OK, the shuttle to the moon thread reminded me of something I think I saw a few months ago on NBC news or something. I mention this because my recollection makes it sound like I got it from Weekly World News or “Chariots of the Gods”.
A bunch of scientists were demonstrating how they could propel a small object using flashes of light. The object looked like a silver bell and they were using something that looked like a strobe light. The strobe was put under the bell and when the intense flashing light was turned on, the bell shot up a pole into the air.
I also remember that they had to catch this bell on the way down in what looked like a giant butterfly net.
Looking back at what I typed, I realize it contains elements that suggest I imagined this during some sort of fever dream.
Yeah, it’s called a light sail. Here’s how it would work in space.
A ship would have a incredibly huge (miles wide), incredibly thin (on the order of microns) sail. The “wind” that propels the sail is the solar wind, the stream of protons that come out of the sun (they’re what cause the aurora). The acceleration is veeeeerrrry small, but constant, so a ship starting out from Mercury’s orbit would be going at a pretty good clip by the time it passed the Earth. The force of the solar wind drops off as you fly away from the sun, so eventually you’d be coasting towards your destination.
There are a couple of operational problems. First, the only was to stop is reel in the sail, use rockets to adjust your course, and try to orbit a planet. Second, without the previously mentioned rockets, it’s difficult to steer. I don’t think you can tack against the solar wind, like you can take against terrestrial wind.
Don’t know about what you’re thinking of, but it is possible to propel objects using light.
The device is called a radiometer. It consists of four vanes, one side black, the other white, set up sort of like a wind speed indicator inside an evacuated globe. Light shining on the vanes cause them to spin.
There isn’t any practical use for this, since you need the vacuum and the rotating mechanism has to rest on a pin; the weight of anything attached to it to get power would stop it from spinning.
It may be that radiometers can work like this, but the ones you see in museum gift shops don’t have a vacuum. Instead they rely on the higher heat of the black sides exciting the air molecules around them, causing the spin. If you look closely, they always spin away from the black sides, not away from the white sides as you would expect if they were being propelled by light.
I saw the same TV program on TLC or Discover channel. They propelled a conical shaped mirrored object along a guide wire using laser pulses up to a couple hundred feet or so…pretty neat, though I guess, at present…useless.
Now I’m big and important one angry Dwarf and 200 solemn faces of you.
These light-powered aircraft do not use light pressure. They have a reaction chamber, and a high-powered laser beam is fired into them from the ground. The beam heats whatever reaction mass in the chamber to high temperatures, which causes it to eject at high speed and create thrust.
I really cant see how this could possible be feasable since shooting a rocket straight up will not put it into orbit. You’ll notice how rockets and shuttle pitch over and start flying more parallel to the ground even before they get out of the atmsphere.
Yeah, that’s a good point - a large part of the energy to put something in orbit is needed to increase its horizontal velocity, not just it’s vertical velocity.
I don’t know anything about this “light craft” thingy in specific, so this is just pure speculation on my part. But it seems to me that if you have a ground based system that can lift things to a certain altitude without having to have the power source and reaction mass on the craft itself, then you haven’t achieved orbit, but you have reduced the amount of fuel you have to carry onboard to achieve orbit. I guess that’s worth something if you can pull it off, especially because with conventional rockets, a good fraction of your fuel goes towards lifting the rest of your fuel. And maybe you can even give something at least a little horizontal velocity this way too. Also, perhaps the thrust vector and the laser don’t have to be colinear, so the craft can thrust horizontally as long as the laser is still tracking it. (I don’t know this to be true - just guessing - but sounds plausible from their description of how it works).
I looked at the link, and it sounded like they’re only talking about using this for ultra light satellites, and that it’s only effective under a certain altitude due to decreasing air pressure as you go up.
Alphagene: I saw a show in i believe the Discovery channel, that was talking about how we could explore space and get around fast enough. The experiment you are reffering to was shown on the show, and described in more detail.
It goes like this: The experiment used a bell or dome shaped piece of metal with a funnel like piece on the underside. The light they used was a high power laser (The laser they used was so powerful, they had to mount something above the laser to keep it from reaching sattelites above and knocking them out of service). The “funnel” was shaped so that it concentrated the light (Basically a parabola). It was also highly polished, and the center had a hole for a pole that would guide the “craft”. When the laser was fired, it would hit the underside of the “craft”, become concentrated, and heat the air into plasma, and this would propel the “craft” upwards. It looked like they could get it to about 40 feet into the air. The laser also had to be fired in pulses to get the lift the “craft” needed. I noticed they also spun the “craft” so that it would be more stable.
Doobieous:
>become concentrated, and heat the air into plasma
This bring up another hitch. It would seem that the efficiency of this kind of propulsion is going to fall of rapidly with altitude.