they did a stretch of the mk1 and added a whole bunch of systems, and moved the flaps and the most likely culprit is resonance cracking fuel lines and fittings,

they did a stretch of the mk1 and added a whole bunch of systems, and moved the flaps and the most likely culprit is resonance cracking fuel lines and fittings, or tanks. Resonance or "shake" testing is a mandatory part of certifying high end satelites, and NASA and others have huge test rigs that simulate the vibrations that will be experienced durring launch. This is slow, and the easiest cures are to add mass dampaning, but that is bulky and heavy. lauching and iterating is just as viable. The sci fi look of exploded rocket parts on re entry is almost worth all the trouble. Third times a charm, or it's realy time to grind hard.