There are definitely many similarities of the themes found in each, but each are approached much differently, each with a stronger emphasis on different areas.

In Ad Astra, while it was a space movie, was actually more about the relationship with the father and the man's internal conflict. It seemed that the sci-fi space aspect of it was secondary, merely the story's setting, but the same story could have been told regardless of it was space or not.

Interstellar had a much stronger emphasis on traditional "space science fiction", and while the family connection did play a pivotal role in the overall story, it was more or less used as a mechanic to give depth to the conflict of the main-characters. You could conceivably tell the story without the family dynamics, and still have a very similar movie. Essentially, family is not "the" story, it is "a" story of the movie. I am struggling to find the right words to describe what I mean, right now...

For all the similarities, the movies are surprisingly very much different in my opinion. While the themes and setting sound the same on paper, watching them play out on screen and the way they are told makes comparing them like "comparing apples to oranges" as the saying goes. They are both good in their own right.

@ForeverZer0 : What a great post you wrote! While I have seen both movies, I have never thought to compare them. I thought that when it came to family relationships, Interstellar was a lot more emotional, especially in the scene where Cooper is crying as he's watching one of the videos from his family (I always cry watching that too).