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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

#181

Post by JoeAltmaier »

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…

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.

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

#183

Post by [deleted] »

tgflynn wrote: post #65
chasing wrote: post #19

Earlier quoted context omitted.

> a swarm of unguided relativistic projectiles In a sense, this is essentially what the universe is .

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.

[deleted]

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

#184

Post by ryao »

Is it going to just do a fly by or will it somehow enter orbit once it reaches Alpha Centauri? How is it going to transmit data back to earth in a manner that would overcome the signal to noise ratio? Will power be solar or nuclear? How would it know when it is there to begin operating, especially if it uses solar power?

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

#185

Post by hinkley »

TheOtherHobbes wrote: post #143
Razengan wrote: post #141

Earlier quoted context omitted.

Technically, we are the universe trying to understand itself.

Technically, we may be the universe trying not to kill itself.

Technically, we may be the universe trying to kill itself.

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

#186

Post by antognini »

pklausler wrote: post #139

How close does a tiny cell-phone camera objective lens have to get to an interstellar object before it can resolve detail better than the High-Def Space Telescope will?

A cell phone camera probably has a resolution of ~1 arcminute (about the resolution of the human eye). The Hubble has a resolution of ~0.05 arcseconds. The HDST would have a resolution of ~0.002 arcseconds. So to get comparable resolution to Hubble the probe would have to be at a distance of (.05 / 60) * 270,000 AU ~ 225 AU and a distance of (.002 / 60) * 270,000 AU ~ 9 AU to beat HDST. A camera on such a telescope would probably be of somewhat higher resolution, however. In fact, it would probably be at the diffraction limit, which for a ~1 cm aperture in visible light would be closer to ~10". This would increase the distances above by a factor of 6 or so.

Resolution isn't the only thing, though. The contrast is extremely important. A little probe in the Alpha Centauri system would be able to take clean images of any planets in the system. A telescope in our solar system trying to directly image these planets has to contend with contamination of light from the stars.

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

#187

Post by ryao »

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…

"The technique uses cryo-cooled nanotubes. The current performance is of order 2 bits per photon."

How do you keep it cool with a 100GW laser pointed at it over 2 minutes?

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

#188

Post by ryao »

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.

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.

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

#189

Post by DavidSJ »

ridgeguy wrote: post #157

What about the energy dissipated by collision with the interstellar medium? Won't that slow the probe considerably? Apologies for significant errors and appreciation for corrections in the following hasty and unchecked calcs. Wikipedia [1] says the ISM density ranges from as little as 1e-4/cm^3 for hot, ionized regions to 1e6/cm^3 for cool, dense regions. Let's say it's all neutral hydrogen, which conveniently masses…

> about 3.9e4m^3 every second, which contains about 3.9e11 hydrogen atoms

I think this step is off by 1e5. It contains 3.9e16 hydrogen atoms at 1e6/cm^3.

So that 631 MJ becomes 63.1 TJ.

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

#190

Post by ryao »

jerf wrote: post #36
0x74696d wrote: post #9

Sending a swarm of unguided relativistic projectiles across the universe seems profoundly rude.

Their speed isn't particularly relevant, what matters more is their energy. As big as that number is to us, it's still pretty insignificant; there's a lot of objects already traveling around with us in our own solar system with 70kT (per PaulHoule in other comments) of energy. A looooooot of objects. In the grand scheme of things, this is a rounding error on a rounding error. We are small .

It would be rather anticlimatic if it hit one of them before reaching Alpha Centauri and no one noticed.
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