JPL Accomplishes Laser Sail First

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.

Comments

Hmmm..., I must have missed something.

[Anonymous Coward]

Wasn't a pellet made of a deuterium and tritium compressed to the point of nuclear fusion by laser light a few years back?

Re:Hmmm..., I must have missed something.

[Chops-Frozen-Water]

Quite possibly. IIRC, the hot fusion problem is one of efficiency, i.e. it's only returning something like 90+ percent of the energy used to start it (it's not self-sustaining yet).
--

Screw lightpressure, use Solar Wind

[Anonymous Coward]

http://www.geophys.washington.edu/Space/SpaceModel /M2P2/

-- Ender, Duke_of_URL

Re:Screw lightpressure, use Solar Wind

[tesserae]

That works pretty well, too (sorta like using the solar light energy, but it's probably easier to do)... the problem is, it only works in the neighborhood of a star, where there's a stellar wind that's significant. What if you want to keep accelerating, right into interstellar space?

The folks thinking up the laser-propelled systems have gotten into some pretty sophisticated concepts: 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. ;>

---

Re:Question about light sails.

[Anonymous Coward]

You could send out a ship that would build a laser "engine" station at the destination system. It would have to go very slowly however, so it could be captured by the gravitational pull of the sun of the other system. Once you have the laser station set up at the destination system, you could accelerate at full speed up to the halfway point, then turn around and have the other laser slow you down. THe problem is it would probably take hundreds of years for the first ship to get there, and that is going to a "nearby" system. Infintiy

Tax Dollars at Work

[Anonymous Coward]

It's amazing to me that we could, someday, "sail on moonbeams," I am truely in awe. If only I could afford to put gas in my car.

Re:How far...?

[JetJaguar]

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.

Question about light sails.

[wen]

Hi all,

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.

[georgeha]

Do light sails only push the ship away from the light source? If so, how does a ship get back from where it came?

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 .1 c, it's practically a one way trip as far as life expectancy goes. But for a colonist ship, it would work. And the cool part is, you can leave your motor (The lasers) at home to send out other light sails.

One of my senior projects as an undergrad was a small solar sail design, it was neat.

George

Re:Question about light sails.

[georgeha]

"And the cool part is, you can leave your motor (The lasers) at home to send out other light sails. "

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

Re:Question about light sails.

[Asparfame]

"And the cool part is, you can leave your motor (The lasers) at home to send out other light sails. "

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.

Re:Question about light sails.

[tesserae]

I know of a couple of proposals for slowing a lightsail starship at the end of its journey, using the original lasers that sent it on its way. I discussed one of these in a post farther down the page (in response to "Screw lightpressure, use Solar Wind"), so I won't repeat it here...

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. 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.

---

Lighcraft

[provolt]

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. (Though this seems to be down right now).

CNN Coverage

ABC Coverage

provolt
Go Geek. Rule the World. gogeek.org

Re:Lighcraft

[Nubrian]

... STARDATE 2040, THE MAYFLOWER SET FORTH IN SEARCH OF A NEW LAND....

Re:Results?

[provolt]

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.

[derobert]

Looks promissing. Maybe now we can get a probe to pluton (let's not make it one of those cheaper missions, though).

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.

--

Results?

[Life Blood]

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...?

[cesar_labal]

I always keep up with science news, dream about someday going to the moon (maybe), etc. And I think That this accomplishment is exciting trying to use another sources of power...but it makes me wonder... about the resources we use to space exploration (or whatever). Do we need that? Can we accomplish that? I look at the world today and there is so many thing to change (for good of course) within OUR world, that I post a question to all /. readers: How far we must go before we look to ourselves? PD: Excuse my english.thanks.

Another nice thing about laser sail systems...

[ca1v1n]

Is that they can also be used to transmit power. Granted, this technology, as they say, is decades away, but NASA has already demonstrated a MAZER system capable of transmitting a house current. Of course, if a massive energy direction system like this were feasible, and they had some sort of ramscoop, ionic drive might also be nice. Of course, for interstellar voyages, that dust can be far between, and you'd have to carry huge quantities of it. One way or the other, it's pretty cool that we're already making advances into a pre-infant field.

Marvel

[akiaki007]

Can you believe this. This is truly incredible. This notion has been around for a while. Using light to move us at incredible speeds, but the only thing we've really been able to do is create the solar powered car.

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.

another sun propulsion system

[logophage]

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

Uhh, this is kinda old news

[f.money]

Check out this link.
Also interesting (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

[Captn Pepe]

From the article:

• Harris compares the experiment's significance to Robert Goddard's firing of the first liquid-fueled rocket in 1926.

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

[PseudonymousCoward]

Sailboats work by coordinating two forces: the pressure of wind on the sails, and the pressure of water on the hull. Adjusting angles allows you to sail somewaht upwind. Space sailing would work by coordinating two forces: the pressure of light on the sail, and the gravitational attraction of the sun/star. By adjusting the angle of the sail, you can sail out toward, say, Jupiter; then later, angle differently and sail back to Earth. Interstellar return flight would likely be problem :)

Take care

[Kaufmann]

While I do understand that this is an exciting feat of engineering with extensive implications, I think it's a scientist's duty to keep his or her head in its place when accessing the results of his or her own research - and these guys seem to be gushing excessively. Feynman wisely warned us to be wary of any scientific paper which doesn't offer any questioning of its own conclusions.

Uhh, actually that's something different

[tesserae]

Your links point to a different technique for using lasers as part of a propulsion system: the laser heats the air that's inside the "combustion chamber" (quotes, because nothing actually burns), which then expands through a nozzle as with any rocket. The laser is providing the energy, instead of chemical reactions. They pulse the laser, so air flows back into the chamber between expansions. (Note that with this method, you must provide some source of gas -- an ablative lining, or somesuch -- at great altitudes where the air is too thin for this trick to work).

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!).

---