Question on the obscure matter of a terraformed moon's ocean

[Junghalli]

The moon is .0123 Earth masses so keep in mind if you do spin it up the lunar oceans will have huge tides, due to Earth's gravity at the moon being much stronger than the moon's gravity at Earth.

[loomer]

Time for a new question, which didn't seem to merit its own topic!

Space elevators are a viable concept in this setting and are routinely built on major settlements because of their huge benefits. Earth, as the centre of human civilization on paper and in the Sol system (though other space systems tend to have their own 'capitol' worlds - normally the world most suited to human life or with the greatest mineral resources), has had one for probably four centuries at this point and requires vast amounts of goods to be shipped in and out weekly.

Would it be feasible to have more than one space elevator active on Earth, assuming no issues with satellite collision, based around the equatorial belt for weather stability? How many would it take before getting risky? Two? More than three? Logic says to me, in my own half-scientific manner, that a properly stabilized space elevator shouldn't have any difficulty with sharing its 'track' with plenty of others, so long as there is sufficient distance between each end platform to avoid gravitational trouble.

[Korvan]

About the original tides question, while at first glance, it would seem the moon would have huge tides due to a combination of the large effect of the earth along with the reduced gravitational pull from the moon itself. However, since the moon keeps the same face pointed at the earth, these large tides would essentially be static. This effect would have to be considered when determining where the actual coastlines will end up, but after that you could consider the moon to have no tides at all.

It does get a bit more complicated though. The moon travels in a slightly elliptical orbit and the varying distance between the earth and moon would affect the tides. There would also be solar tides to consider as well. The math involved in all that frankly scares me a bit so I don't have a good answer as to what the overall effect would be. As a quick guess, I'd say the solar tides would be 6 times the magnitude as solar tides on earth. Apparently the solar tides on earth have about 1/2 the effect of the lunar tides so I'd say tides on the moon would be about 3 times as "high" as tides on the earth, but the tides would occur over a much longer time frame (about 2 weeks between high and low tides).

[Gil Hamilton]

Question, Starglider. Can you have an AI with a pre-optimized system? Like have an AI or smart computer with the SOLE purpose of designing and optimizing hardware and software routines for AIs being constructed. That way, the AI being implemented is already running full steam on the hardware it has available and doesn't have room to improve itself.

[Buritot]

Time for a new question, which didn't seem to merit its own topic!
<...>
Would it be feasible to have more than one space elevator active on Earth, assuming no issues with satellite collision, based around the equatorial belt for weather stability? How many would it take before getting risky? Two? More than three? Logic says to me, in my own half-scientific manner, that a properly stabilized space elevator shouldn't have any difficulty with sharing its 'track' with plenty of others, so long as there is sufficient distance between each end platform to avoid gravitational trouble.

I'm by no means an expert on such things, but my mind is always spinning.
The elevators would need an appropriate mass versus distance ration as to not influence each other to much. You could probably have thousands of them next to each other as long as they don't differ to much on mass.
Furthermore I suspect space elevators are not inherently stable structures. I suppose there is noticeable drag in the upper echelons of the atmosphere. Essentially earth is rotating faster than its air at least in thermosphere and exosphere levels.

The moon as a gravitational impact ought to be taken into account as well. Imagine for example a wheel with coins stringed to it. Spin the wheel. Now place a sufficiently strong magnet at a few centimetres out of the coins orbit. If you spin the wheel slow enough or have a rather strong magnet you will notice a pull while the coins move towards the magnet and a drag moving away. So you coins will have less distance to each other the closer they get to the magnet.
The same applies to the moon and its gravitational pull. This would probably the limiting factor in the amount of space elevators you could employ.

This would also generate an interesting movement pattern of your space elevator. It wouldn't stay at its place on the firmament but wobble due to the inclination of the moon's orbit.

On the naming patterns... after 500 years there ought to be a few changes, so I sincerely hope Earth and earth (ground) are different words, as well as moon (satellite) and moon (Earth). I suppose the same applies to branches of service.

[loomer]

At this point, Buritot, Earth's moon is referred to either as Luna or (following the standard system used for everywhere else, since other systems aren't 'special' in that they don't have millenia of human history. The worlds do end up with individual names, though.) Sol-Earth-A, with Cruithne being Earth-B, and the other moonlet Earth-C. Strictly speaking the name code is S(A1)-C-A for the Moon (A1 is the official, widespread term for Sol within the human territories. This works based on orbital order, of course, with the C referring to the whole '3rd rock' deal.)

Generally, the term Earth no longer refers to 'ground'. Instead, the word soil is used for Earthmovers (so they end up soilmovers or groundmovers) and the like, or just Ground in general. It now refers almost exclusively to the planet - with the main exception being the billions of snobby bastards living on Earth itself, who still call the ground Earth. Right of origination, and whatnot.

At this stage, Earth is home to around fifteen billion people, and is heavily reliant on synthetic proteins, processed algae, and food shot down from the terraformed Moon and the countless hydroponics stations in orbit. The rich live in apartments rarely bigger than those of the middle class of other worlds, and the middle class often have small flats instead - the reason for this is simple. Earth is very expensive due to the cost of shipping the food about and the cost of land in the cities.

Earth is actually a fairly irrelevant body in terms of manufacturing or industry, but it is an incredibly powerful economic and political force in the Sol system and also has a high degree of 'pride' associated with living or visiting, as well as religious significance to many groups that have spread through the stars (the Islamic populations of other worlds find it sometimes very difficult to face Mecca, depending on time of year and day, both local and Solar, for example). It maintains nations, though now they are generally in blocs - the North American Union, the European Union, a reformed Soviet Bloc, the United Middle Eastern Coalition, and so forth. Wars are only rarely fought on the world itself due to the exceptionally strong presence of the UN - a heavily militarized presence.

In fact, the vast majority of wars now take place in freshly colonized settlements as proxy wars between continental groups - on that note, most worlds will be colonized primarily by one superpower (for instance, Mars was colonized by the Russians and remains almost exclusively a USSR territory) but some end up with multiple colonizing groups, normally on different continents - and these worlds also tend to have a realistic range of biomes, with some resembling Earth thanks to ideal conditions (one world in Alpha Centauri is at the right distance to have closely matching temperatures and seasonal variations (very close axial tilt) despite the three suns. It also has nearly identical gravity and size, and almost as much water, and the atmosphere was very close when man first arrived, ands took virtually no tweaking.) and others being inhospitable volcanic wastelands with vast tracts of molten slag deserts or frigid balls of ice (with its own biomes beneath the surface), based on closeness to the sun(s) or other heat sources or bodies, complete with rough ecologies (instead of detailing thousands of species, I instead create a 'generic' form for that world to fill a niche. On Earth, for predatorial ambushers, we have the big tigers, pumas, even lynxes and the like. My system would just have 'ambushing, jungle/swamp carnivores) as a general thing, with elaboration as needed.)

[Buritot]

Well, that's a very interesting setting you have there. Two questions though:

1. ) What is the usual mode of transportation?
To embellish on that, how long is the slowest and fastest crossing of interplanetary as well as interstellar space? You already mentioned mass drivers for material transportation, which leaves you with the danger of intercepting pirates. Is there FTL travel or are you merely close to the speed of light between star systems?

2. ) What is your take on alien life?
2.a ) You just mentioned generic animals and plants which will be further expanded upon as necessary. Are these stemming from large scale genetic engineering or naturally evolved? Both have their advantages and disadvantages. Processing and digesting life which evolved completely different from A1-ian life might be easy, difficult, hard or outright impossible. There are no means of comparison IRL so it's up to you.
2.b ) Sentient life. Did sapiency and sentience evolve separately and are these Sophonts in contact with each other or humans? If so, you can integrate their technological and cultural development in your story. If not - you already have AGI which in turn (except for uploaded minds) would be the most bizarre minds known to man.

To clarify your official terminology:
S(A1)-C-A is Luna. Broken up:
S... Solar System (classification level 1)
(A1)... Our solar system, others would be A2, B4, W359, added as needed (classification level 2, designation)
C... Third main orbiting body, Mars would be logically D while Venus would be B (classification level 3)
A... Suborbiting body, being Luna, or for Mars A & B for Phobos and Deimos

You will run into problems with that at least at the orbiting bodies of gas giants, which can number quite high.

As for your population... why do you have so little? I was under the impression of Earth being close to Curuscant levels. 15 Billion? Unless you mean 15x10^12 with that, 15 billion won't be able to restrict middle-class appartments (200 m² / 2000+ ft²) for the rich. As for the 15x10^12 approach... you would essentially need to import air with this many people.
Maybe. I don't know the numbers.

[loomer]

Well, that's a very interesting setting you have there. Two questions though:

1. ) What is the usual mode of transportation?
To embellish on that, how long is the slowest and fastest crossing of interplanetary as well as interstellar space? You already mentioned mass drivers for material transportation, which leaves you with the danger of intercepting pirates. Is there FTL travel or are you merely close to the speed of light between star systems?

The setting uses a fusion of FTL and STL travel most of the time - they can only use FTL if there are 'beacons', for lack of a better term, in the system they wish to jump to and in the system they are in. As a result, all settlement is done at sublight speeds and normally the exploration vessels have the capacity to build at least two or three of these 'beacons'. In system, it's mainly done via bulk freighters and transports using fusion powerplants to provide thrust. To cross a solar system (let's use ours, for simplicity), you're probably looking at two to three weeks at most.

Interstellar travel is normally done with the same basic vessel hull, just a subset with the necessary FTL equipment. In speeds, you're looking at a few days per jump, depending on distance - Earth to Alpha Centauri is only three days, but Earth to the furthest reaches of human space is around a month. There are exceptions - very specifically designed craft that can travel faster still - but there is normally a significant delay.

2. ) What is your take on alien life?
2.a ) You just mentioned generic animals and plants which will be further expanded upon as necessary. Are these stemming from large scale genetic engineering or naturally evolved? Both have their advantages and disadvantages. Processing and digesting life which evolved completely different from A1-ian life might be easy, difficult, hard or outright impossible. There are no means of comparison IRL so it's up to you.

It's a bit of both. Many worlds (especially those of a hospitable nature) have life already present via natural evolution, some have them from old genetic engineering projects from now extinct (or still present) species, and some are introduced by humans for the environment (the moon, for instance, has specially engineered plant species instead of just planting regular plants from Earth).

2.b ) Sentient life. Did sapiency and sentience evolve separately and are these Sophonts in contact with each other or humans? If so, you can integrate their technological and cultural development in your story. If not - you already have AGI which in turn (except for uploaded minds) would be the most bizarre minds known to man.

Sapience is a tricky subject in the setting. There are many species that are sentient and sapient, but nearly none are granted actual sapience as most are below humanity in technological level - they are instead officially treated as mere livestock by governments, though obviously there are 'xeno rights movements' and such. It does depend on the world and species, of course.

Some of them are actually close enough to humanity in their thought patterns to be able to integrate well (in fact, one species has a significant Islamic population since that was their first exposure to human religion), but the majority are unable to understand certain concepts that are required for such integration. There's a thriving trade in alien artifacts (especially 'sacred' objects from the more 'unusual' religions out there)

To clarify your official terminology:
S(A1)-C-A is Luna. Broken up:
S... Solar System (classification level 1)
(A1)... Our solar system, others would be A2, B4, W359, added as needed (classification level 2, designation)
C... Third main orbiting body, Mars would be logically D while Venus would be B (classification level 3)
A... Suborbiting body, being Luna, or for Mars A & B for Phobos and Deimos

You will run into problems with that at least at the orbiting bodies of gas giants, which can number quite high.

Yeah, I know. It's a very imperfect system (a fact that actually comes into play in the stories and setting), but it does get the job done most of the time.

As for your population... why do you have so little? I was under the impression of Earth being close to Curuscant levels. 15 Billion? Unless you mean 15x10^12 with that, 15 billion won't be able to restrict middle-class appartments (200 m² / 2000+ ft²) for the rich. As for the 15x10^12 approach... you would essentially need to import air with this many people.
Maybe. I don't know the numbers.

Part of it was an intention that Earth, though a densely populated world, has mandated 'pretty' in the form of forcibly preserved oceans and mountains, so people are forced (militarily, if need be) into the major cities. The numbers may be a bit low, though, but as the 'jewel of space and home of humanity', pretty much everyone agrees that it should at least retain a resemblance to Earth of old in terms of landmarks and the like.

[Buritot]

Huh, two to three weeks to cross approximately 60 AU. Discounting accelerating and decelerating this is 3 AU per day... or 0.01 - 0.03 c. Hell, that's fast, but if you put the outer reaches of humans space at 43 ly you had to to be at some time pretty close to 0.5 c if you established the rim colonies decades ago.
All this of course depending on the need of STL-ships to establish a beacon before FTL-ships can reach their precursors.
Which also raises another question: Going on your beacon thing I assume they transmit some kind of signal. Is this signal also FTL or STL - 1.0 c? If the latter is the case, you've got an interesting thing going:

1. An STL-Ship travels from Star B to Star C, establishes beacons, and starts exploring.
2. The beacon emits constantly its signal. This is first received at Star B. An FTL flotilla flies to Star C, where meanwhile the STL-Ship finishes its exploration and either prepares for the flotilla or goes on to the next system, Star D.
3. Until the signal reaches the next beaconed system, Star C can only be reached via Star B. Meaning, you're at Star A and want to settle into C, you have to go over B, unless the signal already reached A.
=> You've got a string of systems, instead of a cloud. At least for the exploration phase, unless the beacons have a very limited strength and only reach the closest star systems, say, up to ten light years. For the case of Sol 10 ly (3 pc) would encompass 7 star systems or 10 stars.

Another issue in this context is communications. While radio and laser communication may be fine intrasolar, intersolar it is less than desirable and a return to postal communications would arise.

On the case of sapients, sentients and such: If they're only technologically inferior and psychologically compatible with humans, it would take only a few generations until at best until they would understand what we do and start to exploit it, until they're freed - unless we're speaking of very different mindsets.

Hm. Earth got an urbanization rate of 99% and up, with the rest of the planet being a natural preserve? Fascinating... *strokes chin*

You see, I really really like building universes, and crushing and revising them until they're internally consistent.

[Enigma]

Confused here. Earth is polluted yet is a natural preserve? Everything clean except at the cities? If someone was on the moon looking at Earth, would they see a blue green jewel with patches of pollution or covered in pollution?

[loomer]

Pretty much, Enigma - it's like how China is wreathed in smog, blurring it out when you look down from space. There are expanses of Earth that are kept meticulously clean, but there are other areas (...like pretty much all of Asia, by that point...) that are horribly polluted and will probably remain that way for centuries, even with the introduction of fusion and other 'clean' technologies.

Buri,
The actual mechanics of the 'beacons' aren't based purely on anything as simple as a signal. They're also required to provide the necessary 'endpoint' space-time warping, since the ship is unable to open a full conduit on its own, and mitigate a number of other effects that take vast amounts of power and computational ability to do so (the beacons are actually going to be the size of a pretty substantial space habitat, not just something like the Voyager probe, filled with the necessary equipment).

Generally, most beacons do only cover the surrounding systems (though Sol and Alpha Centauri both have arrays designed to allow them to 'broadcast' everywhere, with the Sol system's having been deliberate, and Alpha Centauri an accidental, unintended benefit of the orbital patterns of the three suns.)

The actual method of signal propagation is an unknown factor in universe - they know how to build it and what it does, but they're not quite sure how, even though they invented the damn thing. Blame mad scientists and quantum physics (it is essentially FTL at intensely high speeds, though, for the signal. Matter is a different deal, with different methods of 'transmission'.)

There is a return to a roughly postal form of communication, but instead of actual post, you have 'relay ships' that jump from system to system and then broadcast their news from the edge instead of actually docking to deliver it. Actual mail is normally sent with the bulk freighters and passenger ships.

With the sapients, it does vary. The most technologically advanced are slightly ahead of humanity in some regards, but also have similar mindsets (largely because they had similar developments and evolutionary niches), and they tend to exploit humanity right from the get go, as soon as they can get a base level of communication going.

The primitives are often of a radically alien mindset to humans - in fact, the reason so many species haven't advanced beyond the stone age despite being sentient and sapient is because most of them just aren't suited to it mentally. They lack the needed thought patterns or social behaviours to support invention and creativity, or don't have the physical need to develop more and more advanced tools to win out over evolution (some are apex predators by sheer virtue of their physical attributes.)

It really does depend on their mindset, but the ones capable of integrating also tend to be the ones who exploit humanity's less desirable tendencies, like greed and pity. There are some aquatic species (two, living on neighbouring moons of a gas giant actually. One is amphibious, but they both hail from the same original life form.) that have deliberately cultivated a 'peaceful, Native American'-like image in humanity's media to try and win their freedom, even though they're actually pretty brutal and savage as a whole and only a few individuals can really grasp the enormity of what being occupied by a spacefaring species means.

Of course, then you have species who pretty much aren't even aware that humanity is a different species and don't actually think anything has changed, because their herd mentality is so incredibly strong that they believe anything at all told to them by a strong leader - often those same leaders actually sold their species out. One individual, normally the leader of the most powerful group or even the first one met, is expected to sign away their entire world and species to humanity, be they spacepope, Jim from accounting, or the Almighty Warlord Kang.

[Junghalli]

Part of it was an intention that Earth, though a densely populated world, has mandated 'pretty' in the form of forcibly preserved oceans and mountains, so people are forced (militarily, if need be) into the major cities. The numbers may be a bit low, though, but as the 'jewel of space and home of humanity', pretty much everyone agrees that it should at least retain a resemblance to Earth of old in terms of landmarks and the like.

Some math would be useful here (all figures are from Wikipedia unless otherwise stated, but I think for something like this it should be relatively trustworthy):

Earth's land surface area as 148,940,000 km^2. Let's say that 1/3 of that is uninhabitable terrain (deserts, glaciers, high mountains). We get roughly 99 million km^2.

My home town of Berkeley, California has a population of 102,743 as of 2000 and a land area of 27.1 km^2. That gives a population density of roughly 3791 people per km^2. If we crammed every one of the 15 billion people on your Earth in at roughly that density we'd need 3,956,739 km^2 of land. In other words, 4% of Earth's habitable surface, or ~2.66% of its total land surface. This is equivalent to maybe around 1/4 the area of the United States, with the entire rest of the planet being left completely pristine.

Now if you have money in Berkeley this the kind of housing you could buy. It also has significant areas of minimally developed land (parks and the like) and it has almost no real high rise buildings (see this list of its tallest buildings). So compared to how densely you could pack people in it's pretty open.

Let's use San Francisco instead. It has a population of 808,976 and an area of 46.7 km^2, which gives it a population density of roughly 17,323 people per km^2. 15 billion people crammed together approximately that tightly would require an area of a mere 865,909 km^2. For purposes of comparison, this is only a little larger than France. Note that you can still get a reasonably large house in San Francisco if you have the money.

Basically, in terms of physical space 15 billion people can be accomodated pretty comfortably while leaving most of the surface of the Earth free of human habitation. You may need vast farms and industry to support such a population, though with advanced technology you could conceivably switch much of the agriculture to the oceans. However, if you want to give the impression of a pristine Earth while maintaining a large population cramming people into ultra-dense urban areas like sardines, and substantially reducing the standard of living in doing so, isn't really going to help you all that much.

I suggest either dropping this angle or increasingly the population by several orders of magnitude. Unless the people who run Earth are basically indulging in superdickery.

[loomer]

Yeah, a population increase is definitely in order than. Maybe up to to one hundred and fifty trillion, or is that pushing it slightly too far, do you think?

[loomer]

Ghetto edit: Actually, I've just remembered part of why it was intended to be a low-ish population - only five hundred years have passed, so the population had to be within reasonable constraints for the entire human empire, instead of being crazy huge on certain worlds. I was working with a 2 trillion maximum for the entire area of human space.

[Junghalli]

Yeah, a population increase is definitely in order than. Maybe up to to one hundred and fifty trillion, or is that pushing it slightly too far, do you think?

Well, to get something close to the situation you outlined you would basically need a planet-city, or something approaching it, and a quite dense one at that. You'd need to get it to the point where the inhabited areas of the planet are comparable in population density to downtown cities on Earth.

Maybe scale up Manhattan until it covers the whole planet. Manhattan's population density is over 27,000 people per km^2, so you'd need around 4 trillion people to fill up the planet's entire land area (including areas like the Sahara desert) that densely.

At this point you're at the point where the only way this set-up will be feasible is if you run it like the known galaxy's biggest closed ecology habitat. Produce all your food in nanotech synthesizers that are basically poor man's Star Trek replicators, recycle all your waste material (garbage, sewage, waste water etc.), use ocean desalination and aquaculture on a massive scale to make up for inefficiencies in the system.

Land being that expensive with of significantly less than 2 trillion is probably feasible if you go with the explanation that they force people into super-dense urban areas to keep much of the planet looking pristine.

Also, population growth could take off like a rocket if your population is immortal, as people in a starfaring civilization realistically probably would be. Population can grow really quickly when hardly anybody ever dies.

[Buritot]

Also, to address the issue on population growth:

Mid-sixties Earth had a population of above 3 billion people, now we're closing in on the 7th billion. Take a growth rate of 2% which was probably the highest in modern times and the whole population will double every 36 years. To put that into perspective:

2000 - 2^0 x 6 Billion = 6 Billion
2108 - 2^3 x 6 Billion = 48 Billion
2216 - 2^6 x 6 Billion = 384 Billion
2324 - 2^9 x 6 Billion = 3072 Billion = 3 Trillion
2432 - 2^12 x 6 Billion = 24 Trillion
2540 - 2^15 x 6 Billion = 192 Trillion

The current average global population growth is 1.9 % (source, german).
The doubling rate for various rates:

1.5% - 48 Years
2% - 36 years
3.5 - 22 years (some African countries)

With greatly prolonged lifetimes there will be on one hand even more growth since the death rate decreases while on the other hand those in power might desire to keep it that way. Young people, yearning for power and influence, would become obstacles to that. This could lead to a decreasing birth rate.
For inspiration on that issue you could read Battle Angel Alita:Last Order. This is expanded upon before the ZOTT-Arcand and is still a recurring theme.

[loomer]

Well, those are certainly interesting figures and an equation I can use in future - especially given that, though there have been advances in technology that are leading to greatly longer lives (cybernetics, organ cloning, genetic modification of humans, a cure for cancer...) there was a huge die off in the 21st century as two more nuclear world wars swept over the globe. Though they rebuilt, it did pretty badly fuck things up (and also delayed the first extrasolar colonies in Alpha Centauri by a full century) and a great deal of the population died.

These days, I'm thinking the average human lifespan is going to be around two hundred, taking into account the outliers, like people on Earth (who, with access to the cutting edge of technology, will get to be around five hundred before their brain finally conks out - which is pretty much the single last organ they can't yet replace, but no one that old is alive. You'll only see that around 3,000CE) or people in the Third Expansion worlds, where life is hard (probably around 75, what with their lack of access to the cutting edge, general poverty, and hostile wildlife/alien species/robots/sentient clouds/giant bees or whatever the threat is on a particular world. Soldiers and mercenaries in such areas, of course, tend to live far shorter lives.)

Then you get the fun stuff of one of the water worlds mankind found, where it has densely populated hives (Neo-Atlantis, Lemuria, and so forth) with differing politics and lifespans in each. Neo-Atlantis is an incredibly oppressive dictatorship and the average lifespan is only around a hundred there (though of course, the Great Leader is pushing three hundred, as are quite a few of his advisors), while Lemuria is a more permissive democratic republic with better healthcare. Huge populations crammed into deep sunk cylinders beneath the waves - Lemurians get to enjoy roomy quarters and clean surrounds, but the deliberately crippled economy of Neo-Atlantis and its constant 'war with Lemuria and the UN' state leaves its so called citizens to live in dank, damp quarters the size of motel rooms, and endure propaganda posters and cameras in every hallway, scrawled over with graffiti from bored teens high on meth or other drugs.

The only reason the Neo-Atlantean state can exist is because its all propaganda. They aren't at war, and actually enjoy healthy trade with the rest of the world, but their citizens are forbidden from knowing and indoctrinated from birth to obey. The place only has one spaceport, and they keep it guarded at all times to keep everyone from seeing the trade, and on the few levels above the waves live the upper class, with real sunlight and spacious quarters - even furniture from wood genuinely grown on Earth, shipped at great expense. They import food supplements, but only the upper class will ever see anything more than fish, be they intact or pulped, and an algae mash with artificially added fibres and vitamins.

[Buritot]

I advise using the numbers with a bucket of salt, a grain won't suffice. you're dealing with prolonged lifetime, which only adds up. Furthermore you can assume the fertile period of women be the deciding factor of when the next generation spawns, especially in women of 20-30 years. With your described technological progress I suppose women will be fertile for longer than the usual 30-40 years or will store gamete cryo... whatever the adverb for that is.

I propose the following: The closer to the core of civilization the lesser the growth rate. Earth would be 0.1% or stagnant and outer colonies at 3% with the most out / least civilized regions being 1% and less. This way you'll have a decent population in every interesting system (core to outer colonies) and an ever expanding border.

Also, there are limits to what a planet can support, even with heavy imports. Don't forget these have to be bought with something, so there needs to be an equal amount of assets being exported.