Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!

 


Forgot your password?
Close
typodupeerror
×
Space Wireless Networking Hardware

Is a Laser Data Link 1.5 Million Kilometers Feasible? 304

Posted by CmdrTaco from the keep-on-truckin dept.
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."
This discussion has been archived. No new comments can be posted.

Is a Laser Data Link 1.5 Million Kilometers Feasible? More

Is a Laser Data Link 1.5 Million Kilometers Feasible?

Comments Filter:

  • Never saw this coming (Score:5, Interesting)

    by LiquidCoooled ( 634315 ) on Wednesday November 07, 2007 @12:27PM (#21268235) Homepage Journal
    Who would have thought that light could travel such a long distance?

    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.

    • Re: (Score:3, Informative)

      by LiquidCoooled ( 634315 )
      Correction:

      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: (Score:3, Insightful)

      by WormholeFiend ( 674934 )
      I'm assuming that in space, the problem will not be weather conditions, but "aim"

      • Re:Never saw this coming (Score:5, Funny)

        by erroneus ( 253617 ) on Wednesday November 07, 2007 @12:34PM (#21268331) Homepage
        I'm not sure the space-technology people will be using "aim." If anything, I'd suspect they'd lean to something OSS like "Pidgin."

      • Re: (Score:3, Interesting)

        by FuzzyDaddy ( 584528 )
        Aim is an identical issue with both radio and lasers.

        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

    • Re: (Score:3, Insightful)

      by phil reed ( 626 )

      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.
      Yeah, but what's the data rate?

    • Re:Never saw this coming (Score:5, Funny)

      by ricosalomar ( 630386 ) on Wednesday November 07, 2007 @12:49PM (#21268595)
      ...proven with radio, that would seem good enough for me.

      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.

      • we have the Gas engine... it works.. lets forget about all this crazy hybird and electric car talk...

        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)

      by vertinox ( 846076 ) on Wednesday November 07, 2007 @12:53PM (#21268661)
      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?

      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.
      • NASA already does this with the DSN (Deep Space Network, Google/Wikipedia it), although they use the DSN to ensure they can always communication with objects in space no matter what the orientation the Earth is at that moment.

        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)

      by camperdave ( 969942 ) on Wednesday November 07, 2007 @01:02PM (#21268805) Journal
      whats going to happen when they do put 'scopes at the lagrange points?

      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)

        by einhverfr ( 238914 ) <chris...travers@@@gmail...com> on Wednesday November 07, 2007 @01:52PM (#21269651) Homepage Journal
        The basic problem is that the LaGrange points 4-5 are stable, but require a fair bit of energy to get to in part because you have to slow down a lot more (no nice large gravity well to assume an orbit around).

        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.
    • There's also the little matter of, well, matter. Dust clouds, intervening meteors, etc, that would degrade the quality of the signal. The problem with radio isn't that it's not reliable, it's that it's bandwidth is lower and it can't be aimed as precisely. With the proper optical equipment, we could shoot a laser from Alpha Centauri that hit the earth and nothing but the earth. Doing the same with a radio wave would be difficult at best.

      However, as you said, radio's doing just fine for us right now. I i
    • Just be careful to keep the aim right, you don't want to end up blowing up your power station and taking out a few blocks of your city...

    • Re:Never saw this coming (Score:4, Funny)

      by Ron Harwood ( 136613 ) <harwoodr@NOSPAm.linux.ca> on Wednesday November 07, 2007 @01:12PM (#21268989) Homepage Journal
      Either way, your ping times are gonna suck. ;)

    • Re: (Score:3, Insightful)

      by slashdotmsiriv ( 922939 )
      "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"

      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)

    by Greg01851 ( 720452 )
    "laser links like this one will be able to transmit data across huge distances through the universe" I think they mean "through the solar system"... laser wouldn't be very efficient "through the universe"... I think we may have other means of communication by the time we need to think about distances that vast.

  • One important warning (Score:5, Funny)

    by Anonymous Coward on Wednesday November 07, 2007 @12:32PM (#21268299)
    Do not look into laser with remaining eye.

  • Interesting to use this with radio telescopes (Score:4, Insightful)

    by DamonHD ( 794830 ) <d@hd.org> on Wednesday November 07, 2007 @12:33PM (#21268313) Homepage
    Hi,

    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)

    by SailorSpork ( 1080153 ) on Wednesday November 07, 2007 @12:34PM (#21268327) Homepage
    Canary Islands and experiments with laser beams? Ahah! There must be sharks there!
  • Do lasers follow the inverse square law? I'm guessing it doesn't since it's focused.

    Either way, correct alignment seems pretty tough.

    • Re: (Score:3, Informative)

      by rcw-home ( 122017 )

      Do lasers follow the inverse square law? I'm guessing it doesn't since it's focused.

      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.

      • Re: (Score:2, Informative)

        by Anonymous Coward
        I've seen some comments to this post saying that a laser beam dosen't obey the inverse square law and some saying that it does. Actually, everyone is right in a sense. Over "short" distances, laser beams expand at a rate that is slower than inverse square. Over "large" distances, the rate of expansion increases, eventually approaching the inverse square law. The distance that distinguishes "small" from "large" is called the Rayleigh range and it depends on two properties of the beam: the wavelength of th

      • Re: (Score:2)

        by raddan ( 519638 )
        I seem to recall something my father said once about the difficulty of trying to bounce a laser beam off a mirror on the moon (my father built laser-guidance systems), and that was that attenuating a laser beam enough to do that test is extraordinarily difficult. The state of the art may have indeed improved since the 1980's (when he was doing this kind of work), so I'd like to see how they think they have solved that problem.

    • Re: (Score:2, Interesting)

      by kevmatic ( 1133523 )
      Lasers diffuse over a distance, just like normal light bulbs, albeit a much smaller rate.
      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)

      by pedestrian crossing ( 802349 ) on Wednesday November 07, 2007 @12:55PM (#21268687) Homepage Journal

      Do lasers follow the inverse square law?
      No.

      I'm guessing it doesn't since it's focused.
      Close. It is because it is collimated. [wikipedia.org].

      • Re:Question about lasers (Score:5, Informative)

        by Andy Dodd ( 701 ) <atd7NO@SPAMcornell.edu> on Wednesday November 07, 2007 @01:49PM (#21269589) Homepage
        Wrong, they do follow the inverse square law.

        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.

    • Re: (Score:2, Informative)

      by hansraj ( 458504 )
      I could be wrong so someone knowing better please correct me.

      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.
      • My understanding is that with a laser the intensity at a given distance is proportional to 1/((d+c)^2) where d is the distance from the laser and c is a constant dependent on the particular laser. That is the light behaves as if it radiated from a point some distance behind the laser

        So over sufficiantly short distances the intensity is roughly constant but over sufficiantly long distances it roughly obeys inverse square.

        am I misremembering?
      • Inverse square law applies for isotropic (all directions) as well as directional sources (focused beam). The way the difference is handled is by introducing an antenna gain term, where the gain at a given point in space is defined to be the ratio of the power density due to the directional source to the power density of an isotropic source. In communications applications, you use Friis' Transmission Formula to compute received signal-to-noise ratio which includes a factor Pt*Gt/(4*pi*R^2), which is the po

  • Canary Islands? (Score:4, Funny)

    by j-stroy ( 640921 ) on Wednesday November 07, 2007 @12:35PM (#21268367)
    Are there sharks there or something?
    • "Are there sharks there or something?"

      It's good to know that the writers involved in the WGA strike are coming to Slashdot to expand on their art form.
  • One of the biggest problems we'll run into with this is aiming the beam between the sender/reciever. 1.5Mil Kilometers is already enough of a distance, but we also have to keep in mind the fact that both ends will likely be in constant motion.

    • Re: (Score:3, Informative)

      by onion2k ( 203094 )
      When the Apollo mission landed on the Moon they left behind a retroreflector that NASA used (still use?) to bounce a laser back and forth to measure the distance from the Earth very accurately. That's 385,000 km. If they were doing that in the late 1960s I don't see any reason why 1.5m km should be that tricky today.
    • If you think about this like a lever. A change in yaw of 1mm on the sender side could shift the end point many kilometers.

  • "far more rapidly" (Score:5, Funny)

    by InvisblePinkUnicorn ( 1126837 ) on Wednesday November 07, 2007 @12:38PM (#21268407)
    Because lasers travel at least 42 times as fast as radio waves!

    • Re: (Score:3, Insightful)

      by Abcd1234 ( 188840 )
      Well, while I thought the same thing you did at first, I suspect they mean that the actual data rate will be higher due to lower noise on the channel and/or other factors.

    • Re: (Score:2)

      by Kjella ( 173770 )
      Yeah, I was also thinking WTF at that summary. Radio waves and laser light are both electromagnetic waves and travel at the same speed, so this will do nothing for say the responsiveness of say controlling a drone on Mars. It may improve bandwidth so we can transfer more data, but I'd say we're doing pretty good in that department already, I'm not sure what a HDTV feed from Mars would give us.

      • Re: (Score:2)

        by j0nb0y ( 107699 )
        Oh c'mon. You don't want to watch the Mars Bowl in low def, do you? With technological advances like these, soon we'll be able to watch all intergalactic sporting events in Hi Def!
      • You say that now, but in thirty years you'll be watching every episode of Law and Order: Martian Victims Unit along with the rest of us.
    • I was curious about the same comment, but they must just be referring to the higher bandwidth available at optical frequencies compared to radio frequencies. In other words, the latency would be the same, but once the first bit hits, you will get the next million bits "more rapidly" and the next trillion bits "far more rapidly."

    • Re: (Score:3, Funny)

      by huckamania ( 533052 )
      I'm guessing that the laser packs the 1s and 0s better then the radio waves. Or maybe they leave out the 0s.
    • in space!

    • Re: (Score:2)

      by dylan_- ( 1661 )
      Yes, that's how the data is sent more rapidly. It's a little known fact that the UHF waves from 802.11g wireless points travel about 5 times the speed of those from 802.11b points.
    • We'll just get the European Parliment to increase the speed of light. It's such a silly limit, anyway.

  • unfortunately (Score:5, Funny)

    by LM741N ( 258038 ) on Wednesday November 07, 2007 @12:39PM (#21268431)
    They will all stop at the last mile, rendering the project useless.
  • Can't you also make a laser out of radio waves? I know they have microwave "lasers" called masers, so do "rasers" exist?
    • Yeah. Verizon makes em.

    • Re: (Score:2, Funny)

      by Radon360 ( 951529 )

      so do "rasers" exist

      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.)

  • Laser beam has more bandwidgth than radio, but it still travels at the same speed (c).

    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.

    • Re: (Score:2)

      by necro81 ( 917438 )
      The last paragraph of the press release [oerlikon.com] explains. The distance chosen was about the distance to the L1 and L2 Lagrangian Points [wikipedia.org] around the Earth. These are candidate locations for the next generation James Webb Space Telescope [nasa.gov] (also at wikipedia [wikipedia.org]). For that application, high data bandwidth is extremely useful.

      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
    • theres nothing out there to talk to.

      That's what they want you to think.
    • Light IS radio.

      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.
    • In the article, they say that the distance was chosen because it is the distance between the earth and either of the L1 or L2 lagrangian points [wikipedia.org]. SOHO [esa.int] currently sits at L1 and talks to earth with a 200 kbit/s radio, so this isn't exactly a hypothetical scenario. (An interesting question in that case, though, might be whether we can reliably receive a laser signal against the sun's background radiation.)

    • Re: (Score:2)

      by sm62704 ( 957197 )
      The signal travels the same rate, but if the bandwidth is 5 times as great it will send the same amount of data five times as fast. Think about an old 300 baud modem vs an old 55k modem; the signal travels at the same speed, but the web page loads faster on the 55k.

      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)

    by Anonymous Coward
    What the article doesn't mention is the poor crew that were huddled behind the massive metal crate up by the NOT (Nordic Optical Telescope) on these tiny little white plastic chairs (which had to be weighted down by rocks when they got up). I was up there at the WHT/NOT the other week and happened to pass by their setup, the only potential hint at what they were doing being one of those little yellow hazard signs that simply said 'Laser' on it. Glad they got what they wanted - the weather was pretty terribl
  • For a sense of scale:

    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.

  • Would there not be major line of sight issues and percision issues. My crude understanding of radio waves is that you can send a signal across a wide area and it seems to me a laser would have to be more exact to get the data because of the shorter wave length. I see a shorter wave length as a disadvantage; especially over longer distances.

  • 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.

  • Farther... sure, because it's a focused beam.

    But faster? Don't radio waves and laser beams both hit the same speed limit (the speed of light)? Radio waves are photons too.

    • Re: (Score:2, Informative)

      by frith01 ( 1118539 )
      Faster Baud rate, not faster event rate. higher frequency signals can carry more information.
  • The ability to encrypt nefarious messages in a death-ray across long distances.

    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!"
  • It seems strange that they didn't aim for the retro-reflector placed by one of the Apollo missions which has been used for 30+ years for laser ranging experiments. It's location is well known. That would give them a real 800,000 km beam path, roughly half of what they claimed.

    • Re: (Score:2)

      by cnettel ( 836611 )
      It would also give the complete atmosphere, twice, along the way. I could see how data modulation schemes and optics that would handle 1.5E6 m in space could still have problems with that.
    • Funny, I didnt RTFA, but presumed that they did just that and showed a 3-6dB link margin. Oh well, so much for real science.

  • a better test would have (Score:3, Interesting)

    by advocate_one ( 662832 ) on Wednesday November 07, 2007 @01:08PM (#21268915)
    bounced the signal off the reflector that Neil Armstrong left at the Apollo 11 landing site. Round trip could have come pretty close to 768,800 kilometers... bouncing it back up and down again would have made the link as near as damn it = 1,500,000 kilometers

  • InterSatellite Communications (Score:3, Informative)

    by d-Orb ( 551682 ) on Wednesday November 07, 2007 @01:08PM (#21268919) Homepage

    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.

  • This is just more proof of what we already know: that the tighter the beam the more efficient it becomes for point-to-point comms in terms of energy usage and overall loss/noise.

    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, we're going to end up accidentally blinding aliens. Which might be good (if they're chest-explody types), or bad (if they're hot sex-starved space-babes). Your call.

    • Re: (Score:2)

      by bflong ( 107195 )
      if they're hot sex-starved space-babes ...Then maybe some of this crowd could get laid if our aim is right.

  • Fellas and Gals, it was done first in 1948, at zero net cost.

    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)

    by LWATCDR ( 28044 ) on Wednesday November 07, 2007 @01:22PM (#21269141) Homepage Journal
    The US has a several classes of Signal intelligence and Communication intelligence satellites. I would be shocked if they didn't already use an optical link to send their data to relay satellite for downloading to a ground station. An optical data link would make the satellite "silent" so their data link wouldn't interfere with there intercept receivers. Since both the satellites are in space you wouldn't need to worry about weather an since they are both in geostationary orbit you wouldn't need to worry about aiming. Of course the other benefit is that you could beam the data right from your recon satellite parked over Asia to a relay satellite parked over the US and then right down to a ground station in Virgina. No need to have a ground station in a friendly or not so friendly country.
  • ...because I have so many files I need to trade with the aliens.

  • Who would have thought..... (Score:3, Insightful)

    by Groo Wanderer ( 180806 ) <{charlie} {at} {semiaccurate.com}> on Wednesday November 07, 2007 @01:51PM (#21269625) Homepage
    "Who would have thought that light could travel such a long distance?"

    Who would have though the Canary Islands are that big?

              -Charlie

Slashdot Top Deals

"What man has done, man can aspire to do." -- Jerry Pournelle, about space flight

Close