Would it be possible for a civilization with absolutely minimal knowledge and use of electricity (Light-bulbs, basic electric motors, and archaic radios) to reach space?
I was thinking that a solid state rocket of some sort would be usable to reach orbit. Steering functions could be entirely mechanical. The only problems I can think of are air supply and propulsion out-of-atmosphere.
If central computer is your main concern, worry not: Fluidics to the rescue. Your computer will be larger, less efficient and heat up more, but it is possible to build digital computer with such tech. Salient point, is that in fluidics, small stream can steer larger stream, introducing non-linear amplification necessary to build logic gates.
For obvious reasons, we never developed fluidics to significant degree, but you can expect society relying on fluidics for it's computation to put some impressive feats of miniaturisation. You can also expect more compact power sources and better heat management.
According to linked wikipedia article, fluidics are currently worked on, as a way of thrust vectoring and as a way to enhance aircraft control surfaces - in fact, wiki states they are MORE efficient at those tasks than ordinary, fly-by-wire controlled, control surfaces.
Greatest problem would be power generation, you simply couldn't use solar panels, batteries or nuclear thermoelectric generator with efficiency we can use them with. Instead you could use Stirling Radioisotope Generator, but instead of using Stirling engine to drive dynamo generating electric current, you would use it to drive pump generating other type of current. Or perhaps they could figure out some way to do it more directly and more efficiently, without intermediate engine-pump stages.
Unless there are problems in construction of the spaceship itself (like pointed out in comments problem with aluminium), you could go to space without electricity. You would however be unable to communicate with space, and from space, because you would have no radio. Practical radio requires vacuum tubes or transistors for amplification, both can fulfil same role and both can serve as basis for electronics and computers, obviously, transistors proved themselves superior thanks to lowers size, power requirements and higher reliability - your society can't have practical radio with any meaningful range without rendering premise of the question moot.
Hydraulics and cables. You could use liquid fuel. Have the hydraulics powered by a diesel engine, warmed by the thrusters. Control the throttles and control surfaces with cables. Unfortunately, you would need a pilot who is a combination of Schwarzenegger, Einstein, and Evel Knievel.
Diesel engines use pressure to combust the fuel, rather than a spark. Once the engine is warm, they require no electricity to function, unlike a gas/petrol engine.
Potentially yes. I think a good place to start is to lower the escape velocity (on earth 11.2 km/s)and theres a lot that could be done to achieve that. Some planets may be much less massive and less dense. But now to hold an atmosphere they'd need to be colder but if it's to cold it may not be able to sustain large intelligent water based life (on the surface). This can be sub 0 but you have to raise the pressure meaning a larger escape velocity but you may be able to find an ideal point and have hotter regions on parts of the surface. https://www.google.co.uk/search?q=water+sublimation+chart add salt to that
So lets say take it down to 9 for the temp difference lets also say it started thinker so go for 7km/s maybe even 6. Another option is perhaps to have to something orbiting but in a locked orbit so there aren't strong tidal forces. So maybe 6 km/s or 5 maybe even 4. and our orbital velocity is 7.8 for an escape velocity of 11.2 so 70% so you could potentially have an orbital velocity of 4.2 or 3.5 maybe even 2.8. Also rockets don't need air as the oxidiser (assuming it's an oxygen based reaction)they carry it.
So with these unusual conditions and probly others you could conceivably have 1/2 or less of the escape velocity or even go further rocket's. Exhaust velocity of liquid rockets are around 4.5 km/s solid 2.5. exhaust velocity does not have to be as high as escape velocity we get to space with 4.5 and 2.5 with a 11.2 to escape so it's conceivable these aliens could get something to orbit with effectively a very large fire work.
As for lightweight materials well they might not be as good as some of the ones we use but there might be naturally occurring and particularly strong forms of carbon on that planet either produced by plants or animals like with spiders silk or even found in the ground in a concentration that are practical for use.
The technology you're describing is about WWII era. With light bulbs, radios, and motors you can actually do quite a lot. Specifically the inclusion of radios mean that you have vacuum tubes or other such amplifier units, meaning that you actually have most of the simple building blocks of navigational equipment, as well the manufacturing process (such as aluminum smelting) that provide some of the semi-advanced air frames that make spaceflight easier.
The main limitation on your spacecraft, as well as the main feature in construction, will be the lack of computer aided design that has shaped the modern aerospace industry. Dust off your slide-rule and get ready for some 3rd and 4th order differential equations!
Now, hand calculation doesn't sound all that bad (unless you don't enjoy math), but it will have two noticeable effects. 1) Your space vehicle will not be optimized! Hulls will be unnecessarily thick, fuel systems will be less efficient, components will require larger tolerances, etc. If you want some case studies I recommend reading up on WWII era fighters, bombers, and freight aircraft. At the very least use google images and find some visual inspiration from technology of that era. 2) Your space vehicle will require larger crews. Without low-level automation of maintenance tasks, you'll need skilled laborers to keep the ship running smoothly. Additionally, you'll need specially trained navigators and pilot crews to fly the vehicle. A secondary effect on crew size is that your ship--which is not optimized and like an early Soviet ICBM will have to be very over-sized to achieve it's goal--will have to be larger, carry more fuel, require more maintenance, and so forth. This larger size will require a larger crew to maintain and control.
As a side note on computational systems, though, you don't need heavier and harder to maintain digital systems like fluidics or pneumatics to build a computer. If you have radios, you have an amplifier element--the buidling block of a digital switch. Sure, your computer will be the size of a large apartment, but if its fast navigational calculations your trying to run, it may be worth lugging UNIVAC around.
I should note too, as relates to your comment on using solid fuel, that a liquid fueled rocket is very much within the reach of a non-electric society. Also, if you've got motors, it is fairly easy to due fly-by-wire systems with minimal knowledge of how electricity work. The components used in a simple feedback loop like PID controller were available before WWI and where actually tested in a auto-pilot like drive-by-wire system for seagoing vessels. As for the air-supply, all you need is a fan to circulate air, a couple of plates of compressed and chemically processed volcanic ash and some oxygen producing reaction and you've got a low-tech scrubbing system that worked for pre-WWI U-boats BUT is still in use on modern spacecraft.
That fact that your civilization is making it to the exosphere before the advent of digital computers is impressive, but it makes me think that your probably avoiding the development of the digital age, and that the current state of aerospace engineering is the result of a long process of trial and error. That said, the technology you've made available makes it possible to build a surprisingly sophisticated space-craft, so enjoy going inter-planetary (or least back and forth from the space-resort 150 miles above the Adriatic Sea)!
Hope that Helps!
I wonder if a different direction might be possible in your world.
Your tech base has not developed - but how is the biological base? Perhaps your civilisation has not developed electricity because they did not need to. Perhaps they developed something else instead - an advanced level of biological tech. In other words - instead of electrical light, they have developed plants that glow in the dark. Instead of telephones that send electrical signals over wires - they have grown plants that are connected through a root system which can be spoken to one "node" and the words are repeated at another node. In such a system how could you identify what the remote node you wish to connect with is? Each node could have a "pattern" that is unique - a set of symbols which when drawn on any other node in the correct sequence - creates a direct channel for repeating sounds (spoken words etc) at the remote node. These are just a couple of examples about specific tech that could be done differently in biology but achieve a similar outcome as with electricity.
How could such a tech base achieve Space Travel?
In a few ways - first - control systems would be grown - using plants like the communication technology I desribed above. By drawing symbols on control nodes - specific instructions can be issued to remote nodes that have just a few very limited functions. Opening/ closing valves, rythmicaly squeezing bladders (Pump action), twisting surfaces (moving soloar panels to new orientations) Solar panels can capture solar output and convert it to energy to accomplish tasks. Specific "organs" could store the solar energy for later use. Specific organs/ containers can be grown to create heat internally for food preperation or other activities that require heating. - second - fuel requirements. Special trees would be grown that have hollow cylinders which when they mature into the correct hardened capacity/ materials then fill with liquid OR solid fuel. All of the above systems would be grown in place in the crown of the tree. The fuel would be drawn into the tree from root systems that reach out to mineral deposits that contain the fuel elements and refine it as it is brought in to the tree. OR could be collected in other plants that are then transported to where the rocket trees are growing and decanted into the "fuel tank"/ hollow cylinder/ trunk of the tree
I think the problem is going to be fine engine control/navigation once you are in space (versus just a big rocket that lifts something into orbit) and having any ability to monitor systems, provide for life support, and establish a centralized control board. If everything is mechanical that is going to add a lot of weight for dials, gauges, levers, gears, pipes, etc instead of sensors, electrical wiring, automatic pumps, and electrical displays. Think of something more like a WW1 submarine than an Apollo spacecraft. More weight for all that mechanical redundancy means less room for payload and less ability to detect and fix problems.
Probably can be done, but the cost in materials and human lives is gonna be WAAAY higher.
