
Lasers boost space communications - feelthepain
http://www.nature.com/news/lasers-boost-space-communications-1.13396
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nathan_long
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?

~~~
Sharlin
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](http://en.wikipedia.org/wiki/Maser)

[2] [http://www.nature.com/news/microwave-laser-
fulfills-60-years...](http://www.nature.com/news/microwave-laser-
fulfills-60-years-of-promise-1.11199)

~~~
toomuchtodo
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.

~~~
TimSAstro
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](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. "

~~~
toomuchtodo
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.

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mathattack
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?"

~~~
dragonwriter
> 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.

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Sharlin
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](http://en.wikipedia.org/wiki/Mars_Telecommunications_Orbiter)

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binarymax
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.

~~~
noloqy
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](http://en.wikipedia.org/wiki/Redshift)]
and technically there is some similarity to the Doppler effect.

~~~
Sharlin
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.

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jlebrech
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.

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tlarkworthy
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.

~~~
noselasd
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...](http://cwe.ccsds.org/sls/docs/SLS-
OCM/Meeting%20Materials/2012_04_Darmstadt/Presentations/LCRD%20Overview%20for%20IOAG%20-%20Germany%20-%20April%202012.pdf)

