Bare Minimum Tech for Spaceworthy Vessel

Question

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?

Answer 1

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.

Answer 2

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.

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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).

Answer 3

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.

Answer 4

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.

Answer 5

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.

Answer 6

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.

Answer 7

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.

Answer 8

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.

Answer 9

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.

Answer 10

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.

Answer 11

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.

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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...

Answer 12

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.

Answer 13

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.

Answer 14

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

Answer 15

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.

Answer 16

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.

Answer 17

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

Answer 18

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.