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I imagine it has been thought of - using light to push vehicles into orbit.
Set up say three high intensity beam projectors on earth to keep the thing on course (as long as it stays in the triangle while it goes up) and beat light against a very reflective spaceship.
Momentum of light is what? 2*I / c for the ideal reflective case where I= W/m^2 and c = speed of light? So you might need several thousand megawatts (A nuclear plant to run the thing? OK - so you build a Nuclear plant... no big deal right?) to do it and you would have issues with how to not vaporize your craft (OK - so this is where you guys come in). Anyways, theoretically it sounds possible if you could punch that much light into a beam. Once you get high enough you get let it go and it could enter an orbit. (assuming it had enough potential energy to do so).
Interested in what you folks think.
Justin in Calgary
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http://xxx.soton.ac.uk/html/physics/0306050]It won't work.
http://www.sciencenews.org/pages/sn_arc … b1.htm]Not soon.
The efficiency is very low,
maybe if the spacecraft carried some fuel to be heated up ?
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Might work if you replace the light beams with magnetic ones, and a high power magnet on the ship.
A linear induction motor with no tracks in effect.
Big power consumption on the ground, but little on the ship, and no fuel needed on the ship to get to orbit.
The universe isn't being pushed apart faster.
It is being pulled faster towards the clumpy edge.
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Magnetic effects would have too short of a range for effective propulsion.
A laser-augmented solar sail or laser-powerd ion engines that are operated by a laser on Earth are possible, but setting up the lasing stations of requisit power would be very expensive, and the system could not tend multiple spacecraft. Nor would it easily be employed for the return trip for the sail or with any ship in low orbit.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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In one scenario suggested a decade ago by Robert L. Forward of Forward Unlimited in Clinton, Wash., the craft would rely on a light source that has yet to be built—an Earth-orbiting laser as powerful as six suns—and a focusing lens the size of Texas positioned between the orbits of Saturn and Neptune. The craft could fly through space at one-tenth the speed of light. At that rate, it would reach Alpha Centauri, the nearest star, in a few decades, notes Garner.
For space nuts second article I wonder what they mean as powerful as six suns? Certainly
they don’t mean energy output. What would you power that with a primordial black hole? Do
they mean radiation intensity? I don’t think they could get energy densities greater then the
photosphere and if they could the laser would be powerful enough to cause fusion. The suns
atmosphere? That is still pretty hot. Maybe then mean 6 times the intensity of sunlight at 1AU.
That sounds more reasonable. What a badly written sentence.
Anyway I think the solar sail sounds pretty exciting, because of its application for astronomy and
satellites. In the future the sun will be a window into our solar systems and all satellites will hang
in one spot over the earth at every latitude. Thus we don’t have to worry about satellites getting
in the way of space elevator and vice versa. Oh yeah mapping the sun from its pole would be
cool too. But why not just use a polar orbit?
Dig into the [url=http://child-civilization.blogspot.com/2006/12/political-grab-bag.html]political grab bag[/url] at [url=http://child-civilization.blogspot.com/]Child Civilization[/url]
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This has come up a time or to before and the answers are always pretty much always the same. It just doesn't seem very practicle to use a laser to push a craft up into orbit. The amount of energy required to generate the necessary thrust is huge, and you require a gigantic laser as well. And there are a whole host of other issues, from atmospheric interference to focusing such a large laser on a fairly rapidly accelerating target.
Out in the solar system at large it may be a slightly diffrent story though. Much less delta V is needed after you climb out of a gravity well, thrust is no longer a huge issue, and dealing with a large reflective surface also becomes easier. So for a fairly highly developed spacefairing society it may make some sense to build laser propulsion centers on the moon or asteroids or something. But we are a long way from there.
My favorite light sail concept seems to have fallen out of favor as of late though (at least I haven't heard anyone mention it). For launching an insteral mission/probe instead of buiding truely giantic lasers and focusing systems around the solar system, I would build a very large mirror (100's of km) very close to the sun, at a point where it's reflected momentum counters the force of gravity. You then turn that mirror on an equaly large sail and send your probe out into the galaxy. With such a very large mirror in such close proximity to the sun, you could generate ALOT of speed/momentum this way. The system is only good out to about the orbit of Jupiter, but you can generate extream amount of velocity in that period of time. I've seen estimates up to .5c with prolonged periods of +9G acceleration (which in itself could be a problem). But it would certianly be simpler then the multi-gigawatt lasers distributed about the solar system.
He who refuses to do arithmetic is doomed to talk nonsense.
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OK - so assuming the laser is 100% efficient what would be the necessary output to lift say a penny.
I think one nice thing about the light propulsion idea is you could say send up small payloads and potentially construct stuff while in orbit. Anyways, I'd like to see some numbers crunched(I suppose I should start the crunching). I'll post what I get soon...
So what I picture is sending up small pieces of your solar sail at a time, put together the solar sail in orbit and then use a conventional rocket to get your crew into orbit and finally head for Alpha Centauri using the solar wind?
Hehe - yes the complications are giving me a headache too... Anyways, just venting the imagination for what its worth.
Justin in Calgary
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http://science.howstuffworks.com/solar-sail1.htm] If you take 1.4 kw and divide it by the speed of light, you would find that the force exerted by the sun is about 9 newtons (N)/square mile (i.e., 2 lb/km2 or .78 lb/mi2)
http://woodmansee.com/science/rocket/r- … tml]Rocket Science
For takeoff, a beam powered scramjet might be more to the point. Out of the atmosphere, beam heated exhaust, and only later use light by itself. Interstellar space has a molecule or 2 per m^3. And could use the gas as an interstellar scamjet ?
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