Shining a Light on Interplanetary Communication 84
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."'"
Latency (Score:2, Informative)
They keep harping on data rate, but what about latency? Given that Mars are Earth are anywhere from 40 to 160 million miles apart [csmonitor.com], perhaps it suffice merely to:
to estimate its order of magnitude.
Re:Latency (Score:1)
The answer is KLAATU (Score:2)
Actually, we've had the answer for about 30 years....just keep broadcasting:
"Calling Occupants, of Interplanetary Craft......we are your friends...."
Re:Latency (Score:1)
Re:Latency (Score:2)
Of course if you are going to be transmitting data for a few hours, 15 minutes of handshake and setup time doesn't matter so much.
Re:Latency (Score:1)
Re:Latency (Score:2, Interesting)
Re:Latency (Score:2)
Aye, by now we will stay with the 10 minutes latency for *any* communication to Mars because there is no option!
Re:Latency (Score:3, Informative)
Understanding Quantum Entanglement (Score:5, Informative)
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.
Re:Latency (Score:2, Insightful)
Re:Latency (Score:3, Interesting)
This problem could be solved with "interplanetary routers" which just route the signal around the sun (i.e. there's some relay station e.g. at the same orbit around sun as Mars, but at a large enough distance so that if the line of sight to mars is blocked, the line of sight to that station isn't; whenever Mars is behind the sun, the signal is relayed through that station; this gives an additional late
Re:Latency (Score:2)
Re:Latency (Score:2)
Earth and Mars shadow. (Score:2, Informative)
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 t
just spin the laser (Score:4, Funny)
I'm gonna go to the sandbox and play with my Tonka Firetruck now.
Re:just spin the laser (Score:2)
um, no.
well, that's an argument (Score:4, Funny)
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.
Re:well, that's an argument (Score:2)
You can't get past that.
Re:well, that's an argument (Score:2)
Re:well, that's an argument (Score:2)
If someone here doesn't get the joke (Score:1)
Re:well, that's an argument (Score:2, Funny)
That said, I was in complete and total agreement up until your last conclusion here. Unfortunately, tests have shown that nipples, over time, are very much affected by gravity...
lol! (Score:1)
Re:Latency (Score:2)
When earth and Mars are closest, their distance will be about 0.5 AU, when they are furthest (on opposite sides of the sun), about 2.5 AU.
Light travels about 8 minutes per AU, so it's 4 to 20 minutes one way. Ping times would vary between 8 and 40 minutes.
As Mars runs a full circle about every two years, earth only catches up with it (i.e. the "excellent" ping times of just 8 minutes) once every two years.
Yes Yes... (Score:1, Insightful)
SETI? (Score:3, Interesting)
Re:SETI? (Score:2)
http://www.space.com/searchforlife/optical_seti_0
Re:SETI? (Score:1)
The Optical SETI project has efforts in a number of places. The article refers to the Link Observatory but there is also an effort in Boston at the Harvard Observatory. Here is a link which also points to some Whitepapers:
Beam me over Scotty [harvard.edu]Enjoy!
PS. Keep Watching the Skys!
Re:SETI? (Score:2)
The improvement with interplanetary communications is caused by the
Re:SETI? (Score:3, Informative)
You are mixing up the energy of a single photon with the total energy of your transmission. Yes, a single light photon has much more energy than a single microwave photon. But a 100W light source and a 100W radio source both emit exactly the same energy, 100 Joule per second.
Re:SETI? (Score:2)
Re:SETI? (Score:3, Informative)
Re:SETI? (Score:1)
Re:SETI? (Score:2)
Re:SETI? (Score:2)
Redshift (Score:2)
Re:SETI? (Score:2)
Since these waves are propagating through the vacuum of space, you won't have to worry about any frequency-dependant attenuation issues you might get when trying to squirt them through a medium.
Additionally, if you go to really high-frequencies, there's probably less background noise from stars and stuff.
Re:SETI? (Score:2)
Re: (Score:2)
Re:step two (Score:1)
talk about priorities... (Score:5, Funny)
Re:talk about priorities... (Score:1)
S/N? (Score:2)
Re:S/N? (Score:3, Informative)
Re:S/N? (Score:2)
Re:S/N? (Score:2)
You may be interested in Shannon's channel coding theorem [ucl.ac.uk] which relates the maximum possible bandwidth of a communications channel to the SNR. Increasing the deetctor sensitivity increases the SNR and hence the channel capacity.
Ridiculous, if you do the math.... (Score:2, Informative)
Size is an issue for interplanetary travel.. (Score:2, Interesting)
Re:Size is an issue for interplanetary travel.. (Score:2)
Sure, use this better receptor. But this 3x improvement is a one-shot thing. After that you need a bigger lens or mirror. Probably a parabolic mirror as is already used to collect microwaves.
Re:Ridiculous, if you do the math.... (Score:5, Informative)
Meanwhile, the size of a dish is often a limiting factor in space vehicle design, making every advance in getting better reception out of a same-sized or smaller dish that much more important.
Besides, it's a LOT easier to transport and set up the 6' dish compared to the 20'.
Re:Ridiculous, if you do the math.... (Score:2)
I think the improvement you've seen is due to going to higher frequecies, lower n
Re:Ridiculous, if you do the math.... (Score:1)
The LNAs probably contribute to it a lot though.
Re:Ridiculous, if you do the math.... (Score:4, Informative)
1) Cost - creating a mirror that much bigger becomes very very expensive over a certain size. Even if this technology to improve the sensitivity makes the sensor twice as expensive you are still saving money. Remember, these are not bathroom mirrors, we are talking about optically perfect mirrors of great size.
2) Size and Weight - If we are using the satelites to capture this information rather than ground based devices then size and weight are a critical factor. This technology would weigh nothing more (or minimally more) while a 1/3 bigger mirrow would weigh 1/3 more.
3) Currently, I believe, we are using radio waves and so therefore we would not be using mirrors. If we were to go to light transmittion, we would probably need to have detectors in space, and I would bet that at least one of them would be in orbit around mars. That said, a bigger mirror again means more size and weight that would have to be transported all the way to Mars.
Also, your math is wrong, 1.63 is not the square root of 3, 1.732050808 is the square root of 3.
For the latency crowd out there, use UDP packets rather than TCP packets and then re-request the sending of any missing packets over time. This emulates TCP over UDP but at a higher level that allows transmittion to continue while waiting for acknowledgement of packets received..
OT: Counting to 1024 (Score:1)
"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
Relevant Science Fiction (Score:2)
Except that it looked an awful lot like Galactic Usenet, complete with inter-species flame wars.
Doom? (Score:2)
Re:Doom? (Score:2)
bandwidth we can improve fairly easilly by using more power, better antennas etc. Latency is pretty much fixed for radio and free space optical communications unless there is some REALLY radical discovery (e.g. on a similar level to perpetual motion).
What about Gravity Wave Communication (Score:1)
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 "Roswe
Re:What about Gravity Wave Communication (Score:2)
Yes. [milk.com]
Re:What about Gravity Wave Communication (Score:1, Troll)
Re:What about Gravity Wave Communication (Score:1, Offtopic)
Delay tolerant networks (Score:2)
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 art
What about pointing? (Score:1)
Re:What about pointing? (Score:2)
Re:What about pointing? (Score:2)
Re:What about pointing? (Score:2)
More details (Score:4, Informative)
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.
Best way to jam communications. (Score:2)
I can't wait until they use quantum tunneling.
Swamping by reflected light? (Score:2)
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 to
Simply solved (if even a problem) (Score:2)
Re:Swamping by reflected light? (Score:1)
See also, Free Electron Lasers for info on possible UV lasers.