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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

#111

Post by Carrok »

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?

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.

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

#112

Post by david-given »

This is a variation of the old Starwisp idea from 1985:

https://en.wikipedia.org/wiki/Starwisp

tl;dr: a lightweight (about 1kg) vehicle made out of carbon wire mesh. It acts as a microwave mirror. You both use this for propulsion, by blasting it with microwaves from a Sol-system maser cannon, and for data recovery; its sensors cause the reflected microwave signal to be perturbed based on what its sensors see.

So, you accelerate them (in bulk) at about 2G up to .1c. You ignore it until it's about 80% of the way there, and then for fire the maser at it again; the beam reaches the starwisp as it passes through the target system and powers the sensors. A few years later you read back the return signal.

There were a whole bunch of technical problems with it, not least how to build a microwave lens 560km across, but it's still vastly more plausible than trying to push steel cans across the interstellar gulf. I'd be really interested to see if this version works.

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

#113

Post by Zikes »

stdgy wrote: post #29
oabm wrote: post #17

Earlier quoted context omitted.

It might be easier to fire the lasers from the moon, but getting the lasers to the moon would be a huge pain.

Not to mention supplying these hypothetical moon lasers with enough power to blast these mini-probes into another star system.

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

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

#114

Post by saalweachter »

zdkl wrote: post #28
mabbo wrote: post #8

Earlier quoted context omitted.

At 20% the speed of light, time would dilate by around 2%, but that's about the extent of the effects, afaik. Also: why bother decelerating at all? Take a picture as you fly by.

Wouldn't want to program that particular timer. Talk about hard real time requirements!

It'd be hilarious to have a bonus tied to the successful completion of that project. "In twenty years, I may get an $X bonus!"

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

#115

Post by stcredzero »

AnthonyAguirre wrote: post #22

This is a pretty cool initiative — I looked into beamed propulsion a bit while teaching a course this past fall, and it seems to me that if we (or human technologies) are going to reach a star in our lifetimes, this is by far the most likely way. Still very challenging though. For a quite detailed recent treatment of optical/IR propulsion see this paper by Philip Lubim:( http://www.deepspace.ucsb.edu/wp-content/uploa…

I'm disappointed that more people don't mention Robert Forward when this idea is being covered in the media. (Probably because his Usenet posts, papers, and books predate the World Wide Web.)

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

#116

Post by slg »

Carrok wrote: post #111
slg wrote: post #108

Earlier quoted context omitted.

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?

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?

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

#117

Post by stcredzero »

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,…

IIRC, Robert Forward was writing about sails using dielectric mirrors with holes in them back in the 80's.

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

#118

Post by PaulHoule »

zeveb wrote: post #82
PaulHoule wrote: post #24

Oddly the most practical use for this is as an interstellar weapon. You don't need to solve the problem of communicating back to Earth, you just need a little terminal guidance. If an iPhone weighs 100 g and we use a non-relativistic formula for energy at 1/4c, that is 2.8 x 10^14 joules, a ton of TNT equivalent is about 4.1 x 10^9 joules, so that is a cool 70kT -- The impact velocity would be high enough to break th…

> Oddly the most practical use for this is as an interstellar weapon. I completely don't advocate this, but the 9-year-old-boy part of my brain thinks it'd be pretty awesome to announce our presence to the universe by attacking a star system.

One of the explanations of why we are not seeing evidence of ETs is that everybody is hiding and afraid they might get bombed by their neighbors; that's because bombing your neighbors is orders of magnitude easier to do than visiting them -- you don't need to solve the problem of decelerating on the other end for one thing.

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

#119

Post by fapjacks »

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..

Inadvertently starting an interstellar war, provided they survive the impact on their homeworld.

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

#120

Post by Zikes »

drabiega wrote: post #74
LockandByte wrote: post #69

I am a self-proclaimed 'newbie' when it comes to understanding energy, astronomy, and physics in general, but I have a few questions and any answers or opinions would be appreciated: 1.) Why in the world does the 'Light / Laser Beamer' need to be physically located on earth? Why not in space? 2.) Is building 'check-points' for both data and power atop the planets not a possibility? (Solar, chemical, etc).

As for #1 it's just a matter of logistics. It would actually be a little easier to do from space because you don't have to worry about the effects of the atmosphere, but it would be a pretty massive piece of infrastructure and it's likely that within this time frame it would be vastly simpler and cheaper to build it on earth.

For a laser of the proposed magnitude surely a little bit of air isn't going to make a significant difference. From what I can gather the thing would be classified as a WMD and capable of carving a smiley face on Pluto.
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