I haven't read "Blood on the Stars", but I don't think the details of that story matter here, so I'll plunge ahead.
Maybe I should distinguish the legal issue of copyright from the artistic issue of "your story is a rip-off of this other story".
Copyright protects exact words (or pictures or music or whatever). As long as you don't copy somebody else's book word for word, or copy non-trivial sections of it, you're not violating copyright.
The rip-off charge is vaguer. It's not a crime to steal another writers ideas. It's just poor form.
Don't have characters with the same name, or who are so obviously similar that anyone who has read this book and yours would say, "Why, that sounds like ..." Like if I was using Star Trek for inspiration, I certainly would not have a character in my story named "James Kirk". Nor would I have a character described as a pointed-ear alien whose race prides itself on its logic. But don't get totally paranoid here. Lots of sci-fi stories have brave young adventurers, mad scientists, beautiful princesses who need to be rescued, etc. If you start saying, "Oh no, I have a character whose smart and brave and this other story has a character whose smart and brave. Will people think I'm copying?", you'll never succeed in writing anything.
Don't have made-up places with the same name or obviously similar. Exceptions of the place name is derived from a real place. Like having a planet named "Altair IV", well, Altair is a real star and the idea of numbering the planets of a star is pretty standard. Though if you copy several such place names from the same story, that will look bad. Mix it up.
You can freely steel a basic idea, like "civilization has collapsed and people are trying to rebuild". No one will think less of you for that. Writers do it all the time. It becomes an issue when the idea you steal is too specific. Like, "rebels fighting a galactic empire" has been done a thousand times, feel free to explore that idea in your own way. But "rebels who get their power from a mysterious force that pervades the universe, and two young rebels turns out to be the son and daughter of the man who is the power behind the emperor, and another rebel is a hot shot adventurer and smuggler, and ..." etc, and at some point it becomes too obvious a rip-off.
In general, you can borrow any real science. No sane writer supposes that he owns the idea of cloning just because he wrote a story about it. Even if he was the first person to write a story about it. Some ideas have been used so often in science fiction that no one will think twice if you borrow them, like "hyperspace drive" and intelligent aliens. I wouldn't say to never borrow another writers fictional technology, but the more specific it is, the more cautious I would be. Like "energy weapons": sure. "Light sabers": probably no.