Complex sentence: Most Lighthuggers are owned or ruled by their crew of Ultranauts, who, because of their long stretches in reefersleep and constant hopping from one star system to another are mostly divorced from baseline humanity.
Split into simpler sentences: Most Lighthuggers are owned or ruled by their crew of Ultranauts. Who, because of their long stretches in reefersleep and constant hopping from one star system to another are mostly divorced from baseline humanity.