Is a Laser Data Link 1.5 Million Kilometers Feasible?

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

[LiquidCoooled (634315)]

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:

[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:Never saw this coming

[Kinthelt (96845)]

It's okay. Even NASA confuses SI with Imperial measurements.

Re:

[WormholeFiend (674934)]

I'm assuming that in space, the problem will not be weather conditions, but "aim"

Re:Never saw this coming

[erroneus (253617)]

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:

[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:

[Gospodin (547743)]

They'll just have to up the power on those lasers. A lot.

Re:Never saw this coming

[wwphx (225607)]

The laser that my wife blasts the moon with [wikipedia.org] on a regular basis starts at 3.5 meters here [wikipedia.org] and I've heard is over 2km when it hits the moon. I have no idea how big it is when it finally bounces back.

Re:

[wwphx (225607)]

My wife says: "One in 30 million outbound photons strike the retroreflector, after they're reflected, one in 30 million of those photons make it back to the telescope and are detected. So about one in a quadrillion of the photons sent out are returned. And that is a record-breaking rate, no other retroreflector laser experiment has come close."

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.

Re:

[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:

[powerlord (28156)]

and what sort of receiver setup is needed?

Re:

[awehttam (779031)]

http://voyager.jpl.nasa.gov/spacecraft/index.html [nasa.gov]:

"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)."

Re:

[19thNervousBreakdown (768619)]

Why? And, basically the same question, less than 70kb per what?

Re:Never saw this coming

[ricosalomar (630386)]

...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.

Re:Never saw this coming

[vertinox (846076)]

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.

Lagrange points

[camperdave (969942)]

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

[einhverfr (238914)]

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.

Re:Never saw this coming

[Ron Harwood (136613)]

Either way, your ping times are gonna suck. ;)

Re:

[kd5ujz (640580)]

Your "ping" time is a measure of latency, in milliseconds.

Re:Never saw this coming

[ArsonSmith (13997)]

Not to mention the round trip time it's going to take for data to get back and forth over this link.

Re:

[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?

[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.

Re:A bit exaggerated?

[j00r0m4nc3r (959816)]

I dunno, I think if they modulated the laser to the harmonic frequency of dilithium they could route the message through a subspace channel on a tachyon carrier wave. This is pretty elementary stuff.

Re:

[by Anonymous Coward]

Exactly! Like putting too much air in a balloon!

One important warning

[by Anonymous Coward]

Do not look into laser with remaining eye.

Interesting to use this with radio telescopes

[DamonHD (794830)]

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!

[SailorSpork (1080153)]

Canary Islands and experiments with laser beams? Ahah! There must be sharks there!

Question about lasers

[schnikies79 (788746)]

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:

[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:Question about lasers

[by Anonymous Coward]

It doesn't sound like you know much about mathematics. Please check the relation between the diameter of the laser spot and the power/area ratio, then rethink what the inverse square law actually says.

Re:Question about lasers

[pedestrian crossing (802349)]

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

[Andy Dodd (701)]

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.

Laser moon and back feet, more like *miles*

[Overzeetop (214511)]

Correct, they did put corner cubes on the moon (aka retroreflectors, or three mirrored surfaces all at 90 degree angles to one another).

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.

Friis Transmission Formula

[dunc78 (583090)]

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?

[j-stroy (640921)]

Are there sharks there or something?

Aiming will be a major problem

[Constantine XVI (880691)]

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:

[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.

"far more rapidly"

[InvisblePinkUnicorn (1126837)]

Because lasers travel at least 42 times as fast as radio waves!

Re:

[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.

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[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.

unfortunately

[LM741N (258038)]

They will all stop at the last mile, rendering the project useless.

Not exclusive concepts

[mdmkolbe (944892)]

Can't you also make a laser out of radio waves? I know they have microwave "lasers" called masers, so do "rasers" exist?

Speed

[rossdee (243626)]

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.

a better test would have

[advocate_one (662832)]

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

[d-Orb (551682)]

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.

If we start shining huge lasers into space

[caluml (551744)]

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.

Probably already in use.

[LWATCDR (28044)]

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.

Who would have thought.....

[Groo Wanderer (180806)]

"Who would have thought that light could travel such a long distance?"

Who would have though the Canary Islands are that big?

          -Charlie

Re:Targeting that is going to be a bitch.

[meringuoid (568297)]

now try to do the math on all of the floating bodies and the effect of the gravity from neighboring quasars and other space phenomena.

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.

[kebes (861706)]

Great idea, now try to do the math on all of the floating bodies and the effect of the gravity from neighboring quasars and other space phenomena.

For the mentioned application (communicating inside the solar system to the Lagrange points, for instance), gravitational effects will not be a big deal. The light deflection that the Earth or the moon will cause are negligible. The real challenge in targeting, I would imagine, will be accounting for relative motion between the two ends of the link.

Maybe a single shot of data, but maintaining that connection would be very difficult IMHO.

I expect just the opposite to be true. Once a link has been established, I imagine maintaining it wouldn't be that hard. Why? Probably the optics on both ends will measure the positioning of the incoming laser on their detector. They can then send information to each other about alignment (e.g. "you're drifting to the left...") so that they can actively compensate (the time lag [google.com] between them will be ~5 seconds, or ~10 seconds roundtrip).

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.

I could see it working but the receiver would have to be huge. It's hard enough to hit someone with a gun at a mile using a laser sight (windage which would be comparable to space effect on the laser light).

Luckily there is no wind in space, and the motion of objects is measurable and fairly predictable. Obviously over those distances any amount of error or jitter translates to a huge positioning error, but laser-steering systems can also be made quite accurate (not to mention that a laser doesn't have to be perfectly collimated, you can easily tune the aperture so that the beam is 500 m wide at the target... as long as the laser is strong enough, the receiver will still easily be able to measure the signal).