[xpinguin]

Regarding Ivan Efremov, I'd like to mention two of his novels being set in a same "universe" (although separated by something like thousand years):

1. "Andromeda" (literally translated: "Andromeda Nebula"): https://en.wikipedia.org/wiki/Andromeda_(novel)

2. "The Bull's Hour": https://en.wikipedia.org/wiki/The_Bull%27s_Hour

The latter one was even informally prohibited from being published in major media until "perestroyka" had arrived (IMO, due to the author's caricatural depiction of contemporary social and political views towards communism, contraposed - along the story - with what communism should really look like; if you'd ever get to read that, try to guess whom Choyo Chagas (rus. "Чойо Чагас") is intended to resemble).

Some think that both stories (esp. first one) is nothing more than rhapsodic tribute to the communism. Personally, I had read "Andromeda" in my early teens considering it being "just SF". Only after reading "The Bull's Hour" in sixteenth or such and subsequent re-reading in almost decade later, would I realize that SF was for "Social Fantasy" :) The catch is that "communism" in the book stands for the mixture of anarchy (no central government or regulator) and technocracy (councils of recognized specialists - engineers and scientists - were in charge of their corresponding domains of knowledge) with "decision enforcement" being based on high self-consciousness inherent to all and every member of the society (btw, this is explicitly pictured in "Andromeda").