Lasers boost space communications | Hacker News Reader

Lasers boost space communications

nature.com

53 pointsfeelthepain29 comments

Given that visible light and radio waves are the same thing except that visible frequency, my first thought was "why don't they focus the radio waves rather than switching to visible light?"

I suppose that higher frequency waves can encode more information, but I'd guess they also have a harder time penetrating the atmosphere. Maybe we don't have a mechanism for producing "radio laser?"

Can anybody clarify for me?

Yes, actually the "radio laser" (actually, microwave laser [1]) was the first type of *aser invented!

The reason they haven't been proposed for deep-space communication is that thus far, unlike lasers, they have required bulky cooling mechanisms and solid-state semiconductor masers have not been possible. The future does look brighter due to a recent breakthough, though [2].

[1] http://en.wikipedia.org/wiki/Maser

[2] http://www.nature.com/news/microwave-laser-fulfills-60-years...

I'm expecting, one day, for half the moon to be covered in antenna gear and us using it as one large phased array software-defined radio. Like arecibo observatory, but HUGE.

That may be closer than your think (except for the moon bit, space is hard). See LOFAR: http://www.lofar.org/about-lofar/about-lofar "LOFAR is the first telescope of this new sort, using an array of simple omni-directional antennas instead of mechanical signal processing with a dish antenna. The electronic signals from the antennas are digitised, transported to a central digital processor, and combined in software to emulate a conventional antenna. "

There are quite a few sensor networks out there at the moment:

PressureNet: Android barometer sensors ADS-B for flight data AIS for ship traffic CORS for precise GPS positioning data

It would not be out of the realm of possibility to have ~$500 software defined radios across the world with network connections, all funneling back to a data processing facility.

Awesome!

We have MASERs, but they just aren't usefull for that. Because theyr wave-length is bigger, a "radio laser" difuses into a huge area before getting into Earth.

Higher frequency radiation tends to give you a more focused beam for a given lens size. Here's a run related tool for figuring out how much damage a laser beam will do given frequency, energy, lens size, etc.

http://www.5596.org/cgi-bin/laser.php

Whenever I see something inspired by Clarke, Asimov or Roddenberry, I wonder who is inspiring the kids of today. Which movies or authors? Or will be indebted by the guidance of the early SF authors for the next 100 years?

My first guess is Avatar as a grand inspiration, but who are the writers out there standing of the giants before them? Quoting country music usually gets me in trouble, but "Who's gonna fill their shoes?"

> Whenever I see something inspired by Clarke, Asimov or Roddenberry, I wonder who is inspiring the kids of today. Which movies or authors?

Even if there were parallels around (and, really, you aren't going to find an Asimov or even a Clarke every generation), the social, economic, and cultural situation of the early 21st century isn't the same as the one of the mid-20th, and doesn't lend itself to the same kind of popular reception for futurism that occurred especially during what might be described as the golden age of the American middle class from the end of WWII through about 1980, and continued later among the people that grew up in that period.

That's an interesting question.

My guess is that the original/semi-original stuff they will be inspired by are games like Halo, Mass Effect, Portal, StarCraft, Bioshock, movies like Avatar as mentioned, District 9 and Inception.

Anecdotally, I don't see young people reading much and when they are it's wizards or vampires, not science fiction. As best I can recall, there haven't been many strong or particularly popular books, movies or television series in the genre for a good decade now.

Well, to name my personal favourites: William Gibson. Neal Stephenson. Paolo Bacigalupi. Ian M. Banks (sadly no longer with us as of late). I'm sure I've missed a great deal more fine authors.

Neil DeGrasse Tyson's remake of Carl Sagan's COSMOS series is getting me seriously excited. Link: http://www.youtube.com/watch?v=kBTd9--9VMI

Not SF necessarily, but still inspiring.

The Mars Telecommunications Orbiter [1], if flown, would have demonstrated laser communications at Earth-Mars distances already in the early 2010s. It was cancelled because the funds had to be funneled to the last Hubble service mission, as well as to the overbudget James Webb Space Telescope and the Mars Science Laboratory (the Curiosity rover). Also, the Mars Reconnaissance Orbiter, capable of working as a relay, was found to have adequate bandwidth to serve the various surface missions.

[1] http://en.wikipedia.org/wiki/Mars_Telecommunications_Orbiter

Tens of thousands of kilometers sounds good. But millions of kilometers will be a huge challenge. The advantage of the laser is its pinpoint precision. But when you get to the distance where the speed of light is not fast enough, and the receiving end has moved, you have an interesting problem. You will need to point the laser to where the receiver will be. Also, as you start thinking about even further distances and gravity 'refracting' light it gets complicated very quickly.

It isn't that pinpointed, calculating and tracking the position of something in our solar system relative to earth to a few (hundred) thousand square kilometers precision should be little problem.

"For example, a typical Ka-band signal from Mars spreads so wide that when it reaches Earth the diameter of the energy is many times larger than the diameter of the Earth. A typical optical signal, however, will spread only over the equivalent of a small portion of the United States, requiring less energy use and waste."

From http://www.nasa.gov/pdf/742122main_LCRDFactSheet3.pdf

Interesting. That would increase the need for more terrestrial transceivers or satellite transceivers to maintain active communication as objects spin.

They're already working on quantum communications between Earth and satellites, too, but it's obviously still very early days. But it will probably be what we'll use for very large distances in the future.

http://www.extremetech.com/extreme/152906-european-scientist...

http://spectrum.ieee.org/tech-talk/aerospace/satellites/chin...

'Quantum communications' isn't a real thing outside of scifi (and generally the crappier kind).

It's sometimes (inaccurately) used to describe quantum entanglement (or quantum encryption) but it doesn't actually allow for the transfer of information.

It can be used for quantum encryption but the actual information transfer has to take place over a traditional medium. When you hear those stories about quantum teleportation and such that is generally what they are talking about.

As I understand it, this is about "secure" communications and not some magical new way of information transmission. These "quantum communications" would still require a standard channel to communicate over.... which would likely be laser/radio as per normal.

Do you need that for quantum entanglement communication, too?

From various discussions I've had with physicists on the matter I found the answer is yes.

My thoughts were summed up by having a device here on earth that is entangled with a device just above the surface of the sun. Now imagine the sun vanishes and the devices communicate this information over the entanglement, thus (to my mind) breaking the "light barrier" as we receive an 8 minute warning that the lights have gone out. I don't fully remember (or understand!) the answer I got, but it most definitely had a reliance upon a relativistic communication channel.

[also: what H3g3m0n said - entanglement is not about the transfer of information]

Compensating for the movement in the way you mention it shouldn't be too hard I guess.

I'm curious if they will need to compensate for the speed differential between the source and the target. Can anyone explain if the following will cause any problems for this technology? If the source and target move away from eachother quickly, the target will observe an increased wavelength, and vice versa. Apparently this is called Redshift [http://en.wikipedia.org/wiki/Redshift] and technically there is some similarity to the Doppler effect.

The Doppler effect (of which redshift is a special case) already has to be taken into account with radio communications (which is EM radiation just like light). In fact, all data from the Huygens Titan lander was almost lost because the software onboard the Cassini probe, on which Huygens piggybacked, couldn't have locked onto the lander's carrier wave due to too steep a Doppler shift. This was fixed by altering the Titan approach trajectory so that the Huygens' relative velocity didn't grow too high.

The Doppler effect will be present, but will not cause any problems that aren't already present. It exists in current radio communications - light is no different in that regard as it's all just electromagnetic waves.

Would that matter if the information weren't encoded using the wavelength? Eg, imagine that they toggle the light very quickly, Morse-code style, to encode messages. If the frequency changes slightly, no big deal.

EDIT: I suppose this effect could make the speed of the toggling appear faster or slower, but that could be adjusted for.

Not a mention of latency in that article, of course you can stream terabytes of data over radio in space but the time for the request to arrive would hamper controlling things in real time.

funny how FM radio encoding was the technological step forward over radio AM, but now the its laser AM encoding that is the next forward after laser FM.

The intend[1] to use pulse position modulation, which is quite unlike AM.

[1] http://cwe.ccsds.org/sls/docs/SLS-OCM/Meeting%20Materials/20...

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