Laser plane

[arcticpenguin]

http://www.dailydemocrat.com/articles/2003/10/10/news/news91.txt

EDWARDS AIR FORCE BASE (AP) - NASA has built and flown a remote-controlled plane powered from the ground by the beam of an invisible laser.
...
While in flight, the laser tracked the 11-ounce, five-foot wingspan plane, striking the photovoltaic cells that powered the tiny motor that turned its lone propeller.

Helios, a high altitude aircraft that crashed recently was built to be powered by solar power. Using a ground-based laser might enable night time continuity, thus doing away with energy storage (Helios used a regenerative fuel cell, not batteries)

Weight and efficiency of the solar panels would still be crucial.

 

[Bikewer]

One one of the Discovery Wings shows on the "Future of Flight, they showed experimental-stage work on a device that would be powered by a powerful pulsed laser.

The curved lower surface of the small aluminium body was made to reflect the laser pulses, increasing the effect.

This was a few years ago, and they were driving the thing at high speed along a wire, both vertically and horizontally. They were planning a bigger model.

Looked pretty neat, but I wonder how directional control might be achieved. Apparently, they were thinking in terms of a space vehicle, driven to high speed by an orbiting laser.

 

[!Xx+-Rational-+xX!]

I spend a lot of time keeping sharp objects away from myself.

 

[espritch]

One one of the Discovery Wings shows on the "Future of Flight, they showed experimental-stage work on a device that would be powered by a powerful pulsed laser.

I saw an article somewhere (can't recall where) about something similar to this. But as I understood it, the laser heated the air beneath the lifter providing thrust. This would work in the atmosphere but not in the vacumn of space. Of course, light can push an object in a vacumn, (hence the idea of solar sails) but a direct push from light is probably not particularly efficient if you have to provide the light source.

 

[Hamish]

But as I understood it, the laser heated the air beneath the lifter providing thrust. This would work in the atmosphere but not in the vacumn of space

Not if you use the laser to heat the surface of the lifter itself. If you have a solid plate on the bottom and use a sufficiently powerful laser you can ablate material from the plate. This material jets off at high velocity and acts like a rocket engine. The advantage is that you don't need an onboard fuel source. I don't know how efficient this is though.

Of course, light can push an object in a vacumn, (hence the idea of solar sails) but a direct push from light is probably not particularly efficient if you have to provide the light source.

Not really, no. You'd need a Terrawatt CW laser in order to get reasonable lift for a 100kg mass using light pressure alone. That is, a laser which would have a power output greater than that of all the USA's power stations put together. Not particularly efficient compared with conventional launch technology.

 

[DanishDynamite]

Technically, cool. Still, I'm not sure I like the idea of invisible lasers waving around the atmosphere. How strong is the laser? What happens if a bird is hit? Or someone looking out an airplane window?

 

[Hamish]

With the launch vehicle idea, the laser needs to be very strong. I think you need about a Megawatt per kilogram or something. That's really serious laser power. If you're going to vaporise the surface of the launch plate it's going to give a bird a nasty singe. With regard to air traffic, I guess you'd have your launch site well away from commercial flight paths.

With the new NASA Laser plane, I'm not sure of the laser power but there are almost certainly some safety issues. The idea is that these planes are so light that they need very little power to keep them up. According to the article that arcticpenguin cited, they used a theatrical spotlight to power the plane in initial tests. I guess that gives you an idea of the brightness, which certainly isn't lethal but I'm not sure I'd want to stare into a theatrical spot light for too long.

 

[Johnny Pneumatic]

the lasers are infra-red. can't blind you; can burn you(if their strong enough). what is a regenerative fuel cell?

 

[Hamish]

the lasers are infra-red. can't blind you; can burn you(if their strong enough).

Dangerously wrong. Infra-red lasers are very capable of blinding you. Especially so, since you have no idea when you are looking into the beam. Your eye still focusses the beam onto the retina and even if that wavelength does not normally excite the rod or cone cells on the retina, it'll still burn holes in the back of your eye when focussed.

As am aside, UV lasers also damage your eyes but in a different way. UV lasers do not penetrate your cornea and do all their damage on the front surface of your eye. Also nasty.

Your are correct about the burning though. Lasers of this irradiance are certainly a skin hazard.

(Edited to add: All this has inspired me to take on a responsible, laser-hazard avatar!)

 

[arcticpenguin]

what is a regenerative fuel cell?

Runs in either direction; burns H2 to yield electricity, with a source of electricity it can also split water into H2 and O2. So essentially it's equivalent to a battery in application. I don't know why it would be preferred over a battery for any particular application, perhaps energy density.

 

[uneasy]

Has anyone done this using a dirigible? If the fuel could be removed from the craft, the size of it could be much less. Also, the tracking of the laser would be much easier because it would be moving slower. Also, the laser could be off occasionally and the thing wouldn't crash to the ground. And maybe it wouldn't need to be as powerful because the propulsion system wouldn't need to be as strong (to maintain lift).

Wow, I've convinced myself in the span of one minute that laser blimps are the future!

 

[Johnny Pneumatic]

i hope no one burned their eyes out because of me.

 

[Iamme]

Traveller---But I see you are into well rounded objects. (See your avatar.)