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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
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?
To demonstrate a line of sight transmission, from any possible point of orbit? Think about it. They are developing towards a true subspace solution.
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).
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
So that's Pulse Position Modulation, yeah?
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.
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.