
A Laser Message from Space - cromulent
http://science.nasa.gov/science-news/science-at-nasa/2014/18jun_opals/
======
kator
Space-X put took the laser to the ISS...

Reminds me of Paul Simon's song "The Boy in The Bubble" [1]

    
    
        ...
        These are the days of lasers in the jungle
        Lasers in the jungle somewhere
        Staccato signals of constant information
        a loose affiliation of millionaires
        And billionaires, and baby
        
        These are the days of miracle and wonder
        This is the long-distance call
        The way the camera follows us in slo-mo
        The way we look to us all, oh yeah
        The way we look to a distant constellation
        That’s dying in a corner of the sky
        These are the days of miracle and wonder
        ...
    

[1]
[http://en.wikipedia.org/wiki/Graceland_(album)](http://en.wikipedia.org/wiki/Graceland_\(album\))

EDIT: Added link, not bad prediction considering it was released in 1986

~~~
benihana
It was referring to the violence of apartheid. You left out the opening lines
mentioning the shattering of shock windows, the bomb in the baby carriage, and
the soldiers on the side of the road, which change the entire meaning of the
lines you posted.

~~~
moheeb
My guess is that those lines didn't remind the author of lasers in space.

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bsilvereagle
This is a pretty big deal. At the moment there are two main methods to
communicate with the ISS, TDRSS and UHF.

UHF can only be used when the ISS is over the US.

TDRSS is a shared satellite network between several government agencies. NASA
receives "allotments" of time with the network. So if the ISS is outside of
UHF range, and another agency has the TDRSS the ISS goes black - we lose all
comm with it.

A network of laser receivers across the globe could potentially eliminate the
current "black outs" NASA has when communicating with the ISS.

~~~
furyg3
I find this kind of surprising. First off, I'd figure that NASA would set up a
few UHF stations around the world in locations with decent internet access
(friendly countries or military bases), and route comms via that. Maybe you
don't have total coverage, but at least you don't have to wait an hour before
it's back over the US.

Secondly, there many more options available than TDRSS or UHF. Amateur radio
enthusiasts frequently make contact with astronauts (2 meter and 70cm bands,
IIRC). While that doesn't really solve the blackout problem, I find it hard to
imagine that there isn't a lower-frequency radio which could maintain voice
contact with the ISS.

~~~
_delirium
I believe NASA does have a few UHF stations elsewhere, or at least used to. As
of a 1998 document about the shuttle program [1], they listed 6 UHF air-to-
ground stations, 3 of them in other countries. The U.S.-based ones were in
Guam, Hawaii, and Florida; and the others were in Ascension Island (a British
dependency halfway between Africa and South America), Bermuda (a British
dependency off the east coast of Canada), and Dakar, Senegal.

[1] [http://science.ksc.nasa.gov/shuttle/technology/sts-
newsref/s...](http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-
jsc-comm.html)

~~~
jdmichal
Just a clarification: Bermuda is not really close to any major coastline, and
certainly not the Canadian one.

[https://www.google.com/maps/place/Bermuda/@31.2546129,-41.52...](https://www.google.com/maps/place/Bermuda/@31.2546129,-41.5200126,4z)

~~~
toomuchtodo
850 miles (closest point is in North Carolina) isn't necessarily far.

~~~
jdmichal
When someone says "off the coast", I would not expect 850 miles of distance.
And, even more, when they say "off the east coast", I would not expect it to
be almost directly south of the east coast. Those were the points I was
attempting to relay.

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yeldarb
Interesting. If a 2.5 watt laser was used for communication from the ISS to
Earth what wattage would be needed to send a high-bandwidth message back from
Mars (or Titan)? How does that compare to traditional radio-based
communication?

This point-to-point communication is also interesting in relation to the Fermi
Paradox. It seems likely that a sufficiently-advanced race would beam their
messages directly to their recipients rather than wasting energy (and privacy)
transmitting an omnidirectional signal.

~~~
mnw21cam
Well, if the ISS is around 420km up, and Mars is on average 225 million km
away, and all other parameters of the laser are identical, then the laser
would need to be around 700GW.

However, you could probably get away with a slightly less powerful laser if
you decrease the bit-rate a little, improve the sensitivity of the receiver,
and tighten the beam (which wouldn't be a problem if the laser is bigger). I
got the impression that the 2.5W laser was way more powerful than necessary
for basic communication.

Let's face it - Mars Explorer has a total power availability of around 450W,
and it aims its dish at the earth with an accuracy of 0.04 degrees, and it
manages to communicate. Replacing the radio with a laser may improve matters,
but it may also require too much power.

~~~
throwaway_yy2Di
Here's a paper from NASA's (budget-axed) Mars Laser Communications
Demonstration. They estimate 10-100 Mbps bandwidth, on a 5 W laser system (300
W pulsed, but only drawing 5 W from the PSU).

[http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/38254/1/04...](http://trs-
new.jpl.nasa.gov/dspace/bitstream/2014/38254/1/04-0101.pdf) and also

[http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/38024/1/04...](http://trs-
new.jpl.nasa.gov/dspace/bitstream/2014/38024/1/04-0216.pdf)

context:
[https://en.wikipedia.org/wiki/Mars_Telecommunications_Orbite...](https://en.wikipedia.org/wiki/Mars_Telecommunications_Orbiter)

There's a much more interesting paper somewhere that designs a system for
inter _stellar_ lasers..

edit: I can't find what I'm thinking of, but this optical SETI experiment is
relevant. It looked at 577 nearby stars (<50 parsecs = 163 light years), and
claims it could detect a 50 kW (!!) optical laser pointed from one of them
(presumably at a negligible bitrate).

[http://arxiv.org/abs/astro-ph/0112479](http://arxiv.org/abs/astro-ph/0112479)

~~~
mnw21cam
That's cool, thanks. Basically, the ISS laser experiment was not stretching
the bounds of the method at all.

Put a proper telescope at the receiving end, and it changes the game
completely. It's simply amazing how little light modern telescopes are capable
of detecting and measuring.

Note that your arxiv paper describes detecting a 50kW laser that is
diffraction limited for a 10m aperture. That in itself would be a quite
interesting piece of equipment to build.

Edit: Interesting - the abstract seems to have been mis-copy&pasted, with 60kW
instead of 50kW.

------
dynode
Link to the JPL project page with more detail

<[http://phaeton.jpl.nasa.gov/external/projects/optical.cfm>](http://phaeton.jpl.nasa.gov/external/projects/optical.cfm>)

Interestingly this is a Phaeton project. Phaeton projects are designed for
early career engineers to jumpstart their experience. Very cool.

<[http://phaeton.jpl.nasa.gov/external/ProgramOverview/home.cf...](http://phaeton.jpl.nasa.gov/external/ProgramOverview/home.cfm>)

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numlocked
And it got to the ISS via a Space-X Dragon! Lasers, privately funded
spaceships, hello world...too much fun :)

~~~
damon_c
finally, the future!

~~~
HNJohnC
It will never be the future until I have a flying car, sorry.

~~~
saraid216
I'm honestly impressed at someone so self-centered as to claim the future is
unachievable unless and only unless he gets his own personal toy.

~~~
HNJohnC
It's a common "meme" from the past, perhaps you're too young to get it.

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Sir_Cmpwn
A more appropriate use for "Hello, world!" than I have ever written in a new
programming language.

~~~
louthy
At least yours has the correct punctuation.

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throwaway_yy2Di
How close are we to space-based laser ISPs? I imagine that you squeeze
terabits of optical bandwidth into a single mirror "dish"..

~~~
kbar13
imagine a world where this was the norm. You wouldn't need to worry about
outages due to falling trees or utility poles exploding or people screwing
with your wires.

Then you step outside to look up at the sky and you lose your eyesight

~~~
mnw21cam
Day of triffids scenario aside, no you won't lose your sight from a 2.5W laser
pointing downwards from 260 miles up. The power level is too small.

People think that lasers produce a parallel beam. They don't - they are
diffraction limited by the width of the beam. The narrower the beam, the more
it spreads out. For example, a 1cm wide beam produced by a perfect laser would
spread out to around 20m wide when it hits the ground from 260 miles away.
That's assuming visible green light - if it's infra-red (or even just red)
then the spread will be wider.

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logfromblammo
Yes, but how do they keep the sharks alive up there?

Space-to-ground laser communication is a neat trick, but you still have the
problem that you need to have a line of sight to the receiver in order to use
it. The good news is that you are not quite as limited by bandwidth during the
time that you can see the receiver. It would be nice if we could get the sort
of international cooperation that would allow for continuous contact, but
unfortunately, the politicians in charge usually don't care that much about
space research. We'd probably have better luck with one or more reflector
satellites that could bounce the laser signal back to the receiver.

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skierscott
I'm guessing that this is way harder than the article makes it sound. The
satellite is moving very fast and has to hit an extremely precise target, but
adding on another layer of complexity, the atmosphere and temperature
differences effect the transmission.

~~~
mnw21cam
Affect. The laser effects the transmission, but the atmosphere affects it. But
not much. The laser was aimed with an accuracy of 0.01 degrees. Astronomical
seeing (the distortion due to atmospheric disturbance) is on the order of an
arcsecond, or 36 times smaller than this.

~~~
easytiger
Indeed, but the mount the projector and receiver on must be constantly
calibrating movements and adjusting smoothly.

In achievement terms this is almost all software (once you take putting stuff
in space for granted).

Think of proving it to work in theory, ground based prototypes etc.

Error detection is also interesting (though mostly solved but with many
options available). High bandwidth laser comms have been around for a while.
Originally developed for the financial industry for intra city comms.

~~~
mnw21cam
To be honest, it's probably less difficult than the tracking that a compact
disc player has to achieve to play an off-centre bent wobbly CD. The error
correction would be fairly similar too. How long have CDs been around now?

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3rd3
Could we please stop with these headlines that hint at alien life?

~~~
outrightfree
It's the title of the target article.

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damon_c
They don't mention this anywhere, but for light based communication with more
distant targets where the laser would need multiple seconds to reach its
target, would they need to "lead the target" with the lasers pointing in both
directions?

Also, what about the complications due to interspersed massive bodies creating
gravitational lensing?! I guess this can all be accounted for in the aiming
software... but it's not very simple!

~~~
mnw21cam
At the multiple seconds travel time level, gravitational lensing is completely
insignificant. Come back when you have a round trip time of a million years
past a massive galactic supercluster.

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fakeyfake
If you are a fan of videos I definitely recommend their YouTube channel for
brief news updates.

The first thing I thought when I saw this video was definitely about the tech
Li-Fi, there was a new quite long video about it recently here:
[https://www.youtube.com/watch?v=WRG9iXZbuAc](https://www.youtube.com/watch?v=WRG9iXZbuAc)

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Achshar
Why is radio communication slower than visible light based ones? 0s and 1s
should be the same speed no matter what the wavelength.

~~~
_mulder_
Think about it, wavelength (or frequency, they're effectively the same
measurement here) determines how fast you can transmit those 1's and 0's. It's
not slower, it's just that you can't transmit as much information in the same
time period.

Also, laser light for Telecoms is not normally Visible, it's usually Infrared
which has a wavelength shorter than Microwave radio but longer than visible
light.

Another bonus fact; in a vacuum, Radio and Light waves travel at the same
speed. However, when light travels down an optical fibre it is slowed down by
the glass so Fibre Internet is actually slightly slower than radio.

~~~
dm2
So the speed of all fiber and radio is basically the same and it's the
capacity that's different?

Does that mean that saying "internet connection speed" is a faulty term? We
should all be saying "capacity" or data-rate?

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jumpwah
Ah for a second I thought this is it, we're all doomed. Still a pretty cool
demonstration though.

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woodchuck64
Okay, how big is the video and what exactly was the bandwidth? Can't
understand why they won't put the basics in the article.

So I illegally downloaded the video from YouTube; it appears to be 2657084
bytes, so 2657084/3.5 is 759166 bytes per second or 6073328 bits or 5.8
megabit per second. Reporting that as a maximum rate of 50 megabit seems ... a
little "Comcastic". Or am I missing something?

Update: I see another article calling it a 175 megabit transmission so if that
took 148 seconds that's an average rate of 1.2 megabit. It's a mystery to me
why average throughput is just not interesting to the author of the original
article. And presumably the downvoting I'm getting is from a similar sense of
vapid apathy about intriguing detail.

~~~
maxerickson
I wouldn't expect the bits coming down from YouTube to be a meaningful
representation of what they transmitted.

This page describes the mission goal as 10 megabits-per-second or higher, I
guess they aren't making that up:

[http://www.nasa.gov/mission_pages/station/research/experimen...](http://www.nasa.gov/mission_pages/station/research/experiments/861.html)

~~~
woodchuck64
Why wouldn't YouTube be meaningful? It would make sense for the video to be
stored and transmitted as h264 and then uploaded as is to YouTube. I doubt
YouTube recompresses h264.

~~~
burkaman
Because the version they put on Youtube is probably not the exact version they
received from the ISS. The article repeatedly described the video as HD, and
the Youtube version isn't. And if you aren't willing to take NASA at their
word, it's not that hard to imagine how multiple versions of a video end up
getting passed around an organization, and the one that gets uploaded is
compressed for whatever reason.

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pocketstar
>Unlike normal data transmissions, which are encoded in radio waves, this one
came to Earth on a beam of light. >radio waves >beam of light Radio waves are
light...

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ccamrobertson
Congratulations to rwitoff and team at JPL for pulling it off!

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tempodox
So we have our first ad from space. Mankind will never be the same again.

~~~
saraid216
Best reasoning for claiming that mankind will never be the same again:
claiming that mankind is being the same.

