This is only if you discount his early works such as The Magellanic Cloud, where he is a world communism adept wearing rose-coloured glasses, through which many of his readers, including ones in core Soviet Union, would perceive reality and future prospects.

Eastern European writers did contribute a sizeable bookshelf of writings about bright space communist future, until it began to turn sour. One lesser-known one who I remember from my childhood is Pavel Vezhinov's Death of Ajax.

UPD: Maybe we should use Eastern Bloc Science Fiction as a term?

Even if he was a communist it still wouldn't make him soviet.

The issue here is "Soviet" is not a given name but (supposedly) a mode of government.

One like Democracy and Republic and the literal translation is "Council".

So, you can surely be democratic outside of (hypothetical) Democratic Union, much like you may be soviet outside of USSR.

I think that Eastern European would be nuch better term then Soviet. Or post-communist if you limit yourself to after 1989.