[deleted]
A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
91–100 of 274 posts
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#92Earlier quoted context omitted.
I love these napkin calculations. The relativistic effect shifts the frequency by 22.47% for 0.2c. Given a 445nm laser (the powerful blue ones), that's 545nm when redshifted (green). It's a bit of a jump, but that wavelength is still smack in the "solar atmospheric absorbtion spectrum window" -- you won't lose much of the energy in the atmosphere. Reading this page diagonally [ http://www.edmundoptics.com/resources/a…
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%.
Keep in mind that a single spaceship wouldn't take up the whole beam - for one thing, there would be a bunch of them, and for another, we simply can't focus a laser on something the size of an iPhone from even as far away as the moon. That said, it is still a massive amount of power that needs to be reflected.
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#93Oddly 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.
A Nicoll-Dyson laser has much the same effect, but you can fire it again and again as long as you still have a sun.
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#94Earlier 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%.
Keep in mind that a single spaceship wouldn't take up the whole beam - for one thing, there would be a bunch of them, and for another, we simply can't focus a laser on something the size of an iPhone from even as far away as the moon. That said, it is still a massive amount of power that needs to be reflected.
I thought this also, but "[...] to keep the beam tightly focused on one probe at a time would require [...]" in the original article points in the opposite direction.
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#95Earlier quoted context omitted.
> a swarm of unguided relativistic projectiles In a sense, this is essentially what the universe is .
True, the universe is generally a pretty unfriendly place that tries to kill you in any possible way.
To be fair, the universe was pretty friendly and created us in the first place.
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#96Earlier 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.
Cosmic rays are far too small to easily see coming, and we get those all the time here.
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#97Would they slow down when they reach another star? What kind of observations can you do if you move at that speed?
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#98Why don't we focus and reflect the sun's rays instead? Or even combine this and the traditional rocket method by putting the emitters in space to catch the sun and push these tiny craft after they've been shot from the Earth by the zillions in a single satellite. That way we deal with two big problems at once: generating laser energy sufficient for escape velocity, and focusing lasers through an atmosphere layer. Bet…
My guess is the sunlight reaching the earth's atmosphere is already too diffuse. This could maybe work if the collector + launchpad were closer to the sun.
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#99Would they slow down when they reach another star? What kind of observations can you do if you move at that speed?
From my poor understanding of GR, there will be no limit on the measurements. You just have to take relative motion into consideration when interpreting them.