Planets without atmospheres or moons with atmospheres

Well yes, I was working on the assumption that anything that was capable of vertical take off and landing used rockets. It just seemed too pedantic to say "I don't want anything that employs an airfoil to function"

I don't see why the planet configuration would limit us to anything as mundane as realism. Imagine a popup trying to stop you; "sorry, this planet does not have enough mass to have an atmosphere", it's absurd. So I don't think this is a worry.

On planes. I don't really mind whether the atmosphere affects them or not. What I want is readability, relevance and consistency.

• It should be obvious at a glance what can and cannot fly in an atmosphere. This is mainly an artwork thing, gunships should have obvious thrusters and planes should clearly rely on their wings.
• It should also be easy to see if a planet has an atmosphere that allows plane flight.
• Whether or not planes can fly should be significant. Limiting planes is pointless if there are equivalent units which can be used on airless planets.