Ok so first of all, let's imagine a civilisation on a planet. The planet has a relatively low escape velocity, say 6 km/s and maybe an atmosphere 30% - 50% the thickness of earth's atmosphere. Now imagine the species wants to send something (a probe, an object) into space (can be very small, say down to 1kg of mass), what minimum amount of knowledge/technology would this civilisation need to have in order to achieve this goal?

I would imagine, that they would at least need the very basics in the laws of gravity. That would make them a pretty advanced civilisation already. But given perfect circumstances (and maybe a little bit of luck) how primitive could you go, before it becomes too impossible?

EDIT: They would also want the object to stay in space. So reaching an altitude considered "space" and then entering the atmosphere again wouldn't complete the objective.

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    $\begingroup$ Surely you'd want same technology as when we launch the first object into space, it'd just required less fuel and/or physical resources to launch. An "object" could just be fired, a probe would require proper launch. $\endgroup$
    – BMS21
    Aug 8 '18 at 10:21
  • $\begingroup$ Is the payload manned, autonome or remote controlled ? $\endgroup$ Aug 8 '18 at 10:26
  • $\begingroup$ @Magic-Mouse the payload could just be a rock, it doesn't matter as long as it reaches space and does not fall back to the planet. $\endgroup$ Aug 8 '18 at 10:30
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    $\begingroup$ The issue of course is that this is computer game logic where the word technology is used in a very specific way. There is no linear tech path in reality that we follow and that species could reach space after researching X. Technology really means the ability to do stuff. So the obvious answer is: They would need to be able to launch an object into space. While I'm aware that I'm just debating the meaning for words here, it's really important when building a world to use the right vocabulary to accurately describe what you are doing $\endgroup$
    – Raditz_35
    Aug 8 '18 at 10:30
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    $\begingroup$ Is the goal to reach space or reach orbit? Space on earth have a delta-v budget of 1.4 where as orbit has a delta-v budget of 9.4 $\endgroup$ Aug 8 '18 at 10:35

Unfortunately I don't think it really changes the requirements all that much. The main problem is that you need a means of propulsion and lift that doesn't rely on the surrounding air at all (because eventually you will have insufficient air). Even with the lower escape velocity of this setup, imparting all that velocity to a capsule through a fixed mechanism like a gun is still unsurvivable, albeit less so. This is especially true given that you want to end up in a stable orbit, rather than a ballistic trajectory.

It would however be cheaper, and it would be easier to engineer safe and useful vehicles because you would have a higher payload mass fraction - that is, your launchers would be less fuel and more payload, proportionate to their total mass, than ours are. That simplifies a lot of design and management needs of your space program, which in some ways are more difficult than the actual scientific breakthroughs involved. So there is a definite benefit to your scenario, but it won't be in terms of the technologies brought to bear.



Depending on the fuel, rockets can either be simple or complex, less or more efficient. But for a decent rocket that could get something to space, and indeed was used as the model for the Saturn V, let's look to the V2 rocket. That's second world war period (1944). So, look at around that time for rocket technology. You are not just looking at pure thrust, you also need to consider guidance systems. Hypothetically, you could generate the thrust, but if you don't have the technology for the guidance system and control systems, then you may as well just fire it and cover your eyes - hoping it won't hit you.


However, you want to also send a probe. Now, you have to ask yourself: "what kind of information do I need this probe to gather?" a 1kg probe is not large and is limited in the telemetry that it can carry, and thus would be limited in the science that it can perform. Particularly if you are looking at a very early development probe. But there's a lot to consider here.

A probe needs a power source, early batteries were large and heavy. These batteries needed to power not only the transmitter (to send whatever data you're gathering), the data gathering system (gets whatever data you are interested in), and the thermal regulation system (because space is a vacuum, it's actually pretty hard to cool down. Most thermal transfer on Earth is done via convection and conduction. Without air, you're stuck with radiation.) So, already you're looking at something probably way bigger than 1kg. Of course, you can reduce this weight by ditching a science device and just having a transmitter that basically just beeps so that the ground station knows that it's actually up. You would never send up a probe without this, you may as well just launch an empty rocket.

Extra stuff

Remember the more primitive the technology, the bigger and clunkier stuff is. Transistors on circuit boards were larger. Batteries were larger.

Have a look at Sputnik as an example. That big ol' sphere with sticks was a whopping 80kg (or something).

The Space Race caused massive leaps in technology. The huge number of people who worked for the space organizations were often breaking ground and setting new paradigms. So, if your civilisation suddenly decided to totally focus on getting something into space, maybe they would have that huge leap in technology - and all the useful payoffs for general society's technology, particularly once they start launching people.

I love speculative questions like this (: I'm an aerospace engineering master student, so that's where a lot of my info has come from.

  • $\begingroup$ Guidance systems are a good point. Thinner atmosphere and lower gravity don't change the complexity of guiding a vessel into space. $\endgroup$
    – Schwern
    Aug 9 '18 at 5:48

If you want them to be able to reach orbit, then they would need 1950-1960s level technology, that's just where technology and ability to build complex rocket motors, hypergolic fuels, cryo-fuels etc exists and the ability to build very basic computers to act as the guidance systems.

However it its just to reach space, then it depends on how high you determine space, this is still in debate even to this date in real life.

a hydrogen filled balloon can make it the most of the way to space, lower gravity is going to make that slightly easier. so basics of understanding gravity yes, but Newtons laws would be acceptable for that. so it'll be down to the ability to build a weather balloon. which first happened in real life in 1986.

  • $\begingroup$ right. This would be also part of my question though, would you need a computer guidance system in order to reach an orbit? It would certainly help a whole lot, but what if I just burn solid fuel and point at the right direction in the sky? $\endgroup$ Aug 8 '18 at 10:41
  • $\begingroup$ @filedescriptor, yes you would, it is possible to reach an orbit, without, but you would need to spin the craft before and during launch, this is being looked at for the Mini-MAV which hopes to do sample return from Mars, but even then it's not easy. although lots of up will get you to space, to reach orbit you need to be able to go up, then a lot of sideways and then once on the other side of the plant, circularize the orbit, this needs either manual control or a guidance system $\endgroup$ Aug 8 '18 at 12:26
  • $\begingroup$ @filedescriptor you don't need a full-blown computer, but you do need basic electronics to control engine burn and stage separation. The rocket will be unguided, but if you set all parameters right, it will reach the orbit. $\endgroup$
    – Alexander
    Aug 8 '18 at 17:06

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