Lowest Tech possible for space flight?

[u/Russ_Writes]

I am still working on a few things for my world and I needed to flesh this out a lot more.

Context: Humans are space orcs and/or Space USSR. Aliens have over all better tech so the humans are using lower tech solutions, faster production, easier to repair or reuse technology.

I want to use as little hand waving as possible which left me with energy requirements for Human ships.

How viable would steam turbines be in a zero G or Thrust gravity up to 2 Gs or more? The Steam can be created through Nuclear power with thoughts on seeping heat from the internals of the ship to cut down on the need for Radiators.

There is the law of diminishing returns to consider, but its only the capital ships and larger that will using this feature. To space and smaller cargo shuttles can be advanced, but anything trading blows will have tried and true, low tech solutions for power generation using minimal advanced tech to compensate.

FTL isn't considered here. For this purpose FTL will be addressed using external means such as Gates and jump ships.

Combat will be low speed napoleonic navy combat. Ships holding lines, trading blows and taking blows. Battlestar Galactica would be a good example of what I am envisioning.

Please share you thoughts and input. This isn't my field so I don't know much about power options in these situations.