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NASA Achieves Laser Communication With Lunar Satellite
New submitter EngnrFrmrlyKnownAsAC writes "Communicating with lasers has become the hot new thing. While most researchers are seeking faster throughput, NASA set its sights in a different direction: the moon. They recently announced the first successful one-way laser communication 'at planetary distances.' What did they send? An image of the Mona Lisa, of course. 'Precise timing was the key to transmitting the image. Sun and colleagues divided the Mona Lisa image into an array of 152 pixels by 200 pixels. Every pixel was converted into a shade of gray, represented by a number between zero and 4,095. Each pixel was transmitted by a laser pulse, with the pulse being fired in one of 4,096 possible time slots during a brief time window allotted for laser tracking. The complete image was transmitted at a data rate of about 300 bits per second.'"
No budget left over to get FIOS?
My dream of running a BBS on the moon grows ever closer! Who wants to play tw2002 on my moon server?
> Every pixel was converted into a shade of gray, represented by a number between zero and 4,095.
Obviously 50 shades of gray wasn't enough..
...considering how tight this beam was, and that you'd have to be pretty much directly in its path to intercept the transmission.
I do not respond to cowards. Especially anonymous ones.
Each pixel was transmitted by a laser pulse, with the pulse being fired in one of 4,096 possible time slots during a brief time window allotted for laser tracking.
I have an idea. What if, instead of this encoding, they used twelve time slots for each pixel and, by either sending or not sending a pulse, transmitted a small amount of information with each (non)pulse? Then, they could interpret the slots by repeatedly adding a one or zero and multiplying the whole thing by two. I think I've read about it somewhere...
Ezekiel 23:20
The Mona Lisa? Are you serious? Way to break tradition NASA, my heart weeps for Lenna:
http://www.cs.cmu.edu/~chuck/lennapg/lenna.shtml
Shouldn't have been Lena?
Wow, sent an e-mail as suggested when clicking on "use classic" banner, and got a fast response that addressed my msg
i can improve yours. one, zero or penguin allows for all possibilities.
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The inverse square law
Doesn't work that simply or easily over an unreliable medium... A BIRD flying by at the wrong time could turn a string of ones into zeros. Plus there are similar issues of clock-sync... With a long run of zeros, is your timing precise enough on both ends to ensure that you know EXACTLY how many zeros there were supposed to be in that time period of no signal? Maybe it was 200 zeros, maybe it was 199?
But it's probably more of an issue that sending "zeros" at all, ever, wasn't an option. They were piggy-backing on a laser being used for other purposes, they couldn't shut it off for however long they wanted... They could only modify the routine slightly, to test of a proof of concept. And with a proof of concept, a visual representation is a lot easier to comprehend (see the photo before reed-solomon ECC) than a lot of statistics...
Slashdot gets worse every day... Pipedot: News for nerds, without the corporate slant
Because they can't reliably send individual bits. If you RTFA (I know, I know...) it shows that there is a fair bit of error and quite a few lost pixels. Rather than sending bits they send a pulse of a certain length per pixel, and if the edge of that pulse is distorted somehow they just lose some intensity resolution and don't end up with totally corrupted digital data.
It's kind of analogue. The timing method they use is a bit like PWM with one cycle per pixel, and actually there are far fewer than 4096 shades reliably transmissible, that is just the range they measure.
const int one = 65536; (Silvermoon, Texture.cs)
SJW, n: "Someone I don't like, and by the way I'm a fuckwit" - AC
They have mirrors on the moon, that we routinely bounce lasers off of to measure distances and do Relativity experiments with. It's suddenly difficult to transmit information via laser? Why so slow? Why was this an accomplishment?
"Do not look at laser with remaining eye"
"transmitted a small amount of information with each (non)pulse?" ...non pulse? so the absence of light is data too?
doesn't that mean the image would have to be transmitted in momchrome (vs greyscale)
"Every pixel was converted into a shade of gray, represented by a number between zero and 4,095" ..whatever. this whole thing is kind of over my head /woosh
The timing method they use is a bit like PWM with one cycle per pixel, and actually there are far fewer than 4096 shades reliably transmissible, that is just the range they measure.
It would actually be PPM (pulse-position modulation).
So you want to shoot laser penguins at the moon?
I like the way you think, but PETA might not.
If you can't send zeroes, you could encode data in the length of a laser pulse instead. Use error correction techniques to reduce the chance of errors. A checksum should have very low overhead but decrease your chances of errors immensely. If you're feeling silly, you could even use differently coloured lasers and hope they all hit near the same spot. Disco SMS :D
Duration of the pulse or nonpulse. That's how you get 0-4095
If laser communication overtakes radio for our own space equipment, it might explain the Fermi paradox - we cannot detect alien civilizations because the communicate with lasers (emitting no radio signals at all), making them undetectable to those not in the path of the beam.
"That's either incredibly asinine or the most brilliant troll I've ever read. Not sure which." -Anonymous Coward
Friggin sharks communicating with friggin laser beams on their heads.
So that's Pulse Position Modulation, yeah?
Why not use 2 different wavelength lasers (Or even 3 or more)
For two lasers (let it be greeen and blue) it would be binary transmission,
"4096" fits into 13 bits. Image transmission would be 315 times faster.
As I've been saying for years SETI doesn't have a hope in h**l finding the aliens because they use the much more efficient point to point message casting as opposed to the broadcasting in every direction used here on earth. Why use the inefficient method sending your message/data/... everywhere when it is really only destined for 1 place.
I think in 100 years we'll look back and see that the use or radio and the inefficient broadcasting methods was a short segment in our history. It will likely be the same for other developing races.
I recall a few years back they actually found something that looked like real alien communication. It couldn't be captured again. Of course it coul'n't be found again. We were no longer behind the target of the message beam.
Right next to your flying car.
Table-ized A.I.
Fist it is not 4096 bits. It takes 12 bits to make up 4096 possibilities. Also, don't you think that the scientists factored the 12 bits into their 300bps calculation? If there were only 300/12= 25 slots per second the data rate would be 300 bps.
At 300 baud, that movie download is going to take one heck of a long time!
They want their Hayes Smart Modem 300 back.
If you disagree with me on social issues, then it's pretty clear that you are a narrow-minded bigot.
So, the moon, which is 409,073 kilometers away at its furthest is "planetary distances"? What does that make the distance to Venus, which is 41 million kilometers at its closest or Mars, which is 56 million kilometers at its closest. Seems to me that this is only over about 1% of the shortest distance you could actually consider "planetary distances".
Uhm yeah, these are guys at NASA transmitting data to the moon. Maybe you should give them a call and tell them all you know about binary digits, checksums and error correction?
c++;
You just know when you click it, it's gonna be a lame banana store site or something.
Defining Statistics and Social Research
who is completely underwhelmed by this "feat"?
Umm.. no. You seem to be confusing symbol rate / baud rate and serial character frames
The laser-tracking protocol is defined to run at 25 pulses a second; pulling them back and forward by tiny amounts, to take advantage of the electronics in the orbiter that are designed to measure tiny time differences in order to do the LIDAR altimetry, is a really nifty classic NASA hack.
But the press release did not make a good job of pointing out that NASA were working under that restriction. Obviously if you were trying to do laser communication you'd do something else; ESA have done 50Mbit/second laser communication from low-Earth orbit to geostationary and from geostationary back to Earth, with their Artemis satellite.
They way they're doing it is too damned easy. I'd throw a little challenge into it by requiring that low bits must transmitted by bouncing them off the Apollo laser reflectors. Might require spinning up LRO to about 3000 rps unless it has two sensors.
"You must try to forget all you have learned. You must begin to dream." -- Sherwood Anderson
How wide is the beam when it reaches the craft? What are the theoretical limits of the width per distance?
Table-ized A.I.
We could see laser flashes just as easily as hear radio waves from parabolic dishes. http://www.cusabio.com/pro_11.html