Nuclear fission! How hard can that be? Nuclear reactors have been quietly humming under the earth's surface only a few billion years ago after all.
It's very convenient then, that my planet's quite a bit younger than earth, and has many of them deep below, containing naturally enriched uranium (about 3-4%, as in the wiki article), waiting to be discovered by eager inventors.
...The main issue however being, that my civilization has roughly the same tech-level as late 19th to early 20th-Century Europe.
Atoms are known about, but it would probably take some time for the scientists of this world to realize the potential of fission-energy. For this question, we'll assume that they cracked the code, at least enough to understand that radioactive elements can be used for fission and the main application of this question.
The setting is more orientated around steam-punk, so you won't find any digital computers or extremely modern materials to keep these reactors working. Instead, they'll have to settle for mechanical/analog computers, brass, steel, iron and all other materials and chemicals which were commonly used for construction in Europe during the late 19th and very early 20th century. (probably 1880-1915)
Though, i'm not just looking for a reactor...i'm looking for a specific application.
The thruster i linked to isn't the exact type i need. I just want to know how it could even be possible for a civilization of this tech-level to build a type of nuclear thruster with the materials and technology available. The type of thruster that i need, is essentially the one that's most plausible for them to build, though it's intended purpose is inter-orbital travel (and yes, that means no lift-off or re-entry, these thrusters, and the ship they're attached to, will never experience any planetary, atmospheric effects).
I'll try to clarify anything that might be important for the question.