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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

#191

Post by maxander »

jessriedel wrote: post #75
yongjik wrote: post #66

Earlier quoted context omitted.

Umm... 0.5% of 100GW is 500MW, or about the power of a nuclear reactor. The spaceship won't survive a millisecond. We need way better than 99.5%.

Yep. "Use a material with better than 99.999% reflectivity. Usually, highly reflective surfaces are dielectric mirrors, which are composed of ‘sandwiches’ of material, with each layer reflecting back a modest fraction of the total. Each layer needs to be at least a quarter of a wavelength thick. The weight can be reduced by using a monolayer with high reflectivity at the correct wavelength. Based on recent research,…

So it sounds like we'd have a layered sequence of dialectric mirrors (themselves many layers each) each reflecting a different wavelength. The first layer lasts until the laser redshifts out of that layer's efficient reflection range, then vaporizes revealing the next layer tuned to the redshifted laser. That layer lasts until the laser redshifts even further, then vaporizes to reveal the next, and so on.

Sacrificial layers may also help with heat management, I suppose.

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

#192

Post by ant6n »

noir_lord wrote: post #47
nkrisc wrote: post #14

Earlier quoted context omitted.

They're not going to put them into orbit, just a fly-by. Then they'll continue until they hit something some time in the future. In a million years some unlucky alien might get hit by an iPhone.

Travelling at 20% of the speed of light, I think it'll probably bend..

The interstellar medium is holding it wrong.

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

#194

Post by tgflynn »

skykooler wrote: post #96
tgflynn wrote: post #65

Earlier quoted context omitted.

I don't think you'll find 0.2c relative velocities except near very energetic phenomena, especially not of things that are too small to easily see coming.

Cosmic rays are far too small to easily see coming, and we get those all the time here.

I think it should be clear from the context that this discussion was about macroscopic objects. Cosmic rays don't carry the kinetic energy equivalent of a medium size nuke.

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

#195

Post by tim333 »

JoeAltmaier wrote: post #170

Why not accelerate slower with smaller lasers? What harm in taking 2 days? 2 months? to get to speed.

The longer you take the further away it will be and the range of the lasers is only so far. The average speed during acceleration is 0.1c so if you take 2 days it would be 51 billion km away which is out of range.

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

#196

Post by tim333 »

avian wrote: post #42

I wonder what plans they have for communicating with a probe light-years away. Consider New Horizons. It has a power budget and antenna gain way beyond something that can be crammed into a few grams. Yet, the bit rate is so low it's still sending back data it gathered in 2015 from an encounter mere light-hours away. Even if the laser propulsion aspect of this works out, I think communicating with something that far a…

You could write a note on the sail to any aliens at Alpha Centauri asking them to call back.

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

#197

Post by JoeAltmaier »

ryao wrote: post #188
JoeAltmaier wrote: post #181

Earlier quoted context omitted.

I also am skeptical. Why not instead try to send a probe into the interior of the sun? (because its cooler there than at the point of those lasers) Why not create a survey of the Oort cloud (because its an order of magnitude closer). This project seems cool; but maybe not well thought out.

That depends on how much energy that the space craft reflects. If it reflects all of it, the space craft would not gain any heat at all unless there is some weird quantum effect that would mean otherwise.

Likewise, such a spacecraft could survive the inside of the sun.

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

#198

Post by JoeAltmaier »

tim333 wrote: post #195
JoeAltmaier wrote: post #170

Why not accelerate slower with smaller lasers? What harm in taking 2 days? 2 months? to get to speed.

The longer you take the further away it will be and the range of the lasers is only so far. The average speed during acceleration is 0.1c so if you take 2 days it would be 51 billion km away which is out of range.

Ok. 10 minutes then.

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

#199

Post by xbmcuser »

grecy wrote: post #179
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…

You're right to be skeptical, because this is going to be very difficult and has many challenges that need to be overcome. But that doesn't mean we should sit here and say "nope, can't be done". People were skeptical when planes first flew, when it was attempted to put people on the moon, and so on. Jeez, people were skeptical when SpaceX said they could land a first stage on a barge at sea, and posted endlessly abou…

If nothing else they might work out how to send larger probes to far out parts of our solar system that reach in days instead of months and years.

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

#200

Post by xbmcuser »

grecy wrote: post #179
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…

You're right to be skeptical, because this is going to be very difficult and has many challenges that need to be overcome. But that doesn't mean we should sit here and say "nope, can't be done". People were skeptical when planes first flew, when it was attempted to put people on the moon, and so on. Jeez, people were skeptical when SpaceX said they could land a first stage on a barge at sea, and posted endlessly abou…

If nothing else they might work out how to send larger probes to far out parts of our solar system that reach in days instead of months and years.
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