Is a Laser Data Link 1.5 Million Kilometers Feasible? 304
An anonymous reader writes "On the Canary Islands last week, a team from Oerlikon Space demonstrated the feasibility of a laser link across a distance of 1.5 million kilometers for the first time ever. In the future, laser links like this one will be able to transmit data across huge distances through the universe far more rapidly and efficiently than is possible using conventional radio links today."
Never saw this coming (Score:5, Interesting)
In all seriousness, the problem is not the knowledge a laser can travel that far; its whether you can create precise enough targeting equipment.
A radio signal might be more of a splatter, but at least if you point it "over there" with enough power behind it, it will get there.
As they say their simple hilltop to hilltop test failed because of weather conditions, whats going to happen when they do put 'scopes at the lagrange points?
"Oh sorry, we can't get the data today because its cloudy"
Back onto the radio front, we have Voyager 1 which is 15 billion miles away, proven with radio, that would seem good enough for me.
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Voyager is 15 billion kilometres not miles as stated (about 9 billion miles)
http://voyager.jpl.nasa.gov/mission/weekly-reports/index.htm [nasa.gov]
Re:Never saw this coming (Score:5, Funny)
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Re:Never saw this coming (Score:5, Funny)
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Unlike radio stations, most point to point links (for example, satellite uplinks) use a focus beam. That's what the big dish is for. The tighter the beam, the less area your transmitted power is spread over and the greater your received signal strength. The downside, of course, is that a tighter beam has to be aimed that much more accurately. As a point of reference, most geosynchronous satellites are spaced about 2 degrees apart, which requires a te
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They'll just have to up the power on those lasers. A lot.
Re:Never saw this coming (Score:4, Informative)
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She thinks the return beam diameter is probably more than double due to the lensing nature of the atmosphere, but she has no numbers off the top of her head.
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The fastest interplanetary radio link 1977 had to offer!
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"Uplink communications is via S-band (16-bits/sec command rate) while an X-band transmitter provides downlink telemetry at 160 bits/sec normally and 1.4 kbps for playback of high-rate plasma wave data. All data are transmitted from and received at the spacecraft via the 3.7 meter high-gain antenna (HGA)."
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Why? And, basically the same question, less than 70kb per what?
Re:Never saw this coming (Score:5, Funny)
I agree. We should stop all development and research in this area immediately.
Is there anything else that people are working on that you don't see a need to improve? They should have checked with you first, I guess.
This is a very good point... based on that logic.. (Score:2, Insightful)
While we're at it, Coal Plants do a good job at producing energy and they work too... lets forget about all that fandangled alternate energy source stuff...
While were at it.. smoke signals work too.. no need for complicated technology like telephone and email...
okay.. now that my sarcasm limit has been reached... because something works is not a good reason for ignoring technology that can potential
Re:Never saw this coming (Score:5, Interesting)
Huh? The logical thing do to would be have the laser communicators in orbit, and the communication from ground to the laser satellites would be via the conventional means. If its cloudy in your town, then the satellite can talk to another town which isn't cloudy and you can use fiber to talk the rest of the way.
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Running this laser communications system at each DSN ground station, and taking advantage of the ground communications links already in place would be a boon considering the limited bandwidth currently available via radio-only communications systems.
Lagrange points (Score:5, Interesting)
I've been thinking about the Earth/Sun Lagrange points lately. I think they might be an excellent location to test an Earth/Mars transit vehicle. ESL5 is far enough away to be out of Earth's magnetosphere, so it will experience the raw radiation environment. It would be able to remain in position for long periods of time. The only hitch I can see is it may not be easy to get to/from. I can't seem to find any data. If we put a test platform with a "lifeboat" craft there, how quickly could the craft get back here. Is it days away? weeks away? Anybody know?
Re:Lagrange points (Score:4, Informative)
In general the amount of time to get there/back would be dependant on how much energy you want to put into getting there and back.
Finally we do already have a satellite (SOHO) on the L1 point relative to Earth and the Sun. This is an unstable point so some energy is used maintaining position However it is a telescope on an L point relative to the Earth and Sun.
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However, as you said, radio's doing just fine for us right now. I i
Mis-aiming (Score:2)
Re:Never saw this coming (Score:4, Funny)
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Re:Never saw this coming (Score:4, Funny)
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The issue is not whether you get data at all, but whether you can transmit at broadband speeds. I am pretty sure that at this point of
its flight Voyager does nothing else but send a few byte pings every once in a while.
The problems laser links would solve would be in the order of streaming HD video from Mars to Earth.
A bit exaggerated? (Score:2, Interesting)
Re:A bit exaggerated? (Score:5, Funny)
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One important warning (Score:5, Funny)
Interesting to use this with radio telescopes (Score:4, Insightful)
It seems to me that this would be especially useful to reduce the amount of induced radio noise when communicating with L1 (etc) radio telescopes or other instruments potentially sensitive to the normal radio frequencies used for communication, eg keep the comms out-of-band of what is being measured as far as possible.
Rgds
Damon
I figured it out! (Score:3, Funny)
Question about lasers (Score:2)
Either way, correct alignment seems pretty tough.
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Yes they do, since that focus is never perfect. A cheapie laser pointer will show a 1/8" dot at 30 feet and a 1/4" smudge at 60 feet.
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Re:Question about lasers (Score:5, Insightful)
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Looks to me like he got it right and you got it wrong.
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So, the farther away you go, the bigger the "dot" the beam casts is. The inverse square law applies. If it didn't, overall power would have been added as the beam travels (the dot would be bigger, but the same brightness). This is a law of physics.
I'd imagine you'd kinda have to aim carefully, but by the time it could 1.5 billion miles the beam would be, at least, hundreds of miles across. Which means you better have a
Re:Question about lasers (Score:5, Informative)
Re:Question about lasers (Score:5, Informative)
See the article you link to, which states that perfect collimation can never be achieved in reality. Thus, like any other source, laser light follows the inverse square law in the far field.
Note that in general, I believe the inverse square law only applies to a point source, or a source which is effectively a point source at the distances involved. For dealing with cases where the source can't be approximated as a point (either because it's really large, or the radiation intensity is being measured very close to the source), RF engineers use the term "near field gain reduction" for the behavior of RF field intensities in close proximity to an antenna, which probably has an equivalent term for optics. As a result, for an optical source with a large aperture in relatively close physical proximity to the aperture, the inverse square law will appear not to apply, but once the "near field" for that source is exited, the inverse square law holds.
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The inverse square law is applicable only for point sources that are radiating in every direction. The inverse square of distance d arises in the formula that you are interested in the surface of a ball centered at the source with radius d. The surface area is proportional to the square of distance so intensity in some part of the surface relates to the inverse.
Now lasers are not omnidirectional so the inverse square law is not applicable.
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So over sufficiantly short distances the intensity is roughly constant but over sufficiantly long distances it roughly obeys inverse square.
am I misremembering?
Friis Transmission Formula (Score:3, Interesting)
Laser moon and back feet, more like *miles* (Score:5, Interesting)
However, the beam size from a collimated laser is a couple miles across at the moon. Typically, receiving a signal back takes a large telescope which counts single-digit photon returns from a Nd:YAG q-switched laser. It's been almost 2 decades since I worked with the stuff (you might search for Satellite Laser Ranging, Goddard Optical Research Facility and MOBLAS or TLRS) and the units that ranged on the moon cubes were at Mt. Haleakala in Hawaii.
It was neat stuff, but I remember one of the PIs saying the spot on the moon was the size of Georgetown (a section of Washington DC), though I can't remember exactly now. The outgoing laser was about 4" in diameter.
Canary Islands? (Score:4, Funny)
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It's good to know that the writers involved in the WGA strike are coming to Slashdot to expand on their art form.
Aiming will be a major problem (Score:2, Redundant)
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"far more rapidly" (Score:5, Funny)
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Referring to Bandwidth? (Score:2)
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unfortunately (Score:5, Funny)
Not exclusive concepts (Score:2, Insightful)
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Well, Motorola developed something that sounded like this, but from what I understand, they often have to be packaged in an enclosure that's some gaudy shade of pink, occasionally emit short, audible clips of annoying boy-band songs, and they're only useful for conveying gossip between young teenage girls.
(sorry, couldn't resist.)
Speed (Score:2)
And the distance mentioned (1.5 million kilometres) doesn't seem very useful. thats too far for the moon, but not far enough for Mars - theres nothing out there to talk to.
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Very likely, if something like this were incorporated into the Webb design, it would be augmented with traditional radio for tracking, telemetry, and as a backup to the laser link for bulk data tr
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That's what they want you to think.
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It's just EM spectrum that we have receptors for (our eyes).
And it is now known that birds can see magnetic fields [nature.com]... and in red at that.
lagrangian points (Score:2)
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Radio: "Dear Grandma"
Laser: "Dear Grandma, please send another box of cookies"
The end of the message arrives sooner, so it is indeed faster, even though the signals travel at the same speed.
-mcgrew [kuro5hin.org] (yes, I did have a 300 baud modem. I used it on
It's pretty damn cold up there (Score:2, Interesting)
Huge distances through the universe? (Score:2, Informative)
1.5 million kilometers = 1.6 x 10^-7 light year.
Distance to galactic center = 26,000 light years
Distance to nearest (Andromeda) galaxy = 2.5 million light years
"Faster than radio" probably refers to increased bandwidth, because light-speed is light-speed.
puny lights (Score:2)
Line of sight and percise issues? (Score:2)
Great! (Score:2)
I hereby welcome you, Oerlikonians. But could anybody tell me where this Oerlikon space is and how Oerlikonians look like?
But seriously:
Now we only need to get something or someone that far away that it actually makes sense to drop radio waves for laser beams.
Faster? (Score:2)
But faster? Don't radio waves and laser beams both hit the same speed limit (the speed of light)? Radio waves are photons too.
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Coming soon... (Score:2, Funny)
Some popular messages include:
- "If you are reading this message, you are probably toast"
- "PWNED!!!"
- "(Scorpio) Avoid reading under strong light"
- "Knock, knock"
- "Is this the James Bond? Oh sorry, my mistake."
- "Can you hear me now?"
- "Special Delivery!"
- "Ceiling Cat sez hi!"
why didn't they use the lunar retro-reflector? (Score:2, Informative)
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a better test would have (Score:3, Interesting)
InterSatellite Communications (Score:3, Informative)
I remember this being done with Earth Observation satellites. The EO satellite beams data using an optical link to a satellite that is in geostationary orbit. This satellite then beams the information down through a microwave link. This frees the EO satellite (that producue huge amounts of data) of the need of high-power consuming RF transceivers, reduces the need for ground stations, and is seriously cool. This was done in 2001 between SPOT 4 and Artemis (Press release [esa.int]). Note that SPOT sits in an orbit around 800km, and Artemis is geostationary... They then did the same with an aircraft (see here [esa.int]).
So it is really quite useful. When you consider the amount of data the sensors on board ENVISAT (or even MODIS) produce, this is an important tool.
SETI (Score:2)
Its also something to think about with respect to SETI. I mean the universe could be swarming with life forms communcating over great distances, and it would make more sense than not that they use tight beams to do this. In which case SETI won't ever pick anything up because nearly all the energy from their comms is only going each
If we start shining huge lasers into space (Score:5, Funny)
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WTF, it was done in 1948 (Score:2)
Some guys in the US Army Signal Corps aimed their very primitive SCR-348 radar sets at the Moon, and wadda you know, an echo came back. All done with what looks like from now as very primitive vacuum tubes, diode detectors, and magnetrons.
A laser is just a Very high frequency radio transmitter. The latecomers just upped the frequency by a large factor.
Probably already in use. (Score:4, Interesting)
That's good... (Score:2)
Who would have thought..... (Score:3, Insightful)
Who would have though the Canary Islands are that big?
-Charlie
Re:Targeting that is going to be a bitch. (Score:5, Funny)
If an object 1.5 million kilometres away has a neighbouring quasar, you have bigger worries than communication.
Re:Targeting that is going to be a bitch. (Score:5, Interesting)
Instead, I imagine the initial linkup might be the limiting step. The system might require an initially higher-power signal (that is broad so that targeting tolerances are lower) to initialize the link, then active feedback could allow the two ends to narrow the beams for lower-energy high-speed data transfer. Maybe the initial phase will use conventional radio signals (or radar) to establish the locations (and relative movement) of the two endpoints of the link. With that information, the two ends can then aim the laser fairly accurately.
Ozone Layer (Score:2)
The ozone layer of the upper atmosphere really only filters out wavelengths of light that are less than 320nm or so (ultraviolet and higher spectrum). Most LASERS typically operate using wavelengths in the visible spectrum of light or infrared range.
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A) Just because they or us goes to all'p2p communications, doesn't mean we stop listening for radio waves. In fact that would make looking for radio waves marginally simpler.
B) Which 500 hundred year? How far way is this race?
C) If we figure out a way to see laser beans/whatever, we will probably look for those as well.
D) You go to start sometime.
E) maybe they are sending out radio waves intentionally. If you want to communica