JPL Accomplishes Laser Sail First 26
Keith Gabryelski writes, "space.com has an
article on how, in late December 1999, engineers at
JPL
used a laser beam to move extremely lightweight material
using only the pressure of light." For those of you who haven't been keeping up with your science fiction, the idea is that with a tremendously large and incredibly thin sail, you could launch a spacecraft that would be propelled away from the solar system by the miniscule impact force from the light of the sun/gigantic lasers/mirror-focused light striking the sail. The theory is simple enough, but the execution is, shall we say, non-trivial.
Tax Dollars at Work (Score:1)
Re:How far...? (Score:1)
You're not the first person to carry this opinion, and you won't be the last. However, I think it's very flawed.
For example, what if, Alessandro Volta, and other early experimenters with electricity had decided that their intellectual curiosity would be better served by turning it towards more pressing problems? Same thing for Einstein, Bohr, and the other physicists working at the dawn of quantum theory. At the time, it certainly didn't look like any of this stuff would benefit anyone, but look at it now. Without the work done by these people, the WWW wouldn't exist, slashdot wouldn't exist (and those are just some very pedestrian examples).
I submit that by supporting these kinds of projects, we are "looking to ourselves." The application of this work might not be immediately obvious, but I say so what? Sometime in the future this stuff might just come in handy, but if nobody does the work now, it won't be available when we might need it. Long term, open-ended ended research is absolutely imperitive, simply because we never know where or when the next big break-through will be made.
Re:Hmmm..., I must have missed something. (Score:1)
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Question about light sails. (Score:1)
Do light sails only push the ship away from the light source? If so, how does a ship get back from where it came?
In sailing on earth, sailboats can sail into the wind using the same principal as the airplane wing, pressure differental between the sail surfaces. But in space there is no medium to create the pressure differential.
Does this mean, using light ships, you can go out, but you can't come back? This could be a real bummer for manned exploration.
Regards
wen
Re:Question about light sails. (Score:1)
Yes, they only push.
Does this mean, using light ships, you can go out, but you can't come back? This could be a real bummer for manned exploration.
Well, yeah, it's pretty much a one way trip, and braking when you enter another solar system is a trip, to slow down, you "set your controls for the heart of the sun" (See Niven and Pournelle's "A Mote In God's Eye" for a description of this).
Even at
One of my senior projects as an undergrad was a small solar sail design, it was neat.
George
Re:Question about light sails. (Score:1)
Are you sure that's how it works? I though that the idea was to sail on the Sun's light, not try to shoot lasers from Earth. No matter how hard you try, lasers from Earth wont be nearly as powerfull as the Sun's broad-spectrum radiation.
Well, you could do it all from the Sun, but you can get more power by shooting lasers at it, too.
Since the laser's are focused, you can get more power from a laser than from sunlight, which is why people use lasers to cut steel instead of sunlight.
And the laser's would be in orbit, or perhaps on the moon, maybe the asteroids (cf. Niven's Kzinti wars).
Of course, the total energy output from the Sun would far outscale the energy from a laser, but we're talking a small, focused area.
George
Lighcraft (Score:1)
Light Propulsion is pretty sweet. Anyone else remember the Lightcraft? RPI was using lasers to launch small metal objects in the air. The priniciple is a little different here: Light used to heat and propell the craft from a distance, but it's still pretty cool.
Links:
The Lightcraft Site [slashdot.org]. (Though this seems to be down right now).
CNN Coverage [cnn.com]
ABC Coverage [go.com]
provolt
Go Geek. Rule the World. gogeek.org [slashdot.org]
Re:Results? (Score:1)
I love the "lightmill" trickets you can occationaly buy at novelity shops. They are relfective on one side and flat black on the otherside. The idea is that you set it in the sun and the light pressure will make it spin. They do usually spin.... the wrong way. The light just heats up the flat black surface and the air pressure makes is spin.
Still it's fun to impress peopole who aren't thinking very clearyly.
provolt
Go Geek. Rule the World. gogeek.org
Damn, that's neat. (Score:1)
However, how do they plan to scale this to larger objects? It seems like the sail would break. Also, how much energy would a large laser across the solar system take?
Let's just hope Congree doesn't kill -9 this project.
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Re:Question about light sails. (Score:1)
Are you sure that's how it works? I though that the idea was to sail on the Sun's light, not try to shoot lasers from Earth. No matter how hard you try, lasers from Earth wont be nearly as powerfull as the Sun's broad-spectrum radiation.
Results? (Score:1)
I'm kind of doubtful right now. There are tons of things that could cause this deflection that are not light pressure. Most notably the laser probably heats the sail up incredibly, this would create force due to heat convecting off the sails surface. I just can't bring myself to trust someone saying "yes, its the laser we checked", without even giving a list of what he checked.
How far...? (Score:1)
Another nice thing about laser sail systems... (Score:1)
Marvel (Score:1)
Now we can use light at high concentration to push us along in space at 10% the speed of light. That's 30,000,000 KM/s or 18,600,000 miles/s. That's just incredible!!! Moving at those speeds we could quite easily travel everywhere to search for whatever we are tring to search for.
I can't wait to see the JPL in 2 weeks, finding out more about this is gonna be great.
Re:Screw lightpressure, use Solar Wind (Score:1)
The folks thinking up the laser-propelled systems have gotten into some pretty sophisticated concepts [nasa.gov]: for example, they've proposed using a gigantic Fresnel lens, free-flying between the starship and the laser battery, to focus the laser beam onto the lightsail once the starship has gotten far enough that the sail is smaller than the beam diameter. The lens flies toward the target star, too, but much slower than the starship...
They even propose multi-stage systems for deceleration at the far end -- you use concentric rings of sail, and let the outermost of them keep going... but you deform it so it reflects the light back at you, so you can decelerate... and even come back!. (Although it might be easier to do with yet another ring of lightsail.)
Needless to say, it makes control very interesting, when the object you're aiming at is lightyears away, and you wait years to see the effects of your corrections; some say it's impossible, but then so was heavier-than-air flight, a century ago. ;>
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Re:Question about light sails. (Score:1)
The other is pretty interesting. We know there is a large magnetic field associated with the Galaxy (we can detect it from the polarization of light passing through the field), so it has been suggested that we use that field to turn the spacecraft! We'd first accelerate the starship away from Sol on a trajectory that takes it past the target star, at a considerable distance and with the proper angle relative to the galactic magnetic field; well past the target star, we'd charge the starship electrically, to a huge potential, and use the Lorentz force (the force that bends the path of a charged particle travelling through a magnetic field) to travel in a semi-circle, until it is aimed more-or-less back toward Sol, but on the other side of the target star.
Now it's headed back into the lasers, and it can decelerate into the destination system from the far side.
Admittedly, it makes the journey quite a bit longer (talk about "going 'round Robin Hood's barn!"), but at least you can use the existing laser power to slow down. I think the bigger issues have to do with the configuration of the galactic magnetic field (I don't think it's extremely well-mapped), and with getting the whole "train" of lightsail, spacecraft and Fresnel lens (see the post below) all turned around and properly lined up. But it's probably closer to reality than things like the Bussard Interstellar Ramjet [nasa.gov]. Coming back... that would still be a problem with this scheme (although the below discussion covers one method of doing that, without the magnetic turn trick). Larry Niven wrote a short story (was it The Oldest Profession?) in which aliens arrived in a lightsail vehicle, and expected us to build them a laser system so they could continue their trip -- and if we didn't, they'd just make the sun go nova and use that light instead.
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Re:Lighcraft (Score:1)
another sun propulsion system (Score:1)
there have been a few write-ups on magnetospheric propulsion. it works similarly to a solar sail except the "sail" is a bubble of ionized plasma that interacts with the solar wind to create thrust. seems pretty cool.
Mini-Magnetospheric Plasma Propulsion [washington.edu]
Uhh, this is kinda old news (Score:2)
Also interesting [particle.kth.se] (about a quarter of the way down is links to propulsion tech).
I even remember seeing an aluminum disk being shot straight up into the air on a documentary about next gen space propulsion systems (the documentary was on Discovery (I think) sometime late last year. I know they had Lawrence Kraus on it).
The only difference I see is the material for the sail.
Jon
Let's not get ahead of ourselves (Score:2)
I might point out that we don't have very many details of this experiment yet. According to the article, the procedure was to put a fragment of their new carbon-filament mesh on a pendulum, and see how high they could hold it with light pressure from a laser. What we don't know yet is - how much force was produced? how powerful was the laser/how efficient was the energy transfer? how readily does this material scale?
We might compare these experiments to the first demonstrations that force could be generated by burning liquid fuels, but comparing this to Goddard's rocket work is very premature.
Analogy with sailboats (Score:2)
Take care (Score:3)
Uhh, actually that's something different (Score:3)
The news article describes a second method of laser propulsion, in which the momentum of the laser-generated photons are used directly: you bounce the photons off the "sail," and gain a tiny amount of momentum with each photon. This is very much like using a spinnaker sail, which is where the term "light sail" comes from. And because each photon has such a small momentum compared to the sail, it takes huge fluxes to cause a measurable accleration. This is why they talk about the elevated temperatures: they are throwing so much light at the sail that they're seriously heating it. (I glossed over the fact that you can make it work by absorbing the photon instead of reflecting it, which is actually what they appear to do -- with a loss in efficiency. So don't flame me, okay?)
Accelerations with proposed light sail vehicles are generally very small; they are effective because they are continuous, and the velocity builds up over time. This isn't completely novel, though -- we routinely account for the perturbing effects of sunlight on the orbits of spacecraft...
While I'm at it, I might as well point out that there are at least two other propulsion concepts which use lasers: laser-induced fusion concepts, where the laser is just the "trigger" and you use the heat from fusion to heat a working fluid (like more gas) or even directly exhaust the fusion products (definitely high-tech); and the ultimate propulsion system, where you "exhaust" nothing but light itself, substituting photons for atoms in your rocket (not the sort of thing you'd like to be behind, while it was working!).
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