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In my story, a planet of low-tech natives in the midst of war are abruptly brought into contact with a much more advanced empire. There are many historical precedents for this kind of event, and occasionally the natives are able to fight back. Now, in order to mount an effective defense, these natives must have space vessels.

My question is, how basic can I make the natives' tech and still have them be able to create spaceworthy vessels? For example, we build our space vessels with steel. But could it be done with bronze? We propel our spaceships with highly advanced compounds, but could it be done with gunpowder?

Edit: There's no need to take my examples literally. I was not seriously considering the idea of a bronze spaceship, it's just an example of the kind of low-tech making-do I'm looking for.

Edit: So as to help our natives along a little bit, we'll say this planet has half of Earth's gravity.

What technological advancements are absolutely necessary for travel into space?

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    $\begingroup$ Another question this raises is why are they in a war in the first place? If it were between the larger civilisation and someone else, they could potentially try to stay out of the way. If, on the other hand, they were locked in dead-on combat with this greater power, the only real reason for this would be if the natives had a resource or something of value that the other civilisation wanted. Perhaps then they could use this resource directly, or trade it with others to buy space tech from farther-developed civilisations. $\endgroup$ – StickyFingies Jan 4 '18 at 21:27
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    $\begingroup$ I'd say that an obviously necessary requirement is for them to understand celestial mechanics. In our history, Newton published his Philosophiae Naturalis Principia Mathematica in 1687. The experimental basis of the work consisted of Kepler's synthesis of the lifetime observations of Tycho Brahe. $\endgroup$ – AlexP Jan 4 '18 at 22:25
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    $\begingroup$ do they have to reach orbit or just go into space? $\endgroup$ – A. C. A. C. Jan 4 '18 at 22:35
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    $\begingroup$ Read Jerry Pournelle's "King David's Spaceship": amazon.com/King-Davids-Spaceship-Jerry-Pournelle/dp/0671656163/… $\endgroup$ – Thucydides Jan 5 '18 at 1:20
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    $\begingroup$ What about the natives would make them good spacefarers? Could they be used to holding their breaths for long periods or have bodies that can withstand vacuum? Might they be squishy enough to survive being shot out of a cannon? This would also have war implications -- if you could shoot an army over a wall, how would fortifications and weapons be different? A plus is that it's not a stretch to start shooting natives straight up; a minus is the implausibility of a body that can survive hundreds of gees. $\endgroup$ – Lurker Larry Jan 5 '18 at 6:27

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About the minimum you'd need is what the Germans had available to them during WW2.

Their A4/V2 rocket was nominally capable of reaching space (though not of orbiting) and they were working on designs of a functional spaceplane that would fly a suborbital trajectory to the US to drop bombs there and then skip over the atmosphere back to Germany.

More capable rockets were under development that would have been able to launch men or satellites into space (though that was not the primary consideration at the time) in the form of the A9/A10.

As to fuels, liquid oxygen + kerosene does the trick just fine. You don't need "advanced chemicals".

The biggest problem would be navigation and creating and maintaining a pressure capsule and a breathable atmosphere within it.

For navigation, someone with a slide rule and enough paper and time wouldn't need much more than a sextant and maybe a telescope.

The biggest problem with the pressure capsule is making air tight seals that don't fail in vacuum. Plastics, artificial rubbers, and things like that are the most used for that, maybe other things can work as well.

And then there's the problem of maintaining the breathable atmosphere on board. Spacecraft use CO2 scrubbers which need some knowledge of osmosis and processes like that to construct. If you go longer, you might need a means to reduce CO2 to oxygen and carbon so you can reuse the oxygen for longer.

Again, nothing we couldn't do in the 1940s. Bronze pressure vessels can probably work, but the mass may be higher than a comparable internal volume in steel.

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  • $\begingroup$ Thank you very, very much. You actually understood what the question was asking (unlike many), and your answer was helpful. $\endgroup$ – Megalonychidae Jan 6 '18 at 2:31
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    $\begingroup$ You do not need a breathable atmosphere: astronauts could just use breathing masks and air tanks on board for refilling. $\endgroup$ – Revolver_Ocelot Jan 6 '18 at 20:24
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    $\begingroup$ You might be able to go back to the 1920s: a space capsule isn't too different from a submarine, and Goddard was playing around with liquid-fuel rockets then. $\endgroup$ – Mark Jan 7 '18 at 9:35
  • $\begingroup$ "making air tight seals that don't fail in vacuum" is simple. Making ones that also don't fail under the mechanical and temperature stresses of spacecraft is a different thing :-) $\endgroup$ – Bergi Jan 7 '18 at 17:31
  • $\begingroup$ @Bergi many materials become extremely brittle in vacuum, causing a seal made out of them to lose its sealing properties. Rubber for example won't do, while working perfectly fine in atmosphere at normal temperatures $\endgroup$ – jwenting Jan 9 '18 at 7:32
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It's more believable for them to steal a ship

Any one particular technological innovation stands atop a mountain of discovery, innovation, experimentation, experience, and knowledge. The size of that mountain is considerable. Successfully putting a human in space depends on a breathtaking amount of technology, from spacesuits to rocket engines, from electronics to heat absorption, from chemistry to materials science. The hunt for rocketry probably started with the Chinese thousands of years ago. It matured with the Nazis decades ago. It's not exactly a daily event today, despite jaw-dropping advances.

Jules Verne might have been the first to suggest sending a shell (e.g., from the barrel of a gun) into space. Space.SE answered the question of whether or not that was plausible. Their conclusion was if... if... you could scale the physics, it would take over 14,000 Kg of gunpowder, and the g-force would turn humans into a thin pink paste on the back of the capsule.

And that's assuming the bronze didn't collapse, melt, warp, or anything else, which it would.

Low-tech natives would lack everything from the research base to solve the problem to the manufacturing base to produce the materials needed to achieve the solution.

So, for practical reasons, the answer is "it can't be done." Your natives would need at least 1930-1940 tech just to understand how to ask the question.


Edit To resolve the OP's concern: In reality, the first man in space was April 12, 1961. Assuming the low-tech natives had access to information that we had to discover the hard way, it's plausible to believe the achievement could have been done with 1940s technology, had all the answers been provided. If the natives simply look at a space ship, then the earliest tech they could possibly get away with is 1960s. A different answer would require knowing (a) what the current tech of the natives is and (b) what technological insight they have access to other than visual (e.g., documentation).

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    $\begingroup$ @JBH Do they need 1960's level computers, or could they get by with an auditorium of people using slide rulers if they really wanted to? What about an army with abacuses? Etc. I feel you are falling prey to the "technology level" idea. $\endgroup$ – Shane Jan 5 '18 at 2:32
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    $\begingroup$ @Shane, the capsules themselves had computers. It's not enogh to plan the voyage, you must still control the craft while outside the atmosphere. I'd recommend watching the movie Apollo 13. If all you want is a balistic shell that clears the atmosphere, orbits a time or two, then falls to earth in a dramatic ball of flame and a spectacular crash, then you wouldn't need an onboard computer. $\endgroup$ – JBH Jan 5 '18 at 4:35
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    $\begingroup$ +1, since the OP seems to imply that these low-tech vessels will be used in defensive warfare, it might be worth noting that requirements for such an endeavor will be much higher. The tech used by humans to get into orbit or reach the moon will hardly be enough to wage war in space. Much more so against a technologically advanced adversary. $\endgroup$ – r41n Jan 5 '18 at 7:50
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    $\begingroup$ @r41n If the ships have to be advanced enough to be used in defensive space warfare, then who knows what kind of tech level they'd need because we're not there yet. $\endgroup$ – Shufflepants Jan 5 '18 at 15:31
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    $\begingroup$ @Shufflepants We haven't lost a space-war to date, I think defensively we're doing pretty well using the "our ships are too technologically inadequate to be worth contacting or attacking" strategy. $\endgroup$ – Bilkokuya Jan 5 '18 at 15:33
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What technological advancements are absolutely necessary for travel into space?

  1. A good understanding of classical physics. By this I mean that your natives would need to understand how to measure gravity, how gravity interacts with objects in/outside of the atmosphere as well as how force/mass/acceleration work together.
  2. Some sort of material capable of remaining quite airtight and heat resistant in space. This wouldn't necessarily have to be perfectly airtight (air leaks are no where near as devastating in space as sci-fi would have you believe), but it would have to be good enough to keep most of the air in and most of the heat out when re-entering.
  3. A propellant of some sort. It takes a lot of energy to get into space. ~90% of our current spaceships weight is actually fuel and the fuel we use is pretty close to as efficient as possible for chemical fuel. It's possible with gunpowder, though you would need ridiculously large amounts to get even a small payload into space. This would be easier on a planet with much lower gravity than earth. The formula for calculating the escape velocity is $$ v = \sqrt\frac{2GM}{R} $$ where G is the gravitational constant, M is the mass of the planet and R is the radius. If your race understood that equation, I don't see how they couldn't figure out an appropriate fuel.
  4. Some other sort of vehicle that is capable of traveling in extreme environments would help. If they already have some sort of a submarine/airplane it would make things much easier for your natives. I don't think this is absolutely necessary, but it's pretty close.

I think that these four things are the most important advancements for space travel. If you have these you can probably do it no matter where else the rest of your tech is at, though it would be incredibly difficult with pre 18th/19th century tech. Having said that, war speeds up development in leaps and bounds so it's not difficult to imagine us with our curiosity, innovation and fearlessness skipping several levels of technology almost overnight if we got our hands on some advanced alien technology especially if our survival depended on it.

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  • $\begingroup$ Thank you very, very much. You actually understood what the question was asking (unlike many), and your answer was helpful. $\endgroup$ – Megalonychidae Jan 6 '18 at 2:31
  • $\begingroup$ @Megalonychidae, when you give the same thoughtful thanks to multiple answers, it makes the thanks less thoughtful and thankful. ;) $\endgroup$ – paqogomez Jan 8 '18 at 5:54
  • $\begingroup$ Do you really need your point 1? If you aren't entirely concerned for the pilot or resources involved couldn't you just trial and error it until some of your spaceship doesn't come back. Or is it just the knowledge that it is possible for it to get stuck up there? $\endgroup$ – John Heinze Jan 8 '18 at 13:42
  • $\begingroup$ @JohnHeinze The problem is that orbital mechanics are very counter-intuitive. Look at first-time players at Kerbal Space Program (with no prior knowledge). First instinct? Go up to reach orbit (it doesn't work). Once in orbit somehow, how to raise the orbit? Point the nose up and fire the engine (doesn't work). How to get on a point further on the same orbit? Point your nose forward and accelerate (not only it doesn't work, it actually get you even further back on the orbit!) Without a good model of orbital mechanics, and with the lack of margins with rockets in general, it simply won't work. $\endgroup$ – Eth Jan 9 '18 at 12:46
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Assuming a similar gravity well to Earth, you'd at least need to understand the Maxwell equations. These were first conceived (or at least published in a rudimentary form) by James Maxwell in 1861 and integrate magnetic and electrical forces.

It took around a century for that knowledge to be expanded upon and consolidated to a level that we could build the first rockets capable of getting us to space, and being able to communicate with them (via radio), and while at least a part of that was the will to do so, it is important to note that without integrating at least 2 of the fundamental forces as we understand them (doesn't necessarily have to be electricity and magnetism), the ability to use these forces to generate power and harness it in novel ways doesn't exist. Without that, we simply cannot generate, store or take advantage of the power needs required to get a ship off the surface of the earth and into space.

Add to that the need for communication with the ship en route, and Maxwell becomes even more necessary as without his equations we have no radio, TV or other mass communication capability.

So; theoretical knowledge of the late nineteenth century, and engineering knowledge of the mid-twentieth century. Otherwise, we would have done it sooner ourselves as Man has always been fascinated by the stars.

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    $\begingroup$ I think it would help this answer a lot if you more directly tie the Maxwell equations to rocketry. The connection is not quite clear. $\endgroup$ – bendl Jan 5 '18 at 12:55
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I would agree with the 1960s-tech assessment: you don't just need steel, you need high quality, lightweight, high strength steel, etc. You can, however, give your natives a leg up in the non-tech areas. One suggestion that comes to mind is an extremely high mountain range that extends well beyond the atmosphere. Not only would this give them experience with airlessness, it would also provide a useful launch platform -- assuming they could move all the required natives and equipment into such a deadly area. But space is difficult and requires a long learning curve -- read up on the ongoing space programs all over the world; even with the knowledge and technology, the secret sauce is experience and perhaps failure.

What about the natives would make them good spacefarers? One example would be if they were squishy enough to survive being shot out of a cannon. This would also have war implications -- if you could shoot an army over a wall, how would fortifications and weapons be different? A plus is that it's not a stretch to start shooting natives straight up; a minus is the plausibility of a body that can survive hundreds of gees.

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  • $\begingroup$ I don't think mountains sticking out of the atmosphere are likely, if realism is important; worldbuilding.stackexchange.com/a/99188/553 shows that the atmosphere depth and mountain height scale similarly, with the latter staying within the former. But I like the concept! $\endgroup$ – Charles Jan 6 '18 at 7:03
  • $\begingroup$ I note that the height calculated is prominence, height above an arbitrary level. (Inhabited areas could lie far below.) And while it is very presumptuous for me to dispute with someone who bothered with calculation, swiftly-rotating worlds do develop significant equatorial bulges that also distort the local sense of weight, being farther from the center. $\endgroup$ – Lurker Larry Jan 7 '18 at 3:57
  • $\begingroup$ Oh, swift rotation => swift winds => swift wind erosion, in the long term. Also equatorial bulge => wobbly rotation, but a massive satellite (far away?) stabilizes rotation. Speculative fiction question: could this partition the world into separate biomes? $\endgroup$ – Lurker Larry Jan 7 '18 at 5:22
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Short answer: yes.

Long answer: maybe.

It largely depends on the planet they're on, the natural resources and natives readily available to be used in a war, and the full extent of the war they're in. Say, for example, these natives had been long-time trade partners with a larger, more powerful civilisation. Come time for war, these natives could buy / borrow some of these civilisations' tech, without the slightest idea of what is in it or how it works. Then again, any civilisation may be rather unwilling to provide space tech to a group of unindustrialized savages, so that is also a possibility.

Then, keep in mind the planet they're on. One of the fundamental ideas behind space is: once you're in space, it's easy enough to stay there, the problem is getting off the ground. If your little group of natives were on a planet with a rather small gravitational pull, they could potentially form airtight vessels and use the aid of geysers or other such natural propellants to put them into lower orbit.

As for fuel, this is where things get difficult. If they had access to gunpowder, they could use the aforementioned geyser propulsion system to get into the air, then once they started to slow down they could blast different segments of their ship off into the planet to gain some minor speed boosts.

All in all, I'd say your natives are kind of screwed; their best bet is stealing enemy tech and hitching a ride to their base and sabotaging it from within.

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    $\begingroup$ How do you expect a geyser to propel something into LEO? $\endgroup$ – sphennings Jan 4 '18 at 21:26
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    $\begingroup$ Again, it would only be plausible under very low gravity conditions or an extremely thin atmosphere. The most plausible course of action would be stealing tech or, one way or another, getting it from others. $\endgroup$ – StickyFingies Jan 4 '18 at 21:29
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    $\begingroup$ Maybe if you actually read my answer without being so quick to downvote, you would be able to find it in the second paragraph. The OP didn't state any specifics, they just asked if it was plausible or not, and that was how I interpretted it as being possible. $\endgroup$ – StickyFingies Jan 4 '18 at 21:34
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    $\begingroup$ I'm definitely open to physical features of the planet that could help our natives reach space faster. Low gravity is a good idea. $\endgroup$ – Megalonychidae Jan 4 '18 at 21:50
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    $\begingroup$ How can the answer to "how basic can I make the natives' tech and still have the be able to create spaceworthy vessels?" be either "yes" or "maybe"? $\endgroup$ – a CVn Jan 4 '18 at 21:56
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Understanding of Flight and Orbital Mechanics

It is important that our natives understand the basics of flight and orbiting. One of the main setbacks of making it to space in our history was this, and was a problem even after the successful development of liquid-propelled rocket technology. Take Robert Goddard and the Pendulum Fallacy, for example, in which he believed that the engines should be placed at the top of the rocket so that the rocket would hang like a pendulum. Another such example was difficulty rendezvousing with early Gemini tests because of a lack of understanding of orbital mechanics.

Computers (Bonus, probably not necessary)

They should at least be able to run simple automated sequences. Controlling everything by hand in the constricted environment of a space capsule is very difficult and requires too many people, which would just add weight. They don't even have to be able to do computations if the pilot is good at math. But just some basic automation that can run sequences.

Edit: Computers may actually be unnecessary, according to jwenting's comment.

Liquid Fuel

Solid fuel won't cut it, unfortunately. Solid fuels are difficult to control and not as effective for their weight. Liquid fuel is very easy to produce, though. Simple electrolysis of water can produce hydrogen and oxygen, and this technique has been around since the 1700s. Ethanol and oxygen is another good propellant.

Some Sort of Strong Material

If we're going to be realistic, the ability to create steel or some other light and strong alloy is a make or break factor. This they could probably learn very quickly from studying a crashed enemy ship.

Means of Production

They must also be able to create many of these, and fast. Organized factories will be required for producing ships at a decent rate.

Life Support (Maybe)

Just the ability to replenish oxygen for an extended period of time, most likely from a pressurized tank.

Other Things to Consider

How big are these planets? It is not uncommon for terrestrial exoplanets to be much smaller than Earth and still in the habitable zone of their star.

What is the history of this civilization? Not every civilization should be expected to develop just like ours. They may have some accomplishments offset. Maybe they've developed spaceships before boats, or maybe they have large factories producing spears. (These are just exampled, I'm not saying they are valid.)

Conclusion

I think that the biggest setback is going to be computers. If your civilization already has computers, you're all good. But if not, you're probably not going to be able to learn how to make them by salvaging from destroyed enemy ships, because they aren't easy to understand without prior knowledge. They can probably learn to replicate the enemy ships' material fairly quickly, however, and they could probably also learn plenty about orbital mechanics from them as well.

Stealing enemy ships is likely not a possibility. If we are talking about realistic spacecraft, then the capsule and maybe a lander stage would be all that was left and it would be out of the question straight away. If it was more like a space plane, then the if they speak different languages they will not understand controls, and if there is a password then that's about the end of their adventures.

Overall, if the civilization has come into contact with another that can make these ships, then they should be able to learn from them much faster than they would figure things out on their own otherwise.

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    $\begingroup$ The Germans built rockets capable of reaching space with small payloads without the use of computers. They would have had orbital capability probably by 1947 had the war not ended (at least the designs, if maybe not the hardware). So no, computers aren't needed. They make things a lot easier, but you can do everything with a slide rule and a few sheets of paper. $\endgroup$ – jwenting Jan 5 '18 at 8:35
  • $\begingroup$ @jwenting I see your point. After all, airplanes of the day didn't need computers, and rockets are little more than airtight planes with special fuel. I was thinking that computers would be important for a reaction control system or any sort of semi-automated sequence like deploying parachutes in order, but depending on what they need space-worthy crafts for, computers may not be necessary. Just lots of coffee. $\endgroup$ – Elijah Seed Arita Jan 5 '18 at 9:29
  • $\begingroup$ @Elijah Sequencing can be done with cams, mechanical timers, and electrical relays and solenoids -- think automobiles and washing machines. I am not so sure safely de-orbitting is possible without a lot of calculation, but perhaps just a radio link with land-bound computers is the minimum needed to set a sequence. Originally, a computer was a mathematician, often a woman, who could hand-calculate or use a mechanical calculator; many were employed in the Manhattan Project as well as in aerospace. $\endgroup$ – Lurker Larry Jan 5 '18 at 15:45
  • $\begingroup$ @LurkerLarry You are correct - also, I think deorbiting, if not very accurate, would not be a problem without computers as a well designed landing pod should be forced to the correct angle on contacting the atmosphere. $\endgroup$ – Elijah Seed Arita Jan 5 '18 at 20:28
  • $\begingroup$ Thank you very, very much. You actually understood what the question was asking (unlike many), and your answer was helpful. $\endgroup$ – Megalonychidae Jan 6 '18 at 2:32
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In addition to the other answers, there is one component missing. You need some sort of computing platform, and electricity. It doesn't need to be very high tech, at the bare minimum you need the equivalent of transistors. You can't expect to have a mathematician on board calculating course corrections and orbital maneuvers in space with a sextant. The transistor is the single element we could never have gone to space without.

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  • $\begingroup$ What, don't you believe in the feeling of power? $\endgroup$ – ruakh Jan 5 '18 at 5:54
  • $\begingroup$ The first object in space was apparently a V-2 rocket in 1942, and the transistor was invented in 1947. $\endgroup$ – pjc50 Jan 5 '18 at 11:14
  • $\begingroup$ The V2 was more of a ballistic missile than an actual space ship. Plus it never went into orbit, it went to a maximum of around 80Km in altitude, and anything below around 160Km will inevitably decay and fall back down because of drag. It's easy to send something into space if you just want it to follow a ballistic trajectory and fall back down on enemy cities, but quite another to achieve a stable orbit. $\endgroup$ – Drunken Code Monkey Jan 5 '18 at 16:55
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A lot of these answers are saying its not nearly possible for a full spacecraft so I wish to provide an alternative. A way to defend the earth with artillery.

The Verne Gun

Essentially it is a cannon capable of sending a bullet into space. The idea is from 1865 and with the advent of modern artillery you may be able to do this with WW1 era technology.

This comes with a caveat that it has never been built before, along with being unguided and impossible to launch a human with. Although the Germans with the V-3 cannon and the Iraqi military with project HARP have tried in the past.

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  • $\begingroup$ The deceleration is too sudden andhigh for humans to come close to surviving. $\endgroup$ – RonJohn Jan 5 '18 at 17:56
  • $\begingroup$ @RonJohn I noted that it comes with that caveat in the final paragraph $\endgroup$ – Reed Jan 5 '18 at 18:18
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Bare-bare, at half earth gravity?

Getting into space is trivial. Surviving in space is somewhat harder. Being space-worthy (navigable in space well enough to fight another vessel) is considerably harder. And returning to the planet alive is essentially impossible.

So barebones means no coming home. No return trips. You go to space and you either capture one of their ships, or you die trying.

Glass-blowing gives you a good airtight vessel, proof against one earth atmosphere. Since gravity is half earth's, the atmospheric pressure is likely to be far less too, so the pressure will be even lighter. Or just make 'em able to survive in vacuum for a few minutes, then you don't even need to be airtight.

Half the gravity means half the escape velocity. Earth escape velocity is 11m/s, so they'd need 5.5. At a bit over 10G acceleration (approx upper bound of sustained survivable for humans) of 100m/s/s, you'd need 55 seconds of acceleration - call it a minute.

How can you get 55 seconds of acceleration? Well, you could launch them along a rail 124km long, but (assuming you don't want their bubble to melt) you'd need to evacuate a tunnel around that rail and put the end of it above the atmosphere.

Assuming you have a mountain that reaches above the atmosphere of your planet, that's totally doable just with glass-blowing technology, of course. Really, really advanced, industrial-scale glass-blowing technology. But whatever.

So, you can make a tube, you can evacuate it, and you can drop someone down it in a glass sphere or capsule, then accelerate them along it at 10m/s/s for a minute. How you do that without them hitting the side of the glass tunnel in their glass bubble and being vented into space at 5500m/s is an exercise for the reader. You could say "magnets" or "rails" but there's no magnet or rail on earth that can withstand that kinda momentum.

Now he's in interplanetary space. He's higher and faster than the space shuttle or the ISS or even the Apollo missions, since he has escaped the gravity well of his planet.

But there was no way to aim that, other than timing to determine where in the planet's rotation he was fired out. But ships don't sit stationary relative to each other. There's no way that kinda ship could ever match velocities with another ship, without also launching with huge amounts of reaction mass. So you most likely need some kinda directional jets, and computers, and so on - a whole 'nother kettle of fish.

So, barebonesiest, you launch him from basically a catapult on a rail, no craft at all, and hand him a fire extinguisher for propulsion.

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The main problem of building spacecrafts is the tyranny of the rocket equation. This equation says that the amount of propellant that you need grows exponentially with the speed difference you are trying to achieve.

Bummer is, you need to accelerate pretty hard to reach even the lowest orbits, you need to accelerate by no less than 27000 km/h. Fail to do so, and you fall back to earth. And, due to the rocket equation, you need insane amounts of fuel for this. Just to give you some numbers, here are some stats of the Soyuz rocket and space vessel:

Space vessel weight: ca. 7 tons
Weight of rocket without fuel: ca. 19.1 tons
Weight of fuel: ca. 156 tons

You see, the whole rocket is basically a big pile of fuel wrapped in a thin layer of steel.


What does this mean for a low tech population trying to build space-worthy vehicles?

It means, they are screwed. They need to contain liquid fuels, some of which need to be pressurized, within a container that is only allowed to weight about 1/8 of the total fuel mass. It is quite hard even for us today to build such light-weight structures that are still strong enough, and we have lost rockets as recent as 2015 (Falcon 9 launch failure) due to structures that did not hold up under the forces exerted on them.

Low tech means, you need to include high safety margins to avoid catastrophic failure, and high safety margins mean much more fuel, and much more rocket to hold that fuel. The lower your tech level, the larger the rockets need to be. We need rockets that outweight their payloads by a factor 25, just to get some small payload into space. How big will that factor be for your low-tech people?

Can you imagine your low-tech people building significantly larger rockets than the ones we build today? If not, I'd say, any space-faring society needs to be at least at our level of development in the middle of the 20th century, when we first started sending rockets into space.

And all this does not even include any potential for fighting battles in space...

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The bare minimum to get a man into space would be Soviet-level technology in 1961. That's when the USSR put Yuri Gagarin into orbit. Even then, I would not call that reproducible, and as such would not be minimum tech for getting several men up to orbit to do a job (and to get them back safely).

The USSR got ahead of the US, in part, because they were willing to lose men doing it. So it was probably not as safe you'd want.

I am assuming you are talking about manned space vehicles.

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Many of the other answers have pointed out that you need airtight seals for the ship. However, that is not the case.

If you want to go super low tech, the hull can be a solid metal container. Before launch, a circular hole is cut into the sphere so the person and any required equipment can be put inside the craft. Then, the section that was cut out can be sealed up and welded shut. When the spaceship returns to earth, the hull can be cut open to free the person inside. No seals needed.

You may be wondering how the environment inside stays livable. The metal ship radiates heat, but the person also generates heat, which makes me think that the heat would be balanced out in the short-term.

As for food, canned food would suffice, provided it was attached to a wall so it wouldn't wack anyone in the head. Water can be stored in a waterskin or a water bottle of course. A couple extra bottles for waste disposal.

The atmosphere would be the biggest concern. To filter CO2, all you need is some activated carbon exposed to the air. To replace the filtered air, you don't even need air tanks outside of the ship. You don't even need air tanks at all. A large balloon would suffice. As long as you have a basic understanding of atmospheric composition and human air requirements, you can even use normal air provided your tank/balloon is large enough.

These methods should help you stretch the limits of how primitive your space ship can be. Good luck.

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Here is a wonderful resource from 60's era NASA. It's a long read and quite technical but details what is probably the minimum (and maximum at the time) capabilities for space travel. https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710019929.pdf

The reason I wanted to present this is because, being interested in the subject I stumbled across this a few years ago and was blown away at the level of technology that had been developed for getting people into space.

First, I wouldn't worry at all about your natives learning the technologies. Societies with lower tech are not any less capable of utilizing higher tech...they simply don't have access to it. But here's the problem. The technologies have to be created using technologies, assuming your natives don't just steal or trade for it. Even today there are advanced places without the technological capacity to produce the very technology they consume. For example, USA reliance on Russian made RD-180 rocket engines https://en.wikipedia.org/wiki/RD-180

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  • $\begingroup$ There's a difference between not having the technological capacity to do something and not being economical to do something. RD-180 engines are bought because it's more economic to buy the engines from someone already set up to produce them then it is to set up a manufacturing system from scratch. It's the same way Brazil and Canada purchases large airliners from Boeing or Airbus; it's not that they don't have the tech know-how to build large planes--both countries build advanced small and medium airliners--it's just not economic to do so (at the moment, anyway). $\endgroup$ – Keith Morrison Jan 5 '18 at 21:16
  • $\begingroup$ @Keith Yes, I think that was what I was actually trying to say, is that the limitations for many less technologically advanced societies boils down an economical problem rather than a cultural one. Some could argue education is a bigger limitation, but I think this is a lesser problem and lacking infrastructure to support it is the bigger hurdle. $\endgroup$ – Meridian Jan 5 '18 at 21:41
  • $\begingroup$ absolutely true. If an alien species showed up tomorrow with FTL spacecraft and other advanced tech, and shared the information freely, you'd simply start teaching the advanced science instead of the science we know using the regular school system, and you'd have people up to speed within a few years. $\endgroup$ – Keith Morrison Jan 5 '18 at 23:31
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Are you willing to cheat? Harry Turtledove had medieval Teddybears armed with muskets flying ships no more complicated than an airtight classical Greek trireme. The conceit is that they (and everyone else in the universe save humanity) discovered a stupid simple way to accelerate infinitely for very low power use, and a stupid simple FTL drive.

Stephen Baxter has Roman legions flying between stars in giant metal cylinders using alien nigh-infinite thrust engines.

So if you're willing to bend/break the laws of physics (or at least put some magic handwavium ancient alien tech in play) then you can certainly make a story work with savages in space.

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Throw in a little bit of magic.

As others have already pointed out, flying to space requires WW2 level of tech. However, note the word "to" - most of this advanced tech is needed to take off. Once you are in space, you can fly, literally, in a wooden barrel propelled by fireworks. Space itself is not a harsh environment. You would need a hull that can hold 1 atm of pressure, chemical source of new oxygen (easy), and a way to control the fireworks that propell you. I do not know how do it without electricity while keeping air-tight hull, but electricity of that minimum level has been known at times of American Civil War at least. May be hydraulics? Do not forget heat buildup (coolant system) and radiation ( a layer of foil would do).

So, if you create some fantastic way to move spaceship into the space (magic? Permanent teleport from surface to space? capture single enemy ship to use as a launch system?), then, I think, you could do it with Victorian era tech.

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  • $\begingroup$ 1 thing to bare in mind is that the teleport to space would also have to apply an orbital velocity to the pod or it would fall straight to the ground. $\endgroup$ – Douglas Jan 7 '18 at 14:46
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    $\begingroup$ That depends on how far the teleport is. If we talk about satellite orbit, then yes. If, however, is is far beyond, the gravity there would be weak enough to compensate with some fireworks. $\endgroup$ – Barafu Albino Jan 8 '18 at 8:29
  • $\begingroup$ You may end up hurtling at relativistic speeds towards another solar system, black hole, plasma storm, neutron anomaly or space wizard's lair though. So results may vary. I suppose teleporting into intergalactic space is pretty safe. And most of interstellar space is empty but you don't know how fast the space dust is moving there relative to you so if it's going at 80% the speed of light relative to you or something silly like then then a grain of sand hit's like a nuke. $\endgroup$ – Douglas Jan 8 '18 at 18:00
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Not much technology is needed.

Here is a story by Turtledove about a space faring, Renaissance level society: https://eyeofmidas.com/scifi/Turtledove_RoadNotTaken.pdf

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    $\begingroup$ Could you maybe elaborate on how this tech works? $\endgroup$ – Douglas Jan 7 '18 at 14:46
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Give your planet a seafaring warfare history, then as a plot device, adapt submarines for space - the main tech difference would simply be reversing the seals on the hatches so that they resist 1 atmosphere outward pressure rather than many atmospheres of inward pressure. Make the crew from submariners as well - they are already psychologically well suited to that contained environment. Assume that the submarines already have air scrubbing technology and are accustomed to weeks or months below surface.

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