A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away • Hacker News Board

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

#211

Post by e12e » Wed, Apr 13, 2016, 12:09 AM UTC

antognini wrote: post #38

RIMR wrote: post #2

So, how is a tiny smartphone-sized probe supposed to transmit data back to Earth from 4.37ly away?

That is a good question. The Voyager spacecraft send out detectable signals with a ~20 Watt signal. This is larger than the ~3 W signal that a smartphone sends, but by less than an order of magnitude. Voyager is at ~130 AU. Alpha Centauri is at ~275,000 AU. With the 1/r^2 decrease in signal, that means the signal from earth will be smaller by a factor of ~3 x 10^6. Now, supposing we have ~1000 of these smartphone pro…

> Alpha Centauri is at ~275,000 AU.

I wonder if it would be easier to string ~300 of these at ~1000 AU intervals, and use them for a relay? Or perhaps ~3000 at ~100 AU intervals.

And I wonder if that would be construed as mining a common hyperspace lane by the galactic council... ;-)

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

#212

Post by warrenpj » Wed, Apr 13, 2016, 12:37 AM UTC

tgb wrote: post #159

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?

You've gotten pretty poor answers so far. I suspect they'd try to communicate in a wavelength where there is little interference. It's one thing to notice "there is a tiny amount of wavelength X light from the vicinity of alpha centauri" and a whole lot harder to notice the difference between two light sources close together at the same wavelength. The latter requires sensitivity to magnitude AND incredible angular p…

Would it be an accurate analogy to say this is why stars in the night sky appear the same size (point-like), but vary in brightness?

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

#213

Post by digsmahler » Wed, Apr 13, 2016, 12:44 AM UTC

We should send even smaller nano-probes that would be even easier to accelerate and would have the capability to collect dust and build it into larger probes that would talk back to us when they come online!

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

#214

Post by caf » Wed, Apr 13, 2016, 12:47 AM UTC

jessriedel wrote: post #48

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…

Agreed on the extreme skepticism warranted. I am imagining these "solar sails" to be essentially spherical, both for structural reasons and so that their response to applied laser power does not depend on orientation. The electronics in precision guided mortars in the US army survive 50,000g. http://proceedings.ndia.org/C347/Davis.pdf (This is only for the fraction of a second when they are fired, and I don't know ho…

I conjecture that the laser profile will be "shaped", if at all possible, so the trajectory of the projectile is somewhat self-correcting: if the projectile starts to get ahead of the planned trajectory, the acceleration will decrease, while if it lags the acceleration will increase.

This is analogous to the way train bogies go around corners.

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

#215

Post by dTal » Wed, Apr 13, 2016, 1:03 AM UTC

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…

>If the laser is green, by the time it's flying away at 0.2c, the laser won't be green any more thanks to the Doppler effect! I'm too lazy to calculate, but it will definitely shift toward the red.

Interestingly, you also have to deal with Lorenz contraction - at .2c the ship itself will shorten by about half a percent, compounding the apparent wavelength shift. Admittedly this is a much smaller effect.

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

#216

Post by brianwawok » Wed, Apr 13, 2016, 1:08 AM UTC

TallGuyShort wrote: post #178

brianwawok wrote: post #176

Earlier quoted context omitted.

Why return? I bet you can find a lot of volunteers for a one way mission, especially if you offer to follow them with supply trains every year or so.

Even if this is possible, it'll probably be prohibitively expensive to do constant resupplies when you won't know for years if previous trips have worked. A manned mission or a resupply mission would also be orders of magnitude beyond the masses they're talking about, which strains credibility even further.

I am pretty sure you just sent out a new boat of supplies every year make it or not. Worse case the mission fails and the next mission has 20 supply ships in orbit waiting for them. I have no idea on the minimum mass required to send supplies, i.e. if you can recycle 99% of the water you need, would only need a few drops per day. If you can only recycle 50%, you are going to need a bunch.

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

#217

Post by mirekrusin » Wed, Apr 13, 2016, 1:10 AM UTC

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…

Worst case, if it doesn't work, maybe we can at least use built infrastructure to send new iPhones to Mars expedition.

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

#218

Post by marcosdumay » Wed, Apr 13, 2016, 1:17 AM UTC

Zikes wrote: post #180

Zikes wrote: post #113

Earlier quoted context omitted.

https://en.wikipedia.org/wiki/Helium-3 ought to do the trick.

I'm a bit surprised at the downvotes. I'm no scientist, but I meant this suggestion in earnest. As far as my layman's knowledge goes, I've always understood the Moon's He-3 reserves to be a "vast, as-yet-untapped power resource".

People have to learn how to harvest power from fusion before.

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

#219

Post by mirekrusin » Wed, Apr 13, 2016, 1:20 AM UTC

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…

And what exactly happens with reflected laser?

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

#220

Post by grecy » Wed, Apr 13, 2016, 1:25 AM UTC

JoeAltmaier wrote: post #181

grecy wrote: post #179

Earlier quoted context omitted.

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…

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.

These people are obviously very passionate about their project, and they're moving forward on something they want to do. If you're so passionate about those projects you mentioned, start making them happen!

Don't sit around complaining about people who are "doing" stuff because they're not doing the stuff you want them to be doing. Get out there and do the stuff yourself!