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Shining a Light on Interplanetary Communication
An anonymous reader writes "Researchers at the MIT have developed a new device that they claim could one day boost interplanetary communication to broadband speeds. From the article: 'The new light detector improves detection efficiency to 57 percent at a wavelength of 1,550 nanometers--the same wavelength used by optical fibers on Earth to carry broadband signals to homes and offices. Currently, light detectors only absorb about 20 percent of the light they receive. "It can take hours with the existing wireless radio frequency technology to get useful scientific information back from Mars to Earth," said study team member Karl Berggren from the Massachusetts Institute of Technology. "But an optical link can do that thousands of times faster."'"
You won't want to be getting into any Shotgun duels while playing Duke Nuke'em Forever on some Earthly server when you're orbiting Mars. Fine. But for uploading instructions and downloading science the speedboost is pretty freaking handy.
If optical interplanetary communication is not only possible, but actually more efficient than radio wave communication, what does that mean for the SETI project which analyses radio waves? Shouldn't we expect extraterrestrical civilisations to switch to optical as soon as possible? Did we perhaps look at the wrong frequency all the time?
The Tao of math: The numbers you can count are not the real numbers.
Now all they have to do is develop the technology to create fiber-optic cable millions of miles long!
This space available.
No, due to redshift. We could look pretty much at any wavelength, and have a chance of getting something.
we don't even have broadband coverage in like 60% of the united states, and we are seriously talking about broadband access for martians.. c'mon..
Any fool can criticise, condemn, and complain, and most fools do. - Benjamin Franklin
Ok, so they boosted the sensitivity of their detectors. That is good thing, for sure. I would, however, be interested what this technology does to the signal to noise ratio of the transmission. Large bandwidth won't be of much use if you have to repeat every packet one hundred times, because most of it is lost in the noise.
This comment does not exist.
A ridiculous article. Even if they boosted the efficiency by a factor of three, without hurting any other specs, you could accomplish the same thing, or better, just by increasing the diameter of the light-collecting lens. To get three times the light in you just need to increase the diameter by the square root of three-- 1.63 something IIRC. Not a big deal. And lenses and mirrors can be increased in size almost indefinitely, while you can only increase the efficiency of the detector another 30-some percent, and it gets harder and harder to get every extra percentage.
"A Fire on the Deep", by Verner Vinge.
Except that it looked an awful lot like Galactic Usenet, complete with inter-species flame wars.
The living have better things to do than to continue hating the dead.
Most interplanetary vehicles are absolutely tiny. They are also lightweight. Increasing the diameter of the receiver and adding mirrors and lenses would drastically increase the mass of the craft, let alone the size. Doing that when a solution like this is available would be an almost criminal waste of space/weight on the spacecraft.
With a nice broadband speed from Mars to Earth, I can picture more Rovers on Mars doing tasks in prep for humans landing. Just imagine a nice 3d virtual world of Mars with the construction worker on earth. Robots building everything controled from Earth and then waiting for humans to land. Once the humans bounce to landing the robots could go gather them from wherever they bounce to and connect them up to the structure they built. Once on the planet, humans there could take over control of the robots until everything checks out for them to go outside....
Right now people have to sit and think about what they are doing because of the delay. If they don't get it right the first time they have to wait hours to find out.
Basically this sounds like realtime exploring...something we needed.
"Only one thing, is impossible for god: to find any sense in any copyright law on the planet." Mark Twain
Considering that we are talking about communication between 2 satellites orbiting 2 differents planets.
The line of sight will be blocked much more often than that by Earth and Mars. there are no stable orbits that would allow permanent line of sight between 2 spacecrafts.
A system to have almost permanent conection would need 2 or 3 geostationary s/c around each body and 1 at the Earth or Mars lagrange point 4 or 5.
For those who praised the superiority of optical communications : The signal would then need to be radioed to the ground unless you live in the Space Station.
Assuming we had the technology to generate gravity wave beams, It should be possible to create a tiny tunnel through space between earth and mars where the effective distance is far less than the 40 to 160 millon mile distance stated earlier, due to the effects of gravity bending space to reduce the effective distance. Radio waves could pass through this tunnel with reduced latency. It may even be possible to modulate the gravity waves themselves with broadband data
The bigger question is does this "Roswell Technology" all ready exist and is being held captive by our governments in the name of national security?
...between Earth and Mars, but it still takes Windows thirty seconds to refresh a directory listing on my hard drive.
I'm surprised that nobody picked up on this article in Wired on Delay Tolerant networks.
Basically people are considering how to design protocols such that they will survive communications over networks with very large delays, for example between here and Mars. TCP/IP won't cut it as it depends on interacting in real time.
Both light and radio waves will get from here to Mars in the same time, and it is only the sensitivity and selectivity of the receivers that will differentiate them. From reading this article I would say that the choice of transmission protocol used is more important in the overall comms.
I am Slashdot. Are you Slashdot as well?
if we spin it around the beam will be going many order of magnitude faster than light when it reaches mars. That way the long latency is irrelevent. Also, it looks cool. Sorta like a fire engine.
I'm gonna go to the sandbox and play with my Tonka Firetruck now.
I would think that pointing (or aiming for lay-folk) would be the limiting factor in laser communication. It is a fairly difficult task to point a spacecraft accurately and to have the pointing accurate enough for millions of miles would be very difficult. The nice thing about radio waves is they don't require super accurate pointing, even for a high gain antenna. I would imagine that the whole benefit of better bandwidth is achieved by drastically increasing the gain on axis. IANARS (rocket scientist) and IANASCRFE (spacecraft RF engineer), but I work with a bunch or each.
The device in the article is a photon counting device. That means that each individual photon causes an event that can be measured. (Actually, the 57% efficiency means that 57% of the photons cause as event, the other 43% are missed for one reason or another). There are other types of photon counting devices such as avalanche photodiodes, proportional counters (for xrays), and maybe photomultiplier tubes under the right conditions. The problem with avalanche photodiodes is that they take some time to reset after an event, which limits their speed for communications. This is being improved, but this new type of device may offer an intrinsically faster reset time, as well as high efficiency.
How this new device works is that a thin (9 nm?) superconductor wire (100 nm wide) is patterned into a serpentine path. A current, just below the critical current is driven though the superconduncting wire. (The critical current is the current at which the superconductor is no longer superconducting). Any photon that is aborbed by the wire causes local heating, and the wire can no longer be a superconductor with the amount of current going through it. This causes a sudden increase in resistance which can be measured.
"um, no"
No what? That the spinning laser light won't be going faster than light when it reaches Mars? Of course it will! Duh. If you spin light around the farther out it goes the faster it goes until infinity. Then it starts going slower. That's relativity. Einstein said so.
"um, no"
I hear you. You're just not thinking nonlinearly. Stop walking straight and following the cracks in the sidewalk. Jump over them! That's thinking nonlinearly.
"um, no"
Look. What is Gravity? It's just the dents in the felt of a pool table caused by a ball. Sort of like a reverse nipple. Therefore, antigravity is the nipple!
Physics is a snap, dude. You just gotta think.
Well, we now know one way to block a light-link: Put a spaceship in the path of the link.
I can't wait until they use quantum tunneling.
--
# Canmephians for a better Linux Kernel
$Stalag99{"URL"}="http://stalag99.net";
Actually, we've had the answer for about 30 years....just keep broadcasting:
"Calling Occupants, of Interplanetary Craft......we are your friends...."
Light travels faster than sound. This is why some people appear bright until you hear them speak.........
Here is how so-called photon "teleportation" works. This should explain why nothing happens faster than light, and why otherwise this isn't causality-destroying voodoo.
You have a source that spits out pairs of polarization-entangled photons. Each particular photon is random -- it'll either be "horizontal" or "vertical" with 50% probability each. But, entanglement means that when one member of each pair is vertical, the opposite member of that pair is horizontal, and vice-versa.
Because of the way QM works, we can't know the polarization of any particular photon pair in advance -- we only know when we pass the photon through a filter and then try to detect it. Both the filter and the detector change the photon, though, so any photon that we measure becomes completely worthless to us thereafter.
So, we know that our photon pairs always have opposite polarization, but we don't know the exact state for each pair in advance. Now, let's cheat a bit and peek behind the veil, pretending we know the state of each photon in a sample stream. I'll use a 0 to encode one polarization state and 1 to encode its opposite:
Stream 1: 0010110101
Stream 2: 1101001010
Now, right off the bat, suppose we read Stream 1 here and send Stream 2 to Mars. By looking at the values we read locally, and flipping each bit, we know what data Mars will receive. But, there's no way we can inform Mars of the contents of the bitstream ahead of time, because nothing travels faster than light.
So, what's all this quantum teleportation stuff about? Well, it's like this. Our Stream 1 and Stream 2 above are random, so they're useless to us for transmitting anything but white noise. But, we can do a cool trick and transmit information in that white noise. We can't exceed lightspeed with it, but we can guarantee that the information can't be undetectably intercepted.
Let's add in Stream 3, which contains data we want to transmit. I pick an arbitrary message -- suppose I want to send alternating bits, like so:
Stream 3: 101010101010
Now, I want to send Stream 3 to Mars, but I want it encrypted in the randomness of Streams 1 and 2. To do this, I read in Stream 1 and perform an operation on each result based on the contents of the corresponding bit in Stream 3: whenever a bit in Stream 3 is a 1, then I flip the result that I read in from Stream 1. Otherwise, I keep the Stream 1 bit unmodified:
Stream 1: 0010110101
Stream 3: 1010101010
Stream 4: 1000011111
So, Stream 4 now contains the data I want to send, mixed with the randomness in one of the two entangled streams. By itself, Stream 4 is meaningless. Also, Stream 1 has been destroyed by reading it. So, I can only decrypt Stream 4 using the data I have from reading Stream 1 -- or by using Stream 2.
Now, I send Stream 2 to Mars unmodified. Anyone reading that stream destroys it and gets random data out of it. Using a separate beam, I send Stream 4 to Mars. Anyone can intercept this and get the data out of it, but it's useless without Stream 2. At the receiving station, they can combine Stream 2 and Stream 4 using a variation on the rule used to encrypt the data, to learn the contents of Stream 3, and they can be guaranteed that the data wasn't intercepted without them knowing about it:
If someone intercepts Stream 2, reads it, and substitutes in another random photon stream, then the decryption on Mars will fail, and so the interception will be detected. If someone intercepts Stream 2, reads it, and manages to make a passable copy to beam to Mars, the time delay will be detected. (Not only that, but QM "no cloning" says you can't make a good enough copy anyway.).
In all of this, nothing at all is happening faster than light. The veil of QM simply says that we can't know the contents of Stream 1 and Stream 2 until we measure them. When we do our encryption operation, we are putting useful data behind that veil, and when we "teleport" the data to the destination, we are getting it back out from behind that veil. But we still have to send everything at light speed.
Fun with Anagarams! LADS HOST, SHALT DOS. HAS DOLTS. AD SLOTHS, HATS SOLD. ASS HO, LTD.
Electomagnetic radiation?
Here's the problem I see with this concept. Right now we use radio waves to communicate. Suppose you're communicating with a probe on Mars. Mars emits essentially no RF energy. So almost all the signal you get is coming from your probe.
But with light waves it is another matter. The sun radiates enormous quantities of light, and substantial amounts are reflected from Mars. Imagine trying to see a light shining from Mars to Earth using a telescope. It would be impossible, the light from your probe would be totally swamped by the light from the entire surface of Mars.
You might think that you could fix this by going somewhat outside the visible spectrum, but there are third problems. First, going to longer wavelengths planets still radiate substantial amounts; second, I don't know of any technology for ultraviolet lasers; and third, the atmosphere becomes opaque pretty quickly when you move away from the visible spectrum.
Where this technology would be useful is in deep space probes, those that are not orbiting planets. In that case we would not have the reflected light from a planet to compete with and the use of high frequency light waves to carry more data would be a very promising approach. But for probes at planets, I don't think it will work.
"Send a distress signal and then inform the senate that all aboard were killed!"
they should be reading dailykos and not slashdot
Assuming Mars would swamp whatever light bands you would use, simply place a transmitter/receiver repeater sufficiently far enough from Mars so as to be able to resolve the light source as distinct. This could be done with a high polar orbit that always is 90 degrees Sun-ward, or perhaps better yet a pair of halo orbit repeaters to serve both the Sun-ward Side and dark side so all of Mars in in constant communication 24/7. If these orbits prove inadequate to be resolvable from Earth then put a repeater at one of the 5 Lagrange points of mars.
Letter To Iran
yeah, I'll get to that chick nipple research pronto! Science awaits my results!
Your sig, at the moment:
:)
"Computer Scientists can count to 1024 on their fingers" (non-mutant, non-mutilatated, human computer scientists)
I've taught my kids how to count on their fingers in binary, though they're happy enough to count to 0x0F (using just four of the 10 available bits). 0x02, of course, is their favorite number, where the pointer finger is the LSB.
But even using all the available bits, I can only count up to 1023 (1+2+4+8+16+32+64+128+256+512). Although I guess I could use my tongue as an overflow bit.
Stressed? Me? Of course not. Stress is what a rubber band feels before it breaks, silly.