# Interstellar Communication



## Vertigo (Aug 12, 2011)

This is something I've been wondering about recently.

Given our current knowledge of physics (ie no subspace, hyperspace etc.) how could we go about generating a signal strong enough to be detected across interstellar space and thereby be used for communication.

I am not talking about a tight beam directed at a particular target, though that would be interesting as well. Rather I am interested in a broadcast signal that could be detected anywhere, or at least anywhere not in the shadow of any other objects.

To give an idea of the scale of the problem, the largest nuclear bomb ever exploded was 50 megatons. It was originally going to be 100 megatons, so if we assumed 100 megatons and that it was exploded in space then, from what I have been able to find out, that blast could only be detected out to about 0.1 light years away. Not very far 

It seems that with an Arecebo sized dish you would struggle to detect radio leakage from Earth even as close as the extremities of the solar system. This is the most likely reason SETI has never detected anything; for us to detect an extra terrestrial signal it would *have* to be in a tight beam directed exactly in our direction.

Here's a couple of the links that I have based my comments on:
http://www.computing.edu.au/~bvk/astronomy/HET608/essay/ talks about the range of detection of electromagnetic waves.
http://docs.google.com/viewer?a=v&q=cache:Z8dgKrV3tF8J:www.dtic.mil/cgi-bin/GetTRDoc%3FLocation%3DU2%26doc%3DGetTRDoc.pdf%26AD%3DAD0607788+electromagnetic+detection+range+in+space&hl=en&gl=uk&pid=bl&srcid=ADGEESjzMzoKK3jJL6P-kJgif-WYlI6SCHE0ScNnGwSXjEG5iZrRDoBo_MoTPCj2IDs61ytWHt-awDOOXF3jrnCNnmFrm3LruBCHgXFsGnxvlYDaqSV81ckA_co1NZ8yoZ-Kzsd_EZaa&sig=AHIEtbQKBColc_ZuhbgzVph-VCXIokpCdg This one is about the detection range of a nuclear explosion in space.

So it would seem that even lightspeed communication across interstellar distances could be problematical.

Anyone have any thoughts?


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## chrispenycate (Aug 12, 2011)

A hydrogen bomb is basically white noise, and any star is producing hundreds of times that energy _per second_; hardly conducive for easy recognition. If the energy could be tuned into a single frequency burst -- but the only technology that could even give a hope of that would be pumped laser, and that's more or less impossible to render omnidirectional. Besides, modulating the beam to transmit any more information than "ouch" would be very complicated. 

Vacuum state electronics -- an ultra-high-power reflex klystron as in the beginning of radar? Plenty of top quality vacuum available.

Or how about gravity waves? Two good sized lumps of neutronium if a very close orbit around each other, producing sine waves (all, right, it's plane wave propagation, basically a disc, rather than true omnidirectional, but if you aligned it with the Milky Way, you shouldn't miss much) recogniseable to any tuned gravity detector, and frequency modulated by modifying the electrostatic charge between them...

Or how about really long wave radio, with transmitting and receiving antennae the length of planetary orbits, using frequencies that rarely occur in nature?


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## Metryq (Aug 12, 2011)

chrispenycate said:


> Or how about really long wave radio, with transmitting and receiving antennae the length of planetary orbits, using frequencies that rarely occur in nature?



Out of curiosity, do we know that such frequencies _do not_ occur naturally? The first quasar reception created quite a storm of excitement. ("This can't be natural!") We now have the technology to place space probes for such a very long base line. After all the set up, it would be a real bummer if we found out the universe is noisy at such frequencies.


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## Vertigo (Aug 13, 2011)

Ooo I like the gravity waves one and it's also still thought that they might even be faster than light.

What I was thinking of was an idea for a race of space nomads. Long lived and all exploring the galaxy in colony fleets; their spaceships are now effectively their home worlds. Taking centuries to travel between stars. And I was wondering how they would communicate between colonies (other than slowly of course) when you don't actually know where anyone else is at any time.

I have now been thinking that you could leave a network of automated relay stations which would commuicate with each other by some sort of tight beam like a laser (I was reading that apparently you can get more light years to your joule with shorter wavelengths) then individual colonies would log onto a relay station much like mobile phones do. Then regular short bursts of data would allow you and the station to keep track of one another. Then messages could be passed through this network in once again much the same way as mobile telephones.

Oh and Chris I had been thinking along the lines of tuned emissions from the explosion or maybe using those emissions as carrier waves of some sort. But I was pretty skeptical and then when I found the equations for detection range I was surprised just how short it was looking like being.


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## mosaix (Aug 13, 2011)

I'd be interested to know if what I was told the other day is correct.

Apparently the digital television signal now being broadcast in the UK is much weaker than the old analogue signal, so the period during which extra terrestrials could detect British TV broadcasts is now over.

Of course, this would also apply to our ability to detect alien broadcasts: there is a limited time in which this is possible, assuming they bother with analogue at all and don't go straight to digital.

Anyway, is the digital signal weaker than the old analogue signal?


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## Vertigo (Aug 13, 2011)

I don't think it has to be fundamentally weaker but I think it can and is broadcast at a lower level. You only have two states to transmit not an analogue level. However I may be wrong on this. But...

It seems no aliens would have detected us anyway; according to stuff I read whilst looking into this (check out the first link above and scroll down to figure 3) I found a paper that shows that the detection range of FM and UHF tv transmission is considerably less than one light year.


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## RJM Corbet (Aug 13, 2011)

I was also going to suggest gravity, but thought I'd sound stupid ...


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## Nik (Aug 13, 2011)

IIRC, apart from the 'zap' that the radio-telescope tossed towards Andromeda, the USSR's 'woodpecker' early-warning radar may be the easiest to detect. As it was intended to work in presence of *lots* of noise, the infamous 'woodpecker' signal was easy to detect. As the Earth turned, its beam scanned a lot of sky...

IIRC, there is a crucial difference between the analogue and digital signals beyond transmission power: The digital signals are compressed to such an extent that, if degraded, they become difficult to distinguish from noise...

Uh, IMHO, if you wanted to send signals between solar systems, you could do worse than using large lasers. They're monochromatic, so easy to filter from background light. You may have to fly them at least a dozen AUs out from star to allow a distant telescope to distinguish them without difficulty. With minimal gravitational disturbance, you could fly several laser modules in formation rather than have one brute. For power, mine a Kuiper-belt object for fusion fuel...

If big lasers is too likely a tech to be weaponised, a micro-wave phased array composed of hundreds of identical, free-flying modules spread across thousands of kilometres would do nicely. That would have the advantage that it could be pointed electronically, swung in an instant to point anywhere within +/-45 degree solid angle. It could also take advantage of both the low ambient temperature and, as mentioned above, the 'free' vacuum...


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## Vertigo (Aug 13, 2011)

Yes that was exactly the way I've started thinking with a network of laser relay stations similar to mobile phone base stations. Don't forget the problem with my scenario is that you don't know where anyone else is; your signal might not reach it's target for decades or even centuries by which time the person you're trying to talk to has long since moved on.

Oh and Nik that same first article in my OP did talk about military radar being possibly the longest ranged signal but reckoned the duration that it would ever transmit at a single point in space would be so small that the chances of your listeners pointing back at you at exactly that time are very very small. Apparently SETI does look for exactly that kind of signal but...

*



leaked signals- These would be intercepted signals produced by high power military or range finding radar. We would have to be extraordinarily lucky to detect, recognize and confirm a high power radar signal of extraterrestrial origin.
		
Click to expand...

*


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## Metryq (Aug 13, 2011)

Vertigo said:


> Ooo I like the gravity waves one and it's also still thought that they might even be faster than light.



_Gravity_ is faster than light, but gravity waves are light speed. (*See Fig. 1*.)


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## Vertigo (Aug 13, 2011)

Ah, nice illustration Metryq that's much clearer. And it's not really a problem for my scenario everything is based on ong time spans; both journeys and communications taking decades to centuries. Hence the idea that you cannot know where everyone is/will be at any given time.

So it struck me that to communicate they would need omnidirectional broadcasting but now I think a laser linked network would make much more sense.


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## chrispenycate (Aug 13, 2011)

Trouble with tight beam (and good plane-wave lasers in vacuum the principal defocusing influences are going to be variation in matter density, and gravitational fields, so as long as you don't try to transmit through any intermediate systems, they should really not spread much at all) is that you have to know exactly where to aim. If the ship transmits continuously to the relay station (whose position is predictable for millennia), when it is five light years distant and the station wants to send a signal back, it can only know where you were five years ago, not where you're going to be in five years time, when the signal gets to you.

Mobile phones don't have this problem; nobody moves fast enough that delays add up to anything that prevents continuous feedback, and anyway, they're non-directional.

If your beam has spread to a couple of square kilometres by the time it arrives, it only requires a fraction of a second of arc - a slightly higher density of interstellar gas, an unpredicted gravity field, even radiation pressure - to miss.

I suppose you could have a lightweight mobile detector flying alongside the main ship, and a near continuous data stream so it can put itself permanently in the centre of the incoming beam...


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## Vertigo (Aug 13, 2011)

I figured that you would literally send small packets of data on a daily basis stating where you are and your planned course and also feeding back any error in the beam target (they would do likewise for your beam). Should you deviate from that planned course you would have to accept that you would miss all comms until notification of your change reached the relay station you are logged onto. However I would think this would be quite rare. Working on these timescales they won't exactly be zipping around the galaxy on impulse. 

Also I envisage a number of piggy back drive systems (like early steam ships that still had sails as well). One of these would be a bussard ramjet with a magnetic scoop. One thing I read about these is that they could be made much more efficient by "seeding" your route with fuel for you to scoop up. Not essential but more efficient and with the extra fuel faster too. This seeding would take decades with something like a magnetic rail gun, which is fine; having spent decades or centuries on a journey you are not exactly going to dash off a couple of days later. It would also mean you would have to have a very pressing need to change course on route.

See section on pre-seeded trajectory about two thirds down the page: http://en.wikipedia.org/wiki/Bussard_ramjet

Obviously you are correct that any intervening matter (like a dust cloud) would be a major problem but I also anticipate a lot of redundancy in the system. Afterall I'm looking at having automated relay stations that will need to function without service for centuries or even thousands of years. You couldn't have one station breakdown remove your only connection to the network so I would imagine you would stay logged into several stations at a time.

Another thing on the accuracy is that I would envisage each "colony" being a large fleet of habitats. Each colony is essentially a travelling distributed world with millions possibly billions of inhabitants. Therefore the fleet as a whole would cover a significantly large area of space which should handle any drift in the beam accuracy.


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## Metryq (Aug 13, 2011)

This whole thing reminds me of the longitude problem. One of the silly solutions involved imposing a man-made "grid" onto the globe in the form of floating barges to send up signals at regular intervals. Aside from the problem of anchoring and supplying the vast number of barges, the idea was about as practical as running a grid of string over the entire surface of the Earth. 

John Harrison's marine chronometer was the practical solution, although we did eventually form a grid with LORAN and GPS.

The relay idea is as old as communication itself—from relay runners and pony express to smoke signals and heliograph. Many analog and digital communication systems use relays to boost the signal, or bounce a signal over the horizon.

The cell phone analogy, however, is not apt for interstellar communication. Cell phones use lower power transmitters to save power on the handsets. The cell system also allows the same frequencies to be used over and over again. 

Computer networks use "smart" and "dumb" signal routing. A dumb router simply repeats all incoming information to everyone, while a smart router delivers packets of data to only the intended recipient. Smart routing would not work on an interstellar scale because it would dramatically increase the time needed for signaling. The problem with dumb routing on the interstellar scale is that once the civilization grew large enough, they'd either run out of frequencies, or relay stations would be overwhelmed by the amount of data they had to handle. And when does a signal stop? Unless there's some way to determine that a message has reached its target, the relay system would become runaway feedback like a PA system squealing. 

Somewhere there is an interstellar Harrison who will see a "simple" solution.


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## RJM Corbet (Aug 13, 2011)

I know this is slightly off the line of what Vertigo is talking about here but something I've wondered about is that one particle anywhere in the universe knows what another particle is doing. Simplified: if a certain spin is assigned to a certain particle, another particle will automatically have a different spin, no matter where it is?

Quantum entanglement?

Not limited by light-speed? 

But of course any method of checking what the other particle is doing, will be limited by the speed of the measuring instrument: ie light speed max.


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## Vertigo (Aug 13, 2011)

Well Metryq, I've considered most of those (though that dosen't mean I've solved them )

With communications taking decades at best, I don't imagine you would be sending daily letters to your mate on the other side of the galaxy. I was thinking more along the lines of: we are about to depart system X here's a summary of all we discovered whilst we were here. We're off to system Y now and expect to get there at such and such a time. The key thing here is time, I think. With the communications lag I would expect things to be measured in messages per decade rather messages per second.

A particular packet would get sent repeatedly, maybe once a decade, until the relay station recieves the acknowledgement that it has been received. If it does not receive an acknowledgement in the expected time then it would stop sending it and instead send a broadcast message out through the network letting everyone know that there might be a problem with station X or colony Y. Of course messages would get duplicated but that's not a problem; if a station receives a message that it has already relayed on, it will simply ignore it. So eventually each message would drop out of the system as everyone acknowleges they have received it.

Most messaging would be broadcast for everyone. As I said above they would mostly be of the form of an update; here's what we discovered/researched/invented since we last broadcast.

I also imagine the race would split into two; settlers and travellers. A colony might discover a new compatible system and decide to stay and become settlers, others would continue. I see them has having developed almost indefinite longevity and under those conditions I suspect the only motivation for continuing living for thousands of years would be a thirst for knowledge driving them on to explore. The settlers would form convenient hubs where all messages could be held indefinitely and used to update anyone who has missed anything.

A colony would not actually log off one relay station until it has started to receive messages from the new station and the old station would continue to pass on messages to the colony until it receives confirmation that the new station has taken over.

Note that the stations themselves would all be set up in deep space to avoid the problem of nearby star systems shadowing too much of the coverage.


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## Vertigo (Aug 13, 2011)

RJM, your post came in whilst I was typing that last tome 

I have wondered about the ideas of quantum entanglement but I'm not sure it works across interstellar distances in that way. At least not enough for me to accept it might become a future ftl means of communication. However it is certainly an area of physics that might (will?) produce some very interesting technologies in the future.


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## RJM Corbet (Aug 13, 2011)

Vertigo said:


> RJM, your post came in whilst I was typing that last tome
> 
> I have wondered about the ideas of quantum entanglement but I'm not sure it works across interstellar distances in that way. At least not enough for me to accept it might become a future ftl means of communication. However it is certainly an area of physics that might (will?) produce some very interesting technologies in the future.



I think it's also a textbook case of the observer influencing the outcome of the experiment.

It's like music. Western music takes a certain tone and calls it, say 'C' and from there all the other notes fall into a scale, no matter where in the universe they happen.

Oriental scales are different, but equally valid, etc. The physics model works, but another may work just as well, to order things into a pattern that can then be controlled and used and applied. So it becomes where you look at it from, in the end.


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## Vertigo (Aug 13, 2011)

As I understand it quantum entanglement allows super dense compression of data but does not allow ftl transmission, as it works a bit like encryption that requires a key. In order extract the data from your quantum entanglement you need to correlate measurements taken at both ends of the communication and that requires some data to be sent "conventionally", hence no ftl.



> the information encoded in entanglement is only extractable when you look at correlations between measurements on both the entangled systems. So to access that correlation information, you would need communication anyway, and that communication could not be FTL. If you only look at either system, but not the other, then you need no such communication, but you also can extract no information from the entanglement.


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## Nik (Aug 13, 2011)

Uh, I can't follow the math on that link --My browser didn't help, either-- but, IIRC, the work by Flandern & Co that suggested that gravity had a speed in excess of 'c' didn't survive NASA's 'Gravity Probe B' mission. Note that article hasn't been updated since ~2002, and there's a strange lack of links. Also, while NASA were crunchin' the numbers, the Lunar ranging people got a better value for frame dragging that matched Relativity predictions...


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## paranoid marvin (Aug 13, 2011)

As far as interstellar communication is involved, then on the technology scale we're still at the banging-two-rocks-together stage; we have a long way to go before effective communication with other planets - let alone other solar systems or galaxies.

The question at this stage of our extra-terrestrial development - when we are without adequate defences against even a modrately sized lump of rock -  should we even be attempting to contact other worlds?


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## Metryq (Aug 13, 2011)

Nik said:


> IIRC, the work by Flandern & Co that suggested that gravity had a speed in excess of 'c' didn't survive NASA's 'Gravity Probe B' mission. Note that article hasn't been updated since ~2002



Van Flandern died in 2009, so you'll have to look for any continuing work elsewhere. There are many physicists who question various aspects of orthodoxy—some question work all the way back to James Clerk Maxwell. I'm just an armchair fan, but if I understand the work of Van Flandern and others, Einsteinian Relativity has not been "proven" correct (no theory ever is); it simply has not been falsified. Then again, Lorentzian Relativity dovetails with everything to date, as well. Yet almost every source one finds seems to suggest that ER has swept away all other models before it. I would honestly like to read which tests lead to this conclusion. I'm not championing a particular model, I just wade in a little deeper than John Q. Public who is essentially told, "This science is settled. Trust us, because the explanations are too complicated."

Lastly, measuring the speed of gravity was not one of Gravity Probe B's objectives. (As noted in an above post, one should not confuse the force of gravity with gravity waves.)


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## Metryq (Aug 13, 2011)

paranoid marvin said:


> The question at this stage of our extra-terrestrial development - when we are without adequate defences against even a modrately sized lump of rock -  should we even be attempting to contact other worlds?



That reminds me of the HITCH-HIKER'S series. What was it Dent said that piqued two particularly hostile races into battle—"I'm having a bad day," or something like that? Like laughter on Barsoom, maybe we should be tall enough to see over the edge of the bar before grabbing a stool.

"Greetings from Earth!" might translate into...


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## RJM Corbet (Aug 14, 2011)

Vertigo said:


> As I understand it quantum entanglement allows super dense compression of data but does not allow ftl transmission, as it works a bit like encryption that requires a key. In order extract the data from your quantum entanglement you need to correlate measurements taken at both ends of the communication and that requires some data to be sent "conventionally", hence no ftl.



It sounds as if computer terminology has adopted 'quantum entanglement' into it's vocab with a slightly different meaning than it has in quantum physics?



Metryq said:


> Van Flandern died in 2009, so you'll have to look for any continuing work elsewhere. There are many physicists who question various aspects of orthodoxy—some question work all the way back to James Clerk Maxwell. I'm just an armchair fan, but if I understand the work of Van Flandern and others, Einsteinian Relativity has not been "proven" correct (no theory ever is); it simply has not been falsified. Then again, Lorentzian Relativity dovetails with everything to date, as well. Yet almost every source one finds seems to suggest that ER has swept away all other models before it. I would honestly like to read which tests lead to this conclusion. I'm not championing a particular model, I just wade in a little deeper than John Q. Public who is essentially told, "This science is settled. Trust us, because the explanations are too complicated." ...



That's more or less the point I tried to make in my music analogy.

Einstein relativity may be right.

But someone else may come up with a different pattern of reality that is quite different, but also right, only most people might not be able to 'hear' it because it sounds nothing like 'music' to them, so they won't even be able to listen to it?

In short, I believe that an advanced civilization will be using what we regard as purely mental energies to communicate and to get things done, in a way we cannot begin to conceive of who, as Marvin observes, are still banging rocks to make fire, compared to them ...


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## Metryq (Aug 14, 2011)

RJM Corbet said:


> In short, I believe that an advanced civilization will be using what we regard as purely mental energies to communicate and to get things done, in a way we cannot begin to conceive



Wow, what a collision of concepts. The Krell in _Forbidden Planet_ used a mind-controlled machine to project energy and mass, so theirs was not a purely mental energy. For that, one must turn to Arthur C. Clarke's "Overmind" in _Childhood's End_ or the aliens of _2001: A Space Odyssey_. (There's also the Data Integrating Thought Entity and Haruhi herself in _The Melancholy of Haruhi Suzumiya_.) And one might argue that the telepathic twins in Robert Heinlein's _Time For The Stars_ are symbolic of quantum entangled pairs. Actually, the Bartlett brothers are simply Bartlett pairs! <rimshot>.


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## Vertigo (Aug 14, 2011)

RJM Corbet said:


> It sounds as if computer terminology has adopted 'quantum entanglement' into it's vocab with a slightly different meaning than it has in quantum physics?


 
No not at all RJM, data compression is merely one possible application of quantum entanglement as each "bit" can have three states not two as well an immense potential bandwidth. The FTL stuff is purely to do with the physics. Yes, the actual information communicated using quantum entanglement may be FTL but in order to interpret and make any sense of that information you have to compare readings taken at either end of the communication link and that information would have to be communicated by conventional means. The stuff in my post about encryption keys was merely an analogy.


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## RJM Corbet (Aug 14, 2011)

Vertigo said:


> No not at all RJM, data compression is merely one possible application of quantum entanglement as each "bit" can have three states not two as well an immense potential bandwidth. The FTL stuff is purely to do with the physics. Yes, the actual information communicated using quantum entanglement may be FTL but in order to interpret and make any sense of that information you have to compare readings taken at either end of the communication link and that information would have to be communicated by conventional means. The stuff in my post about encryption keys was merely an analogy.



Ok. Thanks Vertigo ...


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## chrispenycate (Aug 14, 2011)

Let us suppose that we have the most efficient reaction drive possible. All the reaction mass is converted into photons, and emitted as a coherent, collimated beam - yes, that's right, like a laser beam. Now, you want to be careful with that beam; even at a thousanth of a gee of acceleration it contains enough energy to vaporise a small moon, and if it hit any of the structures needed for your relay station, it could be catastrophic. So you aim towards a relay station twenty light years away, and you modulate the beam. All the data from the ship, births, marriages and deaths, scientific theories and the results of the experiments to test them (you don't expect them to just sit down and enjoy the ride for a couple of centuries, do you? This is a mobile city, a living community, with industries, arts, politics and other crimes, and scientific research), the latest episodes of the soap opera translated into the archaic language of the launching as the different ships will no longer speak the same language.

High error correction, and multiple copies; navigation will mean some connection is lost, but this is optimised for power, not directivity; the beam will be wide as the orbit of Mars when it arrives.

The relay stations will have to be big, and massive. Even a few gigawatts of radiation pressure is going to spoil the predictability of their position. So, since it's going to take a long time to build them, and once you've got the Von Neumann tugs hauling in mass from all over the system it's hardly worth stopping them, a relatively large population stays behind, inhabiting the 'fixed' station, and building a new mobile installation: a ship. Sure, it takes them a century or two; who's in a hurry? Then the colony splits once again, with all the knowledge, original and arrived from all the ships in the interim, genepools, every improvement that can be invented in the time...

And communication is continuous, so if one ship hits a space boojum all the information up until then will ultimately be distributed to all the other ships and stations, and snark hunting can commence.


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## Vertigo (Aug 15, 2011)

Exactly my thoughts Chrispy, I think it makes a rather nice scenario  And you're absolutely right about time, I Think when each journey takes so long I'd imagine any stop over at a system would probably be at least a century whilst they study it, collect fuel for the next journey, maybe seed that fuel along the next flight path and so on. Also the content of the communication would be exactly the kind of thing you describe. 

However, massive or not, I really would like the relay stations to be automated, it would be a thankless task manning one for centuries. Also thinking of stations whose position would remain stable; how about on planets around brown dwarfs?


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## chrispenycate (Aug 15, 2011)

If you left a few hundred behind to maintain the station then yes, it would be thankless. But in a century or so it would be child's play to double the ship's population, and leave behind a thriving, dynamic colony who would, in the fullness of time, build a new proud ship (or a series of them), a seed that was an essential part of the culture's expansion. After all, to a transit generation there is very little difference between travel and static.

Planets would remove the radiation pressure problem, yes, but I was thinking of being further out from the star than that, to give maximum parallax; in their equivalent of the Oort cloud. A brown dwarf? Still producing enough radiation to be annoying (unless it's blue lasers) while not producing enough solar energy to be interesting (which, as the ships obviously have some highly efficient power generation system, might well not be a problem).

Now I'm elbowing in on your universe, aren't I? Oh, well, at least it's not hijacking.


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## Vertigo (Aug 15, 2011)

chrispenycate said:


> Now I'm elbowing in on your universe, aren't I? Oh, well, at least it's not hijacking.


 
Absolutely not Chrispy, I love to build on the universe and the more believable the more I enjoy it.

I suppose my problem is that any one station is going to want to be in action for millienia and whilst you are right; if they are living in a habitat then it shouldn't make much difference whether they are static or travelling they would still be in a tiny community separate from the fleet of habitats that they came from. I had imagined the expansion of their culture happening more along the lines of periodically building new habitats as system stopovers and when the fleet becomes too unwieldy or their is a division of opinion where to go next that they would divide and go separate ways.

My concern about placing stations near any system was that the system itself would shadow a large part of space but I guess with the timescales involved it would be no problem to re-transmit maybe three or four times per orbit which should give full coverage. The problem there is not really the transmission which could be timed appropriately but the reception at the other end which might be occluded by its own system. I must admit I hadn't considered the drift from radiation "winds" and so hadn't originally conisdered anything that massive. As far as energy goes I suppose there is no reason for the station not to have their own Bussard ramjet just "ticking over" as they orbit though I'm not sure the relative velocities of the station and the matter it would be passing through would be enough for one to operate.


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