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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.
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.
I'd be happy if I could communicate with women. Why don't they work on that first?
The Internet is full. Go Away!!!
Suck on this, inverse-square law!
English is easier said than done.
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.
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!!!
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.
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?
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.
Actually, he lives across the street from The Beast.
664 and 668 live next door.
ft
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!
"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...
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
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.
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