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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."
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.
liqbase
Do not look into laser with remaining eye.
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
http://m.earth.org.uk/
Canary Islands and experiments with laser beams? Ahah! There must be sharks there!
Are there sharks there or something?
Because lasers travel at least 42 times as fast as radio waves!
They will all stop at the last mile, rendering the project useless.
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.
If an object 1.5 million kilometres away has a neighbouring quasar, you have bigger worries than communication.
Real Daleks don't climb stairs - they level the building.
A house divided against itself cannot stand.
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.
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).
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?
When our name is on the back of your car, we're behind you all the way!
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.
Is it just my observation, or are there way too many stupid people in the world?
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.
Get your own free personal location tracker
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.
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.
See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.
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.
retrorocket.o not found, launch anyway?
Exactly! Like putting too much air in a balloon!