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An Interplanetary Laser Communications System
caffiend666 writes "A news article at Yahoo states NASA is planning on testing the first laser-based interplanetary communications system on the Mars Telecommunications Orbiter to be launched in 2009. 'Unlike radio frequency signals that wash over the entire Earth, Fitzgerald and his colleagues will be shooting for a much smaller target - the southwestern corner of the United States.' Does this mean we will soon have telescopes outside of our homes soon to pick up high definition TV signals instead of our current 18 inch dishes?"
Earth - 'Hey' ...' ;)
Mars - 'Hey'
Earth -
Mars - '...'
Earth - 'a/s/l?'
-Teiresias
Does this mean we will soon have telescopes outside of our homes soon to pick up high definition TV signals instead of our current 18 inch dishes?"
.
No.
Because for television broadcast to the general population you want to wash the signal over the whole earth, rather than trying to target each receiver. And if you think your reception sucks when it's raining out now. .
KFG
I always wondered why they would want to use the visible spectrum...
We *CAN* make Laser-Radio waves! They go through atmosphere and trees and buildings....
-Bill
will this be implemented with sharks with frikin lasers on their heads?
"goodbye and hello, as always" ~Prince Corwin, from Zelazny's Amber series
It's unlikely you'd use lasers for wide scale signal distribution. A laser must be aimed, and to provide a signal to a thousand receivers you would need to fire a thousand beams, or have some intricate device that actively retargets thousands of times per second, squirting packets off to each receiver. Moving parts, complicated, no clear advantage.
Lasers for interplanetary communication is another thing. It's one sender to one receiver, and then you can go radio for inside planetary systems. Eg, you could set up a Mars Relay Station that takes low power local radio transmissions and beams the info back to Earth via laser, and vice versa. You get the advantage of cheap, small radio technology plus the range and bandwidth of laser.
Some serious lag in UT2004
If you could reason with religious people, there would be no religious people
a little math...
344 million km / (0.3 million km/sec) = 1147 seconds travel time
1147 seconds * 30 megabits/sec peak rate = 4.3 Gigabytes in transit at any instant.
HIV Crosses Species Barrier... into Muppets
Radio, or electromagnetic radiation, is a fancy name for a special spectrum of invisible light. Yes, Virginia, your radio is replaying music broadcast over light!
Also, a laser is a special form of coherent light. It just means that all the wavelengths in the beam of light are the same wavelength. It also means that the beam of light doesn't disperse very much unlike incoherent light (which no one can make heads or tails of what it is trying to say).
Since the radio requires a specific band to tune in to, it makes sense that the broadcasting station not waste time generating unnecessary wavelengths and focus on only those wavelengths that correspond to our chosen band. This restricts us to AM (amplitude modulation) bands only, but since we're trying to get data signals and not Martian stereo there is no big loss.
So why deal with visible light lasers when it could be invisible and work just as well?
Does that mean that something like this might be in widespread use in advanced alien civilizations, and SETI has no chance of ever finding anything?
Technoli
Its unlikely because Optical Telescopes rely on somewhat precise pieces of equipment such as lenses which are not known for their 'year-round' hardiness.
Speaking from experience, line-of-sight laser communications systems can be a right-royal pain to keep maintained when they are within meters.
I don't know for sure, but I would image that initial targetting of your telescope would be a very tricky operation (and you know that sat dishes are hard enough). And then, once installed, the fixings would need to be exceptionally heavy-duty to hold the telescope on target during gales etc.
Ripping an new rectum in the fabric of spacetime.
I only recently started taking chemistry courses though, somebody correct me if I am wrong.
Careful with names containing L slashdot.org/~AiphaWolf_HK slashdot.org/~AlphaWoif_HK slashdot.org/~AiphaWoif_HK
Here's a story about an ambitious plan to build a laser-based interplanetary communications network and the only thing the story submitter is concerned with is how this will influence his TV reception.
This, my friends, is why the human race is doomed. Here on slashdot, where we care more about science than most people, all some people can think about is how a new technological advancement can facilitate the transmission of market-research-constructed-SitComs or advertisements for the latest yuppie gizmo to their home.
One of the limitations for geosynchronous satelites is that their proximity to each other is limited due to the unavoidable spread of the signal. Shorter wavelength means a tighter signal, which means more satelites.
Of course... cloud cover is a problem, but there are ways around that (like those robot blimps that loiter in a given area above the clouds).
I rarely criticize things I don't care about.
"Does this mean we will soon have telescopes outside of our homes soon to pick up high definition TV signals instead of our current 18 inch dishes?"
:D :D :D :D
Yes!!!! I get it!!! This is a joke in English!!!! Ha ha ha ha ha!!!!!!!! I am laughing at the joke!!!!!!!!!!!!!!!!!!
This is a good day friends!!!!!!! Let as laugh together like old comrades!!!!!
Perhaps I need to read TFA more closely, but I am left wondering what the advantages of using lasers for interplanetary communications would have over our traditional RF or microwave systems. After all, it's all EM radiation, so it's speed of light, and the lasers they're using apparently can't reach through clouds, so what are the reasons why you would want to use lasers instead of radio antennas?
Sleep is futile.
You idiot.
I'd be happy if I could communicate with women. Why don't they work on that first?
The Internet is full. Go Away!!!
Perhaps I need to read TFA more closely, but I am left wondering what the advantages of using lasers for interplanetary communications would have over our traditional RF or microwave systems.
Dude, because it's being done with lasers! That's reason enough.
Ask another question like that and we'll revoke your slashdot membership. You have been warned.
Suck on this, inverse-square law!
English is easier said than done.
Just aim your telescope at Mars and hope someone miscalculates the reply message coordinates.
BZAP!
crazy dynamite monkey
All light is electromagnetic radiation, but not all electromagnetic radiation is light. Light is the small, visible portion of the elecromagnetic spectrum. So, Virginia's radio is *not* replaying music broadcast over light.
"I'm not impatient. I just hate waiting." - My Dad
What does that have to do with anything? Going between planets we will still be limited to sending messanges at the speed of light. aprox 16 minutes from here to mars. There most definitely *will* be a lengthy delay between messages.
Well.. maybe. Or Maybe not. But Definitely not sort of.
That's pretty arbitrary. Where do you set the cutoff? Some animals can see into the infrared range, some reach into the ultraviolet range. Blind people can't see any light at all. So what do you say is visible?
The ultimate system for communications would be using neutrinos. Only two downsides. One producing enough neutrinos to create a signal and coming up with a compact means of detecting them. With current technology it would probably take a detector the size of a football field to recieve a binary SOS and the only major source of them are events like super nova. The benefits would be enormous given a single signal from a single point could reach the entire planet passing directly through the earth with little or no loss. It's doubtful there will ever be a practicle way of doing it but it would be a way of sending a signal with little interference except for naturally occuring neutrinos.
"Does this mean we will soon have telescopes outside of our homes soon to pick up high definition TV signals instead of our current 18 inch dishes?" Yep, I looked into the near-future
cheap labor conservatives - they want to keep you hungry enough to be thankful for minimum wage.
Hams object, not because it's a good and valid method of delivering bits, but because it interferes with emergency communications.
8
There's lots of ways to get good Internet feeds to folks; just look at what Robert X. Cringely has done with 802.11b. Look in the archives of his columns at www.pbs.org and see there are untapped alternatives.
To understand why we're concerned, go switch your hi-fi to AM, tune to a vacant spot between stations, and turn up the volume about half way. Then, try to have a phone conversation over a bad cellular connection with your ear six inches from the speakers, and you will still have an easier time communicating than hams will when we experience the 16 db over S9 interference already demonstrated by BPL.
I will make a small wager with you, shaka999. If you live within North America, I'll wager your state's or province's emergency plan counts on hams. So does your county's emergency plan, and your city's.
You see, hams _practice_ at getting data through emergency conditions. We do it at our expense, with equipment we buy, build and maintain ourselves, without government funds.
There's even a subsection of every national ham organization dedicated to emergency services. Yeah, I belong to one, and was out in the last ice storm, two months ago, delivering nurses to the local hospital because the roads were otherwise impassible, and the locals had already overloaded the cellular network to the point where a fast busy tone or "All Circuits Busy" signal was as likely as dial tone.
BPL threatens the entire ability to function on the frequencies needed the most for long-range communications, the HF bands. If this interfered with TV (VHF and UHF), well, everyone would kvetch, but instead the power companies have designed these systems to use HF (aka shortwave) frequencies.
Long range radio relies on HF, because it takes those lower frequencies to effectively bounce off the inner layer(s) of the ionosphere. Higher frequencies (VHF, UHF, SHF, microwave) just zip right through the F, F1 & F2 layers, so we can't do bank shots to get a signal from Earthquakestan to Resourceland to let them know how many units of Type A to send.
Satellite? Well, gee, that presumes the ground stations survived that quake/tornado/hurricane/typhoon, that the power didn't fail, and the phone lines to the earth station still work. Oh, yeah, and IF there's a free satellite channel for us, which NASA's problems have not made any easier.
Now, America's three-quarters of a million hams are not alone here, as you make it seem. The NTIA (National Telecommunications and Information Administration), who you'd expect to be gung-ho over more bandwidth to previously underserved areas, and also FEMA (Federal Emergency Management Agency), have gone on record to object. They document that BPL was a complete disaster, interference-wise, when tried in Japan. The Austrian trials are on hold because the power companies there were not able to rein in the interference.
But, it's Politics with a Capital P; who is beholden to whom, and who bought whom.
Now, you might say, 'well, if there's a disater, the power's down, right'? Not necessarily. BPL can cause interference for miles and miles, but if a hospital needs to call for blood, what's the power company supposed to do, shut down the entire grid?
Besides, remember that hams buy their own gear to practice and learn with. If we can't use HF, well, no one will buy new HF gear, no one will learn the tricks of HF (which is _very_ different than the skills needed for the garden-variety, talk-around-town two meter and 70 cm band users), and no one will bother to keep the automated packet netowrks in service, the digital backbones of the ham world which move the vast majority of message traffic.
Sometimes, _nothing_ but Morse ("the original digital") will get through, but with BPL jamming the HF spectrum, morse will become a dead letter.
I mean, man, you can put a bra on Michael Powell, and yuk it up all you want (see URL) but, damnit, these changes will *kill* people.
http://www.wweek.com/story.php?story=485
*walking along street* Hmm hmm hmm hmm hmm (humming a tune)... Wha? *looks up* AUUGGGHHHH!!! MY EEEEEEYEEEEESSSSS!!!
Photonic forms of energy. Radio is not photonic, therefore is not visible. You can't shine a beam of light across a stretch of wire and get a current. They are different.
-- Thou hast strayed far from the path of the Avatar.
When you add lasers to anything, the net benefit is multiplied by %5555. Interstella 5555 is a prime example.
Ninjas also benefit from lasers ovbiously.
Talk to the FCC. They're the ones that divvy up the spectrum.
"I'm not impatient. I just hate waiting." - My Dad
Obviously NASA doesn't wany anyone eavesdropping on all the nifty hi-res pictures they intend to take of all the alien tech laying around on Mars. Hey, if flying saucers have crashed on Earth, why not there, too?
No. Broadcast is difficult with lasers, you fool.
Photonic forms of energy. Radio is not photonic, therefore is not visible.
Nope, all electromagnetic radiation is transmitted via photons. Photons just mean that energy is transmitted in discreet packets, and not continuously.
AccountKiller
The real reason is the directed signal takes less energy than a broadcast. This pans out to faster data rates since they can use higher frequencies.
Could someone more knowledgeable about lasers than me explain if this type of laser communication is safe? The article says it will be a 5W laser transmitting from 2.3 AU with a target area of several million square miles. That sounds like the signal would be very weak when it reaches Earth, but I don't know how strong a laser has to be to damage the retina. So, if this plan is implemented, would it be safe for people in the target range to look at Mars with a backyard telescope?
INTERGALACTIC PLANETARY!
...to generate the 1.21 gigawats of electricity needed to power up the flux capacitor.
DarkMantle I been bored, so I started a blog.
Most likely laser communications will be used between planetary objects, and then transmitted at the lower end of the wavelength like Wi-Fi, TV, and radio. Lasers are great for point to point communications over a long distance. Can you image a wide beam laser burning a hole in our atmosphere continiously.
Radio is not photonic
Radio has photons just like x-ray and infrared has photons. They just happen to have significantly less energy than visible light.
The ability to produce current in a wire is a product of the coherence of the photons. You should be able to generate current with a coherent laser beam or microwave.
The world is neither black nor white nor good nor evil, only many shades of CowboyNeal.
In fact a laser system based solely on the presence or absence of laser wavelengths that are transmitted in free space is an absolutely rotten idea. current photo detectors have no way of "synchronising" to the lased radiation they simple detect the presence or absence of a specific wavelength of light.
because at a fundamental level the shorter the wave length used for transmission the higher the possible rate of transfer is.is the parent thread actually basing his/her post on any information or are they simply trying to pass of there misguided opinions as fact, oh wait this is slash dot...
In my asshole there are are little pieces of shit connected to the very hairs of my ass
...no more listening in for the evil nations (TM) ;-)
this can be useful from the perspective of stopping tv piracy. if the satellite companies can beam only what you pay for to your home it would certainly stop you from watching free porn. just my 2 cents. p.s. i know this doesnt do anything for analog cable.
im a hippie
I wonder how Earth weather would effect the propagation of Laser, and not to mention solar wind. I guess we have to wait till US spends a lot of money and then I can hear them say Duh!!!! on their newly built laser system.
the reason SETI has no chance of finding anything is there aren't any aliens!
At least it'll have frickin' laser beams.
Excuse me, I don't mean to impose, but I am the ocean
Laser has at least two major problems that I can think of.
1. Lasers are pretty damn inneficient. At least compared to radio equipment that can be very efficient. When you're in the 2 percent range you're happy.
2. Lasers are very high frequency. This is bad. Higher frequencies are absorbed MUCH more readily and are blocked by interfering objects. They also lose power faster through general attenuation through free space much faster than lower frequencies.
And if you think the laser will make a small dot we can see, you're wrong. The laser light will probably cover half the other planet (this works out to look like attenuation)
Basically, I dont see the reason to use lasers over long distances when lower freq RF works a lot better.
Current in a wire is not produced by any sort of any kind of photon. The electrons in the wire move, and the electrons are the only thing which can create the current.
ESA has been using laser for communication with some satellites and will do so with SMART-1 as well.
But several astronomical units away, things get kinda hairy because you won't receive even the slightest bit of feedback on whether you are actually closer to your target or if you overshot it completely for up to minutes later... Even the smallest hair of a fraction of a degree off and the beam wouldn't come anywhere even _close_ to the earth, so it would have no means to know in which direction to adjust for its next aim-test.
File under 'M' for 'Manic ranting'
So now I cant look up at the sky without staring into the satellite and getting my eyes burned out??
Does this mean we will soon have telescopes outside of our homes soon to pick up high definition TV signals instead of our current 18 inch dishes? What do you think the dish is? It's a telescope.
Actually, he lives across the street from The Beast.
664 and 668 live next door.
ft
Wouldn't doppler shifts due to the scale of interplanetary motion cause the wavelength of a laser beam to change its color? If so, you will need more than a telescope with just a simple receiver of, like say 650nm, to be able to pick up communications accurately. You would need a broadband receiver.
I would sure hate to see another failed mars mission due to a missed conversion between nanometers and angstroms.
In practice, it may work for Satellite - to satellite comms, but weather problems would impede its continous use in wide tracts of the earth.
"If a boss demands loyalty, give him integrity. But if he demands integrity, give him loyalty." (John Boyd, 1927-1997)
Why use LASER?
With a laser, The beamwidth is small allowing a greater energy density. See geometry.
One drawback that may come to mind aiming. This is easy to get around if you have an active target, say a LASER signal from the Earth.
The information carying capacity of a radio (or LASER) signal =
POWER * BANDWIDTH. Power = energy * time.
With a narrow beamwidth you've increased the power*bandwidth. Think of a rectangle. Bandwidth is the length, power the height. The area in the rectangle is available for data. The heght of this boxcar is limited by noise power. Low noise is attractive. There are plenty of low noise 'holes' in the spectrum for NASA's LASER. On top of this, it's easy to filter the LASER signal from broadband background noise.
The GOAL for those who didn't RTFA is higher bandwidth communicatrion in interplanetary exploration. Better photos, wider range of instrumentation. More processing power on Earth can be applied to RAW data which for now has to be dealt with by the remote processors.
Now I'm the grandest Tiger in the Jungle!
Well, Laser light generally have the following five properties:
To my mind at least the interesting thing with lasers are that every one of these characteristics (and multiple combinations) have been used in applications.
That's not to say that all characteristics are necessary at all times and when they're not they can usually be excluded (you do not want a highly intense laser, i.e with a high power output, for reading a CDR for example). In many cases the characteristic will degrade with time/space; i.e. the coherence length of a laser can be from anywhere between nothing much to a kilometer or more. (And incidentally doesn't have much to do with the beam being parallel at that point.)
For interplanetary communication the light being parallel would be the deciding factor, you could induce much higher field strengths at the receiver than with radio at interplanetary distances for the same transmitter power output. You could do away with most others (though I guess it being monochromatic could help if there isn't much atmosphere).
Wikipedia has a good introduction.
Stefan Axelsson
But Verizon is going to have to glue a giant parabolic antenna to the guy's head, and have him wander around in the desert adjusting his azimuth.
sigs, as if you care.
Who cares? It all still travels at the same speed.
2004-08-19 11:20:21 MIT Lays broadband to Mars (Science,Space)(rejected)
"Does this mean we will soon have telescopes outside of our homes soon to pick up high definition TV signals instead of our current 18 inch dishes?"
What kind of asinine question is this? I love it when someone makes themself look like a fucking moron trying to ask some insightful question in their article submission in a thinly veiled attempt at having their submission accepted.
Of course we aren't going to soon use optics for TV distribution. It makes no sense. If a TV station were going to go out of their way to build a transmitter just to serve the house at 123 Any Street, that would be one thing, but TV stations want, and are required by law, to serve as many people as possible. Also, how does it make sense to use this hypothetical optical wide distribution scheme in an atmosphere that is detrimental to the transmission method? You think your dish TV gets bad in thunderstorms? Just wait until the fog rolls in on your laser receiver.
Sheesh, the really sad thing is that freakin' timothy couldn't be bothered to exercise an iota of critical thinking skills on this one... fucking christ...
Let the modding down begin...
WTF has this rant got to do with TFA? BPL is broadband over power lines, and the article is about interstellar laser communications?!
Parent is offtopic and overrated and should be modded down.
I can see it now. There'll be a solar flare, the new advanced dogbot will capture the modulating light and read it as a command. Then he'll start humping the leg of the newly discovered alian humanoids.
Yes, it will work - I've done it myself.
You don't need much modulation of the light beam - just a percent or so will be enough to detect, and you won't see a percent modulation with your eye (unless you have a reference to compare against).
Yes, you aren't going to be pushing 20Hz-20kHz across this - between the thermal mass of the filament and the slow response of the CdS cell you're going to be lucky to get 3kHz, but that is good enough for voice.
www.eFax.com are spammers
Wow. Clueless. What about the displacment term, eh?
Life on another planet is going to love this.
*blink*
*blink*
alien1:Damn humans and their laser pointers, why won't they stop shinning them at me. *sob*.
If this is the typical way interplanetary communications could develop then scanning the universe for stray radio signals with SETI might be fruitless as all the data is sent in a tight beam to its destination.
They could use some loudspeakers and microphones to transmit the data as sound or, better, some wires from Mars to Earth.
The Laser are too dangerous because it could cut the Earth in pieces (at least that I have seen on some Movies).
Interplanetary porn.
arh, it annoys me to know that speed of light is the limit..
Speed of light is not the limit. It's just the natural maxim. We can accelerate beyond it by examining it closely.
Just like a stream of water rushes down a cliff at a particular rate, we can apply pressure to the water and make it go faster.
We're not there yet, but faster than light travel is a thing of the not so distant future (relative to the length of time humanity has existed on Earth).
The dangers of knowledge trigger emotional distress in human beings.
Mr. Planck called and asked his constant back. He also muttered something about "science being wasted on the youth" but I didn't catch it completely. Obligatory do it yourself link here.
These convert photon's energy directly to electric current via an excitable medium.
It is an amazing day to have a project you are working on get posted to the front page of Slashdot. I am actually working on the distributed ground receivers for the MLCD laser signal.
Believe me when I tell you this is an ambitious project, but after months of continuous progress, I am completely confident that we'll achieve full rate comm, in the daytime, with the sun out, with Mars on the other side of the solar system.
To give you an idea of how hard this is, think about this. Each telescope receiver must have a perfectly accurate clock that can track the transmitter within much less than one clock cycle at near GHz rates. That means the clocks, completely unconnected must match (in our case) to better than 0.0000000001% (yes that is the right number of zeros) across the distance. We need an optical system that can filter out all light other than the laser signal and a detector that actually counts individual photons and time tags them to that very precise clock. The whole system must take into account the Doppler shift of the clock and the laser wavelength and then we must aggregate all this photon data.
A year ago, I would have been very skeptical of such a claim. But seeing as how I am about to give a presentation on our success with just such a system, sitting on a lab bench next door to my office, I am a believer.
I'd like to thank /. for making my day.
There's really nothing that exciting going on in this story. We've been using laser-ish communications with KA and other band satellites for years. The only difference is that we're trying to use them over bigger distances and probably a different wavelength. Big whoop.
What would be really cool is if they started using quantum entanglement for communications. So basically, you entangle a huge number of particles, send half of them off to Mars and keep half here. Then you just wiggle or change the spin of a series of entangled particles on Mars and observe the affect instantaneously here on earth. I.e. no 20 minutes of latency in communications, it's instantaneous! Once we got that down to a science we'd just need to ship a canister of new entangled particles on a regular basis. Now that would be cool.
Good point. This technology would be nearly useless for terrestrial communications.
1) Laser easily obstructed by atmosphere
2) Why? Traditional sattelite dishes are able to focus the signal enough to cover the Earth, and not much else.
3) Maybe useful for single-point uplinks, but for mass subscriptions like DSS, you'd need a beam for every subscriber.
However to communicate with a deep space vehicle it would work great... Except how would you aim the thing??? I'm really curious to know that. Its a bit like perfectly lining up a slngle grain of sand in New York and one in Fl, while are both moving!
One more random observation. From the article, is it just me, or did the phrase "growing fleet of unmanned aerial vehicles" worry anyone else? (I'm thinking... Terminator?)
-- Just another unsolicited opinion... from the Peanut Gallery.
You know, the parent's question (and Timothy's suggestion on this being used for terrestrial TV) is showing some disturbing trends here on /. - and this isn't the first article or post that has been like this, it has been brewing for a very long time...
I have seen many posts on other articles and other comments, including this one - that is suggesting a strange trend of this site becoming either a site for geek posers, or just plain norms, or something. Like the parent's "worrying about a 5W laser spread over a very large area" - how can someone call themselves a geek and not know (and more importantly, understand) what the inverse square law is, as it relates to lasers? Hell, you learn about it in high school, so unless the poster is younger, there is no excuse! Or, Timothy - who is an editor, and should have a geek quotient a little bit higher than average - speculating on using a laser system for terrestrial orbiting sattelites using telescopes to pick up the signal - after it is spread over a wide area and attenuated by atmospheric conditions? What kind of thinking is that?
Furthermore, I have seen a disturbing trend of so-called geeks on this site injecting or insisting that fairy-tales should be seriously studied (mainly whenever the story at hand relates to evolution or similar topics), or at least looked into or considered. WTF is happenning?
This kind of non-thinking, non-reasoning isn't only happenning on this forum, but in many forums nationwide. It is leading to a twisted form of fundamentalist-pseudoscience, that seems to snare a lot of otherwise intelligent and open-minded people. I am trying to understand how and why this is possible - all one has to do is keep their eyes open at the larger world (and yes, it is scary, but that should be fascinating, as well), and not let obvious bunk get in their way while seeking knowledge.
I am not saying "don't study religion" - religion has numerous great lessons for humanity, but we seem to ignore those lessons to our own detriment worldwide as a species, and instead focus on the worse parts of religion. I don't expect any answers here, but I just wanted to make this observation aloud. I felt it needed to be voiced, because it feels like /. is slowly becoming a site for anything but real geeks.
Reason is the Path to God - Anon
But maybe a system like online forums where they are just as much a part of the conversation as anyone else really just drags down the quality of discussion for everyone. Slashdot is the biggest blog in the world, so it's silly to hope that its audience would somehow be elite, or even consistently smart. The moderation system helps insulate us (those of us who don't browse at -1) from the dumbest ideas.
So Slashdot really is a frustrating read if you're unwilling to accept a pretty low signal to noise ratio. But some of the "signal" is worth catching, and there is something sociologically interesting about the ideas that the Slashdot horde seems to hold dear. Plus, you do a good thing by calling a bullshit comment what it is. There are plenty of good lessons learned here about how it's not "just your opinion, man" and about how some questions and ideas (and people) really are stupid. And yes, there have been good, deserved "takedowns" in the threads on Slashdot. So we should just accept that there are people here who are learning to think about stuff, and we should help them (which doesn't mean we shouldn't insult them - sometimes, that's the best way to make the point stick).
And what exactly do you think a dish is, if not a telescope?
If you don't know anything about Nikola Tesla pick up a book called "Man Out of TIme", it's a good primer to look deeper.
People have little idea of what this man *continues* to give to our societies, the military certainly does.
http://www.teslascience.org/pages/tesla.htm
"In December of 1900, after wrapping up his preliminary testing he returned to New York to begin work on the full sized prototype worldwide broadcasting station.
The main structure built to house equipment for this station and known as the Wardenclyffe Laboratory Building, is still standing near the Long Island community of Shoreham, New York.  Not a great amount has been learned about the station's specific design details.  It is quite certain that there would have been major similarities between it and the large 1899 apparatus in Colorado.  Tesla's investigations at Wardenclyffe were brought to an end due to a lack of research funding.  The building was abandoned and Tesla's tower was eventually demolished during the early years of World War I.
One interesting feature of Tesla's world system for global communications, had it gone into full operation, would have been its capacity to demonstrate on a limited scale the wireless transmission of electrical power. If the prototype communications station at Wardenclyffe had shown the feasibility of wireless power transmission, then Tesla intended to build a full scale power transmitter at Niagara Falls, site of the first commercial three phase AC power plant mentioned earlier."
http://www.teslascience.org/index.html
http://www.teslasociety.com/dream.htm
http://www.teslasociety.com/picture6.jpg
http://www.teslasociety.com/wirelesssystem.gif
http://www.teslasociety.com/signaltomars.htm
http://www.teslasociety.com/mars.html
~hylas
They're called masers when in the microwave range (the M is for microwave instead of light, the rest of the acronym is the same), and they came before lasers.
NASA is spending profane amounts of money on an interplanetary com system and some mofo is wondering if it could lead to better TV...
Get your torrents...
Laser collimation has to do with the geometry of the gain medium and the mirrors that form the oscillator cavity. In a linear oscillator, there is a fully reflective mirror, a cylindrical gain medium, and a partially reflective mirror, all on the same axis. Light that is even a little bit off-axis won't escape from the partially reflective mirror, and this makes the laser light collimated.
You can have collimation without lasing, for example gamma radiation.
The clearance system sounds logical. It is not. It is completely arbitrary. -- John Bolton
You need to reread your second semester physics texts. Photonic forms of energy...oh that's rich.
I read that as "seismic waves are a far better medium for communicating through the earth". I envisioned communicating with Australians by using a really freakin' big mallet.
Actually, if you look into it, they're using PPM.
Besides that, even if you have a dispersion of less than 0.01 degrees, that will amount to a large physical area after the millions of kilometers involved in interplanetary communications. Over 50Gm (gigameters), unless I am mistaken, 0.01 degrees would amount to around 1,300 kilometers. If you are talking *precision* you'd have to get that down to maybe 1.3 km. That makes for a dispersion on the order of thousands of a degree at most.
Packet loss by meteorite!
A fine group of postings, all.
Of course... cloud cover is a problem, but there are ways around that (like those robot blimps that loiter in a given area above the clouds).
I doubt blimps *above* the clouds are going to be much good at getting signals through the clouds...
Cheers & God bless
Sam "SammyTheSnake" Penny
"I doubt blimps *above* the clouds are going to be much good at getting signals through the clouds..."
The blimp can use radio and microwave to talk to the ground and lasers to talk to the satelite. A tight signal is not needed to talk to the ground because the blimp is much closer.
I rarely criticize things I don't care about.
Lasers from Mars pointed at the US Southwest, with Roswell smack-dab in the middle of it, and you even have to _ask_ if there's Space Alien involvement?
Bill Stewart
New Fast-Compression-only CPR http://preview.tinyurl.com/dy575ks