on Mars [video]

#387

Post by jessriedel »

michaelwilson wrote: post #297
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,…

It turns out that they took 640lbs (!) of weight to mars to be tossed off at various points during EDL. The video is worth watching if you'd like some more of the nitty-gritty behind the process: https://www.youtube.com/watch?v=W0NakShgbHY

Great video! I am also surprised by the fact that they bring that much mass just to jettison. In theory they could mounted some of the useful mass on a slider/rail system to achieve the necessary adjustment to the mass distribution without dropping mass overall, but apparently it wasn't worth the complexity/volume cost.

I'm sort of surprised we don't yet have ML powered "de-accent-ization". His french accent isn't hard to understand at normal speed, but when I set it to 1.5x or 2x speed it becomes hard to decipher in a way native speakers usually are not. If there was just a button (for him or me) to hit to tweak the sounds a bit to reduce the accent, I bet this problem would go away.

Re: Perseverance Rover lands on Mars [video]

#388

Post by randomchars »

unanswered wrote: post #378
fckthisguy wrote: post #264

Earlier quoted context omitted.

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

Why is it acceptable to use the wrong pronoun, such as "they", for someone who chooses the pronoun "she" or "he"?

> used to refer to a person of unspecified gender.

How is this offensive to anyone??

Re: Perseverance Rover lands on Mars [video]

#389

Post by mulmen »

lmm wrote: post #385
mulmen wrote: post #359

Earlier quoted context omitted.

I’m not sure how that sanity check works, can you explain? Do you mean checking conversion between meters and kilometers? Because sure, that’s easier but you could just do everything in meters instead and not run the risk of crashing a spacecraft because of unnecessary conversions or bad assumptions. I estimate my bike ride progress in landmarks and time. Not feet per second. Did I get to the boat ramp in 20minutes?…

> Do you mean checking conversion between meters and kilometers? Because sure, that’s easier but you could just do everything in meters instead and not run the risk of crashing a spacecraft because of unnecessary conversions or bad assumptions. But you'll have small distances and large distances and pieces from external sources who use measurements on a scale that makes sense to them. You can make your external sourc…

My bicycle doesn’t even have a speedometer so I’m not sure how the metric system is supposed to expand my world. I’m happy looking around and glancing at my watch.

Miles per hour is literally a measure of distance over time. If I wanted to use my GPS I could very easily determine how far I can go in a given amount of time. I can do this equally well in the metric or imperial systems, without converting to feet or meters.

Re: Perseverance Rover lands on Mars [video]

#390

Post by mongol »

JohnJamesRambo wrote: post #361
cdelsolar wrote: post #357

Earlier quoted context omitted.

we are very screwed if they find life on Mars. It means life is incredibly common and thus the Great Filter theory is true and we only have a few years left as a species most likely.

I find it extremely hard to believe you could kill every human being on earth at this point. We’ve reached critical mass, we aren’t going anywhere. When we had that few thousand individuals population bottleneck in the past was when it was dicey. What sort of event could kill every human and end our species? I can only think of planet-wide extinction events like massive asteroid impacts that sterilized the whole eart…

I wonder what a huge Carrington solar storm would do to humanity. If electricity went out everywhere, transformers burned up all over, electronics fried. If this caused transport failures, mass starvation could follow. I really hope a severe solar storm would not be as bad as that and hopefully someone could enlighten me on this.
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