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

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!).

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