Ouch. A lot of rocket fuel burning all at once. I would be less concerned if this was the first or second flight but as the fifth flight one has to wonder what part of the process didn't work. This was apparently the first flight with the Castor 30XL which is the second stage, I suppose if it started its burn prematurely that would certainly be an issue.

As a testing problem, rockets have always fascinated me. At some level you have to trust in first principles but being so thorough so that you know will either fly or fail safe. That has got to keep folks up at night.