[arielb1]

Engine failed during qualification testing, not acceptance testing - so it's a new design.

If you don't occasionally blow an engine up on the stand you are either not testing hard enough or not pushing the limits hard enough.

[Robotbeat]

What's interesting is that updated info indicates it happened before the engine (which was a block 5 engine, as you say) was ignited, when they do a "LOx drop" test, basically running liquid oxygen through it to test for any leaks: https://arstechnica.com/science/2017/11/an-experimental-spac...

It may mean they had a simple FOD (foreign object debris) or contamination issue, not a design problem. Powerful oxidizers like liquid oxygen can make contact explosives out of all kinds of organic materials.

[stcredzero]

Stuff that you normally don't think of as flammable -- like hunks of structural metal -- burn quite nicely in the presence of liquid oxygen. So stuff that burns well, burns REALLY WELL in the presence of LOX.

[sunstone]

Oh of course. Test to failure, why didn't that occur to me with respect rocket engines? Thanks for the insight.

[sliverstorm]

Move fast and blow shit up (literally)?