Could they send a satellite in space before the 15th century?

Question

Suddenly, on one of their routine maintenance space missions, NASA or SpaceX (or whoever else) finds a big, clunky piece of metal with some kind of mechanical, crude mechanism and a big mirror with a crack in it, including some wooden parts which appear almost completely burned to coal, orbiting our planet.

After retrieving it and bringing it back to Earth for analysis by massive international team of scientists, live-streamed to the world and, for some reason, given high priority everywhere for huge coverage, it is concluded and scientifically verified that this thing was created at least 500 years ago, maybe as far back as year 1200 or earlier, and was somehow launched into space without any known "sources" on Earth.

It appears to clearly be made by humans, but is frustratingly entirely unmarked. There is a part which seems likely to have had some kind of emblem or something on it, but it's one of the burned wooden parts and cannot be read.

Albeit crude, it does have mechanical wheels which are concluded to adjust the angle and rotation of the mirror. An early theory speculates that this was a rich king of Europe wanting to reflect sun rays in such a way that a specific spot, his beloved garden, would get sun 24/7. There appears to be some sort of built-up "power" through a series of metal springs, technically allowing it to change the rotation/angle of the mirror. It seems like this would have been time-based to perform a one-time adjustment once in orbit, but seems to have failed to activate. Even if it did, it's unclear if it would've done much good since it was a one-time thing with no ability to control it from Earth.

There appears to be no attempt to make a radio transmitter or any kind of remote control.

Would this fundamentally "change everything," or would it just be something that a few people shrugged at like when they found that "ancient computer" in the deep in the ocean?

Is it plausible that they discovered some way to get some metal junk up there in orbit hundreds of years ago? Something about pre-"modern times" and space really fascinates me.

Answer 1

No, it's not plausible that they could have discovered some way to put something into LEO or GEO.

First of all, they lacked the concept of space. Those soaked with Aristotelian philosophy would probable have muttered something about spheres in the skies, while others would have simply lacked any theory to even think something could be set in an orbit. And without knowing that there is a vacuum out there, how could one even think of something keeping its motion (almost) indefinitely? Here on Earth everything that moves stops!

Additionally they lacked any theory of motion which would have allowed them to correctly calculate how to put it in orbit, and let's be fair here: if you shot something into space keeping it there is tricky, for once because you need to give it the right velocity (too slow and it drops back, too fast and your bard can compose Space oddity) and then you also need a corrective maneuver once up there to stabilize the orbit, else what you shot will pass back from the place where you fired it.

Last but not least, firing something in the ballpark figure of 10 km/s is going to put a tremendous load on whatever it is. With no knowledge of aerodynamics whatever you are putting in that cannon, assuming it will survive the launch, will shatter to dust in the first few moments of flight due to drag forces.

Answer 2

Reaching orbit, even briefly, requires modern rockets. Critically, it requires a powerful oxidizer to sustain the rocket when the atmosphere thins out; this is what makes it a rocket and not a jet. Modern rockets use liquid oxygen, which was first isolated in the late 19th century; there are some other options (mostly exotic fluorine compounds) that you absolutely, 100% don't want to use for safety reasons and which tend to be 20th-century discoveries.

The reason you need a rocket, and not a gun or trebuchet, is the atmosphere. Let's say you accelerated an object to orbital velocity all in one go while it was standing on the ground. It will try to rise through Earth's atmosphere and that atmosphere will resist it, slowing it back down again. Also, it will very likely be torn apart by the intense drag forces. The ideal ascent profile for rockets is to have a long, relatively slow burn that lifts it above the lower, thicker parts of the atmosphere, then a faster burn to reach orbit.

The reason you need a strong oxidizer (as opposed to, say, gunpowder or any number of oxygen-containing high explosives) is that energy density - both in terms of mass and volume - is critically important. If your fuel is less dense, it takes up more space, which means more physical rocket structure, which means more weight, which means you need more fuel... and all of this quickly balloons out of hand, and suddenly you're trying to fly into space with a mountain of gunpowder the size of Central Park.

Bottom line: unless your court alchemist was tinkering with liquid oxygen, it's unlikely that you could lob anything of size into orbit, let alone keep it there.

Answer 3

Answering your question more directly: yes, indeed, if we discovered such a thing in orbit, it would change everything. The other answers go into why people of earlier eras would be unable to launch such a thing. That means that if we found such a thing, it would be major evidence that everything we thought we knew about history of humanity was wrong, at least for one branch of humanity somewhere in the world.

Answer 4

Notovny wrote a comment that I think should be promoted to a full answer.

As most of the other answers have pointed out, getting to orbit is damned hard and not possible without near-modern technology.

However, there is another problem. Assume that the people of Atlantis knew as much as we do and sent a satellite to orbit.

The problem is that we would already know about it!

Both NASA and others keep track of every object in orbit down to 10 cm. No room for ancient satellites there.

You could have your characters find a very small object, but I don't know what would be distinct enough that we would know it was ancient.

Answer 5

1400-1500CE Europe is a no

But, 200BCE-200CE Greece, Rome, India, or China is a maybe

The Issue of Fuel

The biggest obstacle many other posts have pointed out is the lack of a proper rocket fuel. For this you need a fuel and an oxidizer. While kerosine (a common rocket fuel used today) was patented in Western civilization 1854, as many other Western discovery go, it turns out that it was already discovered long ago. In China, people have been making the stuff since as early as 1500 BC! That's right, we had rocket fuel in bronze age (sort-of). What gives rockets thier kick and lets them keep propelling once in space is the oxidizer. Most oxidizers are either too weak (saltpeter) or invented after the 15th century, but there is one that is naturally occurring which can be used for space rockets: ammonium nitrate. Although naturally occurring crystallized ammonium nitrate is rather rare, it can often be found in bat caves where the climate is dry enough. There are many such caves throughout the middle east. Kerosine and ammonium nitrate have been used together in many modern rockets and could have at least in theory been used by ancient civilizations without needing to actually have a deep understanding of chemistry.

The Issue of Materials

If you want to make sheet steel like they used for early rockets, you need homogenized, tempered steel which can only be made from reliable and uniform sheet metal. That means you need a finery forge to fully melt iron & skim it for impurities, you need a machine to role it into sheet metal, and you need a kiln to temper it. All of these inventions were first seen by 300BCE in China.

The Issues of Scientific Knowledge

You need to know the Earth is round along with it's approximate diameter which was first calculated around 200BCE in Greece.

You also need to know how to approximately calculate arcs, trajectories, and gravitational forces. Although a specific and precise ballistic trajectory formula was not invented until the 16th century by Galileo, this was a major area of study for Archimedes in the 3rd century BCE. Although a specific formula is not among the 1/4 of his published works to survive to this day, the context of his other works strongly suggest that he either invented such a formula himself or at the very least that he had the fundamental understanding to easily solve the problem had the need arisen.

You may also need to account for the differences between Air and the Vacuum of space. The idea of vacuums were first proposed around 450BCE by the Greek atomists. Then later, Epicurus proposed the theory at some time around 300BCE that space was a vacuum. By 200BCE it was a widely accepted theory in Athens that space was either a vacuum or some other state of matter than air called Aether. If Athens had the funding of NASA to explore a space program, they would already know that they would need to test fuels in voids (using suction pumps which they knew how to make) or in aether (by climbing the highest mountain they can find). While they may not come to as precise of calculations as Torricelli did with his barometer tests in the 17th century, they would have been able to experimentally find fuels that burn in a vacuum and show approximately the rate of falloff in air density as you increase in altitude. Knowledge of the vacume of space is also important for unlocking the understanding that once you get there, you can orbit the Earth.

How it could have happened

The problem here is that the Scientific Knowledge you need was invented in Greece, the fuel and steel making techniques you needed were in China, and the the oxidizing agent would have to come from somewhere in between; so, there was no one civilization that had all the pieces as far as we know. That said, there is strong evidence of trade happening across these ancient civilizations; so, if the right powers that be decided they wanted to work together, they could have conceivably brought all the needed technology and resources into one place to build an ancient space program... I admit that it is a sort of big IF, but not all together inconceivable.

Why none of this matters for your story

Unfortunately the question of if such a satellite could be found is not a matter of if it could happen, but if the satellite would still be in orbit by the modern era. Modern satellites don't entirely stay up there all by themselves. They have thrusters that need to make corrective maneuvers every once in a while. They experience minuet drag from the upper atmosphere that gradually slows them down. They experience an ever so tiny push from solar radiation while on the sun side of the Earth that pushes them slightly down whereas there is no push back out while they are in the Earth's shadow. Over the course of a year or two, this might not seem like a bit deal, but over hundreds of years, your obit will contract enough that your satellite will probably fall into the Earth and burn up.

Instead of NASA finding an ancient satellite, it is far more likely for Archaeologists to find the ancient launch site that put it there. It could be a place with clay tablets covered in ballistic trajectory calculations. Giant ceramic vats with kerosine and ammonium nitrate residue. Large primitive foundries with roller presses and finery forges. All the evidence will be there to say that this ancient site was once used to try to put a satellite into orbit.

Would this fundamentally "change everything", or would it just be something that a few people shrugged at like when they found that "ancient computer" in the deep in the ocean?

It would not fundamentally change everything, atleast not overnight. This is because critics would do everything they could to try to prove that they never made it to space. Even if they found mission logs carved in stone, it would take years of translating and debating translations, and debating the trustworthiness of the texts that it would take years and years of study to prove if thier methods could have "maybe" worked. By the time a scientific consensus is established, the site will already be old news.

It would probably be about as significant of a discovery as Leaf Erickson beating Columbus to the new world. People will acknowledge that it happened but still hail sputnik as "the first satellite", not because it was first, but because it marked the beginning of a new age whereas the Greek/Chinese thing in 200BCE was just an experiment that never lead anywhere.

Answer 6

I will refer you to "The Road Not Taken" by Harry Turtledove. In it, a race with matchlock weapons, blackpowder, and gravity control based FTL travel invades Earth. In their experience, lots of planets got that gravity control, and some flew wooden spaceships. Earth just never worked it out on their own.

But maybe someone did, launched a few things, and then killed off the knowledge. If the remains include the unknown technology, then it might spark some major changes. If the remains don't have the technology, then you just wind up with a big mystery, and probably more alien conspiracy theorists.

Answer 7

Shooting a projectile using primitive technology is not.....a strenuous exercise, China and Korea were some of the first to use rockets as weapons......shooting one into space.......is a more daunting task and highly unlikely. The fuel to weight ratio of a rocket today is several pounds of propellant for every pound you send into orbit, not to mention the weight of the vehicle itself. 15th century metallurgy of bronze, brass and primitive steels. Though early 20th century rockets were made of sheet metal. Versus modern lightweight metals like aluminum (which was discovered in 1825). At 10 meters high, Japans SS-520 is the smallest rocket to deliver an orbital payload and the payload was 9 pounds and required nearly 2 tons of fuel. So....it's unlikely, however the rocket has to survive the intense exhaust and thrust heat, fuselage oscillations and super sonic speed. Plus the specific impulse and fuel economy of the rocket fuel has to last to an altitude of 100km (legal definition of space) and gunpowder simply doesn't have the capacity. Modern rocket fuels are cryogenic liquids, solid monopropellant chemicals or refined kerosene. The energy density of gunpowder is 4.7 Megajoules per kilogram; aluminum 31 per kilogram.

Answer 8

It's surely an interesting question.

There most likely would be a world wide investigation.

But the only way to get something up there into space using the technology of the 15th century would to build a very big cannon, albeit unlikely since while they could do something like that hypothetically, it simply would be unfeasible, and if not, this would be a project that everyone would have known about, so if it did happen, the mission NASA would most likely do is to recover that satellite, albeit also unlikely as Johannes Kepler did not publish his laws of orbital mechanics until 1605.

So let's say they built such a cannon, the satellite would enter an unstable orbit if it achieved orbit at all, than after a while, it would reenter, and burn up.

So sorry about that bad news, but this scenario is unlikely at best to have happened.

Answer 9

Well, if you take what nowadays is retrofuturism, but was Sci-Fi in its time, there this Jules Verne guy. In one novel, people are going to the Moon with a glorified cannon shell, in another one a bomb from an oversized cannon becomes a sattelite. But this is the new time, long away from the medieval times you are looking at. And not real, too.

You'd need some political changes to even try to make this happen. Having a technology to shoot a payload to the space means also having a technology for a much more aggressive warfare. You just don't send some da Vinci tech to space without anyone asking how to weaponise this.

I think that your best bet might be something Asian, with their gunpowder availability and firework skills. Like, a much stronger Chinese empire of that time (because no Manchu conquerers or whatever) or someone like Oda Nobunaga, who was not betrayed. Fast-forward 300 years from the satellite and you have China / Japan / whatever ruling over half a world.

Answer 10

This may be pushing steampunk TOO far beyond the limits of credibility! It could work in a fantasy rather than sci-fi world. Some 'lost art' quasi-scientific magic would be necessary. I wouldn't try to go too deeply into technical details though!

Answer 11

You need the idea that orbits, and putting something there, are a thing

This might be the largest obstacle, because before you assemble a large-scale effort to attempt something, you need to be aware that this something is even a thing.

• The concept of a friction-less vacuum where movement continues forever unhindered, and that the atmosphere quickly gets thinner as you ascend
• A basic understanding of gravity. You won't need Newton's full formulation F=GMm/r² for low earth orbit, but you must understand that F=mg. There will be some calculation errors from this inaccuracy, but they won't be significant enough to jeopardize the project, they'll just mean a few more failed attempts.

From these basic understandings, someone sufficiently brilliant can arrive at Newton's Cannonball thought experiment and get the idea to actually attempt and put something in orbit.

Imagine a king who is very interested in scientific, mathematical, philosophical and engineering matters, who is so absurdly rich that he can employ dozens of the most brilliant minds of his generation without demanding specific results (e.g. better Trebuchets) but instead encourages free discourse. In this environment, these ideas might be discovered.

You need the political will to do it

The project will increase in scale exponentially. The more work you put into it, the more you'll know about the issue at hand, and the more you'll realize the impossibility. At first, the few dozens of great minds at the King's court will work on it, but quickly they'll need laborers who do the more tedious parts of the experiments, engineers who can work with steel, etc. In medieval times, employing a few dozen great minds already consumed most of a rich King's spare resources.

I cannot estimate the amount of manpower that would be required, but it would certainly exceed the Manhattan and Apollo projects, employing millions of scientists, engineers, mathematicians and laborers. In a pre-Industrialization society where food can be neither produced nor transported efficiently, where the largest part of the population must work in agriculture just to secure the food supply, this would be... hard.

• You need a multi-nation effort. An entire continent would need to work together.
• There will be mass starvation, which will trigger revolts. It is impossible to explain to your peasants that they must produce food for the Orbit project while their children are starving. You need tyranny, without an external enemy to threaten the fragile political system.

You need an unprecedented motivational event. Something along the lines of: Jesus himself appears before the court of every king, and not only threatens but demonstrates that if they don't put their quarrels aside and invest everything they have into the Orbit project, they will die and go to hell. Sufficiently advanced technology could do this (it is indistinguishable from magic, after all), but a medieval power couldn't, with certainty.

You need skilled people

This many scientists, mathematicians and other people of learning simply didn't exist, not anywhere in the world, and especially not in medieval Europe. Heck, most people were illiterate. You'd likely need a bootstrap phase where you kidnap the smartest peasant's kids and put them through a school system that was put in place by the few existing scholars, and then those kids can teach more and more people until maybe 50 years later you have a reasonable core of people who are in the right mind to perform some massive engineering feats.

Probably the Eastern Roman Empire along with their Islamic counterparts, or maybe China, are the most likely to succeed in this; they have a significant head-start over Europe.

Jesus will have to make frequent re-appearances to keep people motivated in the mean time.

You need a rocket engine

Launching things with a cannon is not possible because:

• The muzzle velocity is limited by the chemical reaction speed, which is much lower than orbital velocity
• Complex mechanical contraptions are destroyed by the acceleration in a cannon.

You have basically two choices: Liquid-fueled rockets and solid-fueled rockets. Liquid-fueled rockets are much more efficient, but so much more complex that I immediately discarded them as a possibility. If you cannot even build a steam engine, don't try this. Sufficiently precise tooling or advanced materials simply did not and could not exist. Solid-fuel rockets actually did exist in China as early as the 13th century. Fueled by black powder, they achieved an exhaust velocity (specific impulse) of bit under 1km/s. The Tsiolkovsky rocket equation, which will of course also need to be discovered by the Orbit project's mathematicians (certainly one of the more minor feats), tells us:

To achieve orbital velocity (delta-v = 7km/s) with an exhaust velocity (v_e = 1km/s), we need a certain initial mass m0 to result in a final mass mf.

ln(m0/mf) = delta-v/ve

m0 = mf * e^(delta-v/ve)

So to launch a 1000-kg satellite, at launch the rocket must weigh at least 1097 metric tons. Unfortunately, you also have to account for air resistance, gravity drag, and the weight of structural components of the rocket. You can reduce the gravity drag by using higher thrust, reduce the air resistance with an aerodynamic design (or lower thrust), and reduce the weight of the structural components by using multiple rocket stages. Most likely, your rocket will have at least ten-or-so stages.

We can safely assume that the alchemists will be able to increase the specific impulse of the fuel to maybe 1.5km/s - finding some performance-increasing additives is a minor feat for thousands of scientists working on the problem for decades; a 50% increase in specific impulse reduces the required propellant mass ten-fold. Accounting for all expected inefficiencies and improvements, I estimate the final mass of the rocket to be between 1000 and 10,000 metric tons - certainly achievable from an economic point of view, for somebody who manages to feed a million people.

You need an attitude control system

Rocket launches don't just consist of pointing up. You need to pre-calculate a trajectory (hard, but doable, without a computer), then use a control loop that measures the attitude of the rocket (very hard) and uses actuators (movable air fins on the bottom stages, engine gimbaling, little rocket engines) to correct it and make the rocket follow the desired path.

The easiest way is probably to put a human inside a space suit and make them control the rocket. They will die, of course, and making space suits is hard, but somebody willing to starve the population of an entire continent for the Orbit project should have no problem finding a "volunteer". The last few stages, which would be used to circularize the orbit, can be spin-stabilized and sequenced automatically to eliminate the need for the (heavy) human controller.

You need to develop and mass-produce materials

Apart from a greatly improved version of black powder, which you'll need to produce in the thousands of metric tons, you'll need stronger/more lightweight steel alloys (aluminum is out of the question IMO), precise tools, pressure vessels for the human controller, some sort of highly-precise hydraulics system for the human controller to actuate the attitude control system, and many more materials that were unimaginable in medieval times.

It's probably doable

But not without some sort of godly intervention that motivates an entire continent to work together while starving their population.

There would be many, many failed attempts since engineers in that time mostly had a gut-feeling, trial-and-error mindset.

The project would take at least 100 years and involve immense human tragedy, but science and engineering would experience a massive leap forward. It's quite possible that the steam engine would be a minor side-achievement of the Orbit project. The satellite would definitely not be made of wood.

Basically the Orbit project would fast-track humanity, causing it to skip a few centuries.

It is absolutely unimaginable that there would be no historical record of this madness. But it is possible that right after the satellite was launched, the peasant revolt is finally successful and, in its outrage, destroys most of the amazing achievements of the project.

Answer 12

The escape velocity of earth is around 11km/s. A bullet might go 1km/s at best. So, chemical guns are around an order of magnitude too slow to get stuff into orbit.

So yes, it would change everything. The premodern civilization has some way of getting something into space that's vastly easier than the billions we invest into space programs.

Answer 13

Leonardo has done it again? That Da Vinci kid needs watched your highness.

The truly astonishing part? An orbit that didn't decay, and drop it back to Earth in that length of time. We have had satellites that were placed in geosynchronous back in the sixties find their way back to Earth. Anybody who could put one up there 500 years ago that never fell down would have to know something we don't. That said, JP Aerospace has made a lot of headway with the "airship to orbit" concept, so who knows?

Answer 14

Yes, it's potentially doable with the right circumstances.
That's a Science & Engineering based conclusion derived from a good understanding of what's involved.

Scale of project:

Various people have mentioned NASA and Apollo and suggested that the scale needs to be similar. It doesn't. The eg British Black Arrow launcher / Prospero-satellite program was done astoundingly cheaply. The entire program cost 9 million GB pounds in 1970 - and in a total of 7 years was built in workshops similar to those already used in British Industry. Certainly far far far from typical 1500s technology - but further still from Apollo.

In this case we are starting from scratch. An appropriate comparison is the work of Dr Robert Goddard who in parallel with others 'invented' the modern liquid fuel rocket. His best results were trivial by modern standards - and within a decade were utterly eclipsed by the German 'V2' - but it shows what sort of development can achieve. He had the advantage of modern (for 1930) materials, fuels and technology. Our genius team need 'a while longer' to develop their base.

Many decades ago I seriously researched what was required to put the sensibly smallest possible satellite into orbit. Given 1500's technology and the resources of a large kingdom plus the use of brains greater than mine who I could set on the right track, plus maybe a few decades of playing, I believe I would have a fair chance of putting a satellite into earth orbit. I can add far more detail if people are interested. So far nobody seems to be :-).
So, doable.
Maybe.

Guidance & the gravity curve "falling into orbit".

Guidance has been mentioned and claimed as essential. It's not. It's highly desirable, but using a "gravity curve (which is what you often see painted on the sky after an orbital launch) the rocket "falls naturally" along the correct curve. Staging can be by timer and/or drop in acceleration.

From here

While the trajectory is controlled it is designed to follow the self-maintaining gravity-curve thereby minimising dynamic forces on the craft.

All modern satellite launchers start their journey pointing vertical. Guidance systems then orient the vehicle as required.
Older launchers have large or even very large fins. Modern rockets have vestigal fins or none. Dynamic (rocket thruster and engine or jet steering based) guidance has taken over from a mix of dynamic and aerodynamic. At the limit a launcher could use a mix of aerodynamic and spin stablilisation - with perhaps some gyroscopic jet vane steering (as used by eg the V2)

Graphite rocket jet deflectors used to steer V2 rocket.
The vanes are gyroscopically controlled. The Gyroscope was invented by Focault in 1852 - Leonard da Vinci 1452 - 1519, could have 'invented' it on a wet Saturday afternoon if he'd happened to have ever spun a wheel on an axle and noted (as he would have) what happened.

[My photo: Taken in Deutches Museum, Munich]

Examination of images of early high altitude launch platforms shows the rockets mounted at an angle to the ground.

Getting there:

The rocket equation mentioned by others requires two main aspects to be optimised

• The mass ratio (MR) of the rocket = Launch weight/payload - with most of the launch mass needing to be fuel. For multiple stages MR per stage needs to be high. The final MR is the product of the MR of all stages - so the payload gets rather small rather quickly with multiple stages.

• The "Specific Impulse" (Isp) of the fuel. = thrust x seconds per unit mass of fuel.
  eg a propellant with Isp = 300 will give 300 kg.seconds of thrust per kg of fuel.

For orbital success you need an Isp of 300 or better. Lower is possible but the required mass ratios get very very bad indeed. To get an Isp of 300+ you need either advance solid fuels or something like high concentration Hydrogen Peroxide (HTP = High Test Peroxide) + kerosene.

• A solid rocket fuel based on Ammonium Perchlorate Aluminium and Butyl Rubber was used in the STS SRBs (aka Space Shuttle boosters). In 1500 the Aluminium has to wait another 300+ or so years to be discovered. The Ammonium Perchlorate is doable but you need to bring forward electric batteries and the like rather too far. The Butyl Rubber is a problem [tm]. I'd say a solid rocket is too hard.

• HTP (high concentration Peroxide) is conceivably doable in 1500 - you do have a large kingdom behind you to refine the art. Kerosene is easy enough - although the techniques of refining may have to be referred to my learned colleagues who I set on the right track.

Turbo pumps are utterly out of reach.
Large pressurised tanks essentially so.
Fortunately, there exists a slowly developing technology under investigation by NASA that uses gas pressurisation to drive a small gas powered pump to propel a low pressure tanked rocket. within its niche its as good as turbopumps and far far easier and cheaper.
I "invented' this technology long ago (really) BUT so did a number of others in parallel.
Flometrics Pistonless pump 2003 paper, & website & Wikipedia with various references. They are using very high pressure Helium - there are other methods.

SO

Doable? - Just maybe.
Which is good enough for a story :-)

What NASA would make of it is unknown :-).

Note that long lifetime is not a major issue once you can get to orbit at all. The extra needed to provide a much higher lower drag orbit i relatively small. Getting ti geosynchonous orbit is far harder and a small mirror would provide minimal illumonation. The likely use of the mirror was just to show it was there - a small occasional bright flash in the sky. There it goes again!!! :-)

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Black Arrow - 1969

Black Arrow HTP + Kerosene satellite launcher.

Add a "Pistonless Pump" for turbopump free technology.

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Did they know enough?

In 1500 Leonardo da Vinci had 12 years to live.
While he was exceptionally exceptional, he demonstrates the sort of knowledge and brain power that may have been able to be brought to bear on such a project.

Starting from somewhere before 300 BC a growing body of knowledge that could serve as a foundation for orbital calculations existed in many different places - starting starting some 2000+ years before Leibnitz and Newton built on the time honoured foundation.

Archimedes established basic principles of Calculus in about 225 BC.
Ibn al Haytham extended the work in around 900 AD.
Indian mathematicians added to the knowledge base well before Newton.
Various Greek, Chinese Asian and European scholars did related work with the earliest known from around 300 BC or before.

Excellent wide ranging reference here

A Google search of references here

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Discoverability - or lack thereof:

In 2002 an amateur astronomer discovered object J002E3. This is probably the 14,000 kg, 18 metre Apollo 12 S-IVB third stage. If it is (which is likely) then it was 'lost' for 31 years until being discovered in 2002. It's believed to be in an unstable mixture of geocentric and heliocentric orbit with a 40 year cycle between the two. Mass is 14,000 kg, and length 18 metres.

J002E3 orbital path

LEO (low earth orbit) requires a velocity of about 5 miles per second. Earth escape requires 7 miles per second. Between the two are an infinite family of trajectories which may be highly time asymmetric and which may result in objects travelling far from earth, to return at some future or far future date.

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Where and why unknown:

China sounds like a good start. But is by no means unique.
Why emperors create things to help people remember them, who can say.
But that they do is well known.

The Taj Mahal is said to be in memory of a loved wife.
We also remember its sponsor.

The Terracotta Warriors reach across 2000 years of time to remind us of their creator.

The mirrored satellite could have been a demonstration of power - See that glint in the sky - I put it there by my might and ability'.

Why no mention?
Perhaps because it did not work - or not visibly so. The Emperor moved on to easier memorabilia.

Any number of similar tales could be told.

Answer 15

As others have pointed out, medieval people lacked many advances needed for rocketry - physics, chemistry, mathematics and so on. However, they may have had the ability to build a giant cannon (eg. a development from something like the Dardanelles Gun) and use a powerful enough explosive to give some object sufficient velocity to get it into space. But without all the other required knowledge, they would have no control over the object's fate after launch - it would either eventually fall back to Earth or escape the Earth's gravity all together. And lacking knowledge of what is out there, I can't think of a good reason why they would want to do that, except perhaps sending a message to god.

Answer 16

The requisite discovery of physics changes everything afterward

The mathematical facts - the equations, the proofs, the processes using them - all these things existed before mankind discovered physics. But the fact remains that physics was invented by Isaac Newton, who also synthesized a lot of pre-existing work to describe the math (probably simultaneously with Leibnitz) necessary to even understand what the equations mean or why they work - calculus.

This happened in 1687.

Kepler discovered his Laws, explaining interplanetary motion and correctly describing the motion of the planets, between 1609 and 1610. He couldn't explain why the planets moved the way they did; that requires gravity (which would be described by Newton decades later).

Newton invented physics, with the laws of motion and gravitation. You can't get to orbit (or even understand that orbit is falling without ever hitting the ground) without understanding these things. He built on work others had done, so perhaps you could have someone invent these things elsewhere, earlier. This could get a satellite into orbit before 1500.

But...

History looks completely different

The technological advancement necessary to get something into orbit almost has to cause advancement in many other areas, like weapons or hygiene or metallurgy. Essentially everything is different then, because it interacts with political history in unpredictable ways that snowball until the 'modern day' looks completely unrecognizable.

In our history, for instance, the United States exists because it won the Revolutionary War. The fact that democracy was proven to work because of the USA's existence changed a whole lot of things that happened afterwards. Would the French Revolution have happened if the "Revolutionary War" was instead known as the Ingrate's Rebellion after the British crushed it with ease? How about if there never was any fighting at all? Would Napoleon have happened without the French Revolution? Would there have ever even been a British Empire, or British colonies in what is now America to fight a Revolutionary War over in the first place?

What might the world have looked like if someone somewhere had gotten something into orbit in the 1500's? How would technology advanced? Less than a hundred years after Sputnik in ours, we have GPS and the Internet.

TL;DR - Any world in which mankind knows enough to get something into orbit in the 1500's, should reach our level of technology by 1700's. And that means what you're really after - our world, but if ancient astronauts - needs a convincing explanation of how a group so much more advanced than everyone else met its doom without their advanced knowledge or technology leaking out and changing the course of history.