Science and Technology

Above a planet's atmosphere is the Ether. Ether is denser than air. When Ether and Air mix, the result is very flammable (hence meteors flame as they come down).

The Tides - gravity and ether have pockets and patterns that are predictable and help with travel, so ships try to catch the tides. Ether is affected by temperature and forms thermal layers around planets (that ships use for orbit).

Ships propel themselves through the ether by releasing air taken from the recycled air and propelling it out the back of the ship, much like a rocket. Long-range ships also have propellers, called "screws", which drive a ship in much the same way as a submarine. These propellers are the main means of long-term propulsion - the screws are powered by ether combustion engines. This pairing of propulsion mechanisms combined with the fluid nature of ether results is ships that look very much like submarines but often with asymmetric domes or extrusions for various cosmetic or passenger comfort reasons (like observation domes, or starlit dance halls, etc).

Potential for ether turbine engines?

Heating and cooking onboard ships is done by piping some ether inside and mixing it (in small quantities) with the air to produce flame. Zombies are all fitted with goggles to protect their eyes from burning when exposed to ether and making the zombie blind.

Hatches are all fitted with an air pump that lowers the air pressure in the "air lock" to a point, but not so low that ether starts appearing, and then the outer hatch is opened, sparking a flash burn. This is why zombies and robots are the only ones who go outside of starships.

Communication between different rooms is done by "blower", where someone can talk (one at a time) via amplified pipes. Messages can be sent to a specific room, or broadcast from the bridge to the whole ship. There is also the mail service where messages are put into a chute and delivered to their destination.

Where does air come from?

It is liberated from water when heated (which is why water bubbles when you boil it).

What happens if you mix ether & water directly?

It makes light (which is how glow sticks can be created, just don't let them break).