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NASA's Perseverance rover sends stunning images

bbc.com

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Re: NASA's Perseverance rover sends stunning images

#241

Post by gambiting »

histriosum wrote: post #195
dmix wrote: post #181

Earlier quoted context omitted.

My question is why was the “sound of Mars” release only 18 seconds long? Why not record hours of what it sounds like to be on another planet? Even the sound recordings from decades ago on (I think Titan) was only a short creepy clip. I understand it’s mostly going to be wind and interspliced with the robots sounds but I still don’t get how we don’t have hours of Mars already.

My guess would be bandwidth. Every bit of bandwidth is precious, so they probably dont have the spare budget to send long audio files without obvious scientific value...

Yes, but you could record few minutes of sound in the same amount of data taken by one high res photo. I think the good question is why 18 seconds specifically.

Re: NASA's Perseverance rover sends stunning images

#242

Post by gambiting »

idlewords wrote: post #200
marshmallow_12 wrote: post #52

Earlier quoted context omitted.

a glowing green sandwich covered in red sand. But seriously, this stuff is powering those voyager probes 40 years later. Which makes me ask: why do we have to send there technologies 10 billion miles away to make them work? Why can't my fridge be powered this way?

The Russians tried powering a bunch of remote stuff with plutonium batteries during the Soviet era. It did not end well, and cleaning those up has been an ordeal. Pu-238 was also used in pacemakers. The basic problem is just that plutonium is toxic as hell.

I mean, US has been employing RTGs to power all kinds of stuff too, it's not just Russians which did. But yes, actually collecting and decommissioning them after the collapse of the Soviet Union has been an ordeal.

Re: NASA's Perseverance rover sends stunning images

#243

Post by magicalhippo »

tremon wrote: post #239
magicalhippo wrote: post #235

Earlier quoted context omitted.

Given self-clocking signalling[1] exists, why is clock frequency precision the limiting factor? I would imagine signal-to-noise would be the limiting factor, ie how strong is your transmitter and how sensitive is your receiver. [1]: https://en.wikipedia.org/wiki/Self-clocking_signal

Noise, by definition, doesn't have a qualifying characteristic. It just means "all signals we're not interested in". That means your ability to filter out noise is strongly dependent on having pre-existing knowledge about the shape of the signal you're interested in. Self-clocking signals are useful when the ambient noise level is low with respect to the signal, but if your signal is just "these two droplets in an oc…

Wrong clock, gotcha. For some reason I didn't think of the carrier signal generator when I read the word "clock".

It all makes sense now, thanks!

Re: NASA's Perseverance rover sends stunning images

#244

Post by baybal2 »

idlewords wrote: post #200
marshmallow_12 wrote: post #52

Earlier quoted context omitted.

a glowing green sandwich covered in red sand. But seriously, this stuff is powering those voyager probes 40 years later. Which makes me ask: why do we have to send there technologies 10 billion miles away to make them work? Why can't my fridge be powered this way?

The Russians tried powering a bunch of remote stuff with plutonium batteries during the Soviet era. It did not end well, and cleaning those up has been an ordeal. Pu-238 was also used in pacemakers. The basic problem is just that plutonium is toxic as hell.

Not plutonium, strontium

Re: NASA's Perseverance rover sends stunning images

#245

Post by dmurray »

zaik wrote: post #236
TeMPOraL wrote: post #221

Earlier quoted context omitted.

Maybe after they complete their primary and secondary mission objectives, they'll find spare time and compute to stream a couple hours of Martian ambience. Does NASA have a suggestion box for after hours / extended program experiments?

I doubt a NASA suggestion box open to the internet will be very fruitful.

I for one look forward to Rover McRoverface in the 2022 launch window.

Re: NASA's Perseverance rover sends stunning images

#246

Post by pja »

wiz21c wrote: post #214
reilly3000 wrote: post #208

Earlier quoted context omitted.

Yep, that’s the same reason why it runs on a PowerPC750 chip. They cost $200k+ for under 200Mhz on a 150-250 nm process, but can withstand up to 1,000,000 rads of radiation and function within extreme temperature ranges for decades. They have been proven to work in the harshest environments on prior missions, and the risk of an unproven processor is giant; a CPU failure could jeopardize the mission just as much as a…

Could you explain why such a processor is 1000x more expensive than a non-rugged one ? I mean, considering the future of earth, I'd certainly welcome a processor that could withstand a lifespan of decades (including the harsh "I'm going to unsolder it to put it in another device" environment).

IIRC it’s a custom process using wide-bandgap silicon (part of the whole rad-hardening thing) that no-one else needs or wants, so you have to pay the full costs of a fab run for a relatively small number of chips. Hence the cost per chip is huge.

Re: NASA's Perseverance rover sends stunning images

#247

Post by [deleted] »

marshmallow_12 wrote: post #52
11thEarlOfMar wrote: post #44

Stupid question, but where is Perseverance's energy source? Answer: Plutonium It powers a Multi-Mission Radioisotope Thermoelectric Generator. The plutonium decays at a few % per year, so that means it should be able to bring Elon a sandwich when he lands. https://mars.nasa.gov/mars2020/spacecraft/rover/electrical-p...

a glowing green sandwich covered in red sand. But seriously, this stuff is powering those voyager probes 40 years later. Which makes me ask: why do we have to send there technologies 10 billion miles away to make them work? Why can't my fridge be powered this way?

[deleted]

Re: NASA's Perseverance rover sends stunning images

#248

Post by comboy »

londons_explore wrote: post #231
jdmichal wrote: post #190

Earlier quoted context omitted.

Others have posted links to the Reddit thread overall, but I think this is the specific question being referred to: https://old.reddit.com/r/IAmA/comments/lpzbzo/were_scientist... EDIT: Apparently the rover has an antenna that can directly communicate with Earth at 10 bits per second! That's obviously not useful for pictures or anything, but it's an amazing capability for emergency comms.

Very low bandwidth, very low power, very long distance comms are really cool. The limiting factor tends to be the clock frequency precision - if you have precise enough clocks at both ends, there isn't anywhere in the universe you couldn't communicate with, as long as you're happy to go slow enough.

> there isn't anywhere in the universe you couldn't communicate with

Right, assuming you are emitting infinite amount of photons, there are no obstructions, black holes and you ignore universe expansion and GR which can make your precise enough clocks go out of sync.

Re: NASA's Perseverance rover sends stunning images

#249

Post by avar »

matheusmoreira wrote: post #172
scoopertrooper wrote: post #162

Earlier quoted context omitted.

How familiar are you with the human species? There have been several notable accidents where humans have cracked open medical machines and decay powered lighthouses to exactly this effect. Imagine if you started whacking plutonium in consumer products!

> There have been several notable accidents where humans have cracked open medical machines and decay powered lighthouses Indeed. https://en.wikipedia.org/wiki/Goi%C3%A2nia_accident A caesium-137 radioactivity source was left behind and eventually stolen. The thieves successfully dismantled it despite sustaining severe injuries in the process, exposing the radioactive material contained in the shielded capsule. They…

> the scrapyard owner's wife noticed everyone was getting sick and notified the authorities[...]

The Wikipedia article and the Portuguese source it links to seems ambiguous on the matter of whether it was because she notified the authorities, or because a visiting scientist thought to use radiation detectors on other people reporting to the hospital a day after her notification.

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