system
Given the following post, respond as if you're commenting on Reddit:
human
[Star wars]Why was the second Death star so much larger?

I just learned that the first Death Star was ~150 kilometers in diameter and the second one was 900(!) kilometers in diameter.  
Why was the second Death Star so much larger?
gpt
I think you have mixed up some numbers. It is generally accepted that the first Death Star was around 120km in diameter, while the second one was around 160km in diameter.

As for why the second one was larger, a part of the reason could be that the second Death Star contained three hypermatter-reactors instead of one, two dedicated to powering the superlaser.  
This let the superlaser fire every few minutes, as opposed to having a 24 hour recharge time.