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A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

nytimes.com

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Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#121

Post by dysfunction »

slg wrote: post #116
Carrok wrote: post #111

Earlier quoted context omitted.

Because while all we can see is the blinking light, the probe can see the things close to it far more clearly. As the above quote says the probe will "beam back pictures of the star’s planets." We can receive these pictures through the data received from that blinking light, but we can't see the planets in question. Now we can.

But why would we be unable to see the star's planets if we are able to see a probe that small?

We wouldn't be able to see the probe itself, rather we'd see its laser. The planet outputs (or reflects) vastly more total light than the laser, but the laser is pointed directly at the receiver and can output more light in that specific direction than the planet does. Plus, to get interesting data about the planet we need to get quite a lot of light from it, whereas we can get data from the laser over time by pulsing it so long as we can get any light from it at all.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#122

Post by sneezeplease »

This is swindling investors, there is no such star at such distance. This is because the earth is flat with a dome overhead. Watch a video from a high definition zoom camera on the planets and stars in the sky, they are revealed to be much closer and not at all what you think. Take a look, youll be amazed.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#123

Post by onion2k »

valarauca1 wrote: post #54

The project estimates are completely off. Building a 1gigawatt power plant costs 10billion. Let alone building 100 of them. Also making the laser array. Also you can't have reflection without absorption. Also we don't have solar sails that fit the bill. This project is barely physically and economically plausible. Its not a question of scaling, or engineering. The physics just don't work. We have a way to get a space…

I realise this is an appeal to authority, which is bad and wrong in any argument, but I trust Stephen Hawking wouldn't back a project that falls down on the physics.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#124

Post by dragonbonheur »

LyndsySimon wrote: post #60
iwwr wrote: post #39

Earlier quoted context omitted.

A laser capable of propelling an interstellar probe is also a mighty space weapon. Some people proposed constructing that on the far side of the Moon so that it hass less of a chance of being used as against Earth targets (intentionally or by accident).

That sounds like a good idea... as long as no one develops mirrors :)

.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#125

Post by gene-h »

schwarrrtz wrote: post #61
NoGravitas wrote: post #13

Moreover, to keep the beam tightly focused on one probe at a time would require an adaptive optics system that compensated for atmospheric turbulence — something astronomers know how to do over a span of 10 meters, the size of a big telescope mirror now, but not over a mile. Would it be easier just to put the lasers on the moon?

The moon is really dusty, which might be problematic. https://en.wikipedia.org/wiki/Lunar_soil#Moon_dust_fountains...

However, this is much clearer than firing said lasers from under the atmosphere. While charged dust is a problem for the laser equipment itself, this can be mitigated with special dust attracting equipment. Getting the lasers to the moon would be a bigger problem.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#126

Post by cbhl »

yongjik wrote: post #23

So the whole thing should weigh in the order of several grams, yet it should be able to deflect 100GW of incoming radiation near perfectly (otherwise it will instantly vaporize) while maintaining structural integrity under the acceleration of 60,000g for two minutes? And whatever laser sources we're using must track this smartphone-sized object during these two minutes across several million kilometers. Perfectly. (I…

I'm more worried about where the reflected light is going to go once it bounces off the sails. Presumably it'll fall back on earth, where that amount of energy could cause a lot of damage.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#128

Post by jperras »

slg wrote: post #108
rm_-rf_slash wrote: post #85

Earlier quoted context omitted.

Not a scientist but I first read this on The Economist and they summed it up pretty well: "At its destination it would beam back pictures of the star’s planets with its on-board laser. No current observatory could possibly pick up such a signal—but the kilometre-wide launch array should be able to. The optical systems used to meld the output of the lasers could be used in reverse as a vast and sensitive telescope." h…

This might be a stupid question, but if we have the technology to see a blinking light the size of a postage stamp trillions of miles away, why would we need to send a probe with a camera all the way out there in the first place?

To answer that question, you need to know a little bit about diffraction-limited systems in optics and the Rayleigh criterion.

Essentially, point-like sources (the laser emitter array and the target can be considered point sources when on the scale of lightyears) separated by an angle smaller than the angular resolution of the device in question cannot be resolved.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#129

Post by slg »

dysfunction wrote: post #121
slg wrote: post #116

Earlier quoted context omitted.

But why would we be unable to see the star's planets if we are able to see a probe that small?

We wouldn't be able to see the probe itself, rather we'd see its laser. The planet outputs (or reflects) vastly more total light than the laser, but the laser is pointed directly at the receiver and can output more light in that specific direction than the planet does. Plus, to get interesting data about the planet we need to get quite a lot of light from it, whereas we can get data from the laser over time by pulsin…

>The planet outputs (or reflects) vastly more total light than the laser, but the laser is pointed directly at the receiver and can output more light in that specific direction than the planet does.

So then the problem is that you need a laser than can hit a 1 km^2 target from 40 trillion km away?

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