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My story features Renaissance-era feudal society with working space travel. Humans are able to travel around the Solar System (Earth, Mars, asteroid belt, moons of Jupiter) in spacecrafts fitted with solar sails. These crafts are manufactured in space and never see the ground.

My question is, how can these people get into and out of space without rockets and without resorting to handwavy magic? What alternatives exist?

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    $\begingroup$ I would have thought that anybody with an interest in science fiction has read Harry Turtledove's Road Not Taken (1985), or at least knows about it. Turns out that gravity manipulation is actually simple and easy, with most civilizations having discovered it in their equivalent of the Bronze Age. Earth is a rare exception, so when a Renaissance-level alien army attempts to invade Earth they are quickly dispatched by our advanced weaponry, much to their sorrowful surprise. $\endgroup$
    – AlexP
    Dec 6, 2023 at 23:03
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    $\begingroup$ It would help if they live on low gravity moon instead of Earth. $\endgroup$ Dec 6, 2023 at 23:16
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    $\begingroup$ nothing realistic, orbital physics is harsh mistress. so what is your threshold of hadwavium? $\endgroup$
    – John
    Dec 7, 2023 at 0:02
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    $\begingroup$ Is this on Earth or are you free to set up the planet how you like? If the latter there are a lot more possibilities, from low gravity to space elevators left by a long-gone civilisation, to the world actually being a huge space station (also left by aliens) etc. $\endgroup$
    – N. Virgo
    Dec 7, 2023 at 7:36
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    $\begingroup$ Obligatory xkcd. Getting to space is "easy". Staying in space is hard. But still, in a medieval setting, people can't even stay up in the air... Mandatory handwavium. $\endgroup$
    – jcaron
    Dec 7, 2023 at 13:53

15 Answers 15

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Not strictly "medieval", but we're going with sci-fi, so...

Lost Precursor Technology

There were ancient people at a much higher level of technology. Are they the ancestors of the current feudal society who suffered some sort of disaster? Did they leave and did these new people evolve on what was once their homeworld? Were they only here briefly and installed some stuff?

Doesn't matter, what does matter is that they installed a set of large-capacity space elevators around the globe. Many settlements are located around the bases of these impossible structures because they've become items of worship due to their mind-bending scale. Their maintenance and operation is automated - one need only get in and press "up" and one will be dropped off in space.

Automated energy weapons also kill anyone attempting to damage the elevator with no warning, lending an added element of "gods' wrath" to the worship of these colossal relics.

Alternatively...

You could go with the style of The Road Not Taken. Antigravity and/or hyperdrive are easy, we humans just didn't go down the right paths to find them. This is effectively magic, but it's also the only way you're not subject to the rocket equation.

Overall Problems

Even with a hand up into space, a medieval technology society with solar sails beggars belief. Making a vessel air-tight would have been near-impossible. Manufacturing the ultra-thin, ultra-light, ultra-huge material for a solar sail would have been completely impossible. Being able to carry sufficient air and provisions for the months of travel between planets would be completely impossible (spoilage would have done them in before arrival). But this is ultra-soft sci-fi, so as long as you don't draw much attention to them, you can probably get away with it.

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  • $\begingroup$ This helps. The premise I have in mind is that during the Bronze Age, aliens or something landed in Mycenaean Greece. By ways and means, the aliens are all gone now, leaving scraps of their tech behind. Not enough for the human to replicate exactly, but enough that they can MacGuyver their way across the stars $\endgroup$ Dec 7, 2023 at 1:19
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    $\begingroup$ @AmadánDubh It's worth noting that materials science only now allows us to make something that could serve as a solar sail, and unfolding it is an enormous engineering challenge in and of itself. That is, by an enormous margin, the least plausible part of "Renaissance-era solar sail space ships" . $\endgroup$
    – jdunlop
    Dec 7, 2023 at 1:28
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    $\begingroup$ You'd also need a space station with automated manufacturing at the end of the elevator that will make some preprogrammed items (space ships, suits and what else is needed to use them) if a tech priest utters the right words. They dont have the knowledge or access keys to make it manufacture other things, so the rest of the tech thats not connected to space flight remains medieval. $\endgroup$
    – LazyLizard
    Dec 7, 2023 at 9:41
  • $\begingroup$ If OP is going with the precursor tech approach, they might just throw in the spaceships as well. The different planets in the solar system all have space elevators and at the space end of them there are automated shuttles that fly between the different planets. $\endgroup$
    – quarague
    Dec 7, 2023 at 17:37
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    $\begingroup$ @AmadánDubh : The problem is that the infrastructure needs to have been built on other planets too, otherwise all the trips would be one-way. And also deadly, because they would have no means to land safely. Scratch that, even if there was a space elevator at the destination, how to dock with it, and how to achieve a stable orbit to do that? So all trips would be one-way, until they can build up a society to manufacture spacecraft for the return trip. But this raises the question: how to survive atmospheric re-entry (or entry, in this case)? $\endgroup$
    – vsz
    Dec 8, 2023 at 6:24
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Cartoon Physics

Julius Verne was a great author, writing steampunk fiction with broken science that sounded logical to the average reader of his time. Any nerd from even a century or two before him could see the errors though.

But supposing that the physics of the Verneverse are valid, take a page from his book From the Earth to the Moon.

In this book there is a club of Americans who fiercely compete to see who can america the most (i.e.: who can make the biggest gun). Goes to show how timeless this piece of work is.

So at one point one guy tries to outamerica his peers by landing a shot on the expletive Moon, as a manner of greeting whatever people might live there (insert the theme song of Team America here). Then out of the sacre bleu a French guy comes along and says "Bonjour, I'm Michel Ardan and this is Jackass!" Just kidding - Jackass hadn't been invented yet. Instead Ardan said "hey, if you make the bullet hollow then you and me can sit inside and use it as an interplanetary vessel", which is a longwinded way to say the same thing.

And then they do it. They dig a 270m (900 ft) hole to act as a barrel, fill the bottom with gunpowder guncotton and load the "vessel". They shoot and, to add insult to insult, they expletive miss.

Now in our own boring universe, any steel from the 1860's would have been obliterated (edit: to make matters worse, they used... tin). Even if the capsule would survive, it wouldn't fly at enough speed to go into space, and if it did, then the americanauts would become a thin paste on the bottom of the projectile. But in the Verneverse they make it alive into space.

As long as your universe follows the same cartoon physics, people should be able to replicate the feat - even with more rudimentary technology.

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    $\begingroup$ They used guncotton not gunpowder. And the projectile capsule was made of aluminium not steel. And Verne does meet the acceleration problem head-on and provides a (not working, of course) technological solution to avoid becoming paste on the bottom of the projectile. In fact, Verne did a lot of solid engineering research for the novel, basically predicting the Apollo 8 mission almost exactly. $\endgroup$
    – AlexP
    Dec 6, 2023 at 23:26
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    $\begingroup$ Point-by-point comparison. (And, of course the physics doesn't really work. The book was written in 1865! But then I don't remember reading any good science-fiction novel, or seen any good science-fiction film, in which the physics actually works.) $\endgroup$
    – AlexP
    Dec 7, 2023 at 0:05
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    $\begingroup$ This was going to be my answer with a twist... rather than the hollow bullets to move people into space (that part of the story didn't age too well), let's use the idea to send a spool of chain into space. Yup! We need to handwave the fact that the chain's weight would tear itself apart, but that's why I like the science-fiction tag. Once the chain with the big bullet on the end is in orbit, we have a rudimentary space elevator. Now it's just a matter of slowly climbing up and down until there's a carriage - then you can build the ships in space and ignore the gravity well. $\endgroup$
    – JBH
    Dec 7, 2023 at 5:09
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    $\begingroup$ If you want to go with cartoon physiscs the sky is the limit. In Gustav Reuss 'Hviezdoveda' doctor Krutohlav flew around solar system by blasting his hot air baloon really hard (written in 1856). Also the case of Lucian of Samosata shows us that you can be blown to to the moon if you get unlucky with waterspout while sailing around. The question is where this becomes too much of "handwawy magic". $\endgroup$ Dec 7, 2023 at 9:23
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    $\begingroup$ In Vernian cartoon physics, there's also the even more implausible Off on a Comet $\endgroup$
    – Chris H
    Dec 7, 2023 at 14:09
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Naturally occurring space elevators

Your society may live on a world where plant or animal life exists that forms a natural space elevator. For example, giant plants that live in the upper atmosphere that have vines that reach ground level, and seed pods that travel to other worlds to pollinate other space pants that can be used as shuttle craft.

Thinks wind pollination but on a solar system scale

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Tame wild space horses

The Reefs of Space (Frederik Pohl and Jack Williamson, 1964) features a whole ecosystem living in the vacuum of space...including air-breathing mammal-like animals (sleeths) that have mysterious internal organ(s) that keep a bubble of air around them as they swim reactionlessly among the reefs of the Oort cloud.

Sleeths occasionally journey close enough to the sun to wander onto the curious large planets. Being mammalian, they can be somewhat domesticated. Their jetless drive works just as well in atmosphere as space.

Create your own space-horses, have some wander close enough to encounter your Medievals, and then chariot across the cosmos.

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  • $\begingroup$ this whole thread is crazy, but this answer is good. being biological they repair and replicate themselves, which is the trouble with precursor tech from jdunlop answer (also good). organisms possess abilities and produce materials that baffle and inspire science. $\endgroup$
    – Dor1000
    Dec 7, 2023 at 21:56
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    $\begingroup$ @Dor1000 Rationalizing crazy is what we do here. It's when querent's insist on the limitations of realistic answers that things get boring. $\endgroup$
    – JBH
    Dec 8, 2023 at 3:07
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Hyperspace

Usually hyperspace is an alternate dimension where the distances between points is shorter, but that doesn't have to be the case.

In The Long Earth, somebody figures out how to step into an alternate reality Earth with a very simple to reproduce "stepper box." It's a little hand-wavey, but allows for a lot of options. In that story, there are an unlimited number of alternate Earths, but you have to step through them one at a time.

One of them is what's called the "gap Earth," where the planet itself doesn't exist. If you take that to a logical extreme, even if the distances aren't shorter, you're still operating without gravity. You would hop out to that other vacuum and ride your 1000 mph momentum to a spot outside the atmosphere, and accelerate from there.

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    $\begingroup$ Upvoted for The Long Earth. The stepper boxes run on potatoes and rudimentary components, which makes them universally accessible to everyone on Datum Earth (our Earth). $\endgroup$ Dec 7, 2023 at 17:05
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Hot Air Balloons and Ornithopters

According to Wikipedia, Vijaypat Singhania set a world record and reached an altitude of over 20,000m in a hot air balloon in 2005.

So, what I would suggest is to have a hot air balloon lift your space faring capsule to an altitude of ~30km, then detaching from the balloon and using an ornithopter mechanism in combination with your solar sails to reach even higher, before dropping the ornithopter mechanism for weight savings, and using only solar sails to take you the rest of the way.

As with all answers, this wouldn't actually work, but I think it would fit your aesthetic very well

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    $\begingroup$ As you say, this wouldn't work, but I'm curious as to how an ornithopter could gain purchase on air so thin a balloon stopped working. $\endgroup$
    – jdunlop
    Dec 7, 2023 at 19:37
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    $\begingroup$ @jdunlop quite simply, the ornithopter relies not on air but on the Aether which (wikipedia quote) "fills the region of the universe beyond the terrestrial sphere" to fill its luminous wings with hope and lift! ... though that might be a bit too hand-wavy magic. $\endgroup$
    – Syndic
    Dec 8, 2023 at 7:29
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About 50 years I had a dream where the Roman Empire had a space program and other advances. And I had another dream where the Holy Roman Empire in the time of Frederick I had a space program. While I was dreaming those dreams I believed they were real history. I was really disappointed when I woke up. And if you write a really good story about space travel with medieval tech, readers may believe you while reading, and not realize how implausible it is until after reading.

I can add one more way for medieval people to acquire space travel.

Poul Anderson's classic novel The High Crusade (1960) opens with an alien spaceship landing in Medieval England. The English people capture the spaceship and become lost in space. They lead a revolt to overthrow the alien space empire and replace it a new space empire, but can't find their way home to Earth.

And in Larry Niven's Known Space series, the Thrint and the Kzinti acquired space travel the same way, stealing spaceships from visitors and conquering them.

So possibly in your story a group of people with medieval technology have managed to conquer and rule at least one world with advanced interplanetary or interstellar travel.

And they have to live at least part time in a world or worlds with advanced technology they don't understand in order to supervise their more advanced subjects. But they take long vacations from that work, spending vacations on less advanced worlds which are more understandable to them and which may be their main homes. And they travel between medieval and advanced worlds and societies in spacecraft they don't understand and which they decorate to look like they were built by medieval craftsmen.

I also point out at a society with a medieval level of technology doesn't have to be medieval European. And of course technology was different in different parts of Europe at the same time, and usually more advanced in AD 1500 than in 500. Other medieval era societies had technological levels anywhere from stone age hunter-gatherers to Aztecs, Incas, and Mayans, the eastern Roman or "Byzantine" Empire, the Caliphate, the Delhi Sultanate, Song and Ming Dynasty China, etc.

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  • $\begingroup$ While we are on the topic of Larry Niven, Ringworld is a good variant on the idea of a formerly space-faring society that has regressed to a medieval technology because some important system broke irrevocably. $\endgroup$ Dec 7, 2023 at 21:00
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enter image description here

Building stairs might be a very slow process. But trying over the years. I think we can reach the space.

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    $\begingroup$ We're done. this is what we're going with, everyone else can go home, this is THE answer. all hands to the space stairs! $\endgroup$ Dec 7, 2023 at 9:24
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    $\begingroup$ Ahh! That explains it! 😁 $\endgroup$
    – Vilx-
    Dec 7, 2023 at 11:18
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    $\begingroup$ @Vilx- If you make the stairs 36,000km tall instead of just 100km (because why not), you'll be in orbit when you reach the top step. Better bring some sandwiches for the trip, though. $\endgroup$ Dec 7, 2023 at 13:46
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    $\begingroup$ Alas, the stairway to heaven sank straight through the crust under its own weight, so we had to build a foundation to Hell to support it, which was even more time consuming. $\endgroup$
    – g s
    Dec 7, 2023 at 16:44
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    $\begingroup$ The Tower of Babel was constructed eons ago, but then God scrambled the languages of all the people making it, and construction was abandoned. It was rediscovered thousands of years later, still standing. The ancients had made advanced materials and technology allowing construction all for the sole purpose of building to heaven. While they never reached heaven, the tower still went up and up and up for many hundreds of kilometers, into space itself. We found suits in the tower to allow us to survive the vacuum and the rest is history :) $\endgroup$
    – KaffeeByte
    Dec 8, 2023 at 18:51
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What about biological (living!) rocket ships that can survive in the vacuum of space?

Suppose the inhabitants of your world have bred animals, over many millennia, that can generate propulsion via internal chemical reactions.

Passengers and crew are carried inside a chamber in the organism.

Harry Harrison developed a bio-tech civilization similar to this (although there was no space travel) in his West of Eden science fiction novels.

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    $\begingroup$ I feel that if such beasts of burden were available, they would be well past medieval technology simply by having an abundance of non-human power with which to drive machinery and the like. Unless they are very rare. $\endgroup$
    – DKNguyen
    Dec 7, 2023 at 21:19
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    $\begingroup$ Maybe look at Larry Niven's Stage Trees $\endgroup$ Dec 8, 2023 at 23:32
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Babylonian "updraft" tower

Ancestors of your civilization managed to achieve what our did not. Using analogous technology to the solar-sailed craft, they built the hollow tower that extends most of the way you need.

Geothermal energy is used to heat the air at the base to near-lava temperatures. Stack effect gives you whizzing winds in the tower, on which your people would ride in capsules hanging from heat-resistant parashot upwards, even getting considerable momentum at the end, so tower 'shoots' them the last step somewhere, where prepared orbiting craft can dip into sufficiently low orbit to snatch the capsule.

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  • $\begingroup$ Neat idea, but windspeeds can't really exceed the speed of sound in air, which is only about 5% of orbital speed. You might be able to briefly reach an orbital altitude, but not an orbital speed. $\endgroup$ Dec 7, 2023 at 13:52
  • $\begingroup$ @NuclearHoagie ... exactly, and that's why the tower needs to be of a "Babylonian" size and craft needs to prepared to snatch the capsule before it hurls back to thundering winds bellow. $\endgroup$ Dec 7, 2023 at 13:59
  • $\begingroup$ That seems to require that in order to get to orbit, you need to already have something in orbit. How do you get there the first time? You still also have the acceleration problem - the capsule needs orbital speed from somewhere, if it doesn't bring the fuel it needs itself, then the already-orbiting craft needs to bring it. Which brings you back to the exact same problem of how do you get the fuel into orbit in the first place. $\endgroup$ Dec 7, 2023 at 14:09
  • $\begingroup$ How those things got there to pick you up is yet another layer...maybe they shot up all of the homo floresiensis up there to build those things because their slighter frame allowed better acceleration than a robust Norwegian. And how all the florensiensis disappeared. $\endgroup$
    – Rig
    Dec 14, 2023 at 16:14
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You could use an "active support" structure, like a Space Fountain/Tower or Loftrom/Launch Loop. These look similar to a Space Elevator from the outside, but they don't require super-strong materials. Instead, they contain a stream of mass travelling round and round a loop that's either oriented vertically (for a Fountain/Tower) or otherwise angled upwards (for a Loop). That mass is usually assumed to be steel pellets, so it can be guided with magnets; although a continuous cable or chain could be used in principle (but may suffer from large vibrational modes).

Imagine firing a gun vertically, at a target that's lower than the peak of the bullet's trajectory: we get pushed into the ground by the recoil, whilst the bullet will slam into the bottom of the target, pushing it upwards slightly. Now imagine someone attached to the target, who digs out the bullet and fires it back down to us: they get another upwards push from the recoil, whilst we get pushed down again when it hits us. Now imagine doing that over and over, in a constant stream. A practical device would need to replace those guns with something less destructive: in the real world we'd use electromagnets; a medieval setting could use a rope or chain driven by a wheel, or heavy slugs thrown by catapult, etc. (in general we'd want something mechanically powered, to avoid using up gunpowder)

The advantages over a Space Elevator are:

  • No need for unobtainium (since there's no tether)
  • Can be built anywhere, not just over the equator
  • Ability to build up from the ground (rather than down from geostationary orbit)

This last point is interesting, since the system can all be built on the ground, then turned on to gradually lift up the top of the loop. Multiple streams can be used in parallel to support one platform, and towers can be built on top of other towers (as long as the lower towers can support the weight of everything above). The streams can be used to transfer energy up the tower (mechanically or electromagnetically), which is useful for powering the turnaround mechanism at the top. Structures at any point along the stream (either upward or downward) can also "tap into" it to hold themselves up; e.g. wooden or stone architecture that could not support its own weight otherwise.

The main impossibility of such devices is their power requirements. In steady-state we only need to replenish the friction losses; but starting it up and lifting the platforms takes an enormous amount of energy (although, as previously stated, it can be done gradually as desired).

https://en.wikipedia.org/wiki/Space_fountain

https://www.orionsarm.com/eg-article/47e1bb1fc898c

https://hackaday.com/2022/01/01/attack-of-the-eighty-foot-string-shooter/

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Depending on your definitions, it could be argued that some nations in the 20th century and even today are both "feudal" and "spacefaring".

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Actually rockets may be the most realistic scenario. Primitive forms of rockets (fireworks) already existed in China at that time. The problem is having a fuel which could be used to reach escape velocity, without all the knowledge gained only in later centuries. This however could be achieved, if only we allow using some technology without the actual knowledge why it works.

I would opt here for the nuclear power, as it can be justified without such knowledge, if we assume it were discovered accidentally during researching something else. And it could be: e.g. at that time Venice was leading producer of glass products (Murano glass), yet in later centuries it was superseded by Czechia (bohemian glass).

If we assume bohemian glass was a thing a bit earlier than in our reality, and that uranium glass was accidentally invented at that time, by experimenting with various ores (e.g. in Jachymov), it gives a quite plausible explanation for pure uranium being in active use and research, without any knowledge of modern chemistry or nuclear physics.

Let’s suppose then, some alchemist out of curiosity somehow manages to accidentally enrich it on a centrifuge, and causes a nuclear explosion destroying the whole city.

As renaissance Italy was a bunch of independent cities instantly at war, such weapon would gain instant attention of every ruler. Just in this reality, instead of Leonardo da Vinci’s tanks, they will get Leonardo da Vinci’s nuclear warheads (and probably an excommunication of anybody who actually uses it).

And all this assumes only trial and error (and lot of innocent victims) and no actual need for the XX century physics.

From here we can just assume the trial and error (justified and funded by the usefulness in war) leads to finding that this form of energy can be controlled by neutron reflectors. Since those are substances as simple as the graphite, we could still assume it’s reached without understanding why it works.

And having nuclear reactor that can be manually (!) controlled, and its power directed in one direction, you have a rocket propulsion system capable of reaching escape velocity.

Now you only need some religious explanation, why anybody involved in operating such a vessel has burns, ulcers and dies in pain.

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    $\begingroup$ Radiation properties could have accidentally discovered just like our timeline how we almost accidentally came to some of our conclusions when working with things like x-rays and microwaves. $\endgroup$
    – Rig
    Dec 14, 2023 at 16:21
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Alternate Earth.

You don't need an Earth sized planet to have sapient life on it. Make it Moon sized and then you can build a space elevator out of steel.

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Well, all they need is a cannon and a capsule and way to survive the acceleration.

The canon is easy- its just a long stone channel into an active volcano, with a controllable water reservoir overhead.

The capsule seems doable, although reentry and oxygen would be a problem. Lets assume they have oxygen candles with them, as it pleases the gods (which they are visiting).

Now how to survive this acceleration? There are animals that can recover after large traumas. They would be the first test-pilots.

I have no idea how a ancient civilization with marble benches would survive the thousands of Gs.

Maybe transfer "counter" acceleration Gs into a dozens gimbals whirring with rotational energy that chancel out the redirected acceleration? ;)

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  • $\begingroup$ It's easy to prove that it's not possible to get into orbit this way, though. $\endgroup$
    – Hearth
    Dec 9, 2023 at 4:16
  • $\begingroup$ Actually.. why not? if the rail is long enough and the acceleration is linear.. and the capsule is shaped optimal.. $\endgroup$
    – Pica
    Mar 4 at 10:41
  • $\begingroup$ Any trajectory that starts on the surface of the planet, with no acceleration in space, will inevitably either collide with the surface again, or reach escape velocity and leave the system entirely. And no, aerodynamic capsules won't help. $\endgroup$
    – Hearth
    Mar 4 at 15:20
  • $\begingroup$ Think of it this way: A Keplerian orbit is a closed loop, so you have to return to where you started unless you can apply some form of acceleration. Since your last acceleration by this method was necessarily inside the planet's atmosphere, you must return to that same point inside the planet's atmosphere. That means that atmospheric drag will bleed off energy from your orbit, and you'll eventually fall to earth (if you don't just collide with the surface at several km/s first, anyway). $\endgroup$
    – Hearth
    Mar 4 at 15:25
  • $\begingroup$ But if the capsule shape is right and your speed is high enough, you slam on the atmosphere and up again like a flipping stone, and thus your orbit "levels" out. $\endgroup$
    – Pica
    Mar 4 at 15:41

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