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This civilization has computational technology roughly equivalent to Earth's in the late 20th century. We're talking post-moon landing, but pre-Internet (roughly 1969-1983). They may or may not have more advanced material science than Earth (more efficient fuels, stronger/lighter alloys, etc.) but aren't leaps and bounds ahead in any areas (i.e., no fusion power, light speed, constant acceleration engines, etc.). Methods of space travel propulsion would pretty much be what they are now. For a pop culture reference, picture new Battlestar Galactica, but without jump technology.

I want this civilization to have the ability to colonize other solar systems through sub-lightspeed generation ships. Is this broadly feasible with that level of technology? I know plenty of writers have done this, but is it actually scientifically plausible (within reason)?

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    $\begingroup$ When you talk about "colonize other worlds" - do you mean within the same solar system (which might be binary) or interstellar? Generation ships normally bring visions of interstellar travel, but might be needed for heading out to a world in the Oort Cloud. $\endgroup$ Mar 30 at 21:09
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    $\begingroup$ Do you plan them to land in a planet that is virtually identical to their original planet, but inhabited? If yes, then maybe, as some answers have pointed out (specially if theirs is a low-gravity planet). But the problem is not building the starship, nor travelling to the destination. The problem is the systems keeping people alive not failing in tens of thousands of years of continuous use, and how to terraform your Mars-like (or worse, Venus-like) planet with just the resources you have in your ship. They will never survive the travel. $\endgroup$
    – Rekesoft
    Mar 31 at 9:13
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    $\begingroup$ I'd argue that the post-moon landing - pre-Internet era spanned about 100 days in 1969. From July 20 (first moon landing) to October 30 (first message between two computers). $\endgroup$
    – Abigail
    Mar 31 at 19:09
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    $\begingroup$ "Battlestar Galactica" propulsion (even without Jump) is well beyond what is possible. None of their ship designs have anywhere near the storage capacity to hold the reaction mass necessary to travel extensively within a stellar system, let alone travel between systems. Including the additional space that would be needed for extended life support and it falls even farther from what is possible. $\endgroup$ Mar 31 at 19:17
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    $\begingroup$ When I was a teenager (so fully in the period you are targeting) I read this: goodreads.com/en/book/show/405001 ... the author was convinced it could (and should) be done. I still think it's a pity we didn't try. $\endgroup$
    – Rmano
    Apr 2 at 22:05

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Pre 1982 we had space shuttle, skylab, personal computers (though massively slower than today's) the first version of GPS (military only).

The L5 society had the motto "We care because we're going."

So, yes, a space based civ was possible with that level of tech. They would have started fairly small. And they would very likely have had some disasters along the way like crashes and pressure failures and such. But, yes, certainly possible.

Exactly how much equipment and material they put in orbit would depend on how motivated they were and how much they were prepared to "piss off" the folks who didn't go. For example, Project Orion would have used nuclear explosions to launch large masses to orbit. This has all of the usual drawbacks of above-ground nuclear testing, with the additional consideration of doing a bunch of them (from 10 to 100) within a few minutes. And the possibility the ship fails during launch and crashes somewhere. So you have to either convince the neighbors or ignore their complaints.

But it would certainly be possible to launch a huge amount of stuff to orbit. You'd give priority to stuff like iron and other materials that could take being smacked around pretty extremely. That might make some dandy building material.

One plan was to launch the basic material for a lunar base using Orion. This stuff would be impacted on the Moon at about 200 miles per hour to save on fuel. Then the people land in more ordinary rockets and go over and recover the stuff to build the base.

So it would probably be pretty "brute force." But yes, possible.

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Believe it or not, the biggest thing keeping humans out of the rest of the solar system isn't our lack of computers -- it's our inability to keep people alive for long periods of time. The real stopper was, and still is, sealed systems technology.

Getting things into orbit stagnated when we achieved the Saturn V rocket, around 1970. It was good enough, and nobody had the money or connections necessary to design and sell a replacement. We actually hit a point where we'd stopped pushing the effort for so long that the people who put Apollo on the moon got old and retired without passing their knowledge along.

The American Moon Shot was a product of our competitive nature. It was something to keep the people focused on because The Bomb made large military engagements impractical. After the Soviet Union collapsed, we no longer had a badguy to compete against, so we lost interest. We have enough money to research multiple kinds of advanced aircraft, but our sealed systems technology has stagnated for the same reason our infrastructure is crumbling. It's just too boring. We'd rather spend money on killing people than spend money on keeping people (and the planet) alive.

So, yes, if they really felt it was important, it could be done. It would need to be done on a huge scale, and we'd have to be sensible about which technologies we used (instead of freaking out because someone said nuclear). We could have used ballistic launch systems to get enough raw mass into orbit to build a generation ship, and used nuclear powered mass drivers to accelerate it. We could easily have had a space station that roamed the solar system for a few decades while the world figured out them computer gizmos.

It just wasn't important enough to us.

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You're trying to make a plan whose timescale for implementation is longer than all of recorded human history. No matter what technology you have, we don't have the societal capabilities to have any confidence in a plan that will need to outlast every single human institution that has ever existed by a large margin.

The longest-lived civilizations on the planet have lasted a few thousand years at best. The longest spaceflight ever endured was barely over a year. With current technology, it will take a minimum of several thousands of years to reach the nearest star. Humans surely have never built a machine to operate so long.

We could possibly build a generation ship that could begin a voyage to another world, but I feel like it'd be a total crapshoot as to whether it would successfully make it there. Even our 21st century understanding of long-term spaceflight is limited, and there is no data whatsoever on pregnancy and early human development in space. You want to seal off a large population of people in a way that's never been done before, in an environment that's never been permanently inhabited, and expect them to last longer than any societal structure ever developed. Even with more advanced technology, the human element isn't well-enough understood to expect a generation ship to last.

Sending a probe would be a lot easier, the human element is too complex with too many unknowns with our current understanding of biology, psychology, and sociology. I'd be skeptical that you could even build a generation "town" on earth that could successfully be isolated for millennia, and doing it in space will only be harder.

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Sadly I fear that interstellar travel by humans with 20th century technology would not be remotely feasible.

Even with fusion power it would not be feasible and without it there would be no hope.

Any sort of generation ship is going to have a ridiculously high mass, will require and even bigger booster and would require tens of thousands of years to reach its destination. In that time the ship will run out of power and the inhabitants would be cooked by radiation. Adding more radiation protection only makes it even more massive.

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    $\begingroup$ Radiation in interstellar space won't "cook" spacefaring humans. It may reduce their life expectancy a few years because of a higher incidence of cancer. The other barriers remain. $\endgroup$
    – nigel222
    Mar 31 at 9:00
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    $\begingroup$ You only run out of power if you run the engine constantly which you just won't do, you'll get the ship moving continue to accelerate until you've half your fuel left plus an extra reserve for course corrections then switch them off until you need to decelerate πŸ‘Ž .. so not all the other barriers he suggests remain @nigel222 at least not entirely to the degree as depicted by him πŸ€— internal systems power for lighting and heating etc can (arguably) largely be conserved and recycled within a closed system so it's only the thrust that loses you most of your reserves. $\endgroup$
    – Pelinore
    Mar 31 at 10:33
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    $\begingroup$ @Pelinore so what power source would be used to heat and light a generation ship for many tens of thousands of years? /(yes obviously it won't be remotely possible to run the engines continually) $\endgroup$
    – Slarty
    Mar 31 at 15:25
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    $\begingroup$ @nigel222 well I will give you that one. Perhaps cook is the wrong word but the radiation level would have serious health implications and the effects over many generations would be degenerative. $\endgroup$
    – Slarty
    Mar 31 at 15:38
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Low gravity planet.

To achieve your goal you have to sent huge amount of material to space. What prevent us to do so is the Tyranny of the Rocket Equation.

If the home planet has significantly reduced gravity, compared to earth, this would eliminate the need of, for example, nuclear propulsion as cited in Boba Fit answer which otherwise answers the question about the tech level.

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Interstellar - probably not, but maybe ...

The problem is enclosing enough resources to last the journey. (It's orders of magnitude harder still if a return journey is intended.)

A few factors that might bridge the gap include

  • An established space-based civilisation. Large orbital habitats (like John Varley's Gaea, but without the insane goddess). Asteroid mining an established industry.

  • An acceptance of nuclear propulsion. An Orion drive with a vast number of nuclear bombs (fuel) is the best hope for hard-science interstellar travel. A much less warlike species than human?

  • A nearby other star. 0.4 Light years rather than 4. Also knowledge (from space-based interferometers) that there is a planet in that star's "Goldilocks zone" with an oxygen atmosphere containing methane traces (which implies life). This both piques curiosity, and suggests an immediate return journey is not necessary.

  • A species for which hibernation or "cold sleep" is possible. Future medical advances may extend this to Humans, but other Earth mammals have a natural ability to hibernate at least for six months. Extend this to decades, or to frozen solid (like Alaskan wood frogs).

A generation ship using hibernation technology would have lower in-flight energy requirements. However, because of radiation, suspended animation cannot extend beyond a century or so. Upon being thawed, all the radiation damage recieved while frozen would become active at once. So I'd envisage a duty rota. Decades frozen, three months after thawing to recover from moderate radiation sickness, another three months to look after the ship and the next shift recovering from radiation sickness, and back into the freezer again.

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  • $\begingroup$ Personally I'd hollow out and shape one of those two little moons of mars and use nuclear fission with a lot of slingshotting for thrust to get it out of the solar system and on its way, turn it into a bigger Oumuamua, the bulk of the mass you're going to have to lift of planet for the project is (mostly) limited to the nuclear fuel you need that way (unless you can find some asteroids with what you need, then you're golden) and there's more than enough rock there to shield against radiation, that really isn't an issue for large enough 'generation ships'. $\endgroup$
    – Pelinore
    Mar 31 at 11:09
  • $\begingroup$ Shielding against cosmic rays isn't at all easy. Earth's atmosphere is equivalent to 15 feet of water (density 1) or 3 feet of iron (IIRC density 5). Also cosmic radiation is only attenuated at sea level, not eliminated. After some time frozen it would still accumulate to sickness-inducing levels (and after more time, deadly levels). Sensitive physics experiments under a kilometer of rock still get some cosmic ray interference. $\endgroup$
    – nigel222
    Mar 31 at 11:47
  • $\begingroup$ "Shielding against cosmic rays isn't at all easy. Earth's atmosphere is equivalent to 15 feet of water" Sure πŸ™„ and with what I outlined you could have much more than a couple of hundred feet of rock if you wanted and then the water cisterns after that, less radiation would get through than we experience at sea level πŸ™„ did you even read what I wrote and engage your brain before responding? πŸ™„ .. there will be arguments against what I said but the difficulty of radiation shielding is simply not one πŸ€— .. plus, no working cryo in 1900s or now so it has to be a pure generation ship, hence big. $\endgroup$
    – Pelinore
    Mar 31 at 13:14
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Yes, but not for humans

Your basic killer ape is a really bad fit for anything requiring long-term planning. The saying "a week is a long time in politics" exemplifies the problem.

Humans clearly did go to space in the mid-20th-century, so the problem of building a suitable spacecraft is technically possible. Even if it needed to be way larger, that just requires more launches to get all the bits up there. Of course it would need the civilisation collectively to decide that a large part of global productivity should be dedicated to this. US space expenditure peaked at 4.4% of US GDP in 1966, which isn't really that much on a global scale, and that was only achieved by a highly-militarized country already on a war footing. The civilisation might agree that it's a good idea, but they'd either need an existential reason to get off the rock (and even then, that would require a level of working together that is unproven in a species who can't even globally agree that torture is a bad thing), or more generally they'd need an ability to globally follow through on a good idea.

Then you have the problem of living in a confined space for a very long time, not just you but your children and their children for a hundred generations. Even assuming no losses to the outside, and a large enough space inside not to suffer the problems that humans have in enclosed spaces, this still needs well-governed distribution of resources and very careful family planning (both to raise and lower population).

And then your children to the 100th generation need to stay on mission. Of course they are close enough to still stay in contact - not for conversation, but still able to send a message and get a message back a few years later, and there would be no problems with the parent planet keeping a broadcast link going to keep them integrated with society. But still, staying committed to a mission that you were born into and didn't choose could be tough.

I think it's pretty clear from all this that the biggest problem is not the technology, it's us. You can't put killer apes in a can and expect the end result to not be killing each other. This puts real limits on your story. Not only does the generation-ship have to be non-human, but the species within it has to have behavioural characteristics which would enable them to complete that mission.

This makes for a pretty interesting story, because the best sci-fi isn't about the technology, it's about the "what-if" of how people think which can only come from those people not having human patterns of thought.

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I'd say that one of the primary reasons we don't have spaceflight is there's nowhere really to go. Space exploration is propelled as much by egos as fuel as well.

If you had a potentially livable planet nearby - maybe something that doesn't have complex life yet but has similar enough life - not too near, though with shorter travel times when the cycles are right you'd have a reason for fairly 'common' spaceflight. If you had competing superpowers - or private sector development, you'd likely get a head start on the process of building SSTO rockets and life support.

With a new planet to partially terraform - you'd have things like a permanent space presence - space stations to act as transfer points, research into spin simulated gravity and shielding. Most of this is rocket science but not magic, but unlike modern day earth, where research into space has gone in fits and starts, there would be consistent development into space flight.

You can get the fundamental technologies worked out - and then maybe find a reason for generation ships. A large multi-month or year transport freighter that's meant to bring humans and livestock to seed a livable world would be a good start for a generation ship design. You'd build up the infrascture - space docks and such, and gradually scale up.

Then you need motivation - with a generation ship you are leaving forever. Why would folks pack up the life they knew, put their faith in a large tin can, travelling out to the unknown. In the wayfarers series - they did it because earth was unlivable - so ecological collapse? Maybe politics? You could work in religion or some other reason that people built and chose to live in a generation ship.

I personally suspect we're not in space is cause it is hard, and we don't have a good reason to

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The thing is that it is possible, but that would probably work by starting with their solar system and improving tech with all the new resources inter-solar travel provides. You have the Vostok rocket back in 1961 that put the first man in space and the Atlas rocket that put humans in orbit. Having people living in orbital space stations like those developed in the Cold War but bigger & having these in the orbits of planets/moons in the solar system would probably be the best place for these people to start.

After that, living on moons or stable orbital bodies should be next. The first waste reclamation bioreactor for space was implemented by NASA for the International Space Station in 1998 & back in 1965, nuclear power was used to power satellites and other things in space. Unmanned drones were used all the way back in World War I and World War II, so advanced drones and miners can help to collect resources for survival. All of this can evolve to potentially create everything necessary for people to live in space or on areas like moons or somewhat less dangerous planetary bodies, even without having to do something drastic like planetary terraforming. Heck, there were even tests to start growing plants in space all the way back in 1946 and the 1960s with some degree of limited success, so even growing in space is not completely out of the question. However, the main issue would be traveling to a new solar system and having generational ship capabilities unless you have a solar system close by - much closer than the nearest solar system in our world since Alpha Centauri is 4.2 light years away. Even when it is possible, it feels like it would be best to send drones and create some potential stations between a generational ship and any potential solar system you want to travel to before going since there are plenty of issues that make using 90s tech or even modern tech for interstellar travel.

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Space faring would be possible, reaching an other star system would be a far stretch and require centuries of industry development at 1980's tech level.

A lot of technology's we think of as new were actually pioneered in the 60's and 70's. For example the molten salt thorium reactors were build and tested first in the 70's before the project got closed down because of budget constraints and regulations.

Some high performance materials existed like silicon carbide and hafnium carbides and oxides. But now we can make them with an higher purity and better. Lasers, radar, magnetrons and basic computers all existed.

A lot of NASA papers regarding hyper-sonic space-planes and ionic propulsion drives are published with a date from the 60's. So google around for those.

The civilization needs to be incentivized to go all in on space technology and to put in the capital cost of building a permanent space industry. The politics in our current timeline were not conductive for that, and the green movement effectively killed all development on nuclear fusion.

On the propulsion site we have LRP1 and Hydrogen oxide rockets to get mass into space and certain type of ion or plasma drives are possible in combination with solar power or nuclear power to slowly accelerate spaceships to high speeds for interplanetary travel.

Look into old designs for the space-shuttle to see what engineers envisioned and though of as possible before the over engineered monster what we know now as the Space Shuttle got build. There are some awesome designs to get onto space quick.

There are some single-stage-to-orbit concepts which probably would have never worked, so if you go for realism steer away from those. But there were some projects that managed to land booster rockets SpaceX style, so that was clearly possible. And reusing rockets would be a prerequisite to bring enough 'stuff' up to start a Space faring civilization.

Further await from the Sun than about Jupiter would require a nuclear reactor for power generation. We never build them because of international treaties not because we didn't have the technology. Electric propulsion requires tons of energy, so a nuclear power source is the obvious way.

There were a lot of concepts that used tons of electricity to accelerate ions or heat up plasma's using magnetrons for electric propulsion. Few got build and tested. The political will was not there, but the technology was definitely possible. These can slowly accelerate a spaceship to very high speeds, but it would still take at least a century to reach the nearest star.

To colonize an other star would require a spaceship the size of small city. Which is possible. A steel O'Neil cylinder can be made several miles wide with technology of the time. But it would require a massive industrial complex in orbit, complete with moon bases and asteroid mining to supply enough raw material. It is not thinkable to launch that amount of materials from earth.

Some more points.

  • Robots that execute preprogrammed steps are possible.
  • Remote control is possible, consider light-speed related lag.
  • Anything with AI requires Gigahertz computing and is not possible.
  • Maybe early forms of plastic 3d printing?
  • Genetic research is not possible, requires advanced computers.
  • Every design is made with pencil and rulers. CAD design was to primitive to make a real difference in design style.
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    – DMacc1917
    Mar 31 at 14:05
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I think this question is ignoring something important that makes the idea itself nonsensical. We didn't just stop development on one technology because we wanted to start development on another. Computers and spacecraft (among other things) moved forward together - more advanced computers had a reason to exist outside of space, and more advanced spacecraft could take advantage of the increase in computing technology. In order for this story to make sense, you will need some reason that a huge amount of resources are poured into solving the very real spacecraft problems that were already mentioned, but somehow not bothering to increase other sections of the technology industry.

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NO

  1. Space is unimaginably and stupendously larger than you could even hope to conceive. To paraphrase Randall Munroe: however big you think space is, it's bigger than that.
  2. Life As We Know It really hates what's in space (cosmic radiation), and what's not in space (gravity, warmth, air, water, food, dirt, metals, etc).
  3. Life As We Know It is what it is because of chemistry, and every other life form is going to be based on CHO (carbon, hydrogen, oxygen), too, for the same reason it happened on Earth. Carl Sagan's notion of Carbon Chauvinism is utter nonsense.
  4. The Earth's gravity well is shockingly deep, which means expensive. SpaceX's reusable SuperHeavy might mitigate that, but computer technology in the 1970s couldn't even dream of doing that.
  5. There's nowhere habitable to go.
  6. Terraforming as described in sci-fi books glosses over the billion important engineering details.
  7. We rely on hundreds of years of infrastructure. None of that will exist wherever explorers go.

But heck, don't write hard science fiction. We'll gladly gloss over all that if the story is competent.

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As Boba Fit mentioned, you could do it for nearby planets.

For longer voyages:

Have the spaceship be biological would be an internally consistent way to do it. Might require souls existing to animate it, depending on the design (they don't have to do a whole lot for the rest of the story). Things to note about biological spacecraft πŸš€:

  • They would accelerate incredibly slowly (same with deceleration). There are no hard parts, so they cannot tolerate high escape or entry velocities. This also means they have to be incredibly light, to the point they can almost float in the air to get into space 🌌. (They would still move at fast speeds in space.)

  • They would need a shield, either made of matter or some kind of field, to avoid injury with fast moving space debris. They won't have access to a lot of new material in space.

  • They would need to be protected from radiation by some barrier or another.

  • They would need to recycle waste.

Also, the civilization could have just taken a bunch of alien πŸ‘½ technology to do make any type of spacecraft πŸš€.

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    $\begingroup$ The OP is asking if a spacefaring civilisation is plausible (which doesn't necessarily mean likely) with 1900s (presumably late 1900s, so just twenty three years ago) technology, none of this is even remotely 1900s tech and he certainly wasn't fishing for fantasy or magical elements like your vague reference to souls πŸ‘Ž $\endgroup$
    – Pelinore
    Mar 31 at 11:19

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