Laser for Satellite to Satellite Communications

heby writes: "Last night ESA successfully tested the first laser link between two satellites (SPOT 4 and Artemis). SPOT 4 is supposed to serve as a data communications relay between Artemis and the receiving station in Toulouse. The link is running at 50Mbps and the two satellites are currently orbiting at 832km and 31000km respectively.
According to ESA "The main challenge in establishing an optical link between satellites is to point a very narrow beam with extreme accuracy to illuminate the partner spacecraft flying at a speed of 7000 m/s." Way to go, ESA!"

Comments

Now If I could only

[minus23]

Now If I could only pee in the toilet and not on the seat I would be in busisness!

Parking

[ruvreve]

"while Artemis is temporarily in a parking orbit at 31 000 km."

I had to pay $13.00 to park at Navy Pier....I wonder how much parking costs at 310000 km?

Speed

[mroeder]

Is relative - 7000m/s sounds impressive but when BOTH spacecraft are travelling at 7000m/s in the SAME relative direction they are actually travelling ( in relation to each other ) at 0m/s

2c

Re:Speed

[gibodean]

Is relative - 7000m/s sounds impressive but when BOTH spacecraft are travelling at 7000m/s in the SAME relative direction they are actually travelling ( in relation to each other ) at 0m/s

Yeah, but they're not both travelling in the same direction or the same speed.

They're in different orbits, which means that their speed and direction is always different (except for instantaneously occasionally when they can have the same direction, but still different speeds)

Re:Speed

[Anonymous Coward]

this already is the relative speed between thos two.
Artemis probably is at below 2000m/s while SPOT4 should be at around 9000m/s.

Re:Speed

[ZigMonty]

Common misconception. There isn't one velocity called orbital velocity that you have to reach to orbit. The velocity needed for a particular orbit is dependent on it's height: the lower you are the higher the speed. Also if the two satellites are traveling in opposite directions then it's more like 14km/s. The only time the relative velocity will be 0 is if they are both in exactly the same orbit.

Re:Speed

[Usquebaugh]

"The only time the relative velocity will be 0 is if they are both in exactly the same orbit."

The above is not true, the higher the orbit the greater the length of the orbit. The outer sat has to travel faster to keep up with the inner sat.

So they can have a relative velocity of zero when they are not in the same orbit.

Re:Speed

[FlexAgain]

The only time the relative velocity will be 0 is if they are both in exactly the same orbit.

...and on top of each other. Velocity is a vector. Being in the same orbit does not mean that they do not move relative to each other (depending on what reference frame you are using). Even if the two spacecraft were in the same orbit, the tracking system would still have to continuously repoint the laser/reciever.

Re:Speed

[Anonymous Coward]

Orbital speed is given by:

sqrt(g * r^2/(r+h))

where:
g = 9.81 m/s^2
r = 6,378,000 m

The two different heights (832 km and 31000 km) give orbital speeds of
7436 m/s and 3266 m/s

hmm

[Anonymous Coward]

first comment!

first postst

[Anonymous Coward]

first psot!

Re:first postst

[Anonymous Coward]

I count like FOUR before you. MORON

This is just...

[Anonymous Coward]

This is just plain cool. 50MBPS conenction, through space, with that kind of accurace, kinda scary how quickly science is evolving. What will 100 more years bring?

Re:This is just...

[Anonymous Coward]

Maybe science will develop an advanced theory of computing that will allow computers to check spelling.

But do they use decimal?

[Derek Finch]

If they transmit data and later convert it to decimal, it's ust another example of a lame base being used yet again. Why not binary or hexadecimal? Why decimal? Why?

Re:But do they use decimal?

[tomknight]

Because all your bases.....

Tom.

I call it...

[Anonymous Coward]

* pinky to mouth *
...a la-ser.

Muahahahaha.

Muahahahaha!

MUAHAHAHAHA!!

Lasers in Space

[OnyxIR]

I always thought if I got the first post, I would say something witty and hillarious, but the pressure is insane!!!

I cant do it.
Noooooooooooo

Wow.... but how long was the link up for?

[LWolenczak]

How long was the link up for... I'm wondering because one is in a fixed orbit over a single piece of land, while the other is flying around the earth once what? every 90-120 minutes?

The sheer logistics of keeping that link up would be nearly mind boggleing.... So is anybody going to try this with a spot on the planet with a bird up in the sky (satellite)?

Re:Wow.... but how long was the link up for?

[ghoti]

You know, reading the article really helps ... it says "4 to 20 minutes", which is quite impressive. Amazing stuff, next thing you know they will be shooting down starting ICBMs with lasers ... ;-)

Yes!

[Anonymous Coward]

We can finally stream porn 31000km above the Earth!

I wonder what the latency of that link is?

Re:Yes!

[grid geek]

Well the latency between the two sats would be distance/speed of light as there is just a vaccumm in between them. Its the time to downlink the info to the earth station which is the problem due to the atmosphere getting in the way which will increase the latency significantly.

Of course this could just end up as a hub/router with sats taking it in turn to transfer info and then have it down loaded to a base station which would save the hassle of having to include gear to transmit to earth on each one.

Re:fp

[Anonymous Coward]

You wish - you do not have the skill required to get FP.

Now accepting cookies

[nukebuddy]

Article submitter wrote:
SPOT 4 is supposed to serve as a data communications relay between Artemis and the receiving station in Toulouse.

Then, Tollhouse takes the data and uses it to make cookies.

-nukebuddy

Targeting software?

[Anonymous Coward]

Anyone know what this implies in the general development for targeting software (smart bombs, etc?

fp12

[Anonymous Coward]

fp!@@

satellite imaging

[graphicartist82]

maybe this will help out in the future for satellite imaging to stream video back to earth instead of just pictures that take hours to transmit across space. i think it would be cool to get live video from a satellite orbiting jupiter at any given moment :)

Re:satellite imaging

[u.hertlein]

maybe this will help out in the future for satellite imaging to stream video back to earth instead of just pictures that take hours to transmit across space. i think it would be cool to get live video from a satellite orbiting jupiter at any given moment :)

Yeah, right, like it affects the transmission time in any way. The transmission time is still the same due to distance (doesn't change) and speed of light (doesn't change). Remember that radio waves travel just as fast as light?

It mainly affects loss of communication between ground stations and satellites in low-earth orbit since they can't communicate when outside line-of-sight.

Re:satellite imaging

[Anonymous Coward]

I wonder if bandwidth would have any effect here.

Line of Sight

[ectoraige]

I wonder if they have to allow for signal loss caused by bits of space junk floating by...

Okay, the odds are probably pretty damn small, just a thought.

Besides, slashdot seems screwed, I'm curious to see if I can still post...

Re:Line of Sight

[Yazeran]

Well it would only be a problem if a large object (like another satelite) came to be in-between. Even laser light diverge at these distances, so you only point the beam at the other satelite. The beam-diameter would be more than 1 meter, and if a small dust-grain was to come in-between, it would be impossible to detect it. Remember, that light do bend arround corners (quantum mechanics; slit experiments) so even if the dust grain vas directly between the laser and the sensor on the other satelite, it would not 'turn off' the beam. You vould only notice (if at all) a small decrease in light intensity.

Besides, i think they would have included some error-recovery system in their data link, this is standard for all data-transmission links (even home networks on ne2000 compliant netcards).

The real feat here is that they could point a narro beam at a mowing target and keep it there (autonomously that is).

The trick could be to use the gradual decrease in beam intensity as you move to the outer portions of the beam, and send this information back to the other satelite to re-adjust. If you used several sensors spaced some distance apart, you could determine the direction the beam has to be moved (Theoretically that is). I do not know if this could be done in real life as i'm no laser specialist or space engineer.

Yours Yazeran

Plan: To go to Mars one day with a hammer.

Re:Line of Sight

[apsmith]

The trick could be to use the gradual decrease in beam intensity as you move to the outer portions of the beam, and send this information back to the other satelite to re-adjust.

Yeah, I was thinking of the same technique - once you have the communications link up also, you could use the same directional information to transmit power also, something that's been proposed as a way to make use of Solar Power Satellites. This is a very important accomplishment!

Intersting stuff, want to try this "at home"?

[dusty123]

Well, this is indeed a real challenge. Some time ago we also tried to build a laserlink and succeeded with 128kbit (IrDA). The link was very stable, there was no problem accomplishing a link at around 2km. Next we tried to "upgrade" to 10baseT but sadly never found time to finish this. If anyone is interested, have a look at: http://strike.wu-wien.ac.at/~dusty/projekte/laserl ink/index.shtml

Re:Intersting stuff, want to try this "at home"?

[Anonymous Coward]

slashdot inserted a space into that url. here's a clickable link:
http://strike.wu-wien.ac.at/~dusty/projekte/laserl ink/index.shtml

Re:Intersting stuff, want to try this "at home"?

[Anonymous Coward]

Work was looking into importing wireless networking gear last summer. We had some 3rd world produced Laser Networking stuff that was claimed to perform upto 155mbit over 3-5km. Personally I don't want my network to drop everytime a flock of birds decides to fly between the transmitters & receivers.

Re:Intersting stuff, want to try this "at home"?

[Anonymous Coward]

Goiles projekt :)

du hast da ein space in deinem link :p

Re:Intersting stuff, want to try this "at home"?

[FlippyTheSkillsaw]

I personally wouldn't want my network to drop every time I used a piece of flakey hardware. Like a cheap hub or whatever.

I'm thinking that, given 25 pieces of network hardware, you'll lose more packets due to those than you would to rogue birds.

You must got some really BIG slow birds around.

However, 3-5km is pretty impressive. Maybe I'll see about ditching my DSL and making arrangements with a local ISP. "Could I use _this_ as a colocation? Could I leave my colocation on the roof like so?"

I'm amazed it took so long...

[Cwaig]

I worked on this back when I was working at BAe Space Systems (since taken over by Matra Marconi).
We had to high accuracy laser targeting systems for the Sat2Sat laser link working in the lab at BAe's Stevenage site 6 or more years ago...

Re:I'm amazed it took so long...

[Anonymous Coward]

You're amazed it took six years for something as crazy and problem-prone as a sat-to-sat laser link to move from the lab into field testing? Maybe it's time to re-evaluate your expectations (or remember that this is aerospace engineering, not computer science).

First post

[Anonymous Coward]

Mouahahahhaha

Damn

[Graymalkin]

I was just wondering the other day how feasible it would be to use a laser as a communication device between two birds. You can get really nice range with little EM interference with only a wee bit or output power. The one obstacle I kept running into whilst pondering a laserlink was keeping the beam aimed at another bird in a different orbit. Well hot damn and way to go. I guess I was hit in the face with the same muse as the dudes at the ESA just a little bit late and without any satellites under my control to play with...so far.

Re:Damn

[onion2k]

Yes.. the Lesser Spotted Marsh Warbler is famous in ornithological circles for its advanced SatComms..

Re:Damn

[Graymalkin]

I was thinking more along the lines of African swallows. Weird. 20 damned seconds to reply. Has it been 20 seconds yet?

Re:Damn

[Anonymous Coward]

But imagine the kind of bandwidth you could get if your carrier pigeons had advanced satellite communications! You'd need a high speed printer and a mechanical message-to-foot-binder in order not to waste bandwidth...

go ESA go!

[Anonymous Coward]

I wonder when they start selling these lasers for home-to-satellite internet connections... :)

Side effects of lasers?

[billn]

I know it's minimal, but does anyone have any info on how much force the laser they use might exert?

Re:Side effects of lasers?

[abrett]

According to the specs, the link laser will operate at a mean power of 60mW. Using F = P/c, we get a force of roughly 200fN (200 femto Newtons!). Just to give you some idea of the effect that would have, Artemis' mass at launch is 3100kg, so this means that if it was to emit a 60mW beam in the same direction for 10 years, its speed would change by approximately .01 mm per sec.

Re:Side effects of lasers?

[ZigMonty]

Compared to the exceedingly thin but still significant outer atmosphere they're flying in (well, the lower one anyway)? These would not be strong lasers by any stretch of the word. Hell, sunlight would be pushing on them much harder.

I'd say undetectable. I could be wrong though. We seem to have a nack for measuring (or calculating) very small quantities. I'd like to hear an answer from someone who can work out a number though.

Re:Side effects of lasers?

[Sentry21]

Almost none.

I'm assuming you mean kinetic force, and the kinetic force applied to the recieving end of the laser varies inversely (according to some formula) with the reflectivity of the surface the laser is hitting and the distance between the objects (maybe), and it's only really noticable when you get into the gigawatt ranges.

--Dan

hmm

[vectus]

I doubt this will become widespread

In high school, some of my geekier friends and I communicated small messages via small laser-pointers. It was ok when just a couple of us were doing it, but when we graciously tried to extend this mode of communication with our teachers and fellow classmates, our lasers were taken away by our teachers.

I doubt the ESA would want my high school teacher to take their lasers away.

wow

[Anonymous Coward]

wow

Both going at 7000m/s-1?

[onion2k]

Considering the vastly different orbit heights (832km and 31000km) surely the two satellittes must be going at very different velocities. A little basic mathes show us :

2 * PI * 832 = 5,227,610m
2 * PI * 31000 = 194,778,744m

So the total linear distance travelled in each orbit is very different (assuming that the two heights are taken from the centre of the Earth. Which they aren't. Can't be bothered to factor in Earth's radius). So, at 7000m/s-1, the outer satellitte would take about 8 hours longer per orbit, evidently showing the relative distance would be changing, and making the targetting process much more of a challenge.

So.. presumably 7000m/s-1 is the speed of one of the satellittes (I'm guessing inner)..

PS. I think my mathes is screwy. Its early. I have no coffee.

Re:Both going at 7000m/s-1?

[Anonymous Coward]

Sorry, but orbital mechanics indeed work a bit different :)

1st: earth radius is about 6700km, added this to the 800km of SPOT makes a difference
2nd: are you sure they are on circular orbits and not elliptical ones?
3rd: the 7000m/s are indeed the speed difference.
4th: why to hell should ESA be so stupid to publsih press releases with data that is _that_ wrong?

Coffee, is a good idea anyways :-D

Re:Both going at 7000m/s-1?

[Yazeran]

Well you are a bit wrong about this, yes tha outer orbit is much longer than the inner orbit. An other thing you have to include is that it is gravity that keep satelites in orbit, and this scales with the square of the radius or the orbit. This boils down to Keplers third law:

the square of the orbits period are proportional to the cube of the orbits radius (for a circular orbit).

This results in that the outer orbit (which is a geo-stationary orbit) takes 24 hours whereas the inner orbit only takes some 100 minutes (give or takte).

Re:Both going at 7000m/s-1?

[onion2k]

Even factoring in the Earths radius in makes the two orbits 7532km and 38000km .. thats a difference of a factor of 5 and a bit. 7000m/s-1 surely wouldn't be enough to keep the relative distance the same? (And, rereading the article, it doesn't say the relative speed in 7000m/s.. it says, and I quote, the partner spacecraft flying at a speed of 7000 m/s.. there is no mention of the second crafts speed.

Re:Both going at 7000m/s-1?

[Anonymous Coward]

ok, right, the press release isn't clear like a technical specification.
Nevertheless, I can ensure you that the 800km spacecraft flies at about 9000m/s (sure below 10000m/s) and the other one at a speed of about 2000 m/s.
Both speeds depend on the position on the orbits, which in case of Artemis probably is not circular.
The SPOT spacecraft passes by below Artemis, and at the point below has a relative speed of 7000m/s, I think.

Re:Both going at 7000m/s-1?

[imrdkl]

I wondered about this. But the article says that eventually the outer (SPOT) satellite will go stationary, and then initiate up to 5 ordinary uploads per day. I think this is the orbit dependency on the inner (Artemis) satellite? I also dont know what, exactly, the SPOT is taking pictures of, but at 50mb, it can probably get alot of them down to the people who are interested in them. I tried a 20min period using bc(1) and came up with about 10 CDROMS worth SPOT pics.

Wow. Now, if we could just get laser-pens to be this accurate, then they may actually someday actually replace wooden pointer sticks and fumbling fingers under the overhead lamp trying to make a point during a conference session. heh.

Re:Both going at 7000m/s-1?

[Anonymous Coward]

The outer satellite is parked in geostationary orbit, that's why its used as a downlink, its directly above the ground station all of the time. Satellites in geostationary orbit have no velocity (relative the the Earth's rotation) so it's the inner satellite which has a velocity of 7000m/s.

At 7000m/s the inner satellite orbits once every 112 minutes, but as far as it's concerned, everything else is moving and it's not. aligning the laser probably uses a model and some form of feedback, but then the divergence of the beam is huge (about 1 km) so what starts off as a pencil beam becomes a city sized beam, it's more of a spot light approach than actually aiming at the satellite.

The linear distance changes by the radius of the Earth, about 6400km in 38000km. Thats no problem for the laser beam, it's space, there's no atmosphere to kill the beam so it's only problems are quantum effects.

I'm guessing the whole point of the using the laser is that the bandwith of a laser is much high than radio or microwaves, the inner satellite bursts the data to the outer when it can, which slowly sends it down to Earth over 24 hours.

Space Monkey

Re:Both going at 7000m/s-1?

[Talaran]

Artemis is the outer satellite destined to go stationary (it's the relay/communications satellite), and SPOT is the inner, earth observing satellite (an optical multi-spectral remote sensing satellite, to be specific).

Artemis should have been stationary already, but when it was launched earlier this year, the Arianne 5 rocket it was launched on failed in the upper stage and didn't get it out far enough to achieve it's intended geostationary orbit. They've been using the on board thrusters to move it out into the intended position since then.

I'm surprised and impressed that they even attempted this given that Artemis is not in position, and that it worked. This bodes well for ESA's ENVISAT satellite, due to launch next year: Artemis will be relaying ENVISAT's data in a similar fashion.

Re:Both going at 7000m/s-1?

[The Raven]

All irrelevant. One satellite is in geostationary orbit, at about 38000km up. In other words, relative to the ground, it isn't moving at all. The 7000km/hr figure is for the low orbit satellite, which is orbiting quite fast. This ain't no record player... they are not orbiting at different speeds. Thus, the circumfrence of their orbit has little to do with the speed at which they orbit. I don't know the orbital equations, but I know that much.

The 'stationary' satellite and the low orbit satellite only communicate for short periods, in which the low orbit satellite uploads its accumulated data to the stationary one, which then relays it to the ground.

Communicating with low orbit satellites has always been a pain. You need to track them accurately as they zoom across the sky. This new technology lets the ground crew track the stationary satellite instead, saving them lots of effort, and probably reducing costs.

Raven

Re:Both going at 7000m/s-1?

[Anonymous Coward]

The SPOT satellite has most probably a highly inclined orbit (i.e. non aequatorial), maybe polar, because it is a mapping satellite. This means Artemis' and SPOT's speed vectors are almost perpendicular, which prevents any simple analysis like the above.

FP

[Anonymous Coward]

This time, surely, it is FIRST POST!!!!!! Oh, the horror.

Another use?

[Anonymous Coward]

Surely from what i have seen it could double up as an early warning sytem for aliens ;) As in an entire grid of laser tripwires accross the planet?

just and idea!

fp

[Anonymous Coward]

ownage

first multi speed LAN

[Anonymous Coward]

Man scietists just have to much time to spare

I can immagine the conversation now:
Joe:hey bob wana play lets set up a high speen LAN moving at sonic speeds?

Bob:Yeah joe and after that lets go get lunch.

First post btw.

Can you imagine...

[Anonymous Coward]

... a Beowulf cluster of these?

Thank you.

--Patrick Bateman, Esq.

Re:Can you imagine...

[Anonymous Coward]

...my cock tearing appeart you mothers ass while your sista is licking my ballz?

fp

[Anonymous Coward]

stream outta me erse (bitches)

Er..

[TA]

I think you got that wrong. Artemis is the relay satellite, SPOT4 is not.

Kick ass

[Anonymous Coward]

Lan parties in space? Hmmmm? I dig, I dig...

Just wait...

[Anonymous Coward]

Until they can point those lasers at the ground, too ;)

*sizzle*

Military Application

[arminh1974]

Now that's actually more scary than anything else. If a civil institution is capable of laser-linking satellites, I'd say it's pretty much a given that the military is perfectly capable and probably has been for years to deploy lasers for destructive purposes in earth orbit. Who knows what's meanwhile up there? And I thought Star Wars (SDI) has just been US-propaganda to speed up the USSR's economic meltdown...

Re:Military Application

[ZPO]

It's a whole different ballgame. For comms purposes in space you need microwatts/milliwatts. For comms purposes to ground (the article mentions establishing a link ground-space) the system probably uses a few watts.

To get a hard kill on an ICBM you'd probably need something on the order of: megawatts/gigawatts (???). You are talking about going from a semiconductor laser (not too different than a laser pointer) on a very sexy tracking platform to something that currently takes up 2 lab buildings not including the generators and capacitors and is probably good for a limited number of shots.

Also, notice that there is a 2-way beacon mode at the start of communications. This makes it simpler (note: I didn't say simple!) to establish 2-way comms. I just don't see anyone placing beacons on ICBMs. The IR signature of the exhaust plume is a pretty good indication, but that's about all you'll see.

Re:Military Application

[esonik]

Actually the important parameter is not bare power (Watts) but fluence=power/area (Watts/cm^2).This is important in this case because over the large distances you have enormous widening of the beam.
Second thing important is the temporal structure of your beam. It's a large difference whether you deposit 10 W continous wave or whether you have 10 W average power but concentrate that in very short pulses.
Taking both points into account you can reach with todays femtosecond pulse Lasers a peak fluence of many Terawatts/cm^2 (of course only for short times on very small spots). Btw. you can cram such a laser setup in 1 or 2 m^3 if you really want. That doesn't mean you can use it for SDI, but you can definitely burn holes with it (in the lab).

First

[Anonymous Coward]

aint I pleased

Just a thought!

[Pete (big-pete)]

Is it just me who wonders in amazement at the cynicism over the missile defence tests about whether it's possible to hit a missile travelling at great speed (GPS or no GPS) - and yet now everyone oohs and ahhs and has no problem with NASA aiming a laser at something moving at 7000 m/s... :)

-- Pete.

Re:Just a thought!

[DarenN]

Not NASA.

ESA == European Space Agency.
Yes, europeans can do stuff in space too!

Besides, aiming at something that you know the size, speed and direction of can be nowhere near as hard as hitting something as small as an ICBM that is being tracked from space. I think

Re:Just a thought!

[Pete (big-pete)]

Doh - my mistake, sorry about that...I'm a European as well...so even less excuse for such a mistake!

-- Pete.

Re:Just a thought!

[Dyolf Knip]

I thought that exact same thing. They spend billions on missile-based defense systems and as an afternoon exercise the ESA does the same job with a laser. Non-projectile weapons are obviously the way to go.

Strategic Intelligence

[Anonymous Coward]

I would put this into context with the latest European military goals. One of the major goals is independence from the US in strategic intelligence gathering. Real-time satelitte images that nobody can intercept are an important step in this direction.

First troll!

[Anonymous Coward]

First troll for Osama bin Lager!

Re:First Troll!

[Anonymous Coward]

The troll was made by AC, so how the fuck can you claim it faggot

Hmmm

[Anonymous Coward]

Just what we need - Satellites with friggen laser-beams attached to their heads

earth to satellite link

[dario_moreno]

however, it was demonstrated in the sixties
by concurrent US and Soviet teams (Tatarskii) that
a laser link (although very secure and
promising in terms of bw ) between an earth station and a satellite was not feasible
due to atmospheric turbulence. Maybe
things have evolved now...

Re:earth to satellite link

[Shortwave]

It appears that things have evolved significantly. Do a search on adaptive optics and all sorts of incredible stuff will come up. I would bet that adaptive optics combined with the lastest in signal processing could do alot barring the weather. I don't know. Niche application perhaps?

Re:earth to satellite link

[isorox]

Appently you can get satelistse that read your licence plate - optics are that good now!

What about Space Debris?

[shaunak]

Sure, you get the laser link up and running fine, transferring all your data, and suddenly a piece of space debris intercepts the path of the laser. So some amount of data is lost.
What kind of redundencies are employed to work around this problem?
Or isn't it a problem at all?

Re:What about Space Debris?

[T-Punkt]

This is no problem:
Every single low-level communication protocol for longer distances (i.e. more than 2m) I know of has a way to detect (and sometimes correct) nearly all kind of transmission errors. And every higher-level communication protocol (say, TCP/IP) knows how to deal with them (usually with retransmission).

(BTW: It's extremely unlikely that it will ever happen that some kind of space debris, a meteorite or another sattelite will ever come into the laser beam and interrupt it...)

Re:What about Space Debris?

[shaunak]

"BTW: It's extremely unlikely that it will ever happen that some kind of space debris, a meteorite or another sattelite will ever come into the laser beam and interrupt it..."

What do you base this statement upon?
Do you have any specific stats?
AFAIK communications sats are high up above the atmosphere. So even if small fragments from other sats/meteorites come along, they won't burn up (as they do, fortunately, for us).
And last I heard, there's quite a lot of debris up there to make the scenario I implied quite probable.

Re:What about Space Debris?

[T-Punkt]

Very simple: The number of fragmets larger than a few centemeters is know, IIRC it's about 10k, the vast majority of them in the lower orbits (~400km, i.e. the orbits of space shuttle and second or third stage burn-outs).
Considering the vast amount of space around the earth this is not much more than nothing.
And now do some maths (if you want). Let's estimate a laser beam of 1cm area, satellites 50000km apart, which makes 5km of "space".
the whole space between 800km and 31000 circular orbits is 4/3*pi*((31000+6000)-(800+6000))~2.1*10^14km of space. Let's assume 10000 fragmets are equally distributed in this space, wich means one fragment for 2.1*10^9km, which means for a given time the chance that a fragment is in the "beam array" is about 1:4200000000. (seing fragments as points here).

And this is a over simplefied calculation - first the "effective" laser beam is no cylinder, it's more like a cone and the base is the sensor area of the receiver. For a fragment to have an effect on the communication it has to cover (say) at least 50% of the sensor area (no idea how big that is) for at least half the time of a bit at 50*10^6 Bit/s this is 10ns - given the size and speed of the average fragment and considering the calculations above it's extremly unlikely that this will ever happen in the up to 5 periods per day of communication for 4 to 20 minutes between the two satellites.

wow

[gnudutch]

Now all they have to do is increase the intensity and they've beaten us to Strategic Defense Initiative.

HOLY MOTHER OF CANUCK!

[Anonymous Coward]

Now that is cool :)

auto262814@hushmail.com

I Can`t Help It

[Anonymous Coward]

fp

Slashbug

[Anonymous Coward]

The artical appears to be hit by a bug that makes it look like there are no comments, hence the number of FP-s

well, then

[Anonymous Coward]

this is not a uhm
no

Interesting...

[Anonymous Coward]

The post has been there for over an hour and no post yet. Do most slahsdotters have trouble digesting turkey ?

Seen from this side (Europe) of the pond (and from somebody who actually lived for 2 years in Toulouse,
and visited once the space installations, but that's off-topic) I find this rather interesting for inter communication betwen satellites.

Such a system allows global coverage with a few geostationnary satellites in a ring (say six or 8) which communicate with each other. You only need two hops between two opposite satellites because of the pesky obstacle called the earth in the middle (actually, now that I think a little about it, an odd number of regularly spaced satellites might be better to avoid said obstacle). Note that communication between
geostationary satellites is far easier since their relative position is fixed.

With this you cover most of the globe, except high latitudes and the distance to the satellite might be a problem for some applications (antenna size, emitter power required). So for the non-fixed/low altitude situations, you need lower altitude stallites which communicate with the geostationnary ones (hopping from one to the other depending on its position). This makes a lot of communication channels, however the advantages of optical links are the extremely high directivity which allows you to use the same channels (actually optical wavelengths) without risking interference. Of course this is this part of the communication which is tricky because of tracking.

This eliminates a lot of the base station system infrastructure (you still need one station to control the whole system, but that's unavoidable). I believe that a system like this will in the long term make satellite phones affordable. Iridium, etc, failed because of cost in my opinion, but that's exactly a case where a lower cost will make the demand explode
and turn it into a profitable business (perhaps even very profitable once you get the cost down to the point where many people can afford it).
I also prefer it very much to having the coutryside peppered with antennas for mobile phones, which does not prevent me from being
outside coverage when moutaineering, etc.

Oh, well, speleologists would still have problems, but that's their choice to remain hidden inside the earth :-)

Re:Interesting...

[Shortwave]

Good post. And I bet even the high lattitudes could be covered too if we just shoot it up to something in a Molniya orbit and then relay that to the constellation.

73,
dit dit

Re:Interesting...

[Anonymous Coward]

I did not mean otherwise, the low altitude satellites would be on high inclination orbits.

First Kut

[Anonymous Coward]

djjj jjjjjj jjjjjjj jjj jjjjjjj jjjj jjjjjj

Not geo-stationary

[ZigMonty]

31,000 km is not geo-stationary, 35,785 km is. I made the same mistake at first because they are so close. Also, it didn't say that the orbit was above the equator, which is crucial. You are still correct that the period would be very close to 24 hours as it is about the same size and velocity as a geo-stationary orbit.

So, yes i'm nit picking.

Now the question is: Why isn't it in Geo-stationary orbit? Am I missing something?

Re:Not geo-stationary

[Anonymous Coward]

it's 19 hours as they mention in the article

Laser alignment

[SomethingOrOther]

I work with free space lasers as part of my PhD and I can assure you they can be an absolute b*stard to align properley, even accross a small lab bench into a detector. Hats off to em!
I'd be interested to know what wavelength these devices operate on. (I'm assuming they are semiconductor devices as nothing else would be light enough to launch into space) Blue semicondutor lasers (with nitrogen doping) are becomming cheaper and cheaper and can carry more data (because of the shoter wavelength) per sec but may not be as reliable as "traditional" longer wavelengths.

A few months ago we tried rigging up a "laser ethernet" conection from our physics dept to our house (its line of sight). Only by making teh beam very divergent did we manage to get any sort of alingment, and that was on a clear day! It was nowhere near good enough for us to be able to use the universitys fat pipes from home!

Re:Laser alignment

[Hedon]

Operating wavelength is between 800 and 860 nanometer. Probably a GaAs laserdiode.

Re:Laser alignment

[isorox]

Really? I'm looking at laser systems for broadcasting the campus TV to different buildings. http://www.canon-europa.com/products/network_produ cts/canobeam came up on my search, the network version operates up to 622Mbps, upto 1000m [depending on weather], or 156MBps upto 2000m. It works at 785nm (+-15).

ESA is cool

[Anonymous Coward]

There's also an article on the Artemis satelite.
It was put in a too low orbit but fortunately it
carries two different experimental ion propulsion
systems. With the ion propulsion the satelite
it now being put into geostationary orbit, which
is quite a feat as the satelite has to travel
thousends of km's against Earth's gravity.

fp

[Anonymous Coward]

first post

Donkey luvin Man-Beast found at Slashdot!

[Anonymous Coward]

You read it here first!

first......

[Anonymous Coward]

....motherfucking tacosnotting post beotch!

gay

[Anonymous Coward]

gay homo

Ungh

[Anonymous Coward]

Ungh

Operating wavelength

[SomethingOrOther]

Operating wavelength is between 800 and 860 nanometer. Probably a GaAs laserdiode

I thought it might be.
Most space stuff tends to rely on older tried and trusted technology, rather than anything that might go wrong (Its not easy to fly into space to replace a blown diode!) That and I'm sure the bit-rate available over ~830nm is more than adiquate.

Craft shoter

[Anonymous Coward]

I would like to see the scoope of this thing

Fr!5t Psot!

[Anonymous Coward]

Wooo!

Tell it like it is!

Wingnut

hmmm

[Anonymous Coward]

nice one but isnt there alot of stuff out there to get in the way of the beam?

lasers create crop circles

[Anonymous Coward]

first post mozilla 0.9.6

Good luck - (explosion)

[Anonymous Coward]

I live in Toulouse - the AZF chemical factory exploded on sep 21 (terrorism?), killing 100, seriously injuring 2,000 and destroying 15,000 habitations + 1 hospital.

I don't think the ground station for satellites went unharmed, especially because it was not far from the chem factory.

Uninterceptible communications

[The Dodger]

Interesting side effect of this is that these communications can't be intercepted, unlike RF/microwave broadcasts.

D.

Re:Uninterceptible communications

[isorox]

Actually they can, just put a receiver in the beam :)

You'll notice it though, unless the receiver was small enough (a few cm's), and near the destination, to only get a small amount of the beam (which diverges by a lot at these distances). The intensity would be lowe rat the destination, but with a small enough bug it would be possible. The bug would have to be very sensitive though!

50mbps - nice

[Anonymous Coward]

50mbps is a great advance in speed, if i remember correctly, the spacestation MIR had just about 9600 bps data connection.

The optical transfer is a very interesting way to go for high bandwidth.

Using this instead of microwave?

[Compunerd]

Perhaps this could be a better solution for communicating between sites down on earth as well. Today's microwave solutions may be cheeper, but they're really speed limited...

Script kiddies are passe

[Ukab the Great]

Now 15 year-olds can launch DOS attacks with laser pointers.

NASA?

[ONU CS Geek]

Isn't NASA doing something to this effect, only using Cisco gear to help with the wireless link?

My girlfriend works at NASA as a Tech, and something I hear all the time is about their funding, and how it's really hard to get anything real done around there without a whole lot of BS. PHB's trying to get Win2K on P5-75's; and some other obsurd stuff to just make you question why we've cut their budge a lot.

Re:NASA?

[Anonymous Coward]

That is correct. Two thirds of your time at NASA is spent worrying about whether you will have funding next year and attending stupid meetings. I wish the government would just solidify the budget a bit more and maybe raise it to $30 billion up from the paltry $12-$14 billion it has now. Hell, the military gets a whopping $400 billion or more.

Cool

[Anonymous Coward]

Something as important as satellites should all be running open source software though. Is this satellite to satellite software open source?

Adaptive Optics?

[Shortwave]

Anyone know anything more about this? Could this be a way to get a link to and from the ground?

73,
dit dit

Just so you know

[_typo]

We (the Europeans) did put lasers on satelites but we're not pointing them at one another to chat. It's our new tactical warfare rig. Very cool. It can kill someone from orbit with pin-point acuracy. Compared to this the American Missile Shield is a just a neat toy.

So the sentence:

The link is running at 50Mbps and the two satellites are currently orbiting at 832km and 31000km respectively.

Is just code for:

The system is running at Full Power and the two satellites are currently orbiting above Washington and Moscow respectively.

Insert "Bad Guys Laughter" here...

Satelllite-to-Satellite AI Mind Transfers

[Mentifex]

It is called metempsychosis -- soul travel (of the psyche) from one place to another. If this astounding SlashDot report is true, then our lush, green planet Earth stands on the space-port doorstep of intelligent ethereal beings flitting about from satellite to satellite on a beam of laser light.

But what happens, Scottie, if you are beaming up an AI Laser-Mind and you miss the receiving satellite? Does the robot soul or consciousness sail off eternally into the far reaches of the universe?

And how will this satellite-to-satellite laser-beam technology be used more mundanely, before the arrival of Technological Singularity?

1st?

[Anonymous Coward]

1st?

Where's the first post

[jungle_ted]

Come on boys

http://www.mn-net.com/

[Anonymous Coward]

HTTP Web Server: Lotus Notes Exception - File does not exist
Error 404
http://www.mn-net.com/

That's amazing

[natsith]

Laser's that accurate must have many other applications.

sadf

[Anonymous Coward]

weeeeeee
fp
woot
woot
woot
w00t
!!HHahahahahaha

listening in

[Anonymous Coward]

How feasible is it to listen in on point to point laser transmissions like this - is it possible at all without subverting the original laserbeam ? maybe reading from point of origin (i.e. line of sight to signal originator?) ...

!gyggugiu

[Anonymous Coward]

broken?!

impressive...

[trellick]

Now THAT is what I call P2P communication!

if only mir was still around..

[Anonymous Coward]

russians vs the world... in quake via satellite laser!
on that topic, when are we gonna see paintball parks in space? rocketjumps...

Sounds really difficult

[Anonymous Coward]

That sounds like a difficult task to me, especially two satellite running at different orbit. With distance that well over 2000 km, a .1cm error could lead to few hundred meter different and the other end. I am not sure how they did it, since the satellites are not exactly stable objects in the space.

how's the burn hole here effort going?

[Erris]

Well, light does have less momentum and is easier to redirect at a distance than a BB is. Knowing where the object is does you no good if you can't put holes in it.

So, how much energy can you cram into a laser beam these days? Anyone lazed ionizing UV and soft Xrays yet? Imagine a nice sharp beam of gammas. Yikes, I'm vaporized.

Re:how's the burn hole here effort going?

[Anonymous Coward]

Yes.

Who cares about linear speed...

[javatips]

What amaze me with this kind of PR is that they always use large number to impress people.

The fact that the linear speed difference between the two satellites (from previous post, I assume that the 7000m/s is the speed difference between the two satellites) is not very important. What is important is the angular speed.

It is a lot easier to target an object moving at 100Km/h at a distance of 100 meters than to target the same object at a distance of 10 meters.

I've seen this before...

[El Camino SS]

...In science fiction. larry Niven wrote about using lasers to communicate with other ships out in the solar system via a series of sattelites that had "relatively fixed" position relative to the solar system. It was for his "Gil the ARM" series and others. And that was a while back.

Ver precise, and even better, incapable of intercepting transmissions. Good to see this coming to light. "Weeeeery eeenteresting."

Of course, when are we going to see this technology used to guide in laser guided bombs and missiles from sattelite? Or, do we already have it and we don't know about it?

Sat2Sat communications evolution

[Markonen]

It seems to me that this is just an incremental advance from older satellite-to-satellite communications systems.

Military satellite networks, for example MILSTAR have already implemented very narrow beam communications between satellites. This has been necessary to prevent interception or jamming of the signal.

The advances here probably relate mostly to greater-precision mechanics and more powerful CPUs. I don't know if the data rate mentioned is a big leap or not, but considering the fact that the MILSTAR network carries all the photographic and video intelligence gathered by NRO's Improved CRYSTAL satellites the MILSTAR bandwidth must be pretty impressive too...

Re:Sat2Sat communications evolution

[FlexAgain]

It seems to me that this is just an incremental advance from older satellite-to-satellite communications systems.

Military satellite networks, for example MILSTAR have already implemented very narrow beam communications between satellites. This has been necessary to prevent interception or jamming of the signal.

Hardly "just" an incremental advance, since beamwidth is effectively a function of wavelength, the beamwidth is going to be around 10000 times narrower for optical vs microwave communications. For an optical communications link, you have to use active tracking systems to keep the transmitter and reciever continuously aligned (with some sort of feedback). With RF systems, you would need some tracking for any long term communications, but you could base that purely on satellite ephemeris, a much simpler problem.

Re:Sat2Sat communications evolution

[blair1q]

> With RF systems, you would need some tracking for any long term communications, but you could base that purely on satellite ephemeris, a much simpler problem.

You'd start the beam search using ephemerides, but RF crosslinks do use signal-strength components for feedback-based antenna steering control.

You're dead right that getting it done with lasers is several orders of magnitude more cool.

This also has the potential to tack a few more zeroes onto the accuracy of orbital position determination. Interferometry could get you sub-nanometer resolution. I can't imagine why you'd want that, but I can imagine someone else can.

--Blair

has been done already?

[Anonymous Coward]

McDonnell Douglas (now part of Boeing) received a defense contract to do this exact thing in 1986 - That's right, 15 years ago. As far as I can discern, they actually accomplished the goal. I believe the technology was called "laser crosslink". Anyone know more? Is this junk classified like all the other good stuff?

Look, up in the sky!

[kr4jb]

It's a bird!
It's a plane!
Ow, that thing blinded me!

First?

[Anonymous Coward]

I had an interview with Lincoln Labs last month (www.ll.mit.edu) and the interviewer was the project manager for a similar project. He said that they were able to establish an optical link between two satilites last summer under a grant from DoD.
DoD generally doesn't release anything until its old news, but its interesting that ESA is trying this.
JPL has in the works a mission to link three (possibly more) small satilites together, preping the way for doing large apature astonomical work, using three seperated mirrors with the distances precisly calulated between them. Something similar to the Keck, but up in space.