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Old September 17 2012, 06:26 PM   #151
sojourner
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Re: Envisioning the world of 2100

gturner wrote: View Post
Ironically, for a while ships from Earth will probably arrive at the nearest star in the reverse order that they launched.
I actually think this will be the biggest deterrent to launching slow boats to other stars.
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Old September 17 2012, 06:32 PM   #152
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Re: Envisioning the world of 2100

^ But that's just the point, a 300 km/sec starship could be built by the end of this century using off the shelf technology.

A 3000 km/sec starship would require at least a fusion power source, that is 1% of the speed of light the rule here is take the distance to the star in light years and multiply it by 100 years, so a 3000 km/sec could reach Alpha Centauri in 440 years, I don't know if we'll have the technology to build it by the end of this century, possibly if we have reliable fusion by the end of this century. Its likely the fusion fuel would be deuterium and tritium same stuff to make hydrogen bombs out of, another possibility is helium-3 and deuterium, but that is harder to fuse and would require the mining of a gas giant to obtain enough Helium-3, the most likely gas giant probably would be Saturn due to its lower gravity, though I think it might be a stretch to expect mining operations in the vicinity of Saturn by 2100.

A 30,000 km/sec starship would require a staged fusion rocket or antimatter, it would be a hideously expensive thing to have throw-away rocket parts, probably only a massive government program could attempt this, another wild possibility is a giant laser to push a starship up to 10% of the speed of light, to calculate travel time, simply multiply the distance of the star in light years by 10 years, for a trip to Alpha Centauri it would take 44 years.

I think in all cases, we need a 500 meter habitat sphere even for starships that reach 10% of the speed of light, as 44 years is half a human lifetime they'll need somewhere comfortable to live for 44 years. I think acceleration should be limited to 1% of Earth gravity max, as where talking about a rotating sphere.

1% of Earth's gravity is 10 cm per second squared, and at that rate it would take 9.51 years to reach 10% of the speed of light or 30,000 km/sec.

At 0.1% of Earth gravity or 1 cm per second squared it would take 9.51 years to reach 1% of the speed of light or 3000 km/sec.

At 0.01% of Earth gravity or 1 mm per second squared it would take 9.51 years to reach 0.1% of the speed of light or 300 km/sec.

If we wait for these more advanced technologies, we are allowing ourselves more time to destroy ourselves. If the goal is to preserve the human race, there really is no hurry to get there, but there is a hurry to launch a starship, the sooner we launch this ship the sooner we would have "bought" the insurance policy against the extinction of the human race. I think it would be easier to develop artificial intelligence than fusion reactors or antimatter reactors and a way of mass producing antimatter in a large enough scale to power a starship, and if we could do that, how much easier would it be to destroy ourselves with control over energies like that? I would feel safer if we launched as starship sooner rather than waiting for the technologies to arrive to send a human crew over there within their own lifetimes.
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Old September 17 2012, 07:00 PM   #153
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Re: Envisioning the world of 2100

Well, the crux of the launch issue is time and economic expansion. You say staging would be prohibitively expensive, but that's only true at the time that you're building your single-stage mission. If we're building a rocket to another star we'd obviously be mining the solar system and expanding out into its vast supply of resources, creating a huge boom. Let's give that period a very conservative 5% economic growth rate. In 40 years, when the economy has expanded four-fold, launching a staged rocket with a mass ratio of four and the same payload will be the same relative cost as launching your original rocket, and be guaranteed to arrive much, much earlier. That earlier arrival time translates into economic and population growth at the other star, because there aren't any resources to exploit in-transit.

That leap-frogging of the missions just through economic expansion can be counted on to occur, even assuming no technological advances in propulsion. It's the same effect we see with Earth launches using chemical propulsion, which hasn't really advanced since the 1950's or 1960's. Even with the massive drawdown of launch funding after Apollo, the expansion of the economy means that we can keep putting mass into space at a higher and higher rate, even without concentrating on it, as long as there is a justification to expand into space. These same forces will be at work once we're living and working in space, at least by the time we can even contemplate an interstellar mission.

The implication of that is that the early, slow, single-stage ships will arrive at their destination so long after the ships launched later that their existence will be entirely irrelevant (10,000 new people will arrive at a star whose population is already in the tens of millions or billions), at least aside from the practical example their flight provides (we can do this! And oh, don't use terbillium coatings and remember to bring avacado seeds, because we just ate the last of a guacamole).

It may be that you're chosing the wrong destination. The nearest stars are guaranteed to get populated by later missions. Perhaps you need to switch destination stars to someplace obscure, or treat your mission as an ark whose destination doesn't so much matter as the fact of its existence, or design your mission to accomodate technological upgrades in-flight by including an ability to bootstrap new manufacturing abilities on board, so the latest Earth-tech propulsion innovations can be re-created with materials and equipment on hand.
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Old September 17 2012, 08:11 PM   #154
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Re: Envisioning the world of 2100

Mars wrote: View Post
newtype_alpha wrote: View Post
Mars wrote: View Post
So tell me why can't you run a nuclear reactor for 5000 years?
Because running at full power, a typical fuel rod will only last for 20 (25 if you're lucky) before it decays to the point of no longer producing useable heat and subsequently becoming a serious radiation hazard.
Ah, but you forget, in space no longer usable fuel rods can be tossed overboard and never seen again, you don't need to store them anywhere or worry about their radiation.
I didn't forget that at all. It's immaterial, because whether you store them or eject them, radioactive waste can't be used as a fuel source and the reactor must be completely overhauled at regular intervals to replace those fuel elements.

But slow starships are relatively cheap to build
Spoken like someone who knows anything at all about how much it would cost to build a starship.

As for World hunger, AIs alone could solve this problem
Not in the next 50 years they won't. Though, admittedly, automation will probably begin to raise the quality of life for the third world long before it empowers humanity to build utterly impractical traveling space colonies.

Machines would be in the same peril from obsolescence as humans.
Humans are not in peril from obsolescence. Humans are imperiled by the greedy machinations of other humans. AIs, on the other hand, are no more threatened by obsolescence than a fork is threatened by a spork.

Well this ship can certainly be launched by 2100
On the Islamic calendar, sure. But not any time in the next 80 years; we don't have anywhere near the spaceflight infrastructure needed to even dream about that sort of thing, and we'll be lucky to even be DEVELOPING it by the end of the century.

More to the point: the advent of AIs might make that entire concept moot, since by then we'd have developed computerized spacecraft that can explore the solar system by proxy and will avoid the expense of maturing manned spaceflight altogether. Your generation ship would simply be a probe the size of a winnebago containing three thousand frozen embryos and a set of really beefy landing thrusters.

I remove myself from immediate consideration, it is the rest of humanity, those that will come after me that I am concerned about
I am not sufficiently concerned with the rest of humanity to make a substantial financial investment to ensure the continuation of the species against a threat that may or may not never materialize in a plan whose outcome will probably never be known. That is simply not a smart thing to EVER invest money on. Because I am probably not in the minority in this opinion, a generation starship of the type you describe will remain another "cool but impractical" concept in science fiction.

Why does one buy life insurance, this is life insurance for the human race, I think it is worth some effort and expense.
It is. So freeze the embryos and hide them in an ultra-secret bunker a thousand feet underground. We could do that with TODAY'S technology... IF we had any reason to believe humanity was threatened with extinction at any point in the near future.

People buy life insurance because they know they're going to die. We don't know this is true of humanity yet, so there's no reason to ensure against it.

I hate to tell you this, but its not working, North Korea has acquired the nuclear bomb and Iran is acquiring it
And before them, Pakistan and India, none of which were signatories to the non-proliferation treaty at the time (North Korea is sufficiently isolated and sufficiently broke to render this a non-issue).

And Iran is not interested in a nuclear weapon (if they were, no one would care). They're after nuclear POWER, which is economically and politically destabilizing in ways that a nuclear weapon can never be. With the capacity to build warheads, Iran can only make empty threats and rattle their nuclear sabers to make their voters feel better. With nuclear ENERGY, they can apply leverage to oil production and commercial transit through the Persian Gulf, hiking global energy prices to impose political change to their own advantage. It is this reason, also, why nobody cares that North Korea has nukes: with a nuclear warhead you can only destroy one really really big target and then duck your head down and suffer the consequences, which otherwise still leaves you politically powerless on the world's stage.

Keeping AIs out of the hands of pariah states becomes a far greater imperative because that sort of technology would have the effect of economically and politically empowering anyone who masters it. The treaty would doubtless be written to reflect this, allowing powerful first world countries to continue to use and develop AIs while everyone else gets carpet bombed if they get caught researching the subject without a U.N. permit.

Its hard to predict the unpredictable
Really? You don't seem to have any trouble throwing around suspiciously accurate predictions as if they were certainties.

And we're back to starting a nuclear war aren't we.
You don't need nukes for something like that. Just ask the Iraqis.

Its not the numbers but how far they are spread out that matters. If you can pack one billion human beings within the radius of one nuclear bomb blast, then they all die if one goes off
No they won't. ALOT of them will die instantly, and a lot of them will die days and weeks later to medical complications due to radiation poisoning. Even then, a nuclear detonation in a metropolitan area can be expected to produce casualty rates between 40 and 70%.

So even if half of the human race is clustered together in a densely urbanized society, then of the 4 billion people endangered by the attacks, at least 1 billion will survive, and humanity's overall population would drop by about 30% at most.

A nuclear war or even a really bad conventional war will not threaten the survival of the human species unless a targeted campaign of genocide goes from town to town specifically targeting individual communities that otherwise have no strategic value except that people live there. This sort of campaign would require a MASSIVE military force, easily larger than the combined armed forces of all the nations on Earth, which is only to say that even if every soldier everywhere decided to kill every non-soldier on Earth, it would STILL take decades to accomplish this. It would take twice as long if this was being attempted by an outside force independent of those military forces (e.g. an AI rebellion). And if somehow this happens at a time when the AIs control all the military assets of the world, then it wouldn't NEED to happen because humans would no longer be in control of their own defense anyway.

It is the limited scope of humanity on one planet that is the danger.
Absolutely. Just not in danger of EXTINCTION, not on anything less than a geologic timescale. Simply put, there are too many of us and our resources too well developed, and a huge number of things would have to go south before we get anywhere near that point.
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Old September 17 2012, 08:41 PM   #155
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Re: Envisioning the world of 2100

publiusr wrote: View Post
Because, last time I checked, the STS is no longer operational and its replacement won't be ready before the end of the decade.

And its enemies would love to kill it thereby wasting money when they should be supporting it.
Flawed logic. The first thing they tell you in systems analysis is that bad money is bad money and throwing good money after it won't change that fact. If the system you're developing isn't feasible in the first place, terminating future development is a savings, not a waste.

Apollo was thinking big. STS was thinking reusable.
STS was thinking "let's build five space stations and use them as construction docks to build the Battlestar Galactica and then cruise around the solar system in style!" As such, the space shuttle was the first in a SERIES of big things NASA was dreaming about but never bothered to secure funding for.

We are not just starting out
Yes we are. We never got past the starting stages because our various big projects never develop into anything sustainable. We essentially have to start over from scratch every single time, because we can't afford the kind of incremental development timescales enjoyed by the rest of the aerospace industry.

Of course, the EELVS could, and for the most part they have. Mainly because they operate on a smaller scale, spreading experience and technical knowledge over a higher flight rate allows them to make developmental improvements a few at a time and evolve their capabilities into new technologies. Thus the EELV program has made technical and capability improvements in the past two decades, during which NASA has made no technical progress whatsoever and wound up REDUCING the shuttle's capabilities due to safety concerns.

In more familiar terms: when you move to a new area and start a new town, you start with houses, not skyscrapers.

What does NASA doe when any rocket blows up?
Suspend any further launches, pending two years of handwringing, technical reviews, theatre and apologia in front of congress, committees, consultations, more committees, studies, and a billion dollars worth of safety upgrades that reduce the rocket's capabilities by 30%.

Significantly, that means NASA's entire manned spaceflight program will come to a screeching halt until their Next Big Thing comes out of its mourning cycle and is cleared to fly again 25 months later at severely increased cost and severely reduced capacity.

So Griffin--who wrote AIAA texts is unsourced.
When you fail to provide the name of the person you're quoting or the context of that quote, yes, that means the quote is unsourced.

A man on Augustine who trashed HLVs, gave us the Roton.
A man on Augustine who supported HLVs is still beating his wife.

See, I can do that too.

what do you think launches heavy reactors--Delta IIs?
Delta-IVs, or IV heavies, probably.
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Old September 17 2012, 09:58 PM   #156
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Re: Envisioning the world of 2100

This is why slow boats are a bad idea.
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Old September 17 2012, 10:38 PM   #157
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Re: Envisioning the world of 2100

newtype_alpha wrote: View Post
publiusr wrote: View Post
what do you think launches heavy reactors--Delta IIs?
Delta-IVs, or IV heavies, probably.
But the Delta-IV is a dead-end because they can't make a Delta-V without confusing the f**k out of everybody.
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Old September 17 2012, 10:52 PM   #158
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Re: Envisioning the world of 2100

They're not necessarily a bad idea, even though they'll have no impact at the destination. It's the journey that matters.

With a warp drive, people from Earth could routinely venture to the millenia ship and take tours of it, staring at the spooky frozen embryos or aging crew, still stuck in the world of 2100 like cavemen stuck on a raft going in circles in an eddy in the Pacific.

In inflation adjusted constant 2010 dollars, I'm thinking $350 for the flight out to the millenia ship and $50 for admission. The souvernier shop would make a killing and could easily be restocked from the warp ships. Of course the actual crew would quickly abandon the effort, so you'd have to pay college kids to dress up in crazy year-2100 costumes and speechify in the old way, but they work cheap. Since the journey is going to take thousands of years, the return on investment should be astronomical.

After the first thousand years of profitable business you'd even hire people to play tourists from earlier centuries, so new visitors could see what it was like to gawk at the "Twenty-One Hundreders" back in 2350.
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Old September 18 2012, 01:22 AM   #159
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Re: Envisioning the world of 2100

gturner wrote: View Post
Well, the crux of the launch issue is time and economic expansion. You say staging would be prohibitively expensive, but that's only true at the time that you're building your single-stage mission. If we're building a rocket to another star we'd obviously be mining the solar system and expanding out into its vast supply of resources, creating a huge boom. Let's give that period a very conservative 5% economic growth rate. In 40 years, when the economy has expanded four-fold, launching a staged rocket with a mass ratio of four and the same payload will be the same relative cost as launching your original rocket, and be guaranteed to arrive much, much earlier. That earlier arrival time translates into economic and population growth at the other star, because there aren't any resources to exploit in-transit.

That leap-frogging of the missions just through economic expansion can be counted on to occur, even assuming no technological advances in propulsion. It's the same effect we see with Earth launches using chemical propulsion, which hasn't really advanced since the 1950's or 1960's. Even with the massive drawdown of launch funding after Apollo, the expansion of the economy means that we can keep putting mass into space at a higher and higher rate, even without concentrating on it, as long as there is a justification to expand into space. These same forces will be at work once we're living and working in space, at least by the time we can even contemplate an interstellar mission.

The implication of that is that the early, slow, single-stage ships will arrive at their destination so long after the ships launched later that their existence will be entirely irrelevant (10,000 new people will arrive at a star whose population is already in the tens of millions or billions), at least aside from the practical example their flight provides (we can do this! And oh, don't use terbillium coatings and remember to bring avacado seeds, because we just ate the last of a guacamole).

It may be that you're chosing the wrong destination. The nearest stars are guaranteed to get populated by later missions. Perhaps you need to switch destination stars to someplace obscure, or treat your mission as an ark whose destination doesn't so much matter as the fact of its existence, or design your mission to accomodate technological upgrades in-flight by including an ability to bootstrap new manufacturing abilities on board, so the latest Earth-tech propulsion innovations can be re-created with materials and equipment on hand.
You have to take into consideration that this slow starship will take 4100 years to reach Alpha Centauri, if what you say happens and it is bypassed by more advanced ships, the slow ship would still arrive 4100 years in the future around the years 6200 AD, by this time after 4100 years of technological advancement, I would be surprised to find flesh and blood humans populating the system, not that humans couldn't have got there, but if they got there 4000 years before the slow humans arrived then 4000 years of technological advancement may have advanced them beyond their physical flesh and blood human bodies, in other words they'd likely be no longer human, they might have uploaded their minds to machines or computers and become a society of AI, and as such they wouldn't need oxygen, wouldn't need an earth like environment, they could live anywhere that would allow their machines to operate, the humans arriving in the slow ship might find an already terraformed planet that was discarded by humans who had uploaded themselves into machines thousands of years ago, but these just arrived throwback humans could still use the planet.

Think of it not so much as a starship but as a one way time machine. The humans raised in the ship would be in a miniature world surrounded by 21st century technology, although they themselves have never lived in the 21st century, that would be the world they grew up in until they reached planet-fall.
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Old September 18 2012, 01:33 AM   #160
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Re: Envisioning the world of 2100

gturner wrote: View Post
They're not necessarily a bad idea, even though they'll have no impact at the destination. It's the journey that matters.

With a warp drive, people from Earth could routinely venture to the millenia ship and take tours of it, staring at the spooky frozen embryos or aging crew, still stuck in the world of 2100 like cavemen stuck on a raft going in circles in an eddy in the Pacific.

In inflation adjusted constant 2010 dollars, I'm thinking $350 for the flight out to the millenia ship and $50 for admission. The souvernier shop would make a killing and could easily be restocked from the warp ships. Of course the actual crew would quickly abandon the effort, so you'd have to pay college kids to dress up in crazy year-2100 costumes and speechify in the old way, but they work cheap. Since the journey is going to take thousands of years, the return on investment should be astronomical.

After the first thousand years of profitable business you'd even hire people to play tourists from earlier centuries, so new visitors could see what it was like to gawk at the "Twenty-One Hundreders" back in 2350.
Think of it this way, if you buy a ten year life insurance policy on your self, and within that ten years you don't die, would you feel that was wasted money?

If we launched that slow starship and humanity destroyed itself before building a faster ship, that would be a good investment as it would have saved the human race, humans would get to start all over again on a new planet.

If the starship was launched and humanity did not destroy itself and faster ships bypassed it on their way to the destination, then it is just like the life insurance policy you bought but never needed because you didn't die, that life insurance policy still cost you money however, would you feel cheated if you bought a life insurance policy on yourself and you didn't die, or are you paying just to ease your mind that your heirs and dependents will be taken care of in the event you did actually die?

A slow starship that eventually gets there is like paying money for life insurance it turned out was never needed, its purpose is to save humanity should the worst happen, and at least its development would be a step on the path to even faster starships.
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Old September 18 2012, 03:42 AM   #161
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Re: Envisioning the world of 2100

Mars wrote: View Post
You have to take into consideration that this slow starship will take 4100 years to reach Alpha Centauri, if what you say happens and it is bypassed by more advanced ships, the slow ship would still arrive 4100 years in the future around the years 6200 AD, by this time after 4100 years of technological advancement, I would be surprised to find flesh and blood humans populating the system...
Which means our putative cybermen would have passed your space ark fifty times on the way to and from alpha centauri and will be fully aware of its position and nature. Even if you send it off to some other distant star system, you merely give the cybermen -- or worse, the Dalek hordes they later evolve into -- more time to develop a warp drive capable of intercepting the ark and destroying it. The craft therefore utterly fails to escape the human hyper-evolution which, due to the growth of technology, is destined to expand the Cyberman/Dalek/SuperBorg empire much faster than the generation ship can actually fly. And this before we consider the AI you've already placed on board the ship which otherwise COMPLETELY defeats the purpose of building it in the first place.

I've said before, and I'll say it again: bury the embryos in a bunker and tell no one where it's hidden. That would accomplish the exact same goal as the generation ship, except 1) no need for an active AI custodian 2) no risk of damage in interstellar space 3) smaller risk of accidental discovery 4) the bunker has the ability to activate the embryos in the event of a catastrophe and would thus actually succeed in populating a habitable Earthlike planet. Most importantly, that project would about 1000 times cheaper; while still far from practical, it is at least feasible.

Mars wrote: View Post
Think of it this way, if you buy a ten year life insurance policy on your self, and within that ten years you don't die, would you feel that was wasted money?
That depends on how much money I spent. $30 a month for ten years aint all that bad in the scheme of things; it's a small expenditure, just in case.

The time and expense of building a generation starship is not a small "just in case" expense. People who are afraid of the nuclear apocalypse build a bomb shelter in their back yard and stock it with emergency supplies, bottled water and shotguns; if nothing happens in five decades, at least it's an interesting place to stash the loot from last month's bank heist.

You know what they probably DON'T do? They don't buy ocean liners and then maroon their children on them with fifty years worth of food and no particular destination.
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Old September 18 2012, 04:55 AM   #162
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Re: Envisioning the world of 2100

^ Yeah, the generation ship would have to be nothing but frozen embryos, because no group of people can be cooped up that long and not go nuts, and since the first or second generation would realize that it's 20 or 30 years back to Earth, and 4000 years if they don't turn around, they'll turn around, or at least stop (if reaction mass is only sufficient for one start and one stop), radio back, and await rescue.

The reason is that the early generation of people will look around and realize that for 4,000 years they can't expand. They can't really modify much. They can't go anywhere, they just exist. Their only purpose is to reproduce, die, and get recycled. Their children's only purpose is the same, ad naseum. It's too much for a human to face day in and day out, especially human parents.
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Old September 18 2012, 11:47 AM   #163
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Re: Envisioning the world of 2100

gturner wrote: View Post
^ Yeah, the generation ship would have to be nothing but frozen embryos, because no group of people can be cooped up that long and not go nuts, and since the first or second generation would realize that it's 20 or 30 years back to Earth, and 4000 years if they don't turn around, they'll turn around, or at least stop (if reaction mass is only sufficient for one start and one stop), radio back, and await rescue.

The reason is that the early generation of people will look around and realize that for 4,000 years they can't expand. They can't really modify much. They can't go anywhere, they just exist. Their only purpose is to reproduce, die, and get recycled. Their children's only purpose is the same, ad naseum. It's too much for a human to face day in and day out, especially human parents.
Very good, I realized much the same myself, the fact that it travels through space is only incidental, its main purpose is to travel through time, and setting it on a journey to Alpha Centauri forces it to wait 4100 years, it could instead go in a wide orbit around the Sun for 4100 years, but then it could always come back early, going on a one-way journey to the nearest star commits it to leap 4100 years into the future, in case humans have technologically evolved into something inhuman, become drones or somehow destroyed themselves. We wouldn't want the ship's occupants rejoining humanity just in time for their destruction, at least if they skipped ahead 4100 years they may at least get a chance to see the peril and possibly prepare for it themselves.
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Old September 18 2012, 07:43 PM   #164
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Re: Envisioning the world of 2100

Well, your insurance policy works by seeding humans across great gulfs of time and distance, insulating them from single-event catastrophes. It seems the parameter to optimize is thus the product or sum of space and time. By that measure, getting to Alpha Centauri faster might not be an actual improvement.

But if we switch to looking at two states in time, humanity at t0 and humanity at t(year), we'd want to maximize the distance between clusters of humans and the total number of seperate clusters. In that case, if we had an improvement in travel velocity, we wouldn't use it to reduce the time, we'd use it to increase the distance.
We'd also not send multiple ships to the same destination, which wouldn't add to the number of seperate clusters, we'd scatter them out to cover as many destination stars as possible.

Since the greatest threat to their long-term survival comes from humanity itself (or its remnants or replacments), it also indicates that many of these ships should go long, go deep, change course multiple times, and run silent, just like they were hiding from an alien species bent on human extermination.
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Old September 19 2012, 02:44 AM   #165
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Re: Envisioning the world of 2100

gturner wrote: View Post
Well, your insurance policy works by seeding humans across great gulfs of time and distance, insulating them from single-event catastrophes. It seems the parameter to optimize is thus the product or sum of space and time. By that measure, getting to Alpha Centauri faster might not be an actual improvement.

But if we switch to looking at two states in time, humanity at t0 and humanity at t(year), we'd want to maximize the distance between clusters of humans and the total number of seperate clusters. In that case, if we had an improvement in travel velocity, we wouldn't use it to reduce the time, we'd use it to increase the distance.
We'd also not send multiple ships to the same destination, which wouldn't add to the number of seperate clusters, we'd scatter them out to cover as many destination stars as possible.

Since the greatest threat to their long-term survival comes from humanity itself (or its remnants or replacments), it also indicates that many of these ships should go long, go deep, change course multiple times, and run silent, just like they were hiding from an alien species bent on human extermination.
Sensible precaution, perhaps the best way to do this is have the ship loiter at the edge of the solar system, and then suddenly decide to undertake the journey at some random unannounced point in time, and vary the acceleration rate and cut off the acceleration within some interval so the precise velocity position is unknown by outsiders. Probably the vast bulk of humanity would not care after the ship disappears beyond the edge of the solar system. As for potential stars to travel to there is:

Alpha Centauri A G2 V 4.4 light years
Procyon A F5 V 11.4 light years
Tau Ceti G8 V 11.9 light years
Delta Pavonis G6 V 18.6 light years
Eta Cassiopeia A G0 V 19.2 light years
82 Eridani G5 V 20.3 light years
Beta Hydri G1 V 20.5 light years
all approximately yellowish sunlike stars.
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